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Role of Protein Oxidation in Water-binding and Hydration of Meat
Department of Animal and Food Sciences
The ability of meat to retain natural and added moisture during storage and cooking critically affects meat juciness, tenderness, and mouthfeel. The purpose of the study is to learn how oxidation affects water-binding in meat through analyzing morphological and biophysical properties of muscle and muscle proteins.
2011 Project Description
In 2011, four graduate students (3 Ph.D., 1 M.S.) participated in this project. Progressive results were summarized in two refereed journal articles and in four abstracts presented at the 2011 Institute of Food Technologists (IFT) annual meeting in New Orleans. One of the abstracts received the Third-place prize award at the graduate paper competition of Muscle Foods Division of IFT. One graduate student who worked on this project completed his M.S. degree with a written thesis.
In addition, an update of the research progress was presented at the 2011 NRI (NIFA) Project Directors (PD) annual meeting held in conjunction with the annual IFT conference. The PDs' meeting provided a unique forum for the interaction and idea exchange among researchers and clienteles representing food companies, government agencies, consumer groups, and other universities to share major discoveries from this research project.
In 2011, the PD visited a research lab in a university in China that was also studying meat protein oxidation. One Ph.D. student from that lab who was working on a related project joined the University of Kentucky as a visiting student to conduct collaborative research.
Two experiments were conducted. In experiment 1, pork longissimus muscle samples were subjected to the following three marination conditions: A) oxidation (40 min) in hydroxyl radical-generating solutions (HRGS: 10 uM FeCl3/100 uM ascorbate with 5 or 20 mM H2O2, pH 6.2) containing 0.1 M NaCl, then marination (40 min) in 0.6 M NaCl with 15 mM pyrophosphate (PP); B) simultaneous oxidation/marination (40 min) in the HRGS containing 0.6 M NaCl and 15 mM PP; or C) same as B except that PP was omitted.
Protein oxidation, measured by the carbonyl and tryptophan fluorescence changes, enhanced hydration but increased cooking loss of meat. Light microscopy revealed a dense muscle structure characterized by swollen fibers and reduced intercellular spacing in intermediately oxidized muscle samples marinated with 0.6 M NaCl and 15 mM PP. However, oxidized fibers were more susceptible to transverse shrinkage upon cooking than non-oxidized fibers, which was supported by the dynamic ultrastructural changes in myofibrils observed using phase contrast microscopy.
These findings provide a further understanding of the complex impact of oxidation on meat hydration and water-binding.
In experiment 2, myofibrillar proteins (PM) isolated from postrigor chicken Pectoralis major (predominantly white) and Gastrocnemius (predominantly red), were subjected to a hydroxyl radical (OH)-oxidizing system (10 uM FeCl3, 0.1 mM ascorbate, with 5, 10, or 20 mM H2O2) at pH 6.2, 4C for 18 h. Nonoxidized (control) and oxidized MPs were analyzed for sulfhydryls, disulfides, solubility, aggregation, and particle size (Z-average).
Chymotryptic digestion followed by SDS-PAGE was conducted to identify the cross-linking site(s) in protein aggregates. The solubility of control white MP (63%) was higher than that of control red MP (44%). After oxidation with OH at 5 mM H2O2, the solubility decreased due to aggregation by 42% and 25%, for white and red fibers, respectively (P < 0.05). Chemical and electrophoretic analyses indicated H2O2-dose-dependent losses of sulfhydryls and the concomitant formation of disulfides in MP, which were more pronounced in white MP (P < 0.05). Oxidation favored cross-linking of myosin rod or tail in white MP, compared to an equal susceptibility of myosin subfragment-1 or head in red MP. Particles formed from oxidized white MP were 17% larger that those from the oxidized red MP counterpart.
The predisposition of white fiber myosin to tail-tail cross-linking compared to tail/head random associations in red fiber myosin might explain the inferior network-forming and gelling properties of red MP during meat processing. Although the impact of the research results is not immediately known, it is expected that meat processors can use the research findings as guide for their product formulation and processing condition design so that an optimal product quality and yield can be achieved.
Liu, Z., Xong, Y.L., and Chen, J. 2011. Morphological examinations of oxidatively stressed pork muscle and myofibrils upon salt marination and cooking to elucidate the water-binding potential. Journal of Agricultural and Food Chemistry 59:13026-13034.
Delles, R.M., Xiong, Y.L., and True, A.D. 2011. Mild protein oxidation enhanced hydration and myofibril swelling capacity of fresh ground pork muscle packaged in high-oxygen atmospheres. Journal of Food Science 76:C760-C767.
Delles, R.M. and Xiong, Y.L. 2011. The opposing effects of a high-oxygen atmosphere packaging system on hydration (enhanced) and water-holding (reduced) in fresh pork loins. Book of Abstracts. Annual Meeting of the Institute of Food Technologists. (Abst. No. 152-34).
Liu, Z., Xiong, Y.L., and Chen, J. 2011. Oxidation desensitizes actomyosin to dissociating pyrophosphate in the presence of magnesium chloride. Book of Abstracts. Annual Meeting of the Institute of Food Technologists. (Abst. No. 240-06).
Li, C. and Xiong, Y.L. 2011. Efficacy of microbial tansglutaminase mediated cross-linking of pork myofibrillar proteins as influenced by protein oxidative status. Book of Abstracts. Annual Meeting of the Institute of Food Technologists. (Abst. No. 240-08).
Liu, C. and Xiong, Y.L. 2011. Influence of muscle fiber types on oxidation-induced protein cross-linking in chicken myofibrils. Book of Abstracts. Annual Meeting of the Institute of Food Technologists. (Abst. No. 240-09).