Using biobased solvents for the extraction of phenolic compounds from kiwifruit industry waste

Abstract

Valorization of wastes rich in valuable compounds is one of the most relevant topics in biorefinery and circular economy. Kiwifruit industry wastes are a potential source of bioactive compounds, such as phenolic compounds, which, in turn, exhibit many biological activities with potential health benefits. With the aim of developing a green approach for the valorization of kiwifruit waste, a study combining biobased solvents, and alternative extraction techniques for the recovery of phenolic compounds from by-products of kiwifruits (Actinidia deliciosa) ‘Hayward’ are presented. First, a pre-selection of the most suitable by-product for the recovery of phenolic compounds was done, being the peels the most promising. After, extractions using different biobased solvents mixtures with ethanol and/or water, was carried out. Gamma-valerolactone (GVL) mixtures yielded extracts with the highest phenolic compounds and antioxidant activity levels. The composition of GVL mixtures was optimized to GVL:ethanol in a ratio of 7:3 (wt/wt). Response surface methodology was used to optimize the operating conditions of different extraction techniques namely, conventional extraction and alternative techniques of ultrasound-assisted extraction (UAE) and microwave-assisted extraction (MAE). MAE has shown to be the most promising technique to obtain an extract with high levels of phenolic compounds (TPC: 29.7 ± 0.6 mg GAE/g DW; epicatechin derivatives as the main constituents, achieving a total of 2.295 ± 0.005 mg/g DW) and the highest antioxidant activity (FRAP: 87 ± 4 mg TE/g DW, ABTS: 131 ± 1 mg TE/g DW), in a shorter extraction time, as well as, when considering the estimated costs of the extraction processes. The results obtained showed the potential of using bio-based solvents (i.e. GVL) especially combined with alternative extraction techniques, to efficiently extract phenolic compounds from kiwifruit peels, paving the way for their use in the valorization of other waste rich in high-value compounds.