INHIBITION OF MUSHROOM TYROSINASE AND SOYBEAN LIPOXYGENASE BY REGIOLONE, A PHENOLIC COMPOUND FROM WALNUT HUSKS: A NEW POTENTIAL ADDITIVE FOR PREVENTION OF OXIDATIVE DETERIORATION OF FOOD

Walnut husks and related washing waters are produced in large scale as a waste product during walnut processing. We recently identified a dihydronaphthalenone compound, known as regiolone, as the main phenolic component of walnut husk washing waters (WHWW). 1 We report now that regiolone inhibits dopa and linoleic acid oxidation mediated by mushroom tyrosinase and soybean lipoxygenase, respectively, in a dose-dependent manner (Figure 1).2 IC50 values of 53 nM (mushroom tyrosinase) and 480 M (soybean lipoxygenase) were determined. Regiolone was found to be more active than known tyrosinase and lipoxygenase inhibitors such as kojic acid and caffeic acid. Model studies aimed at assessing the mechanism of inhibition revealed that regiolone is a poor chelating agent but a strong reductant toward the active metals of tyrosinase and lipoxygenase, namely copper and iron ions. These results open new perspectives in the exploitation of regiolone as a food preservative. Its easy availability by a scalable and low cost extraction from WHWW would warrant efforts along this direction.