The identification by 1H- and 13C-n.m.r. spectroscopy of sucrose, 1-kestose, and neokestose in mixtures present in plant extracts

✍ Scribed by André De Bruyn; Jan Van Loo

• Publisher: Elsevier Science
• Year: 1991
• Tongue: English
• Weight: 367 KB
• Volume: 211
• Category: Article
• ISSN: 0008-6215
• DOI: 10.1016/0008-6215(91)84151-4

✦ Synopsis

In the food industry, a knowledge of the presence and proportions of certain sugars in vegetables is important. In seeking to ascertain the presence of sucrose, l-kestose (1, isokestose), and neokestose (2) in enriched mixtures extracted from vegetables without isolating the individual sugars, we have found that 13C-and, to a limited extent, 'H-n.m.r. spectroscopy is the method of choice. The analysis depends on the unequivocal assignment of the n.m.r. spectra.

The relevant 'H-and the complete '3C-n.m.r. data for sucrose, 1-kestose, and neokestose are given in Tables I andII, respectively.

'H-N.m.r. data for sucrose have been published'Y2, but because of the complexity of the spectra, only partial data for isokestose and neokestose have been obtained. However, these data are useful.

'H-N.m.r. data for sucrose octa-acetate and 1-kestose hendeca-acetate have been reported3, as have those for trimethylsilylated sucrose, I-kestose, 6-kestose, and neo-kestose4. Because of the complexity of the spectra, only the relevant data extracted from the spectrum of I-kestose and neokestose are given. The data for neokestose were extracted from the spectrum of an enriched extract of onion that contained l-kestose (1) and neokestose ( 2) in the ratio 3: 1. The presence of neokestose and I-kestose in onions has been shown by several authors>'. The chemical shift of the H-l resonance of the a-D-glucopyranosyl moieties are S 5.44 (1-kestose), 5.42 (sucrose), and 5.40 (neokestose). The resonance of H-3 in neokestose is at 0.05-0.06 p.p.m. to lower field than the corresponding resonance for the two other oligosaccharides. The chemical shifts of the H-3,4 resonances of the p-D-fructofuranosyl moieties are diagnostic, namely, 4.25 (d) and 4.06 (t) for sucrose, 54.28 and 4.22 (2 d for H-3) and * Author for correspondence.