Comparison of Chromatographic and Titrimetric Methods for the Determination of the a-amino Nitrogen in Standard Solution and Fish Protein Hydrolysates

Two analytical methods, reverse phase high-performance liquid chromatography (RP-HPLC) and formol titration, were compared for their accuracy and precision for the determination of a-amino nitrogen (a-AN) concentration in fish protein hydrolysates. The result showed that, when tested with pure amino acid solutions, RP-HPLC method had a better standard deviation (S. D.), coefficient of variation (C. V.), and standard error (S. E.) but a poorer recovery rate compared with formol titration technique. The observed a-AN value by RP-HPLC has good coincidence with the actual a-AN value and their correlation coefficient (r) is 0.9981, which was close to the r value (0.9995) between the a-AN by formol titration and the actual a-AN. However, when tested with protein hydrolysates, the a-AN obtained from RP-HPLC technique were significantly (p<0.05) lower than that from formol titration for the same sample. Therefore, the formol titration method can be used as a quick screening method to assess the quality fish hydrolystaes.