Effect of hydrolysis time on the determination of amino acids in samples of soybean products with ion-exchange chromatography or precolumn derivatization with phenyl isothiocyanate

Accurate determination of amino acid levels in soy products facilitates opt imum diet formulation and amino acid supplementation. A study was carried o ut to investigate the effect of hydrolysis time and method of amino acid me asurement on amino acid levels. Correction factors to standardize amino aci d levels to 24 h of hydrolysis mere also determined. Six different soybean products were evaluated. Hydrolysis was carried out for 10 different period s of time. amino acids were analyzed by both ion-exchange chromatography an d precolumn derivatization with phenyl isothiocyanate. Both hydrolysis time and measurement method affected (P < 0.05) amino acid levels. Standard hyd rolysis conditions (hydrolysis in 6 M HCl at 110 degrees C for 24 h) rarely provide the maximal amino acid values. Therefore, sequential hydrolyses cu rves were very useful and should be used.