Effects of structural barriers on digestive properties of highland barley as compared with unpolished rice and oats

Abstract

Highland barley (HB), oats, and unpolished rice (UR) are known to inhibit starch digestion. β-Glucan and structural barriers are the main factors contributing to low digestibility; however, the hypoglycaemic mechanism of these grains is still unclear. Here, food systems in the forms of flour and chymes were constructed to understand their roles. There was little difference in starch digestibility for the flours of the various grains. We speculated that β-glucan in flours could not delay digestion, and the low viscosity of gelatinised HB flour supported this hypothesis. The digestibility of chymes was lower than flours, especially for HB chyme. After cooking, more bran structures and granular starch were still observed in the HB kernels. The digested grain structure showed that the starch hydrolysis level of UR and oats was higher than that of HB. Also, the starches in the bran encapsulated exhibited a good ability of anti-hydrolysis than those in the exposed endosperm. These results all indicate that intact physical structures effectively hindered gelatinisation and digestion. This study demonstrates that structural barriers exert a more important effect on starch bioaccessibility than β-glucan, which can provide useful guidance for glycaemia management.