PURPOSE: To obtain an inhibitor of decomposition useful for prevention of the rottenness and discoloration of processed foods of soybean protein and of the propagation of sanmaku yeast of soy souce, by extracting rice-bran oil or by-products obtained in its purification with an alkali-alcoholic solution to give a viscous material.

CONSTITUTION: Rice-bran oil or it by-products obtained in its purification is extracted with an alkali-alcoholic solution and the extracted solution is made weakly acidic to precipitate a dark brown viscous material. A residue solution remained after removal of the viscous material is cooled to a temperature not higher than room temperature to deposite a white precipitate. A solution remained after removal of the precipitate is distilled to prepare an alcohol and a residue. One or a mixture of two or more selected from the viscous material, the white precipitate, and the residue is treated to give an inhibitor of decomposition for processed food. For example, the inhibitor of decomposition can prevent the occurrence of waki (undesirable fermentation), the rottenness by microorganisms, browing, are sanmaku yeast of soy sauce.