Processes and Products Based on Isomerization Reactions

This Section is concerned with the reversible isomerization of D-glucose to D-fructose. Other isomerizations of carbohydrates of potential value to the sweetener industry will not be discussed in this Chapter. 

The studies of the nonenzymic interconversion involving D-glucose and D-fructose have proved important to the development of certain fundamental principles of carbohydrate chemistry. Industrial scientists have always been interested in applying this knowledge to de- 

At the present time, commercial isomerization processes based on enzymic catalysis are predominant, so only brief mention will be made of some of the nonenzymic processes that have been considered for commercialization in the past. Probably the major reasons for the current commercial use of enzymic rather than nonenzymic systems are that the nonenzymic systems so far developed result in products having one or more of the following defects too much ash, color, acid, off-flavor, a content of D-mannose or D-psicose, and high ratios of D-glucose to D-fructose. Probably, further advances in our understanding of the isomerization reaction and the mechanisms of the catalysis will lead to more efficient, nonenzymic processes that could replace the enzymic-isomerization systems now used commercially. 

Some of the nonenzymic processes for the isomerization of D-glu-cose to D-fructose described in the literature are as follows. 

D-glucose yields 67 g of D-fructose and 10 g of D-glucose. After isomerization, the pH of the solution is so adjusted as to cause precipitation of aluminum hydroxide, and the D-fructose is isolated by precipitation as its calcium complex, from which a solution of pure D-fructose is obtained by treatment of a slurry of the complex27 in water with carbon dioxide. 

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