Effect of acid hydrolysis time on amino acid determination in casein and processed cheeses with different fat content

This work deals with hydrolysis curves for 15 amino acids (aspartic acid, threonine, serine, glutamic acid, proline, glycine, alanine, valine, isoleucine, leucine, phenylalanine, tyrosine, histidine, lysine and arginine) in bovine casein and in model-processed cheeses with 30, 45 and 60% (w/w) fat in dry matter. The effect of a different fat content on hydrolysis curves of the amino acids was observed. The hydrolysis curves were obtained by means of nonlinear regression using 13 hydrolysis intervals (range, 0-144 h). The amino acid content in hydrolysates was measured using ion exchange chromatography. Correction factors were calculated with the aim of increasing the accuracy of the amino acid determinations. With the rising fat content in samples, the correction factors increased for the majority of amino acids observed. The highest correction factors were determined for threonine, serine and tyrosine. (C) 2009 Elsevier Inc. All rights reserved.