Valorization of Dextrose from Cassava Starch and Sugarcane Vinasse as Polyhydroxyalkanoates by Submerged Cultures of Cupriavidus necator: A Physicochemical–Biotechnological Approach

Abstract

The production of polyhydroxyalkanoates using submerged cultures of Cupriavidus necator DSM 428 was evaluated using low-cost substrates from agroindustry: (i) dextrose from cassava starch and (ii) a mixture of sugarcane vinasse from the bioethanol industry and dextrose from cassava starch. The effects of vinasse composition (2.5, 5.0, 7.5, 25, 50, and 75% v/v) and the use of raw and activated carbon-pre-treated vinasse were assessed. The results indicate that cultivations using only cassava starch dextrose reached 4.33 g/L of biomass as the dry cell weight and a poly(3-hydroxybutyrate) (PHB) production of 47.1%. Raw vinasse proportions of 25, 50, and 75% in the culture medium resulted in total inhibition. Vinasse treated at the same ratios led to biomass production in the range 1.7–4.44 g/L. The higher PHB production scenario was obtained in a medium containing dextrose and treated vinasse (7.5%), yielding 5.9 g/L of biomass and 51% of PHB accumulation. The produced PHB was characterized by XRD and FTIR for an analysis of crystalline structure and chemical functional groups, respectively. EDS was employed for a semi-quantitative analysis of the chemical composition, and SEM was used to analyze the morphology of the microgranules. The results of DSC and TGA analyses demonstrated the thermal stability of the obtained PHB.