The Activity Of Endogenous Proteinases And Its Effect On The Quality Of Cured Fish During Salting

Cured fish is a kind of Chinese traditional food which is popular for its unique taste and flavor. The unique tasting quality of cured fish is formed under the common effect of endogenous proteases and enzymes of microbial origin, and studies concern the effect of endogenous proteases on the tasting quality of cured fish is rarely reported so far. In order to figure out the forming mechanism of the unique quality of cured fish, we use silver carp as research object, after selecting suitable bacteriostat, the effects of different curing and processing conditions on activity of endogenous proteases, the changes of endogenous proteases’activity during processing and the effect of endogenous proteases on the quality of cured fish were studied. Main contents and results of the study were summarized as follows:The antibacterial effects of four kinds of bacteriostat were studied. It is reported that with addition of suitable amount of sodium azide during curing can provide significant bacteriostatic effect in cured fish while having little influence on the edible quality, among the four kinds of bacteriostat, the antibacterial effect of sodium azide was stable during salting. The concentrations of sodium azide in dry-curing and wet-curing were0.8%(m/m) and1%(m/v), and the aerobic bacterial count is under1×101CFU/g after curing for7days.The effects of different curing methods and bacteriostat on the activity of protease and the quality of cured fish were studied. The curing methods and processing had effects on salt content1、activity of cathepsin B、cathepsin L、calpain, and the contents of peptide nitrogen and non-proteinaceous nitrogen, except for the contents of ammonia nitrogen. During the dry-curing, activity of cathepsin B、cathepsin L were lower than the blank with bacteriostatic treatment, while higher than brining. Except for the ammonia nitrogen, total nitrogen, peptide nitrogen and non-proteinaceous nitrogen during the brining were lower than the dry-curing. Adding5%of salt, curing under the temperature of5℃, vacuum-rolling for10min, activity of endogenous proteases were highest.The effects of endogenous proteases on the formation of the unique edible quality of cured fish were studied. It is indicated that adding bacteriostat had little effect on the hardness, viscosity and chewiness (p>0.05) of the product while had significant effect on the elastic, cohesiveness, resilience and yellow lightness (p<0.01) of it,and the product had higher cohesiveness, resilience, and a lower yellow lightness with bacteriostat treatment. Adding bacteriostat have significant effect on the Cathepsin B, Land total amino acids and the amino acid composition and little effect on the calpain.besides, there were higher protease activity and total amino acids in the fish cured under natural conditions. During the processing the flavor had changed, adding bacteriostat had made differences in the flavor compound composition, which had more aldehyde compounds、 less alkane compounds and ester compounds. During the processing, microorganism has important effects on the formation of flavor.The correlations between processing conditions and endogenous protease activity, endogenous protease activity and the quality of cured fish were studied. The results indicated: The nature pH and salt content of fish associated with endogenous protease activity significantly, associated with microbial origin protease activity to a certain extent. The processing conditions have effects on the endogenous protease and little effect on microbial origin protease and microorganism. In the processing, endogenous protease and calpain play an important role in tasting quality, while little effect on the formation of flavor. And microbial origin protease contributed less.