Abstract: Provided is an agent for improving intestinal bacteria that contains a proteolytic enzyme-decomposed residue of a soybean protein material and inhibits the growth of opportunistic bacteria.

Abstract: It is intended to provide a soybean protein material which has an excellent taste without showing astringency or bitterness and satisfies physicochemical characteristics required for acidic foods and drinks, for example, low viscosity, high solubility and high stability. In the process for producing an acidic-soluble soybean protein, an additional step, wherein a soybean protein-containing solution is digested with protease at a pH value higher than the isoelectric point of soybean protein and then the pH value is adjusted to a level lower than the isoelectric point of soybean protein, is conducted. Thus, astringency can be significantly reduced while preventing the generation of undesirable bitterness. The TCA (0.22 M) solubilization rate of the acidic-soluble soybean protein thus obtained is preferably 10% or more, while the phytic acid content of the acidic-soluble soybean protein thus obtained is preferably 0.5% by weight or less.

Abstract: The object is to provide a soybean protein hydrolyzate which can be produced by hydrolysis of a soybean protein produced by “method B” as defined in the description and produces no dreg even when refrigerated under acidic conditions, particularly a soybean peptide mixture having a relatively low molecular weight. Disclosed is a method for production of a soybean peptide mixture, comprising the steps of: (a) extracting a concentrated soybean protein with water to yield an extract; (b) treating the extract with a protease under alkaline to neutral conditions; (c) further treating the resulting product with a protease under acidic conditions; (d) treating the resulting product with a phytic acid (phytase)-decomposing enzyme; and (e) separating and removing an insoluble material from the product.