Protein precipitating capacity of condensed tannins of beach pea, canola hulls, evening primrose and faba bean

Condensed tannins (CT) from beach pea, Cyclone canola hulls, evening primrose and faba bean were extracted into 70% (v/v) aqueous acetone. The lyophilized extracts were then purified on a Sephadex LH-20 column using first 95% ethanol as a mobile phase for elution of non-tannin phenolics and then 50% aqueous acetone to elute CT. Condensed tannins isolated from beach pea possessed shorter polymer chains than those isolated from canola hulls, evening primrose or faba bean. Bovine serum albumin (BSA) was effectively precipitated by beach pea CT at pH values between 3.5 and 5.0. CT of canola hulls, evening primrose and faba bean precipitated BSA at pH 4.0–5.0. A statistically significant (P=0.0001) linear relationship existed between the amount of tannin-protein complex formed and the amount of CT added to the reaction mixture. The slopes of these lines indicated that evening primrose CT were the most effective protein precipitants, followed by canola hulls, faba bean and beach pea CT. Based on the amount of gelatin and BSA required to inhibit 50% of dye-labelled BSA-CT complex precipitation, gelatin was 10 times more effective as a precipitation inhibitor than unlabelled BSA.