Glucose oxidase has become an important tool in several different industries, its uses ranging from a glucose biosensor for the control of diabetes, to a food preservative and colour stabiliser. Some of its current applications in industry are described below.
Glucose biosensor for diabetes monitoring
People with diabetes mellitus need to constantly monitor their blood glucose levels in order to detect fluctuations in glucose level that could lead to hyperglycaemia (high blood glucose levels) and hypoglycaemia (low blood glucose levels) so as to control the disease. Currently, such monitoring is done using finger-prick blood samples and a portable meter several times a day.
Biosensors are also being developed to measure blood glucose levels. Glucose oxidase is one of the possible enzymes that a biosensor can use. Biosensors work by keeping track of the number of electrons that pass through the enzyme by connecting it to an electrode and measuring the resultant charge. Alternatively, some biosensors use sensitive fluorescence measurements, monitoring changes in the intrinsic FAD fluorescence of glucose oxidase.
Bio-electronic devices are energy demanding, requiring small power sources to sustain operations. Biofuel cells are able to convert biochemical energy into electrical energy using a biocatalyst. One type of biofuel cell uses enzymes as a biocatalyst. For example, glucose oxidase and microperoxidase-8 can be used on the cathode, where the hydrogen peroxide produced by glucose oxidase acts to oxidise microperoxidase-8 to directly accept electrons from the carbon rod electrode.
Food and beverage additive
Glucose oxidase has been used successfully to remove residual glucose and oxygen in foods and beverages in order to prolong their shelf life. The hydrogen peroxide produced by the enzyme acts as a good bactericide, and can be later removed using a second enzyme, catalase, that coverts hydrogen peroxide to oxygen and water. For example, glucose is removed from egg whites before they are dried for use in the baking industry using the glucose oxidase/catalase system. Glucose oxidase can also be used to remove oxygen from the top of bottled beverages before they are sealed.
In addition, glucose oxidase is used to prevent colour and flavour loss from foods and beverages. For example, they are used to reduce the discolouration occurring in wines and mayonnaises.
Glucose oxidase has potential for use in the wine industry, where it can lower the alcohol content of wine through the removal of some of the glucose (by converting it to D-glucono-1,5-lactone), which would otherwise be converted to alcohol. Tests showed that the glucose oxidase treatment of wine-must could reduce the potential alcohol content of wine by about 2%. In addition, glucose oxidase is able to inhibit wine spoilage through its bactericidal effect on acetic acid bacteria and lactic acid bacteria during the fermentation process. The bactericidal effect of the enzyme means fewer preservatives need to be added to the wine. Some strains of Saccharomyces cerevisiae have been genetically engineered to carry the glucose oxidase gene itself.
Glucose oxidase, as well as lactoperoxidase, can be used as anti-microbial agents in oral care products. The oral cavity houses several species of Streptococci bacteria, such as Streptococcus mutans, which is a significant contributor to tooth decay and is carried by virtually everyone. The hydrogen peroxide produced by glucose oxidase acts as a useful bacteriocide. The ability of glucose oxidase to kill S. mutans appears to be enhanced by the fusion of the enzyme with heavy chain antibodies.
Glucose oxidase is also used as a commercial source of gluconic acid, which can be produced by the hydrolysis of D-glucono-1,5-lactone, the end-product of glucose oxidase catalysis. Gluconic acid has been used as a food additive to act as an acidity regulator, in sterilization solution or bleaching in food manufacturing, and as a salt in chemical components for medication. It has even been used in the construction industry as an additive to cement to increase its resistance and stability under extreme weather conditions. It occurs naturally in honey, fruit and wine.