Sequential ultrasound-assisted extraction of pectin and phenolic compounds for the valorisation of ‘Granny Smith’ apple peel

Abstract

This study aims to evaluate the impact of the sequential extraction system for phenolic compounds and pectin from waste ‘Granny Smith’ apple peel using ultrasound. The effects of solvent, formic acid concentration (CFA), and the number of extraction steps on the content of individual and total phenolic compounds (TPC), total flavonoids, and antioxidant capacity, were determined. Then, pectin was obtained from apple peel before (BE) and after (AE) phenolic compounds extraction, using conventional (TR) or ultrasound-assisted procedures (US). The two-steps 80% Acetone (0% CFA) extraction system had the highest TPC (3.47 g GAE/Kg). Procyanidin B2 (0.03–0.77 g/kg) was the major phenolic compound extracted from ‘Granny Smith’ apple peel. AE pectin extraction yield (6.38% for US and 4.92% for TR) was higher than BE. Pectin obtained had 57–60% DE, 9.3–10.3% Methoxyl content, and 436–460 equivalent weight. Wasted apple peel is a great low-cost source of phenolic compounds and pectin. Furthermore, it is possible to achieve the highest yields of both compounds through appropriate extraction sequences (AE: phenolic compound extraction followed by pectin extraction) and alternative technologies like ultrasound-assisted extraction.