Enhanced conversion of crude glycerol to α-ketoglutaric acid by wild-type Yarrowia lipolytica through feeding strategy optimization: An environmentally sustainable approach to industrial waste valorization

The aim of this study was to develop a microbiological process enabling the efficient valorization of crude glycerol into α-ketoglutaric acid. The study focused on assessing the effect of thiamine availability and substrate feeding strategy on α-ketoglutarate biosynthesis by the wild-type strain Yarrowia lipolytica A-8. The bioreactor cultures were performed in a fed-batch system, under thiamine growth-limiting conditions, using both pure and crude glycerol (300 g/L) as sole carbon sources. Optimization of thiamine level was found to be a key factor reducing pyruvic acid by-production, while modifying the substrate dosing strategy, from pulse to continuous feeding, allowed erythritol formation to be limited. Crude glycerol application supported enhanced biomass growth and α-ketoglutaric acid production. A continuous feeding strategy of crude substrate combined with optimized thiamine supplementation (20 μg/L) resulted in relatively high biomass growth (∼40 g/L) while maintaining high α-ketoglutarate production efficiency and selectivity (up to 95 %). The best results were obtained in the process where 50 g/L of crude glycerol was present in the initial medium, followed by continuous feeding of 250 g/L at a constant rate of 4.6 g/L/h starting from the 24th hour of cultivation. In these conditions, α-ketoglutarate production reached 117.7 g/L, with volumetric productivity of 0.81 g/L/h and a yield of 0.39 g/g, surpassing values obtained with pure glycerol. Thus, the proposed process offers a sustainable waste-to-resource solution for crude glycerol utilization.