Effect of temperature on milk fats of cow, buffalo, and goat used for frying local food products

Effect of temperature on milk fats of cow, buffalo, and goat used for frying local food products Objectives: Thermal processes, such as refining and frying, result in the formation of trans fatty acids (TFAs) in edible oils or fats. Concerning the detrimental effect of TFAs on human health, milk fat samples of cow, buffalo, and goat are collected in order to elucidate TFAs accumulation during thermal processing. Methods: The increased amount of TFAs due to heating is analyzed by attenuated total reflection- Fourier transform infrared (ATR-FTIR) spectroscopy in conjunction with second-derivative treatment and gas chromatographic (GC) analysis. Results: The total amount of TFAs has been increased from 7.71 to 8.25 per cent for cow milk fat, 7.12 to 7.82 per cent for buffalo milk fat, and from 6.82 to 7.61 per cent for goat milk fat on heating the samples to 125°C–175°C as predicted by GC. Conclusions: Local food products fried in these milk fats are hence very harmful to human health. These results demonstrate that thermally induced TFAs in milk fats are closely related to the process temperature and time, which should be considered to reduce the formation of TFAs during thermal treatment. Key words: Milk fat; Trans fatty acid; Local food products; Heating phenomenon; FTIR spectroscopy. oils, but the accumulation of TFAs in edible oils, including milk fats Introduction or oils by heating, has also attracted growing consideration. Milk Among the naturally occurring fats known, milk fat is one of the fat, in the form of ghee, has also been a part of nutrition and fre- most complex fat, containing more than 400 different fatty acids quently used in India and near sub-continents for frying a variety of (FAs) in its triglycerols (Schröder and Vetter, 2013). Among the food products. In India, most of the restaurants use milk fats or oils FAs present, C18:1 is most abundant FA in milk fat. Oleic acid for frying a number of local fast foods. Because milk fats are cost- (cis-9 C18:1) is the main monoenoic acid contributing around 21 lier than other fats, these restaurants repeatedly heated the oil (milk per cent to the total FAs, whereas trans-C18:1 monoenoic FAs are fat) to fry the products for a long time which ultimately affects the typically found in range of 5 per cent in milk fat (Martínez Marín human health because of development of TFAs as confirmed from et  al., 2015). Of the trans-18:1 FA, vaccenic acid (trans-11 C18:1) the earlier and recent Indian reports (Herzallah et al., 2005; Tsuzuki, is the most abundant, with 50–60 per cent of the group in most 2011; Bhardwaj et  al., 2016). The quantitative increment of TFA diets. Numerous studies, related to the occurrence of trans fatty acid due to trans isomerization and oxidative degradation during heat- (TFA) composition in cow, buffalo, and goat milk fats, have been ing process and isomerization, involving sigmatropic rearrangement reported in the literature (Le Doux et al., 2002; Stefanov et al., 2013; at 180°C or 240°C, is also reported (Destaillats and Angers, 2005; Martínez Marín et al., 2015; Pegolo et al., 2016; Pegolo et al., 2017). Tsuzuki, 2011). The major sources of TFAs for consumers are partially hydrogenated © The Author(s) 2018. Published by Oxford University Press on behalf of Zhejiang University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact jour- nals.permissions@oup.com Downloaded from https://academic.oup.com/fqs/article-abstract/2/1/51/4823025 by Ed 'DeepDyve' Gillespie user on 16 March 2018 52 M. Umar Khan et al., 2018, Vol. 2, No. 1 The direct relation of TFA intake and development of cardiovas- carbon tetrachloride after each scan and dried. All the absorbance spec- cular diseases have been confirmed by a number of epidemiologic tra were electronically converted to second-derivative using GC Solution evidences and case–control studies which also confirmed that intake software to show the peaks clearly. Air was used as a background. of only 2 per cent TFAs increased the risk of cardiovascular diseases by 23 per cent (Mozaffarian et al., 2006; Kremmyda et al., 2011). In GC analysis view of the impact of TFAs on human health, development of accur- The GC methods recommended by AOCS offered the use of 100 ate methods for the quantification of TFAs present in oils and food m cyanopropyl polysiloxane columns, for example, the SP-2560 or products has become an important task in the research area of food CP-Sil 88 (Chrompack, Middleburg, The Netherlands) (Ratnayake safety and toxicology. For the accurate determination of FA compos- et  al., 2006; AOCS Ce 1j-07, 2009). GC-2010 chromatograph ition in milk fat, official gas chromatography (GC) method American (Shimadzu, Japan), fitted with a CP-SIL column (100 m × 0.25  μm × Oil Chemical Society (AOCS) Ce 1h-05 was used (Delmonte et al., 0.2 mm) and a flame ionization detector, was used for desired GC 2012). GC is one of the most widely used techniques for the quantifi- analysis. Cross-linked siloxane polymer was used as stationary phase cation of composition of FAs in milk fats, but it has some drawbacks and nitrogen as carrier gas. The temperature programming process such as long and complicated calculation. included an initial temperature of 80°C holding for 2 minutes and FTIR spectroscopy has been used as an accurate and effective tech- increased to 255°C and maintained for 10 minutes. GC Solution nique for the quantitative analysis of the adulteration of goat milk software was used for recording chromatogram. with cow milk in different binary and tertiary mixtures (Mossoba et al., 2004). The attenuated total reflection-Fourier transform infrared Data processing and calibration (ATR-FTIR) procedure in conjunction with second-derivative analysis Multivariate calibration models including second-derivative treat- had been used for the determination of total TFA by measuring the ment, associated with FTIR spectroscopy, are used for accurate height of the second-derivative spectra (AOCS Cd 14e-09, 2009). determination of low trans fat level (Christy et al., 2003; Birkel and Observing these fats and in continuation of our research on the Rodriguez-Saona, 2011). Measured ATR-FTIR bands were converted determination of TFA content in some of the selected Indian fast food to their corresponding second-derivative spectra with second-order