Dynamic Changes Of Lactic Acid Bacteria Flora During The Fermentation Of Sichuan Pickle And Its Effects On The Flavor Of Pickle

Lactic acid bacteria is the major microbial flora in the pickle, it plays an important role in the formation of pickle flavor. The species and quantities of lactic acid bacteria were changed with the extension of pickle fermentation time.The active phase of different lactic acid bacteria during the fermentation of pickle was not the same,and nor did their function in pickle. In this paper, the dynamic changes of lactic acid bacteria flora were studied during the fermentation of pickle, and the flavor substances of pickle inoculated with different lactic acid bacteria were compared. The main conclusions are as follows:1.The analysis of lactic acid bacteria flora was studied by culture dependent method. Seven different colony morphology strains were separated from spontaneous fermentation of radish pickle, after some physiological and biochemical tests and sequencing the 16S rDNA sequence, seven different colony morphology strains were identified as Leuconostoc lactis,Lactococcus lactis, Weissella cibaria, L. plantarum, L. fermentum. Lactococcus lactis and L. plantarum displayed two different phenotypes on modified Chalmers medium; While during the old brine fermentation, Seven different colony morphology strains were separated, after some physiological and biochemical tests and sequencing the 16S rDNA sequence, seven different colony morphology strains were identified as L. plantarum, pediococcus ethanolidurans, L.buchneri, L.paracollinoides, L. namurensis, L. plantarum displayed three different kinds of phenotypes on modified Chalmers medium.2. The dynamic changes of lactic acid bacteria flora were different during the two kinds of fermentation. Results showed that Leuconostoc lactis,Lactococcus lactis, Weissella cibaria, L. plantarum, L. fermentum dominated the fermentation during the spontaneous fermentation of radish pickle,Lactococcus lactis and Weissella cibaria were present in the brine as soon as the vegetable was pickled while other three species were isolated successively during the later fermentation. Lactococcus lactis,Weissella cibaria and Leuconostoc lactis were mainly present in the early stage of fermentation and died at the later stage;L. plantarum, L. fermentum and Weissella cibaria dominated the middle stage of fermentation, L. fermentum and L. plantarum dominated the last stage of fermentation,and the maximum viable cell count of each lactic acid bacteria in spontaneous fermentation was 6.2 log CFU/mL.8.0 log CFU/mL,7.1 log CFU/mL,8.3 log CFU/mL,7.2 log CFU/mL;While during the old brine fermentation, each lactic acid bacteria displayed no obvious dynamic changes. L. buchneri, Pediococcus ethanolidurans. L.paracollinoides, L. namurensis were maintained at 6 log CFU/mL or so, L. plantarum was maintained at 8 log CFU/mL,which was the most dominant bacteria.3.The growth rate, salt tolerance,acid tolerance,ability to produce acid and degrade nitrite of different lactic acid bacteria were compared.The results showed that L. plantarum displayed best performance in salt tolerance,acid tolerance, ability to produce acid; Leuconostoc lactis,Lactococcus lactis and Weissella cibaria grew fast; each of lactic acid bacteria could degrade nitrite, the nitrite degradation rate of Leuconostoc lactis was 65.9%, and other species of nitrite degradation rate was more than 95%.4.Nine lactic acid bacteria separated from radish pickle was inoculated to fresh radish, and the mature radish pickle was taken to analyze the flavor compounds. Volatile flavor compounds of radish pickle were analyzed by headspace solid-phase micro-extraction (HS-SPME) and gas chromatography-mass spectrometry (GC-MS), a total of 37 kinds of volatile substances detected, of which thiocyanate esters took the most abundant, accounting for 28% to 65% of the total volatile components.There was some obvious difference in volatile flavor compounds among the radish pickles inoculated with different lactic acid bacteria. Organic compounds of radish pickle were analyzed by HPLC,organic acid to be detected were oxalic acid, malic acid, ascorbic acid, lactic acid, acetic acid, citric acid, succinic acid.The pickle inoculated with L. fermentum also detected tartaric acids. The dfferences of organic compounds and content between radish pickle inoculated with different lactic acid bacteria was not obvious. Total acid content in radish pickle inoculated with L. fermentum was the lowest, total acid content of other pickles were above 4.0 g/kg; Sensory analysis revealed that differences between radish pickles inoculated with different lactic acid bacteria was obvious, radish pickles inoculated with Weissella cibaria and L. plantarum tastsd best, radish pickles inoculated with L. fermentum tasted worst.