Production of polyhydroxybutyrate by coupled saccharification-fermentation of inulin.

Inulin is a fructose-based polysaccharide that can be found in several plant species, from grass and onions to chicory roots; thus, it has the potential to be an excellent renewable source of fructose for several industrial applications. Among them, inulin hydrolysis can be coupled to a fermentation operation to produce polyhydroxybutyrate (PHB) by Cupriavidus necator H16. Here, we report a PHB production process involving the chicory-root inulin hydrolysis using the inulinase Novozym 960 followed by a C. necator fermentation. We found that the maximum saccharification (95% wt.) was reached at 269 U/g_inulin after 90 min. The hydrolysates were then inoculated with C. necator, leading to a biomass concentration of 4 g/L with 30 % (w/w) polymer accumulation. Although PHB production was low, during the first hours, the cell growth and polymer accumulation detected did not reflect a fructose concentration decrease, suggesting a simultaneous saccharification and fermentation process, which could elude the product inhibition inherent to the system. Moreover, characterization of the PHB obtained through this process showed that the polymer obtained was more homogeneous, in Mw, and thermally stable than that produced using pure fructose as a fermentation substrate. These results demonstrate a viable alternative carbon substrate for PHB production, opening the possibility for inulin-rich renewable feedstocks valorization.