HPAEC-PAD analysis for determination of the amino acid profiles in protein fractions from oat flour combined with correction of amino acid loss during hydrolysis

Current derivatization-dependent approaches for amino acid composition analysis of cereal proteins have sig-nificant variability due to lack of direct analysis opportunities and loss of amino acids during protein-hydrolysis. To tackle these drawbacks, a novel direct, derivatization-free approach was successfully introduced, using HPAEC-PAD, and applied for analysis of hydrolyzed defatted oat flour and extracted flour protein fractions. The approach ensured reliable detection of amino acids, including L-tryptophan, as well as oxidation products of L-cysteine and L-methionine. A time course study, analysed by nonlinear least-square regression to determine rates of hydrolysis and loss of each amino acid, allowed comparison of the original mass fraction (AA0) of the respective amino acid in the oat flour mixture with the mass fraction obtained after 24 h hydrolysis (AA24). The difference between (AA0) and (AA24) was less than 0.05%, except for L-arginine (0.61%), glycine (0.14%), L-isoleucine (0.27%), and L-tryptophan (0.17%). The (AA0)s obtained corresponded to literature-data, and fitted with the amino acid composition estimated from deduced proteins encoded in the oat genome, except for L-arginine (27%) and L-glutamic acid/L-glutamine (10%). The amino acid composition estimation from sequence data indirectly confirmed that the high presence of L-arginine observed was a result of co-elution with unknown flour components.

Automated summary

Current derivatization-dependent approaches for amino acid composition analysis of cereal proteins have significant variability, but a novel direct, derivatization-free approach using HPAEC-PAD was successfully introduced for analysis. The approach ensured reliable detection of amino acids and oxidation products. Comparison of the original mass fraction of amino acids with the mass fraction obtained after hydrolysis showed small differences, except for a few specific amino acids. The amino acid composition estimation from sequence data indirectly confirmed the presence of unknown flour components.