Integration of cross-peak contours of H/C-2’,6’ signals from prodelphinidin (PD) and of H/C-6’ signals from procyanidin (PC) units in 1H-13C HSQC NMR spectra of condensed tannins yielded nuclei adjusted PC/PD estimates that were highly correlated with PC/PD ratios obtained by thiolysis (R2 = 0.99) with benzyl mercaptan. Cis/trans flavanol ratios, obtained by integration of the respective H/C-4 cross-peak contours, were also related to determinations made by thiolysis (R2 = 0.89). The method was developed using a diverse array of 22 condensed tannin (CT) fractions from 9 plant species and fractions containing 44 to ~100 g CT/100 g fraction, PC/PD ratios ranging from 0/100 to 99/1, and cis/trans ratios from 58/42 to 95/5 as determined by thiolysis. Overall, 1H-13C HSQC NMR appears to be a viable alternative to thiolysis for estimating PC/PD and cis/trans ratios of CT if precautions are taken to avoid integration of cross-peak contours of contaminants.

Estimation of procyanidin/prodelphinidin and cis/trans flavanol ratios of condensed tannin fractions by 1H-13C HSQC NMR spectroscopy: Correlation with thiolysis

249th National Meeting (2015)

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