REPRINTS, COPIES

In the browning of fruit tissue, polyphenol oxidases catalyze the oxidation of certain phenolic compounds related to catechol. The nature of the R group gives rise to differences in reactivities of the substrates (Corse, 1964). Subtle differences may render one compound a substrate for polypneol oxidase and a simliar compound unaffected. For example, Shannon and Pratt (1967) found that dihydroquercetin was a substrate for apple polypneol oxidase but quercetin was not. The two molecules differ only in the bonding between carbons at the 2 and 3 positions. Quercetin is more planar and less soluble than dihydroquercetin and contains a double bond conjugated to an aromatic ring which confers stability. Stability, decreased solubility, or perhaps steric effects may explain the difference in reactivity of the two compounds.

Updated: Wednesday, June 20, 2007.