A multi-glycomic tool for characterization of resistant starch

Resistant starch (RS) escapes digestion in the small intestine and is fermented by the gut microbiota in the colon, producing short-chain fatty acids that modulate human health. Although the physiological impacts of RS are well studied, the chemical structure that results in digestion resistance remains unclear. In this study, we coupled an enzymatic starch digestion assay and liquid chromatography-mass spectrometry (LC-MS) to elucidate RS structure. RS was isolated using a commercially available enzyme assay and analyzed by glycosidic linkage profiling. We applied this workflow to commercial standards and commonly consumed high-starch foods. Based on the glycosidic linkage results, we generated ratios to represent the chain length and branching frequency of starch. Starches with high RS content are characterized by high (4-Glc)/(T-Glc) ratio and low (4,6-Glc)/(4-Glc) ratio. The production of α-limit dextrin post enzymatic digestion also contributes to starch resistance. Application of this method to actual food samples revealed that many starch-rich staple foods exhibit amylopectin-like structures and were low in RS while whole grain products contained more diverse polysaccharides that affect starch digestion.