Study On The Technology Of Rapid-fermented Fish Sauce Made With Freshwater Fish By-products

Fish sauce is the typical seasoning of Southeast Asia.The fermentation period of traditional fish sauce is long while the flavor of the rapid-fermented fish sauce is poor.To solve the problems including growing production of freshwater fish by-products without proper utilization,security concerns along with by-products application and low protein utilization rate of materials,this study investigated the processing technology of fish sauce made with freshwater fish by-products.First of all,the effect of storage conditions of by-products on fish sauce quality was investigated.A.oryzae koji was inoculated into by-products stored under different conditions to ferment fish sauce at 35 oC for 30 days.The results of physiochemical properties determination of byproducts showed that the content of thibabituric acid(TBA),total viable counts and biogenic amines(putrescine,cadaverine and histamine)in by-products stored at room temperature for 8 h exceeded the standard,thus such by-products was not qualified for fish sauce fermentation.The results of fish sauce quality evaluation illustrated that,at the end of fish sauce fermentation,the content of amino nitrogen and total soluble nitrogen in fish sauce made with by-products stored at room temperature for 4 h were the highest while the content of total biogenic amines and histamine were highest in fish sauce made with by-products stored refrigerated for 4 h;compared to fish sauce made with freeze-stored by-products,the content of total free amino acid in fish sauce made with by-products stored at room temperature and refrigeration decreased while the content of glutamic acid increased;the numbers of different volatile compounds groups in fish sauce made with by-products stored at room temperature and refrigeration was lower while content of different volatile compounds groups was higher;ammonia,fishy and umami notes in fish sauce made with by-products stored at room temperature and refrigeration were stronger while sour note weakened.All the results showed that freshwater fish by-products stored at room temperature for less than 4 h was available for fish sauce fermentation.Then,mixed kojis was inoculated to improve protein utilization of materials.The proteinase activity were determined to optimize the processing parameters of A.oryzae koji and A.niger koji via orthogonal test.The results showed that the optimal parameters for A.oryzae koji making were as follows: culturing time was 44 h,the ratio of defatted soy meal with bran was 2?1,steaming temperature was 120 oC and steaming time was 20 min;the optimal parameters for A.niger koji making were as follows: culturing time was 48 h,the ratio of defatted soy meal with bran was 3?1,steaming temperature was 120 oC and steaming time was 20 min.The ratio of A.oryzae koji and A.niger koji in mixed kojis was optimized by determination of amino nitrogen and total soluble nitrogen content in fermented fish sauce.The optimal ratio was verified to be 3?1 and protein utilization rate reached 80.33%.Lastly,fish sauce fermentation technology was optimized and fish sauce properties were evaluated.The content of amino nitrogen and total soluble nitrogen in fish sauce were measured to optimize fermentation technology and the results showed that the optimal fermentation technology were as follows: koji additive content was 15%,salt additive content was 15% and fermentation temperature was 35 oC.Fish sauce was prepared according to the optimal technology to investigate the impact of mixed kojis on fish sauce properties.The results indicated that acid proteinase activity of mixed kojis dramatically increased by 170.51% while its neutral proteinase activity decreased slightly by 7.19%;compared to fish sauce inoculated with A.oryzae koji,the content of amino nitrogen and total soluble nitrogen in fish sauce inoculated with mixed kojis were 1.29 g/100 mL and 1.65 g/100 mL,increased by 7.50% and 7.84% respectively;the content of total volatile base nitroten decreased by 4.47% inducing higher security of the fish sauce;p H was lower and the content of total acidity was higher;the degree of non-enzymatic browning increased meaning bette r color and flavor properties;the content of total free amino acid,especially glutamic acid increased by 9.80% and 28.43%,respectively,contributing to better amino acid profiles;the results of SPME-GC-MS showed higher content of phenols,ketones groups and nitrogen-containing compounds;the results of sensory evaluation ind icated that inoculation of mixed kojis would help improve umami and caramel notes,weaken sour and ammonia notes.