Resistant-type starch in sorghum foods-factors involved and health implications

Abstract

Sorghum grain has a higher content of resistant starch (RS) than other cereals and seems to be more slowly digestible. However, people consume foods where the grain has been processed by thermal and other treatments. This review addresses whether sorghum foods generally have unusually high levels of RS and slowly digestible starch (SDS), what intrinsic factors are responsible and how processing conditions affect RS and SDS, and the health-related implications of sorghum food consumption. With non-tannin type sorghums, if the endosperm structure is little disrupted during food processing, as with conventional wet cooking, then the food can exert positive health effects on glycemic response related to its high RS content. Thermally induced cross-linking of the kafirin matrix proteins appears to be responsible for the low starch digestibility. However, when non-tannin sorghum is processed using high-shear technologies like extrusion cooking, the endosperm, and starch granule structure are disrupted, rendering the starch fully digestible. Regarding tannin-type sorghums, the tannins have a strong inhibitory effect on starch digestibility, notably by binding with the starch, which can improve glycemic response and other health related parameters. Future research on RS in sorghum foods must focus on the mechanisms responsible and interactions between intrinsic- and processing-related factors.