Study On The Fermentation Characteristics Of Lacyic Acid Bactieria Isolated From Pickling Vegetables

In this paper, the grass carp was fermentated by Lactobacillus plantarum separatedfrom pickle of natural fermentation. The changes of sensory evaluation, colony ofmicroorganism, chemical and physical analysis during the fermentation were studiedunder the optimal conditions of fermented grass carp by Lactobacillus plantarum. At thesame time, the electronic nose was used to analyse the changes of flavor compoundsduring the fermentation.The major content and results of this study are:(1) One strain of lactic acid bacteria was isolated and purified from pickle of naturalfermentation. The strain was identified as Lactobacillus plantarum by physiological andbiochemical tests, and sequences analysis of16SrDNA.(2) In order to improve the flavor of grass carp, the grass carp was fermented byLactobacillus plantarum.The suitable synthesis conditions were defined by usingorthogonal experiments as follows: the grass carp was pickled for4hours in the shadeplace with five percent of salt and three percent of sugar. Then the grass carp, afterinoculated by six percent of Lactobacillus plantarum in the sterile condition, wasfermented with the temperature of35degrees centigrade for20hours. After fermentationproducts aromas and texture have been improved.(3) Under the uptimal processing conditions of fermentation, the number ofmicroorganism was counted by using the Selective Agar compared with the noneinoculated sample.The results were as follows: that the dominant microbial groups in grasscarp were lactic acid bacterial in the whole fermentation;the total bacteria and thepopulation of Lactic acid bacteria had an increase during the early and middle stage offementation, but had a little decrease in the telophase; Staphylococcus had a continuinggrowth during the fermentation and tended to being stable; in compare with the controlsample, the growth of Bacillus subtilis, Enterobacteriaceae, Yeasts and Molds wererestrained. (4) The results after analyzing the changes of nonvolatile components showed that thepH of fermented samples decreased more rapidly than the control samples. At20hours pHof fermented samples was5.02, but pH of control samples was5.21.The content of waterchanged slightly after the finish of fermentation. The content of crude protein had adecrease with the extending of fermentation time, from48.04%at the prophase to43.17%at the final stage. The content of amino acid nitrogen(AAN) had an increase from0.14%to0.41%, and the content of organic acid increased from0.31%to0.62%. The TVBN valueof the sample inoculated by Lactobacillus plantarum increased slowly and at the finalstage of fermentation the TVBN value was only15.78%with no smell of corruption. Butthe control sample had increase to30.21%and the fish has already corrupted.(5) The analysis was made on the correlations between the nonvolatile componentsand the microorganism by SPSS sofeware. It was found that Lactic acid bacteria weresignificantly and negatively correlated with the content of crude protein, and positivelycorrelated with AAN and organinc acid, and Bacillus subtilis were significantly andpositively correlated with the content of AAN. In theory, it suggested that Lactic acidbacteria and Bacillus subtilis have the ability of producing protease which can degradethe protein into peptides, amino acids and other small molecules.(6) An electronic nose(PEN3) was used to analyze the grass carp femented by usingLactobacillus plantarum.The volatile components emanating from the fermented grasscarp were dynamically sampled by a PEN3system and then data analysis was conductedby using principal component analysis(PCA) and linear discrimination analysis(LDA).Theresults showed that during the fementation the flavor was not changed a lot in12hours,butafter16hours the flavor changed obviously and changed a little until the fementation wasfinished.The correlation between electonic nose output signal and sensory evaluation scoreare well.The LDA method appearing with better unidirectivity can distinguish the flavor indifferent periods of the fermentation better. Moreover the Loadings analysis proved thatsensors W1S,W1C,W3C and W2S had the similar impact during the detecion.Thisprovides the basis for further optimizing sensors and searching for convenient and shortcutinspection technology.