The Effects And Control Of Fat Oxidation And Protein Oxidation On The Grass Carp By Bacteria Reduction Processing

With consumption concept, consumption demand and consumption patterns changing, frozen prepared aquatic products are developing fast. In China, the prepared aquatic products often made from freshwater fish. However, freshwater fish are easy to spoil by microbes because of its nutrition and high water content. Bacteria-reducing could reduce the surface microbes of fish and prolong its shelf life, but it also may cause fat and protein oxidation. Limited literatures had been reported the oxidation degree and its control methods after bacteria- reduction. Therefor, this research studied the effects of bacteria-reducing and tea polyphenols on fish quality, fat oxidation and protein oxidation and established a method to control fat oxidation and protein oxidation by use of tea polyphenols. The main research contents and results were as follows:(1) The influence of different bacteria-reducing modes on storage quality of grass carp slices and the bacteria reduction effect were studied. Using ultraviolet irradiation(UV), microwave, chlorine dioxide soaking and ozone water soaking to reduce bacteria of grass carp slices. Changes of volatile components, whiteness and sensory quality of grass carp slices during storage were studied.The results showed that the physical methods(UV and microwave) was better than chemical methods(chlorine dioxide and ozone soaking). Microwave had the highest bacteria reduction percentage, 80.06%. Chlorine dioxide soaking had lowest reduction rate, 61.67%. Bacteria-reducing groups were better than the control group on volatile component. Chemical methods were better than physical methods on whiteness and sensory quality.(2) The effects of different bacteria-reducing modes on the fat oxidation and protein oxidation during storage were studied. After bacteria-reducing, the acid value(AV), TBA, peroxide value(POV), carbonyl value(COV), protein carbonyl content and free radical content of grass carp slices increased in different degrees and the protein sulfhydryl content decreased compared with the control group. The AV of grass carp slices after microwave treatment reached the highest value, 5.61 mg KOH/gmeat. The TBA and protein carbonyl content of grass carp slices after chlorine dioxide soaking were higher than that of other groups. The highest content of protein carbonyl was 2.46×10-4meq/gmeat. The highest value of POV was 0.21meq/gmeat when the grass carp slices treating with UV during the storage. The lowest content of protein carbonyl was 8.49mmol/gmeat when the grass carp slices treating with ozone during the storage. The effects of bacteria-reducing on fat oxidation and protein oxidation of grass carp slices during storage were different.(3) The influence of tea polyphenols on grass carp quality, fat oxidation and protein oxidation during storage were studied. After tea polyphenols treatment, the whiteness, AV, TBA, POV, COV, protein carbonyl content as well as free radicals content of grass carp slices were generally lower than those without tea polyphenols treatment. Meanwhile, an increase in the protein thiol content of grass carp slices were observed. Both of the AV and the TBA values of each treatment group were reduced from the higher values to lower or similar values of the control group during storage. POV was not detected before storage, but hydroperoxide was found in the control group from the 8th day, the UV from the 2nd day, the chlorine dioxide as well as the ozone from the 6th day. It was observed that the POV could reach to as high as 0.039meq/kg meat. A delay of the carbonyl peak value was found in each reduced bacteria group. To be more specific, the carbonyl peak value of the UV group and the chlorine dioxide group were delayed from the 4th day to the 14 th day, the ozone group from the 6th day to the 14 th day, the microray group from the 4th day to the 8th day. As to the control group, there was no difference on the carbonyl peak value. For the UV group, the final protein sulfhydryl content was 1.08mmol/g, which was higher than that of the control group. Protein carbonyl content wa s basically same for each group. Therefore, it was revealed that tea polyphenols has effectively retarded the oxidation of the fillet fat and protein in storage, and it has helped to control the promotion of oxidation causing by bacteria- reducing methods.