Rice varieties with a high endosperm lipid content have reduced starch digestibility and increased γ-oryzanol bioaccessibility

Abstract

The amount and distribution of rice endosperm lipids can influence starch digestibility and nutritional properties of white rice. However, this aspect has been poorly investigated thus far. We investigated the digestion properties of five rice varieties and common rice having different lipid contents (8.1–24.2 g kg⁻¹) showing that the lipid content is positively correlated with the resistant starch content and negatively correlated with digestion extent (C_∞) and estimated glycemic index (eGI). After non-starch lipid (NSL) removal from selected high-lipid mutants (ALK3 and RS4), C_∞ was significantly enhanced compared to native samples when digested by α-amylase, while this phenomenon was not observed in low-lipid rice (GZ93). When pancreatin was used, starch digestion was only delayed; triglycerides were gradually hydrolyzed by pancreatic lipase and the lipids–starch complex became no longer resistant to hydrolysis by α-amylase. These results indicated that rice endosperm lipids inhibited starch digestion, by transforming part of the starch into a slowly digestible starch fraction. High-lipid mutants also had a higher total amount of, and more bioaccessible, γ-oryzanol than low-lipid varieties. This study indicates that high-lipid white rice has great potential in designing functional rice-based foods, combining a relatively lower eGI and a high γ-oryzanol content.