Effects of chicken feet gelatin extracted at different temperatures and wheat fiber with different particle sizes on the physicochemical properties of gels

Effects of chicken feet gelatin extracted at different temperatures and wheat fiber with... Abstract The objectives of this study were to determine the effects of 1) the extraction temperature (65, 75, 85, and 95°C) of chicken feet gelatin (CFG) and 2) CFG extracted at different temperatures and wheat fiber (WF) with different particle sizes (80, 250, and 500 μm) on the physicochemical properties of the resultant gels. Raw chicken feet (CF) were swelled by treatment of an acidic solution [i.e., 0.1 N HCl (pH 2)]. The CFG was extracted from the swelled CF at different temperatures. Samples of 4% CFG or a mixture of 3% CFG and 3% WF were prepared using distilled water at 42 ± 1°C and then cooled to form gels. The physicochemical properties of the prepared CFG or the gel with CFG and WF were then investigated. The results indicate that the extraction yield, protein content, and L* values for the CFG samples significantly increased as the extraction temperature increased, whereas the viscosity, melting point, and a* values decreased. For the gel with CFG and WF, the gel strength, melting point, viscosity, and L* and b* values were significantly affected (P < 0.05) by the extraction temperature of CFG, but they partially were not affected (P > 0.05) by the particle size of WF. The gel with WF and extracted CFG at 65°C had the highest (P < 0.05) gel strength, melting point, viscosity, and a* values. In conclusion, CFG or the gel with CFG and WF could be utilized to prepare gelatins or gel with different physicochemical properties by controlling the extraction temperature or particle size of WF, depending on the specific application. Moreover, with its distinct physicochemical properties, the gel with CFG and WF could possibly be used as a non-meat ingredient for fat replacement. INTRODUCTION Over the past few decades, the global consumption of chicken meat, which possesses a well-balanced amount of amino acids and is low in both fat and calories, has risen continually (Silva and Glória, 2002). Naturally, the amount of chicken by-products, such as feet, bone, heart, liver, and gizzard, also will increase as chicken meat consumption increases. However, the utilization of chicken by-products as a human food source has been rather limited. Chicken feet (CF) contain an abundance of collagen, which is composed of 3 polypeptides (α-chains) (Liu et al., 2001) that can be converted into gelatin and soluble proteins by hydrolysis. Note that gelatin's properties are affected by both the source and type of collagen (Johnston-Banks, 1990; Du et al., 2013). The extraction yield, color, gel strength, melting point, and viscosity are important properties for applications of gelatin, with the latter 3 properties being the main criteria to determine the quality of gelatin. Being one of the most widely used biopolymers, gelatin is used in food, pharmaceutical, cosmetic, and photographic applications because of its unique functional and technological properties (Schrieber and Gareis, 2007). In the food industry, for example, gelatin is utilized in confections (to provide chew, texture, and foam stabilization), low-fat spreads (to provide creaminess, fat reduction, and mouth feel), dairy (to provide stabilization and texturization), baked goods (to provide emulsification, gelling, and stabilization), and meat products (to provide water binding or reduce addition levels of fat) (Johnston-Banks, 1990; Schrieber and Gareis, 2007; Choe et al., 2009; Choe et al., 2013). However, frequent outbreaks of bovine spongiform encephalopathy (BSE) and foot and mouth disease have been a barrier for the widespread use of gelatin in the food industry. Thus, identification of new gelatin sources such as poultry skin, feet, and bone has increased to replace mammalian sources (Gudmundsson, 2002; Schrieber and Gareis, 2007). Dietary fiber is an important functional food component that contains numerous health benefits, such as maintaining bowel integrity and health, lowering blood cholesterol levels, controlling blood sugar levels, and providing a non-caloric bulking agent that can aid in weight loss by replacing caloric food components such as fat. In addition to the benefits of increased fiber consumption, dietary fibers in meat products also have other advantages, such as being a fat replacement, increased water-holding capacity, and oil-holding capacity. Collectively, these properties can improve the emulsion stability, viscosity, and texture in meat products (Elleuch et al., 2011). The physicochemical properties of meat products also can be affected by particle size of dietary fiber due to its hydration ability (Raghavendra et al., 2004). Insoluble dietary fiber such as cellulose, hemicellulose, and lignin is mostly obtained from grains. Insoluble dietary wheat fiber (WF), which is obtained from wheat straw, has been studied by several authors in meat products as a fat substitute (Mansour and Khail, 1999; Choe et al., 2013). The aims of the present study were to determine: 1) the effect of extraction temperature of CF on properties of gelatin, and 2) the most suitable particle sizes of WF to generate the best properties (high gel strength, viscosity, and melting point) of gel with chicken feet gelatin (CFG) and WF in meat products as a fat replacement. MATERIALS AND METHODS Preparation of Chicken Feet Gelatin and Wheat Fiber CF (broiler) with skin were provided by a slaughterhouse (Maniker F&G Co., Yonginsi 388–278, Korea) and stored at −21 °C (up to 2 wk) until further analysis. The chicken feet (2 kg/batch) were thawed at 4 °C for 24 h and then washed using tap water. The extraction procedures are shown in Figure 1. The cleaned chicken feet were soaked in 10 volumes (v/w) of 0.1 N HCl (pH 2) at 18 °C for 24 hours. After the acid treatment, the pH of the feet was neutralized for 48 h with flowing tap water. For extraction at different temperatures (65, 75, 