| Abstract: | ![]()
The precipitation of protein by condensed and hydrolysable tannins was evaluated with the radial diffusion method of Hagerman (1987) using bovine serum albumin (BSA) and isolated leaf protein from fresh alfalfa (Medicago sativa). Alfalfa leaf protein (AALP) was included at two concentrations, 25 and 156 mg N litre-1, at pH 6·8 and 39°C to simulate rumen conditions. The condensed tannins were purified from lyophilised samples of Arachis pintoi, Desmodium ovalifolium, Gliricidia sepium, Manihot esculenta and quebracho (Schinopsis balansae). Hydrolysable tannins from tannic acid (TA) were used as well. There was a significant interaction (P<0·001) between tannin and protein source, and protein level on protein precipitation. Most purified condensed tannins (CTs) precipitated more AALP than BSA when protein was included at the same level. Purified CT from quebracho and hydrolysable tannin from TA failed to precipitate AALP at both protein levels. In a second experiment, tannins from crude plant extracts were studied in the radial diffusion method using BSA and two levels of AALP. The crude plant extracts were obtained from lyophilised plant samples of A pintoi, Centrosema macrocarpum, Clitoria ternatea, D ovalifolium, Erythrina berteroana, E poepigiana, G sepium, M esculenta, Pueraria montana and P phaseoloides. The protein precipitated by soluble tannins in the plant samples was correlated to the total phenolic content and to the soluble CT estimated by the acid butanol assay or by the radial diffusion method. Tannins from different plant species precipitated different amounts of BSA and AALP. Therefore, the measures of the biological activity of tannins based on BSA precipitation may not reflect the ability of tannins to precipitate proteins of plant origin such as those commonly found in the diets of herbivores. The present study offers the possibility of using the radial diffusion method with plant proteins at precipitation conditions similar to those in the rumen. © 1997 SCI. |
