Antifungal Activity of Lactobacillus pentosus ŁOCK 0979 in the Presence of Polyols and Galactosyl-Polyols

Antifungal Activity of Lactobacillus pentosus ŁOCK 0979 in the Presence of Polyols and... Probiotics & Antimicro. Prot. (2018) 10:186–200 https://doi.org/10.1007/s12602-017-9344-0 Antifungal Activity of Lactobacillus pentosus ŁOCK 0979 in the Presence of Polyols and Galactosyl-Polyols 1 2 2 3 Lidia Lipińska & Robert Klewicki & Michał Sójka & Radosław Bonikowski & 2 2 1 Dorota Żyżelewicz & Krzysztof Kołodziejczyk & Elżbieta Klewicka Published online: 6 November 2017 The Author(s) 2017. This article is an open access publication . . Abstract The antifungal activity of Lactobacillus pentosus Keywords Antifungal activity Galactosyl-polyols . . . ŁOCK 0979 depends both on the culture medium and on the Lactobacillus Metabolites Polyols SEM fungal species. In the control medium, the strain exhibited limited antagonistic activity against indicator food-borne molds and yeasts. However, the supplementation of the bac- Introduction terial culture medium with polyols (erythritol, lactitol, maltitol, mannitol, sorbitol, xylitol) or their galactosyl deriva- Filamentous fungi and yeasts are present in almost all types of tives (gal-erythritol, gal-sorbitol, gal-xylitol) enhanced the an- ecosystems due to their high adaptation ability and low nutri- tifungal properties of Lactobacillus pentosus ŁOCK 0979. Its tional requirements. Filamentous fungi are widespread food metabolites were identified and quantified by enzymatic spoilage microorganisms responsible for significant economic methods, HPLC, UHPLC-MS coupled with QuEChERS, losses in the agri-food industry [6]; they are also a major and GC-MS. The presence of polyols and gal-polyols signif- health concern due to mycotoxin production. The most com- icantly affected the acid metabolite profile of the bacterial mon genera of spoilage fungi include Penicillium, Fusarium, culture supernatant. In addition, lactitol and mannitol were Aspergillus, Cladosporium,and Rhizopus [21]. Commercial used by bacteria as alternative carbon sources. A number of foodstuffs are usually protected from such microorganisms by compounds with potential antifungal properties were identi- physical and chemical techniques. However, as chemical pre- fied, such as phenyllactic acid, hydroxyphenyllactic acid, and servatives have become less socially acceptable, natural pres- benzoic acid. Lactobacillus bacteria cultivated with mannitol ervation methods are being sought. Lactic acid fermentation synthesized hydroxy-fatty acids, including 2-hydroxy-4- has been known and used these purposes since antiquity. In methylpentanoic acid, a well-described antifungal agent. recent years, lactic acid bacteria (LAB) have been extensively Scanning electron microscopy (SEM) and light microscopy investigated for their antifungal properties and bioprotective confirmed a strong antifungal effect of L. pentosus ŁOCK cultures have been proposed as a promising biotechnological 0979. approach [22, 24, 25]. Of particular application interest are lactobacilli, which convert carbohydrates into lactic and acetic acids (primary metabolites), as well as a range of secondary metabolites, such as carbon dioxide, ethanol, hydrogen perox- * Lidia Lipińska lidialipinska8@gmail.com ide, fatty acids, acetoin, diacetyl, cyclic dipeptides, bacterio- cins, and bacteriocin-like inhibitory substances [3]. Since these metabolites exhibit only weak antifungal properties, Lodz University of Technology, Institute of Fermentation many research teams are seeking Lactobacillus strains with a Technology and Microbiology, Wolczanska 171/173, 90-024 Lodz, Poland higher natural ability to inhibit fungal and yeast growth [4, 9, 14, 15, 26]. Ryu et al. [26] reported that Lactobacillus Lodz University of Technology, Institute of Food Technology and Analysis, Stefanowskiego 4/10, 90-024 Lodz, Poland plantarum HD1 synthesizes 5-oxododecanoic acid (MW 214), 3-hydroxydecanoic acid (MW 188), and 3-hydroxy-5- Lodz University of Technology, Institute of General Food Chemistry, Stefanowskiego 4/10, 90-024 Lodz, Poland dodecenoic acid (MW 214), which are considered antifungal. Probiotics & Antimicro. Prot. (2018) 10:186–200 187 In turn, Magnusson [14, 16] showed that some LAB can erythritol, gal-xylitol, and gal-sorbitol are modern prebiotics convert glycerol to 1,3-propanediol, which inhibits fungal which confer beneficial effects [8], as related in the blood and growth. While the qualitative and quantitative composition digesta of laboratory rats (Klewicki 2007). of antifungal compounds generated by LAB is species- or even strain-specific, it can be modulated by culture medium Synthesis of Galactosyl Derivatives of Erythritol, Sorbitol, modification. For instance, Lipińska et al. [13] adjusted the and Xylitol antifungal spectrum of lactobacilli by adding polyols and their galactosyl derivatives, proving that the antagonistic activity of Galactosyl derivatives of erythritol, sorbitol, and xylitol were LAB depends on culture medium composition, the LAB obtained by enzymatic transglycosylation using β- species, and the sensitivity of the fungal species. It was found galactosidase EC 3.2.1.23 from Kluyveromyces lactis that in the presence of xylitol and gal-xylitol in the bacterial (Novozymes A/S, Bagsvaerd, Denmark). The procedure for culture medium Lactobacillus pentosus ŁOCK 0979 galactosyl-xylitol synthesis was described by Klewicki [11]. effectively inhibited the growth of A. niger, A. alternata, A. brassicicola, F. lateritium,and M. hiemalis [13]. The Determination of Antifungal Activity of Lactobacillus modulation of LAB metabolism by supplementing the culture pentosus ŁOCK 0979 in the Presence of Polyols medium with various, often atypical, compounds may give and Galactosyl-Polyols rise to new systems inhibiting the growth of spoilage microorganisms. The antagonistic activity of L. pentosus ŁOCK 0979 against The objective of the study was to determine the antifungal the indicator fungi was tested using the double-layer method properties, metabolite profile, and enzymatic activity of the described by Lipińska et al. [13]. First, 10 μL of overnight strain L. pentosus ŁOCK 0979 cultured in the presence of bacterial culture was dropped on MRS agar plates (Merck or polyols, namely, erythritol, xylitol, maltitol, mannitol, sorbi- BTL) supplemented with 1% (m/v) polyols, galactosyl- tol, and lactitol, and their transglycosylation derivatives (gal- polyols, or galactose, separately. The control group consisted erythritol, gal-xylitol, and gal-sorbitol). of MRS agar plates (Merck) with lactobacilli colonies cultured with neither polyols nor gal-polyols. After 18–24 h, the plates were overlaid with Sabouraud 4% dextrose agar (Merck) in- 5 6 Materials and Methods oculated with an indicator fungal strain (10 –10 −1 spores × mL ). Indicator strain inhibition zones around Microbiological Strains and Polyols Lactobacillus sp. colonies were measured after 24–72 h of cultivation at 30 °C. The results were given as fungal inhibi- The study material consisted of the bacterial strain L. pentosus tion diameters minus the diameter of Lactobacillus sp. ŁOCK 0979 and 10 fungal strains deposited with the Pure colonies. Cultures Collection of Industrial Microorganisms of the Institute of Fermentation Technology and Microbiology, Preparation of Cell-Free Supernatant After Lactic Acid Lodz University of Technology (ŁOCK 105). The indicator Fermentation fungi included the yeasts Candida vini 0008 and 0009 and the molds Mucor hiemalis 0519, Geotrichum candidum 0511, Following lactic acid fermentation by L. pentosus ŁOCK Alternaria alternata 0409, Alternaria brassicicola 0412, 0979 in media with one of polyols or galactosyl-polyols, sam- Aspergillus niger 0433, Fusarium lateritium 0508, ples of cell-free supernatant (CFS) were prepared in order to Aspergillus ochraceus,and Penicillium sp. Two of the tested identify and quantify the antifungal agents produced by the fungi, A. ochraceus and Penicillium sp., were newly isolated bacteria in the modified MRS media. from spoiled food. The media consisted of MRS broth (Merck) containing 1% Fungi were grown in Sabouraud 4% dextrose agar (Merck) (m/v) glucose supplemented with 1% (m/v)ofone of the and bacteria in MRS medium (Merck) supplemented with 1% polyols (erythritol, lactitol, maltitol, mannitol, sorbitol, or xy- (m/v) polyols (erythritol, lactitol, maltitol, mannitol, sorbitol, litol) or one of the gal-polyols (gal-erythritol, gal-sorbitol, or xylitol) or galactosyl polyols (gal-erythritol, gal-sorbitol, gal- gal-xylitol). The final pH was 5.7 ± 0.2. In the first step of the xylitol). The microorganisms were cultured at 30 °C under experiment, 200 mL of a medium was inoculated with 3% (v/ aerobic conditions. Fungi were stored at 4 °C on Sabouraud v) of overnight L. pentosus ŁOCK 0979 culture (10 – 6 −1 dextrose agar slants (Merck), and bacteria were kept at 10 cfu × mL ), andincubatedfor 48 hat30°C. − 20 °C in 20% (v/v) glycerol. Subsequently, the samples were centrifuged (10 min, The polyols used in the study (erythritol, lactitol, maltitol, 12,000×g, 20 °C), and the supernatants were filtered using mannitol, sorbitol, xylitol) occur naturally in some foodstuffs 0.22-μm syringe filters. CFS were stored at − 20 °C for further and may be added to others, e.g., as sweeteners. In turn, gal- study. 188 Probiotics & Antimicro. Prot. (2018) 10:186–200 Determination of the Content of Polyols and Saccharides Quantification of Antifungal Acids Using UHPLC-MS Using HPLC in Conjunction with QuEChERS Each CFS sample was diluted 10-fold. The obtained solution Antifungal metabolites produced by L. pentosus ŁOCK 0979 was passed through a 5-mL column BAKERBOND® spe in the presence of polyols and their galactosyl derivatives were Octadecyl (18) (J.T. Baker, USA) with cation and anion ex- quantified using the QuEChERS method and an ultra-high- change resins (1:2 v/v). The first fraction (3 mL) was performance liquid chromatography-mass spectrometry discarded, and the second one (3 mL) was collected for (UHPLC-MS) system according to a protocol modified from HPLC analysis. The content of saccharides and polyols was Oliveira et al. [20]. In the sample preparation step, 1 mL of determined using an Aminex HPX-87C column from Bio-Rad formic acid, 10 mL of ethyl acetate, and 10 mL of a CFS (0.78 × 30 cm, mobile phase: water, flow rate: sample were added to a Falcon test tube containing 4 mg of −1 0.5 mL × min , 85 °C). An RI detector and an integrating magnesium sulfate and 1 g of sodium chloride. The mixture system from Knauer were used. The tests were done in tripli- was shaken for 1 min and centrifuged (10 min, 1077×g). Then cate and prepared in three parallel columns. Statistical analysis 5 mL of the organic solvent was removed and added to an consisted of the Duncan test (p ≤ 0.05). Agilent dSPE kit (150 mg of C18, 900 mg of magnesium sulfate). The mixture was shaken for 1 min, centrifuged Spectrophotometric Determination of Glucose (10min,1077×g),anddecantedintoatest tubewith 100 mL of dimethyl sulfoxide (DMSO). The solutions were Glucose concentration in the pure culture medium and in post- concentrated for 3.5 h in a ScanVac ScanSpeed 40 centrifuge fermentation CFS was determined spectrophotometrically ac- evaporator (2000 rpm, 45 °C) equipped with a CoolSafe 110-4 cording to the instructions supplied with the enzymatic kit Pro