85, and 95 °C), the feet were placed in polyethylene bags, vacuum packaged (FJ-500XL, Fujee Tech, Seoul, Korea), and then heated at different temperatures for 2 hours. The extracted gelatin was frozen at −70 ± 1 °C and dried at −40 °C under 80 × 10−3 torr of pressure using a freeze-dryer (PVTFD20R, Ilshinlab, Yangju, Korea). The gelatin was dehydrated until it reached a constant weight (<3% final moisture) for 48 h in the freeze-dryer. Figure 1. View largeDownload slide Procedures for preparation of the gelatin from the chicken feet. Figure 1. View largeDownload slide Procedures for preparation of the gelatin from the chicken feet. The WF (Vitacel®, J. Rettenmaier & Söhne GmbH, Rosenberg, Germany) consisted of 74% cellulose, 26% hemicellulose, and <0.5 of lignin, with different particle sizes [80 μm (WF80), 250 μm (WF250), and 500 μm (WF500)]. All reagents were of analytical grade. All processes were examined in 3 batches. The experiments were performed in duplicate with at least 3 replicates. The results were expressed as mean ± standard error. Preparation of CFG and WF Mixture Samples of the 4% CFG or 3% CFG extracted at different temperatures and 3% WF (particle size, 500 μm) or 3% CFG extracted at 75°C and 3% WF with different particle size mixtures were prepared using distilled water at 42 ± 1°C. The mixtures were then cooled at 10 ± 1°C and cut into 2 × 2 × 2 cm cubes for analysis. All conditions of the gelatin and CFG and WF mixture were based on a preliminary study. Analytical Methods pH. A 5 g mass of the 4% (w/v) gelatin samples was homogenized (Ultra-Turrax® T25, Janke & Kunkel, Staufen, Germany) with 20 mL of distilled water for 60 seconds. The pH was measured using a pH meter (Model 340, Mettler-Toledo GmbH Analytical, Schwerzenbach, Switzerland). All measurements were performed in triplicate. Yields. The yields were determined by calculating the weight differences of the samples before and after processing as follows:   \begin{eqnarray*} {\rm{Soaking}}\,{\rm{yield}}\left( \% \right) &=& \big( {\rm{sample}}\,{\rm{after}}\,{\rm{soaking}}/ \nonumber\\ &&{\rm{raw}}\,{\rm{material}} \big) \times 100 \end{eqnarray*}   \begin{eqnarray*}{\rm{Washing}}\,{\rm{yield}}\left( \% \right) &=& \big( {\rm{sample}}\,{\rm{after}}\,{\rm{washing}}/\nonumber\\ &&{\rm{raw}}\,{\rm{material}} \big) \times 100\end{eqnarray*}   \begin{eqnarray*}{\rm{Extraction}}\,{\rm{yield}}\left( \% \right) &=& \big( {\rm{sample}}\,{\rm{after}}\,{\rm{extraction}}/\nonumber\\ &&{\rm{raw}}\,{\rm{material}} \big) \times 100\end{eqnarray*}   \begin{eqnarray*}{\rm{Gelatin}}\,{\rm{yield}}\left( \% \right) &=& \big( {\rm{sample}}\,{\rm{after}}\,{\rm{freezer}}\,{\rm{drying}}/\nonumber\\ &&{\rm{sample}}\,{\rm{before}}\,{\rm{freezer}}\,{\rm{drying}} \big) \times 100\end{eqnarray*} Protein Content. The protein content was determined by the Kjeldahl method using an automatic Kjeldahl nitrogen analyzer (Kjeltec® 2300 Analyzer Unit, Foss Tecator AB, Höganas, Sweden). Gel Strength. Samples of the raw (before freeze drying) or 4% gelatin (w/v) or gel samples with added CFG and WF were cooled at 10 ± 1 °C for 16 to 18 h and then cut into 2 × 2 × 2 cm cubes. Measurements were conducted at 8 ± 1 °C using a Texture Analyzer (TA.XT2, Stable Microsystems LTD, Surrey, UK) with a 10 mm depression at a rate of 0.5 mm/s using a 10 mm diameter probe. Color Evaluation. Samples of the 4% gelatin (w/v) or gel samples with added CFG and WF were formed into 2 × 2 × 2 cm cubes, and their surface colors were measured using a colorimeter (Chroma meter CR-210, Minolta, Osaka, Japan; illuminate C, calibrated with a standard white plate: L* = 97.83, a* = − 0.43, b* = +1.98). The instrument consisted of an 8 mm diameter measuring area and a 50 mm diameter illumination area. The color values (i.e., CIE L*, a*, and b*) were measured on the sample surfaces, and the results of each sample were recorded in triplicate. Melting Point. The melting points of the 4% gelatin (w/v) or gel samples with added CFG and WF were determined by averaging the temperatures between the starting and ending melting points measured using a melting point analyzer (ATM-01, AS-ONE, Japan) as follows:  \begin{eqnarray*} {{\rm{Melting}}\,{\rm{point}}\left( {^\circ {\rm C}{}} \right)}&=& \big( {\rm{starting}}\,{\rm{melting}}\,{\rm{temperature}}\nonumber\\ &&+ {\rm{ending}}\,{\rm{melting}}\,{\rm{temperature}} \big)/2 \end{eqnarray*} Viscosity. The flow behavior and time dependency of the 4% gelatin (w/v) or gel samples with added CFG and WF were measured in triplicate with a rotational viscometer (HAKKE Viscotester® 500, Thermo Electron Corporation, Karlsruhe, Germany) at 10 rpm. The tests were performed using a standard cylinder sensor (SV-2) at 35 ± 1 °C. The time dependency of the samples was evaluated by measuring the apparent viscosity (ηapp) under a constant share rate of 10 s−1 for 60 seconds. Statistical Analysis The experimental design was completely randomized. The data obtained from 3 replicates were analyzed using the General Linear Model (GLM) procedure of the SAS statistical package (SAS, 2011). Duncan's multiple range test (P < 0.05) was used to determine the differences between the treatment mean values. For analysis of the CFG and WF mixtures, batch was included as a random effect, and the CFG extraction temperature and WF particle size were considered as fixed effects. RESULTS AND DISCUSSION pH, Soaking, and Washing Yield of CFG All gelatin manufacturing processes consisted of 3 main steps: pretreatment of the raw material, extraction of the gelatin, and purification and drying. Depending on the method with which the collagen was pretreated, 2 different types of gelatin (each with distinct characteristics) can be produced. Type A gelatin (pI 6 to 9) is produced from acid-treated collagen, whereas type B gelatin (pI of ca. 5) is produced from alkali-treated collagen (Stainsby, 1987). Acidic treatment is most suitable for less covalently cross-linked collagens found in pig or chicken skins, whereas alkaline treatment is suitable for more complex