Effects Of Lactic Acid Bacteria And Flavourzyme On The Quality Of Fermented Grass Carp(Ctenopharyngodon Idellus)

In this article,the back meat of grass carp(Ctenopharyngodon idellus)was taken as research object.The effects of lactic acid bacteria and the combination of lactic acid bacteria and flavourzyme on the quality and flavor of fermented grass carp were studied.Firstly,the lactic acid bacteria suitable for fermentation conditions of fermented grass carp were selected from several common lactic acid bacteria based on physicochemical properties.Secondly,flavourzyme was added to assist the fermentation of grass carp.The effects of lactic acid bacteria,exogenous protease and their combination on the physicochemical characteristics,safety,and flavor quality of fermented grass carp were compared to provide technical support for the processing of aquatic products.To explore the effects of different lactic acid bacteria on the quality of grass carp during fermentation(0～15 days),the microorganism,pH,total acid,moisture content,whiteness,amino acid nitrogen,thiobarbituric acid,and volatile base nitrogen of grass carp back muscle fermented by different lactic acid bacteria(Lactobacillus plantarum,Pediococcus pentosus and Lactobacillus paracasei)were determined.The natural fermentation were used as the control.The results showed that compared with natural fermentation,lactic acid bacteria grew rapidly in fish meat after inoculation.With increase of fermentation,the pH of each fermented grass carp group meat significantly decreased to 4.03 ± 0.02 and the total acid content significantly increased to 23.70 ± 1.06g/kg,which indicated that three lactic acid bacteria can effectively inhibited the reproduction of spoilage bacteria.At the same time,the whiteness of fermented grass carp meat was improved.The content of amino acid nitrogen in fermented grass carp meat was increased.The moisture content and the production of volatile basic nitrogen were reduced.At the end of fermentation,Pediococcus pentosus had the greatest impact on the decline of moisture content.Compared with the other two groups,LP group had higher whiteness and lower TVB-N value.However,ANN of LP group was significantly lower than the two groups,indicating that the protein decomposition ability of Lactobacillus plantarum was poor.The research showed that inoculating lactic acid bacteria for fermentation can reduce the lag time at the beginning of fermentation,delay the deterioration of fish meat,improve the nutrition value and color,and the quality of fermented grass carp.To explore the effects of lactic acid bacteria and flavourzyme on the physicochemical characteristics and safety of grass carp during fermentation(0～15 days),the pH,Aw,AAN,TBARS,TVB-N,harmful bacteria and biogenic amines of the fermented products of grass carp back muscle treated with different starter(flavourzyme,Lactobacillus plantarum and the combination of flavourzyme and Lactobacillus plantarum)were determined.The NF,FL,and FF were used as control.The results showed that the addition of Lactobacillus plantarum could effectively reduce the pH of fermented grass carp from 6.67 ± 0.06 to below 4.40,while the addition of flavor protease had no effect on the acidification of the system.The increase rate of Enterobacter,Staphylococcus aureus and Pseudomonas in LP group and FL + LP group was lower than that in NF group and FL group.The addition of Lactobacillus plantarum had a significant effect on inhibiting the growth of three harmful bacteria,slowing down the production of TVB-N and inhibiting the formation of biogenic amines,while the addition of flavor proteinase had no significant effect on the above indexes.The content of AAN in FL group and FL + LP group increased rapidly,which was significantly higher than that in the other two groups at each time point(P < 0.05),indicating that the addition of flavor protease can improve the hydrolysis of protein.The addition of Lactobacillus plantarum had no effect on the flavourzyme activity of fish.The combination of bacteria and enzyme could effectively improve the physical and chemical quality and safety of fermented grass carp.To explore the effect of starter treatment on protein degradation and taste of grass carp during fermentation(0～15 days),the changes of TCA-soluble peptide,TN,NPN,PI,free amino acid,nucleotides,EUC and electronic tongue of grass carp back muscle fermented by different fermentation agents(flavourzyme,Lactobacillus plantarum and the combination of flavourzyme and Lactobacillus plantarum)were analyzed.The NF,FL,and FF were used as control.The results showed that the content of TCA-soluble peptide,NPN and PI in FL group and FL+LP group were significantly higher than those in NF group and LP group,indicating that the addition of flavor protease can effectively accelerate protein hydrolysis and improve nutritional quality.Flavor nucleotides contribute little to the taste of fermented grass carp and free amino acids are the main flavor contributing substances of fermented grass carp.The addition of flavourzyme can effectively increase the content of fresh and sweet amino acids,among which the fresh amino acid Glu contributes greatly to the taste of fermented grass carp.Taking natural fermentation as the control,the grass carp back muscle fermented by different fermentation agents(flavourzyme,Lactobacillus plantarum and the combination of flavourzyme and Lactobacillus plantarum)were determined by the microbial diversity,electronic nose and volatile compounds.The microbial diversity of fermented grass carp samples was distributed based on pacbio high-throughput sequencing technology.The types and contents of volatile flavor substances in fermented grass carp samples were determined by GC-MS to explore their effects on the formation of volatile flavor substances in the process(0～15 days).The results showed that Firmicutes was the most important phylum in the fermentation process of grass carp.The addition of Lactobacillus plantarum can effectively promote the growth of Lactiplantibacillus and flavourzyme may have a positive effect on the growth of Staphylococcus.A total of 52 volatile compounds were identified in fermented grass carp,among which hexanal,nonanal,decanal,3-octanone,3-methyl-1-butanol,1-octene-3-ol and ethyl acetate were the main flavor substances in the four groups of samples.After 15 days of fermentation,under the condition of combined fermentation of bacteria and enzymes,the total content of final volatile compounds in grass carp meat was the largest and the smell of fish meat was the strongest.The correlation analysis showed that the growth of Lactobacillus was conducive to the rapid production of aldehydes(hexanal,nonanal and decanal),alcohols(3-methyl-1-butanol,2-methyl-1-butanol,1-pentanol,2-heptanol,1-heptanol,1-octene-3-ol and 1-octanol),ketones(3-octanone)and esters(ethyl acetate,3-methyl-1-butanol acetate,and ethyl palmitate)in grass carp meat.