The enzyme pectinesterase (PE) reduces the quality of citrus juices. Current inactivation of the enzyme is accomplished by heat, resulting in a loss of fresh fruit flavor in the juice. We explored the use of pressurized treatments of orange and grapefruit juices to bypass the use of extreme heat during processing. PE inactivation using isostatic high pressure in the range of 500-900 MPa was accomplished in orange and grapefruit juices. The higher pressures (600 MPa) caused instantaneous inactivation of the heat labile form of the enzyme but did not inactivate the heat stable form of PE. Treatment times caused significantly different (alpha = 0.05) total PE activity losses in orange but not in grapefruit juices, and PE inactivation at different pressures was significantly different in both juices. Heat labile grapefruit PE was also more sensitive than orange to pressure. D(p) values for orange PE inactivation at 500 and 600 MPa were 83.3 and 2.4 min, respectively; while the z(p) value between 500 and 600 MPa was 65 MPa. Orange juice pressurized at 700 MPa for 1 min had no cloud loss for 50 days