Tannin−Protein Complexes as Radical Scavengers and Radical Sinks

Abstract

The 2,2'-azinobis(3-ethylbenzothiazoline 6-sulfonic acid) radical cation (ABTS(*)(+)) decolorization assay has been used to determine the antioxidant activity of the polyphenol epicatechin(16) (4 --> 8) catechin (procyanidin, PC) alone or in complex with the model proteins bovine serum albumin (BSA) or gelatin. PC had a molar antioxidant capacity of approximately 54, 92, or 108 radicals at pH values of 3.0, 4.9, or 7.4, respectively. Radical scavenging occurred via a rapid step followed by a slow step. Interaction with gelatin reduced the rate of rapid scavenging by 50% (PC-BSA mixtures reduced by 15%). Inhibition paralleled formation of precipitable PC-protein complexes over a range of protein/PC ratios. However, inhibition was virtually overcome in 10 min. Reaction with ABTS(*)(+) converted the PC-protein complexes from a dissociable form to a form resistant to dissociation by strong denaturants such as SDS. This study demonstrates that PC is a potent ABTS(*)(+) scavenger even when bound to protein and that the complexes may act as a radical sink within the gastrointestinal tract.

Stability and quality of herb (Pueraria Tuberosa)-milk model system

“…They also reported that the antioxidant activity and phenol content increased on heat treatment (65°C/30 min) of skim milk. This could be due to excess phenol released due to breaking off bonds between polyphenols and milk protein in the complexation compound or may be due to formation of radical scavenging complexation compounds formed by covalent interaction between oxidised phenolic compounds and amino acid residues of proteins (Arts et al 2001;Ridle and Hagerman 2001;Rohn et al 2004). Karaaslan et al (2011) also found higher antioxidant power in grape extract fortified yogurt with higher anthocyanin content than control yogurt.…”

Effects of Sulla forage (Sulla coronarium L.) on the oxidative status and milk polyphenol content in goats

“…Hagerman et al (1998) suggested that tannins or polymeric polyphenolics may be much more potent antioxidants than simple monomeric phenolic substances. A further study demonstrated that procyanidins, which are typical CT, are potent scavengers even when bound to proteins and that such complexes might act as a radical sink within the gastrointestinal tract (Riedl and Hagerman, 2001). …”

The free radical scavenging and antioxidant activities of pod and seed extract of Clitoria fairchildiana (Howard)- an underutilized legume

“…The tannin-protein complexes that are formed as a result of conventional food processing have been shown to be potential free radical scavengers and have been suggested to be one of the major contributors for the nutraceutical property. These complexes are able to prevent free radical-mediated diseases occurring in the gastrointestinal tract (Riedl and Hagerman 2001).…”