Raman and thermal (TGA and DSC) studies of gluten proteins supplemented with flavonoids and their glycosides

FT-Raman spectroscopy, thermogravimetry and differential scanning calorimetry were applied to study interactions between gluten proteins and three flavonoids and their glycosides in the model dough. As flavonoids were used quercetin, naringenin, hesperetin and their glycosides rutin, naringin, hesperidin in the amount of 0.05%, 0.1% and 0.2%. The analysis of the Raman spectra showed that the tested compounds caused changes in the secondary and tertiary structure of gluten proteins. These changes are mainly related to the molecular structure of flavonoids. Among the flavonoids, a slightly different type of changes was caused by hesperetin, which, apart from OH groups, has a OCH3 group in its structure. The changes caused by glycosides were related to the site of attachment of the glycosidic part to the aglycone. Additionally, the added polyphenols changed the conformation of the disulphide bridges. The greatest changes in the tyrosine environment were observed after the addition of quercetin and the formation of hydrogen bonds between tyrosine and this flavonoid. The tryptophan microenvironment changed under the influence of hesperetin into a more hydrophobic one. TGA results showed that the gluten network enriched in flavonoids and glycosides remained thermally stable.