The Relationships Of Frozen Storage, Porcine Myofibrillar Protein Oxidation And Quality Of Pork Products

As an important storage method, freezing techique has been becoming the current and future needs of meat industry in China. Oxidation still occurs in frozen meat, influencing taste, color and texture of meat and meat products. Two experiments were conducted to evaluate oxidation in meat by hydraxyl radical-genearating system (HRGS) or freezing with three different packing methods for certain period of time.In experiment 1, myofibrils were isolated from pork thigh muscle, and oxidized by 15 mmol/L PIPES buffer (pH 6.0) solution containing 0.1 M NaCl, 0.1 mmol/L ascorbic acid, 0.01 mmol/L FeCl3, 5, 10, 20 mmol/L H2O2 at 4°C for 6 h. In experiment 2 pork chops were cut from thigh muscle and then diced, subsequently, pork dices were randomly divided into three groups with three different packaging methods described as follows: a) regular sealing air package ; b) mixed with ascorbic acid, tocopherol and tea polyphenol (each 0.2%, w/w) then packed by a) ; c) vacuum packaging , and stored in freezer (-18°C) for 2, 4, 8 and 24 weeks. Comparing to the experiment 1, oxidation occurs during frozen storage (experiment 2) and increase the production of protein carbonyl and disulfide bonds, leading to protein cross-linking (mainly myosin) and conformational change with altered protein solubility, ATPase activities and UV spectra. But addition of antioxidants and removal of oxygen can effectively inhibit oxidation-induced protein carbonyl and TBARS increase. But less sulfhydryl groups were found in SPAn samples, also, troponin T and tropomyosin were found to be degraded and some sarcoplasmic proteins such as phosphorylase b and enolase may deposit on myofibrillar proteins that illustrated by SDS-PAGE. During frozen storage, oxidation can enhance thaw exudate, decrease water holding capacity in pork muscle. In addition, oxidation transform myoglobin to metmyoglobin, resulting in brownish red color on the surface of pork samples. For both experiments, oxidation can promoted myofibrillar protein (MP) network formation (storage modulus) during thermal gelation, however, the strength and water holding capacity of oxidized MP gels were lower than the non-oxidized. Those of SPAn myofibriilar protein gel were weaker than the others, probably due to excessive loss of sulhydryl group by the treatment.Overall, oxidation during frozen storage can notably affect water holding capacity of muscle tissue, gelation properties of myofibrillar proteins and other characteristics. Therefore, development of appropriate packaging strategy is required to maintain good quality for frozen meat.