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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.
2008 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.
In 2008, antioxidative protein hydrolysates and peptides were prepared from maize zein and buck wheat protein by means of in vitro pepsin-pancreatin digestion. Antioxidants were also prepared from soy protein through alcalase hydrolysis. In addition, antioxidant activity of three commercial yeast extracts was studied. In 2008, four graduate students were assigned to the project. One of them, whose thesis research was on buckwheat protein hydrolysates, successfully completed her M.S. degree in December. The second student was a visiting graduate student from another university; he spent six months in the lab to be trained while generating meaningful data from antioxidant soy protein hydrolysate experiments. The remaining two graduate students were conducting preliminary studies to determine radical scavenging and metal ion chelation properties of mixed soy peptides and yeast peptides. All four graduate students have obtained significant results from their individual studies, and have submitted research abstracts to a national conference to be help in 2009.
The project director (PD) attended an international conference (International Biotechnology Symposium) where he presented a research seminar 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 200 students and faculty on subjects related to this HATCH project. Domestically, the PD contacted 5 high-performance college students through e-mails and telephone calls to introduce the research and share some of the results. Two of these contacts were subsequently recruited to University of Kentucky. Moreover, through the outreach effort, a number of academically strong students and postdoctoral scholars from overseas schools are applying for graduate studies at the University of Kentucky.
In the first study, buckwheat protein (BWP) isolate was subjected to a two-stage in vitro digestion (1 h pepsin followed by 2 h pancreatin at 37°C). The antioxidant potential of the BWP digests was compared by assessing their capacity to scavenge 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS+.) and hydroxyl (.OH) radicals. The 2-h pancreatin digest, which demonstrated the strongest activity against both radicals, 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. These results indicated that small peptide fractions (<500 Da) were primary contributors to the potent antioxidatant activity of BWP in vitro digests. The above results have been summarized in a paper that has been submitted to a peer reviewed journal for publication consideration.
In the second study, hydrolysates 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.
In the third study, the antioxidant yeast peptide study, three commercial hydrolyzed yeast protein samples were compared for their ABTS+. scavenging activity. All samples exhibited significant radical stabilizing effects, and their efficacy increased with peptide concentration (P < 0.05). However, two of the yeast hydrolysates showed stronger Fe2+ chelation activity than the third one (P < 0.05), and the radical scavenging capacity also differed among them, reflecting peptide composition differences. Additional studies were performed to evaluate various intact and hydrolyzed proteins (zein, soy, wheat, and muscle) for their texture-modifying properties of selected food products, such as wheat dough, tofu, and cooked meat emulsion.
In general, protein hydrolysates tended to impair gel-forming and binding properties of formulated foods but they promoted fat-emulsifying capacity of food products. The findings from the individual protein hydrolysate studies clearly indicated the antioxidant power of mixed peptides produced enzymatically from buckwheat, soy and yeast proteins. The results suggested that dietary zein and buckwheat proteins may have the benefit to promote the health of the human digestive tract. 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 human beings.
Chen, G., Guttmann, R.P., Xiong, Y.L., Webster, C.D., and Romaire, R.P. 2008. Protease activity in post-mortem red swamp crayfish (Procambarus clarkii) muscle stored in modified atmosphere packaging. J. Agric. Food Chem. 56:8658-8663.
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