Recovery of bioactive compounds and manufacture of bacterial cellulose nanocrystals from citrus processing wastewater

Abstract

Although citrus processing wastewater is rich in bioactive compounds and nutrients, the significant potential of the specific feedstock for valorization still remains largely unexploited. Thus, a citrus processing wastewater-based biorefinery was employed to recover carotenoids and polyphenols, while producing microbially derived bacterial cellulose nanocrystals. The solid fraction of the effluent was applied in solid-liquid extraction using various green- and petrochemical-based solvents, yielding 1.97 ± 0.03 mg of carotenoids per g of dry solid via a mixture of D-limonene/ethanol/acetic acid. A continuous adsorption/desorption system was developed, adsorbing 89.1 ± 0.63% (w/v) of the initial phenolic content. Different solvents were assessed as elution agents maximizing the desorption of the phenolic content (76 ± 7.25%, w/v) using 75% ethanol. The remaining sugar-rich liquid was subsequently utilized for bacterial cellulose manufacture employing Komagataeibacter sucrofermentans DSM 15973. Elevated fermentative production was achieved at pH-value 6.0 using a surface-to-volume ratio of 1.53 cm⁻¹, yielding 4.98 ± 0.28 g L⁻¹ of the biopolymer following 6 d of incubation. The bacterial cellulose formed was processed using sulfuric acid, aiming to hydrolyze the amorphous fraction and produce a biomaterial of higher crystallinity as well as enhanced stability and mechanical properties as compared to the pristine biopolymer. The nanocrystals produced exhibited colloidal stability (−24.73 ± 1.11 mV), enhanced crystallinity (85.2%) and reduced thermal stability (297.1 °C) as compared to bacterial cellulose. The study demonstrated a sustainable biorefinery approach for efficient valorization of citrus processing wastewater towards production of industrially important bioactive compounds and biopolymers.