Improving propionic acid production from a hemicellulosic hydrolysate of sorghum bagasse by means of cell immobilization and sequential batch operation.

Propionic acid (PA) is an important organic compound with extensive application in different industrial sectors and is currently produced by petrochemical processes. The production of PA by large-scale fermentation processes presents a bottleneck, particularly due to low volumetric productivity. In this context, the present work aimed to produce PA by a biochemical route from a hemicellulosic hydrolysate of sorghum bagasse using the strain Propionibacterium acidipropionici CIP 53164. Conditions were optimized to increase volumetric productivity and process efficiency. Initially, in simple batch fermentation, a final concentration of PA of 17.5 g⋅L-1 was obtained. Next, fed batch operation with free cells was adopted to minimize substrate inhibition. Although a higher concentration of PA was achieved (38.0 g⋅L-1 ), the response variables (YP/S = 0.409 g⋅g-1 and QP = 0.198 g⋅L-1 ⋅H-1 ) were close to those of the simple batch experiment. Finally, the fermentability of the hemicellulosic hydrolysate was investigated in a sequential batch with immobilized cells. The PA concentration achieved a maximum of 35.3 g⋅L-1 in the third cycle; moreover, the volumetric productivity was almost sixfold higher (1.17 g⋅L-1 ⋅H-1 ) in sequential batch than in simple batch fermentation. The results are highly promising, providing preliminary data for studies on scaling up the production of this organic acid.