Valorization of Zante currant side‐streams for the production of phenolic‐rich extract and bacterial cellulose: a novel biorefinery concept

Abstract BACKGROUND Utilization of renewable resources for the production of added‐value bioeconomy products, within the concept of developing integrated biorefineries, is a crucial step towards the establishment of sustainable processes. In this framework, a novel biorefinery has been proposed based on ‘Zante currant’ side‐stream valorization. RESULTS ‘Zante currant’ raisins discarded during the production process were initially treated in order to obtain a sugar‐rich and a phenolic‐rich fraction, implementing wastewaters for all of the extraction and dilution procedures. Total phenolics and antioxidant activity index (AAI) were determined indicating that Zante currants could be considered as a phenolic‐rich source, whereas the fractionated phenolic extract possesses a moderate antioxidant activity (AAI = 0.71). In addition, quantitative analyses using high performance liquid chromatography‐diode array detector revealed that the main phenolics present in Zante currants were caffeic acid, ellagic acid, 4‐hydroxybenzaldehyde, catechin and rutin; homoprotocatechuic acid, epicatechin, vanillic acid and gallic acid also were detected in lower concentrations. Likewise, sugar recovery reached 88% and the sugar‐rich stream was subsequently utilized in batch fermentations for the production of bacterial cellulose (BC), using the bacterial strain Komagataeibacter sucrofermentans DSM 15973. The obtained results showed that BC was produced efficiently, reaching higher concentrations (2.76 g L −1 ) than previous studies in which synthetic fructose‐ and glucose‐based media were used. CONCLUSION This is the first study proposing the development of a novel raisin‐based biorefinery for the production of added‐value products, namely antioxidants and BC. © 2019 Society of Chemical Industry