products and hydrogenated fats (Khan et al., 2017), in this paper, we polynomial (Mossoba et al., 2014). In the second-derivative spectrum, reported the variation of TFA content in local food products fried in −1 peak height at 966 cm was evaluated for each sample, which is the cooking milk fats of cow, buffalo, and goat at different temperatures. characteristic peak of isolated trans double bond (Blanco et al., 2000). To the best of our knowledge, study of thermally induced TFA in In most of the cases, on taking double derivatives of the spectra, some milk fats of cow, buffalo, and goat has been done for the first time. changes has been observed in spectral profiles, e.g. removal of the base The objective of this study is to quantify thermally induced TFA by line effect from the spectral profiles and appearance of some hidden ATR-FTIR spectroscopy with second-derivative treatment and GC absorptions bands in the broad IR spectral profiles (Sébédio et  al., analysis. FTIR spectroscopy has been used to quantify total TFA, 2008). A series of calibration standards were prepared in the concentra- compared with the results obtained by GC and found to have a good tion range of 0.2 to 5 per cent of TFAs with R ≥ 0.99 (Supplementary agreement between the two findings. Table 1S, see online supplementary material). Concentration of calcu- lated calibration standards was compared with ATR-FTIR predicted results and found to have good agreement (Table 1). The measurement Materials and methods of spectra for test samples was done against air. Heights of second- Chemicals derivative spectra were used for quantification of TFAs. A series of fatty acid methyl esters (FAMEs), including trans-C14:1, trans-C15:1, trans-C16:1, trans-C17:1, cis-C18:1, trans-9C18:1, trans- Statistical analysis 10C18:1, trans-11C18:1, cis-9, trans-11C18:2, cis-15, trans-11C18:2, All the experiments used in the present protocol were done in trip- and trans-C18:3 isomers, were purchased from Nu-Chek Prep, Inc. licate to obtain precise data. To check the difference and similarities (Elysian, MN, USA) and Sigma Aldrich (USA). All the reagents and inter- in the mean values of TFAs obtained from GC and ATR-FTIR meth- nal standard used in GC were purchased from Fischer Scientific (UK). ods, t-test was applied at 5 per cent significance level (Supplementary Table  2S, see online supplementary material). Origin Pro 6.0 soft- Sampling ware was used for all the statistical calculations. The heating temperature for milk fat (ghee) of local fast food items during frying process in various restaurants has been found to be in Results the range of 120°C to 200°C. In view of these findings, 10 g of each ATR calibration milk fat sample (total 60 milk fat samples including normal fresh milk fats before heating) was collected from different markets which A linear regression plot between per cent TFA and height of sec- was found in the range of 120°C to 200°C. Then, we categorize the ond-derivative spectra obtained from the standard artificial samples samples in four types as unheated, 120°C–130°C, 140°C–150°C, (Figure 1A) resulted in the following regression equation: and 160°C–170°C) in paraffin oil bath for 5 hours. Temperature was measured with accuracy of ±2°C. Table  1. Independent t-test on gravimetrically calculated attenu- ated total reflection-Fourier transform infrared (ATR-FTIR) and FTIR instrumentation results at 5 per cent confidence level. FTIR spectra of each heated and normal sample were obtained in ATR Data Mean N R SD t P mode using a Perkin Elmer (Spectrum Two) spectrometer with a total of −1 −1 65 scans at a resolution of 4 cm in the range of 500 to 4000 cm . The 0.9998 0.03407 0.0196 0.9846 Calculated 2.3514 7 sample was placed on an ATR crystal made of zinc selenide, and IR spec- ATR-FTIR 2.3685 7 trum was recorded. The crystal was rubbed with tissue paper wet with Downloaded from https://academic.oup.com/fqs/article-abstract/2/1/51/4823025 by Ed 'DeepDyve' Gillespie user on 16 March 2018 Effect of temperature on milk fat, 2018, Vol. 2, No. 1 53 gravimetrically calculated per cent TFA and the results were obtained (1) Y =+ 0.. 000078x 0 000049, by (1) (Table 1). A bar graph has been plotted to show the closeness where Y is per cent TFA and x is the height of second-derivative of calculated and ATR-FTIR–predicted results (Figure 1B). −1 spectra at 966  cm . Standard deviation and square of regression coefficient in (1) were 0.01 and 0.9901, respectively. Equation (1) FTIR analysis was used as a model equation to quantify the per cent TFA in milk ATR-FTIR spectral studies have received a lot of attention because of fats by substituting the second-derivative peak height of milk fat enhanced spectral absorbance features such as identification of func- samples of cow, buffalo, and goat as x in (1). Heights of IR bands tional groups (e.g. specific unsaturated C=C bonds) and for the quanti- increased when samples were heated at different temperatures, fication of total trans fat content in food and dietary supplements using which resulted in the increased amount of TFA (Figure 2). Validation official method (Mossoba et  al., 2009). Representative FTIR spectra of the applied ATR-FTIR method was checked by comparing the Figure 1. (A) Second-derivative spectra of gravimetrically prepared standards of trielaidate spiked in triolein. (B) Comparison between calculated and attenuated total reflection-Fourier transform infrared (ATR-FTIR)–predicted results. Figure 2. Fourier transform infrared (FTIR) spectra of cow (A), buffalo (B), and goat (C) milk fat samples collected at different temperature (A = unheated, B = at 120°C–130°C, C = 140°C–150°C, and D = 160°C–170°C). Downloaded from https://academic.oup.com/fqs/article-abstract/2/1/51/4823025 by Ed 'DeepDyve' Gillespie user on 16 March 2018 54 M. Umar Khan et al., 2018, Vol. 2, No. 1 −1 resulted from milk fat samples of cow, buffalo, and goat afforded the area of interest in IR region was to evaluate the peak at 966  cm information about the functional group and different FA chains present resulting from =CH-deformation as confirmed by the earlier studies −1 in triglyceride of fat sample (Figure 2). Qualitatively all the three types (Mossoba et  al., 2004). The height of absorption bands at 966 cm of fat analyzed were found to be almost the same. Major IR absorp- was increased to a significant extent with heating at different tempera- tion bands observed for milk fat samples were C–H stretching band tures (120°C–130°C, 140°C–150°C, and 160°C–170°C). This result −1 of alkyl chain (2800–3050 cm ), C=O absorption band of carbonyl confirmed the increased quantity of TFAs in analyzed fat samples due −1 −1 group (1760–1770  cm ), C–O stretching band (1150–1160  cm ), to increased temperature which was confirmed by earlier report. −1 and for isolated trans (=CH) bond at ~966 cm (Table 2). The main Fatty acid composition of milk fat Fatty acid composition of milk fat of Indian animals is found to Table  2. Major IR bands of control samples of cow, buffalo, and be similar as reported earlier for animals of France (LeDoux et al., goat samples. 