Formulation studies on stability of solid-state proteases for detergent applications

Enzymes are one of the most important components in the laundry detergents. They effectively contribute to the washing process by decreasing energy and water consumption, reducing environmental load of detergent products, leaving non-toxic water effluents and providing fabric care. Ensuring proper storage stability of enzyme granulates in the chemically hostile detergent matrix is a major challenge.

It is believed that the main factors responsible for activity loss are humidity and H2O2 released from the bleaching agents. In this study, the mechanism and inactivation kinetics of freeze-dried detergent protease, Savinase, were determined in a newly developed experimental setup, providing rapid assessment of solid-state enzyme stability under oxidizing conditions.

The method was based on exposure of an enzyme column to known concentrations of H2O2 (g) and humidity in a thermally stabilized chamber. The kinetic studies revealed that the inactivation rate constant depends on the square of moisture adsorbed by the enzyme at corresponding temperature; and the inverse of the reaction rate constant is proportional to inverse of H2O2 concentration in the system.

The peptide mapping studies showed that, the inactivation was caused by single-oxidation of the enzyme at Met222 residue. Formulation studies revealed that, having an anti-oxidative property,Na2S2O3 had a better activity-preservation effect compared to Na2CO3, retaining 80% and 60% residual activity, respectively.

In addition, mixing the antioxidant homogeneously with the enzyme was found to provide a better protection than coating the salt as a separate layer due to crack formation and/or deliquescence of Na2S2O3 at high humidity.