Studies On Changes Of Soybean Protein And Dietary Fiber During The Production Of Douchi

Soy paste, soy sauce, sofu and Douchi are four most famous Chinese traditionally fermented soybean products with good flavor and plenty nutrients. Moulded Douchi made in Yongchuan was used as experimental material in this paper to investigate biological changes of soy bean composition during its production with emphasis on protein and dietary fiber. The following results were achieved.Along with the extension processing of Yongchuan Douchi from material to product, protein content, crude fiber content, polysaccharide content and total energy of soybean were found decreased from a overall point. Otherwise, fatty content, water content, ash content and reducing sugar content increase slowly with the processing extended. Acid content and browning strength in soybean were found changed in a stepwise styled and S curve, respectively. Calcium, magnesium and phosphorus in soybean significantly decreased during the pre-preparation of Douchi production.2. Research work concerning on the biological changes of protein during Douchi production indicated that protein was partly degraded during fermentation. Compared with material soybean, the water-soluble nitrogen content of finial product was significantly increased with a softer texture, but the total nitrogen content and ethanol-soluble nitrogen content of final product kept stable. At the same time, non-protein nitrogen and amino acid nitrogen content showed an increasing trend over Douchi production. A large amount of free amino acid was formed during Douchi production, and that free amino acid content in final product was about 21.74 times of that in material soybean. Along with development of Douchi production, in vitro protein digestibility of Douchi was evidently elevated.3. The dietary fiber was extracted with enzymatic method from the Douchi at different processing extent in this paper. Changes of physicochemical properties and ferment ability of dietary fiber in soybean during Douchi production were recorded. It was found the proportion of water-soluble dietary fiber in total dietary fiber was increased along with development of Douchi production. Comparing with the corresponding properties of dietary fiber in material, swelling capacity of dietary fiber of soaked soybean was increased significantly, but swelling capacity first decreased sharply when soybean subjected to inoculation and fermentation, then it kept stable. Otherwise, water-holding capacity and water-binding capacity of dietary fiber showed an evident decrease during Douchi production. The dietary fiber was subjected to human faeces fermentation in vitro and animal test for fermentation in vivo. It was found that no significant difference was tested between short chain fatty acids in faeces collected from rats given with different dietary fiber. Dietary fibre in Douchi production at different stages could enhance short chain fatty acid forming remarkably in vitro fermentation. At the same time, it was shown that acetic acid content in rat's faces was decreased but propionic acid and butyric acid content were increased gradually.