Assessing antioxidant and prooxidant activities of phenolic compounds

Methods for determining primary antioxidant activity were evaluated. A beta -carotene bleaching method and a free radical method using 2,2-diphenyl-1-p icrylhydrazyl (DPPH.) were modified to rapidly test samples for potential a ntioxidant activity. Malonaldehyde production in a linoleic acid emulsion s ystem assayed by an HPLC method was also used to determine antioxidant and prooxidant activities initiated by a metal catalyst (Cu2+). All methods wer e used to assess activity of selected phenolic compounds including several anthocyanidins/anthocyanins and selected berry extracts. Most phenolic comp ounds had prooxidant activity at low concentrations, unlike synthetic antio xidants (BHA and BHT). Compounds with similar structures exhibited comparab le trends in antioxidant activity. Antioxidant activity usually increased w ith an increase in the number of hydroxyl groups and a decrease in glycosyl ation. The antioxidant activity of many phenolic compounds and extracts was comparable to those of synthetic antioxidants using the beta-carotene blea ching and HPLC methods.