cold trap (Labogene, Lynge, Denmark) until only 100 μL (BioMaxima) and a calibration curve. CFS and pure culture DMSO remained. The concentrated solution was mixed with medium samples were diluted 50- and 100-fold, respectively, 400 μL of 10% (v/v) acetonitrile, centrifuged (10 min, relative to the initial glucose content of the medium 10,000×g), and transferred into a 1.5-mL amber vial. −1 (10 g × L ). Subsequently, 1 mL of the reagent (glucose The following 13 antifungal compounds were quantified: oxidase and glucose peroxidase) and 0.01 mL of a tested sam- DL-3-phenyllactic acid, DL-p-hydroxyphenyllactic acid, ple (diluted culture or pure medium) were placed in a cuvette benzoic acid, hydrocaffeic acid, hydrocinnamic acid, vanillic and mixed. After 5 min (37 °C), the absorbance of the tested acid, 4-hydroxybenzoic acid, catechol, caffeic acid, ferulic sample was measured relative to the reagent blank acid, 3-hydroxybenzoic acid, 2,4-dihydroxybenzoic acid, (λ = 540 nm), with the results being proportionate to glucose and p-coumaric acid. content in the sample. Based on the prepared calibration curve A Dionex UltiMate 3000 ultra-high-performance liquid −1 (in the range of 0.01–4 g glucose × L ) glucose concentration chromatograph from Thermo Fisher Scientific (Germering, was determined both in medium and CFS samples, accounting Germany) coupled with a diode array detector (DAD) and a for their dilution. The tests for each sample were done in Q Exactive Orbitrap mass spectrometer (MS, Thermo Fisher triplicate, and statistical analysis involved one-way ANOVA Scientific, Bremen, Germany) was used for LC-MS analysis. (p ≤ 0.05). Chromatographic separation was performed using a 150-mm C18 column with a 2.1-mm internal diameter and 2.6-μm Concentration of D-Lactic Acid, L-Lactic Acid, and Acetic particle size (Kinetex 2.6u, Torrance, CA, USA). The column Acid temperature was maintained at 30 °C, and the injection vol- ume was 2.5 μL. The mobile phase consisted of the following: The quantification of D-lactic, L-lactic, and acetic acid requires Awas water containing 0.1% formic acid and B was a mixture enzymatic reactions described in the assay procedures: K- of acetonitrile and water (90:10, v/v) containing 0.1% formic DLLATE 07/14 and K-ACET 11/05 (Megazyme acid. The flow rate was 0.5 mL/min. The following gradient International Ireland). In the case of D-and L-lactic acids, the was used: 0–16.5 min, 5–40% B; 16.5–17.5 min, 40–95% B; manufacturer’s procedure for the sequential assay of both op- 17.5–20 min, 95% B; 20–22 min, 95–5% B; 22–27 min, 5% tical isomers was applied. The concentration of all tested acids B. After DAD detection, the separated compounds entered was estimated using colorimetric tests with the absorbance into the MS system via a heated electrospray ionization (H- measured (λ = 340 nm) in a control sample (non-inoculated ESI) source with a flow rate of 0.5 mL/min. Analyses were medium) and diluted CFS. The calculations were made ac- carried out in the negative ion mode. Chromatographic data cording to the manufacturer’s recommendations, taking into were collected using Xcalibur software (Thermo). The source consideration the dilution factor (F = 50). The tests were done parameters were as follows: a vaporizer temperature of in triplicate, and statistical analysis involved one-way 400 °C, an ion spray voltage of 4 kV, a capillary temperature ANOVA (p ≤ 0.05). of 380 °C, and sheath and auxiliary gas flow rates of 60 and Probiotics & Antimicro. Prot. (2018) 10:186–200 189 15 units, respectively. The detector was operated in either full The samples were analyzed by gas chromatography MS or full MS/dd-MS2 scan modes. In the full MS mode, the coupled with mass spectrometry (TRACE GC Ultra—ISQ) scan rage of m/z 50–400 was used. The full MS/dd-MS scan using a Stabilwax-DA capillary column (30 m × 0.25 mm mode was used to generate MS2 data. In this mode, the se- i.d., film thickness 0.25 μm). The operating conditions were lected precursor ions entered into a high-energy collision-in- as follows: temperature program—50 °C (3 min)–240 °C duced dissociation (CID) cell, where they were fragmented (30 min) at 4 °C/min, injection temperature—240 °C, carrier with normalized collision energy (NCE) to obtain product gas—helium (constant flow 1 mL/min). Mass spectrometer ion spectra (MS ). In our experiments, the NCE used to gen- parameters were as follows: 33–550 amu, ionization energy erate MS spectra was set to 30. Tuning and optimization were 70 eV, ion source temperature 200 °C. Identification of com- performed using direct injection of the standard solution dilut- pounds was based on a comparison of their mass spectra with ed in an 80:20 (v/v) mixture of mobile phases A and B at a computerized libraries (Wiley Registry 10th Edition/NIST flow rate of 0.25 mL/min. Acids were quantified using the Mass Spectral Library 2012). selected ion monitoring (SIM) mode. The standard curves of Mannitol was chosen as one of the best agents enhancing these compounds were used for quantification. Table 1 gives the antifungal effect of L. pentosus ŁOCK 0979. Moreover, in acquisition parameters for 13 acids in the tested solution. the presence of mannitol, many signals from acidic com- Acid quantification was performed in triplicate, and statis- pounds were obtained using UHPLC-MS analysis, but they tical analysis was conducted using the Duncan test (p ≤ 0.05). could not be identified by the UHPLC-MS method due to their molecular structure (data not presented). Identification of Fatty Acids and Hydroxylated Fatty Acids by Gas Chromatography Coupled with Mass API®ZYM 25200 Test of Bacterial Enzymatic Activity Spectrometry Bacteria were grown for 24 h in 9 mL of MRS broth Lactobacillus pentosus ŁOCK 0979 was grown at 30 °C in (Merck) with 1% (m/v) polyols or galactosyl-polyols, 150 mL of MRS broth (Merck) with 1% (m/v) mannitol. The added one by one. The cultures were centrifuged (10 min, 48-h culture was centrifuged (10 min, 12,000×g,20 °C), and 12,000×g, 20 °C), and the biomass was suspended in saline supernatant pH was adjusted to 4.0 with hydrochloric acid. to obtain a cell concentration corresponding to 5–6onthe 9 −1 Then, 100 mL of the sample was extracted with 30 mL of McFarland scale (approx. 1.5 × 10 cells × mL ). API dichloromethane, mixed for 3 min, and settled for 10 min. ZYM strips were placed in API ZYM boxes humidified Extraction of the aqueous phase was repeated twice using by distilled water. The strips were inoculated with 65 μL further portions of dichloromethane. The organic phases were of the sample and incubated for 4 h at 37 °C. Then, the combined, dried over anhydrous sodium sulfate, and, follow- reagents ZYM A and ZYM B (bioMerieux) were added ing filtration, concentrated to approx. 0.5 mL in a rotatory dropwise. The strips were placed under a powerful light evaporator. The residue was derivatized with 200 μLof source for 10 s and then exposed to daylight for 5– 0.25 M trimethylsulfonium hydroxide solution (TMSH, 10 min. Results were read according to the manufacturer’s Sigma Aldrich) in methanol. recommendations. Table 1 LC-MS acquisition Compound Retention time (min) Confirmation ion (m/z) Quantitation ion (m/z) parameters for acids detected in post-fermentation cell-free Catechol 3.27 – 109 supernatant 3.44 163, 135, 119 181 DL-p-Hydroxyphenyllactic acid 3-Hydroxybenzoic acid 4.38 93 137 Hydrocaffeic acid 4.88 137, 109 181 2,4-Dihydroxybenzoic acid 5.47 109 153 4-Hydroxybenzoic acid 5.47 93 137 Vanillic acid 5.52 152, 123, 108 167 Caffeic acid 5.88 135 179 6.80 147, 119 165 DL-3-Phenyllactic acid p-Coumaric acid 7.88 119 163 Ferulic acid 8.74 178, 134 193 Hydrocinnamic acid 12.17 121 149 190 Probiotics & Antimicro. Prot. (2018) 10:186–200 The Effects of Cell-Free Supernatants on Fungal Growth Mold inhibition by L. pentosus ŁOCK 0979 depended both and Morphology Evaluated with Scanning Electron on the culture medium composition and on mold species. The Microscopy and Light Microscopy A. alternata test strain and the A. ochraceus and Penicillium sp. strains isolated from the environment exhibited the greatest Fungal strains sensitive to the metabolites of polyols or gal- sensitivity to lactic acid fermentation products both in the polyols were selected based on the antagonistic activity of controls and in samples with polyols and gal-polyols L. pentosus ŁOCK 0979 cultured in different culture media. (Table 2). In contrast, the growth of A. brassicicola and CFS samples were added to Sabouraud 4% dextrose agar A. niger was inhibited by L. pentosus ŁOCK 0979 only if (Merck) in the amount of 10% (v/v). The medium was subse- the bacterial culture medium was supplemented with polyols quently placed in 6-well plates and inoculated with selected (both mold strains) or gal-polyols (only A. brassicicola). The fungal strains using an inoculation loop. Microscopic examina- antifungal activity of L. pentosus ŁOCK 0979 was also im- tion was carried out after 2 days (yeasts) and 7 days (molds) proved by polyols and their galactosyl derivatives with respect using a light microscope. Additionally, yeast morphology was to F. lateritium. Its growth was inhibited by the bacteria cul- examined using a scanning electron microscope (JEOL JCM- tured in the presence of maltitol and sorbitol, as well as all 6000, Tokyo, Japan) after coating with gold particles for 45 s tested galactosyl-polyols. Antagonistic activity against (JEOL JFC-1200 Fine Coater, Tokyo, Japan). The experiments G. candidum and M. hiemalis was weak (Table 2). were conducted in duplicate. The control samples consisted of In a similar way, additional control trials were conducted fungi cultured on Sabouraud agar without bacterial CFS. using MRS medium with glucose (Merck) and 1% (m/v)galac- tose, as well as a glucose-free MRS medium (BTL) with 1% (m/ v) galactose. These media enhanced the antagonistic activity of L. pentosus ŁOCK 0979 only against one indicator fungal strain Results (F. lateritium)ascomparedtobacteriacultivatedonMRS agar (Merck). Therefore, it can be assumed that the small amounts of Antifungal Activity of Lactobacillus pentosus ŁOCK 0979 galactose released as a result of galactosyl-polyol hydrolysis in the Presence of Polyols and Galactosyl-Polyols (Table 3) are not a critical determinant of antifungal properties. The antagonistic activity of L. pentosus ŁOCK 0979 against the tested yeasts was weak, but its anticandidal properties were Content of Polyols and Saccharides in Cell-Free enhanced in the presence of galactosyl-polyols, and especially Supernatant gal-erythritol. The addition of gal-sorbitol and gal-xylitol to the bacterial culture medium led to inhibition of only one of the two The content of polyols and saccharides before and after lactic strains of yeast, that is, C. vini ŁOCK 0009 (Table 2). acid fermentation by L. pentosus ŁOCK0979inthepresence of Table 2 Antifungal activity of Growth media Yeasts Molds Lactobacillus pentosus ŁOCK 1 2 3 4 56 78 9 10 MRS (control) –– + + +++ – + – +++ +++ MRS + erythritol –– + + ++ + ++ + ++ +++ MRS + lactitol – ––– +++ ++ + ++ +++ +++ MRS + xylitol –– + – + ++ ++ + +++ +++ MRS + maltitol –– + – +++ +++ ++ ++ +++ MRS + mannitol –– + – +++ +++ ++ + +++ +++ MRS + sorbitol –– + – +++ – +++ – +++ ++ MRS + gal-erythritol ++ + +/− – ++ +++ ++ – +++ +++ MRS + gal-xylitol – +/− ++/− +++ +++ +++ +/− +++ +++ MRS + gal-sorbitol – ++ – +++ +++ +++ +/− X+++ MRS + galactose –– + – +++ +++ +++ – ++ MRS + galactose (glucose-free) –– + – ++ ++ ++ – ++ 1. C. vini 0008, 2. C. vini 0009, 3. M. hiemalis,4. G. candidum,5. A. alternata,6. A. brassicicola,7. F. lateritium, 8. A. niger,9. A. ochraceus,10. Penicillium sp. X no tested, − no inhibition zone, +/− inhibition zone between 0.5 and 2 mm, + inhibition zone between 2.1 and 10 mm, ++ inhibition zone between 10.1 and 20 mm, +++ inhibition zone above 20 mm, nt not tested Probiotics & Antimicro. Prot. (2018) 10:186–200 191 Table 3 Concentration of −1 −1 Media Compounds Initial content (g × L ) Residual content (g × L ) polyols and saccharides before and after lactic acid fermentation MRS (control) Glucose 20.9 ± 3.61 – by Lactobacillus pentosus ŁOCK 0979 in media containing polyols MRS + erythritol Glucose 25.4 ± 0.01 – and their galactosyl derivatives Erythritol 10.6 ± 0.27a 10.1 ± 0.10a MRS + lactitol Glucose 20.2 ± 0 – Lactitol 10.0 ± 0a 9.03 ± 0.11b MRS + xylitol Glucose 18.7 ± 0.92 – Xylitol 10.3 ± 0.10a 10.0 ± 0a MRS + maltitol Glucose 20.2 ± 0.77 – Maltitol 10.4 ± 0.54a 10.0 ± 0a MRS + mannitol Glucose 13.14 ± 0.11 – Mannitol 10.0 ± 0.04a 7.4 ± 0.70b MRS + sorbitol Glucose 19.0 ± 0.34 – Sorbitol 10.0 ± 0a 9.7 ± 0.22a MRS + gal-erythritol Glucose 18.9 ± 0.01 – Gal-erythritol 10.03 ± 0a 5.8 ± 0.73b Erythritol – 1.7 ± 0.09 Galactose – 0.6 ± 0.09 MRS + gal-xylitol Glucose 20.6 ± 0 – Gal-xylitol 9.9 ± 0.68a 7.7 ± 0.21b Xylitol – 1.0 ± 0.07 MRS + gal-sorbitol Glucose 18.7 ± 0 – Gal-sorbitol 10.5 ± 0.07a 7.8 ± 0.38b Sorbitol – 0.7 ± 0.08 Galactose – 0.1 ± 0.02 Means designated with the same lowercase letter are not significantly different (Duncan’s multiple range test) – below the limit of detection −1 polyols and gal-polyols was determined using HPLC, and the , while that of lactic acid 4.09 ± 0.178 to 7.62 ± 0.010 g × L −1 concentration of glucose was evaluated spectrophotometrically was from 4.58 ± 0.390 to 20.26 ± 1.489 g × L ; in all sam- (Table 3). The results show that in lactic acid fermentation the ples, the dominant stereoisomer was L-lactic acid accounting bacteria used glucose as a primary carbon source, while the for 61–100% of the total (Table 4). The mean pH of the post- galactosyl-polyols and polyols (lactitol, mannitol) were used fermentation supernatant was higher in the case of gal-polyols as additional carbon sources to varying degrees (Table 3). (pH 4.13 ± 0.12) than polyols (pH 3.88 ± 0.290), except for The mannitol and lactitol present in the culture media were sorbitol (pH 4.4). Samples with higher pH (gal-polyols, partially used by L. pentosus ŁOCK 0979 (as reflected in 10 sorbitol) exhibited a lower concentration of lactic acid −1 and 26% decline in concentration after lactic acid fermenta- (4.58–9.49 g × L ) and a higher concentration of acetic acid −1 tion, respectively). Galactosyl-polyols (gal-erythritol, gal-xy- (5.76–7.62 g × L ). L. pentosus ŁOCK 0979 generated the litol, and gal-sorbitol) were hydrolyzed to galactose and the highest amounts of lactic and acetic acids in the presence of − 1 respective polyols. Residual galactose was found in post- xylitol (20.26 ± 1.489 g × L ) and gal-xylitol −1 fermentation CFS from samples supplemented with gal- (7.62 ± 0.010 g × L ), respectively (Table 4). erythritol and gal-sorbitol (Table 3). The content of erythritol, xylitol, maltitol, and sorbitol in the medium did not change Effects of Polyols and Gal-Polyols on the Content significantly following lactic acid fermentation (Table 3). of Antifungal Acids Acidity and Production of Acetic and Lactic Acids The following 13 antifungal acids were quantified: DL-3- phenyllactic acid (PLA), DL-p-hydroxyphenyllactic acid The concentration of acetic acid and lactic acid (L- and D- (HPLA), benzoic acid (BA), hydrocaffeic acid (HCaA), enantiomers separately) was evaluated enzymatically using hydrocinnamic acid (HCiA), vanillic acid (VA), 4- Megazyme kits. The total content of acetic acid was from hydroxybenzoic acid (4-HBA), catechol (Cat), caffeic acid 192 Probiotics & Antimicro. Prot. (2018) 10:186–200 Table 4 Production of acetic, D- Medium pH Production of lactic acid Production of acetic lactic, and L-lactic acids by −1 acid (g × L ) Lactobacillus pentosus ŁOCK % D-lactic % L-lactic 0979 in the presence of polyols DL-Lactic acid −1 acid [%] acid [%] and gal-polyols (g × L ) Non-inoculated medium 5.7 ± 0.2–– – 0.07 ± 0.000 MRS MRS (control) 3.6 13.89 ± 0.448 7.0 93.0 4.39 ± 0.105 MRS + erythritol 3.7 12.77 ± 0.015 0.0 100.0 4.75 ± 0.178 MRS + lactitol 3.7 15.01 ± 3.458 6.6 93.3 4.09 ± 0.178 MRS + xylitol 4.0 20.26 ± 1.489 14.2 85.8 5.71 ± 0.024 MRS + maltitol 3.9 10.89 ± 0.000 0.0 100.0 4.87 ± 0.003 MRS + mannitol 3.6 15.26 ± 1.619 5.1 94.9 5.76 ± 0.020 MRS + sorbitol 4.4 5.74 ± 1.257 34.8 65,2 6.52 ± 0.010 MRS + gal-erythritol 4.2 9.49 ± 0.234 37.7 62.3 6.61 ± 0.023 MRS + gal-xylitol 4.2 8.81 ± 1.685 38.6 61.4 7.62 ± 0.010 MRS + gal-sorbitol 4.0 4.58 ± 0.390 31.9 68.1 7.17 ± 0.020 Significantly different from the control test (CaA), ferulic acid (FA), 3-hydroxybenzoic acid (3-HBA), Enzymatic Activity of Lactobacillus pentosus ŁOCK 0979 2,4-dihydroxybenzoic acid (2,4-dHBA), and p-coumaric acid (p-CoumA), using a UHPLC-MS system coupled with Examination of the activity of enzymes metabolizing lipids, QuEChERS. It was found that the minimum inhibitory con- proteins, and phosphates revealed some minor differences be- centrations of the tested acids are many times higher than their tween L. pentosus ŁOCK 0979 cultures conducted in media actual concentrations in CFS (Table 5). Statistically significant supplemented with various polyols and gal-polyols (Table 7). differences in the content of PLA and HCaAwere linked to the As compared to the controls, esterase activity was found only composition of the culture medium. PLA content in CFS from in the presence of lactitol and gal-sorbitol, while that of ester- the bacterial culture with gal-xylitol differed from that found ase lipase in the presence of gal-erythritol. in cultures with lactitol and xylitol. In the presence of gal- erythritol and gal-xylitol, L. pentosus ŁOCK 0979 produced Effects of Polyols and Gal-Polyols on Fungal Growth double to triple the amount of vanillic acid and half the and Morphology amount of Cat as compared to the other CFS. The content of HCaA, HCiA, VA, 4-HBA, Cat, CaA, FA, 3-HBA, 2,4- The yeasts C. vini ŁOCK 0008 and ŁOCK 0009 and the mold dHBA, and p-CoumA was low and ranged from approx. 0 A. brassicicola were examined microscopically following cul- −1 (<LOD) to 0.161 mg × L (Table 5). ture in Sabouraud agar with 10% (v/v) CFS. The results are given in Tables 8 and 10. Scanning electron micrographs of C. vini ŁOCK 0009 cultivated in the presence of CFSs are Production of Hydroxy Fatty Acids in the Presence presented in Table 9. of Mannitol Light microscopy revealed greater cell differentiation in the yeast C. vini ŁOCK 0008 grown in Sabouraud agar with 10% Volatile compounds with potential antifungal properties (v/v) CFS from L. pentosus ŁOCK 0979 cultured in the pres- (fatty acids, hydroxy fatty acids) synthesized by ence of gal-erythritol than the control (Table 8). Candida vini L. pentosus ŁOCK0979culturedinMRS andinthe ŁOCK 0008 cells were at different developmental stages and presence of 1% (m/v) mannitol were identified included both single cells and some initial degrees of (Table 6). Mannitol induced antagonistic activity of pseudomycelium formation. The same was true of C. vini L. pentosus ŁOCK 0979 against some of the test fungi ŁOCK 0009 grown in Sabouraud agar with 10% (v/v)CFS (A. brassicicola, A. niger, F. lateritium), which must from L. pentosus ŁOCK 0979 cultured in the presence of gal- therefore be attributable to one or more metabolites syn- polyols (gal-erythritol, gal-xylitol, gal-sorbitol). What is more, thesized in the presence of this polyol. Moreover, CFS the addition of gal-polyols to the bacterial medium led to samples revealed 2-hydroxy-4-methylpentanoic acid, a fungal deformation and gave rise to blastoconidia (CFS gal- compound described by Ndagano et al. [19]asastrong erythritol, CFS gal-xylitol, CFS gal-sorbitol) (red arrows in antifungal agent. the Table 8). The yeast cells were narrower, and some of them Probiotics & Antimicro. Prot. (2018) 10:186–200 193 Table 5 Content of antifungal acids produced by Lactobacillus pentosus ŁOCK 0979 as determined by HPLC coupled with QuEChERS −1 Polyols in medium Production of antifungal acids and their referential MIC (mg × L ) PLA HPLA BA* 3-HBA* HCaA MRS—non-inoculated 0.107 ± 0.001 0.033 ± 0.003 0.339 ± 0.010 0.062 ± 0.002 0.006 ± 0.001 MRS (control) 41.513 ± 1.175 4.255 ± 0.069 0.623 ± 0.049 0.072 ± 0.002 0.090 ± 0.001 Erythritol 40.319 ± 0.865 4.132 ± 0.045 0.614 ± 0.103 0.072.002 0.062 ± 0 Lactitol 51.228 ± 0.482 x 4.872 ± 0.161 0.504 ± 0.022 0.078 ± 0.001 0.088 ± 0.001 Xylitol 49.988 ± 1.026z 4.869 ± 0.052 0.504 ± 0.017 0.079 ± 0.001 0.083 ± 0.003 Maltitol 24.224 ± 16.272 2.844 ± 1405 0.249 ± 0.094 0.050 ± 0.023 0.060 ± 0.033 Mannitol 40.992 ± 0.875 4.128 ± 0.096 0.582 ± 0.007 0.073 ± 0.001 0.085 ± 0.003 Sorbitol 31.962 ± 14.709 3.93 ± 0.852 0.49 ± 0.282 0.06 ± 0.017 0.06 ± 0.032 Gal-erythritol 21.91 ± 5.455 6.13 ± 4.311 0.03 ± 0.010 0.06 ± 0.013 0.04 ± 0.010 Gal-xylitol 16.65 ± 1.679 X, Z 2.46 ± 0.217 0.34 ± 0.005 0.05 ± 0.005 0.03 ± 0.003 X Gal-sorbitol 24.89 ± 8.188 3.14 ± 0.753 0.40 ± 0.106 0.06 ± 0 0.04 ± 0.018 MIC (Oliveira et al. 2015) 7500–10,000 – 20–2000 – >10,000 −1 Polyols in medium Production of antifungal acids and their referential MIC (mg × L ) HPLA 2,4-dHBA Cat 4-HBA Vanillic acid HCiA MRS—non-inoculated 0.033 ± 0.003 0.031 ± 0.001 0.015 ± 0.002 < 0.008 0.186 ± 0.006 < 0.017 MRS (control) 4.255 ± 0.069 0.012 ± 0.002 0.045 ± 0.003 < 0.008 0.003 ± 0 < 0.017 Erythritol 4.132 ± 0.045 0.010 ± 0 0.037 ± 0 < 0.008 0.086 ± 0.007 < 0.017 Lactitol 4.872 ± 0.161 0.011 ± 0.001 0.048 ± 0.004 < 0.008 0.070 ± 0.003 < 0.017 Xylitol 4.869 ± 0.052 0.011 ± 0.001 0.039 ± 0.003 < 0.008 0.075 ± 0.007 < 0.017 Maltitol 2.844 ± 1405 0.009 ± 0.002 0.034 ± 0.007 < 0.008 0.041 ± 0.015 < 0.017 Mannitol 4.128 ± 0.096 0.011 ± 0.001 0.049 ± 0.008 < 0.008 0.086 ± 0.003 < 0.017 Sorbitol 3.93 ± 0.852 0.01 ± 0.002 0.040 ± 0.003 < 0.008 0.084 ± 0.012 < 0.017 Gal-erythritol 6.13 ± 4.311 0.02 ± 0.001 0.018 ± 0.005 < 0.008 0.161 ± 0.057 < 0.017 Gal-xylitol 2.46 ± 0.217 0.02 ± 0.001 0.017 ± 0.001 0.012 ± 0.001 0.127 ± 0.001 < 0.017 Gal-sorbitol 3.14 ± 0.753 0.01 ± 0.005 0.044 ± 0.001 < 0.008 0.005 ± 0 < 0.017 MIC (Oliveira et al. 2015) –– > 1000 > 1000 > 100 100–1000 Distributions with both a capital and small letter are significantly different from each other (Tukey’stest p ≤ 0.05) PLA DL-3-phenyllactic acid, HPLA DL-p-hydroxyphenyllactic acid, BA benzoic acid, 3-HBA 3-hydroxybenzoic acid, HCaA hydrocaffeic acid, 2,4-dHBA 2,4-dihydroxybenzoic acid, Cat catechol, 4-HBA 4-hydroxybenzoic acid, VA vanillic acid, CaA caffeic acid, p-CoumA p-coumaric acid, FA ferulic acid, HCiA hydrocinnamic acid *p value estimated in Tukey’stest ≤ 0.05 (significance of differences may not be estimated) became pear-shaped as compared to the controls (Table 8). were found for all gal-polyols in the bacterial medium SEM provided more details about the form and surface of (Table 10). The addition of lactitol and mannitol to the bacte- C. vini ŁOCK 0009. In the control, yeasts were elliptical and rial medium led to complete inhibition of fungal growth developed pseudohyphae with smooth and flat surfaces (hence