CONDENSED TANNINS INTERACTION WITH AND MODIFICATION OF WHEAT GLUTEN PROTEINS

Abstract

Proanthocyanidins (PA) strongly complex proteins, which could be exploited in food systems to modify protein polymer structures and their functionality to benefit nutrition and health. Wheat is widely consumed, and its gluten proteins are structurally favorable for interaction with PA. In this work, we investigated effect of PA of different MW on gluten protein rheology and film properties, and assessed the mechanisms behind these interactions. Polymeric PA from sorghum (mean degree of polymerization, mDP 19.5) dramatically strengthened wheat gluten; e.g., at 2.5 mg/g flour, PA doubled insoluble polymeric protein (IPP) in weak gluten flour, increased mix time by 75% and dough elasticity by 29%. Oligomeric PA from grape seed (mDP 8.3) was less effective (increased IPP by 75% and dough elasticity by 16%). Uniquely for a gluten strengthening agent, PA did not decrease dough extensibility. Polymeric PA increased gluten film strength (e.g., at 10 mg/g gluten, force to extend was 2.2X greater than control without reduced extensibility). Thus, PA may improve gluten film flexibility and structural integrity. Polymeric PA also significantly (p < 0.05) increased gluten film stability to protease enzyme degradation versus tannic acid and control, which could allow for targeted delivery of micronutrients in the gastrointestinal tract. Polymeric and oligomeric PA had equilibrium dissociation constants of 0.6 and 2.1 mol PA/mol of glutenins, respectively, indicating polymeric PA interacted with glutenins more efficiently; a similar effect was seen in gliadins. Compared to the control, polymeric PA at 30 mg/g protein decreased soluble glutenins (31%) and gliadins (20%). Within glutenins, polymeric PA decreased soluble high molecular weight glutenin subunits (HMW-GS) more so than low MW-GS (79 vs 6%) and further reduced solubility of the larger x-type HMW-GS more than y-type. Similarly, polymeric PA decreased solubility of the largest ω-gliadin fraction the most, suggesting increased complexing efficiency with higher MW gluten fractions. Surface hydrophobicity of glutenins, but not gliadins, was reduced by PA (69 – 75% vs control). Overall evidence indicates PA complexed glutenins by hydrophobic interaction and hydrogen bonding, but gliadins mainly by hydrogen bonding.