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

Area of Science:

• Food science and technology
• Biochemistry
• Materials science

Background:

• Protein gelation is crucial for food texture and biomaterial development.
• Lysozyme, a common protein, undergoes heat-induced gelation influenced by environmental factors.
• Understanding gelation mechanisms is key to controlling protein-based material properties.

Purpose of the Study:

• To investigate the impact of ionic strength and dithiothreitol on lysozyme heat-induced gelation.
• To compare the properties of lysozyme gels formed by single and two-step heating methods.
• To characterize the microstructure of gels formed under different conditions.

Main Methods:

• Lysozyme solutions were subjected to heat-induced gelation at pH 7.
• Ionic strength (NaCl concentration) and dithiothreitol concentration were varied.
• Single and two-step heating processes were employed.
• Gel properties (transparency, turbidity, firmness) were assessed.
• High-resolution scanning electron microscopy (HR-SEM) was used for microstructural analysis.

Main Results:

• Ionic strength and dithiothreitol concentration significantly influenced the gelation of lysozyme.
• A 5% lysozyme solution with 7.5 mM dithiothreitol formed transparent, translucent, and turbid gels with increasing NaCl concentrations (0-60 mM) after single heating.
• A transparent sol (0 mM NaCl) reheated with 50 mM NaCl yielded a firm, transparent gel.
• The two-step heated gel was over six times harder than the single-step heated transparent gel.
• HR-SEM revealed a fine network of linear polymers in the two-step heated transparent gel.

Conclusions:

• Two-step heating is a promising method for producing firmer, transparent lysozyme gels.
• Controlling ionic strength and heating protocols allows for tunable gel properties.
• The microstructure of heat-denatured lysozyme polymers dictates gel characteristics.