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Antioxidative Properties of Hydrolyzed Protein in Muscle Foods
Department of Animal and Food Sciences
Hydrolyzed proteins have been used in muscle foods to modify the products' texture and sensory properties. Preliminary studies have shown that antioxidant activity also exists in some of the protein hydrolysates. This study is to produce and characterize antioxidative protein hydrolysates from common food proteins, and to evaluate their efficacy in inhibiting lipid and protein oxidation in muscle foods and the possible mechanisms. Success of the research will establish new uses of food proteins thereby enhancing their marketability and economic value.
2009 Project Description
The goal of this research project is to develop antioxidative peptides as natural antioxidants by means of protein hydrolysis. The efficacy of protein hydrolysates and mixed peptides was evaluated in meat products. For the duration of this project, antioxidative protein hydrolysates and peptides were prepared from maize zein protein, potato protein, soy protein, and buck wheat protein by means of in Alacalase, papain, or in vitro pepsin-pancreatin digestion.
In addition, antioxidant activity of three commercial yeast extracts was studied. A total of six graduate students (3 Ph.D. and 3 M.S.) have participated in this project, and four have completed their degrees on antioxidant protein hydrolysates. Of the six graduate students trained in this research, two were international students who upon completion of their studies returned to their home countries (Spain, China). All these students have obtained significant results from their individual studies, and have presented their research findings at national meetings or published papers in scientific journals.
The project director (PD) attended a number of domestic and international conferences (Institute of Food Technologists; American Meat Science Association; American Oil Chemists Society; International Congress of Meat Science and Technology; International Biotechnology Symposium) where he gave presentations and communicated with delegates and audiences representing various food companies, consumer groups, and other universities from around the world to share major discoveries from this research project. As a part of outreach and promotion of the research, the PD visited several overseas universities (Japan, China) where he presented seminars and talks to over 500 students and faculty on subjects related to this project. Domestically, the PD contacted a number of high-achieving college students through e-mails and telephone calls to introduce the research and share some of the results. Three of these contacts were subsequently recruited to food science graduate programs at the University of Kentucky. Moreover, through the outreach effort, three academically outstanding graduate students and one postdoctoral scholar from overseas schools have been recruited to the University of Kentucky.
In the first study, antioxidant potato protein hydrolysates (PPHs) were prepared by hydrolysis of intact potato proteins for 0.5, 1 and 6 h using Alcalase. The ferric reducing/antioxidant power (FRAP) of nonhydrolyzed protein (23 umol/g) drastically increased to 597-643 umol/g after hydrolysis. Similarly, the 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS.+) radical-scavenging activity increased by hydrolysis (P<0.05). The peroxide value (PV) and thiobarbituric acid-reactive substances (TBARS) in beef patties after 7 days of storage were lowered 44.9% and 74.5%, respectively (P<0.05), by the treatment of 4% 1-h PPH. The 1-h PPH at a 2.5% application level also suppressed lipid oxidation (TBARS) by up to 67% in pork batters containing 15 or 30% fat.
However, the presence of PPH reduced the gel-forming ability of myofibrillar proteins, which was attributed to inhibited oxidation of sulfhydryls (thus, less disulfide bond formation between peptides). In the second study, maize zein was hydrolyzed for 0.5 to 5 h by Alcalase or papain. Alcalase zein hydrolysates (ZH) exhibited stronger (P < 0.05) antioxidant activity than papain-hydrolyzed zein, as indicated by PV and TBARS in a liposome-oxidizing system. ZH possessed strong copper-chelation capability and marked reducing power. ZH also showed strong radical-scavenging ability, which was not influenced by hydrolysis time. When the Alcalase ZH was subjected to in vitro digestion, the pancreatic digests still retained considerable radical scavenging potential.
In the third study, buckwheat protein (BWP) isolate was subjected to a two-stage in vitro digestion (pepsin, pancreatin at 37C). The 2-h pancreatin digest was subjected to Sephadex G-25 gel filtration. Of the six fractions collected, fractions IV (456 Da) and VI (362 Da) showed the highest ABTS.+ scavenging activity and were 23-27% superior to mixed BWP digest (P<0.05). Fraction VI was most effective in neutralizing .OH and was 86% and 24% more efficient (P<0.05) than mixed BWP digest and fraction IV, respectively. LC-MS/MS identified Trp-Pro-Leu, Val-Pro-Trp, and Val-Phe-Pro-Trp (IV), Pro-Trp (V) and tryptophan (VI) to be the prominant peptides/amino acid in these fractions.
In the fourth study, soy protein hydrolysates (SPHs) with different degrees of hydrolysis (DH, up to 5) were prepared by Alcalase treatment of soy protein isolate. Results showed drastically increased ABTS.+ scavenging activity, by up to 150%, of SPHs compared to non-hydrolyzed soy protein (P<0.05). The ABTS.+ scavenging capacity of SPHs generally increased with DH. Ferrous ion chelation capacity was also enhanced by hydrolysis. The findings from the individual protein hydrolysate studies indicated the antioxidant power of mixed peptides produced enzymatically from potato, maize, buckwheat, and soy proteins.
The potential impact is that the food and nutraceutical industries could use the research results in their developments of natural antioxidants to preserve the quality and extend the shelf-life of raw and processed foods as well as to promote the health of humans.
Peng, X., Xiong, Y.L., and Kong, B. 2009. Antioxidant activity of peptide fractions from whey protein hydrolysates as measured by electron spin resonance. Food Chemistry 113:196-201.
Nieto, G., Castillo, M., Xiong, Y.L., Alvarez, D., Payne, F.A., Garrido, M.D. 2009. Antioxidant and emulsifying properties of Alcalase-hydrolyzed potato proteins in meat emulsions with different fat concentrations. Meat Science 83:24-30.
Ma, Y.Y. and Xiong, Y.L. 2009. Antioxidant and bile acid binding activity of buckwheat protein in vitro digests. Journal of Agricultural and Food Chemistry 57:4372-4380.
Agyare, K.K., Addo, K., and Xiong, Y.L. 2009. Emulsifying and foaming properties of hydrolyzed wheat gluten treated with microbial transglutaminase. Food Hydrocolloids 23:72-81.
Liu, Q., Kong, B. Xiong, Y.L., and Xia, X. 2010. Antioxidant activity and functional properties of porcine plasma protein hydrolysate as influenced by the degree of hydrolysis. Food Chemistry 118:403-410.
Ma, Y.Y., Xiong, Y.L., J. Zhai, H. Zhu, and Dziubla, T. 2010. Fractionation and evaluation of radical-scavenging peptides from in vitro digests of buckwheat protein. Food Chemistry 118:582-588.
Cheng, Y., Xiong, Y.L., and Chen, J. 2010. Antioxidant and emulsifying properties of potato protein hydrolysate in soybean oil-in-water emulsions. Food Chemistry 120:101-108.
Tang, X., He, Z., Dai, Y., Xiong, Y.L., Xie, M., and Chen, J. 2010. Peptide fractionation and free radical scavenging activity of zein hydrolysate. Journal of Agricultural and Food Chemistry (In press).