Integral valorization of fruit waste from wine and cider industries

Abstract

Agro-industrial waste disposal is becoming a key issue as a consequence of the increasing number of by-products generated. Within this context, this work proposes an integral, effective and sustainable use of biowaste from regional food industries as a drive towards cleaner production. Apple and grape waste from cider and wine industries was valorized by extracting bioactive compounds and pyrolyzing/gasifying the residual solid to obtain value-added chemical products, such as biochar. The extraction conditions were as follows: a solvent/fruit ratio of 2/1 (w/w), an extraction temperature of 348 K and an extraction time of 1.25 h. The extracts were analysed for soluble solids, sugars, acids, total polyphenol content, antiradical activity and superficial colour. The grape stalk extract presented the highest polyphenol content (1,758 ± 24 g gallic acid/100 kg) and antioxidant capacity (156 ± 6 g gallic acid/100 kg). The liquid fractions can be used to develop functional ingredients. After the extraction process, the remaining solid fraction was subjected to pyrolysis or gasification at low heating rates (10, 15 and 20 K/min). The resulting biochars presented low to moderate surface areas (0.9–266 m2/g) and low H/C ratios (high aromaticity). The obtained biochar can be used for the production of activated carbon to be used in fuel applications and as soil structure reinforcement. The proposed methods allowed for the optimization of waste reclamation with two applications: the development of ingredients for the nutraceutical and food industries and the production of biochar and renewable energy.