Optimizing Glucose Isomerization to Fructose: A Comprehensive Exploration

In the realm of industrial processes, the reversible isomerization of glucose to fructose holds paramount importance. With an equilibrium conversion rate of 50% under industrial conditions, this slightly endothermic reaction is typically conducted at 60°C and a pH range of 7-8. To circumvent prolonged reaction times, the conversion is usually limited to about 45%. Achieving economic viability in this isomerization reaction necessitates the utilization of an immobilized enzyme, where optimal conditions are crucial for obtaining a satisfactory yield of fructose.

Immobilized Enzyme System: Sweetzyme T

To meet the economic demands of the isomerization reaction, an immobilized enzyme system proves indispensable. Sweetzyme T, developed by Novo Nordisk using a mutant strain of Streptomyces murinus, exemplifies an effective solution. The immobilization process involves disrupting cell concentration, cross-linking with glutaraldehyde, dilution, flocculation, extrusion, fluid-bed drying, and sieving. This meticulous process results in rigid enzyme granules, preventing compaction during operation.

Isomerization Conditions: Striking the Optimal Balance

The success of the isomerization process hinges on maintaining optimal conditions. The pH plays a pivotal role, necessitating levels around 7.5 or higher to ensure high enzyme activity and stability. However, under such conditions, glucose and fructose are prone to decomposition, leading to the formation of organic acids and colored by-products. To mitigate these challenges, a fixed-bed reactor process employing a continuous flow of glucose is employed, limiting the reaction time.

Isomerization Temperature: Balancing Act

The isomerization temperature significantly influences enzyme activity, stability, and byproduct formation. While the standard operating temperature is 60°C, higher temperatures enhance enzyme activity at the cost of stability and productivity. Lowering temperatures improves stability and productivity but heightens the risk of microbial infection. The choice of temperature, therefore, involves a delicate balance, with hygiene levels and feed purity dictating the decision.

Isomerization pH: Striving for Optimal Conditions

The pH level during isomerization affects enzyme activity, stability, and byproduct formation. While maximum activity occurs at pH levels above 8, stability peaks between pH 7.2 and 7.5. A delicate balance is essential to achieve optimal enzyme economy and high syrup quality. Inlet pH levels between 7.5-8.0, measured at 25°C, are recommended, with the potential use of mild buffering agents for pH control.

Isomerization Glucose and Fructose Concentration: Striking Efficiency

The concentration of glucose and fructose in the feed syrup plays a crucial role in optimizing the isomerization reaction. Higher feed syrup dry-substance content (40-50%) is preferred to maximize the isomerization rate. However, caution is advised against excessive fructose content, as it can lead to decreased isomerization rates approaching chemical equilibrium. Managing fructose content and maintaining an optimal dry-substance concentration ensures efficiency in the isomerization process.

In conclusion, the isomerization of glucose to fructose is a nuanced process that demands meticulous attention to various parameters. The delicate interplay between temperature, pH, and substrate concentrations ultimately determines the success and economic viability of this industrial transformation. Sweetzyme T, with its carefully engineered properties, stands as a testament to the continuous pursuit of efficiency in glucose-fructose conversion processes.

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