EVALUATION OF LIQUID-CHROMATOGRAPHIC ANALYSIS OF NUTRITIONALLY IMPORTANT AMINO-ACIDS IN FOOD AND PHYSIOLOGICAL SAMPLES

Significant advances have been made in standardizing methods for amino acid analysis of foods. The methods included standardized hydrolysis of the food proteins followed by separation and quantitation of the re leased amino acids by ion-exchange chromatography (IEC). IEC is still the main method in use. Its use is, however, being replaced by the fas ter high-performance liquid chromatographic (HPLC) methods of derivati zed amino acids. The HPLC separation of precolumn phenylisothiocyanate (PITC) derivatives has been adapted for rapid analysis of all amino a cids in protein hydrolysates (12 min) and nutritionally important amin o acids in deproteinized physiological samples (20 min). The inter-lab oratory variability of the PITC derivatization method has not been det ermined although the intra-laboratory variation of the HPLC method was found to be similar to that of IEC. When similar hydrolytic condition s were used in preparing protein hydrolysates, amino acid results obta ined with the PITC derivatization method were generally in close agree ment with those obtained by IEC. There is, however, room for improveme nt in the HPLC analysis of amino acids in physiological samples.