Interaction of tannins and other sorghum phenolic compounds with starch and effects on in vitro starch digestibility.

This study investigated interactions of sorghum proanthocyanidins (PAs) with starch molecules and the effect on in vitro starch digestibility. High tannin (predominant in PA), black (monomeric polyphenols), and white (low in polyphenols) sorghum phenolic extracts were mixed and cooked with starches varying in amylose content. Starch pasting properties, polyphenol profile, and resistant starch (RS) were determined. PAs decreased setback of normal starch and were least extractable after cooking with all starches. Pure amylose interacted more strongly with oligomeric and polymeric PA compared to amylopectin. The PA extract increased the net RS in normal starch by about 2 times more than the monomeric polyphenol extract; debranching amylopectin increased the difference by 4.3 times. Only treatments with PA increased RS in high amylose starch (52% higher than the control). Sorghum PAs interact strongly with starch, decreasing starch digestibility. The interactions appear to be specific to amylose and linear fragments of amylopectin, suggesting hydrophobic interactions are involved.