2001), Spain (Núñez-Sánchez et  al., 2016), and Italy (Di Francia −1 et al., 2007) (Table 3). Mode of vibration Functional group Frequency (cm ) Cow Buffalo Goat Determination of TFAs in heated samples by GC The peaks of FAME, prepared by the standard AOCS procedure Symmetric stretching =CH 3018 3021 3012 (AOCS Ce 2–66, 2009), were identified according to the standards Asymmetric stretching CH (–CH ) 2935 2938 2934 Asymmetric stretching CH (–CH ) 2961 2959 2962 supplied with chromatograph by comparing retention time of each Symmetric stretching CH (–CH ) 2869 2868 2870 standard with identified peaks of sample. The total of ten trans iso- Symmetric stretching C=O (ester) 1760 1761 1763 mers was detected which might be formed through the isomerization Symmetric stretching C=C 1643 1639 1641 cis FAs to trans FAs during heat treatment as previously reported Bending CH (–CH ) 1458 1462 1460 by Wakkao Tsuzuki (Tsuzuki, 2011). Formation of trans isomers Bending CH 1314 1314 1316 (mostly trans-9, 18:1) was obtained when triolein (cis-9, 18:1) Deformation =CH (trans) 966 966 966 was heated at 180°C for 4 hours and trans-18:2 isomers (mainly Table 3. Fatty acid contents (g/100 g fatty acid methyl esters) in unheated milk fat of cow, buffalo, and goat determined by gas chroma- tography (GC; N  =  7 for each animal fat). SD, standard deviation; SFA, saturated fatty acid; MUFA, monounsaturated fatty acid; PUFA, polyunsaturated fatty acid. Fatty acid Animal fats Cow Buffalo Goat Mean SD Mean SD Mean SD C4:0 2.87 0.12 3.02 0.10 2.98 0.17 C6:0 1.92 0.09 1.84 0.08 1.88 0.05 C8:0 1.87 0.11 1.91 0.05 1.92 0.13 C10:0 2.85 0.10 2.72 0.14 2.75 0.12 C12:0 3.14 0.14 3.25 0.11 3.34 0.15 C14:0 11.53 0.64 11.40 0.79 11.59 0.74 trans-9C14:1 0.28 0.02 0.31 0.01 0.26 0.01 C15:0 1.22 0.11 1.28 0.16 1.25 0.11 trans-10 C15:1 0.25 0.01 0.28 0.02 0.22 0.03 C16:0 32.63 0.93 31.94 0.78 32.71 0.85 cis-C16:1 1.42 0.08 1.44 0.10 1.43 0.09 trans-10C16:1 0.68 0.03 0.62 0.02 0.58 0.04 C17:0 0.84 0.04 0.79 0.05 0.81 0.04 trans-9C17:1 0.14 0.02 0.16 0.04 0.12 0.01 C18:0 10.67 0.35 11.01 0.44 10.92 0.45 cis-9C18:1 21.36 1.08 21.25 1.14 20.95 1.01 trans-9C18:1 1.16 0.01 1.09 0.01 1.01 0.02 trans-10 C18:1 0.45 0.04 0.41 0.02 0.37 0.01 trans 11C18:1 1.28 0.02 1.36 0.03 1.34 0.02 cis-9 trans-11C18:2 0.97 0.03 0.89 0.04 0.92 0.03 cis-15,trans-11 C18:2 0.30 0.02 0.34 0.03 0.26 0.04 ΣtransC18:3 1.82 0.03 1.91 0.02 1.74 0.01 ΣSFA* 69.54 2.63 69.21 2.64 70.15 2.84 ΣMUFA** 27.02 0.65 26.87 1.69 26.28 1.24 ΣPUFA*** 3.09 0.07 3.14 0.09 2.92 0.08 *Total saturated fatty acid. **Total monounsaturated fatty acid. ***Total polyunsaturated fatty acid. Downloaded from https://academic.oup.com/fqs/article-abstract/2/1/51/4823025 by Ed 'DeepDyve' Gillespie user on 16 March 2018 Effect of temperature on milk fat, 2018, Vol. 2, No. 1 55 Table 4. Effect of heating on trans fatty acid contents (g/100 g fatty acid methyl esters) of cow, buffalo, and goat milk fat determined by gas chromatography (GC). Cow milk fat Fatty acids Unheated* 120°C–130°C* 140°C–150°C* 160°C–170°C* trans-9C14:1 0.28 ± 0.02 0.29 ± 0.01 0.29 ± 0.03 0.31 ± 0.01 trans-10 C15:1 0.25 ± 0.01 0.26 ± 0.04 0.28 ± 0.02 0.29 ± 0.02 trans-10C16:1 0.68 ± 0.03 0.66 ± 0.02 0.69 ± 0.01 0.71 ± 0.03 trans-9C17:1 0.14 ± 0.02 0.56 ± 0.01 0.57 ± 0.03 0.58 ± 0.01 trans-9C18:1 1.16 ± 0.01 1.16 ± 0.02 1.19 ± 0.02 1.20 ± 0.03 trans-10 C18:1 0.45 ± 0.04 0.48 ± 0.04 0.49 ± 0.01 0.53 ± 0.02 trans 11C18:1 1.28 ± 0.02 1.29 ± 0.02 1.28 ± 0.02 1.32 ± 0.03 cis-9 trans-11C18:2 0.97 ± 0.03 1.02 ± 0.03 1.05 ± 0.01 1.06 ± 0.02 cis-15,trans-11 C18:2 0.30 ± 0.02 0.31 ± 0.01 0.32 ± 0.02 0.31 ± 0.04 ΣtransC18:3 1.82 ± 0.03 1.83 ± 0.02 1.85 ± 0.04 1.87 ± 0.02 ΣTFA** 7.71 7.86 8.01 8.25 Buffalo milk fat Fatty acids Unheated 125°C 150°C 175°C trans-9C14:1 0.31 ± 0.01 0.33 ± 0.0 0.34 ± 0.04 0.38 ± 0.01 trans-10 C15:1 0.28 ± 0.02 0.29 ± 0.03 0.29 ± 0.01 0.31 ± 0.02 trans-10C16:1 0.57 ± 0.02 0.59 ± 0.01 0.59 ± 0.04 0.62 ± 0.03 trans-9C17:1 0.16 ± 0.04 0.17 ± 0.02 0.17 ± 0.03 0.18 ± 0.01 trans-9C18:1 1.09 ± 0.01 1.10 ± 0.04 1.14 ± 0.02 1.19 ± 0.03 trans-10 C18:1 0.41 ± 0.02 0.42 ± 0.02 0.45 ± 0.01 0.49 ± 0.03 trans 11C18:1 1.36 ± 0.03 1.36 ± 0.02 1.39 ± 0.01 1.43 ± 0.03 cis-9 trans-11C18:2 0.89 ± 0.04 0.92 ± 0.04 0.92 ± 0.01 0.98 ± 0.02 cis-15,trans-11 C18:2 0.34 ± 0.03 0.36 ± 0.02 0.37 ± 0.01 0.41 ± 0.01 ΣtransC18:3 1.71 ± 0.02 1.75 ± 0.04 1.78 ± 0.01 1.83 ± 0.04 Σ TFA** 7.12 7.29 7.44 7.82 Goat milk fat Fatty acids Unheated 125°C 150°C 175°C trans-9C14:1 0.26 ± 0.01 0.26 ± 0.03 0.29 ± 0.01 0.30 ± 0.01 trans-10 C15:1 0.22 ± 0.03 0.23 ± 0.02 0.26 ± 0.01 0.28 ± 0.03 trans-10C16:1 0.58 ± 0.04 0.58 ± 0.02 0.65 ± 0.02 0.67 ± 0.01 trans-9C17:1 0.12 ± 0.01 0.13 ± 0.01 0.16 ± 0.03 0.19 ± 0.02 trans-9C18:1 1.01 ± 0.02 1.03 ± 0.01 1.06 ± 0.04 1.10 ± 0.01 trans-10 C18:1 0.37 ± 0.01 0.38 ± 0.03 0.41 ± 0.01 0.46 ± 0.03 trans 11C18:1 1.34 ± 0.02 1.36 ± 0.04 1.39 ± 0.01 1.45 ± 0.02 cis-9 trans-11C18:2 0.92 ± 0.03 0.91 ± 0.02 0.97 ± 0.02 0.99 ± 0.01 cis-15,trans-11 C18:2 0.26 ± 0.04 0.25 ± 0.01 0.31 ± 0.02 0.34 ± 0.01 ΣtransC18:3 1.74 ± 0.01 1.75 ± 0.03 1.80 ± 0.02 1.83 ± 0.01 Σ TFA** 6.82 6.98 7.30 7.61 *Values are given as the means of triplicate analyses ± standard deviation. **Total trans fatty acid. trans-9, cis-12, 18:2 and cis-9, trans-12, 18:2) accrued when trilin- Discussions olein (cis-9, cis-12, 18:1) was heated at 180°C for 4 hours. In the present study, trans-9C18:1 content of cow milk fat was increased GC and FTIR-predicted results, for the analysis of TFA content in milk from 1.16 ± 0.01 to 1.20 ± 0.03, buffalo milk fat was increased from fat of cow, buffalo, and goat, were represented collectively in Figure 3 1.09  ±  0.01 to 1.19  ±  0.03, and goat milk fat was increased from (Table  5). Out of three