Molecular weight and protein-precipitating ability of condensed tannins from warm-season perennial legumes

The beneficial effects of forages containing condensed tannins (CTs) on ruminants are well documented, but the chemical features of CT that yield benefits have not been defined. Some evaluations of limited numbers of highly purified compounds have resulted in positive correlations between CT molecular weight (M_W) and biological activity, while others have failed to show a correlation. The objectives of this study were to determine if M_W of CT could predict biological activity relative to protein precipitability. M_W of condensed tannin, protein-precipitable phenolics (PPP), and the amount of protein bound (PB) were determined for nine species of warm-season perennial legumes. There was no correlation between PPP or PB and M_W (R² 0.11 and R² 0.02, respectively). However, CT concentration did correlate with PPP and PB (R² 0.81 and R² 0.69, respectively). It was concluded that CT M_W does not explain the variation in protein precipitation by CT from the forage legumes surveyed.