The Oxidative Activity of Ellagitannins Dictates Their Tendency To Form Highly Stabilized Complexes with Bovine Serum Albumin at Increased pH.

Many food and forage plants contain tannins, high molecular weight polyphenols that characteristically interact strongly with protein, forming complexes that affect taste, nutritional quality, and the health of the consumer. In the present study, the interaction between bovine serum albumin (BSA) and each of seven hydrolyzable tannins or epigallocatechin gallate was examined. The objective was to define the effect of tannin oxidation, measured as oxidative activity (browning) or as oxidizability (degradation monitored by HPLC), on the formation on highly stabilized tannin-protein complexes and to determine how the reaction depended on the pH conditions. Gel electrophoresis and MALDI-TOF-MS were used to assess the formation of tannin-protein complexes. The results showed that tannin oxidizability was directly correlated with the tendency of the tannins to form highly stabilized complexes with BSA at increased pH (7.6). However, at slightly lower pH (6.7), other tannin features, such as the size and flexibility of the tannin, appeared to dictate the formation of highly stabilized tannin-protein complexes.