Isolation and enzymatic digestion of body complex of soybean seed.

The body complex of the soybean seed (BCSS) was isolated from the single cells (27.2%) by a sequential procedure of autoclaving with water, cellulase digestion for the primary cell wall, pectinase digestion for the secondary cell wall, and defatting with hexane washing. Its characteristics were then investigated. The defatted BCSS (DBCSS) consisted of protein (76.5%) and mannose-rich carbohydrates (3.2%). Screening of the food-processing protease for the digestion of DBCSS was carried out, and a kind of alkaline protease was selected. The inner protein of DBCSS was easily extracted with 0.1 M sodium carbonate buffer, pH 10, and the insoluble shell of the body complex (SDBCSS) was left. SDBCSS consisted of hydrophobic amino acid-rich protein. SDBCSS was easily digested by the selected alkaline protease. SDBCSS was dissolved by boiling with sodium dodecyl sulfate-mercaptoethanol, and it was found to consist of a protein of approximately 3 kDa. The high enzymatic digestion including the selected protease for soybean seed and defatted soybean meal was carried out; both were extracted and digested with a yield of >99.5%. The final indigestible residue was found as paired hexagonal and filamentous organs of the soybean cells.