Study On The Technology And Flavor Of Low-salt Fish Sauce Using By-products Of Freshwater Fish

Freshwater fish processing waste has been used as raw materials to produce a low salt fish sauce with modern biotechnology and enzyme engineering and technology. In order to provide a way of high-value utilization for fresh water fish processing. The fermentation technology, biochemical characteristics and the changes of flavour of low salt fish sauce were studied in this paper.The main results were summarized as follows:(1) The by-products from fresh water fish were used as raw material, and they were hydrolyzed by endogenous proteinase. The content of amino acid nitrogen was used as the index of the degree of hydrolysis. The salt content was fixed as 7% and the effects of p H value, temperature, water additional ratio and time on autolysis hydrolysis were analyzed. Box-Behnken design(BBD) and response surface methodology(RSM) were adopted to obtain the optimum formula of autolysis on the basis of results of single-factor experiments. The results were as follows: time 48 h,temperature 42.31℃, p H 5.78 and water additional ratio0.25:1. On this condition, the content of amino acid nitrogen in hydrosate was up to(0.959±0.03)g/100 ml and approximately agree with model parameters(0.9735g/100ml).(2) The exploration of low salt fish sauce fermentation. Two kinds of fermentation process were designed, which were used to produce fish sauce. Changes of p H, total nitrogen(T-N), amion acid nitrogen(AA-N), total volatile base nitrogen(TVB-N), the non-enzymatic browning index, total acid, composition of amino acid were periodically detected. Results showed that the contents of AA-N, T-N, and non-enzymatic browning index increased prolonging the fermentation time but decreased the p H values under the condition of two kinds of fermentation process.The TVB-N and total acid content increased first during the initial fermentation time and then slightly decreased thereafter, generally remaining stable for the rest of the fermentation period. In addition, the TVB-N and salt content in fish sauce B were lower than fish sauce A. And after 7 days flavoured fermentation, the non-enzymaticbrowning index increased but decreased the TVB-N and salt content. The products were in rich of Asp, Arg, Glu, Ala, Lys and Leu. Besides, the QDA-test showed that the fish sauce was delicious and salty with caramel flavor. By comparing two kinds of fermentation process of fish sauce, the results show that the fermentation process of B is better than A.(3) The optimization of Fish sauce fermentation technology. Fermentation technology B was used to produce low salt fish sauce. By L9(34) orthogonal test fermentation conditions to determine the fermentation conditions of low salt fish sauce optimum: fermentation temperature 50℃, koji content 20%,enzyme concentration 0.1%, p H6.0. In optimum conditions, the content of amino acid nitrogen in fish sauce was up to 1.396g/100 ml.(4) The biochemical characteristics and the changes of flavour of low salt fish sauce during fermentation were studied. The change of biochemical index in fish sauce during different fermentation time was complex. The AA-N, TSN, total acid and TVB-N content were increased first during the initial fermentation time and then slightly decreased thereafter and decreased significantly after flavour fermentation,which were up to 1.289±0.01g/100 ml, 1.747g/100 ml, 1.760±0.03g/100 ml and174.35±2.52mg/100 g, respectively; The p H value decreased prolonging the fermentation time and generally remaining stable for the rest of the fermentation period and was 5.01±0.01 at the end of fermentation; the salt content increased slightly during the fermentation; the change of viable count and mixed protease activity was complex during the fermentation; the content of free amino acid increased first during the initial fermentation time and then slightly decreased thereafter. The flavor of fish sauce was significantly different during different fermentation time, and the progress of the fermentation can promote superior flavor and reduce bad flavor. Flavour fermentation was favorable for the formation of flavour.The difference of the flavour between low salt fish sauce and commercial fish sauce was obvious. The score of caramel flavor and umami was higher than that of commercial fish sauce and bad flavour was lower than commercial fish sauce. Low salt fish sauce was better than that of commercial fish sauce as a whole from the sensory evaluation results.