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Catherine N. Cutter |
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Department of Food Science |
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Penn State University |
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Ionizing radiation |
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Surface pasteurization |
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Electronic pasteurization |
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E-beam sterilization/pasteurization |
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Irradiation can directly impair critical cell
functions or components (DNA) |
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Single strand breaks (repairable in most cases) |
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Double strand breaks (not repairable in most
cases) |
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Irradiation can indirectly form radiolytic
products/free radicals from water (oH, oOH) |
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oOH radicals are responsible for 90%
of DNA damage |
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Growth phase: |
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Some microorganisms (L. monocytogenes) are more
susceptible to irradiation at low doses when irradiated during the
logarithmic phase of growth then during the stationary phase |
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Type of food |
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The more complex the food, the greater the
competition of the food for the energy and less for the microorganisms |
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Fat content of ground beef does not change the
dose needed to eliminate E. coli O157:H7 |
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C. jejuni was more resistant to irradiation in
low fat frozen beef |
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Moisture content |
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The lower the water activity in a food, the less
free radicals produced by water--> less DNA damage to microorganisms |
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Temperature of food |
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Higher temperatures enhance the lethal effect of
irradiation |
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Microorganism repair mechanisms are impaired at
the higher temperatures |
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Freezing immobilizes water and prevents
diffusion of free radicals to microorganisms |
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Presence of oxygen |
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Higher oxygen concentration = greater lethal
effect of radiation on microorganisms |
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Anaerobic conditions = less lethal effect of
radiation on microorganisms |
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Storage conditions can enhance recovery of some
microorganisms after irradiation |
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Packaging atmosphere: |
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Irradiation of L. monocytogenes in ground turkey
was more lethal when performed in the presence of air, followed by modified
atmosphere packaging (MAP, >50% carbon dioxide) or vacuum packaging
(VP), |
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Irradiation was less effective against LM or Salmonella
spp. when performed under MAP or VP |
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Spoilage organisms, especially pseudomonads, are
susceptible to low dose irradiation |
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Spoilage of low dose irradiated meats may be due
to yeast, LAB, or Moraxella spp. (increased lag time) |
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Gram negative bacteria < Gram positive
bacteria/molds/yeast < spores and viruses |
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Differences in resistance are due to: |
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chemical and physical structure of microorganism |
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ability to recover from radiation injury |
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Deinococcus radiodurans is highly resistant to
irradiation |
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Acid resistant E. coli O157:H7 exhibit radiation
resistance |
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Of pathogens tested in ground beef, C. jejuni has lowest resistance to
irradiation; Salmonella spp. has the highest resistance |
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Determination of processes (heat,
antimicrobials, curing agents, etc.) that may affect radiation resistance
of pathogens in fresh meats |
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The effect of multi-hurdle approach with
irradiation to enhance pathogen reduction or improve shelf life in fresh
meats |
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Determining effects of irradiation on different
cooked meat products to inhibit organisms such as LM |
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Determining effects of atmospheres and packaging
regimens on pathogens associated with cooked meats subjected to low dose
irradiation |
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Notes