PH-Controlled fermentation of strawberry waste as phenol solubilisation method

Abstract

The present study aims to use pH as a control parameter for the accumulation of target compounds. Solubilisation of wasted strawberry through fermentation at different operational pH (pH 4, 7, and 9) was evaluated. Methane as a target compound was achieved at pH 7, reaching a value up to 353 ± 10 mL CH4/g VS (VS, volatile solids). Operation at pH 9 was hardly controlled due to the low pH of the substrate and the accumulation of VFA. pH 9 resulted in the highest accumulation of VFA, mainly acetic acid. The operation at pH 4 resulted in the inhibition of the biogas production, leading to the concentration of soluble phenols up to 3 times the initial concentration in the reactors. The concentrations of pelargonidin 3-glucoside and p-coumaric acid showed a significant increase at pH 4 (p = 0.157 and p = 0.058, respectively). Acidogenic fermentation could be a suitable method to solubilise bioactive compounds from wasted strawberries without the necessity of high-energy pre-treatments. The low energy demand, i.e. 19 equivalent kJ/g gallic acid, as well as the high phenol solubilisation capacity, indicates that the acidogenic fermentation at pH 4 it is a promising method for the recovery of phenols from wasted strawberry.