Characterization of rice glutelin fibrils and their effect on in vitro rice starch digestibility

Here we investigated and characterized the formation of thermal-induced rice glutelin fibrils at 85 °C and pH 2.0. The potential effects of rice glutelin fibrils on the in vitro starch digestibility were also evaluated. Thioflavin T fluorescence spectral analysis revealed extensive formation of rice glutelin fibrils after 4 h of incubation at pH 2.0 and 85 °C. Long, branched fibrils that were 20–45 nm in width and about 1–5 μm in length were observed by transmission electron microscopy (TEM), demonstrating a high aspect ratio of the fibrils. The resistance of rice glutelin fibrils to in vitro pepsin and pancreatin hydrolysis determined by ThT fluorescence analysis indicated that in the mixtures of fibrils-rice starch, residual fibrils could possibly mitigate the attack of amylase/amyloglucosidase on the starch and were associated with significant decreases in the starch digestion rate. Further, rice glutelin fibrils showed no in vitro cytotoxicity, supporting the potential for future applications. These findings may inspire novel protein fibril applications in low glycemic food products.