The Quality Improvement For Mullet During Storage By Ethanol Extracts Of Ginger

Mullet contains rich nutrition and unsaturated fatty acid, whose protein content was up to18%. The endogenous enzymes are active, making it easier to become putrid during transportation, storage and sales. Therefore, it makes sense to optimize the frozen process to effectively maintain the original flavor, taste and nutrition value of mullet. In this work,choosing the mullet muscle as the research object, the property variation regulations of mullet stored at-24 ℃ and influence on its physical and chemical properties(including water retaining capacity, freshness, sensory and texture property), lipid oxidation and structure features about myofibrillar protein through dipping process with extracts of ginger by 75%(v/v) ethanol were systematically studied. The main results are as follows:(a) The physical and chemical property changes of mullet during 30-day frozen storage were evaluated. It was found that during storage, the water retaining capacity gradually decreased as drip loss rate and cook loss rate both increased(p < 0.05). The freshness also declined with the TVB-N value gradually increasing(p < 0.01). The sensory and texture property declined to some extent, as the scores of smell and taste, also the data of hardness,cohesiveness, springiness and chewiness all decreased(p < 0.05).(b) The lipid oxidation and structure features about myofibrillar protein during 30-day frozen storage were evaluated. Results showed that the lipid oxidation became more serious since the TBARS value increased(p < 0.05). Moreover, the myofibrillar protein structure features changed gradually as the oxidation degree deepened. 1) The content of carbonyl and bityrosine both increased while the total sulfhydryl content decreased(p < 0.05). 2) The emission wavelength peak in the fluorescence spectra had a red-shift firstly then blue-shift.The surface hydrophobicity was also gradually increased(p < 0.05). 3) The SDS-PAGE patterns showed that the structure of myofibrillar protein was changed, which was proved by high molecular weight compounds generated by inter-molecular through cross-linking or aggregation effects.(c) The anti-oxidation activity of ethanol extracts of ginger and its influence on the physical and chemical properties of mullet were evaluated. The active substances in ginger were extracted by 75%(v/v) ethanol by heat, whose main components were determined to be ginger saccharides and polyphenols, while the total content of sugar and phenolic were respectively 77.74±0.35% and 21.17±0.04%. The antioxidant activity of the crude ethanol extracts of ginger was determined by ORAC value, DPPH ? scavenging activity and reducing power. It was found that compared with Vc, the ORAC value of the crude ethanol extracts of ginger showed no significant difference(p > 0.05), whose reducing power were slightly lower than Vc but it was significantly weaker than Vc in the DPPH ? scavenging capacity(p <0.01). Then the physical and chemical properties of mullet were evaluated which was dipped with different concentrations(0.05%-2.00%, w/v) of ethanol extracts of ginger then frozen under the same circumstance. Results showed that mullet dipped with impregnation solution containing 0.10%(w/v) crude ethanol extracts of ginger could retard the water loss also freshness decline with better taste, and the 0.05%(w/v) one took the next place while samples with the ratio of 0.50%(w/v), 1.00%(w/v) and 2.00%(w/v) seemed similar to the control group in flavor and texture.(d) The impact of the crude ethanol extracts of ginger on the lipid oxidation and myofibrillar protein structure characteristics of mullet during frozen storage were studied.During 30-day storage, the concentration of 0.05%(w/v) and 0.10%(w/v) could significantly retard the lipid oxidation(p < 0.05), with the TBARS value dramatically lower than other groups(p <0.05) and 0.10%(w/v) proved to be the best one. In addition, the ratio of 0.10%(w/v) provided better protection for myofibrillar protein, with fewer changes of its structural characteristics. Compared to other groups, its contents of carbonyl and bityrosine were lower,whose total sulfhydryl content only declined by 10.46%. Changes of the emission wavelength peak in the fluorescence spectra occured to a less extent. The surface hydrophobicity increased just by 22.96%. The SDS-PAGE patterns showed that the crude ethanol extracts of ginger in low concentrations retarded myofibrillar protein oxidation to some extent.