Quality of frozen mackerel during storage as processed by different freezing methods

The fresh mackerel was frozen using four different quick-freezing methods, such as refrigerator freezing, quick freezer freezing, spiral tunnel freezing and plate freezing. Water retention, color, texture, electrical conductivity, total volatile base nitrogen (TVB-N), K value, malondialdehyde (MDA), sulfhydryl group and protein secondary structure were used as physicochemical indicators to evaluate the changes in fish quality, and water migration in the fish was observed by low field NMR. The results showed that the mackerel treated with spiral tunnel freezing method was the closest to the fresh samples, with the best water retention capacity during freezing, slow decrease in hardness and elasticity, low rate of increase in conductivity values, TVB-N content, MDA content and K value, slow decrease in total sulfhydryl content, and more stable protein secondary structure. This indicated that fat oxidation was the lowest and protein degradation was the least, which effectively maintained the moisture and freshness of the samples and was the most favorable treatment to maintain the quality of mackerel compared with other groups.