Optimization of Subcritical Water Mediated Extraction of Apple Pomace Polyphenolics and their Antioxidant Activity

Abstract

Apple pomace, a by-product of apple juice and cider production is considered a potential source of pectin, citric acid and bioethanol and polyphenolic compounds. Polyphenolic compounds are known to possess antioxidant properties; hence, their isolation is a rout to add value to the apple pomace waste. The current research investigated the efficacy of subcritical water in the recovery of the polyphenolic antioxidant compounds from the apple pomace using a batch reactor system at 100-bar over a temperature range of 100-200°C. Experimental factors such as; nature of apple pomace, solid-to-solvent ratio, temperature, and residence time were studied and their impact on the yields of polyphenolic content and antioxidant activity were examined. Response surface methodology was used to design the experiment to study the potential interaction of operational parameter effects on overall recovery of polyphenolic compounds. Designed conditions demonstrated selectivity towards significant recovery of the polyphenolic compounds and antioxidant activity by Oxygen Radical Absorbance Capacity (ORAC). Optimized total Phenolic content and antioxidant activity of the wet apple pomace were achieved at 200°C for 1% solid-to-solvent ratio at a residence time of 30 minutes. Optimum Total phenolic content and ORAC activity of subcritical water extract were 49.86 mg GAE /g dw and 99285 μmol TE/g dw of apple pomace respectively. High Performance Liquid Chromatography (HPLC-DAD) in a reverse mode was applied to identify polyphenolic contents of the pomace extracts. Representative Hydrocinnamic acid and flavonoids were, Chlorogenic acid, Phloridzin, Procyanidin B2, Epicatechin and Quercetin glycosides. Water soluble antioxidant compound Protocatechuic aldehyde was identified for the first time only in the subcritical water extract and to date have not been identified in solvent extracts of cider apple pomace.