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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.
2010 Project Description
In 2010, four graduate students (2 Ph.D., 2 M.S.) participated in this project. Progressive results were summarized in two refereed journal articles published and in one abstract presented at the 2010 Institute of Food Technologists (IFT) annual meeting in Chicago. The abstract received the first-place prize award at the graduate paper competition of Muscle Foods Division of IFT. One graduate student who worked on this project completed her M.S. degree with a written thesis.
In addition, an update of the research progress was presented at the 2010 NRI Project Directors (PD) annual meeting held in conjunction with the annual IFT conference. One journal article resulting from the study was published during this period. 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 2010, the PD visited a research lab in a university in China that was also studying 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 was oxidized at 4C by mixed 10 μM FeCl3/100 μM ascorbate with 1, 5, 10, 20, 30, 40, or 50 mM H2O2 (pH 6.2). Oxidation with > 1 mM H2O2 for 40 min significantly enhanced (P < 0.05) hydration of muscle samples, while oxidation with 40 and 50 mM H2O2 for 2 min or with 20 mM H2O2 for 40 min caused pronounced declines in water-holding capacity and product yield.
The changes coincided with marked increases in the protein carbonyl content, TBARS formation, and cross-linking of both myofibrillar and sarcoplasmic proteins. Dye-tracing tests showed that the enhanced hydration at > 1 mM H2O2 was due to facilitated water diffusion into muscle tissue. This result was strongly corroborated by microscopic images that illustrated enlargements of intercellular spacing, i.e., gaps, in oxidized muscle tissue which served as canals for water diffusion.
In experiment 2, boneless pork loin chops (longissimus) were packaged in an oxygen-enriched atmosphere packaging system (MAP: 80% O2/20% CO2), on Styrofoam trays with an air-permeable polyvinylchloride (PVCP) overwrap, or a partial vacuum (60%) packaging system and stored at 2C for 14, 7, and 21 days, respectively. Muscle sample stored in MAP had marked increases (P < 0.05) of TBARS and carbonyls, and a loss in sulfhydryls, indicating lipid and protein oxidation. PVCP and VP showed lesser or negligible effects on these oxidation parameters. On day 4, MAP samples had higher redness (a* value) than PVCP and VP samples. SDS-PAGE revealed major losses of myosin heavy chain (MHC) in MAP and PVCP samples from day 0 to day 4, but in VP samples no significant loss of MHC was noted until day 14.
Microscopic images of muscle fiber cross-sections indicated an increase in extracellular spaces in all packaging systems during extended storage, which was most remarkable on day 14 MAP samples. Water-holding capacity decreased significantly (P < 0.10) in muscle stored in MAP but not in PVCP and VP samples. Day 4 and 7 MAP muscles, brine-marinated for 40 and 20 min, respectively, had a greater (P < 0.05) hydration capacity (brine pick-up) than PVCP and VP samples. The results were corroborated by the phase contrast data where extended storage in MAP produced the most extensive myofibril swelling upon brine irrigation. Despite enhanced hydration, MAP muscle samples were least capable of holding moisture upon cooking.
The results suggested that enhanced protein oxidation in MAP system when compared with PVCP and VP was responsible for these altered hydration properties of pork loin muscle. 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.
Xiong, Y.L., Blanchard, S.P., Ooizumi, T., and Ma, Y. 2010. Hydroxyl radical and ferryl-generating systems promote gel network formation of myofibrillar protein. J. Food Sci. 75:C215-221.
Liu, Z., Xiong, Y.L., and Chen, J. 2010. Protein oxidation enhances hydration but suppresses water-holding in porcine longissimus muscle. J. Agric. Food Chem. 58:10697-10704.
Liu, Z., Xiong, Y.L., and Chen, J. 2010. Protein oxidation enhances hydration but suppress water-holding in porcine longissimus muscle: A possible mode of action. Book of Abstracts. Annual Meeting of the Institute of Food Technologists. (Abst. No. 192-05).