THERMAL INACTIVATION OF LYSOZYME AS INFLUENCED BY PH, SUCROSE AND SODIUM-CHLORIDE AND INACTIVATION AND PRESERVATIVE EFFECT IN BEER

Thermal stability of lysozyme in aqueous buffer solutions was studied at selected temperatures (73-100 degrees C), pH values (4.2-9.0) and l evels 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 decim al reduction time (D), inactivation rate constant (k), decimal reducti on temperature (z) and Arrhenius activation energy (E(a)) indicated th at lysozyme was most stable at pH 5.2, and thermal stability decreased sharply as the pH increased to 9.0. A regression equation for predict ion of k as a function of pH and temperature was derived, with the bes t fit obtained for the model in the pH range of 5.2-7.2 (adjusted mult iple r(2)=0.98). At pH 7.2 and 9.0, sodium chloride had a clear stabil izing effect against heat inactivation of lysozyme. Sucrose stabilized lysozyme against heat inactivation at 75 degrees C but not at 91 degr ees C. Thermal inactivation kinetics of lysozyme and its potential to prevent or delay microbial growth were investigated in beer. Lysozyme at concentrations of 10 and 50ppm appeared to delay growth of the spoi lage bacteria L. brevis and P. damnosus in beer, but did not prevent g rowth of the bacteria. (C) 1997 Canadian Institute of Food Science and Technology. Published by Elsevier Science Ltd.