Polyphenol-induced protein structural modifications in sorghum on pasting properties

Black sorghum contains a high amount of anthocyanins and proanthocyanidins, whereas white sorghum predominantly comprises phenolic acids. Polyphenols covalently and non-covalently interact with protein, whereas the structure of both compounds affects these interactions. This study investigated the interactions between phenolic acids, anthocyanins, proanthocyanidins and prolamin, which is the major protein fraction in sorghum, and their effect on the pasting properties of white and black, whole and milled sorghum using different chemical agents. Urea increased the pasting viscosity of black sorghum, but not that of white sorghum, indicating that hydrogen bonds and hydrophobic interactions between prolamin and anthocyanins and proanthocyanidins play an important role in the viscosity development of black sorghum. The addition of sodium chloride (NaCl) and guanidium hydrochloride (GdnHCl) enhanced the peak viscosity of all samples. Proanthocyanidins increased the molecular size, diminished the α-helical structure, and altered the tertiary structure of prolamin, which may have decreased the breakdown viscosity of black sorghum in the presence of dithiothreitol (DTT) and in both acidic and alkaline environments. Polyphenol-protein interactions in black sorghum may, therefore, be used to develop clean-label ingredients to improve paste stability in starch-based products. • Polyphenol-protein interactions enhance paste stability of black sorghum. • Polyphenols had no effect on the molecular weight of prolamin. • Phenolic acids did not affect the prolamin structure. • Proanthocyanidins increased the molecular size of prolamin. • Proanthocyanidins altered the secondary and tertiary structure of prolamin.