Enzyme production of D-gluconic acid and glucose oxidase: successful tales of cascade reactions.

This review is focused on the use of glucose oxidase, mainly in the production of D-gluconic acid, a reactive of undoubtable interest in different industrial areas. The enzyme has been used in many instances as a model reaction to study the problems of oxygen supply in bioreactors. One of the main topics in this review is the problem of the generated side product, hydrogen peroxide, as this is an enzyme-inactivating reagent. Different ways to remove it have been used (metal catalysts, use of whole cells) but the preferred way is the coupling of glucose oxidase with catalase. The different possibilities of combining these enzymes have been discussed (use of free enzymes, independently immobilized enzymes or co-immobilized enzymes). Curiously, some papers propose the addition of hydrogen peroxide to this co-immobilized enzyme system to produce oxygen in situ. Other cascade reactions directed to the production of gluconic acid from polymeric substrates, will be presented, mainly involved in the transformation of polysaccharides (amylases, cellulases, etc) but will not be limited to those (e.g., gluconolactonase). In fact, glucose oxidase is perhaps one of the enzymes more successfully involved in a wider range of cascade reactions. Finally, other applications of the enzyme have been revised, always based on the production of D-gluconic acid (that produces a decrease in the pH), a decrease in the oxygen availability or the production of hydrogen peroxide, in many instances also utilizing cascade reactions. Thus, this review presents many different cascade reactions and discusses the advantages/drawbacks of the use of co-immobilized enzymes