Linkage-resolved profiling of isomalto-oligosaccharides using porous graphitic carbon liquid chromatography–orbitrap tandem mass spectrometry

The digestibility and glycemic response of isomalto-oligosaccharides are determined by their glycosidic linkage and chain length. However, linkage-resolved profiling beyond tetrasaccharides remains limited. Herein, forty structures from disaccharides to hexasaccharides in eight commercial materials were characterized using porous graphitic carbon liquid chromatography-Orbitrap tandem mass spectrometry. Linkage profiles were dominated by α-1 → 6 and α-1 → 4, displaying a chain-length-dependent shift. Generally, α-1 → 4 linkages accounted for ∼10% of total linkages in disaccharides, rising to ∼80% in hexasaccharides. In one sample, α-1 → 4 linkages were 1.6-fold more abundant than α-1 → 6. With contents of 62.5-81.5%, no product met the European Food Safety Authority description for isomaltose plus trisaccharide-nonasaccharide content (≥90% dry basis). Even in products labeled "total isomalto-oligosaccharides ≥90% (dry basis)," α-1 → 6 linkages accounted for only ∼50% of glycosidic linkages. This suggests the need for linkage-resolved isomalto-oligosaccharide labeling frameworks that extend beyond total content claims to more precisely reflect the digestibility and glycemic impact.