collagens found in bovine hides. On the basis of a previous study, which reported that improved properties of acid-treated (24 h) CFG were obtained compared with those of alkali-treated CFG (Jang et al., 2002), this study used acidic treatments to extract the collagen. The swelling yields of the CF increased dramatically (140%) until 18 h (pH 1.88) at 4 °C, with slightly different soaking yields between 18 and 24 h (Figure 2). Swelling occurs because of a weakened binding ability within the interior molecular structure of the collagen (Liu et al., 2008). The pH value of the soaked CF was 1.88 at 6 h, followed by a constant pH value (1.68 to 1.70). According to Shin (2002), optimal swelling times are achieved when the soaking solution has a constant pH value. In the present study, the swelling procedure continued for 24 h in accordance with a preliminary study that found the pH values became constant after 24 hours. Note that the pH value was 5.2 following the washing step. Figure 2. View largeDownload slide Changes in swelling, washing yields, and pH of chicken feet. Figure 2. View largeDownload slide Changes in swelling, washing yields, and pH of chicken feet. Effect of Extraction Temperature on the Physicochemical Properties of CFG Higher extraction yields were observed as the extraction temperature increased (Figure 3; P < 0.05), which is similar to results reported previously. That is, the extraction yields were found to be the greatest at 70°C compared with lower temperatures (of 40, 50, and 60°C) during a 3-hour extraction process (Cho et al., 2006). In addition, the gelatin powder yield and protein content increased significantly as the extraction temperature increased (Table 1). However, the gel strength, viscosity, melting point, and redness decreased as the extraction temperature increased (Table 1 and Figure 4). Previous studies reported that gelatin yields increased slightly with increasing extraction temperature due to hydrolysis of the collagen cross-linkages and other proteins (Kim and Lee, 1988; Cho et al., 2006). A smaller amount of proline and hydroproline, which stabilize the molecular structure of collagen, also may be extracted as the extraction temperature increases, giving rise to a lower molecular weight of the collagen with fewer amino acids (Norziah, et al., 2009; See et al., 2010). This phenomenon may contribute to the lower gel strength, viscosity, and melting point of extracted CFG compared with those at a higher temperature (Haug et al., 2004). In this regard, the melting point was highly correlated with both the gel strength (R2 = 0.913) and viscosity (R2 = 0.953). Similarly, Imeson (1997) found that the melting point of gelatin was correlated with gel strength and viscosity as the amount of carbon tetrachloride decreased (gel softening). Taken together, it appears that a higher extraction temperature can extract more protein, whereas a lower gel strength, viscosity, and melting point of the extracted CFG were determined, which likely result from the extraction of proline and hydroxyproline. Figure 3. View largeDownload slide Extraction yields of gelatin from chicken feet at different temperatures. a-c Means values with different letters among the treatment are significantly different (P < 0.05). Figure 3. View largeDownload slide Extraction yields of gelatin from chicken feet at different temperatures. a-c Means values with different letters among the treatment are significantly different (P < 0.05). Figure 4. View largeDownload slide Gel strength of raw (before freeze drying) and 4% gelatin (after freeze drying) various temperatures extracted from the chicken feet. a-d Means values with different letters among the raw gelatin treatment are significantly different (P < 0.05). A-D Means values with different letters among the 4% gelatin treatment are significantly different (P < 0.05). Figure 4. View largeDownload slide Gel strength of raw (before freeze drying) and 4% gelatin (after freeze drying) various temperatures extracted from the chicken feet. a-d Means values with different letters among the raw gelatin treatment are significantly different (P < 0.05). A-D Means values with different letters among the 4% gelatin treatment are significantly different (P < 0.05). Table 1. Effect of different extraction temperatures on the physicochemical properties of chicken feet gelatin (CFG).   Extraction temperature (°C)  Traits  65  75  85  95  Gelatin powder yield (%)  4.65 ± 0.07d  4.84 ± 0.06c  5.12 ± 0.08b  5.31 ± 0.05a  Protein content (%)  4.61 ± 0.07d  4.80 ± 0.06c  5.08 ± 0.04b  5.27 ± 0.03a  Viscosity (pa·s)  7.61 ± 0.51a  6.89 ± 0.87b  5.89 ± 0.45c  5.12 ± 0.17c  Melting point (°C)  38.5 ± 0.41a  37.88 ± 0.63a  36.50 ± 0.41b  36.38 ± 0.48b  CIE L*  45.44 ± 0.62b  50.95 ± 1.42a  51.04 ± 2.90a  54.28 ± 3.51a  CIE a*  –0.94 ± 0.04a  –1.22 ± 0.11b  –1.32 ± 0.11b  –1.51 ± 0.09c  CIE b*  1.38 ± 0.36  1.40 ± 0.39  1.65 ± 0.77  1.76 ± 0.21    Extraction temperature (°C)  Traits  65  75  85  95  Gelatin powder yield (%)  4.65 ± 0.07d  4.84 ± 0.06c  5.12 ± 0.08b  5.31 ± 0.05a  Protein content (%)  4.61 ± 0.07d  4.80 ± 0.06c  5.08 ± 0.04b  5.27 ± 0.03a  Viscosity (pa·s)  7.61 ± 0.51a  6.89 ± 0.87b  5.89 ± 0.45c  5.12 ± 0.17c  Melting point (°C)  38.5 ± 0.41a  37.88 ± 0.63a  36.50 ± 0.41b  36.38 ± 0.48b  CIE L*  45.44 ± 0.62b  50.95 ± 1.42a  51.04 ± 2.90a  54.28 ± 3.51a  CIE a*  –0.94 ± 0.04a  –1.22 ± 0.11b  –1.32 ± 0.11b  –1.51 ± 0.09c  CIE b*  1.38 ± 0.36  1.40 ± 0.39  1.65 ± 0.77  1.76 ± 0.21  All values are mean ± standard deviation of 3 replicates. a-dMeans within a row with different letters are significantly different (P < 0.05). View Large Effect of CFG Extraction Temperature on the Physicochemical Properties of Gels with CFG and WF In a preliminary study, a 3% gelatin and 3% WF mixture gel was found to possess the highest gel strength and viscosity compared with the other mixtures examined (i.e., 3 different compositions of gelatin (2 and 3%) × 4 different compositions of WF (0 to 3%)). The present study was conducted on the basis of the results from this preliminary study. The addition of extracted CFG at the lowest temperature (65°C) in the gel with WF resulted in the highest gel strength, melting point, viscosity, and a* values (P < 0.05; Table 2). These results can be explained in terms of a decrease in the gel forming ability of the sample and a smaller molecular weight, resulting from cleavage of the hydrogen bonds and free amino acid hydroxyl groups as the extraction temperature increased above 50°C (Tomka, 1983; Ward and Courts, 1997). The highest a* value and lowest L* and b* values were obtained in CFG extracted at 65°C (P < 0.05). Note that the addition of extracted CFG above 75°C did not significantly influence the a* and b* values in gel with CFG and WF. Table 2. Effect of extraction temperature of chicken feet gelatin (CFG) on physicochemical properties of gel with CFG and wheat fiber (WF) with 500 μm.   