Polymeric tannins significantly alter properties and in vitro digestibility of partially gelatinized intact starch granule

• Polymeric tannins form non-digestible complexes with amylose.
• Degree of starch swelling has major impact on starch-tannin interactions.
• Tannin interact more strongly with intact normal than waxy maize starch.
• Tannin-starch complexes can block digestibility of intact waxy and normal starch.
• Opportunities to utilize tannins to reduce caloric impact of starchy foods.

Excess calorie intake is a growing global problem. This study investigated effect of complexing partially gelatinized starch with condensed tannins on in vitro starch digestibility. Extracts from tannin and non-tannin sorghum, and cellulose control, were reacted with normal and waxy maize starch in 30% (30E) and 50% ethanol (50E) solutions at 70 °C/20 min. More tannins complexed with the 30E than 50E starches (mean 6.2 vs 3.5 mg/g, respectively). In the 30E treatments, tannins significantly increased crystallinity, pasting temperature, peak viscosity, and slow digesting starch (from 100 to 274 mg/g) in normal, but not waxy starch, suggesting intragranular cross-linking with amylose. Tannins doubled resistant starch (RS) to approx. 300 mg/g in both starches. In 50E treatments, tannins made both maize starches behave like raw potato starch (>90% RS), suggesting granule surface interactions dominated. Non-tannin treatments generally behaved similar to cellulose. Condensed tannins could be used to favorably alter starch digestion profile.