no photomicrographs). (Table 9). The cells of C. vini ŁOCK 0009 cultivated with the CFS of L. pentosus ŁOCK 0979 in the presence of gal- polyols were strongly deformed. Their shape was warped and Discussion the surface rough, and cell damage was visible in the form of concave areas on the surface (Table 9). Additionally, in the The control of spoilage microorganisms and, by the same presence of CFS gal-xylitol yeasts, cells were coated by ex- token, the extension of the shelf-life of foodstuffs still pose tracellular matrix (Table 9). formidable challenges. While the use of Lactobacillus sp. as Morphological changes were also observed in the myceli- natural bioprotective agents was already reported by um of the mold A. brassicicola grown in Sabouraud agar with Magnusson [14], a definitive explanation of their mechanism 10% (v/v) CFS from L. pentosus ŁOCK 0979 cultured in of action against undesirable fungi was not provided. bacterial media supplemented with erythritol and xylitol. Lactobacilli inhibit the growth of other bacteria (of the Furthermore, growth inhibition and mycelium deformation same or different species) as well as that of fungi, including 194 Probiotics & Antimicro. Prot. (2018) 10:186–200 Table 6 Volatile compounds No. Media produced by Lactobacillus pentosus ŁOCK 0979 in MRS Compound MRS—non-inoculated MRS (control) MRS + mannitol broth and in the presence of mannitol 1Butanoicacid + + + 2 2-Methylbutanoic acid + + – 3 Isovaleric acid + + + 4 Caproic acid + + + 5 3-Hydroxypropanoic acid – ++ 7 2-Hydroxypropanoic acid + + + 8 2-Hydroxyisocaproic acid – ++ 9 Octanoic acid + + + 10 2-Hydroxy-3-methylbutyric acid – ++ 11 2-Hydroxybutanoic acid + + – 12 2-Methylthioacetic acid + + – 13 Acetic acid + + – 14 Acetoxyacetic acid + –– 17 2-Hydroxy-3-methylpentanoic acid – + – 18 2-Hydroxy-4-methylpentanoic acid – ++ 19 3-(Methylthio)propanoic acid – + – 20 3-Hydroxypropanoic acid – + – 21 Decanoic acid + –– 22 Butanedioic acid + – + 23 2-Oxopentanedioic acid – + – 24 Benzoic acid + + + 25 2-Hydroxypropanoic acid + – + 27 Phenylacetic acid + + + 28 Dodecanoic acid – ++ 29 Hydrocinnamic acid – + – 30 Myristic acid + + + 32 Pentadecanoic acid – + – 33 Azelaic acid, dimethyl ester + + – 34 Palmitic acid + + + 35 2-Pyrrolidone-5-carboxylic acid –– + 36 Palmitoleic acid + + + 37 2-Hydroxybenzenepropanoic acid – ++ 38 Heptadecanoic acid (C17:0) + + – 39 Citric acid, trimethyl ester + –– 40 Methyl stearate + + + 37 9-Octadecenoic acid + + + 38 11-Octadecenoic acid – + – 39 Linoleic acid – ++ 40 9,12-Octadecadienoic acid + –– 37 Linolelaidic acid –– + 38 9,12-Octadecadienoic acid + + + 39 Eicosanoic acid + + – 40 11-Eicosenoic acid –– + 41 3-Octyloxiraneoctanoic acid + + + 42 10-hydroxyoctadecanoic acid – + – Probiotics & Antimicro. Prot. (2018) 10:186–200 195 Table 7 Effects of culture medium on the enzymatic activity of Lactobacillus pentosus 0979 Enzymes Enzymatic activity of Lactobacillus pentosus ŁOCK 0979 cultured with polyols and gal-polyols MRS MRS + MRS + MRS + MRS + MRS + MRS + MRS + MRS + MRS + (control) erythritol lactitol xylitol maltitol mannitol sorbitol gal-erythritol gal-xylitol gal-sorbitol Control – ––– –––– – – Alkaline phosphatase EC – ––– –––– – – Esterase (C4) –– +/− – –––– – +/− Esterase Lipase (C8) – ––– ––– + –– Lipase (C14) – ––– –––– – – Leucinearylamidase + +++ ++++ + + Valinearylamidase + +++ ++++ + + Cystine arylamidase – –– –––– – – Trypsin – ––– –––– – – α-Chymotrypsin – ––– –––– – – Acid phosphatase +/− ++ – ++ – + – + Naphthol-AS-BI-phosphohydrolase – ––– –––– – – α-Galactosidase + +++ +++/− ++ + β-Galactosidase + +++ ++++ + + β-Glucuronidase + + – + ++++ +/− + α-Glucosidase – ++/− +/− ––– + – ++ β-Glucosidase + +++ ++++ + + N-Acetyl-β-glucosaminidase – ––– –––– – – α-Mannosidase – ––– –––– – – α-Fucosidase – ––– –––– – – 196 Probiotics & Antimicro. Prot. (2018) 10:186–200 Table 8. Micrographs of yeasts grown for 2 days in Sabouraud medium with 10% (v/v) cell-free supernatant of Lactobacillus pentosus ŁOCK 0979 cultivated 48 h in the media containing gal-polyols Yeast strain/ Incubation time Photomicrographs, magnification 400 × C. vini ŁOCK 0008/ 48 h Control (Sabouraud agar) Sabouraud agar + CFS gal-erythritol C. vini ŁOCK 0009/ 48 h Control (Sabouraud agar) Sabouraud agar + CFS gal-erythritol Sabouraud agar + CFS gal-xylitol Sabouraud agar + CFS gal-sorbitol pathogenic and toxin-producing molds [1, 7]. While many of lactic acid fermentation is 3-phenyllactic acid (PLA), authors have reported the antifungal properties of LAB [3, synthesized by LAB such as L. casei, L. fermentum, 10], their exact underlying mechanisms remain elusive. L. rhamnosus, L. reuteri,and L. sakei [14, 17, 18]. While Nevertheless, it is known that a major role is played by L. pentosus ŁOCK 0979 does produce PLA, its concentra- some bacterial metabolites, and especially by organic tion in the CFS is much lower than its minimum inhibitory acids, hydroxy fatty acids, cyclic dipeptides, and low mo- concentration reported by other authors [20]. lecular weight proteinaceous compounds [22]. In addition The antifungal metabolites of Lactobacillus sp. constitute a to primary metabolites (lactic and acetic acids), which are rich mixture of active compounds whose qualitative and quan- produced by all Lactobacilli. sp., some LAB species syn- titative composition largely depends on the compounds found thesize secondary metabolites, which may selectively af- in the bacterial culture medium. Ndagano et al. [19], who fect other microorganisms; these include propionic, evaluated the effects of different concentrations and propor- hexanoic, salicylic, succinic, formic, 2-pyrrolidone-5-car- tions of acetic and lactic acids on fungal viability, observed boxylic, 3-phenyllactic, and 4-hydroxyphenyllactic acids significant synergies: the mixture was more potent than the [2, 14, 17]. One of the best described antifungal products sum of its individual components taken together. Synergies Probiotics & Antimicro. Prot. (2018) 10:186–200 197 Table 9. Scanning electron micrographs of yeasts grown for 2 days on Sabouraud agar medium with 10% (v/v) CFS from 48 h culture of Lactobacillus pentosus ŁOCK 0979 in media containing gal-polyols Scaning electron micrographs of Candida vini ŁOCK 0009, magnification 2000 × Sabouraud agar + CFS gal-erythritol Control medium (Sabouraud agar) Sabouraud agar + CFS gal-xylitol Sabouraud agar + CFS gal-sorbitol may also be found for some parameters of the culture medium, enhanced antifungal activity of lactobacilli on fruits have such as pH. been presented by Lipinska et al. [13]. The study presented herein was preceded by evaluation In the presented experiments, L. pentosus ŁOCK 0979 ex- of 60 Lactobacillus sp. strains, including L. pentosus hibited the ability to partially absorb lactitol, mannitol, and all ŁOCK 0979, cultured in the presence of polyols and the tested galactosyl-polyols. While Tyler et al. [30]isolated galactosyl-polyols as alternative carbon sources [13]to Lactobacillus florum 2F, a heterofermentative strain which select bacteria with strong antagonistic properties against can biosynthesize erythritol and mannitol, the consumption as many indicator fungal strains as possible. L. pentosus of polyols and galactosyl-polyols by Lactobacillus bacteria ŁOCK 0979 was selected for further research as one of represents a new line of research with scant available the most prospective antifungal strain. In this context, the literature. use of polyols and their galactosyl derivatives to enhance Since the antifungal activity of lactobacilli consists of a the inhibitory properties of lactobacilli is a novel solution complex set of interactions beginning at the cellular level, which offers a promising method for modulating LAB in this study considerable attention was given to the en- metabolism. In situ studies on food products describing zymatic activity of the bacteria in the presence of polyols 198 Probiotics & Antimicro. Prot. (2018) 10:186–200 Table 10. Morphological changes in the mycelia of Alternaria brassicicola grown for 7 days in Sabouraud medium with 10% (v/v) CFS from 48 h cultures of L. pentosus ŁOCK 0979 in media containing polyols and gal-polyols Photomicrographs of the morphological changes in the mycelia of Alternaria brassicicola, (magnification 400 ×) Control medium (Sabouraud agar) Sabouraud agar + CFS erythritol Sabouraud agar + CFS xylitol Sabouraud agar + CFS gal-erythritol Sabouraud agar + CFS gal-xylitol Sabouraud agar + CFS gal-sorbitol and gal-polyols. Some small differences were found in Conclusions enzymes metabolizing lipids, proteins, and phosphates, and in particular in esterase and esterase lipase, which The antifungal activity of L. pentosus ŁOCK 0979 depends on catalyze the hydrolysis and synthesis of organic acid es- the bacterial culture medium as well as on the fungal strain. ters, primarily from water-soluble substrates, such as tri- The present study shows changes in the antifungal profile of acylglycerols containing short chain fatty acids. Bacterial the studied bacterial strain linked to the composition of the esterase activity promotes the hydrolysis of a wide spec- culture medium. Although no single decisive factor trum of substrates to acids [5, 28], including antifungal (metabolite) was found to be responsible for inhibiting fungal metabolites. LAB enzymes can be used to modify the growth, the results indicate how bacterial metabolite profiles gustatory and olfactory properties of wines and cheeses may be beneficially modulated. Thus, the authors have broken and to produce some ingredients of foodstuffs, pharma- new ground in developing natural ways of ensuring the mi- ceuticals, and cosmetics [12]. Fatty acids and hydroxy crobiological safety of food. fatty acids synthesized by LAB affect fungal viability by irreversibly weakening and deforming the lipid bilayer Acknowledgements The authors thank Jaroslaw Arkusinski for tech- [23]. The morphological changes in the structure of the nical assistance. cell walls of C. vini (strains 0008 and 0009) and Funding This study was funded by the National Science Center (grant A. brassicicola mycelia, which were revealed in this study no. 2013/09/B/NZ9/01806). using SEM and light microscopy, corroborate that mech- anism of action for the obtained CFSs, which led to strong Compliance with Ethical Standards deformation of yeasts’ surface; similar morphological Ethical Statement All authors of this paper have read and approved the changes of Candida sp. were described by Shengli et al. final version submitted. The contents of this manuscript have not been [27]. In the presence of CFSs, yeasts can produce extra- copyrighted or published previously. cellular matrix to promote their adherence and protect 1. The contents of this manuscript are not now under consideration for cells from environmental insults [29]. publication elsewhere. Probiotics & Antimicro. Prot. 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Taff HT, Mitchell KF, Edward JA, Andes DR (2013) Mechanisms grade antifungal agent for bakery products. Int J Food Microbiol of Candida biofilm drug resistance. Future Microbiol 8:1325–1337. 146:276–283. https://doi.org/10.1016/j.ijfoodmicro.2011.02.036 https://doi.org/10.2217/fmb.13.101 26. Ryu EH, Yang EY, Woo ER, Chang HC (2014) Purification and 30. Tyler C, Kopit L, Doyle C, AO Y, Hugenholtz J, Marco ML (2016) characterization of antifungal compounds from Lactobacillus Polyol production during heterofermentative growth of the plant plantarum HD1 isolated from kim chi. Food Microbiol 41:19–26. isolate Lactobacillus florum 2F. J Appl Microbiol 120:1336– https://doi.org/10.1016/j.fm.2014.01.011 1345. https://doi.org/10.1111/jam.13108 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Probiotics and Antimicrobial Proteins Springer Journals