Extraction temperature (°C)  Traits  65  75  85  95  Gel strength (g)  359.60 ± 26.95a  280.77 ± 12.98b  237.90 ± 5.86c  182.13 ± 7.27d  Viscosity (pa·s)  52.45 ± 2.07a  47.50 ± 0.87b  44.49 ± 1.84b  40.60 ± 1.71c  Melting point (°C)  37.50 ± 0.50a  36.17 ± 0.29b  34.43 ± 0.40c  32.13 ± 0.32d  CIE L*  67.69 ± 1.40c  73.68 ± 1.61b  75.69 ± 1.39a,b  77.95 ± 1.87a  CIE a*  –1.37 ± 0.11a  –1.69 ± 0.01b  –1.77 ± 0.12b  –1.83 ± 0.10b  CIE b*  0.53 ± 0.09b  0.84 ± 0.11a  0.92 ± 0.05a  0.95 ± 0.07a    Extraction temperature (°C)  Traits  65  75  85  95  Gel strength (g)  359.60 ± 26.95a  280.77 ± 12.98b  237.90 ± 5.86c  182.13 ± 7.27d  Viscosity (pa·s)  52.45 ± 2.07a  47.50 ± 0.87b  44.49 ± 1.84b  40.60 ± 1.71c  Melting point (°C)  37.50 ± 0.50a  36.17 ± 0.29b  34.43 ± 0.40c  32.13 ± 0.32d  CIE L*  67.69 ± 1.40c  73.68 ± 1.61b  75.69 ± 1.39a,b  77.95 ± 1.87a  CIE a*  –1.37 ± 0.11a  –1.69 ± 0.01b  –1.77 ± 0.12b  –1.83 ± 0.10b  CIE b*  0.53 ± 0.09b  0.84 ± 0.11a  0.92 ± 0.05a  0.95 ± 0.07a  All values are mean ± standard deviation of 3 replicates. a-dMeans within a row with different letters are significantly different (P < 0.05). View Large Effect of WF Particle Size on the Physicochemical Properties of Gels with CFG and WF In general, the addition of WF in gel significantly increased the gel strength, melting point, viscosity, and L* values compared with the gel without WF (i.e., the control, Table 3). Similarly, Moe et al., (1994) found that the addition of dietary fiber containing insoluble and soluble fiber increased gel strength due to its hydration ability. However, the a* and b* value of the control were significantly higher compared with the gel containing WF (P < 0.05). Further, the gel strength and L* and b* values were not significantly affected by the WF particle size. Previous studies reported that a reduction of particle size in various ingredients led to a decrease in hydration ability because of structural damage caused by grinding (P < 0.05) (Zhu et al., 2010), which could lead to different physicochemical properties. In this study, the viscosity and a* values were significantly influenced by the WF particle size. Table 3. Effect of particle size of wheat fiber (WF) on physicochemical properties of gel with chicken feet gelatin (CFG) extracted at 75°C and WF.   Treatment (particle size, μm)  Traits  Control1)  WF80 (80)1)  WF250 (250)1)  WF500 (500)1)  Gel strength (g)  186.03 ± 15.33b  269.85 ± 9.76a  273.39 ± 20.29a  280.77 ± 12.98a  Viscosity (pa·s)  5.91 ± 0.01c  42.55 ± 1.95b  44.63 ± 2.38a,b  47.50 ± 0.87a  Melting point (°C)  35.17 ± 0.29b  35.67 ± 0.29a,b  35.75 ± 0.29a  36.17 ± 0.29a  CIE L*  53.96 ± 0.08b  71.56 ± 1.45a  72.01 ± 1.34a  73.68 ± 1.6a  CIE a*  –0.60 ± 0.05a  –1.36 ± 0.03b  –1.44 ± 0.04c  –1.69 ± 0.01d  CIE b*  3.18 ± 0.20a  0.87 ± 0.14b  0.81 ± 0.09b  0.81 ± 0.16b    Treatment (particle size, μm)  Traits  Control1)  WF80 (80)1)  WF250 (250)1)  WF500 (500)1)  Gel strength (g)  186.03 ± 15.33b  269.85 ± 9.76a  273.39 ± 20.29a  280.77 ± 12.98a  Viscosity (pa·s)  5.91 ± 0.01c  42.55 ± 1.95b  44.63 ± 2.38a,b  47.50 ± 0.87a  Melting point (°C)  35.17 ± 0.29b  35.67 ± 0.29a,b  35.75 ± 0.29a  36.17 ± 0.29a  CIE L*  53.96 ± 0.08b  71.56 ± 1.45a  72.01 ± 1.34a  73.68 ± 1.6a  CIE a*  –0.60 ± 0.05a  –1.36 ± 0.03b  –1.44 ± 0.04c  –1.69 ± 0.01d  CIE b*  3.18 ± 0.20a  0.87 ± 0.14b  0.81 ± 0.09b  0.81 ± 0.16b  All values are mean ± standard deviation of 3 replicates. 1)Treatment: Control, gel with CFG; WF 80, gel with CFG and WF with 80 μm; WF 250, gel with CFG and WF with 250 μm; WF 500, gel with CFG and WF with 500 μm. a-dMeans within a row with different letters are significantly different (P < 0.05). View Large CONCLUSION In conclusion, extraction yield, color, gel strength, melting point, and viscosity are important properties for applications of gelatin, with the latter 3 properties being the main criteria to determine the quality of gelatin. In this study, an increase in the extraction temperature led to increases of the extraction yield, gelatin powder yield, and protein content of CFG, which most likely resulted from hydrolysis of collagen and other proteins. In addition, different rheological and physicochemical properties, including viscosity, gel strength, and melting point of CFG, were determined using various extraction temperatures. Taken together, these results suggest that CFG could be utilized as an extracting gelatin to obtain distinct rheological and physicochemical properties by controlling the temperature, depending on the specific application. 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K., Ng K. L., Wam Aida W. M., Babji A. S.. 2010. Physicochemical properties of gelatins extracted from skins of different freshwater fish species. Int. Food Res. J.  17: 809– 816. Shin M. H. 2002. Properties of collagen extracted from chicken foot skins. Korean J. Culinary Res.  8: 95– 105. Silva C. M. G., Glória M. B. A.. 2002. Bioactive amines in chicken breast and thigh after slaughter and during storage at 4 ± 1°C and in chicken-based meat products. Food Chem . 78: 241– 248. Google Scholar CrossRef Search ADS   Stainsby G. 1987. Gelatin gels. Pages 209– 222 in Advances in Meat Research, Collagen as a Food . Pearson A. M., Dutson T. R., Bailey A. J., ed. Van Nostrand Reinhold Company, Inc., New York, USA. Tomka I. 1983. Gelatine. Page 47 in Die Kapsel–Grundlagen, Technologie und Biopharmazie einer modernen Arzneiform . Fahrig W., Hofer U., ed. Wissenschaftliche Verlagsgesellschaft mbH, Stuttgart, Germany. Ward A. G., Courts A.. 1997. The Science and Technology of Gelatin . 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Effects of chicken feet gelatin extracted at different temperatures and wheat fiber with different particle sizes on the physicochemical properties of gels

