Abstract: In order to promote the industrialization of not from concentrated orange juice (NFCOJ), ultra-high pressure (UHP) sterilization was used for the inactivation of pectin methylesterase (PME) and peroxidase (POD) in orange juice. UHP treatment for fresh juice was performed at ambient temperature and pressures ranging from 200 to 600 MPa. The remaining activity of PME (pectin methylesterase) and POD (peroxide dismutase) in processed juice was measured by titration and UV-visible spectroscopy, respectively. The results showed both enzymes were slightly activated after 10-min treatment at 200 MPa. An obvious inactivation of PME and POD were observed when the pressure was higher than 300 MPa up to 600 MPa and the treatment time was prolonged, and the inactivation in the pressure range from 300 to 600 MPa was fitted well to the first-order kinetic model. Moreover, PME was more sensitive to pressure than POD.

Key words: orange juice, high pressure processing, peroxidase (POD), pectin methylesterase (PME), activation, first-order kinetic reaction