Study On The Reduction Of Nitrite In Salted Fish By The Composite Microbial Fermentation Agent

Salted fish,a kind of tradition characteristic salted aquatic products,is an important and a typical representative salted product of China.Human beings started to produce salted fish for preventing corruption and long storage at the earliest time.With the development of processing technology,salted fish has been highly nutritional,particularly flavored,long-term storable and convenient to be consumed that bring a vast consumer market at home and abroad.Especially in recent decades,salted fish technology has been developed rapidly.However,the epidemiological survey showed that the high incidence of gastric cancer in the coastal areas was closely related to the higher nitrite content in salted aquatic products.Therefore,one of the urgent problems to be solved in the salted aquatic products processing industry is how to ensure the food safety and protect the interests of consumers.At present,a variety of methods have been established all over the world to reduce nitrite content,in which the use of microbial fermentation is the most studied and safe method.Researches have been done a little on the application of microbial fermentation to marinated aquatic products.Among the various microorganisms used in meat fermentation,lactic acid bacteria(LAB)is the most important category.LAB,used in kimchi and sausage extensively,has the characteristics of reduction of nitrite and the high feasibility and significance to apply LAB to practice,.In this study,five strains of bacteria were selected,of which three was applied in salted fish by mixing a certain proportion.The optimum technological conditions were determined by studying the biological characteristics of five strains,the effect of nitrite reduction and the physical and chemical indexes.Furthermore,the differences of the types and relative percentages of volatile flavor compounds were compared in salted fish between the groups with and without the composite microbial fermentation agent.Firstly,five strains were screened for antagonistic,salt tolerance and nitrite reduction test,including Lactobacillus plantarum(L.plantarum),Pediococcus pentosaceus(P.pentosaceus),Lactobacillus brevis(L.brevis),Lactobacillus casei(L.casei)and Staphylococcus xylose(S.xylose).According to the results of antagonistic test,it was found that there was antagonism between P.pentosaceus and L.casei,S.xylose.S.xylose and L.plantarum,P.pentosaceus were also antagonistic.Salt tolerance test results showed that the salt tolerance of S.xylose was weaker than that of other four strains.The results of nitrite reduction test showed that L.plantarum,P.pentosaceus and L.brevis had a strong ability to reduce nitrite.Therefore,in this part of the experiment,the composite microbial agent was prepared by L.plantarum,P.pentosaceus and L.brevis.Secondly,the composite microbial fermentation agent prepared by three bacteria selected from above part was applied into the salted fish processing.By testing the changes of nitrite,peroxide value,total volatile basic nitrogen(TVB-N)and histamine content in different temperatures,time and inoculation amounts during the microbial fermentation,the results showed that the nitrite reduction rate reached 84.34%,the peroxide value,TVB-N and histamine content were at a low level when the fermentation temperature was 30°C,the fermentation time was 24 h and inoculation amount was 1.0×108 cfu/m L.At this point the salted fish has the lowest nitrite content and the best quality.Finally,the differences of the types and relative percentages of volatile flavor compounds were compared in salted fish between the groups with and without the composite microbial fermentation agent according to the technological conditions from above part.The results showed that the group with the composite microbial fermentation agent increased the types and relative percentages of alcohol,acid and ketone flavor compounds,which contributed greatly to the salted fish flavor.Little effects were found on the types and relative percentages of ester and aldehyde flavor compounds whereas the content of the undesirable flavor substances hexldehydes was reduced.The use of the composite microbial fermentation agent can also reduce undesirable odorants such as indole and pyrimidine.