Bioconversion of Glycerol to Dihydroxyacetone by immobilized Gluconacetobacter xylinus cells

Abstract

Dihydroxyacetone, (DHA) is one of the primary ingredients used in tanning products by the cosmetic industry. DHA reacts with the free amino acids on the epidermis to form a tan-like appearance. DHA is also a building block for lactic acid; that is, a common ingredient in the food industry. In the pharmaceutical industry, DHA is used as a precursor for 1, 2-propylene glycerol and methotrexate. Due to the Food and Drug Administration’s strict regulations, DHA is produced via microbial synthesis. This is because the chemical synthesis involves toxic chemical reactions with epichlorohydrin. This poses problems with a chemical widely used for human application. Currently, the industrial process of DHA is carried out under microbial synthesis of glycerol. The strain, Gluconobacter oxydans produces high DHA yields although its productivity is low. As a result, its high cost of production is reflected in its price. Glycerol is the only organic compound that can be converted into DHA. The conversion requires oxidation of the secondary hydroxyl group by glycerol dehydrogenase (GlyDH). In this study, DHA was converted from glycerol using Gluconacetobacter xylinus (G.xylinus) in a large-scale reactor. Previously the strain, G.xylinus, has been shown to produce high DHA yields under immobilization. In this study, G.xylinus was immobilized inside two carrier materials- calcium alginate and chitosan-coated alginate beads. A series of investigations were carried out to determine the DHA conversion efficiency using the mentioned carriers. The conversion efficiency of alginate immobilized cells was investigated under varying initial glycerol concentrations of: 1%, 2%, 4% and 7% (w/v) and aeration rates of: 0.3, 0.6 and 1.0 vvm. This study found that the optimal glycerol concentration was at 2% (w/v) and the optimal aeration rate was at 0.3 vvm. The DHA conversion efficiency of chitosan-alginate immobilized cells was also tested under the same aeration rate previously mentioned. The investigation found that chitosan coating provided greater stability to the alginate matrix with increased aeration rate. The optimal aeration rate was found at 1.0 vvm.