Research On Fast-Fermentation Of Low-salinity Fish Sauce With Tilapia Byproducts

In this paper, study focued on improving the fast fermentation process of fish sauce with tilapia byproducts,Aslo,the volatility flavor materials contained in the fish sauce were preliminary investigated.To shorten the fermentation time,compound enzymolysis and Aspergillus oryzae were combined for preparation of low-salty fish sauce.Researchs were focused on mould starter preparation and domestication,complex enzymatic hydrolysis, fermentable condition optimization, volatility flavor materials detection and evaluation on various indexes of product.The details of the paper were as follows:1. The activation of Aspergillus oryzae, the configuration of koji medium,koji-making conditions and domestication were investigated, and the examination indexes were the enzyme activity and the amount of the spores. Experimental results suggested that the optimal configuration of koji medium were: the mass ratio of bran to bean cake powder is 9:1, moisture content 54.5%,inorganic salt KH₂PO₄; the optimal conditions of koji-making are concluded as follows:temperature 28℃,inoculation 0.1%(amount to 4.67×10⁷cfu/g),maturate period 4days.And under this condition As.3801 is cultivated,then the neutral protease activity can achieve (9970±64.1)u/g,the amount of spores is (4.03±0.08)×10¹⁰cfu/g.The flour was added as the source of carbon when the domestication proceeded,and after domestication,the protease activity can achieve (7578±67.3)u/g,the amount of spores is (4.51±0.06)×10¹⁰cfu/g.2.For providing reference basis to the choice of hydrolysis degree on fermentation experiment,enzymolysis process was studyed in this paper. Experimental results suggested that after using trypsin and flavourzyme for compound enzymolysis , not only the amino nitrogen content was high, but aslo the clarify degrees was well. The optimal enzyme composition were 0.5% trypsin + 0.5% flavourzyme(equal to 1600u/ml+90u/ml),the solid-liquid ratio was 1:2,pH8.5+pH7.0, enzymolysis time was 2.5h(trypsin) then 1.5h (flavourzyme), the temperature was 50℃.3. Effects of the fermentation conditions on the result of fermentation was investigated.Theeffect of various factors of fermentation such as hydrolysis degree, saltness, temperature and koji-inoculation was researched respectively.And then base on the single factor experimental results, Multi-factor analysis of variance were draw the interaction between various factors, which determined the response surface optimization factors, and their levels and coding. On that basis the quadratic regression response surface optimization was conducted, and the conclusion of the optimal fermentation parameters were: hydrolysis degree 20%, saltness 10%,temperature 32℃, koji-inoculation 0.2%, fermentation time 10days. Under this condition the fermention liquor present clear brownish red and the flavor was aslo well,the nitrogen amino acid could reach 0.574 g/dL, protein utilization ratio reached 61.7%.4. After flavouring experiments, the following conclusions could be obtained: selected beta cricoid dextrin as deodorization additives, the optimum conditions was amount of addtion 1.0%, 35℃, 60min; Chose 10% citric acid and 10% L-malic acid to adjust acidity, the amounts of addtion were 0.837 and 0.837%, respectively; Color mixing chose caramel pigment (color ratio 2985, red index 7.2).The color rate increased to 1094 and red index declined to8.1, when the addition of caramel pigment was1.0%; Sterilization experimental results suggested the patten of 90℃,20min sterilization methods influenced on product flavor lightly, and the precipitation amount was less, so it was chosen as the sterilization method.5. The HS - SPME and GC-MS coupled method was used to detect volatile flavor substances, meanwhile , its flavor substances were researched. Experimental results suggested as follows: There were 42 constituents identified in the original fermention liquids, including 8 kinds of aldehyde compounds, 13 kinds of esters, 5 kinds of acid compounds, 4 kinds of alcohols compounds, 4 kinds of ketone compounds, 3 kinds of amine compounds, 1 kind of etherified compounds, 1 kind of phenolic compounds, 2 kinds of heterocyclic compounds, 1 kind of other compounds; 57 constituents were identified in finished products, including 10 kinds of aldehyde compounds,14 kinds of esters,9 kinds of acid compounds, 8 kinds of alcohols compounds, 4 kinds of ketone compounds, 1 kind of amine compounds,2 kinds of etherified compounds, 3 kinds of heterocyclic compounds,6 kinds of other compounds.Aldehyde compounds, esters, acid compounds and nitrogenous compounds, sulphocompounds, aromatic compounds were the main volatile organic compounds of fish sauce products. Volatile flavor specific components were complicated, not only contained the direct offered flavor compounds such as ethyl acetate, 2 - methyl propionic acid, trimethylamine etc,but also had the organic acids and carbonyl compounds, which could provide synergistic action on flavor. Their common role formed the special characteristic of fish sauce.The mixing processes of this experiment included four procedures,they were deodorization, adjustable acid process, toning, filtration, sterilization process.The experimental data showed that after mixing processes,the volatile flavor substances were significantly increased, especially the esters and acid compounds, other substances were obviously reduced,such as nitrogenous compounds, aromatic compounds and heterocyclic compounds.After deodorization, the odor material content was effectively reduced, also some nitrogenous compounds such as trimethylamine and acetobromoglucose;After adjustable acid process,the value of pH droped, and the seafood taste release has been further promoted; Caramel pigment was choosed for toning,it could improve the color of products, and enhance flavor simultaneously , such as caramel flavor; After microfiltration membrane filtration and secondary sterilization, some high molecular weight substances such as heterocyclic compounds reduced significantly,meanwhile, the purity and safety of product was improved.6.Each index of product were detected and the quality safety critical control point has been preliminary established. The experiment results were as follows: on sensory, the colour of product was reddish brown, without the suspended solids and sediment, and had inherent fragrance and delicious taste that the fish sauce owned, which achieved the one's senses requirements of fish sauce professional standard; Physicochemical indexes, the total nitrogen content was 0.93 g/dL, the amino nitrogen content 0.574 g/dL,the total acid content 0.0675 g/dL, the protein utilization ratio could reached 61.7%, which achieved the third level requirements of fish sauce(GB); Other indicators, the saltness was 9.94%, the ash content 4.96%, the carbohydrates 13.11%, the moisture 81.0%, the soluble salt-free solids 9.0612 g/dL,all of that achieved related requirements; At the same time , the free amino acids composition of product were analyzed, in which aspartic acid and glutamic acid took up the one third of total free amino acid. The percentage of essential amino acids in the total of free amino acid reached 24.0%; Heavy metal ions,such as Cd, Pb ,As, Hg, etc,and the content of biogenic amines were accorded with aquatic products hygiene standards(GB 10133-2005); The shelf life of the product was 2 years by quick measurement approach.