Sweet syrups are widely used in the baking, confectionery and beverage industries, for example. These syrups generally consist of sucrose (cane sugar) or dextrose-containing products obtained from starch hydrolysis as the principal sweetening agent. When a syrup is needed that is sweeter than that obtained from sucrose, an invert sugar syrup is employed. This is produced by acid hydrolysis of sucrose to produce a mixture of about 50 percent glucose (dextrose) and about 50 percent fructose (levulose). While glucose is somewhat less sweet than sucrose, the fructose is considerably sweeter than sucrose so that the overall sweetness is increased as compared to sucrose.
It is well known that dextrose can be converted under alkaline conditions to fructose. This conversion has great potential value in the production of sweet syrups. However, the alkaline conversion has not been commercially successful because the alkaline reaction produces an undesirably high ash level in the product syrup which is uneconomical to remove. The syrup is not acceptable unless this ash is removed. Alkaline isomerization and its attendent problems are discussed in U.S. Pat. No. 3,383,245.
The prior art then turned to an enzyme conversion of glucose to fructose. It was found that species of Pseudomonas hydrophila, Streptomyces flavovirens, Streptomyces achromogenus, Streptomyces echinatur, Streptomyces albus, Streptomyces olivaceus, and Bacillus coagulans, for example, could be grown in appropriate nutrient media to form enzymes having glucose isomerase properties. This is described in U.S. Pat. Nos. 2,950,228; 3,616,221; 3,625,828; and 3,979,261, for example. None of the known prior art suggests the use of a Bacillus licheniformis species to produce a glucose isomerase having the desirable characteristics of being stable under a wide range of pH and temperature conditions.