Co-production of gluconic acid and 5-hydroxymethyl furfural

Gluconic acid (GA), released as a result of the oxidation of glucose, is the third most commercially produced organic acid due to its widespread use. 5-Hydroxymethyl furfural (HMF) is one of the important bio-based platform chemicals that can be converted into useful chemicals as well as promising biofuels. In this study, it is aimed to produce these valuable platform chemicals, which are currently produced with different plants, mechanisms, and raw materials, in a single process with lower costs from the same substrate source. In the study, sucrose, consisting of glucose and fructose monomers, was first hydrolyzed by the invertase enzyme. GA was produced from glucose in the hydrolyzate obtained by hydrolysis of sucrose in a two-step experimental design in erlenmeyers using the E. coli W pqq+ recombinant strain. In the first step, the important medium components for GA production were determined as hydrolyzate, calcium carbonate (CaCO3), peptone, and ammonium phosphate using Placket-Burman (PB) screening experiments. In the second stage, detailed optimization of the medium components that are important in the production of GA with PB screening experiments was carried out using the Central Composite Design (MKD) method. As a result of the MKD design, the optimum values of the independent variables examined in maximum GA (93.5 ± 2.95 g/L) production were determined as hydrolyzate 190 g/L, ammonium phosphate 1.13 g/L, CaCO3 25 g/L, and peptone 2 g/L. Before examining the GA production situation in the bioreactor, another medium optimization was performed with MKD in order to determine the medium conditions in addition to the fermentation medium components in the erlenmeyers. As a result of the design, the temperature was determined to be 36.3 oC, the stirring speed was 250 rpm, and the inoculation concentration was 9%. Using the results obtained in the erlenmeyer experiments, the operating conditions of the bioreactor for the production of GA in the bioreactor were also investigated by MKD. Maximum GA efficiency (3.20 g/L.hr) in the bioreactor was obtained under conditions where the aeration rate was 10.82 L/min, the stirring speed was 656.87 rpm, and the CaCO3 concentration was 16.90 g/L. In the erlenmeyer and bioreactor experiments, the amount of fructose remained almost unchanged in the fermentation medium since the recombinant strain used only glucose as the substrate source. Finally, in the biphasic system consisting of bioreactor broth containing GA and fructose and organic solvent 2-Methyltetrahydrofuran, HMF production and yield from fructose were determined as 0.052 g and 54.30%, respectively, at the optimum point using MKD. The amount of GA in the liquid phase of the biphasic system was preserved at a rate of 98.35%. GA and HMF produced in different phases of the biphasic system were separated from each other with the help of a separating funnel. Then, with the help of a vacuum evaporator, HMF and organic solvent were separated from each other, and about 70% of the organic solvent was recovered.