Antifungal Activity of Lactobacillus pentosus ŁOCK 0979 in the Presence of Polyols and Galactosyl-Polyols

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Probiotics & Antimicro. Prot. (2018) 10:186–200 https://doi.org/10.1007/s12602-017-9344-0 Antifungal Activity of Lactobacillus pentosus ŁOCK 0979 in the Presence of Polyols and Galactosyl-Polyols 1 2 2 3 Lidia Lipińska & Robert Klewicki & Michał Sójka & Radosław Bonikowski & 2 2 1 Dorota Żyżelewicz & Krzysztof Kołodziejczyk & Elżbieta Klewicka Published online: 6 November 2017 The Author(s) 2017. This article is an open access publication . . Abstract The antifungal activity of Lactobacillus pentosus Keywords Antifungal activity Galactosyl-polyols . . . ŁOCK 0979 depends both on the culture medium and on the Lactobacillus Metabolites Polyols SEM fungal species. In the control medium, the strain exhibited limited antagonistic activity against indicator food-borne molds and yeasts. However, the supplementation of the bac- Introduction terial culture medium with polyols (erythritol, lactitol, maltitol, mannitol, sorbitol, xylitol) or their galactosyl deriva- Filamentous fungi and yeasts are present in almost all types of tives (gal-erythritol, gal-sorbitol, gal-xylitol) enhanced the an- ecosystems due to their high adaptation ability and low nutri- tifungal properties of Lactobacillus pentosus ŁOCK 0979. Its tional requirements. Filamentous fungi are widespread food metabolites were identified and quantified by enzymatic spoilage microorganisms responsible for significant economic methods, HPLC, UHPLC-MS coupled with QuEChERS, losses in the agri-food industry [6]; they are also a major and GC-MS. The presence of polyols and gal-polyols signif- health concern due to mycotoxin production. The most com- icantly affected the acid metabolite profile of the bacterial mon genera of spoilage fungi include Penicillium, Fusarium, culture supernatant. In addition, lactitol and mannitol were Aspergillus, Cladosporium,and Rhizopus [21]. Commercial used by bacteria as alternative carbon sources. A number of foodstuffs are usually protected from such microorganisms by compounds with potential antifungal properties were identi- physical and chemical techniques. However, as chemical pre- fied, such as phenyllactic acid, hydroxyphenyllactic acid, and servatives have become less socially acceptable, natural pres- benzoic acid. Lactobacillus bacteria cultivated with mannitol ervation methods are being sought. Lactic acid fermentation synthesized hydroxy-fatty acids, including 2-hydroxy-4- has been known and used these purposes since antiquity. In methylpentanoic acid, a well-described antifungal agent. recent years, lactic acid bacteria (LAB) have been extensively Scanning electron microscopy (SEM) and light microscopy investigated for their antifungal properties and bioprotective confirmed a strong antifungal effect of L. pentosus ŁOCK cultures have been proposed as a promising biotechnological 0979. approach [22, 24, 25]. Of particular application interest are lactobacilli, which convert carbohydrates into lactic and acetic acids (primary metabolites), as well as a range of secondary metabolites, such as carbon dioxide, ethanol, hydrogen perox- * Lidia Lipińska lidialipinska8@gmail.com ide, fatty acids, acetoin, diacetyl, cyclic dipeptides, bacterio- cins, and bacteriocin-like inhibitory substances [3]. Since these metabolites exhibit only weak antifungal properties, Lodz University of Technology, Institute of Fermentation many research teams are seeking Lactobacillus strains with a Technology and Microbiology, Wolczanska 171/173, 90-024 Lodz, Poland higher natural ability to inhibit fungal and yeast growth [4, 9, 14, 15, 26]. Ryu et al. [26] reported that Lactobacillus Lodz University of Technology, Institute of Food Technology and Analysis, Stefanowskiego 4/10, 90-024 Lodz, Poland plantarum HD1 synthesizes 5-oxododecanoic acid (MW 214), 3-hydroxydecanoic acid (MW 188), and 3-hydroxy-5- Lodz University of Technology, Institute of General Food Chemistry, Stefanowskiego 4/10, 90-024 Lodz, Poland dodecenoic acid (MW 214), which are considered antifungal. Probiotics & Antimicro. Prot. (2018) 10:186–200 187 In turn, Magnusson [14, 16] showed that some LAB can erythritol, gal-xylitol, and gal-sorbitol are modern prebiotics convert glycerol to 1,3-propanediol, which inhibits fungal which confer beneficial effects [8], as related in the blood and growth. While the qualitative and quantitative composition digesta of laboratory rats (Klewicki 2007). of antifungal compounds generated by LAB is species- or even strain-specific, it can be modulated by culture medium Synthesis of Galactosyl Derivatives of Erythritol, Sorbitol, modification. For instance, Lipińska et al. [13] adjusted the and Xylitol antifungal spectrum of lactobacilli by adding polyols and their galactosyl derivatives, proving that the antagonistic activity of Galactosyl derivatives of erythritol, sorbitol, and xylitol were LAB depends on culture medium composition, the LAB obtained by enzymatic transglycosylation using β- species, and the sensitivity of the fungal species. It was found galactosidase EC 3.2.1.23 from Kluyveromyces lactis that in the presence of xylitol and gal-xylitol in the bacterial (Novozymes A/S, Bagsvaerd, Denmark). The procedure for culture medium Lactobacillus pentosus ŁOCK 0979 galactosyl-xylitol synthesis was described by Klewicki [11]. effectively inhibited the growth of A. niger, A. alternata, A. brassicicola, F. lateritium,and M. hiemalis [13]. The Determination of Antifungal Activity of Lactobacillus modulation of LAB metabolism by supplementing the culture pentosus ŁOCK 0979 in the Presence of Polyols medium with various, often atypical, compounds may give and Galactosyl-Polyols rise to new systems inhibiting the growth of spoilage microorganisms. The antagonistic activity of L. pentosus ŁOCK 0979 against The objective of the study was to determine the antifungal the indicator fungi was tested using the double-layer method properties, metabolite profile, and enzymatic activity of the described by Lipińska et al. [13]. First, 10 μL of overnight strain L. pentosus ŁOCK 0979 cultured in the presence of bacterial culture was dropped on MRS agar plates (Merck or polyols, namely, erythritol, xylitol, maltitol, mannitol, sorbi- BTL) supplemented with 1% (m/v) polyols, galactosyl- tol, and lactitol, and their transglycosylation derivatives (gal- polyols, or galactose, separately. The control group consisted erythritol, gal-xylitol, and gal-sorbitol). of MRS agar plates (Merck) with lactobacilli colonies cultured with neither polyols nor gal-polyols. After 18–24 h, the plates were overlaid with Sabouraud 4% dextrose agar (Merck) in- 5 6 Materials and Methods oculated with an indicator fungal strain (10 –10 −1 spores × mL ). Indicator strain inhibition zones around Microbiological Strains and Polyols Lactobacillus sp. colonies were measured after 24–72 h of cultivation at 30 °C. The results were given as fungal inhibi- The study material consisted of the bacterial strain L. pentosus tion diameters minus the diameter of Lactobacillus sp. ŁOCK 0979 and 10 fungal strains deposited with the Pure colonies. Cultures Collection of Industrial Microorganisms of the Institute of Fermentation Technology and Microbiology, Preparation of Cell-Free Supernatant After Lactic Acid Lodz University of Technology (ŁOCK 105). The indicator Fermentation fungi included the yeasts Candida vini 0008 and 0009 and the molds Mucor hiemalis 0519, Geotrichum candidum 0511, Following lactic acid fermentation by L. pentosus ŁOCK Alternaria alternata 0409, Alternaria brassicicola 0412, 0979 in media with one of polyols or galactosyl-polyols, sam- Aspergillus niger 0433, Fusarium lateritium 0508, ples of cell-free supernatant (CFS) were prepared in order to Aspergillus ochraceus,and Penicillium sp. Two of the tested identify and quantify the antifungal agents produced by the fungi, A. ochraceus and Penicillium sp., were newly isolated bacteria in the modified MRS media. from spoiled food. The media consisted of MRS broth (Merck) containing 1% Fungi were grown in Sabouraud 4% dextrose agar (Merck) (m/v) glucose supplemented with 1% (m/v)ofone of the and bacteria in MRS medium (Merck) supplemented with 1% polyols (erythritol, lactitol, maltitol, mannitol, sorbitol, or xy- (m/v) polyols (erythritol, lactitol, maltitol, mannitol, sorbitol, litol) or one of the gal-polyols (gal-erythritol, gal-sorbitol, or xylitol) or galactosyl polyols (gal-erythritol, gal-sorbitol, gal- gal-xylitol). The final pH was 5.7 ± 0.2. In the first step of the xylitol). The microorganisms were cultured at 30 °C under experiment, 200 mL of a medium was inoculated with 3% (v/ aerobic conditions. Fungi were stored at 4 °C on Sabouraud v) of overnight L. pentosus ŁOCK 0979 culture (10 – 6 −1 dextrose agar slants (Merck), and bacteria were kept at 10 cfu × mL ), andincubatedfor 48 hat30°C. − 20 °C in 20% (v/v) glycerol. Subsequently, the samples were centrifuged (10 min, The polyols used in the study (erythritol, lactitol, maltitol, 12,000×g, 20 °C), and the supernatants were filtered using mannitol, sorbitol, xylitol) occur naturally in some foodstuffs 0.22-μm syringe filters. CFS were stored at − 20 °C for further and may be added to others, e.g., as sweeteners. In turn, gal- study. 