Critical analysis of the effect of metal ions on gluconic acid production by Aspergillus niger using a treated Indian cane molasses

Gluconic Acid: Properties, Applications and Microbial Production

Abstract: Summary Gluconic acid is a mild organic acid derived from glucose by a simple oxidation reaction. The reaction is facilitated by the enzyme glucose oxidase (fungi) and glucose dehydrogenase (bacteria such as Gluconobacter). Microbial production of gluconic acid is the preferred method and it dates back to several decades. The most studied and widely used fermentation process involves the fungus Aspergillus niger. Gluconic acid and its derivatives, the principal being sodium gluconate, have wide applications in food and pharmaceutical industry. This article gives a review of microbial gluconic acid production, its properties and applications.

Statistical media optimization studies for growth and PHB production by Ralstonia eutropha

Abstract: Poly-β-hydroxybutyric acid (PHB) is a natural, biodegradable polymer, which is accumulated as an energy reserve material by a large number of bacteria when, nutrients such as nitrogen or phosphorous sources are available in limiting concentrations in the presence of excess carbon source. The major problem associated with the industrial production of PHB is its high production cost. In the present study, efforts were made to optimize the growth of Ralstonia eutropha NRRL B14690 in the presence of nutrients, which would not only decrease the production cost of PHB but also help in increasing the productivity. Using fructose and ammonium sulphate as carbon and nitrogen source (with the media reported in literature), R. eutropha exhibited a maximum biomass of 3.25 g/L with a PHB concentration of 1.4 g/L in 48 h. To determine the possibility of growth potential of R. eutropha , it was grown in different carbon sources of which fructose, lactic acid, sucrose and glucose yielded good growth and PHB production. In order to incorporate cheaper nitrogen source and growth factors in media, ammonium sulphate was substituted by ammonium nitrate, urea and ammonium chloride. Urea featured highest PHB accumulation of 3.84 g/L after 60 h of growth. In place of yeast extract as a source of minerals and vitamins, corn steep liquor was used which yielded a PHB concentration of 2.66 g/L. Statistical media optimization design was then used to optimize the composition of culture medium for maximizing the productivity of PHB. A maximum of 6.65 g/L residual biomass and 6.75 g/L PHB was obtained using optimized concentrations, representing 94 and 83% validity of the predicted models for residual biomass and PHB production, respectively. A significantly higher maximum biomass of 20.73 g/L with a PHB content of 9.35 g/L was obtained in a 7 L lab scale bioreactor thus giving a yield of 0.24 g PHB/g fructose consumed. Batch kinetics can be used for model development, which will facilitate simulation of nutrient limited cultivation(s) for over accumulation of PHB.

Chemically defined media for commercial fermentations

Abstract: The use of chemically defined media is gaining popularity in some commercial fermentations, particularly for the preparation of biological products. Although these media are still not frequently developed for industrial processes, they do exhibit favorable characteristics at large scale that are not observed with traditional complex media. This review focuses on the application, development, and practical considerations, especially process economics, of fermentations in chemically defined media in an industrial environment.

Biotechnological production of gluconic acid: future implications

Abstract: Gluconic acid (GA) is a multifunctional carbonic acid regarded as a bulk chemical in the food, feed, beverage, textile, pharmaceutical, and construction industries. The favored production process is submerged fermentation by Aspergillus niger utilizing glucose as a major carbohydrate source, which accompanied product yield of 98%. However, use of GA and its derivatives is currently restricted because of high prices: about US$ 1.20–8.50/kg. Advancements in biotechnology such as screening of microorganisms, immobilization techniques, and modifications in fermentation process for continuous fermentation, including genetic engineering programmes, could lead to cost-effective production of GA. Among alternative carbohydrate sources, sugarcane molasses, grape must show highest GA yield of 95.8%, and banana must may assist reducing the overall cost of GA production. These methodologies would open new markets and increase applications of GA.

Manufacture of gluconic acid: A review towards process intensification for green production

Abstract: In view of the huge application potential of gluconic acid and its derivatives, this manuscript critically reviews literature of the last thirty years on evolution of production processes of this important organic acid for the purpose of directing further research towards process intensification for innovative green processes. Fermentative process and catalytic oxidation are found to be the two basic approaches in production of gluconic acid. In both the approaches, downstream purification involves several steps such as centrifugation, carbon adsorption, evaporation, crystallization and ion-exchange. Cost-effective and eco-friendly production of high purity gluconic acid has remained a challenge, mainly due to involvement of multiple downstream processing units and their associated energy consumption and cost factors. In the recent years, possibility of integration of tailor-made and highly selective membranes and modules with fermenter in downstream purification of gluconic acid appears to have brightened the prospects of gluconic acid manufacture. This paper through a comprehensive review of the critical aspects of production of gluconic acid suggests ways towards development of green processes through process intensification leading to the prospects of sustainable business.

Partial purification and regulatory properties of phosphofructokinase from Aspergillus niger.

Abstract: Phosphofructokinase (EC 2.7.1.11) from a citric acid-producing strain of Aspergillus niger was partially purified by the application of affinity chromatography on Blue Dextran--Sepharose and the use of fructose 6-phosphate and glycerol as stabilizers in the working buffer. The resulting preparation was still impure, but free of enzyme activities interfering with kinetic investigations. Kinetic studies showed that the enzyme exhibits high co-operativity with fructose 6-phosphate, but shows Michaelis--Menten kinetics with ATP, which inhibits at concentrations higher than those for maximal activity. Citrate and phosphoenolpyruvate inhibit the enzyme; citrate increases the substrate (fructose 6-phosphate) concentration for half-maximal velocity, [S]0.5, and the Hill coefficient, h. The inhibition by citrate is counteracted by NH4+, AMP and phosphate. Among univalent cations tested only NH4+ activates by decreasing the [S]0.5 for fructose 6-phosphate and h, but has no effect on Vmax. AMP and ADP activate at low and inhibit at high concentrations of fructose 6-phosphate, thereby decreasing the [S]0.5 for fructose 6-phosphate. Phosphate has no effect in the absence of citrate. The results indicate that phosphofructokinase from A. niger is a distinct species of this enzyme, with some properties similar to those of the yeast enzyme and in some other properties resembling the mammalian enzyme. The results of determinations of activity at substrate and effector concentrations resembling the conditions that occur in vivo support the hypothesis that the apparent insensitivity of the enzyme to citrate during the accumulation of citric acid in the fungus is due to counteraction of citrate inhibition by NH4+.

Manganese deficiency leads to elevated amino acid pools in citric acid accumulating Aspergillus niger

Abstract: Free amino acid pools have been investigated in a citric acid accumulating strain of Aspergillus niger during batch growth under manganese sufficient and deficient conditions by means of an improved chromatographic method. Studies on the mycelial content of several nitrogenous compounds under manganese sufficient and deficient conditions showed that manganese deficiency resulted in lower amino acid pool sizes during trophophase and considerable accumulation during idiophase, and in a reduction of the protein and nucleic acid contents. Addition of cycloheximide to mycelia grown with sufficient manganese also caused an elevation of free amino acid pool sizes, thus indicating that impairment of protein synthesis by manganese deficiency is responsible for the observed rise in amino acid concentration. Furthermore it was observed that the manganese deficient mycelia excreted high amounts of all amino acids suggesting that manganese deficiency may also affect membrane permeability.