Structural changes in Listeria monocytogenes treated with gamma radiation, pulsed electric field and ultra-high pressure
Posted: April 16th, 2012 - 12:58pm
Source: Journal of Food Safety, Volume 32, Issue 1, pages 66–73, February 2012
Understanding the mode of action of gamma (γ) radiation, pulsed electric field (PEF) and ultra-high pressure (UHP) against targeted pathogens should help improve implementation of these technologies. Listeria monocytogenes Scott A was treated with γ radiation, PEF and UHP at doses that caused equal lethality (3-log inactivation). These doses were 0.57 kGy at 5C (γ radiation), 30 kV/cm at 22C for 216 µs (PEF) and 400 MPa at 24 ± 1C for 6 min (UHP). When structural changes in cells of L. monocytogenes were compared using transmission electron microscopy (TEM), the nucleoid region of γ -irradiated cells appeared to have spread throughout the cytoplasm. UHP-treated cells showed aggregated cytoplasm, indicating extensive protein denaturing. Structural differences between PEF-treated and untreated cells were minimal, as revealed by TEM. Electrophoresis of genomic DNA from γ-irradiated L. monocytogenes showed considerable fragmentation. These DNA lesions were not detected when L. monocytogenes was treated with PEF or UHP. When irradiated cells were analyzed by pulsed field gel electrophoresis, the banding pattern changed into smearing. In conclusion, γ radiation, PEF and UHP targeted different loci in the cell, and thus synergy between these treatments against L. monocytogenes is likely.
Recently, there is an increase in the use of gamma (γ) radiation and ultra-high pressure (UHP) in food processing as alternatives to heat. Other promising technologies, such as pulsed electric field (PEF), are in the experimental stage. This is a side-by-side investigation of γ radiation, UHP and PEF that helps in understanding the mechanism of bacterial inactivation by these technologies. The study could also help food processors in determining the suitability of these technologies for particular applications.