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Abstract

Abstract The objectives of this study were to determine the effects of 1) the extraction temperature (65, 75, 85, and 95°C) of chicken feet gelatin (CFG) and 2) CFG extracted at different temperatures and wheat fiber (WF) with different particle sizes (80, 250, and 500 μm) on the physicochemical properties of the resultant gels. Raw chicken feet (CF) were swelled by treatment of an acidic solution [i.e., 0.1 N HCl (pH 2)]. The CFG was extracted from the swelled CF at different temperatures. Samples of 4% CFG or a mixture of 3% CFG and 3% WF were prepared using distilled water at 42 ± 1°C and then cooled to form gels. The physicochemical properties of the prepared CFG or the gel with CFG and WF were then investigated. The results indicate that the extraction yield, protein content, and L* values for the CFG samples significantly increased as the extraction temperature increased, whereas the viscosity, melting point, and a* values decreased. For the gel with CFG and WF, the gel strength, melting point, viscosity, and L* and b* values were significantly affected (P < 0.05) by the extraction temperature of CFG, but they partially were not affected (P > 0.05) by the particle size of WF. The gel with WF and extracted CFG at 65°C had the highest (P < 0.05) gel strength, melting point, viscosity, and a* values. In conclusion, CFG or the gel with CFG and WF could be utilized to prepare gelatins or gel with different physicochemical properties by controlling the extraction temperature or particle size of WF, depending on the specific application. Moreover, with its distinct physicochemical properties, the gel with CFG and WF could possibly be used as a non-meat ingredient for fat replacement. INTRODUCTION Over the past few decades, the global consumption of chicken meat, which possesses a well-balanced amount of amino acids and is low in both fat and calories, has risen continually (Silva and Glória, 2002). Naturally, the amount of chicken by-products, such as feet, bone, heart, liver, and gizzard, also will increase as chicken meat consumption increases. However, the utilization of chicken by-products as a human food source has been rather limited. Chicken feet (CF) contain an abundance of collagen, which is composed of 3 polypeptides (α-chains) (Liu et al., 2001) that can be converted into gelatin and soluble proteins by hydrolysis. Note that gelatin's properties are affected by both the source and type of collagen (Johnston-Banks, 1990; Du et al., 2013). The extraction yield, color, gel strength, melting point, and viscosity are important properties for applications of gelatin, with the latter 3 properties being the main criteria to determine the quality of gelatin. Being one of the most widely used biopolymers, gelatin is used in food, pharmaceutical, cosmetic, and photographic applications because of its unique functional and technological properties (Schrieber and Gareis, 2007). In the food industry, for example, gelatin is utilized in confections (to provide chew, texture, and foam stabilization), low-fat spreads (to provide creaminess, fat reduction, and mouth feel), dairy (to provide stabilization and texturization), baked goods (to provide emulsification, gelling, and stabilization), and meat products (to provide water binding or reduce addition levels of fat) (Johnston-Banks, 1990; Schrieber and Gareis, 2007; Choe et al., 2009; Choe et al., 2013). However, frequent outbreaks of bovine spongiform encephalopathy (BSE) and foot and mouth disease have been a barrier for the widespread use of gelatin in the food industry. Thus, identification of new gelatin sources such as poultry skin, feet, and bone has increased to replace mammalian sources (Gudmundsson, 2002; Schrieber and Gareis, 2007). Dietary fiber is an important functional food component that contains numerous health benefits, such as maintaining bowel integrity and health, lowering blood cholesterol levels, controlling blood sugar levels, and providing a non-caloric bulking agent that can aid in weight loss by replacing caloric food components such as fat. In addition to the benefits of increased fiber consumption, dietary fibers in meat products also have other advantages, such as being a fat replacement, increased water-holding capacity, and oil-holding capacity. Collectively, these properties can improve the emulsion stability, viscosity, and texture in meat products (Elleuch et al., 2011). The physicochemical properties of meat products also can be affected by particle size of dietary fiber due to its hydration ability (Raghavendra et al., 2004). Insoluble dietary fiber such as cellulose, hemicellulose, and lignin is mostly obtained from grains. Insoluble dietary wheat fiber (WF), which is obtained from wheat straw, has been studied by several authors in meat products as a fat substitute (Mansour and Khail, 1999; Choe et al., 2013). The aims of the present study were to determine: 1) the effect of extraction temperature of CF on properties of gelatin, and 2) the most suitable particle sizes of WF to generate the best properties (high gel strength, viscosity, and melting point) of gel with chicken feet gelatin (CFG) and WF in meat products as a fat replacement. MATERIALS AND METHODS Preparation of Chicken Feet Gelatin and Wheat Fiber CF (broiler) with skin were provided by a slaughterhouse (Maniker F&G Co., Yonginsi 