Effect of medium pH on chemical selectivity of oxalic acid biosynthesis by Aspergillus niger W78C in submerged batch cultures with sucrose as a carbon source

Abstract

The pH of the medium is the key environmental parameter of chemical selectivity of oxalic acid biosynthesis by Aspergillus niger. The activity of the enzyme oxaloacetate hydrolase, which is responsible for decomposition of oxaloacetate to oxalate and acetate inside the cell of the fungus, is highest at pH 6. In the present study, the influence of pH in the range of 3–7 on oxalic acid secretion by A. niger W78C from sucrose was investigated. The highest oxalic acid concentration, 64.3 g dm−3, was reached in the medium with pH 6. The chemical selectivity of the process was 58.6% because of the presence of citric and gluconic acids in the cultivation broth in the amount of 15.3 and 30.2 g dm−3, respectively. Both an increase and a decrease of medium pH caused a decrease of oxalic acid concentration. The obtained results confirm that pH 6 of the carbohydrate medium is appropriate for oxalic acid synthesis by A. niger, but the chemical selectivity of the process described in this paper was high in comparison to values reported previously in the literature.

Acetate as substrate for l-malic acid production with Aspergillus oryzae DSM 1863

“…Oxalic acid is a rather strong acid (pK A,1 = 1.23) and therefore might be produced to outcompete other species by medium acidification. This theory is supported by the observation that oxalic acid is mainly accumulated if the pH of the culture broth is at a value of 6 or above [ 34 – 36 ]. Furthermore, oxalic acid acts as efficient chelator for cations which supports fungal growth by mobilizing metal ions [ 37 ].…”

“…The cause for this observation might be the different pH development observed with the substrates. The acid spectrum produced by filamentous fungi is strongly influenced by the pH and citric acid is produced most efficiently at low pH values [ 36 ]. While during the acid production with glucose, the pH value decreased, it strongly increased when acetate was used as carbon source.…”

Citric Acid: Properties, Microbial Production, and Applications in Industries

“…Furthermore, a pH below 3 prevents the production of oxalic and gluconic acids [ 124 ]. Conversely, increasing the pH to 4.5 can lead to a significant reduction in citric acid production efficiency by up to 80% [ 50 , 125 ].…”

Towards Sustainable Oxalic Acid from CO2and Biomass

“…Scheme 1 shows all pathways that use biomass as feedstock. Besides nitric acid oxidation, biomass can be directly converted to oxalic acid by a process called alkali heating and fermentation [43,67–100] . Furthermore, biomass can also be used as a feedstock for the production of other oxalic acid precursors such as CO (gasification), CO 2 (fermentation or combustion), AF, and EG (via bio‐ethylene or direct hydrogenolysis) [101,102]…”

“…established that green syrup, lactose permeate, and molasses are suitable substrates, and they could reach 80 % conversion and 38.7 % oxalic acid selectivity [69] . Recent research has seen this number increase to 58.8 %, which still requires separation of oxalic acid from the cell media and gluconic acid by‐product [74,97] …”