The protein particles in soymilk were fractionated in size by differential centrifugation. Particles of more than 100nmin diameter (LSP) constituted 40%of the total protein in raw soymilk, 70% of the protein components being IIS globulin. LSPwas not formed in the presence of2-mercaptoethanol and sodium ascorbate. LSP was decreased by heating, and particles of 100-40 nmin diameter (MSP) were increased. The formation of MSPwasnot due to any degradation of LSPbut to the combination of supernatant proteins of less than 40nm in diameter with each other. MSP formed by heating contained the ft subunit of 7S and the basic subunit of USas main components. The particles of more than 40nm in diameter (LSP+MSP)constituted 50%of the total protein in both raw soymilk and soymilk. Tofu (bean-curd) is made by coagulating the proteins from soymilk with calcium or magnesium salt, which itself is made by grinding and heating soaked soybeans. were stored at 5°C until being used. All chemicals were of the highest purity available and were used without further purification.Preparation of soymilk. The beans were soaked in de-ionized water with or without 1% 2-mercaptoethanol for 20hr at 4°C. The swollen beans were then ground to a homogenate containing 10% of solids with the soaking water by an Oster blender. The homogenate was next filtered through a de-fatted cotton sheet, the filtrate being designated as raw soymilk. The homogenate was heated in boiling water for 5min and then filtered through a de-fatted cotton sheet, this filtrate being designated as soymilk. The raw soymilk heated in this way is designated as heated raw soymilk. When the swollen beans were ground to prepare the raw soymilk, it was treated by the following methods: replacement of the air by nitrogen gas and the addition of mercaptoethanol, 2% hydrogen peroxide or 0.2 m ascorbate, respectively, before grinding;and aeration for 20min and sonication for 5min after grinding. These treatments are expressed in Table II as substitution with N2, mercaptoethanol, 2% H2O2, 0.2m Na-ascorbate, aeration and sonication, respectively.Preparation of protein particles. Protein particles of a definite size were prepared from the soymilks by the method of differential centrifugation.6) The average size of the fractionated particles was calculated by using 1.2 f Present address:

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