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 optimum diet formulation and amino acid supplementation. A study was carried out to investigate the effect of hydrolysis time and method of amino acid measurement on amino acid levels. Correction factors to standardize amino acid levels to 24 h of hydrolysis were also determined. Six different soybean products were evaluated. Hydrolysis was carried out for 10 different periods of time. Amino acids were analyzed by both ion-exchange chromatography and precolumn derivatization with phenyl isothiocyanate. Both hydrolysis time and measurement method affected (P < 0.05) amino acid levels. Standard hydrolysis conditions (hydrolysis in 6 M HCl at 110 °C for 24 h) rarely provide the maximal amino acid values. Therefore, sequential hydrolyses curves were very useful and should be used. Keywords: Amino acids; soybean products; measurement methods; hydrolysis time