Protein precipitating capacity of phenolics of wild blueberry leaves and fruits

Phenolics (PP) were extracted from blueberry leaves and fruits with 70% (v/v) acetone and 95% (v/v) ethanol. The lyophilized crude PP extract was then fractionated on a Sephadex LH-20 column using first 95% (vv) ethanol as a mobile phase for elution of fraction of phenolics low in tannins then 50% (v/v) acetone to elute fraction rich in condensed tannins. Bovine serum albumin (BSA) was effectively precipitated by crude PP extracts at pH values between 4 and 5. A statistically significant (P < 0.05) linear relationship exists between the amount of PP–protein complex precipitated and the amount of PP added to the reaction mixture. The slope values of these lines indicated the tannin-rich fractions of crude PP extracts to be more effective protein precipitants than the other examined fractions. Based on the amount of gelatin, fetuin and BSA required to inhibit the formation of the dye-labeled BSA-PP complex by 50%, gelatin was 4–15 times more effective as a precipitation inhibitor than unlabeled BSA and fetuin.