| Douchi, one of the four most popular traditional fermented soybean products, along with soy sauce, soy paste and sufu, was consumed as a kind of food and medicine from ancient time. Nowadays, it is still used as one of the materials in several Chinese traditional medicines. However, till now, Spontaneous fermentation and household method are mainly used for douchi making, and there were few studies on its fermentation, nutrition and healthy function. In the present dissertation, an Aspergillus strain for fermentation was screened from spontaneous fermented Aspergillus-type douchi qu. Its fermentation properties, douchi pure-cultured technology, and its component changes during the fermentation period were studied, along with the healthy function changes fermented by different strains. The main contents are as following:1. Varieties and population of microflora in Aspergillus-type douchi qu were studied, and the Aspergillus strains were isolated and parts of them were identified. It showed that A. Egyptiacus and A. oryzae were the dominate strains, and there may be some safety problems for A. fumigatus and A. parasiticus which were found in douchi qu.2. Aspergillus Egyptiacus Y20 was screened as the fermented microorganism strain by its high activities of neutral protease and b-glucosidase, for protein ( or peptide) and isoflavone are the main healthy functional components in soybean,3. The fermentation temperature, humidity and time were varied according to a Central Composite Design with the aim of assessing the effects of these variables and their interactions on the activities of neutral protease and b-glucosidase. The models of predictive polynomial quadratic equations were obtained. An analysis of the response surfaces permitted the identification of the operational conditions needed to optimize the performances of the tested strain. The second step fermentation condition was determined by the changes of formal nitrogen and total acid content during fermentation.4. The evolutions of nutrition, flavor and healthy function components were analyzed. The changes of protein, amino acid and organic acids indicated that fermentation is favorable to nutrition and flavor of products. In final product, about 83.4% genistin and 95.3% daidzine were hydrolyzed to genistein and daidzein, which can improve the healthy function of products.5. Douchi showed high antioxidant activity and angiotensin converting enzyme inhibitory activity(ACEIA). The ACEIA was increased following the qu fermentation and raised after the second fermentation.6. ACE had no effect on the ACEIA of douchi qu, but it increased greatly after hydrolyzed by gastrointestinal proteases, the results suggested that the ACE inhibitor in douchi qu should be a mixture of prodrug-type and inhibitor-type. Gel chromatogram of qu extract, which was pure-cultured by A. egypiicus, revealed that there were four components with ACEIA. Eachcomponent was analyzed by HPLC, the results showed that component 2 had only one peak. The amino acid analysis of component 2 demonstrated that it was a peptide composed by phenylalanine, isoleucine and glycin. After hydrolyzed by gastrointestinal proteases, the molecular of peptide was lower than the intact.7. Spontaneous fermented douchi qu had a high a -glucosidase inhibitory activity, but the differences were evident among products pure-cultured by different strains. In final products they were lower than that of the corresponding qu. The treatment heated at 10CTC showed few effect on the a -glucosidase inhibitory activity.
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