Study Of DGGE Analysis Of Microbial Community And Probiotic Effect In Yogurt And Douchi

Fermentation technology is an ancient, traditional food processing and storage methods, which possesses the advantages of low cost, nutrient-rich, unique flavor and high stability. However, the whole-niveau in traditional fermentation technology in China is in quite low-level, and the production process mainly depended on the experience of the technicist, and its product quality may easily be affected and fluctuated by the enviroment factors. For most of the fermented foods, the complexity of microflora in fermentation results in some potential problems for food safety. Therefore, it is necessary to combine the traditional viable cell counting method and denaturing gradient gel electrophoresis (DGGE) method to monitor the dynamic microbial changes, which is beneficial for the processing control for high quality and food safety in traditional fermentation industry.Chapter one reviewed the development and principle of the DGGE, the selection of the technical conditions, as well as its application in meat product, grain product, dairy product, vegetables and other traditional fermented foods.In chapter two, several probiotics (e. g. Lactobacillus rhamnosus, Lactobacillus plantarum, Lactobacillus acidophilus and Lactobacillus saliva) normally isolated from food were selected as the target strains and used for preparation of DGGE marker to monitor their dynamic changes during food fermentation, and the accuracy and repeatability of the DGGE marker were verified. The results indicated that the self-made DGGE markers consisting of PCR products from either the lactobacilli specific primers or the universal primers could be found in the correspondentbands in the DGGE gels, indicating its good potential application in microbial monitoring. Then, these markers were verified valid in sourdough, for shortening the procedure and time for identification of target strains.In chapter three, the combination of the viable cell counting, DGGE and sequencing was used to monitor the microbial diversity caused by Viili and several other self-made yogurts. The results showed that five different strains were isolated, and S. thermophilusand L. delbrueckii were identified as the dominant bacteria in Viili; the curd experiment and EPS yield experiment showed that Viili possessed the shortest curd time and a low EPS products; the combination of L. paracasei+Bacillus cereus+L. plantarum possessed the highest EPS yield while its curd time is 3h longer than Viili. During the drinking stage of Viili, though the dominant bacteria in the intestines of the donators received some changes, these strains mentioned above had been detected during the control stage, and a similar band number was observed between the recovery stage and the control stage, indicating that Viili was beneficial for the stabilization of the inhere microbial ecology. In addition, the viable cell counting results demonstrated that Viili significantly increased the number of the total bacteria and lactobacilli, indicating that the beneficial effects of Viili was a kind of overall promotion, and it seemed that a better promoting effect of Viili was observed when compared with yogurt fermented by single strain.In chapter four, the dynamic microbial changes of the processing and commercial product of Daoxiangyuan Douchi, and the composition and dynamic change of flora in major brands of Douchi in China, had been monitored using the vialble cell counting and DGGE method. During the Douchi production, the cells of bacteria, bacilli and fungi reached a stable state (105CFU/g,104CFU/g and105CFU/g), while maintained stably in species on10th day, mainly composed by Staphylococcus gallinarum, Enterobacter sp., Lactococcus lactis subsp and an unculturable strain. The microbial diversity in Douchi surface and underlayer was various. A100-fold density of the microbial number was observed in upper parts when compared with underlyer parts of Douchi, and the Staphylococcus gallinarum, Enterobacter sp., Lactococcus lactis subsp and a unculturable strain were identified as the common strains both in upper and underlyer Douchi. While the Bacillus thermoamylovorans possessed the dominant position in upper Douchi. In addition, the microbial results of the Douchi in China indicated that the bacterial composition was various because of the Douchi types, origins and production process, while Bacillus subtilis, Lactobacillus plantarum, Pediococcus pentosaceus and Bacillus amyloliquefaciens were identified as the common strains in most Douchi. Moreover, the functional material of black beans and Douchi possessed the inhibitation effect on a-glucosidase, and it seemed that the Douchi had a better effect, which is benifical for the treatment of diabetic diseases.