milk samples analyzed, a linear increment 1.01  ±  0.02 to 1.10  ±  0.01 when temperature was increased from was observed for cow milk sample found at different temperatures 120°C to 170°C (Table 4). Isomerization of linolenic acid (18:3) also (120°C–130°C, 140°C–150°C, and 160°C–170°C), whereas in case of produced 9-trans, 12-cis, 15-cis C18:3, 9-cis, 12-trans, 15-cis C18:3, buffalo milk sample, a linear variation was observed at 120°C–130°C 9-cis, 12-cis, 15-trans C18:3, 9-trans, 12-trans, 15-cis C18:3, 9-trans, and 140°C–150°C and relatively higher increment was obtained at 12-cis, 15-trans C18:3, 9-cis, 12-trans, 15-trans C18:3, 9-trans, 160°C–170°C. A significant increment has been observed for goat milk 12-trans, 15-trans C18:3 FAs (Mihalache et  al., 2012). It indicates sample as when heating the sample at 120°C–130°C, 140°C–150°C, that occurrence of 18:3 TFA might be the result of isomerization of and 160°C–170°C shown in Figure 3. As milk fat (ghee) has been very linolenic acid. In our study, total increment in cis-9, trans-11C18:2 commonly used for frying purpose in most of the developed coun- and cis-15, trans-11 C18:2 was found in the range of 0.01 to 0.09 tries, studying the effect of heating on these fats (ghee) has become per cent (Table 4). Identification of each peak in the chromatograms an urgent issue to solve because of induction of TFAs which is a main was confirmed by comparing their retention time with peaks of cause of coronary heart diseases. On viewing the damaging nature standard FAMEs. of TFA, Food and Drug Administration (FDA) and Health Canada Downloaded from https://academic.oup.com/fqs/article-abstract/2/1/51/4823025 by Ed 'DeepDyve' Gillespie user on 16 March 2018 56 M. Umar Khan et al., 2018, Vol. 2, No. 1 Figure  3 Effect of heating on milk fat (ghee) of cow, buffalo, and goat analyzed by (A) gas chromatography (GC) and (B) attenuated total reflection-Fourier transform infrared (ATR-FTIR). Table 5. Comparison of gas chromatography (GC) and attenuated total reflection-Fourier transform infrared (ATR-FTIR)–predicted results. No. Heating temperature (°C) Total amount of TFA Total amount of TFA determined by determined by GC ATR-FTIR Cow Buffalo Goat Cow Buffalo Goat 1 25* 7.71 7.12 6.82 7.98 7.62 7.12 2 125 7.86 7.29 6.98 8.05 7.94 7.51 3 150 8.01 7.44 7.30 8.56 8.27 7.74 4 175 8.25 7.82 7.61 8.83 8.42 7.93 *Sample was not heated. have proposed food-labelling rules which compelled the food manu- helpful for consumer welfare of India to minimize the use of products facturers to mention the content of TFA on the products as asterisked frying in ghee at a high temperature. They should also instruct the footnote, ‘*Includes g trans fat’ which contains >0.5 g TFA per serving restaurants to change the ghee repeatedly which could minimize the (Ruth, 2002). In our country, most of the restaurants use these milk induction of TFA. The local people of India should be aware of highly fats for frying purpose in the temperature range of 120°C to 200°C. detrimental nature of TFA because prevention of ghee for frying pur- As confirmed from the present study, a significant amount of TFA has poses is quite challenging. been developed on heating the ghee up to 200°C. It indicates that the food items which have been fried in ghee contain a sufficient amount Conclusion of TFA which ultimately causes the coronary heart diseases. In add- ition, they use the ghee several times repeatedly because of its high cost In conclusion, heat treatment induced the formation of TFAs in which is more dangerous for human health as it will cause the induc- milk fats of cow, buffalo, and goat which would increase the risk tion of more TFA in the ghee. Among the three milk samples analyzed, of cardiovascular diseases. By comparison of the results obtained, it production of goat milk seems relatively less compared with the cow may be concluded that goat milk fat, having the lowest TFA content and buffalo milk production. In our country, consumption of milk fat among the three samples analyzed, should be the choice of people. in rural areas is more than urban areas because rural people are hav- Repetition of the same ghee for many times while frying the food ing comparatively more livestock. But overall consumption of these items should be avoided. A significant increase of TFA in milk fats milk fats is very high in India, which ultimately affects the human (ghee) during thermal process increased the attention of consumers health due to the presence of TFA in all milk fats. This study might be in maintaining healthy dietary practices. Downloaded from https://academic.oup.com/fqs/article-abstract/2/1/51/4823025 by Ed 'DeepDyve' Gillespie user on 16 March 2018 Effect of temperature on milk fat, 2018, Vol. 2, No. 1 57 Kremmyda, L. S., Tvrzicka, E., Stankova, B., Zak, A. (2011). Fatty acids as bio- Supplementary Material compounds: their role in human metabolism, health and disease: a review. Supplementary material is available at Food Quality and Safety online. Part 2: fatty acid physiological roles and applications in human health and disease. Biomedical Papers of the Medical Faculty of the University Palacky, Olomouc, Czechoslovakia, 155: 195–218. Funding Le Doux, M., Rouzeau, A., Bas, P., Sauvantt, D. (2002). Occurrence of trans- Financial assistance in the form of Non-Net fellowship from C18:1 fatty acid isomers in goat milk: effect of two dietary regimens. University Grants Commission is gratefully acknowledged. Journal of Dairy Science, 85: 190–197. Martínez Marín, A. L., et al. (2015). Associations between major fatty acids in plant oils fed to dairy goats and C18 isomers in milk fat. The Journal of Acknowledgement Dairy Research, 82: 152–160. The authors thank USIF, A.M.U., and SAIF, Panjab University, Chandigarh for Mihalache, M., Bratu, A., Hanganu, A., Chira, N. A., Maganu, M., Todasca, M. providing spectral data. C., Rosca, S. (2012). Thermal formation of trans fatty acids in Romanian Conflict of interest statement. None declared. vegetable oils monitored by GC-MS and FT-IR techniques. Revista de Chimie, 63: 984–988. Mossoba, M. M., Seiler, A., Kramer, J. K.  G., Milosevic, V., Milosevic, M., References Azizian, H., Steinhart, H. (2009). Nutrition labeling: rapid determination AOCS. (2009). Official Method Cd 14e-09 Negative Second Derivative of total trans fats by using internal reflection infrared spectroscopy and a Infrared Spectroscopic Method for Rapid (5 min) Determination of Total second derivative procedure. 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Determination of trans fat in nation of minor odd- and branched-chain saturated and trans unsaturated selected fast food products and hydrogenated fats of india using attenu- milk fatty acids. Journal of Agricultural and Food Chemistry, 61: 3403–3413. ated total reflection fourier transform infrared (ATR-FTIR) spectroscopy. Tsuzuki, W. (2011). Effects of antioxidants on heat-induced trans fatty acid Journal of Oleo Science, 66: 251–257. formation in triolein and trilinolein. Food Chemistry, 129, 104–109. Downloaded from https://academic.oup.com/fqs/article-abstract/2/1/51/4823025 by Ed 'DeepDyve' Gillespie user on 16 March 2018 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Food Quality and Safety Oxford University Press

