Effect Of Enzymes On The Microbial Community And Volatile Flavor Compounds Of Fermented Fish

Enzymes are widely used in food processing industry to improve the quality of food because of their mild conditions,specificity and high efficiency.Chinese fermented fish is one of the traditional delicacies with a long history and national characteristics.It is popular in China due to its unique taste and rich nutrition.In this study,enzymes were added into Chouguiyu and Suanzhayu to improve their flavor quality.The reasons for the changes of volatile flavor compounds in fermented fish after addition of enzymes were discussed by combination with the results of microbial community structure and other physicochemical indicators.The results were as follows:1.Chouguiyu were fermented with different levels(0,10,50,100,200 and 400 U/g)of papain.The effects of papain on free amino acids,fatty acids composition,biogenic amines,volatile flavor compounds,odor and taste evaluation,bacterial community diversity in Chouguiyu were studied and the appropriate amount of papain was determined.The results showed that 200 or 400 U/g of papain was appropriate for fermentation of Chouguiyu.After addition of papain(200 or 400 U/g),fermentation period could be shorten from 10 days to 7days,and the shortcomings of flavor substances,sensory quality and nutritional quality caused by shortening the fermentation period could be avoided,and the production of biogenic amines could be inhibited.Papain was able to increased the content of some flavor compounds(1-octen-3-ol,hexanal,heptanal,(Z,Z)-3,6-nonadienal and pentanal)which contributed to main aromas(fruity,grassy,fatty,mushroom)in Chouguiyu.Furthermore,Lactobacillus,Carnobacterium,Serratia and Psychrilyobacter could significantly affect the formation of odor in Chouguiyu.2.Suanzhayu were fermented with different levels(0,50 U/g)of flavorzyme.The dynamic changes of p H,total titriable acid content,TCA soluble peptides,water activity,volatile flavor compounds and microbial community succession during fermentation were studied.In addition,flavorzyme was able to increased the content of some flavor compounds(1-octen-3-ol,octanal,nonanal,2-pentyl-furan)which contributed to main aromas(grassy,fruity,flowery,bean)of Suanzhayu,accelerated the process of establishing predominance for the dominant bacteria(Lactobacillus)in the final product and the ripening of Suanzhayu.Bacteria contributed more to the volatile flavor compounds in Suanzhayu than Fungi.Lactobacillus,Lactococcus,Vagococcus and Morganella might play an important role in the late stage of fermentation and be highly correlated with the production of aroma in Suanzhayu.3.Suanzhayu were fermented with different levels(0,100 U/g)of lipase.The dynamic changes of p H,lactic acid content,volatile flavor compounds and bacterial community succession during fermentation were studied.The results showed that addition of lipase(100U/g)could promote the formation of volatile flavor compounds and shorten the fermentation period.Lipase could promote the production of some odor-active compounds in Suanzhayu,such as pentanal,hexanal,octanal,3-methyl-1-butanol and hexanoic acid ethyl ester,and enhance mian aromas(grassy,fruity)of Suanzhayu.Lactobacillus,Proteus,Vagococcus,Hafnia-Obesumbacterium might play an important role in the formation of main aromas in Suanzhayu,such as mushroom,fatty,almond,bouquet,pungent,floral.