ANALYSIS OF PROTEIN HYDROLYSATES .2. CHARACTERIZATION OF CASEIN HYDROLYSATES BY A RAPID PEPTIDE QUANTIFICATION METHOD

Casein hydrolysates prepared in the laboratory or purchased from a manufacturer were characterized for the proportion of amino acids in free form, in short-chain (di- and tripeptides) or larger peptides. The hydrolysates were fractionated be size exclusion chromatography on a poly(2-hydroxyethylas-partamide)-silica column (PHEA), and the fractions were analyzed by amino acid analysis. This led to an accurate characterization of hydrolysates which allowed a classification of the hydrolysates according to the extent of hydrolysis and their nutritional quality. A rapid method for quantifying peptides in SE-HPLC fractions was also proposed. It was based on UV absorbance measurement at 230 nm, with a correction for the absorbance of aromatic amino acid measured at three wavelengths (230, 280, and 300 nm). A good correlation was obtained between corrected areas and the amino acid analysis. Because of nonideal size exclusion behavior on the PHEA column, further analysis of free amino acids would be required to correct the data obtained from the chromatographic patterns. The quantitative technique described here proved to be a valuable tool for characterizing unknown protein hydrolysates.