1H-13C HSQC NMR spectroscopy for estimating procyanidin/prodelphinidin and cis/trans flavanol ratios of condensed tannin fractions: correlation with thiolysis. J. Agric. Food Chem. 2015, 63, 1967−1973
Zeller, W.E., Ramsay, A., Ropiak, H.M., Fryganas, C., Mueller-Harvey, I., Brown, R.H., Drake, C., Grabber, J.H.
ABSTRACT: Studies with a diverse array of 22 purified condensed tannin (CT) samples from nine plant species demonstrated that procyanidin/prodelphinidin (PC/PD) and cis/trans-flavan-3-ol ratios can be appraised by 1H-13C HSQC NMR spectroscopy. The method was developed from samples containing 44 to ~100% CT, PC/PD ratios ranging from 0/100 to 99/1, and cis/trans ratios from 58/42 to 95/5 as determined by thiolysis with benzyl mercaptan. Integration of cross-peak contours of H/C-6ˈ signals from PC and of H/C-2ˈ,6ˈ signals from PD yielded nuclei adjusted estimates that were highly correlated with PC/PD ratios obtained by thiolysis (R2 = 0.99). Cis/trans-flavan-3-ol ratios, obtained by integration of the respective H/C-4 cross-peak contours, were also related to determinations made by thiolysis (R2 = 0.89). Overall, 1H-13C HSQC NMR spectroscopy 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.