188 Probiotics & Antimicro. Prot. (2018) 10:186–200 Determination of the Content of Polyols and Saccharides Quantification of Antifungal Acids Using UHPLC-MS Using HPLC in Conjunction with QuEChERS Each CFS sample was diluted 10-fold. The obtained solution Antifungal metabolites produced by L. pentosus ŁOCK 0979 was passed through a 5-mL column BAKERBOND® spe in the presence of polyols and their galactosyl derivatives were Octadecyl (18) (J.T. Baker, USA) with cation and anion ex- quantified using the QuEChERS method and an ultra-high- change resins (1:2 v/v). The first fraction (3 mL) was performance liquid chromatography-mass spectrometry discarded, and the second one (3 mL) was collected for (UHPLC-MS) system according to a protocol modified from HPLC analysis. The content of saccharides and polyols was Oliveira et al. [20]. In the sample preparation step, 1 mL of determined using an Aminex HPX-87C column from Bio-Rad formic acid, 10 mL of ethyl acetate, and 10 mL of a CFS (0.78 × 30 cm, mobile phase: water, flow rate: sample were added to a Falcon test tube containing 4 mg of −1 0.5 mL × min , 85 °C). An RI detector and an integrating magnesium sulfate and 1 g of sodium chloride. The mixture system from Knauer were used. The tests were done in tripli- was shaken for 1 min and centrifuged (10 min, 1077×g). Then cate and prepared in three parallel columns. Statistical analysis 5 mL of the organic solvent was removed and added to an consisted of the Duncan test (p ≤ 0.05). Agilent dSPE kit (150 mg of C18, 900 mg of magnesium sulfate). The mixture was shaken for 1 min, centrifuged Spectrophotometric Determination of Glucose (10min,1077×g),anddecantedintoatest tubewith 100 mL of dimethyl sulfoxide (DMSO). The solutions were Glucose concentration in the pure culture medium and in post- concentrated for 3.5 h in a ScanVac ScanSpeed 40 centrifuge fermentation CFS was determined spectrophotometrically ac- evaporator (2000 rpm, 45 °C) equipped with a CoolSafe 110-4 cording to the instructions supplied with the enzymatic kit Pro cold trap (Labogene, Lynge, Denmark) until only 100 μL (BioMaxima) and a calibration curve. CFS and pure culture DMSO remained. The concentrated solution was mixed with medium samples were diluted 50- and 100-fold, respectively, 400 μL of 10% (v/v) acetonitrile, centrifuged (10 min, relative to the initial glucose content of the medium 10,000×g), and transferred into a 1.5-mL amber vial. −1 (10 g × L ). Subsequently, 1 mL of the reagent (glucose The following 13 antifungal compounds were quantified: oxidase and glucose peroxidase) and 0.01 mL of a tested sam- DL-3-phenyllactic acid, DL-p-hydroxyphenyllactic acid, ple (diluted culture or pure medium) were placed in a cuvette benzoic acid, hydrocaffeic acid, hydrocinnamic acid, vanillic and mixed. After 5 min (37 °C), the absorbance of the tested acid, 4-hydroxybenzoic acid, catechol, caffeic acid, ferulic sample was measured relative to the reagent blank acid, 3-hydroxybenzoic acid, 2,4-dihydroxybenzoic acid, (λ = 540 nm), with the results being proportionate to glucose and p-coumaric acid. content in the sample. Based on the prepared calibration curve A Dionex UltiMate 3000 ultra-high-performance liquid −1 (in the range of 0.01–4 g glucose × L ) glucose concentration chromatograph from Thermo Fisher Scientific (Germering, was determined both in medium and CFS samples, accounting Germany) coupled with a diode array detector (DAD) and a for their dilution. The tests for each sample were done in Q Exactive Orbitrap mass spectrometer (MS, Thermo Fisher triplicate, and statistical analysis involved one-way ANOVA Scientific, Bremen, Germany) was used for LC-MS analysis. (p ≤ 0.05). Chromatographic separation was performed using a 150-mm C18 column with a 2.1-mm internal diameter and 2.6-μm Concentration of D-Lactic Acid, L-Lactic Acid, and Acetic particle size (Kinetex 2.6u, Torrance, CA, USA). The column Acid temperature was maintained at 30 °C, and the injection vol- ume was 2.5 μL. The mobile phase consisted of the following: The quantification of D-lactic, L-lactic, and acetic acid requires Awas water containing 0.1% formic acid and B was a mixture enzymatic reactions described in the assay procedures: K- of acetonitrile and water (90:10, v/v) containing 0.1% formic DLLATE 07/14 and K-ACET 11/05 (Megazyme acid. The flow rate was 0.5 mL/min. The following gradient International Ireland). In the case of D-and L-lactic acids, the was used: 0–16.5 min, 5–40% B; 16.5–17.5 min, 40–95% B; manufacturer’s procedure for the sequential assay of both op- 17.5–20 min, 95% B; 20–22 min, 95–5% B; 22–27 min, 5% tical isomers was applied. The concentration of all tested acids B. After DAD detection, the separated compounds entered was estimated using colorimetric tests with the absorbance into the MS system via a heated electrospray ionization (H- measured (λ = 340 nm) in a control sample (non-inoculated ESI) source with a flow rate of 0.5 mL/min. Analyses were medium) and diluted CFS. The calculations were made ac- carried out in the negative ion mode. Chromatographic data cording to the manufacturer’s recommendations, taking into were collected using Xcalibur software (Thermo). The source consideration the dilution factor (F = 50). The tests were done parameters were as follows: a vaporizer temperature of in triplicate, and statistical analysis involved one-way 400 °C, an ion spray voltage of 4 kV, a capillary temperature ANOVA (p ≤ 0.05). of 380 °C, and sheath and auxiliary gas flow rates of 60 and Probiotics & Antimicro. Prot. (2018) 10:186–200 189 15 units, respectively. The detector was operated in either full The samples were analyzed by gas chromatography MS or full MS/dd-MS2 scan modes. In the full MS mode, the coupled with mass spectrometry (TRACE GC Ultra—ISQ) scan rage of m/z 50–400 was used. The full MS/dd-MS scan using a Stabilwax-DA capillary column (30 m × 0.25 mm mode was used to generate MS2 data. In this mode, the se- i.d., film thickness 0.25 μm). The operating conditions were lected precursor ions entered into a high-energy collision-in- as follows: temperature program—50 °C (3 min)–240 °C duced dissociation (CID) cell, where they were fragmented (30 min) at 4 °C/min, injection temperature—240 °C, carrier with normalized collision energy (NCE) to obtain product gas—helium (constant flow 1 mL/min). Mass spectrometer ion spectra (MS ). In our experiments, the NCE used to gen- parameters were as follows: 33–550 amu, ionization energy erate MS spectra was set to 30. Tuning and optimization were 70 eV, ion source temperature 200 °C. Identification of com- performed using direct injection of the standard solution dilut- pounds was based on a comparison of their mass spectra with ed in an 80:20 (v/v) mixture of mobile phases A and B at a computerized libraries (Wiley Registry 10th Edition/NIST flow rate of 0.25 mL/min. Acids were quantified using the Mass Spectral Library 2012). selected ion monitoring (SIM) mode. The standard curves of Mannitol was chosen as one of the best agents enhancing these compounds were used for quantification. Table 1 gives the antifungal effect of L. pentosus ŁOCK 0979. Moreover, in acquisition parameters for 13 acids in the tested solution. the presence of mannitol, many signals from acidic com- Acid quantification was performed in triplicate, and statis- pounds were obtained using UHPLC-MS analysis, but they tical analysis was conducted using the Duncan test (p ≤ 0.05). could not be identified by the UHPLC-MS method due to their molecular structure (data not presented). Identification of Fatty Acids and Hydroxylated Fatty Acids by Gas Chromatography Coupled with Mass API®ZYM 25200 Test of Bacterial Enzymatic Activity Spectrometry Bacteria were grown for 24 h in 9 mL of MRS broth Lactobacillus pentosus ŁOCK 0979 was grown at 30 °C in (Merck) with 1% (m/v) polyols or galactosyl-polyols, 150 mL of MRS broth (Merck) with 1% (m/v) mannitol. The added one by one. The cultures were centrifuged (10 min, 48-h culture was centrifuged (10 min, 12,000×g,20 °C), and 12,000×g, 20 °C), and the biomass was suspended in saline supernatant pH was adjusted to 4.0 with hydrochloric acid. to obtain a cell concentration corresponding to 5–6onthe 9 −1 Then, 100 mL of the sample was extracted with 30 mL of McFarland scale (approx. 1.5 × 10 cells × mL ). API dichloromethane, mixed for 3 min, and settled for 10 min. ZYM strips were placed in API ZYM boxes humidified Extraction of the aqueous phase was repeated twice using by distilled water. The strips were inoculated with 65 μL further portions of dichloromethane. The organic phases were of the sample and incubated for 4 h at 37 °C. Then, the combined, dried over anhydrous sodium sulfate, and, follow- reagents ZYM A and ZYM B (bioMerieux) were added ing filtration, concentrated to approx. 0.5 mL in a rotatory dropwise. The strips were placed under a powerful light evaporator. The residue was derivatized with 200 μLof source for 10 s and then exposed to daylight for 5– 0.25 M trimethylsulfonium hydroxide solution (TMSH, 10 min. Results were read according to the manufacturer’s Sigma Aldrich) in methanol. recommendations. Table 1 LC-MS acquisition Compound Retention time (min) Confirmation ion (m/z) Quantitation ion (m/z) parameters for acids detected in post-fermentation cell-free Catechol 3.27 – 109 supernatant 3.44 163, 135, 119 181 DL-p-Hydroxyphenyllactic acid 3-Hydroxybenzoic acid 4.38 93 137 Hydrocaffeic acid 4.88 137, 109 181 2,4-Dihydroxybenzoic acid 5.47 109 153 4-Hydroxybenzoic acid 5.47 93 137 Vanillic acid 5.52 152, 123, 108 167 Caffeic acid 5.88 135 179 6.80 147, 119 165 DL-3-Phenyllactic acid p-Coumaric acid 7.88 119 163 Ferulic acid 8.74 178, 134 193 Hydrocinnamic acid 12.17 121 149 190 Probiotics & Antimicro. Prot. (2018) 10:186–200 The Effects of Cell-Free Supernatants on Fungal Growth Mold inhibition by L. pentosus ŁOCK 0979 depended both and Morphology Evaluated with Scanning Electron on the culture medium composition and on mold species. The Microscopy and Light Microscopy A. alternata test strain and the A. ochraceus and Penicillium sp. strains isolated from the environment exhibited the greatest Fungal strains sensitive to the metabolites of polyols or gal- sensitivity to lactic acid fermentation products both in the polyols were selected based on the antagonistic activity of controls and in samples with polyols and gal-polyols L. pentosus ŁOCK 0979 cultured in different culture media. (Table 2). In contrast, the growth of A. brassicicola and CFS samples were added to Sabouraud 4% dextrose agar A. niger was inhibited by L. pentosus ŁOCK 0979 only if (Merck) in the amount of 10% (v/v). The medium was subse- the bacterial culture medium was supplemented with polyols quently placed in 6-well plates and inoculated with selected (both mold strains) or gal-polyols (only A. brassicicola). The fungal strains using an inoculation loop. Microscopic examina- antifungal activity of L. pentosus ŁOCK 0979 was also im- tion was carried out after 2 days (yeasts) and 7 days (molds) proved by polyols and their galactosyl derivatives with respect using a light microscope. Additionally, yeast morphology was to F. lateritium. Its growth was inhibited by the bacteria cul- examined using a scanning electron microscope (JEOL JCM- tured in the presence of maltitol and sorbitol, as well as all 6000, Tokyo, Japan) after coating with gold particles for 45 s tested galactosyl-polyols. Antagonistic activity against (JEOL JFC-1200 Fine Coater, Tokyo, Japan). The experiments G. candidum and M. hiemalis was weak (Table 2). were conducted in duplicate. The control samples consisted of In a similar way, additional control trials were conducted fungi cultured on Sabouraud agar without bacterial CFS. using MRS medium with glucose (Merck) and 1% (m/v)galac- tose, as well as a glucose-free MRS medium (BTL) with 1% (m/ v) galactose. These media enhanced the antagonistic activity of L. pentosus ŁOCK 0979 only against one indicator fungal strain Results (F. lateritium)ascomparedtobacteriacultivatedonMRS agar (Merck). Therefore, it can be assumed that the small amounts of Antifungal Activity of Lactobacillus pentosus ŁOCK 0979 galactose released as a result of galactosyl-polyol hydrolysis in the Presence of Polyols and Galactosyl-Polyols (Table 3) are not a critical determinant of antifungal properties. The antagonistic activity of L. pentosus ŁOCK 0979 against the tested yeasts was weak, but its anticandidal properties were Content of Polyols and Saccharides in Cell-Free enhanced in the presence of galactosyl-polyols, and especially Supernatant gal-erythritol. The addition of gal-sorbitol and gal-xylitol to the bacterial culture medium led to inhibition of only one of the two The content of polyols and saccharides before and after lactic strains of yeast, that is, C. vini ŁOCK 0009 (Table 2). acid fermentation by L. pentosus ŁOCK0979inthepresence of Table 2 Antifungal activity of Growth media Yeasts Molds Lactobacillus pentosus ŁOCK 1 2 3 4 56 78 9 10 MRS (control) –– + + +++ – + – +++ +++ MRS + erythritol –– + + ++ + ++ + ++ +++ MRS + lactitol – ––– +++ ++ + ++ +++ +++ MRS + xylitol –– + – + ++ ++ + +++ +++ MRS + maltitol –– + – +++ +++ ++ ++ +++ MRS + mannitol –– + – +++ +++ ++ + +++ +++ MRS + sorbitol –– + – +++ – +++ – +++ ++ MRS + gal-erythritol ++ + +/− – ++ +++ ++ – +++ +++ MRS + gal-xylitol – +/− ++/− +++ +++ +++ +/− +++ +++ MRS + gal-sorbitol – ++ – +++ +++ +++ +/− X+++ MRS + galactose –– + – +++ +++ +++ – ++ MRS + galactose (glucose-free) –– + – ++ ++ ++ – ++ 1. C. vini 0008, 2. C. vini 0009, 3. M. hiemalis,4. G. candidum,5. A. alternata,6. A. brassicicola,7. F. lateritium, 8. A. niger,9. A. ochraceus,10. Penicillium sp. X no tested, − no inhibition zone, +/− inhibition zone between 0.5 and 2 mm, + inhibition zone between 2.1 and 10 mm, ++ inhibition zone between 10.1 and 20 mm, +++ inhibition zone above 20 mm, nt not tested Probiotics & Antimicro. Prot. (2018) 10:186–200 191 Table 3 Concentration of −1 −1 Media Compounds Initial content (g × L ) Residual content (g × L ) polyols and saccharides before and after lactic acid fermentation MRS (control) Glucose 20.9 ± 3.61 – by Lactobacillus pentosus ŁOCK 0979 in media containing polyols MRS + erythritol Glucose 25.4 ± 0.01 – and their galactosyl derivatives Erythritol 10.6 ± 0.27a 10.1 ± 0.10a MRS + lactitol Glucose 20.2 ± 0 – Lactitol 10.0 ± 0a 9.03 ± 0.11b MRS + xylitol Glucose 18.7 ± 0.92 – Xylitol 10.3 ± 0.10a 10.0 ± 0a MRS + maltitol Glucose 20.2 ± 0.77 – Maltitol 10.4 ± 0.54a 10.0 ± 0a MRS + mannitol Glucose 13.14 ± 0.11 – Mannitol 10.0 ± 0.04a 7.4 ± 0.70b MRS + sorbitol Glucose 19.0 ± 0.34 – Sorbitol 10.0 ± 0a 9.7 ± 0.22a MRS + gal-erythritol Glucose 18.9 ± 0.01 – Gal-erythritol 10.03 ± 0a 5.8 ± 0.73b Erythritol – 1.7 ± 0.09 Galactose – 0.6 ± 0.09 MRS + gal-xylitol Glucose 20.6 ± 0 – Gal-xylitol 9.9 ± 0.68a 7.7 ± 0.21b Xylitol – 1.0 ± 0.07 MRS + gal-sorbitol Glucose 18.7 ± 0 – Gal-sorbitol 10.5 ± 0.07a 7.8 ± 0.38b Sorbitol – 0.7 ± 0.08 Galactose – 0.1 ± 0.02 Means designated with the same lowercase letter are not significantly different (Duncan’s multiple range test) – below the limit of detection −1 polyols and gal-polyols was determined using HPLC, and the , while that of lactic acid 4.09 ± 0.178 to 7.62 ± 0.010 g × L −1 concentration of glucose was evaluated spectrophotometrically was from 4.58 ± 0.390 to 20.26 ± 1.489 g × L ; in all sam- (Table 3). The results show that in lactic acid fermentation the ples, the dominant stereoisomer was L-lactic acid accounting bacteria used glucose as a primary carbon source, while the for 61–100% of the total (Table 4). The mean pH of the post- galactosyl-polyols and polyols (lactitol, mannitol) were used fermentation supernatant was higher in the case of gal-polyols as additional carbon sources to varying degrees (Table 3). (pH 4.13 ± 0.12) than polyols (pH 3.88 ± 0.290), except for The mannitol and lactitol present in the culture media were sorbitol (pH 4.4). Samples with higher pH (gal-polyols, partially used by L. pentosus ŁOCK 0979 (as reflected in 10 sorbitol) exhibited a lower concentration of lactic acid −1 and 26% decline in concentration after lactic acid fermenta- (4.58–9.49 g × L ) and a higher concentration of acetic acid −1 tion, respectively). Galactosyl-polyols (gal-erythritol, gal-xy- (5.76–7.62 g × L ). L. pentosus ŁOCK 0979 generated the litol, and gal-sorbitol) were hydrolyzed to galactose and the highest amounts of lactic and acetic acids in the presence of − 1 respective polyols. Residual galactose was found in post- xylitol (20.26 ± 1.489 g × L ) and gal-xylitol −1 fermentation CFS from samples supplemented with gal- (7.62 ± 0.010 g × L ), respectively (Table 4). erythritol and gal-sorbitol (Table 3). The content of erythritol, xylitol, maltitol, and sorbitol in the medium did not change Effects of Polyols and Gal-Polyols on the Content significantly following lactic acid fermentation (Table 3). of Antifungal Acids Acidity and Production of Acetic and Lactic Acids The following 13 antifungal acids were quantified: DL-3- phenyllactic acid (PLA), DL-p-hydroxyphenyllactic acid The concentration of acetic acid and lactic acid (L- and D- (HPLA), benzoic acid (BA), hydrocaffeic acid (HCaA), enantiomers separately) was evaluated enzymatically using hydrocinnamic acid (HCiA), vanillic acid (VA), 4- Megazyme kits. The total content of acetic acid was from hydroxybenzoic acid (4-HBA), catechol (Cat), caffeic acid 192 Probiotics & Antimicro. Prot. (2018) 10:186–200 Table 4 Production of acetic, D- Medium pH Production of lactic acid Production of acetic lactic, and L-lactic acids by −1 acid (g × L ) Lactobacillus pentosus ŁOCK % D-lactic % L-lactic 0979 in the presence of polyols DL-Lactic acid −1 acid [%] acid [%] and gal-polyols (g × L ) Non-inoculated medium 5.7 ± 0.2–– – 0.07 ± 0.000 MRS MRS (control) 3.6 13.89 ± 0.448 7.0 93.0 4.39 ± 0.105 MRS + erythritol 3.7 12.77 ± 0.015 0.0 100.0 4.75 ± 0.178 MRS + lactitol 3.7 15.01 ± 3.458 6.6 93.3 4.09 ± 0.178 MRS + xylitol 4.0 20.26 ± 1.489 14.2 85.8 5.71 ± 0.024 MRS + maltitol 3.9 10.89 ± 0.000 0.0 100.0 4.87 ± 0.003 MRS + mannitol 3.6 15.26 ± 1.619 5.1 94.9 5.76 ± 0.020 MRS + sorbitol 4.4 5.74 ± 1.257 34.8 65,2 6.52 ± 0.010 MRS + gal-erythritol 4.2 9.49 ± 0.234 37.7 62.3 6.61 ± 0.023 MRS + gal-xylitol 4.2 8.81 ± 1.685 38.6 61.4 7.62 ± 0.010 MRS + gal-sorbitol 4.0 4.58 ± 0.390 31.9 68.1 7.17 ± 0.020 Significantly different from the control test (CaA), ferulic acid (FA), 3-hydroxybenzoic acid (3-HBA), Enzymatic Activity of Lactobacillus pentosus ŁOCK 0979 2,4-dihydroxybenzoic acid (2,4-dHBA), and p-coumaric acid (p-CoumA), using a UHPLC-MS system coupled with Examination of the activity of enzymes metabolizing lipids, QuEChERS. It was found that the minimum inhibitory con- proteins, and phosphates revealed some minor differences be- centrations of the tested acids are many times higher than their tween L. pentosus ŁOCK 0979 cultures conducted in media actual concentrations in CFS (Table 5). Statistically significant supplemented with various polyols and gal-polyols (Table 7). differences in the content of PLA and HCaAwere linked to the As compared to the controls, esterase activity was found only composition of the culture medium. PLA content in CFS from in the presence of lactitol and gal-sorbitol, while that of ester- the bacterial culture with gal-xylitol differed from that found ase lipase in the presence of gal-erythritol. in cultures with lactitol and xylitol. In the presence of gal- erythritol and gal-xylitol, L. pentosus ŁOCK 0979 produced Effects of Polyols and Gal-Polyols on Fungal Growth double to triple the amount of vanillic acid and half the and Morphology amount of Cat as compared to the other CFS. The content of HCaA, HCiA, VA, 4-HBA, Cat, CaA, FA, 3-HBA, 2,4- The yeasts C. vini ŁOCK 0008 and ŁOCK 0009 and the mold dHBA, and p-CoumA was low and ranged from approx. 0 A. brassicicola were examined microscopically following cul- −1 (<LOD) to 0.161 mg × L (Table 5). ture in Sabouraud agar with 10% (v/v) CFS. The results are given in Tables 8 and 10. Scanning electron micrographs of C. vini ŁOCK 0009 cultivated in the presence of CFSs are Production of Hydroxy Fatty Acids in the Presence presented in Table 9. of Mannitol Light microscopy revealed greater cell differentiation in the yeast C. vini ŁOCK 0008 grown in Sabouraud agar with 10% Volatile compounds with potential antifungal properties (v/v) CFS from L. pentosus ŁOCK 0979 cultured in the pres- (fatty acids, hydroxy fatty acids) synthesized by ence of gal-erythritol than the control (Table 8). Candida vini L. pentosus ŁOCK0979culturedinMRS andinthe ŁOCK 0008 cells were at different developmental stages and presence of 1% (m/v) mannitol were identified included both single cells and some initial degrees of (Table 6). Mannitol induced antagonistic activity of pseudomycelium formation. The same was true of C. vini L. pentosus ŁOCK 0979 against some of the test fungi ŁOCK 0009 grown in Sabouraud agar with 10% (v/v)CFS (A. brassicicola, A. niger, F. lateritium), which must from L. pentosus ŁOCK 0979 cultured in the presence of gal- therefore be attributable to one or more metabolites syn- polyols (gal-erythritol, gal-xylitol, gal-sorbitol). What is more, thesized in the presence of this polyol. Moreover, CFS the addition of gal-polyols to the bacterial medium led to samples revealed 2-hydroxy-4-methylpentanoic acid, a fungal deformation and gave rise to blastoconidia (CFS gal- compound described by Ndagano et al. [19]asastrong erythritol, CFS gal-xylitol, CFS gal-sorbitol) (red arrows in antifungal agent. the Table 8). The yeast cells were narrower, and some of them Probiotics & Antimicro. Prot. (2018) 10:186–200 193 Table 5 Content of antifungal acids produced by Lactobacillus pentosus ŁOCK 0979 as determined by HPLC coupled with QuEChERS −1 Polyols in medium Production of antifungal acids and their referential MIC (mg × L ) PLA HPLA BA* 3-HBA* HCaA MRS—non-inoculated 0.107 ± 0.001 0.033 ± 0.003 0.339 ± 0.010 0.062 ± 0.002 0.006 ± 0.001 MRS (control) 41.513 ± 1.175 4.255 ± 0.069 0.623 ± 0.049 0.072 ± 0.002 0.090 ± 0.001 Erythritol 40.319 ± 0.865 4.132 ± 0.045 0.614 ± 0.103 0.072.002 0.062 ± 0 Lactitol 51.228 ± 0.482 x 4.872 ± 0.161 0.504 ± 0.022 0.078 ± 0.001 0.088 ± 0.001 Xylitol 49.988 ± 1.026z 4.869 ± 0.052 0.504 ± 0.017 0.079 ± 0.001 0.083 ± 0.003 Maltitol 24.224 ± 16.272 2.844 ± 1405 0.249 ± 0.094 0.050 ± 0.023 0.060 ± 0.033 Mannitol 40.992 ± 0.875 4.128 ± 0.096 0.582 ± 0.007 0.073 ± 0.001 0.085 ± 0.003 Sorbitol 31.962 ± 14.709 3.93 ± 0.852 0.49 ± 0.282 0.06 ± 0.017 0.06 ± 0.032 Gal-erythritol 21.91 ± 5.455 6.13 ± 4.311 0.03 ± 0.010 0.06 ± 0.013 0.04 ± 0.010 Gal-xylitol 16.65 ± 1.679 X, Z 2.46 ± 0.217 0.34 ± 0.005 0.05 ± 0.005 0.03 ± 0.003 X Gal-sorbitol 24.89 ± 8.188 3.14 ± 0.753 0.40 ± 0.106 0.06 ± 0 0.04 ± 0.018 MIC (Oliveira et al. 2015) 7500–10,000 – 20–2000 – >10,000 −1 Polyols in medium Production of antifungal acids and their referential MIC (mg × L ) HPLA 2,4-dHBA Cat 4-HBA Vanillic acid HCiA MRS—non-inoculated 0.033 ± 0.003 0.031 ± 0.001 0.015 ± 0.002 < 0.008 0.186 ± 0.006 < 0.017 MRS (control) 4.255 ± 0.069 0.012 ± 0.002 0.045 ± 0.003 < 0.008 0.003 ± 0 < 0.017 Erythritol 4.132 ± 0.045 0.010 ± 0 0.037 ± 0 < 0.008 0.086 ± 0.007 < 0.017 Lactitol 4.872 ± 0.161 0.011 ± 0.001 0.048 ± 0.004 < 0.008 0.070 ± 0.003 < 0.017 Xylitol 4.869 ± 0.052 0.011 ± 0.001 0.039 ± 0.003 < 0.008 0.075 ± 0.007 < 0.017 Maltitol 2.844 ± 1405 0.009 ± 0.002 0.034 ± 0.007 < 0.008 0.041 ± 0.015 < 0.017 Mannitol 4.128 ± 0.096 0.011 ± 0.001 0.049 ± 0.008 < 0.008 0.086 ± 0.003 < 0.017 Sorbitol 3.93 ± 0.852 0.01 ± 0.002 0.040 ± 0.003 < 0.008 0.084 ± 0.012 < 0.017 Gal-erythritol 6.13 ± 4.311 0.02 ± 0.001 0.018 ± 0.005 < 0.008 0.161 ± 0.057 < 0.017 Gal-xylitol 2.46 ± 0.217 0.02 ± 0.001 0.017 ± 0.001 0.012 ± 0.001 0.127 ± 0.001 < 0.017 Gal-sorbitol 3.14 ± 0.753 0.01 ± 0.005 0.044 ± 0.001 < 0.008 0.005 ± 0 < 0.017 MIC (Oliveira et al. 2015) –– > 1000 > 1000 > 100 100–1000 Distributions with both a capital and small letter are significantly different from each other (Tukey’stest p ≤ 0.05) PLA DL-3-phenyllactic acid, HPLA DL-p-hydroxyphenyllactic acid, BA benzoic acid, 3-HBA 3-hydroxybenzoic acid, HCaA hydrocaffeic acid, 2,4-dHBA 2,4-dihydroxybenzoic acid, Cat catechol, 4-HBA 4-hydroxybenzoic acid, VA vanillic acid, CaA caffeic acid, p-CoumA p-coumaric acid, FA ferulic acid, HCiA hydrocinnamic acid *p value estimated in Tukey’stest ≤ 0.05 (significance of differences may not be estimated) became pear-shaped as compared to the controls (Table 8). were found