Cereals & Grains Association
Log In

Interactions Involved in the Formation of Starch-Tannin Complexes

Amylose–tannin interactions have promising potential to be utilized to modulate glucose metabolism and reduce the calorie density of starch-based foods. However, knowledge on the specific interaction mechanisms involved is lacking. Starch-tannin complexes were formed by incubating sorghum tannin extract with normal and waxy maize starch, in 30% (30E) and 50% (50E) ethanol solutions at 70°C/20 mins. The complexes were reacted with urea (2-6 M) and dioxane (10-15% v/v of water) to evaluate the contribution of H-bonding and hydrophobic interactions to starch-tannin complexes, respectively. The controls and treatments were analyzed for<i> in-vitro</i> digestibility (Rapidly Digestible Starch – RDS, Slowly Digestible Starch – SDS, Resistant Starch, RS) and Proanthocyanidins (PA) content and distribution. Urea reduced SDS by 58% and increased RDS by 55% in 30E normal maize. Dioxane showed a similar trend, but to a lesser extent (28% decrease in SDS and 20% increase in RDS). In 50E, urea increased RDS (mg/g starch) from 19 – 50 mg/ g to 432 – 602, and decreased RS from 810 - 870 to 306 – 398 mg/ g. Dioxane also increased RDS to 91 – 197 mg/ g of starch and decreased RS to 394 – 706 mg/g of starch. Amount of PA (mg/g of starch) released from the starch-tannin complex in 30E was slightly higher in urea (PA = 5.3 – 6.7) than dioxane (PA= 4.3 - 5.5).  In 50E, however, dioxane released higher PA (~ 1.3 – 1.5) than urea (~ 0.8 – 1.0). H-bonding appears to be dominant in starch-tannin interactions, with hydrophobic interactions also playing an important role.