Starch-tannin interactions: Influence of grape tannins on structure, texture, and digestibility of starches from different botanical sources

This study investigated the effect of grape seed (GSd) and grape skin (GSk) tannins on the physicochemical, rheological properties and in-vitro digestibility of starches (corn, pea and wheat) derived from three different botanical sources. Quantification of bound and unbound tannins using MCP and HPLC analysis demonstrated that majority of the tannins were bound to starch molecules. The results of particle size distribution, starch-iodine binding and FTIR studies indicated the development of inclusion complexes through hydrophobic interactions with tannins in pea starch, while other two starches prominently formed non-inclusion complexes via hydrogen bonding. Back extrusion analysis of textural properties indicated that wheat starch-tannin complexes resulted in firmer starch-tannin gels compared to other two starches. Rheological studies revealed an increase in the viscoelastic modulus (G’ and G”) with improved elastic behavior for all starch-tannin gels. Starches complexed with tannins demonstrated strong antioxidant properties and in-vitro starch digestion studies revealed significant reductions in rapidly digestible starch (RDS) and slowly digestible starch (SDS), along with an increase in resistant starch (RS), particularly in pea starch complexed with GSd tannins. This study enhanced our understanding of how GSd and GSk tannins influence the properties of starches from various botanical origins, helping in understanding starch-tannin interactions and enabling the creation of foods with improved texture and digestibility. • Grape seed and grape skin tannins were complexed with starches from various botanical origins. • Inclusion complexes formed in pea starches and non-inclusion complexes formed in corn and wheat starches. • Grape seed and skin tannins improved the elastic behavior of starch gels. • Grape seed and skin tannins increased the antioxidant properties and reduced the digestibility of starches.