PARAMETRIC STUDY AND OPTIMIZATION OF D-GLUCOSE ISOMERIZATION USING SWEETZYME IT: A FACTORIAL DESIGN APPROACH

Abstract

High-fructose corn syrup (HFCS) is produced industrially by the immobilized glucose isomerase Sweetzyme IT (from Streptomyces murinus), one of the most widely used biocatalysts in the food industry. Although its individual operating parameters are well established, simultaneous interactions between operational variables over time have rarely been systematically quantified. In this study, a two-level full factorial design modeled the combined effects of initial glucose concentration, temperature and Mg²⁺ cofactor concentration on the process. Reaction progress was followed polarimetrically through a dedicated glucose-fructose calibration; concurrent refractometric monitoring proved insensitive due to total dissolved solids conservation. The regression models (R² > 0.99) identified temperature as the dominant operational factor. Incorporating reaction time as a factor revealed a significant temperature × time interaction and a shift of rate control from initial substrate concentration to temperature near equilibrium. A maximum conversion of 45.98 % (close to the thermodynamic equilibrium of the reaction) was obtained at 0.2 M glucose, 60 °C and 1.5 mM Mg²⁺ after 24 h. A comparative screening of divalent cations confirmed MgSO₄·7H₂O as the superior chemical activator, over Ni²⁺, Mn²⁺, Cu²⁺ and Ca²⁺ with Ca²⁺ among the poorest, consistent with its known inhibitory role. This study establishes a reliable mathematical approach that can be extended to predict and optimize other complex bioprocesses.