Enzymatic synthesis and physicochemical characterisation of phloridzin oxidation products (POP), a new water-soluble yellow dye deriving from apple

摘要

Phloridzin is a phenolic compound specifically found in apple and particularly concentrated in the pomace. Its oxidation by mushroom polyphenol oxidase followed a very specific pathway: phloridzin was first almost totally converted to a colourless intermediate (POPi), which was then converted to a yellow pigment (POPj) without any significant side reactions. The pigment could be an alternative to tartrazin for use as a food dye. Maximum yields were 84% for both compounds, depending on the incubation time. POPj had a bright yellow colour at pH 3 to 5, turning to orange for higher pHs. Half saturation at pH 3 was obtained for a concentration close to 30 mg/L. Kinetics of degradation of POPj in aqueous solution were determined as a function of pH and temperature. Treatments for several hours at high temperature (above 80 degrees C) resulted in a partial degradation, which was accelerated when the pH increased. However, POPj was only weakly degraded by prolonged storage at ambient temperature. Esterification of POPi and POPj in ethanol/HCl yielded the corresponding ethyl esters with 60 and 98% yields, respectively. POPi and its ethyl ester showed free radical scavenging activities (DPPH method) comparable to those of well-known antioxidants such as ascorbic acid, trolox or (-)-epicatechin..