γ‐GLUTAMYL DIPEPTIDE CONTENT IN SOYBEAN PROTEIN PRODUCTS AND OTHER COMMODITIES

The amount of γ-glutamyl dipeptides (γ-glutamyl tyrosine and γ-glutamyl phenylalamine) present in soybeans and other commodities was measured by a method consisting of alcohol extraction, preliminary purification and determination with an automated amino acid analyzer. Defatted soybean flakes of four varieties and one commercial sample contained 1.17–1.60 mg of the dipeptides per g. Most of the dipeptides in soybean concentrates and isolates were lost through processing. Corn, wheat, cottonseed meal, pork, beef, chicken and lamb appeared to contain only traces, but peanut flour has a content of 0.20 mg per g. The method adequately measures 50 μg of the dipeptides and recovers more than 95% of γ-glutamyl phenylalanine standard added to samples of soybean flour and meat-soybean flour mixtures.