Abundant proteins associated with lecithin in soy protein isolate

A new method for fractionating acid-precipitated soy proteins, so called soy protein isolate, involving three step acidification of a water extract of defatted soy flour was developed. Soy protein isolate was shown to be mostly composed of not only β-conglycinin and glycinin, but also a group of lipophilic proteins associated with lecithin (phospholipids). The proportions of three major proteins were 23%, 46%, and 31%, respectively. The proportions changed as the nitrogen solubility index (NSI) of defatted soy flour changed. The yield of lipophilic proteins depended on the NSI of defatted soy flour, different from those of β-conglycinin and glycinin. The variation in the proportions of the three major proteins may be due to the yield of lipophilic proteins.