Understanding the structure and digestibility of heat-moisture treated starch

• HMT transformed RDS into SDS and RS for both regular and high-amylose starches.
• HMT induced more intense structural disorganizations for high-amylose starch.
• HMT was more effective at inducing molecular rearrangements for high-amylose starch.
• With HMT, high-amylose starch exhibited a greater increase in the SDS + RS content.

To rationalize the effects of heat-moisture treatment (HMT) on starch digestibility, the HMT-induced alterations in the mesoscopic and molecular scale structures of regular and high-amylose maize starches, as well as in their digestibility, were evaluated. Accompanying the supramolecular structural disorganizations and certain molecular degradation induced by HMT, somewhat molecular rearrangements occurred to probably form densely packed starch fractions, which eventually weakened starch digestion and thus transformed RDS into SDS and RS for regular and high-amylose starches. Interestingly, due to its larger amount of inter-helical water molecules that could be induced by HMT, B-polymorphic high-amylose starch was more susceptible to HMT (relative A-polymorphic regular starch), causing more prominent structural evolutions including molecular re-assembly and thus increasingly slowed digestion. In particular, the treated high-amylose starch with 30% moisture content showed a high SDS + RS content (48.3%). The results indicate that HMT-treated starch may serve as a functional ingredient with adjustable enzymatic digestibility for various food products.