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 significant 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.