Volumetric oxygen transfer coefficient as fermentation control parameter to manipulate the production of either acetoin or D-2,3-butanediol using bakery waste

The formation of either acetoin or D-2,3-butanediol (D-BDO) by Bacillus amyloliquefaciens cultivated on bakery waste hydrolysates has been evaluated in bioreactor cultures by varying the volumetric oxygen transfer coefficient (k_La). The highest D-BDO production (55.2 g L^-1) was attained in batch fermentations with k_La value of 64 h^-1. Batch fermentations performed at 203 h^-1 led to the highest productivity (2.16 g L^-1h^-1) and acetoin production (47.4 g L^-1). The utilization of bakery waste hydrolysate in fed-batch cultures conducted at k_La of 110 h^-1 led to combined production of acetoin, meso-BDO and D-BDO (103.9 g L^-1). Higher k_La value (200 h^-1) resulted to 65.9 g L^-1 acetoin with 1.57 g L^-1h^-1 productivity. It has been demonstrated that the k_La value may divert the bacterial metabolism towards high acetoin or D-BDO production during fermentation carried out in crude bakery waste hydrolysates.