Role of benzyl alcohol in the prevention of heat-induced aggregation and inactivation of hen egg white lysozyme.

The aim of the study was to investigate the stability of a model protein, lysozyme, in the presence of the commonly used preservative benzyl alcohol. Techniques including lytic assay, size exclusion chromatography, circular dichroism, differential scanning calorimetry, native polyacrylamide gel electrophoresis and dynamic light scattering were used to study the overall stability of lysozyme in the presence of benzyl alcohol. The stability of lysozyme against thermal stress was higher in the presence of benzyl alcohol. In the presence of 0.5%, 0.9% and 2% v/v benzyl alcohol, the enzyme showed 33%, 42% and 75% residual activity, respectively, when exposed to 75 degrees C for 2 h, as compared to the 22% activity of control sample. A gradual increase in the size of aggregates was observed for the control sample relative to the samples containing benzyl alcohol, as a result of loss of monomer concentration. The effect was found to be concentration-dependent with 2% benzyl alcohol showing maximum prevention of heat-induced unfolding and aggregation. This effect is remarkable since the thermal transition temperature of the enzyme decreases in the presence of benzyl alcohol. Benzyl alcohol favours the thermal denaturation of lysozyme but stabilizes the lysozyme against the heat-induced aggregation.