Monitoring in-vitro digestion of rice starch using capillary electrophoresis online

Starch digestion is integral to human nutrition and starch digestibility can have a profound impact on an individuals’ health. For example, resistant starches are promoted to combat obesity due to their resistance to digestion. Human in vivostarch digestibility assays such as the widely used glycaemic index (GI) are expensive and prone to generation of variable data. The blood glucose response to any food varies widely in large part because of the wide metabolism variability between individuals. For these reasons, more reproducible in vitro digestibility assays with relatively few tightly controlled components have been developed to generate equivalent results to in vivo GI. However, these methods are typically end-point assays which only monitor glucose. Capillary electrophoresis (CE) with direct UV detection was shown to be robust when quantifying sugars released from in vitro digestion of heterogeneous breakfast cereals offline and sugar consumption during fermentation. In this study, CE with direct UV detection was applied to measure glucose as a starch digestibility marker, and glucose precursor intermediatesugars, maltotriose and maltose as alternative starch digestibility markers that may further our understanding of starch digestibility. The release of these sugars was monitored with CE from in vitro digested rice starch online with little to no sample preparation. The protocol was robust and precise using various hydrolytic enzymes. It identified sugars with ≤1% relative standard deviation (RSD) and quantified sugars with ~10% RSD. We envision this method will have an application in the determination of in vitro glycaemic response and in vitro glycaemic potential between different rice varieties and other starchy foods and provide new insights into the kinetics of in vitro starch digestion which can complement in vivo starch digestibility assays.