Effect of high-hydrostatic-pressure on molecular microstructure of mushroom (Agaricusbisporus) polyphenoloxidase

Abstract

To elucidate the mechanism of the high-hydrostatic-pressure (HHP)-induced inactivation of mushroom polyphenoloxidase (PPO), the enzyme was treated under the pressures ranging from 100 to 1600 MPa for 1 min. The PPO activity and molecular microstructure were examined using SDS-PAGE, native-PAGE, particle size distribution (PSD) analysis, atomic force microscopy (AFM) and transmission electron microscopy (TEM). The results showed that HHP treatment had little influence on PPO activity below 1000 MPa for 1 min, but it was almost completely inactivated at 1600 MPa for 1 min. Based on electrophoretic pattern, the pressure treatment had little influence on the primary structure of the PPO. Considering the molecular microstructure, the HHP-treated PPO exhibited a lower ζ-potential, higher average particle (PSD) and molecular diameters (TEM) and a blurred PPO boundary (AFM), indicating the aggregation of PPO after HHP treatment (>1000 MPa). Moreover, the changes in PPO after treatment at 80 °C for 1 min were similar to those observed after treatment at 1600 MPa. Combined with previous results for the molecular secondary and tertiary structure, a possible enzyme inactivation mechanism is proposed, in which the inactivation of PPO by HHP treatment was attributed to the disruption of the catalytic environment and the aggregation of the enzyme.