Study On Dilute-Mash Fermentation Process (DMFP) Of Anchovy Fish Sauce

Anchovy is the main species of the food chain in Yellow and East Seas of China, which was up to one million tons only in 2006. However, it’s still widely used for feed of cage culture fish without being fully utilized for its low economic value and perishable. Fish sauce is widely consumed as a traditional fermented condiment. However, the healthy development of fish sauce industry has been hindered due to high salt content and long fermentation period. Therefore, some new fermentation technologies have been studied by some scholars to accelerate the fermentation process and reduce the salt content of fish sauce through increasing the fermentation temperature, using commercial enzymes, or even using koji of soya sauce and protease-rich viscera of fish. Unfortunately, the flavor and colour of the products produced by these new technologies were far less than that brewed by the traditional process. For all these reasons, dilute-mash fermentation process (DMFP) of anchovy fish sauce (AFS) has been studied by adding protease and koji of soya sauce in this study. The chemical compositions of AFS, produced at the optimal conditions, has been analyzed systematically. The main results are described as follows.1. Materials analysis and optimization of hydrolysis conditionsThe percentages of protein was as high as 18.66% according to the analysis of anchovy components. Anchovy was used as the raw material of preparing fish sauce, in which the rich content of protein bring good flavor of fish sauce in amino acids.Anchovy before and after steam cooking were used as substrate, and they were hydrolyzed by Protamex. AN/TN (the content of amino nitrogen in fermentation broth /the content of nitrogen in substrate,%) was used as the decision index of hydrolysis efficiency. The results showed that the hydrolysis efficiency of Protamex was 14.6% to the anchovy before steam cooking, which was higher then 12.8% of anchovy after steam cooking.Three kinds of enzyme, Protamex, Neutrase and Alcalase which were used widely in food Industry, were chosen to hydrolyze the Anchovy and AN/TN (%) as the hydrolysis efficiency of them. The results showed that the AN/TN (%) of Neutrase, Protamex and Alcalase to Anchovy were14.6%,15.1%,13.6%, respectively. Protamex was chosen as the enzyme which was used to optimization of hydrolysis conditions.After deciding the species of enzyme, the single change rule of every factor during the course of hydrolysis was analyzed by single factor test which got ready for the further conditions optimization. The best hydrolysis time was about 2h, the best water addition was between 40%-60% and the hydrolysis temperature was about 55℃. At the base of single factor experiment, response surface methodology (RSM) was chosen to optimize the hydrolysis condition and the best hydrolysis condition were as follows:the water addition was 60%, hydrolysis temperature was 55.6℃, hydrolysis time was 2 h. Under this best conditions, the best AN/TN (%) we got was 20.68%.2. Optimization of DMFP conditionsSix factors (water addition, salt addition, proportion of soya sauce koji and red yeast rice, the content of soya sauce koji and red yeast rice, fermentation time and fermentation temperature) were studied by single factor experiment. The relationships between various factors and the content of amino nitrogen (AN, g/100mL) in the fermentation broth had been studied, and the content of AN in the fermentation broth was used as decision index to determine the efficiency of fermentation. The ranges of optimal value of each factor were obtained:fermentation time was 15-20d; fermentation temperature was 40℃; salt addition was 14%-16%; proportion of soya sauce koji and red yeast rice was from 6:4 to 8:2. The proportion of soya sauce koji and red yeast rice, the total content of soya sauce koji and red yeast rice and salt addition were further optimized by orthogonal design. Finally, the optimum fermentation technology were obtained:the total content of soya sauce koji and red yeast rice was 15%, proportion of soya sauce koji and red yeast rice was 8:2 and fermentation at 40℃for 20 days.3. Product analysisThe results of chemical analysis of AFS showed that there were 15.21% salt and 0.92 g/100mL amino nitrogen in AFS, and the total content of free amino acids in the AFS was 5398.05 g/100L. Glutamate, Lysine, Leucine, Alanine and valine were prominent amino acids in CFS, which account for 48.6%. Volatile flavor compounds were detected by Gas Chromatography-Mass Spectrometry (GC-MS) after headspace solid phase micro extraction (HS-SPME). The peak-area ratios of alcohols, aldehydes, esters, nitrogen compounds and sulfur compounds were 12.85%,23.87%, 5.65%,13.51%,0.22% respectively. The content of amino nitrogen in AFS has reached the national standard level of first grade fish sauce, and salt content of AFS was significantly lower than 20%-30% of fish sauce which producted by traditional process. Compared with the commercial fish sauce (CFS, producted by the traditional process), the type and content of amino acids and volatile flavor compounds were more balanced which bringing more harmonious flavor for fish sauce.The sensory characteristics of AFS and CFS were analyzed by Quantitative descriptive analysis (QDA). The result showed that the colour of AFS was similar to that of CFS, the salty of the AFS was significantly lower than that of CFS, and fishy of AFS was more obvious than that of CFS. AFS has a more harmonious flavor than CFS.