Effect of temperature on milk fats of cow, buffalo, and goat used for frying local food products

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Abstract

Objectives: Thermal processes, such as refining and frying, result in the formation of trans fatty acids (TFAs) in edible oils or fats. Concerning the detrimental effect of TFAs on human health, milk fat samples of cow, buffalo, and goat are collected in order to elucidate TFAs accumulation during thermal processing. Methods: The increased amount of TFAs due to heating is analyzed by attenuated total reflection- Fourier transform infrared (ATR-FTIR) spectroscopy in conjunction with second-derivative treatment and gas chromatographic (GC) analysis. Results: The total amount of TFAs has been increased from 7.71 to 8.25 per cent for cow milk fat, 7.12 to 7.82 per cent for buffalo milk fat, and from 6.82 to 7.61 per cent for goat milk fat on heating the samples to 125°C–175°C as predicted by GC. Conclusions: Local food products fried in these milk fats are hence very harmful to human health. These results demonstrate that thermally induced TFAs in milk fats are closely related to the process temperature and time, which should be considered to reduce the formation of TFAs during thermal treatment. Key words: Milk fat; Trans fatty acid; Local food products; Heating phenomenon; FTIR spectroscopy. oils, but the accumulation of TFAs in edible oils, including milk fats Introduction or oils by heating, has also attracted growing consideration. Milk Among the naturally occurring fats known, milk fat is one of the fat, in the form of ghee, has also been a part of nutrition and fre- most complex fat, containing more than 400 different fatty acids quently used in India and near sub-continents for frying a variety of (FAs) in its triglycerols (Schröder and Vetter, 2013). Among the food products. In India, most of the restaurants use milk fats or oils FAs present, C18:1 is most abundant FA in milk fat. Oleic acid for frying a number of local fast foods. Because milk fats are cost- (cis-9 C18:1) is the main monoenoic acid contributing around 21 lier than other fats, these restaurants repeatedly heated the oil (milk per cent to the total FAs, whereas trans-C18:1 monoenoic FAs are fat) to fry the products for a long time which ultimately affects the typically found in range of 5 per cent in milk fat (Martínez Marín human health because of development of TFAs as confirmed from et  al., 2015). Of the trans-18:1 FA, vaccenic acid (trans-11 C18:1) the earlier and recent Indian reports (Herzallah et al., 2005; Tsuzuki, is the most abundant, with 50–60 per cent of the group in most 2011; Bhardwaj et  al., 2016). The quantitative increment of TFA diets. Numerous studies, related to the occurrence of trans fatty acid due to trans isomerization and oxidative degradation during heat- (TFA) composition in cow, buffalo, and goat milk fats, have been ing process and isomerization, involving sigmatropic rearrangement reported in the literature (Le Doux et al., 2002; Stefanov et al., 2013; at 180°C or 240°C, is also reported (Destaillats and Angers, 2005; Martínez Marín et al., 2015; Pegolo et al., 2016; Pegolo et al., 2017). Tsuzuki, 2011). The major sources of TFAs for consumers are partially hydrogenated © The Author(s) 2018. Published by Oxford University Press on behalf of Zhejiang University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact jour- nals.permissions@oup.com Downloaded from https://academic.oup.com/fqs/article-abstract/2/1/51/4823025 by Ed 'DeepDyve' Gillespie user on 16 March 2018 52 M. Umar Khan et al., 2018, Vol. 2, No. 1 The direct relation of TFA intake and development of cardiovas- carbon tetrachloride after each scan and dried. All the absorbance spec- cular diseases have been confirmed by a number of epidemiologic tra were electronically converted to second-derivative using GC Solution evidences and case–control studies which also confirmed that intake software to show the peaks clearly. Air was used as a background. of only 2 per cent TFAs increased the risk of cardiovascular diseases by 23 per cent (Mozaffarian et al., 2006; Kremmyda et al., 2011). In GC analysis view of the impact of TFAs on human health, development of accur- The GC methods recommended by AOCS offered the use of 100 ate methods for the quantification of TFAs present in oils and food m cyanopropyl polysiloxane columns, for example, the SP-2560 or products has become an important task in the research area of food CP-Sil 88 (Chrompack, Middleburg, The Netherlands) (Ratnayake safety and toxicology. For the accurate determination of FA compos- et  al., 2006; AOCS Ce 1j-07, 2009). GC-2010 chromatograph ition in milk fat, official gas chromatography (GC) method American (Shimadzu, Japan), fitted with a CP-SIL column (100 m × 0.25  μm × Oil Chemical Society (AOCS) Ce 1h-05 was used (Delmonte et al., 0.2 mm) and a flame ionization detector, was used for desired GC 2012). GC is one of the most widely used techniques for the quantifi- analysis. Cross-linked siloxane polymer was used as stationary phase cation of composition of FAs in milk fats, but it has some drawbacks and nitrogen as carrier gas. The temperature programming process such as long and complicated calculation. included an initial temperature of 80°C holding for 2 minutes and FTIR spectroscopy has been used as an accurate and effective tech- increased to 255°C and maintained for 10 minutes. GC Solution nique for the quantitative analysis of the adulteration of goat milk software was used for recording chromatogram. with