Insights into the Structure-Capacity of Food Antioxidant Compounds Assessed Using Coulometry

CDAC (coulometrically determined antioxidant capacity) involves the determination of the antioxidant capacity of individual compounds or their mixtures using constant-current coulometry, with electrogenerated Br-2 as the titrant, and biamperometric detection of the endpoint via Br-2 excess. CDAC is an accurate, sensitive, rapid, and cheap measurement of the mol electrons (mol e(-)) transferred in a redox process. In this study, the CDAC of 48 individual antioxidants commonly found in foods has been determined. The molar ratio CDAC (CDAC chi, mol e(-) mol(-1)) of representative antioxidants is ranked as follows: tannic acid > malvidin-3-O-glucoside similar or equal to curcumin > quercetin > catechin similar or equal to ellagic acid > gallic acid > tyrosol > BHT similar or equal to hydroxytyrosol > chlorogenic acid similar or equal to ascorbic acid similar or equal to Trolox (R). In many cases, the CDAC chi ranking of the flavonoids did not comply with the structural motifs that promote electron or hydrogen atom transfers, known as the Bors criteria. As an accurate esteem of the stoichiometric coefficients for reactions of antioxidants with Br-2, the CDAC chi provides insights into the structure-activity relationships underlying (electro)chemical reactions. The electrochemical ratio (ER), defined as the antioxidant capacity of individual compounds relative to ascorbic acid, represents a dimensionless nutritional index that can be used to estimate the antioxidant power of any foods on an additive basis.