Non-starch constituents influence the in vitro digestibility of naked oat (Avena nuda L.) starch

The present study investigated the effects of proteins, lipids and beta-glucan in naked oat flour (NOF) on the in vitro digestibility of starch. The content of rapidly digested starch (RDS) increased, and the content of resistant starch (RS) decreased in NOF after removing the non-starch constituents. The estimated glycemic index (eGI) of starch in NOF increased after the removal of the non-starch constituents, with a decreasing order of naked oat starch (NOS) > de-beta-glucan flour > de-proteins flour > de-lipids flour > NOF. NOS was found to have an A-type crystalline pattern, but the removal of proteins or beta-glucan rendered NOS a V-type crystalline pattern. The relative crystallinity decreased after removing non-starch constituents. The in vitro digestibility was positively correlated with the short-range molecular order and negatively correlated with the relative crystallinity. These results clearly illustrate the effects of non-starch constituents on the low digestibility of naked oat.