388–278, Korea) and stored at −21 °C (up to 2 wk) until further analysis. The chicken feet (2 kg/batch) were thawed at 4 °C for 24 h and then washed using tap water. The extraction procedures are shown in Figure 1. The cleaned chicken feet were soaked in 10 volumes (v/w) of 0.1 N HCl (pH 2) at 18 °C for 24 hours. After the acid treatment, the pH of the feet was neutralized for 48 h with flowing tap water. For extraction at different temperatures (65, 75, 85, and 95 °C), the feet were placed in polyethylene bags, vacuum packaged (FJ-500XL, Fujee Tech, Seoul, Korea), and then heated at different temperatures for 2 hours. The extracted gelatin was frozen at −70 ± 1 °C and dried at −40 °C under 80 × 10−3 torr of pressure using a freeze-dryer (PVTFD20R, Ilshinlab, Yangju, Korea). The gelatin was dehydrated until it reached a constant weight (<3% final moisture) for 48 h in the freeze-dryer. Figure 1. View largeDownload slide Procedures for preparation of the gelatin from the chicken feet. Figure 1. View largeDownload slide Procedures for preparation of the gelatin from the chicken feet. The WF (Vitacel®, J. Rettenmaier & Söhne GmbH, Rosenberg, Germany) consisted of 74% cellulose, 26% hemicellulose, and <0.5 of lignin, with different particle sizes [80 μm (WF80), 250 μm (WF250), and 500 μm (WF500)]. All reagents were of analytical grade. All processes were examined in 3 batches. The experiments were performed in duplicate with at least 3 replicates. The results were expressed as mean ± standard error. Preparation of CFG and WF Mixture Samples of the 4% CFG or 3% CFG extracted at different temperatures and 3% WF (particle size, 500 μm) or 3% CFG extracted at 75°C and 3% WF with different particle size mixtures were prepared using distilled water at 42 ± 1°C. The mixtures were then cooled at 10 ± 1°C and cut into 2 × 2 × 2 cm cubes for analysis. All conditions of the gelatin and CFG and WF mixture were based on a preliminary study. Analytical Methods pH. A 5 g mass of the 4% (w/v) gelatin samples was homogenized (Ultra-Turrax® T25, Janke & Kunkel, Staufen, Germany) with 20 mL of distilled water for 60 seconds. The pH was measured using a pH meter (Model 340, Mettler-Toledo GmbH Analytical, Schwerzenbach, Switzerland). All measurements were performed in triplicate. Yields. The yields were determined by calculating the weight differences of the samples before and after processing as follows:   \begin{eqnarray*} {\rm{Soaking}}\,{\rm{yield}}\left( \% \right) &=& \big( {\rm{sample}}\,{\rm{after}}\,{\rm{soaking}}/ \nonumber\\ &&{\rm{raw}}\,{\rm{material}} \big) \times 100 \end{eqnarray*}   \begin{eqnarray*}{\rm{Washing}}\,{\rm{yield}}\left( \% \right) &=& \big( {\rm{sample}}\,{\rm{after}}\,{\rm{washing}}/\nonumber\\ &&{\rm{raw}}\,{\rm{material}} \big) \times 100\end{eqnarray*}   \begin{eqnarray*}{\rm{Extraction}}\,{\rm{yield}}\left( \% \right) &=& \big( {\rm{sample}}\,{\rm{after}}\,{\rm{extraction}}/\nonumber\\ &&{\rm{raw}}\,{\rm{material}} \big) \times 100\end{eqnarray*}   \begin{eqnarray*}{\rm{Gelatin}}\,{\rm{yield}}\left( \% \right) &=& \big( {\rm{sample}}\,{\rm{after}}\,{\rm{freezer}}\,{\rm{drying}}/\nonumber\\ &&{\rm{sample}}\,{\rm{before}}\,{\rm{freezer}}\,{\rm{drying}} \big) \times 100\end{eqnarray*} Protein Content. The protein content was determined by the Kjeldahl method using an automatic Kjeldahl nitrogen analyzer (Kjeltec® 2300 Analyzer Unit, Foss Tecator AB, Höganas, Sweden). Gel Strength. Samples of the raw (before freeze drying) or 4% gelatin (w/v) or gel samples with added CFG and WF were cooled at 10 ± 1 °C for 16 to 18 h and then cut into 2 × 2 × 2 cm cubes. Measurements were conducted at 8 ± 1 °C using a Texture Analyzer (TA.XT2, Stable Microsystems LTD, Surrey, UK) with a 10 mm depression at a rate of 0.5 mm/s using a 10 mm diameter probe. Color Evaluation. Samples of the 4% gelatin (w/v) or gel samples with added CFG and WF were formed into 2 × 2 × 2 cm cubes, and their surface colors were measured using a colorimeter (Chroma meter CR-210, Minolta, Osaka, Japan; illuminate C, calibrated with a standard white plate: L* = 97.83, a* = − 0.43, b* = +1.98). The instrument consisted of an 8 mm diameter measuring area and a 50 mm diameter illumination area. The color values (i.e., CIE L*, a*, and b*) were measured on the sample surfaces, and the results of each sample were recorded in triplicate. Melting Point. The melting points of the 4% gelatin (w/v) or gel samples with added CFG and WF were determined by averaging the temperatures between the starting and ending melting points measured using a melting point analyzer (ATM-01, AS-ONE, Japan) as follows:  \begin{eqnarray*} {{\rm{Melting}}\,{\rm{point}}\left( {^\circ {\rm C}{}} \right)}&=& \big( {\rm{starting}}\,{\rm{melting}}\,{\rm{temperature}}\nonumber\\ &&+ {\rm{ending}}\,{\rm{melting}}\,{\rm{temperature}} \big)/2 \end{eqnarray*} Viscosity. The flow behavior and time dependency of the 4% gelatin (w/v) or gel samples with added CFG and WF were measured in triplicate with a rotational viscometer (HAKKE Viscotester® 500, Thermo Electron Corporation, Karlsruhe, Germany) at 10 rpm. The tests were performed using a standard cylinder sensor (SV-2) at 35 ± 1 °C. The time dependency of the samples was evaluated by measuring the apparent viscosity (ηapp) under a constant share rate of 10 s−1 for 60 seconds. Statistical Analysis The experimental design was completely randomized. The data obtained from 3 replicates were analyzed using the General Linear Model (GLM) procedure of the SAS statistical package (SAS, 2011). Duncan's multiple range test (P < 0.05) was used to determine the differences between the treatment mean values. For analysis of the CFG and WF mixtures, batch was included as a random effect, and the CFG extraction temperature and WF particle size were considered as fixed effects. RESULTS AND DISCUSSION pH, Soaking, and Washing Yield of CFG All gelatin manufacturing processes consisted of 3 main steps: pretreatment of the raw material, extraction of the gelatin, and purification and drying. Depending on the method with