Tannin levels and their degree of polymerisation and specific activity in some agro-industrial by-products

Tannins were determined by various chemical and biological methods in 15 agro-industrial by-products. Tannins in terms of total phenols (TP), condensed tannins (CT) and protein-precipitation capacity (PPC) were very high in Acacia nilotica and Theobroma cacao pods, Mangifera indica seed kernel, Panicum miliaceum polish and cakes of Madhuca indica seed and Garcinia indica. The correlation coefficients of PPC (measure of biological activity) with TP (0·81), degree of polymerisation (−0·83) and protein-precipitable phenolics (0·96) were significant (P < 0·05), but that with CT (0·34) was not significant. It is inferred that TP rather than CT contribute significantly towards PPC and that highly-polymerised tannins do not bind proteins as efficiently as the lesser-polymerised ones.

The TP and CT were low in pods of Prosopis juliflora and Pithecolobium saman, Cassia tora seeds, cakes of Guizotia abyssinica, Pongamia glabra, Schleichera oleosa, Hevea brasiliensis and Hibiscus cannabinus and Panicum miliaceum bran. The PPC could not be detected in these by-products, suggesting that these nine by-products can be considered safe for incorporation in livestock feed, subject to absence of other deleterious factors.