| Just like the soy sauce, fermented bean curd and miso,douchi is originated in pre-Qin era and classified as Chinese traditional fermented soybean. During douchi production, whole soy (or Douban) is chosen, and then processed with soaking, cooking, starter adding and fermentation; there of the important progresses are starter adding and fermentation. As a kind Chinese functional food, douchi not only possesses the nutritional and medicinal values, but also helps inproving appetite and indigestion, as well as detoxification.Till now, studies on douchi were mainly focused on their functional components, and little research was carried out to analyze the microbiota during fermentation, most of the studies commonly depended on the traditional separation methods. To investigate the microbial changes, a kind of traditional douchi in southern China-"Fragrant Rice Park" had been approached, and its microbial biomass and species had been monitored by using the combination of viable cell counting and denaturing gradient gel electrophoresis (DGGE). In addition, the a-glycosidase inhibition activities of polysaccharides, isoflavones, saponins and water extract in douchi had also been evaluated.The results showed that obvious change took place on douchi surfaces during koji-making process, and the soy beans were covered with thick mycelium since 3th day. During koji-making process, the highest biomasses of bacteria, bacilli and fungi reached as high as 10.8,10.4 and 9.5 Lg CFU/mL, respectively. From the DGGE patterns, we concluded that the species of bacteria, bacilli and fungi obviously changed, and their maximum similarities were only 78%,74% and 79%, respectively. Though the key microbe Aspergillus oryzae and Bacillus subtilis occupied the dominant position during koji-making process, some pathogens, e.g. Micrococcus sp. and Staphylococcus sciuri had also been detected by DGGE method. In addition,11 isolates named Bacillus subtilis, Bacillus amyloliquefaciens, Aspergillus oryzae, Brachybacterium sp., Aspergillus niger, Staphylococcus saprophyticus, Micrococcus sp., Staphylococcus gallinarum, Absidia corymbifera, Saccharomyces cerevisiae and Malassezia sp. was harvested by pure culture method.Compared with the koji-making process, the amounts of bacteria, bacilli and fungi obviously decreased during production phase, which might be caused by changes of temperature, humidity, salt adding and deep fermentation. The viable counts showed that the biomass reached a stable situation (5.0 Lg CFU/mL) on 4th day, and the bacteria species were mainly composed by Staphylococcus gallinarum, Enterobacter sp., Lactococcus lactis subsp and an uncultured bacterium; the bacilli were mainly composed by Alcaligenes sp., Enterobacter sp. and Bacillus subtilis; and the fungi were mainly composed by Absidia corymbifera and Pichia guilliermondii.Microorganisms conferred douchi multiple functions during fermentation process. Based on many references, we extracted polysaccharides, isoflavones, saponins and water-soluble substances from douchi and evaluated their inhibition effect onα-glycosidase, and thus examined their potential role in typeⅡdiabetes treatment. The results indicated that all the extractions possessed the inhibited effects onα-glucosidase, and their inhibition efficiency increased as their concentration increased. As expected, the aqueous extract containing polysaccharides, isoflavones, saponins and water-soluble possessed the best inhibitory effect (as high as 90%).In Summary, monitoring the dynamic changes of microflora in the production of douchi provided great technical support for controlling pollution, mimicing the fermentation process, achieving the modernization production of douchi. The preliminary results of inhibitingα-glucosidase by active substances from douchi offered a promising protocol for curing typeⅡdiabete. |
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