cow milk in different binary and tertiary mixtures (Mossoba et al., 2004). The attenuated total reflection-Fourier transform infrared Data processing and calibration (ATR-FTIR) procedure in conjunction with second-derivative analysis Multivariate calibration models including second-derivative treat- had been used for the determination of total TFA by measuring the ment, associated with FTIR spectroscopy, are used for accurate height of the second-derivative spectra (AOCS Cd 14e-09, 2009). determination of low trans fat level (Christy et al., 2003; Birkel and Observing these fats and in continuation of our research on the Rodriguez-Saona, 2011). Measured ATR-FTIR bands were converted determination of TFA content in some of the selected Indian fast food to their corresponding second-derivative spectra with second-order products and hydrogenated fats (Khan et al., 2017), in this paper, we polynomial (Mossoba et al., 2014). In the second-derivative spectrum, reported the variation of TFA content in local food products fried in −1 peak height at 966 cm was evaluated for each sample, which is the cooking milk fats of cow, buffalo, and goat at different temperatures. characteristic peak of isolated trans double bond (Blanco et al., 2000). To the best of our knowledge, study of thermally induced TFA in In most of the cases, on taking double derivatives of the spectra, some milk fats of cow, buffalo, and goat has been done for the first time. changes has been observed in spectral profiles, e.g. removal of the base The objective of this study is to quantify thermally induced TFA by line effect from the spectral profiles and appearance of some hidden ATR-FTIR spectroscopy with second-derivative treatment and GC absorptions bands in the broad IR spectral profiles (Sébédio et  al., analysis. FTIR spectroscopy has been used to quantify total TFA, 2008). A series of calibration standards were prepared in the concentra- compared with the results obtained by GC and found to have a good tion range of 0.2 to 5 per cent of TFAs with R ≥ 0.99 (Supplementary agreement between the two findings. Table 1S, see online supplementary material). Concentration of calcu- lated calibration standards was compared with ATR-FTIR predicted results and found to have good agreement (Table 1). The measurement Materials and methods of spectra for test samples was done against air. Heights of second- Chemicals derivative spectra were used for quantification of TFAs. A series of fatty acid methyl esters (FAMEs), including trans-C14:1, trans-C15:1, trans-C16:1, trans-C17:1, cis-C18:1, trans-9C18:1, trans- Statistical analysis 10C18:1, trans-11C18:1, cis-9, trans-11C18:2, cis-15, trans-11C18:2, All the experiments used in the present protocol were done in trip- and trans-C18:3 isomers, were purchased from Nu-Chek Prep, Inc. licate to obtain precise data. To check the difference and similarities (Elysian, MN, USA) and Sigma Aldrich (USA). All the reagents and inter- in the mean values of TFAs obtained from GC and ATR-FTIR meth- nal standard used in GC were purchased from Fischer Scientific (UK). ods, t-test was applied at 5 per cent significance level (Supplementary Table  2S, see online supplementary material). Origin Pro 6.0 soft- Sampling ware was used for all the statistical calculations. The heating temperature for milk fat (ghee) of local fast food items during frying process in various restaurants has been found to be in Results the range of 120°C to 200°C. In view of these findings, 10 g of each ATR calibration milk fat sample (total 60 milk fat samples including normal fresh milk fats before heating) was collected from different markets which A linear regression plot between per cent TFA and height of sec- was found in the range of 120°C to 200°C. Then, we categorize the ond-derivative spectra obtained from the standard artificial samples samples in four types as unheated, 120°C–130°C, 140°C–150°C, (Figure 1A) resulted in the following regression equation: and 160°C–170°C) in paraffin oil bath for 5 hours. Temperature was measured with accuracy of ±2°C. Table  1. Independent t-test on gravimetrically calculated attenu- ated total reflection-Fourier transform infrared (ATR-FTIR) and FTIR instrumentation results at 5 per cent confidence level. FTIR spectra of each heated and normal sample were obtained in ATR Data Mean N R SD t P mode using a Perkin Elmer (Spectrum Two) spectrometer with a total of −1 −1 65 scans at a resolution of 4 cm in the range of 500 to 4000 cm . The 0.9998 0.03407 0.0196 0.9846 Calculated 2.3514 7 sample was placed on an ATR crystal made of zinc selenide, and IR spec- ATR-FTIR 2.3685 7 trum was recorded. The crystal was rubbed with tissue paper wet with Downloaded from https://academic.oup.com/fqs/article-abstract/2/1/51/4823025 by Ed 'DeepDyve' Gillespie user on 16 March 2018 Effect of temperature on milk fat, 2018, Vol. 2, No. 1 53 gravimetrically calculated per cent TFA and the results were obtained (1) Y =+ 0.. 000078x 0 000049, by (1) (Table 1). A bar graph has been plotted to show the closeness where Y is per cent TFA and x is the height of second-derivative of calculated and ATR-FTIR–predicted results (Figure 1B). −1 spectra at 966  cm . Standard deviation and square of regression coefficient in (1) were 0.01 and 0.9901, respectively. Equation (1) FTIR analysis was used as a model equation to quantify the per cent TFA in milk ATR-FTIR spectral studies have received a lot of attention because of fats by substituting the second-derivative peak height of milk fat enhanced spectral absorbance features such as identification of func- samples of cow, buffalo, and goat as x in (1). Heights of IR bands tional groups (e.g. specific unsaturated C=C bonds) and for the quanti- increased when samples were heated at different temperatures, fication of total trans fat content in food and dietary supplements using which resulted in the increased amount of TFA (Figure 2). Validation official method (Mossoba et  al., 2009). Representative FTIR spectra of the applied ATR-FTIR method was checked by comparing the Figure 1. (A) Second-derivative spectra of gravimetrically prepared standards of trielaidate spiked in triolein. (B) Comparison between calculated and attenuated total reflection-Fourier transform infrared (ATR-FTIR)–predicted results. Figure 2. Fourier transform infrared (FTIR) spectra of cow (A), buffalo (B), and goat (C) milk fat samples collected at different