Rapid structural characterization of tobacco hemicellulose via non-uniform sampling accelerated 2D HSQC NMR

Hemicellulose structure strongly affects the high-value utilization of agricultural wastes, rendering its characterization critical. In this research, hemicellulose was extracted from tobacco using deep eutectic solvents (DESs), and a rapid structural characterization method was established by integrating Non-Uniform Sampling (NUS) with 2D heteronuclear single quantum coherence NMR (2D HSQC NMR). Structural differences of hemicellulose in tobacco leaves, stems, stalks, and roots were revealed. Three DESs-choline chloride-monoethanolamine (C-M), choline chloride-glycerol (C-G), and choline chloride-formic acid (C-F)-were compared. The C-M system achieved the highest hemicellulose yield, removal rate, and optimal structural preservation. After optimizing temperature, time, and solid-liquid ratio for C-M, a yield of 63.97% was attained. 2D HSQC NMR results at NUS ratios of 40%, 35%, 30%, 25%, and 20% were assessed, with 25% selected as optimal. This 25% NUS/2D HSQC NMR method outperformed conventional 2D HSQC NMR in spectral resolution, experimental duration, and structural information content, shortening NMR time by approximately fivefold with relative errors of 0.12%-1.26%. Through the established method, it was revealed that tobacco leaves exhibited a coexisting structure of arabinogalactan (AG) and glucuronoarabinoxylan (GAX), stems were primarily dominated by glucuronoarabinoxylan (GAX), and both stalks and roots were predominantly characterized by a glucuronoxylan (GX) structure. This NUS/2D HSQC NMR method enabled rapid, accurate hemicellulose characterization, providing an efficient analytical tool for the high-value utilization of agricultural wastes.