| Nonthermal methods of food preservation include the application of high hydrostatic pressure, oscillating magnetic fields, high intensity pulsed electric fields, intense light pulses, chemical and biochemicals, and combined methods. The present study discusses the development and potential applications of high hydrostatic pressure, oscillating magnetic fields, and high intensity pulsed electric fields for food preservation. The high intensity pulsed electric field induced ultrastructural changes in Escherichia coli and Staphylococcus aureus are also discussed.;High pressure causes inactivation of microorganisms including Escherichia coli, Salmonella typhimurium, Salmonella senftenberg, Listeria monocytogenes, Vibrio parahaemolyticus, Campylobacter jejuni, Staphylococcus aureus, Pseudomonas aeroginosa and others at a pressure of 4,000 to 9,000 atm. In addition spores and enzymes can also be inactivated using high pressure. However certain enzymes are activated with high pressure treatment.;Oscillating magnetic fields (5 to 50 Tesla) inactivate microorganisms including Saccharomyces cerevisiae, Streptococcus thermophilus, Escherichia coli and mold spores. Food products sealed in plastic containers are subjected to the magnetic fields. One of the advantages of using magnetic fields for food preservation is the reduced risk of contaminating the food during packaging. Magnetic field processing is safe to perform and does not induce detectable changes in the quality of food.;High intensity pulsed electric fields (;Scanning (SEM) and transmission electron microscopy (TEM) were used to examine the ultrastructures of pulsed electric field treated Escherichia coli and Staphylococcus aureus. SEM of E. coli did not indicate significant differences in the ultrastructure while some roughening of the surface was seen in S. aureus. TEM of E. coli indicated drawing away of cytoplasmic membrane from the outer membrane, crenations in the outer membrane, and changes in the cytoplasmic material structure. TEM of S. aureus showed rupture of cell wall, and changes in the cytoplasmic material structure.;Nonthermal methods of food preservation are energy efficient compared to the thermal methods and can produce better quality food products. |
