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The influence and consequences of free versus protein bound amino acids on the efficacy of analytical methods
Analysis of sample protein-bound amino acids via acid hydrolysis and chromatographic identification has long been the standard method of quantitation for foods and feeds, and for an endless list of other matrices. The Association of Official Analytical Chemists, International, (AOAC) Official Methods of Analysis 982.30 (a,b,c) and 994.12 address the three separate basic steps that go into the making of a final report of uncorrected results, i.e., acid hydrolysis, oxidation of cysteine and methionine followed by acid hydrolysis, and tryptophan analysis. Little difficulty is encountered with the analysis of free supplemental amino acids, via AOAC Official Methods of Analysis 999.13, or other more suitable method that addresses a specific sample type. For samples possessing both free and protein-bound amino acids, such as complex feeds, foods, rumen supplements and samplings, digesta, hypoallergenic foods, and more, analytical quantitation of each necessitates difference methodological approaches as significant underestimation of free amino acids and total amino acids will result if solely analyzed by acid hydrolysis and reported. This presentation will discuss the influence and consequences of free versus protein bound amino acids, their analytical outcomes, the comparisons of amino acid hydrolysis curves and methods of addressing them.
Keywords: amino acids, analytical methods