Research On The Storage Characteristics Of Semi-dry Freshwater Fish

As the health awareness increasing, semi-dry fish will gradually replace the traditional cured fish. Semi-dry fish is a fish product which has soft texture and good flavor, and the moisture content is between fresh goods and dry goods with low salt content. As the high water activity and the effects of microorganisms and enzymes, it leads to a series of biochemical changes, such as protein hydrolysis, lipid hydrolysis and oxidation, amino acid decarboxylation and deamination, nitrate reduction and so on, volatile nitrogen substances, acidity, aldehydes and ketones and nitrite content increasing, which makes quality changed. In this study, firstly defined the moisture content range of semi-dry fish with best eating quality, then researched on water activity controlling of semi-dry fish, the change tendence of each index during 4℃ and -18℃ storage of semi-dry fish with different moisture content, the quality change dynamics model was established to predict the shelf life and used the electronic nose to distinguish the quality change during storage. The main contents and results were as follows:1. The effects of different moisture content on the eating quality of semi-dry fish were studied and defined the moisture content range of semi-dry fish with best eating quality. The results showed that:the best eating quality could be evaluated indirectly by moisture content, crude protein, crude fat, soluble protein, free amino acids, sodium chloride content and so on, also the eating quality of semi-dry fish could be divided into five types, such as delicate, daintiness, peculiar smell, salt taste, texture and mouthfeel. The regression equation expressed by the main ingredients could describe the eating quality of semi-dry fish. The moisture content of suitable eating quality should be controlled between 40.5% to 56.4%(wet basis). Different moisture content semi-dry fish had different volatile substances and flavor substances.2. The effects of different water activity lowering agents on the water activity of semi-dry fish were studied. The strength of reducing water activity were:amino acid food moisturizer> sorbitol> lactate> trehalose> maltitol. The best dosages of trehalose, sodium lactate, amino acid food moisturizer and sorbitol were 2%-3%,2%-3%, 1%-2% and 0.02%-0.04%. The best complex dosages were 2.0% trehalose,3.0% sodium lactate, 2.0% amino acid food moisturizer and 0.04% sorbitol, and the water activity were 0.794.3. The quality variation of different moisture content semi-dry crucian carp and semi-dry wuchang fish during 4℃ and -18℃ storage were studied. The results showed that:TVB-N values, total number of bacteria and sensory evaluation were suitable as the indicators of forecasting the shelf life of semi-dry fish. Each index kinetic model had high fitting accuracy. The shelf lifes of low and high moisture content semi-dry crucian carp stored at 4℃ were 40 days and 35 days, the shelf lifes of low and high moisture content semi-dry crucian carp stored at -18℃ were 171 days and 145 days. The shelf lifes of low and high moisture content semi-dry wuchang fish stored at 4℃ were 46 days and 33 days, the shelf lifes of low and high moisture content semi-dry wuchang fish stored at-18℃ were 152 days and 131 days. The electronic nose PC A analysis and DFA analysis could separate volatile substances of semi-dry crucian carp and semi-dry wuchang fish stored at different time.4. The electronic nose was used to separate the different fish and the semi-dry fish stored at different temperature. The results showed that:The electronic nose PCA analysis and DFA analysis could separate volatile substances of semi-dry crucian carp and semi-dry wuchang fish stored at the same time, also the semi-dry wuchang fish stored at 4℃ and -18℃. The distinguishing ability of DFA analysis were better than PCA analysis.