temperature (A = unheated, B = at 120°C–130°C, C = 140°C–150°C, and D = 160°C–170°C). Downloaded from https://academic.oup.com/fqs/article-abstract/2/1/51/4823025 by Ed 'DeepDyve' Gillespie user on 16 March 2018 54 M. Umar Khan et al., 2018, Vol. 2, No. 1 −1 resulted from milk fat samples of cow, buffalo, and goat afforded the area of interest in IR region was to evaluate the peak at 966  cm information about the functional group and different FA chains present resulting from =CH-deformation as confirmed by the earlier studies −1 in triglyceride of fat sample (Figure 2). Qualitatively all the three types (Mossoba et  al., 2004). The height of absorption bands at 966 cm of fat analyzed were found to be almost the same. Major IR absorp- was increased to a significant extent with heating at different tempera- tion bands observed for milk fat samples were C–H stretching band tures (120°C–130°C, 140°C–150°C, and 160°C–170°C). This result −1 of alkyl chain (2800–3050 cm ), C=O absorption band of carbonyl confirmed the increased quantity of TFAs in analyzed fat samples due −1 −1 group (1760–1770  cm ), C–O stretching band (1150–1160  cm ), to increased temperature which was confirmed by earlier report. −1 and for isolated trans (=CH) bond at ~966 cm (Table 2). The main Fatty acid composition of milk fat Fatty acid composition of milk fat of Indian animals is found to Table  2. Major IR bands of control samples of cow, buffalo, and be similar as reported earlier for animals of France (LeDoux et al., goat samples. 2001), Spain (Núñez-Sánchez et  al., 2016), and Italy (Di Francia −1 et al., 2007) (Table 3). Mode of vibration Functional group Frequency (cm ) Cow Buffalo Goat Determination of TFAs in heated samples by GC The peaks of FAME, prepared by the standard AOCS procedure Symmetric stretching =CH 3018 3021 3012 (AOCS Ce 2–66, 2009), were identified according to the standards Asymmetric stretching CH (–CH ) 2935 2938 2934 Asymmetric stretching CH (–CH ) 2961 2959 2962 supplied with chromatograph by comparing retention time of each Symmetric stretching CH (–CH ) 2869 2868 2870 standard with identified peaks of sample. The total of ten trans iso- Symmetric stretching C=O (ester) 1760 1761 1763 mers was detected which might be formed through the isomerization Symmetric stretching C=C 1643 1639 1641 cis FAs to trans FAs during heat treatment as previously reported Bending CH (–CH ) 1458 1462 1460 by Wakkao Tsuzuki (Tsuzuki, 2011). Formation of trans isomers Bending CH 1314 1314 1316 (mostly trans-9, 18:1) was obtained when triolein (cis-9, 18:1) Deformation =CH (trans) 966 966 966 was heated at 180°C for 4 hours and trans-18:2 isomers (mainly Table 3. Fatty acid contents (g/100 g fatty acid methyl esters) in unheated milk fat of cow, buffalo, and goat determined by gas chroma- tography (GC; N  =  7 for each animal fat). SD, standard deviation; SFA, saturated fatty acid; MUFA, monounsaturated fatty acid; PUFA, polyunsaturated fatty acid. Fatty acid Animal fats Cow Buffalo Goat Mean SD Mean SD Mean SD C4:0 2.87 0.12 3.02 0.10 2.98 0.17 C6:0 1.92 0.09 1.84 0.08 1.88 0.05 C8:0 1.87 0.11 1.91 0.05 1.92 0.13 C10:0 2.85 0.10 2.72 0.14 2.75 0.12 C12:0 3.14 0.14 3.25 0.11 3.34 0.15 C14:0 11.53 0.64 11.40 0.79 11.59 0.74 trans-9C14:1 0.28 0.02 0.31 0.01 0.26 0.01 C15:0 1.22 0.11 1.28 0.16 1.25 0.11 trans-10 C15:1 0.25 0.01 0.28 0.02 0.22 0.03 C16:0 32.63 0.93 31.94 0.78 32.71 0.85 cis-C16:1 1.42 0.08 1.44 0.10 1.43 0.09 trans-10C16:1 0.68 0.03 0.62 0.02 0.58 0.04 C17:0 0.84 0.04 0.79 0.05 0.81 0.04 trans-9C17:1 0.14 0.02 0.16 0.04 0.12 0.01 C18:0 10.67 0.35 11.01 0.44 10.92 0.45 cis-9C18:1 21.36 1.08 21.25 1.14 20.95 1.01 trans-9C18:1 1.16 0.01 1.09 0.01 1.01 0.02 trans-10 C18:1 0.45 0.04 0.41 0.02 0.37 0.01 trans 11C18:1 1.28 0.02 1.36 0.03 1.34 0.02 cis-9 trans-11C18:2 0.97 0.03 0.89 0.04 0.92 0.03 cis-15,trans-11 C18:2 0.30 0.02 0.34 0.03 0.26 0.04 ΣtransC18:3 1.82 0.03 1.91 0.02 1.74 0.01 ΣSFA* 69.54 2.63 69.21 2.64 70.15 2.84 ΣMUFA** 27.02 0.65 26.87 1.69 26.28 1.24 ΣPUFA*** 3.09 0.07 3.14 0.09 2.92 0.08 *Total saturated fatty acid. **Total monounsaturated fatty acid. ***Total polyunsaturated fatty acid. Downloaded from https://academic.oup.com/fqs/article-abstract/2/1/51/4823025 by Ed 'DeepDyve' Gillespie user on 16 March 2018 Effect of temperature on milk fat, 2018, Vol. 2, No. 1 55 Table 4. Effect of heating on trans fatty acid contents (g/100 g fatty acid methyl esters) of cow, buffalo, and goat milk fat determined by gas chromatography (GC). Cow milk fat Fatty acids Unheated* 120°C–130°C* 140°C–150°C* 160°C–170°C* trans-9C14:1 0.28 ± 0.02 0.29 ± 0.01 0.29 ± 0.03 0.31 ± 0.01 trans-10 C15:1 0.25 ± 0.01 0.26 ± 0.04 0.28 ± 0.02 0.29 ± 0.02 trans-10C16:1 0.68 ± 0.03 0.66 ± 0.02 0.69 ± 0.01 0.71 ± 0.03 trans-9C17:1 0.14 ± 0.02 0.56 ± 0.01 0.57 ± 0.03 0.58 ± 0.01 trans-9C18:1 1.16 ± 0.01 1.16 ± 0.02 1.19 ± 0.02 1.20 ± 0.03 trans-10 C18:1 0.45 ± 0.04 0.48 ± 0.04 0.49 ± 0.01 0.53 ± 0.02 trans 11C18:1 1.28 ± 0.02 1.29 ± 0.02 1.28 ± 0.02 1.32 ± 0.03 cis-9 trans-11C18:2 0.97 ± 0.03 1.02 ± 0.03 1.05 ± 0.01 1.06 ± 0.02 cis-15,trans-11 C18:2 0.30 ± 0.02 0.31 ± 0.01 0.32 ± 0.02 0.31 ± 0.04 ΣtransC18:3 1.82 ± 0.03 1.83 ± 0.02 1.85 ± 0.04 1.87 ± 0.02 ΣTFA** 7.71 7.86 8.01 8.25 Buffalo milk fat Fatty acids Unheated 125°C 150°C 175°C trans-9C14:1 0.31 ± 0.01 0.33 ± 0.0 0.34 ± 0.04 0.38 ± 0.01 trans-10 C15:1 0.28 ± 0.02 0.29 ± 0.03 0.29 ± 0.01 0.31 ± 0.02 trans-10C16:1 0.57 ± 0.02 0.59 ± 0.01 0.59 ± 0.04 0.62 ± 0.03 trans-9C17:1 0.16 ± 0.04 0.17 ± 0.02 0.17 ± 0.03 0.18 ± 0.01 trans-9C18:1 1.09 ± 0.01 1.10 ± 0.04 1.14 ± 0.02 1.19 ± 0.03 trans-10 C18:1 0.41 ± 0.02 0.42 ± 0.02 0.45 ± 0.01 0.49 ± 0.03 trans 11C18:1 1.36 ± 0.03 1.36 ± 0.02 1.39 ± 0.01 1.43 ± 0.03 cis-9 trans-11C18:2 0.89 ± 0.04 0.92 ± 0.04 0.92 ± 0.01 0.98 ± 0.02 cis-15,trans-11 C18:2 0.34 ± 0.03 0.36 ± 0.02 0.37 ± 0.01 0.41 ± 0.01 ΣtransC18:3 1.71 ± 0.02 1.75 ± 0.04 1.78 ± 0.01 1.83 ± 0.04 Σ TFA** 7.12 7.29 7.44 7.82 Goat milk fat Fatty acids Unheated 125°C 150°C 175°C trans-9C14:1 0.26 ± 0.01 0.26 ± 0.03 0.29 ± 0.01 0.30 ± 0.01 trans-10 C15:1 0.22 ± 0.03 0.23 ± 0.02 0.26 ± 0.01 0.28 ± 0.03 trans-10C16:1 0.58 ± 0.04 0.58 ± 0.02 0.65 ± 0.02 0.67 ± 0.01 trans-9C17:1 0.12 ± 0.01 0.13 ± 0.01 0.16 ± 0.03 0.19 ± 0.02 trans-9C18:1 1.01 ± 0.02 1.03 ± 0.01 1.06 ± 0.04 1.10 ± 0.01 trans-10 C18:1 0.37 ± 0.01 0.38 ± 0.03 0.41 ± 0.01 0.46 ± 0.03 trans 11C18:1 1.34 ± 0.02 1.36 ± 0.04 1.39 ± 0.01 1.45 ± 0.02 cis-9 trans-11C18:2 