Terahertz spectroscopic identification and assignment of molecular excitations of sucrose and isomaltulose isomers

Sucrose and isomaltulose are disaccharide isomers with identical molecular formulas but distinct crystal structures and physiological functions, requiring rapid nondestructive differentiation for food quality monitoring. Here, terahertz time-domain spectroscopy (THz-TDS) was used to measure absorption spectra from 0.3 to 2.4 THz. A PCA–SVM classification model achieved 96.67% accuracy. PCA loading analysis identified 1.5–2.4 THz as the key region, where the experimentally observed characteristic peaks of sucrose (1.43, 1.64, 1.80, 2.16, 2.37 THz) and isomaltulose (1.48, 2.03, 2.18, 2.32 THz) differ systematically. DFT simulations assign these peaks to collective vibrations, including hydroxyl wagging, glycosidic torsion, and hydrogen-bond motions, originating from differences in glycosidic linkage and crystal packing. The THz-PCA-SVM method enables accurate, efficient, and interpretable identification of sugar isomers.