Tagatose

Tagatose is a monosaccharide whose main application is as a sweetener in products for diabetics. It received GRAS status in 2001. Due to its sweetness and sucrose-like taste, it can be used as supplement in a wide variety of foods. Tagatose can also be used as an additive in detergents, cosmetics, and pharmaceutical formulations [77]. D-Tagatose can be produced via oxidation of D-galactitol. However, due to the limited availability of the substrate, large-scale productions are not feasible. The monosaccharide can be obtained both by chemical isomerization and by enzymatic synthesis. The major disadvantage of chemical isomerization is the lack of specificity, which leads to the loss of sweetness and functionality due to side product formation. However, it is so far the most economical method [81].

Hydrolyzed whey permeate is a good substrate for tagatose production, as it is rich in the substrates glucose and galactose. For the chemical reaction, basic catalysts such as calcium hydroxide or aluminates are necessary. [77]. Enzymatic synthesis has been explored to avoid reduced purity associated with chemical isomerization procedures. Current research focuses on the isomerization of D-galactose with the enzyme L-arabinose isomerase, although those procedures have their disadvantages. Wanarska et al. [82] constructed both a recombinant P- D-galactosidase and a recombinant L-arabinose isomerase from a yeast strain and psychrotolerant bacterium, respectively. They focused on the developing of a single-step method for the production of D-tagatose from whey permeate where hydrolysis of lactose, glucose utilization and galactose isomerization into D-tagatose take place simultaneously. This process led to a 90% yield of lactose hydrolysis and overall 30% yield of D-galactose bioconversion. Although the tagatose yield is low, the process is promising as it is more economically viable and less complicated than multistep techniques.

 
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