Impact of micro wet milling process on pomegranate peel phenolics extraction using multi‐response optimization

Abstract

Pomegranate peel is a rich source of various phenolics. Many extraction methods were developed and utilized for pomegranate peel extraction (PPE) with varying effect on its bioactive compounds. We hypothesized that micro wet milling (MWM) can be used to extract such compounds from fresh peel without drying to powder, as their particle size is reduced to micrometers. This will preserve the bioactive compounds as no heat treatment is involved in this proposed extraction method. To assess the MWM extraction process, response surface methodology (RSM) was used to determine the optimum extraction conditions. The main influential factors such as rotational speed (RS) 20–50 rpm, solid to solvent ratio (SS) 5–30 g/100 mL, and ethanol to water ratio (EW) 30–80% were optimized for total phenolic content (TPC), total anthocyanin content (TAC), punicalagin, ellagic acid (EA), gallic acid (GA), catechin, and epicatechin. The optimum operational conditions were 50 rpm of RS, 19.62 g/100 mL of SS, and 49.65 % v/v of EW. The most significant influential factor for pomegranate peel extraction was SS. The optimum phenolic compound values were 225.7 mg GAE/g dw of TPC, 3.1 mg/g dw of TAC, 71.6 mg/g dw of punicalagin, 6.9 mg/g dw of ellagic acid, 6.2 mg/g dw of gallic acid, 13.1 mg/g dw of catechin and 14.8 mg/g dw of epicatechin. Validation of the model and its comparison with the results obtained from the ultrasonic bath extraction method and scanning electron microscopy (SEM) revealed that MWM can be used to mill the peel into micro-scale particles making the extraction of pomegranate peel phenolics easier.