Effects of microwave treatment on sorghum grains: Effects on the physicochemical properties and in vitro digestibility of starch

Abstract Microwave processing has attracted much attention in the field of cereal processing due to its positive effect on improving the nutritional quality of cereals and prolonging the shelf life of cereal food. Microwave (MW) treatment (600 W, 6 min) was studied to evaluate its effect on the physicochemical properties and in vitro digestibility of three kinds of sorghum ( Sorghum bicolor [L . ] Moench ) starch, including Longmiliang No. 1 (LML1), Longza No. 13 (LZ13), and Hongnuo (HN). After microwave treatment, the contents of insoluble dietary fiber, soluble dietary fiber and total dietary fiber of the three kinds of sorghum were significantly increased by 3.72–7.45 g/100 g, 0.33–0.64 g/100 g, and 4.36–7.78 g/100 g, respectively. Microwave treatment also resulted in sorghum starch granules with rough surfaces, an increase in pasting temperature and pasting time, and a decrease in pasting viscosity and transition enthalpy ( p < .05). However, Fourier transform near infrared spectroscopy showed that microwaves did not change the chemical groups of sorghum starch. Additionally, after microwave treatment, the in vitro digestibility of sorghum starch was significantly reduced by 3.21–6.61%, the rapidly digestible starch content decreased by 5.88–9.24%, the slowly digestible starch and resistant starch contents increased by 4.63–6.65% and 1.03%–2.41%, and the hydrolysis index (HI) and glycemic index (GI) decreased by 4.98–5.74% and 2.73–3.15%, respectively. These results indicate that microwave treatment is an effective method for decreasing the in vitro digestibility and improving the physicochemical properties of starch. Practical applications Sorghum, as an important raw material in the food industry, plays an irreplaceable role in the development of cereal food. Additionally, microwaves have been used as a novel approach for improving the edible quality and functional characteristics of cereals. A comparative study of the microstructure, pasting properties, thermal properties, and in vitro digestion of sorghum starch was performed. The results showed that compared with the original starch, microwave treatment changed the physicochemical properties of sorghum starch and decreased the GI. The results can be used to improve the properties of sorghum starch and provide a theoretical basis for the development of sorghum food.