Method for preparing soybean protein isolate

The present invention provides a method for preparing a soybean protein isolate, the method is as follows: a) counter-current extraction process, to be more specific, using a neutral-to-alkaline-range aqueous medium for counter-current extraction of defatted soybean meal for separation to remove soybean residue to obtain soybean milk; b) ultrafiltration process, to be more specific, first using an ultrafiltration membrane for concentrating the soybean milk obtained by the step a) to obtain concentrated soybean milk, then adding percolation water into the concentrated soybean milk, using an ultrafiltration membrane for percolation of the concentrated soybean milk to remove small-molecular proteins, sugar and salt to obtain a concentrated liquid, and discarding the percolate; and c) the process of neutralizing, flashing and drying, to be more specific, neutralizing, flashing and drying the obtained concentrated liquid to obtain the soybean protein isolate. The method can improve the recovery rate of the soybean