Heat-induced Transparent Gel from Hen Egg Lysozyme by a Two-step Heating Method

The effects of ionic strength and dithiothreitol concentration, a reducing agent, on the heat-induced gelation of a lysozyme solution were examined at pH 7. Two different heating methods were used, one involving single heating, and the other, a two-step heating process in which a sample solution was heated twice under different medium conditions. With 7.5 mM dithiothreitol, a 5% lysozyme solution gave a transparent sol, a transparent gel, a translucent gel and a turbid gel after a single heating with 0, 40, 50, and 60mM NaCI, respectively. When the transparent sol obtained without NaCI was reheated with 50mM NaCI, it produced a firm and transparent gel. This gel was at least 6 times harder than the transparent lysozyme gel obtained by the one-step heating method. High-resolution scanning electron microscopy showed that the transparent gel produced by the two-step heating method had a fine network of linear polymers composed of heat-denatured lysozyme molecules.