0.92 ± 0.03 0.91 ± 0.02 0.97 ± 0.02 0.99 ± 0.01 cis-15,trans-11 C18:2 0.26 ± 0.04 0.25 ± 0.01 0.31 ± 0.02 0.34 ± 0.01 ΣtransC18:3 1.74 ± 0.01 1.75 ± 0.03 1.80 ± 0.02 1.83 ± 0.01 Σ TFA** 6.82 6.98 7.30 7.61 *Values are given as the means of triplicate analyses ± standard deviation. **Total trans fatty acid. trans-9, cis-12, 18:2 and cis-9, trans-12, 18:2) accrued when trilin- Discussions olein (cis-9, cis-12, 18:1) was heated at 180°C for 4 hours. In the present study, trans-9C18:1 content of cow milk fat was increased GC and FTIR-predicted results, for the analysis of TFA content in milk from 1.16 ± 0.01 to 1.20 ± 0.03, buffalo milk fat was increased from fat of cow, buffalo, and goat, were represented collectively in Figure 3 1.09  ±  0.01 to 1.19  ±  0.03, and goat milk fat was increased from (Table  5). Out of three milk samples analyzed, a linear increment 1.01  ±  0.02 to 1.10  ±  0.01 when temperature was increased from was observed for cow milk sample found at different temperatures 120°C to 170°C (Table 4). Isomerization of linolenic acid (18:3) also (120°C–130°C, 140°C–150°C, and 160°C–170°C), whereas in case of produced 9-trans, 12-cis, 15-cis C18:3, 9-cis, 12-trans, 15-cis C18:3, buffalo milk sample, a linear variation was observed at 120°C–130°C 9-cis, 12-cis, 15-trans C18:3, 9-trans, 12-trans, 15-cis C18:3, 9-trans, and 140°C–150°C and relatively higher increment was obtained at 12-cis, 15-trans C18:3, 9-cis, 12-trans, 15-trans C18:3, 9-trans, 160°C–170°C. A significant increment has been observed for goat milk 12-trans, 15-trans C18:3 FAs (Mihalache et  al., 2012). It indicates sample as when heating the sample at 120°C–130°C, 140°C–150°C, that occurrence of 18:3 TFA might be the result of isomerization of and 160°C–170°C shown in Figure 3. As milk fat (ghee) has been very linolenic acid. In our study, total increment in cis-9, trans-11C18:2 commonly used for frying purpose in most of the developed coun- and cis-15, trans-11 C18:2 was found in the range of 0.01 to 0.09 tries, studying the effect of heating on these fats (ghee) has become per cent (Table 4). Identification of each peak in the chromatograms an urgent issue to solve because of induction of TFAs which is a main was confirmed by comparing their retention time with peaks of cause of coronary heart diseases. On viewing the damaging nature standard FAMEs. of TFA, Food and Drug Administration (FDA) and Health Canada Downloaded from https://academic.oup.com/fqs/article-abstract/2/1/51/4823025 by Ed 'DeepDyve' Gillespie user on 16 March 2018 56 M. Umar Khan et al., 2018, Vol. 2, No. 1 Figure  3 Effect of heating on milk fat (ghee) of cow, buffalo, and goat analyzed by (A) gas chromatography (GC) and (B) attenuated total reflection-Fourier transform infrared (ATR-FTIR). Table 5. Comparison of gas chromatography (GC) and attenuated total reflection-Fourier transform infrared (ATR-FTIR)–predicted results. No. Heating temperature (°C) Total amount of TFA Total amount of TFA determined by determined by GC ATR-FTIR Cow Buffalo Goat Cow Buffalo Goat 1 25* 7.71 7.12 6.82 7.98 7.62 7.12 2 125 7.86 7.29 6.98 8.05 7.94 7.51 3 150 8.01 7.44 7.30 8.56 8.27 7.74 4 175 8.25 7.82 7.61 8.83 8.42 7.93 *Sample was not heated. have proposed food-labelling rules which compelled the food manu- helpful for consumer welfare of India to minimize the use of products facturers to mention the content of TFA on the products as asterisked frying in ghee at a high temperature. They should also instruct the footnote, ‘*Includes g trans fat’ which contains >0.5 g TFA per serving restaurants to change the ghee repeatedly which could minimize the (Ruth, 2002). In our country, most of the restaurants use these milk induction of TFA. The local people of India should be aware of highly fats for frying purpose in the temperature range of 120°C to 200°C. detrimental nature of TFA because prevention of ghee for frying pur- As confirmed from the present study, a significant amount of TFA has poses is quite challenging. been developed on heating the ghee up to 200°C. It indicates that the food items which have been fried in ghee contain a sufficient amount Conclusion of TFA which ultimately causes the coronary heart diseases. In add- ition, they use the ghee several times repeatedly because of its high cost In conclusion, heat treatment induced the formation of TFAs in which is more dangerous for human health as it will cause the induc- milk fats of cow, buffalo, and goat which would increase the risk tion of more TFA in the ghee. Among the three milk samples analyzed, of cardiovascular diseases. By comparison of the results obtained, it production of goat milk seems relatively less compared with the cow may be concluded that goat milk fat, having the lowest TFA content and buffalo milk production. In our country, consumption of milk fat among the three samples analyzed, should be the choice of people. in rural areas is more than urban areas because rural people are hav- Repetition of the same ghee for many times while frying the food ing comparatively more livestock. But overall consumption of these items should be avoided. A significant increase of TFA in milk fats milk fats is very high in India, which ultimately affects the human (ghee) during thermal process increased the attention of consumers health due to the presence of TFA in all milk fats. This study might be in maintaining healthy dietary practices. Downloaded from https://academic.oup.com/fqs/article-abstract/2/1/51/4823025 by Ed 'DeepDyve' Gillespie user on 16 March 2018 Effect of temperature on milk fat, 2018, Vol. 2, No. 1 57 Kremmyda, L. S., Tvrzicka, E., Stankova, B., Zak, A. (2011). Fatty acids as bio- Supplementary Material compounds: their role in human metabolism, health and disease: a review. Supplementary material is available at Food Quality and Safety online. Part 2: fatty acid physiological roles and applications in human health and disease. Biomedical Papers of the Medical Faculty of the University Palacky, Olomouc, Czechoslovakia, 155: 195–218. Funding Le Doux, M., Rouzeau, A., Bas, P., Sauvantt, D. (2002). Occurrence of trans- Financial assistance in the form of Non-Net fellowship from C18:1 fatty acid isomers in goat milk: effect of two dietary regimens. University Grants Commission is gratefully acknowledged. Journal of Dairy Science, 85: 190–197. Martínez Marín, A. L., et al. (2015). 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