Selective release of phenols from apple skin: Mass transfer kinetics during solvent and enzyme-assisted extraction

This work examines the influence of the extraction conditions, temperature, apple skin particle size, solvent composition, and enzymatic maceration on extraction yields and mass transfer rates of the main phenolic compounds of apple skins. Mass transfer of the phenolics was assessed by linearization of Fick's second law. Increased temperature, size reduction and presence of ethanol in the solvent generally increased the mass transfer rates of phenolics, although each one of these variables had a different effect on the release of each individual phenol compound studied: epicatechin, procyanidin B2, rutin, chlorogenic acid, phloridzin, and a phloridzin derivative. Application of cell wall degrading enzyme preparations, Pectinex Smash (pectinase), Celluclast 1.5 L (cellulase) and Sumizyme (protease) prior to extraction, resulted in a general increase in Fick's module, defined as (π2Deff/r2). Values of Fick's module for total phenols ranged from 0.0859 to 0.1552 s−1 with solvent extraction and from 0.0981 to 0.1834 s−1 with enzyme-assisted extraction. Enhanced pectinase and protease dosages thus significantly improved the phenol transfer. This study showed that phenols can be selectively extracted by varying the extraction conditions and by adding cell wall degradation enzymes.