Cascading and precise regulation of the selective bio-production of 2- or 5-ketogluconic acid from glucose with whole-cell catalysis technology

Abstract

Ketogluconic acid is widely applied in several industries as the bio-precursor of vitamin C and tartaric acid, while the selective production of 2-ketogluconic acid (2-kGA) or 5-ketogluconic acid (5-kGA) from glucose is so far still a challenge for chemical and biotechnical processes. The latest studies have demonstrated that Gluconobacter oxydans effectively catalyzes glucose to a mixture of gluconic acid, 2-kGA and 5-kGA under moderate conditions. In order to develop a novel and efficient technology for the selective production of 2-kGA or 5-kGA without by-products, cascading and precise regulation with calcium cations was explored and investigated using whole-cell catalysis by G. oxydans. CaCO₃ was used as a neutralizer, which not only intensified the whole-cell catalysis to a better productivity, but also significantly reduced the solubility of 5-kGA. The in situ separation of 5-kGA-Ca was achieved with a crystallization yield of 97.3% thanks to the different solubilities of kGA-Ca salts. The 2-kGA-Ca crystals were subsequently obtained with a crystallization yield of 94.3% from the bacterial fermentation broth. The high purity of the two kGA salt crystals was confirmed by chromatography and NMR, respectively. Finally, totals of 640.2 g of 2-kGA and 249.2 g of 5-kGA were obtained by the addition of 1000 g of glucose in the processing experiment. This cascading and precise regulation method might provide a promising technical approach for the selective bio-production of 2- or 5-kGA and glucose bioconversion.