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Thermal inactivation kinetics of lysozyme and preservative effect beer Makki, Farid


Thermal stability of lysozyme in aqueous buffer solutions was studied at different temperatures (73-100°C), pH values (4.2-9.0) and levels of sucrose (0, 5%, 15%) and sodium chloride (0, 0.1M, 1M). The results, fitted to a first order model and expressed in terms of decimal reduction time (D), inactivation rate constant (k), decimal reduction temperature (z) and Arrhenius activation energy (Ea indicated that lysozyme was most stable at pH 5.2, and thermal stability decreased sharply as the pH increased to 9.0. A regression equation for prediction of k as a function of temperature and pH was derived, with the best fit obtained for the model in the pH range of 5.2-7.2 (adjusted multiple r2=0.975). At pH values of 7.2 and 9.0, sodium chloride had a clear stabilizing effect against heat inactivation of lysozyme. Sucrose stabilized lysozyme against heat inactivation at 75°C but not at 91°C. Results of the study of the thermal inactivation kinetics of lysozyme proved to be practical and useful for prediction of residual lysozyme activity in the pH and temperature range studied. Thermal inactivation kinetics of lysozyme and its potential to prevent or delay microbial growth were also investigated in beer. Lysozyme at concentrations of 10 and 50 ppm appeared to delay growth of the spoilage bacteria L. brevis and P. damnosus in beer, but did not prevent growth of the bacteria.

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