Radical scavenging properties of a flavouring agent-Vanillin

Using pulse radiolysis technique, the one-electron oxidation of vanillin V-OH) with azide radicals. at pH 6 and 9 resulted in the formation of vanillin phenoxyl radical with k = 6.7 x 10(7) and 2.5 x 10(9) dm(3) mol(-1) S-1, respectively. The transient absorption spectra of the vanillin phenoxyl radical (V-O-.) formed either at pH 6 or 9, showed a lambda (max), at 410 nm. At pH 5, the (OH)-O-. radicals seem to form an adduct with vanillin. lambda (max) at 430 nm and k((OH)-O-. + V-OH) = 3.3 x 10(9) dm(3) mol(-1) s(-1), while at pH 9, the (OH)-O-. radical reaction resulted in the formation of vanillin phenoxyl radical with lambda (max) at 410 nm and k((OH)-O-. + V-O-) = 6.6 x 10(9) dm(3) mol(-1) s(-1). The reactivity of NO2. radicals with vanillin is lower by orders of magnitude signifying an incomplete reaction. In general, the rate constants for the reaction of (OH)-O-., N-3(.), NO2. radicals with vanillin were higher at pH 9 than at the lower pH. Its reactivity with other one-electron oxidants like CCl3OO., CHCl2OO. and CH3. radicals and the ability to chemically repair tryptophanyl and guanosyl radicals with k = 1.5 - 4 x 10(7) dm(3) mol(-1) s(-1) indicate its antioxidative behaviour.