which the collagen was pretreated, 2 different types of gelatin (each with distinct characteristics) can be produced. Type A gelatin (pI 6 to 9) is produced from acid-treated collagen, whereas type B gelatin (pI of ca. 5) is produced from alkali-treated collagen (Stainsby, 1987). Acidic treatment is most suitable for less covalently cross-linked collagens found in pig or chicken skins, whereas alkaline treatment is suitable for more complex collagens found in bovine hides. On the basis of a previous study, which reported that improved properties of acid-treated (24 h) CFG were obtained compared with those of alkali-treated CFG (Jang et al., 2002), this study used acidic treatments to extract the collagen. The swelling yields of the CF increased dramatically (140%) until 18 h (pH 1.88) at 4 °C, with slightly different soaking yields between 18 and 24 h (Figure 2). Swelling occurs because of a weakened binding ability within the interior molecular structure of the collagen (Liu et al., 2008). The pH value of the soaked CF was 1.88 at 6 h, followed by a constant pH value (1.68 to 1.70). According to Shin (2002), optimal swelling times are achieved when the soaking solution has a constant pH value. In the present study, the swelling procedure continued for 24 h in accordance with a preliminary study that found the pH values became constant after 24 hours. Note that the pH value was 5.2 following the washing step. Figure 2. View largeDownload slide Changes in swelling, washing yields, and pH of chicken feet. Figure 2. View largeDownload slide Changes in swelling, washing yields, and pH of chicken feet. Effect of Extraction Temperature on the Physicochemical Properties of CFG Higher extraction yields were observed as the extraction temperature increased (Figure 3; P < 0.05), which is similar to results reported previously. That is, the extraction yields were found to be the greatest at 70°C compared with lower temperatures (of 40, 50, and 60°C) during a 3-hour extraction process (Cho et al., 2006). In addition, the gelatin powder yield and protein content increased significantly as the extraction temperature increased (Table 1). However, the gel strength, viscosity, melting point, and redness decreased as the extraction temperature increased (Table 1 and Figure 4). Previous studies reported that gelatin yields increased slightly with increasing extraction temperature due to hydrolysis of the collagen cross-linkages and other proteins (Kim and Lee, 1988; Cho et al., 2006). A smaller amount of proline and hydroproline, which stabilize the molecular structure of collagen, also may be extracted as the extraction temperature increases, giving rise to a lower molecular weight of the collagen with fewer amino acids (Norziah, et al., 2009; See et al., 2010). This phenomenon may contribute to the lower gel strength, viscosity, and melting point of extracted CFG compared with those at a higher temperature (Haug et al., 2004). In this regard, the melting point was highly correlated with both the gel strength (R2 = 0.913) and viscosity (R2 = 0.953). Similarly, Imeson (1997) found that the melting point of gelatin was correlated with gel strength and viscosity as the amount of carbon tetrachloride decreased (gel softening). Taken together, it appears that a higher extraction temperature can extract more protein, whereas a lower gel strength, viscosity, and melting point of the extracted CFG were determined, which likely result from the extraction of proline and hydroxyproline. Figure 3. View largeDownload slide Extraction yields of gelatin from chicken feet at different temperatures. a-c Means values with different letters among the treatment are significantly different (P < 0.05). Figure 3. View largeDownload slide Extraction yields of gelatin from chicken feet at different temperatures. a-c Means values with different letters among the treatment are significantly different (P < 0.05). Figure 4. View largeDownload slide Gel strength of raw (before freeze drying) and 4% gelatin (after freeze drying) various temperatures extracted from the chicken feet. a-d Means values with different letters among the raw gelatin treatment are significantly different (P < 0.05). A-D Means values with different letters among the 4% gelatin treatment are significantly different (P < 0.05). Figure 4. View largeDownload slide Gel strength of raw (before freeze drying) and 4% gelatin (after freeze drying) various temperatures extracted from the chicken feet. a-d Means values with different letters among the raw gelatin treatment are significantly different (P < 0.05). A-D Means values with different letters among the 4% gelatin treatment are significantly different (P < 0.05). Table 1. Effect of different extraction temperatures on the physicochemical properties of chicken feet gelatin (CFG).   Extraction temperature (°C)  Traits  65  75  85  95  Gelatin powder yield (%)  4.65 ± 0.07d  4.84 ± 0.06c  5.12 ± 0.08b  5.31 ± 0.05a  Protein content (%)  4.61 ± 0.07d  4.80 ± 0.06c  5.08 ± 0.04b  5.27 ± 0.03a  Viscosity (pa·s)  7.61 ± 0.51a  6.89 ± 0.87b  5.89 ± 0.45c  5.12 ± 0.17c  Melting point (°C)  38.5 ± 0.41a  37.88 ± 0.63a  36.50 ± 0.41b  36.38 ± 0.48b  CIE L*  45.44 ± 0.62b  50.95 ± 1.42a  51.04 ± 2.90a  54.28 ± 3.51a  CIE a*  –0.94 ± 0.04a  –1.22 ± 0.11b  –1.32 ± 0.11b  –1.51 ± 0.09c  CIE b*  1.38 ± 0.36  1.40 ± 0.39  1.65 ± 0.77  1.76 ± 0.21    Extraction temperature (°C)  Traits  65  75  85  95  Gelatin powder yield (%)  4.65 ± 0.07d  4.84 ± 0.06c  5.12 ± 0.08b  5.31 ± 0.05a  Protein content (%)  4.61 ± 0.07d  4.80 ± 0.06c  5.08 ± 0.04b  5.27 ± 0.03a  Viscosity (pa·s)  7.61 ± 0.51a  6.89 ± 0.87b  5.89 ± 0.45c  5.12 ± 0.17c  Melting point (°C)  38.5 ± 0.41a  37.88 ± 0.63a  36.50 ± 0.41b  36.38 ± 0.48b  CIE L*  45.44 ± 0.62b  50.95 ± 1.42a  51.04 ± 2.90a  54.28 ± 3.51a  CIE a*  –0.94 ± 0.04a  –1.22 ± 0.11b  –1.32 ± 0.11b  –1.51 ± 0.09c  CIE b*  1.38 ± 0.36  1.40 ± 0.39  1.65 ± 0.77  1.76 ± 0.21  All values are mean ± standard deviation of 3 replicates. a-dMeans within a row with different letters are