Optimisation of radio frequency assisted extraction of apple peel extract: Total phenolic contents and antioxidant activity

Abstract

The objective of this study is to determine the optimum operating conditions of apple peel extraction process using a novel extraction method known as radio frequency assisted extraction (RFAE). Apple peel extract with the highest total phenolic contents and antioxidant activity is targeted in this study. RFAE is a green extraction method which operates based on the dielectric heating concept. Response surface methodology was employed for designing the experiment, analysing the effects and optimising the extraction conditions for RFAE of apple peel phenolic compounds. The effects of ethanol concentration (10 - 70 %), mixing speed (10 - 320 mL N2/min), solid to liquid ratio (0.002 - 0.02 g/mL) and RF power (200 - 400 W) on total phenolic compounds and DPPH radical scavenging activity efficiency were investigated in order to understand and improve the RFAE performance. All processing parameters exert significant effects on the total phenolic compounds and radical scavenging activity of the apple peel extract. The highest recovery of TPC with a value of 121.87 mg GAE/ g DW can be achieved if the extraction is performed using 42.67 % ethanol concentration, mixing speed of 320 mL N2/min, solid to liquid ratio of 0.0114 g/mL and power at 400 W. The maximum value of DPPH (94.54 %) can be achieved if the extraction is performed using an ethanol concentration, mixing speed, solid to liquid ratio and power of 37.33 %, 165 mL N2/min, 0.02 g/mL and 400 W.