Effects of gluten-phenolic acids interaction on the gluten structure and functional properties of gluten and phenolic acids

Changes in gluten structure as well as in phenolic acid antioxidant properties after protein-acids complexes formation were analysed with application of spectroscopic techniques (Fourier Transform Infrared Spectroscopy, UV-VIS and fluorescence spectroscopy). Changes within gluten-acids complexes were correlated with chemical structures of acids belonging to hydroxybenzoic (4-hydroxybenzoic, protocatechuic, vanilic, syringic) and hydroxycinnamic group (p-coumaric, caffeic, ferulic, sinapic). Analysis showed that modification of gluten by hydroxybenzoic acids resulted in appearance of aggregated structures with simultaneous formation of hydrogen bonds between polypeptide chain and acid functional groups. It suggests that hydroxybenzoic acids are located between polypeptide chains. Therefore, after interaction with protein, a significant reduction in antioxidant activity of hydroxybenzoic acids was observed. Supplementation of gluten with hydroxycinnamic acids led to formation of a greater amount of pseudo-β-sheets. These acids can incorporate into gluten network less efficiently, therefore they exhibit higher antioxidant activity in the complexes, compared to hydroxybenzoic acids. Both groups of acids led to formation of greater amount of β-turns and α-helices within gluten structure which indicates that despite the fact that dough samples were taken after dough breakdown, gluten network is not completely destroyed. Basic secondary structures (β-turns and α-helices) can be stabilized by phenolic acids.