significantly different (P < 0.05). View Large Effect of CFG Extraction Temperature on the Physicochemical Properties of Gels with CFG and WF In a preliminary study, a 3% gelatin and 3% WF mixture gel was found to possess the highest gel strength and viscosity compared with the other mixtures examined (i.e., 3 different compositions of gelatin (2 and 3%) × 4 different compositions of WF (0 to 3%)). The present study was conducted on the basis of the results from this preliminary study. The addition of extracted CFG at the lowest temperature (65°C) in the gel with WF resulted in the highest gel strength, melting point, viscosity, and a* values (P < 0.05; Table 2). These results can be explained in terms of a decrease in the gel forming ability of the sample and a smaller molecular weight, resulting from cleavage of the hydrogen bonds and free amino acid hydroxyl groups as the extraction temperature increased above 50°C (Tomka, 1983; Ward and Courts, 1997). The highest a* value and lowest L* and b* values were obtained in CFG extracted at 65°C (P < 0.05). Note that the addition of extracted CFG above 75°C did not significantly influence the a* and b* values in gel with CFG and WF. Table 2. Effect of extraction temperature of chicken feet gelatin (CFG) on physicochemical properties of gel with CFG and wheat fiber (WF) with 500 μm.   Extraction temperature (°C)  Traits  65  75  85  95  Gel strength (g)  359.60 ± 26.95a  280.77 ± 12.98b  237.90 ± 5.86c  182.13 ± 7.27d  Viscosity (pa·s)  52.45 ± 2.07a  47.50 ± 0.87b  44.49 ± 1.84b  40.60 ± 1.71c  Melting point (°C)  37.50 ± 0.50a  36.17 ± 0.29b  34.43 ± 0.40c  32.13 ± 0.32d  CIE L*  67.69 ± 1.40c  73.68 ± 1.61b  75.69 ± 1.39a,b  77.95 ± 1.87a  CIE a*  –1.37 ± 0.11a  –1.69 ± 0.01b  –1.77 ± 0.12b  –1.83 ± 0.10b  CIE b*  0.53 ± 0.09b  0.84 ± 0.11a  0.92 ± 0.05a  0.95 ± 0.07a    Extraction temperature (°C)  Traits  65  75  85  95  Gel strength (g)  359.60 ± 26.95a  280.77 ± 12.98b  237.90 ± 5.86c  182.13 ± 7.27d  Viscosity (pa·s)  52.45 ± 2.07a  47.50 ± 0.87b  44.49 ± 1.84b  40.60 ± 1.71c  Melting point (°C)  37.50 ± 0.50a  36.17 ± 0.29b  34.43 ± 0.40c  32.13 ± 0.32d  CIE L*  67.69 ± 1.40c  73.68 ± 1.61b  75.69 ± 1.39a,b  77.95 ± 1.87a  CIE a*  –1.37 ± 0.11a  –1.69 ± 0.01b  –1.77 ± 0.12b  –1.83 ± 0.10b  CIE b*  0.53 ± 0.09b  0.84 ± 0.11a  0.92 ± 0.05a  0.95 ± 0.07a  All values are mean ± standard deviation of 3 replicates. a-dMeans within a row with different letters are significantly different (P < 0.05). View Large Effect of WF Particle Size on the Physicochemical Properties of Gels with CFG and WF In general, the addition of WF in gel significantly increased the gel strength, melting point, viscosity, and L* values compared with the gel without WF (i.e., the control, Table 3). Similarly, Moe et al., (1994) found that the addition of dietary fiber containing insoluble and soluble fiber increased gel strength due to its hydration ability. However, the a* and b* value of the control were significantly higher compared with the gel containing WF (P < 0.05). Further, the gel strength and L* and b* values were not significantly affected by the WF particle size. Previous studies reported that a reduction of particle size in various ingredients led to a decrease in hydration ability because of structural damage caused by grinding (P < 0.05) (Zhu et al., 2010), which could lead to different physicochemical properties. In this study, the viscosity and a* values were significantly influenced by the WF particle size. Table 3. Effect of particle size of wheat fiber (WF) on physicochemical properties of gel with chicken feet gelatin (CFG) extracted at 75°C and WF.   Treatment (particle size, μm)  Traits  Control1)  WF80 (80)1)  WF250 (250)1)  WF500 (500)1)  Gel strength (g)  186.03 ± 15.33b  269.85 ± 9.76a  273.39 ± 20.29a  280.77 ± 12.98a  Viscosity (pa·s)  5.91 ± 0.01c  42.55 ± 1.95b  44.63 ± 2.38a,b  47.50 ± 0.87a  Melting point (°C)  35.17 ± 0.29b  35.67 ± 0.29a,b  35.75 ± 0.29a  36.17 ± 0.29a  CIE L*  53.96 ± 0.08b  71.56 ± 1.45a  72.01 ± 1.34a  73.68 ± 1.6a  CIE a*  –0.60 ± 0.05a  –1.36 ± 0.03b  –1.44 ± 0.04c  –1.69 ± 0.01d  CIE b*  3.18 ± 0.20a  0.87 ± 0.14b  0.81 ± 0.09b  0.81 ± 0.16b    Treatment (particle size, μm)  Traits  Control1)  WF80 (80)1)  WF250 (250)1)  WF500 (500)1)  Gel strength (g)  186.03 ± 15.33b  269.85 ± 9.76a  273.39 ± 20.29a  280.77 ± 12.98a  Viscosity (pa·s)  5.91 ± 0.01c  42.55 ± 1.95b  44.63 ± 2.38a,b  47.50 ± 0.87a  Melting point (°C)  35.17 ± 0.29b  35.67 ± 0.29a,b  35.75 ± 0.29a  36.17 ± 0.29a  CIE L*  53.96 ± 0.08b  71.56 ± 1.45a  72.01 ± 1.34a  73.68 ± 1.6a  CIE a*  –0.60 ± 0.05a  –1.36 ± 0.03b  –1.44 ± 0.04c  –1.69 ± 0.01d  CIE b*  3.18 ± 0.20a  0.87 ± 0.14b  0.81 ± 0.09b  0.81 ± 0.16b  All values are mean ± standard deviation of 3 replicates. 1)Treatment: Control, gel with CFG; WF 80, gel with CFG and WF with 80 μm; WF 250, gel with CFG and WF with 250 μm; WF 500, gel with CFG and WF with 500 μm. a-dMeans within a row with different letters are significantly different (P < 0.05). View Large CONCLUSION In conclusion, extraction yield, color, gel strength, melting point, and viscosity are important properties for applications of gelatin, with the latter 3 properties being the main criteria to determine the quality of gelatin. In this study, an increase in the extraction temperature led to increases of the extraction yield, gelatin powder yield, and protein content of CFG, which most likely resulted from hydrolysis of collagen and other proteins. In addition, different rheological and physicochemical properties, including viscosity, gel strength, and melting point of CFG, were determined using various extraction temperatures. Taken together, these results suggest that CFG could be utilized as an extracting gelatin to obtain distinct rheological and physicochemical properties by controlling the temperature, depending on the specific application. 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Poultry ScienceOxford University Press

Published: Mar 1, 2018

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