HSQC‐NMR‐based profiling approaches for raffinose family oligosaccharides in pulses

Background and Objectives
Due to insufficient resolution, $^{1}$H nuclear magnetic resonance (NMR) spectroscopy-based methods are limited to quantify carbohydrates. In the past, heteronuclear single quantum coherence (HSQC)-based methods were demonstrated to be superior as the second dimension greatly improves resolution. However, whether these experiments are also suitable to determine structurally similar oligosaccharides such as raffinose family oligosaccharides (RFO) still needs to be demonstrated.

Findings
By optimizing NMR parameters, well resolved signals for the analysis of glucose, fructose, galactose, sucrose and the RFO raffinose, stachyose, and verbascose were identified. Application of fast HSQC methods in combination with nonuniform sampling enables analyses of sucrose and RFO in pulses (blue lupin seeds, red lentils, kidney beans) within 24 min. If the analytes are present at levels greater than 0.5 g/100 g, HSQC-based methods provide data equivalent to an anion-exchange chromatography-based reference method.

Conclusions
High resolution fast HSQC-based approaches are suitable tools to analyze complex carbohydrate mixtures as demonstrated for RFO in different pulses.
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Significance and Novelty
Fast HSQC experiments were applied for the first time to analyze structurally similar oligosaccharides. In the future, this approach will be a most valuable tool to analyze complex mixtures of carbohydrates in food products.