1H–13C HSQC NMR Spectroscopy for Estimating Procyanidin/Prodelphinidin and cis/trans-Flavan-3-ol Ratios of Condensed Tannin Samples: Correlation with Thiolysis

Zeller, W. E., Ramsay, A., Ropiak, H. M., Fryganas, C., Mueller-Harvey, I., Brown, R. H., Drake, C. and Grabber, J. H. (2015) 1H–13C HSQC NMR Spectroscopy for Estimating Procyanidin/Prodelphinidin and cis/trans-Flavan-3-ol Ratios of Condensed Tannin Samples: Correlation with Thiolysis. Journal of Agricultural and Food Chemistry, 63 (7). pp. 1967-1973. ISSN 1520-5118 doi: 10.1021/jf504743b

Abstract/Summary

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–∼100% CT, PC/PD ratios ranging from 0/100 to 99/1, and cis/trans ratios ranging from 58/42 to 95/5 as determined by thiolysis with benzyl mercaptan. Integration of cross-peak contours of H/C-6′ signals from PC and of H/C-2′,6′ 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.