High hydrostatic pressures affect chemical reactions and phase changes of matter, denaturing proteins, solidifying lipids and disrupting biological membranes. The consequences of this in food systems has importance in killing spoilage microbes without the need for heat. Some applications of high pressure treatment to the processing of citrus juices are included herein. Effective pressures for pasteurization of yeasts and yeast ascospores in citrus juice fall in the range of 43,000–72,000 psi. The corresponding Dp (time for 1 log cycle reduction) values for inactivation of ascospores were 10 min at 43,000 psi or 8 sec at 72,000 psi. Pressure treatments of orange and grapefruit juices to by-pass thermal processing for pectinesterase (PE) inactivation were in the range of 72,000–130,000 psi. Dp values for orange PE inactivation at 72,000 and 87,000 psi were 83.3 minutes and 2.4 minutes, respectively. Pressures ≥87,000 psi caused instantaneous inactivation of the heat labile form, but did not inactivate the heat stable form of PE. Heat labile grapefruit PE was also more sensitive than orange to pressure. Orange juice pressurized at 100,000 psi for 1 minute had no cloud loss for >50 days.
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