Method for preparing protein nitrogen source applicable to fermentation and food by rice

The invention discloses a method for preparing organic nitrogen source applicable to fermentation and food by taking rice or rice flour as raw material and carrying out acid process or enzymatic hydrolysis for scum left through pressing and filtering in the process of filtering starch syrup produced in an enzymatic method. The method comprises the following steps: the rice or the rice flour is washed and ground to be milk, calcium chloride and liquefying amylase are added to the milk for consecutive spraying liquefaction to obtain liquefied liquid, various saccharifying enzymes and/or germinating malts and lipase are added to the liquefied liquid for synergistic saccharification, the starch syrup is obtained by filtering saccharified product and refining and concentrating filtrate; the scum obtained by filtering and pressing is washed by water, the residual sugar in the scum is obtained by filtering and pressing, and the washing liquor is used for size mixing; alkaline lipase is addedto the left washed sugar-free grains to further hydrolyze the fat in material, rice sugar-free grains protein with higher protein content is obtained by filtering and washing, and rice sugar-free grains protein is hydrolyzed by edible hydrochloric acid or protease to prepare the organic nitrogen source which can be used as the fermentation raw material of a biopharmaceutical process.