Optimization of the components concentrations of the lactoperoxidase system by RSM

The aim of this work was to use response surface methodology (RSM) approach, a statistical mathematical tool, to model effects and interactions of glucose oxidase (GOD), glucose, lactoperoxidase (LPO) and pH-values on the thiocyanate (SCN[superscript [-]]) peroxidation, to determine the best concentrations of lactoperoxidase system (LP-s) components in order to obtain maximal SCN[superscript [-]] peroxidation and so to enhance the LP-s antibacterial effects. Experimental design using RSM was used for modelling effects and interactions of GOD (28·5-142·5 IU l[superscript [-]1]), glucose (0·55-11·11 mmol l[superscript [-]1]), LPO (0-6284 IU l[superscript [-]1]) concentrations, and pH-values (6·0-7·4) on thiocyanate peroxidation. A fixed SCN[superscript [-]] concentration of 0·5 mmol l[superscript [-]1] was used. Experiments were carried out at 4 or at 25°C in 0·1 mol l[superscript [-]1] phosphate buffer. Optimized concentrations for both temperatures (4 and 25°C) were quite similar and were 85·5 IU l[superscript [-]1] for GOD, 8 mmol l[superscript [-]1] for glucose and 3927·5 IU l[superscript [-]1] for LPO at an initial pH-value of 6·5. SCN[superscript [-]] peroxidation was more efficient at 25 than at 4°C. At 4°C, no interaction between factors occurred. At 25°C, thiocyanate peroxidation was affected by GOD/glucose, GOD/pH and LPO/pH. Thiocyanate peroxidation was mainly increased by glucose and LPO factors. The optimized system had a bacteriostatic effect on Listeria monocytogenes CIP 82110[superscript T] and a strong bactericidal effect on Pseudomonas fluorescens CIP 6913[superscript T]. Appropriate combinations of LPO, GOD, glucose concentrations and pH-values allowed maximal thiocyanate peroxidation and enhanced the antibacterial effect of the LP-s. This optimization by RSM approach allowed a better understanding of the LP-s functioning, the description of the component impacts on the SCN[superscript [-]] peroxidation, and the observation of different interactions between the factors. The antimicrobial efficiency of LP-s can be enhanced by better concentration ratios of the LP-s components.