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内容記述 |
The tofu (soybean curd), which is a traditional food in Japan & China, includes 38% lipid and 52% protein in dry matter. The lipid in the curd is extremely stable against ooze and oxidation by cooking and storing. Thus the tofu is an important food source for a stable lipid supply. Soy milk was prepared from the soybean ground with water, heated, and filtered. We have already proposed that the soy milk proteins consist of particulate and soluble proteins. The particulate protein is made up of mainly basic peptide (B) of 11S globulin and β subunit of 7S globulin. The soluble protein is made up of acidic peptide (A) of 11S, α and α' subunits of 7S. The tofu was made from soy milk by the addition of CaSO4 or glucono-δ-lacton (GDL) as coagulants. The protein and lipids from tofu were extracted by the addition of urea or guanidine hydrochloride (GuHCl) as a denaturant with or without 2-mercaptoethanol. The proteins extracted from tofu were up to 40% even by the addition of 8M urea or 5M GuHCl without 2-mercaptoethanol. The yield of lipids was also low. In the presence of 2- mercaptoethanol, yield of both protein and lipid increased to 100% with each denaturant. The composition of extracted proteins was analyzed with SDS-PAGE. Proteins liberated from tofu, in turn, A,α and α', and β and B with increasing denaturants. These results indicate that oil body particle covered with oleosin in tofu is packed with three protein layers, that is, oleosin, protein particles (mainly B and β), and soluble proteins (A, α and α'). Therefore, the lipid of tofu is extremely stable against ooze and oxidation by cooking and storing. |
sprj-v7p42-47.pdf (356.1 kB)