for all gal-polyols in the bacterial medium SEM provided more details about the form and surface of (Table 10). The addition of lactitol and mannitol to the bacte- C. vini ŁOCK 0009. In the control, yeasts were elliptical and rial medium led to complete inhibition of fungal growth developed pseudohyphae with smooth and flat surfaces (hence no photomicrographs). (Table 9). The cells of C. vini ŁOCK 0009 cultivated with the CFS of L. pentosus ŁOCK 0979 in the presence of gal- polyols were strongly deformed. Their shape was warped and Discussion the surface rough, and cell damage was visible in the form of concave areas on the surface (Table 9). Additionally, in the The control of spoilage microorganisms and, by the same presence of CFS gal-xylitol yeasts, cells were coated by ex- token, the extension of the shelf-life of foodstuffs still pose tracellular matrix (Table 9). formidable challenges. While the use of Lactobacillus sp. as Morphological changes were also observed in the myceli- natural bioprotective agents was already reported by um of the mold A. brassicicola grown in Sabouraud agar with Magnusson [14], a definitive explanation of their mechanism 10% (v/v) CFS from L. pentosus ŁOCK 0979 cultured in of action against undesirable fungi was not provided. bacterial media supplemented with erythritol and xylitol. Lactobacilli inhibit the growth of other bacteria (of the Furthermore, growth inhibition and mycelium deformation same or different species) as well as that of fungi, including 194 Probiotics & Antimicro. Prot. (2018) 10:186–200 Table 6 Volatile compounds No. Media produced by Lactobacillus pentosus ŁOCK 0979 in MRS Compound MRS—non-inoculated MRS (control) MRS + mannitol broth and in the presence of mannitol 1Butanoicacid + + + 2 2-Methylbutanoic acid + + – 3 Isovaleric acid + + + 4 Caproic acid + + + 5 3-Hydroxypropanoic acid – ++ 7 2-Hydroxypropanoic acid + + + 8 2-Hydroxyisocaproic acid – ++ 9 Octanoic acid + + + 10 2-Hydroxy-3-methylbutyric acid – ++ 11 2-Hydroxybutanoic acid + + – 12 2-Methylthioacetic acid + + – 13 Acetic acid + + – 14 Acetoxyacetic acid + –– 17 2-Hydroxy-3-methylpentanoic acid – + – 18 2-Hydroxy-4-methylpentanoic acid – ++ 19 3-(Methylthio)propanoic acid – + – 20 3-Hydroxypropanoic acid – + – 21 Decanoic acid + –– 22 Butanedioic acid + – + 23 2-Oxopentanedioic acid – + – 24 Benzoic acid + + + 25 2-Hydroxypropanoic acid + – + 27 Phenylacetic acid + + + 28 Dodecanoic acid – ++ 29 Hydrocinnamic acid – + – 30 Myristic acid + + + 32 Pentadecanoic acid – + – 33 Azelaic acid, dimethyl ester + + – 34 Palmitic acid + + + 35 2-Pyrrolidone-5-carboxylic acid –– + 36 Palmitoleic acid + + + 37 2-Hydroxybenzenepropanoic acid – ++ 38 Heptadecanoic acid (C17:0) + + – 39 Citric acid, trimethyl ester + –– 40 Methyl stearate + + + 37 9-Octadecenoic acid + + + 38 11-Octadecenoic acid – + – 39 Linoleic acid – ++ 40 9,12-Octadecadienoic acid + –– 37 Linolelaidic acid –– + 38 9,12-Octadecadienoic acid + + + 39 Eicosanoic acid + + – 40 11-Eicosenoic acid –– + 41 3-Octyloxiraneoctanoic acid + + + 42 10-hydroxyoctadecanoic acid – + – Probiotics & Antimicro. Prot. (2018) 10:186–200 195 Table 7 Effects of culture medium on the enzymatic activity of Lactobacillus pentosus 0979 Enzymes Enzymatic activity of Lactobacillus pentosus ŁOCK 0979 cultured with polyols and gal-polyols MRS MRS + MRS + MRS + MRS + MRS + MRS + MRS + MRS + MRS + (control) erythritol lactitol xylitol maltitol mannitol sorbitol gal-erythritol gal-xylitol gal-sorbitol Control – ––– –––– – – Alkaline phosphatase EC – ––– –––– – – Esterase (C4) –– +/− – –––– – +/− Esterase Lipase (C8) – ––– ––– + –– Lipase (C14) – ––– –––– – – Leucinearylamidase + +++ ++++ + + Valinearylamidase + +++ ++++ + + Cystine arylamidase – –– –––– – – Trypsin – ––– –––– – – α-Chymotrypsin – ––– –––– – – Acid phosphatase +/− ++ – ++ – + – + Naphthol-AS-BI-phosphohydrolase – ––– –––– – – α-Galactosidase + +++ +++/− ++ + β-Galactosidase + +++ ++++ + + β-Glucuronidase + + – + ++++ +/− + α-Glucosidase – ++/− +/− ––– + – ++ β-Glucosidase + +++ ++++ + + N-Acetyl-β-glucosaminidase – ––– –––– – – α-Mannosidase – ––– –––– – – α-Fucosidase – ––– –––– – – 196 Probiotics & Antimicro. Prot. (2018) 10:186–200 Table 8. Micrographs of yeasts grown for 2 days in Sabouraud medium with 10% (v/v) cell-free supernatant of Lactobacillus pentosus ŁOCK 0979 cultivated 48 h in the media containing gal-polyols Yeast strain/ Incubation time Photomicrographs, magnification 400 × C. vini ŁOCK 0008/ 48 h Control (Sabouraud agar) Sabouraud agar + CFS gal-erythritol C. vini ŁOCK 0009/ 48 h Control (Sabouraud agar) Sabouraud agar + CFS gal-erythritol Sabouraud agar + CFS gal-xylitol Sabouraud agar + CFS gal-sorbitol pathogenic and toxin-producing molds [1, 7]. While many of lactic acid fermentation is 3-phenyllactic acid (PLA), authors have reported the antifungal properties of LAB [3, synthesized by LAB such as L. casei, L. fermentum, 10], their exact underlying mechanisms remain elusive. L. rhamnosus, L. reuteri,and L. sakei [14, 17, 18]. While Nevertheless, it is known that a major role is played by L. pentosus ŁOCK 0979 does produce PLA, its concentra- some bacterial metabolites, and especially by organic tion in the CFS is much lower than its minimum inhibitory acids, hydroxy fatty acids, cyclic dipeptides, and low mo- concentration reported by other authors [20]. lecular weight proteinaceous compounds [22]. In addition The antifungal metabolites of Lactobacillus sp. constitute a to primary metabolites (lactic and acetic acids), which are rich mixture of active compounds whose qualitative and quan- produced by all Lactobacilli. sp., some LAB species syn- titative composition largely depends on the compounds found thesize secondary metabolites, which may selectively af- in the bacterial culture medium. Ndagano et al. [19], who fect other microorganisms; these include propionic, evaluated the effects of different concentrations and propor- hexanoic, salicylic, succinic, formic, 2-pyrrolidone-5-car- tions of acetic and lactic acids on fungal viability, observed boxylic, 3-phenyllactic, and 4-hydroxyphenyllactic acids significant synergies: the mixture was more potent than the [2, 14, 17]. One of the best described antifungal products sum of its individual components taken together. Synergies Probiotics & Antimicro. Prot. (2018) 10:186–200 197 Table 9. Scanning electron micrographs of yeasts grown for 2 days on Sabouraud agar medium with 10% (v/v) CFS from 48 h culture of Lactobacillus pentosus ŁOCK 0979 in media containing gal-polyols Scaning electron micrographs of Candida vini ŁOCK 0009, magnification 2000 × Sabouraud agar + CFS gal-erythritol Control medium (Sabouraud agar) Sabouraud agar + CFS gal-xylitol Sabouraud agar + CFS gal-sorbitol may also be found for some parameters of the culture medium, enhanced antifungal activity of lactobacilli on fruits have such as pH. been presented by Lipinska et al. [13]. The study presented herein was preceded by evaluation In the presented experiments, L. pentosus ŁOCK 0979 ex- of 60 Lactobacillus sp. strains, including L. pentosus hibited the ability to partially absorb lactitol, mannitol, and all ŁOCK 0979, cultured in the presence of polyols and the tested galactosyl-polyols. While Tyler et al. [30]isolated galactosyl-polyols as alternative carbon sources [13]to Lactobacillus florum 2F, a heterofermentative strain which select bacteria with strong antagonistic properties against can biosynthesize erythritol and mannitol, the consumption as many indicator fungal strains as possible. L. pentosus of polyols and galactosyl-polyols by Lactobacillus bacteria ŁOCK 0979 was selected for further research as one of represents a new line of research with scant available the most prospective antifungal strain. In this context, the literature. use of polyols and their galactosyl derivatives to enhance Since the antifungal activity of lactobacilli consists of a the inhibitory properties of lactobacilli is a novel solution complex set of interactions beginning at the cellular level, which offers a promising method for modulating LAB in this study considerable attention was given to the en- metabolism. In situ studies on food products describing zymatic activity of the bacteria in the presence of polyols 198 Probiotics & Antimicro. Prot. (2018) 10:186–200 Table 10. Morphological changes in the mycelia of Alternaria brassicicola grown for 7 days in Sabouraud medium with 10% (v/v) CFS from 48 h cultures of L. pentosus ŁOCK 0979 in media containing polyols and gal-polyols Photomicrographs of the morphological changes in the mycelia of Alternaria brassicicola, (magnification 400 ×) Control medium (Sabouraud agar) Sabouraud agar + CFS erythritol Sabouraud agar + CFS xylitol Sabouraud agar + CFS gal-erythritol Sabouraud agar + CFS gal-xylitol Sabouraud agar + CFS gal-sorbitol and gal-polyols. Some small differences were found in Conclusions enzymes metabolizing lipids, proteins, and phosphates, and in particular in esterase and esterase lipase, which The antifungal activity of L. pentosus ŁOCK 0979 depends on catalyze the hydrolysis and synthesis of organic acid es- the bacterial culture medium as well as on the fungal strain. ters, primarily from water-soluble substrates, such as tri- The present study shows changes in the antifungal profile of acylglycerols containing short chain fatty acids. Bacterial the studied bacterial strain linked to the composition of the esterase activity promotes the hydrolysis of a wide spec- culture medium. Although no single decisive factor trum of substrates to acids [5, 28], including antifungal (metabolite) was found to be responsible for inhibiting fungal metabolites. LAB enzymes can be used to modify the growth, the results indicate how bacterial metabolite profiles gustatory and olfactory properties of wines and cheeses may be beneficially modulated. Thus, the authors have broken and to produce some ingredients of foodstuffs, pharma- new ground in developing natural ways of ensuring the mi- ceuticals, and cosmetics [12]. Fatty acids and hydroxy crobiological safety of food. fatty acids synthesized by LAB affect fungal viability by irreversibly weakening and deforming the lipid bilayer Acknowledgements The authors thank Jaroslaw Arkusinski for tech- [23]. The morphological changes in the structure of the nical assistance. cell walls of C. vini (strains 0008 and 0009) and Funding This study was funded by the National Science Center (grant A. brassicicola mycelia, which were revealed in this study no. 2013/09/B/NZ9/01806). using SEM and light microscopy, corroborate that mech- anism of action for the obtained CFSs, which led to strong Compliance with Ethical Standards deformation of yeasts’ surface; similar morphological Ethical Statement All authors of this paper have read and approved the changes of Candida sp. were described by Shengli et al. final version submitted. The contents of this manuscript have not been [27]. In the presence of CFSs, yeasts can produce extra- copyrighted or published previously. cellular matrix to promote their adherence and protect 1. The contents of this manuscript are not now under consideration for cells from environmental insults [29]. publication elsewhere. Probiotics & Antimicro. Prot. 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Journal

Probiotics and Antimicrobial ProteinsSpringer Journals

Published: Nov 6, 2017

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