Effect of ultrahigh hydrostatic pressure on the activity and structure of mushroom (Agaricus bisporus) polyphenoloxidase.

High hydrostatic pressure (HHP, treatment pressure ≤700 MPa) is approved to be the most successful commercial nonthermal processing due to its minimal modifications in nutritional and sensory quality. However, for some pressure stable enzymes such as PPO, this unique technology can hardly inactivate them at treatment pressure below of 700 MPa. This study investigated the effects of ultrahigh hydrostatic pressure (UHHP, treatment pressure >700 MPa) on the activity of Agaricus bisporus mushroom polyphenoloxidase (PPO) both in the phosphate buffer and in the mushroom puree, and on the structure of the enzyme by means of circular dichroism (CD), fluorescence emission spectra, and sulphydryl group detection. The results showed that UHHP treatment at pressure from 800 to 1600 MPa caused significant inactivation on the PPO both in the phosphate buffer and in the mushroom puree. UHHP treatment at 1400 and 1600 MPa for 1 min reduced the enzyme activity by 90.4% and 99.2% in the buffer;, however, higher enzyme activity remained in the puree after UHHP treatment at the same condition. CD and fluorescence spectra analysis showed that the secondary and tertiary structures of UHHP treated mushroom PPO were changed. The sulphydryl group (SH) detection revealed that the SH content on the surface of UHHP treated mushroom PPO was increased. It has been suggested that the inactivation of mushroom PPO by UHHP treatment at pressure higher than 1000 MPa was due to the synergistic effect of the pressure and the heat arising from pressurization, in which heat plays a major role.