The influence of hydrochloric acid concentration and measurement method onthe determination of amino acid levels in soya bean products

Accurate determination of amino acid levels in soya products facilitates op timum diet formulation and amino acid supplementation. A study was carried out to investigate the effect of hydrochloric acid (HCl) concentration and method of amino acid measurement on the measurement of amino acid levels. S ix different soya bean products were evaluated. Hydrolysis was carried out with five different acid concentrations (1, 3, 6, 9 and 12 M HCl). Amino ac ids were analysed by both ion-exchange chromatography with ninhydrin detect ion and pre-column derivatisation with phenyl isothiocyanate. Both acid con centration and measurement method affected (P < 0.05) measurements of most amino acids. Standard hydrolysis conditions (hydrolysis in 6 M HCl at 110<d egrees>C for 24 h) rarely provided the maximal amino acid values, and thus, correction factors were calculated to standardise amino acid levels by div iding the maximum value by the value obtained with 6 M HCl. Therefore, when determining amino acid concentrations, the patterns of release and degrada tion of amino acids, as well as correction factors, should be considered to obtain the most accurate values. (C) 2000 Elsevier Science B.V. All rights reserved.