Effect of compressed fluids on the enzymatic activity and structure of lysozyme

•Activity and structure of lysozyme in SC-CO2, LPG and R134a were investigated.•The highest residual activity for high-pressure treatment was 141.0 ± 1.80%.•Alterations of secondary and tertiary structures of treated lysozyme were observed.•Exposure of residual groups of tryptophan to outer surface of enzyme was detected.

This study aimed at investigating the effect of pressure, ionic strength and depressurizing rate on the activity and structural conformation of lysozyme using pressurized CO2 (scCO2), liquified petroleum gas (LPG) and R134a as solvents. For this purpose, the experiments were carried out using a variable volume reactor under a 2 h of exposure time, at a temperature of 40 °C, varying pressure (100-200 bar), depressurizing rate (10-50 bar min−1) and concentration of sodium chloride (0-50 mmol L−1). The highest residual activity observed for high-pressure treatment was 141.0 ± 1.80% for the condition of 150 bar and depressurizing rate of 30 bar min−1. Analysis of conformational changes of the control and treated enzyme demonstrated that the primary structure of the enzyme remained unchanged and the level of secondary and tertiary structure measured by CD spectra and fluorescence showed potential conformational changes of lysozyme for all the conditions tested.

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