A method is described for analysing amino acids released from food proteins by the combined but sequential action of papain and pronase E. Amino acids liberated in this way were analysed by gas-liquid chromatography (g.l.c.) as their N-trifluoroacetyl n-butyl esters. Prior to proteolysis, presolubilisation of the proteins was achieved in 0.05MHCl. Of over 30 different food proteins analysed, more than 90% of the total nitrogen was recovered, showing that the process achieved virtually complete enzymic hydrolysis with little destruction of amino acids. The amino acid data obtained by g.l.c. analysis of enzymic hydrolysates were compared to those of cation-exchange (CIE) analysis and to profiles obtained from acid, performic acid and alkaline hydrolytic procedures. Intraclass repeatability analysis was used to test reproducibility of each amino acid value within the three procedures used to obtain the profile. Although individual amino acid values differed somewhat, on the whole, there was good agreement (r=0.742) between values from g.l.c., CIE analysis of enzymic hydrolysates and CIE analysis of acid, performic acid and alkaline hydrolysates.
Journal of the Science of Food and Agriculture 10/1985; 36(10):1004 – 1012. DOI:10.1002/jsfa.2740361016