Composition of condensed tannins from Calliandra calothyrsus and correlation with in sacco digestibility

Abstract

Calliandra calothyrsus accessions differ widely in digestibility for livestock. It is not clear, however, whether this is related to differences in condensed tannin levels or to other factors. Condensed tannins (CT) were extracted from seven different accessions of C. calothyrsus, and were examined for protein binding, pH stability of protein tannin complexes and CT composition. The compositional data was correlated with dry matter and nitrogen digestibility in sacco. Calliandra CT formed insoluble complexes with casein, bovine serum albumin and rubisco protein in an approximate ratio of 1:2 (w/w, tannin:protein) and the insoluble complexes were relatively stable to pH within the range of pH from 2.5 to 8.0. Polymeric proanthocyanidins were associated with both insoluble and soluble protein fractions, but the flavonols and flavonol glycosides were only associated with the soluble fraction. Total CT from each accession was fractionated by SepPak C18 reverse phase column chromatography into phenolic acids, monomers, oligomers/flavonols and polymeric proanthocyanidin fractions and quantified as total phenolics. There was wide variation between fractions across the seven accessions. Fractionation data were correlated with dry matter and nitrogen digestibility in sacco for each accession. Correlations were strongly negative (−0.799) and strongly positive (+0.800) for oligomers/flavonols and polymeric proanthocyanidins, respectively. Fractions were analysed by HPLC and by acid degradation in the presence and absence of phloroglucinol; the data show that across seven different accessions of calliandra, the composition of condensed tannins differed widely. The data suggest that for calliandra, total phenolics is not a good predictor of digestibility, and that the concentration of oligomers/flavonols or the ratio of polymers to oligomers may be more indicative.