Antioxidant activity of tea theaflavins and methylated catechins in canola oil

The present study examined the antioxidant activity of black tea theaflavins and catechin derivatives in canola oil. Oxidation was conducted at 95°C by monitoring the oxygen consumption and decreases in the linoleic and α‐linolenic acids of canola oil. All were tested at a concentration of 0.5 mM. Catechins, including (−)‐epicatechin, (−)‐epicatechin gallate, (−)‐epigallocatechin, and (−)‐epigallocatechin gallate (EGCG), were more effective than theaflavins, namely, theaflavin‐1, theaflavin‐3‐gallate, theaflavin‐3′‐gallate, and theaflavin‐3,3′‐digallate (TF3), against the lipid oxidation of canola oil. Among the four theaflavins, TF3 was the most effective, whereas among the four catechins, FGCG was the most potent. Under the same conditions, all theaflavins and catechins were more powerful than BHT as an antioxidant in heated canola.oil. Little or no difference in antioxidant activity was observed between each catechin and epimer pair. Methylation of the 3′‐OH led to a significant loss of antioxidant activity of the catechins.