A New, Rapid Method for Examining Potential Skin-Brightening Ingredients Using Apple Slices

Darkening of fruits is the result of the oxidative activation of polyphenol oxidase converting low-molecular weight phenols present in the fruit body into quinone intermediates. Then, through polymerization, these reactive quinones convert to light yellow and red low-molecular weight melanin and, given enough time, to darker, higher molecular weight brown and black melanin. The process that occurs in the flesh of cut fruit is very similar to the process that human skin cells use to make melanin: the oxidative activation of tyrosinase and conversion of tyrosine to dopaquinone and eventually to darker melanin. The conversion of the phenols by tyrosinase to quinones is the rate-limiting step in the biochemical manufacture of melanin. This article will discuss a new and cost effective way to screen skin-brightening ingredients by the use of apple slices as a model for skin using a chromameter to measure the change in color that occurs in apple slices over a short time course. Such measurements have been popularly used by food manufacturers to examine ingredients that inhibit fruit browning. Interestingly, as will be noted, many of the ingredients used commercially to inhibit food browning are also popular skin-brightening ingredients. We have found that a DermaLab (Cortex Technologies, Hadsund, Denmark) chromameter measuring the erythema index of apple slice darkening appears to be able to differentiate the benefit of a formulation containing azelaic acid, a known skin-lightening ingredient, to minimize the darkening effects that occur in sliced apples. We will discuss how different apples behave differently when cut and how to best use the chromameter to analyze the changes that occur that can potentially help rapidly screen ingredients for their skin-brightening benefits.