Polyhydroxybutyrate (PHB) production by Cupriavidus necator from sugarcane vinasse and molasses as mixed substrate

Vinasse and sugarcane molasses are abundant residues from the ethanol mills that were used as substrate for polyhydroxybutyrate (PHB) production in this study. The molasses was previously hydrolyzed by acid (HCl or H2SO4) or enzymatic procedures (invertase or bakers yeast), and C. necator growth kinetics were compared, whereby enzymatic hydrolysis was chosen for subsequent tests based upon maximum specific growth rate (mu(max)). The addition of vinasse in a medium containing molasses increased mu(max) from 0.19 to 0.36 h(-1) due to the presence of organic acids in this substrate, which were consumed in the first hours of cultivation. In the production stage, two pulses of molasses were added, reaching 11.7 g.L-1 of PHB and 56% of product accumulation. The nitrogen content in molasses (around 1.8 g.L-1) was responsible for an atypical increase in biomass concentration during the production phase, which renders this substrate interesting, depending on the cultivation method.