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.