Dynamic And Functional Analysis Of Microbial Community Structure During The Processing Of Low-salinity Pickled Mustard Tuber

During the processing of low salinity pickled mustard tuber, microbial community structure were investigated by using single strand conformation polymorphism(SSCP)technology. In PAGE gel atlas, 11 distinct dominant bands were retrieved and cloned, sequence contrasting results showed that Leuconostoc mesenteroides is the dominant microorganism in the initial stage of fermentation; Lactobacillus plantarum and Lactobacillus brevis showed up accompany with the alteration of fermentation condition. At the later stage, the dominant microorganism are Lactobacillus plantarum and Lactobacillus versmoldensis. Total DNA are extracted by modified SDS high salinity extractio, and this method got a high microbial diversity. By using Diffusion Buffer(0.5 M ammonium acetate;10 mM magnesium acetate;1 mM EDTA,pH 8.0;0.1%SDS) and agarose gel retrieve kit, the DNA fragment can be retrieved from PAGE gel, conveniently and efficiently.In order to study the function of lactic acid bacteria in the processing of pickled mustard tuber, 3 lactic acid bacteria strains were isolated from low-salinity pickled mustard tuber. By primarily physiological and biochemical experiment, the result indicated that they are gram negative, spore negative, catalase negative bacteria; The result of glucose fermentation experiment showed that L32 and L34 are homofermentative lactic bacteria, L33 is heterofermentative lactic bacteria. The 16S rRNA sequence comparation results showed that L32 is Lactobacillus curvatus, L33 is Leuconostoc citreum, L34 is Lactobacillus plantarum. This coincidence with SSCP result. Their optimum growth temperature are 30℃, optimum growth pH are 6.5, the stationary phase are about 6 h, 0-8% salinity had little influence on their growth.The characters of low salt pickled mustard tuber processing were investigated. During the processing of low salt pickled mustard tuber, pH was descending all the time, from incipient pH 6.0, to ultimum pH 3.7; Lactic acid bacteria quantity experienced a hastily rise, when reached to a peak of 3×10⁸ cfu/mL in 10^th day, it began to descend slowly, and finally maintained on a stable quantity of 1×10⁸ cfu/mL; Nitrite content experienced a hastily rise, when reached to a peak of 8.39 mg/kg in 3th day, it began to descend hastily, and finally maintained on a stable quantity of about 1 mg/kg.Fermentation supernate of 3 lactic acid bacteria L32, L33 and L34 exhibited strong inhibitory activity against Escherichia coli, Staphylococcus aureus, Bacillus subtilis, respectively. The pH of MRS liquid culture medium is adjusted to the pH of lactic acid bacteria fermentation broth, as a result, the bacteriostasis circle descented 30%, this illustrated that the main bacteriostasis material is lactic acid; The lactic acid bacteria fermentation broth was digested by katalase, pepsase, parenzyme and caroid, and the bacteriostasis circle descented by different level, this illustrated there are other bacteriostasis materials besides lactic acid, such as hydrogen dioxide and bacteriocin.In summary, lactic acid bacteria are dominate microbial population during the processing of low salinity pickled mustard tuber, lactic acid bacteria are important for the fermentation of mustard tuber and its quality character, such as: Lactic acid bacteria produce lactic acid, pH was descended; Reduce the nitrite content; Inhibitory activity against harmful and contaminating microorganism.