Microbiological Aspects of Novel Food Processing Technologies

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Microbiological Aspects of Novel Food Processing
Technologies

• Margaret Patterson, Food Microbiology Branch,
  Agri-Food and Biosciences Institute, Newforge
  Lane, Belfast, UK
• margaret.patterson_at_afbini.gov.uk

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What do consumers expect from their food?

• Consumers expect safety and most want quality
  fresh, good to eat, good nutrition, natural,
  additive free, convenience, shelf-life, novelty.
• Traditional thermal processing (pasteurisation,
  retorting, chilling, freezing) well accepted.

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Overview of Presentation

• Brief discussion of new food processing
  technologies.
• Managing the microbiological safety of foods
  produced using novel processes.
• Importance of correctly identifying process
  criteria to ensure food safety (and quality).

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What are the alternatives to conventional
processing technologies?
Thermal technologies Ohmic heating
Microwave Radio frequency heating Inductive
heating Super chilling
Non-thermal technologies High pressure
processing (HPP) Pulsed electric
fields Irradiation Pulsed light Cold
plasma Ultrasound Oscillating magnetic fields
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How High is High?
High Pressure Processing (HPP)

Weight of 3 elephants on a strawberry 500 MPa
Treatment usually applied for lt 5 min and at
20oC
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Units of Pressure

• 100 MPascals (1 Pascal 1 Newton/m2)
• 1000 bar
• 987 atmospheres
• 15,000 psi
• Most food applications 300-600 MPa

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High Pressure Processing

• High hydrostatic pressures (up to 600 MPa)
• usually applied lt 5 min.
• Kills vegetative bacteria, yeasts and moulds.
• Less effective on spores unless combined
• with heat.
• Shelf-life similar to heat pasteurisation but
  less
• detrimental effects on quality.

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How does High Pressure work?
Relatively simple structures, such as vitamins,
colour and flavour molecules not affected by
pressure.
Quality attributes
More complex molecules, such as proteins are
denatured.
Kills microorganisms (safety shelf-life) Produce
s new product concepts e.g. shucking of shellfish
Avure
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What pressure-treated foods are available
commercially?
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Pulsed Electric Fields

• High voltage pulses (20-80kV/cm) applied
• to food passing between 2 electrodes
• (2-100 µsec).
• Kills vegetative bacteria, yeasts and moulds.
• Less effective against spores.
• Shelf-life similar to heat pasteurisation but
  less
• detrimental effects on quality.

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How does PEF kill bacteria? - Zimmermans theory
and Electroporation

Membrane
Electrodes
Ec Critical electric field
From Manas, 2004
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Pulsed Electric Fields

• High voltage pulses (20-80kV/cm) applied
• to food passing between 2 electrodes (2-100
  µsec).
• Kills vegetative bacteria, yeasts and moulds.
• Less effective against spores.
• Shelf-life similar to heat pasteurisation but
  less
• detrimental effects on quality.

Potential applications include juices, Milk,
yoghurt, soups, liquid eggs.
Food must be liquid or semi-liquid. Particulate
size limited. Foods must have no air
bubbles Foods need to have low conductivity
PEF facility at Ohio State University
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Irradiation

• lt10 kGy sufficient for most
• applications.
• Effective against bacteria, yeast and moulds
• High doses can be used to
• sterilise foods.

Source hoists
Radiation room
Radiation shield
Unloading area
Controls
Loading area
Co60 in Storage Pool
Can be used on a wide range of products Equipment
commercially available
Great consumer resistance Regulatory/approval
issues
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Pulsed Light Technology

• Uses intense short duration pulses of broad
  spectrum white light (UV, visible, near
  infra-red)
• Microbial kill through photochemical and
• photothermal mechanisms.
• Little/no effect on vitamins.
• Limited studies on enzymes suggest some
  inhibition.

Econos Japan Co.Ltd
Surface decontamination of unpackaged food and
liquids. Can be used for foods packaged in PLT
transparent films. Sterilisation of packaging
films
No commercial food facilities as yet, although
patented.
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Heat v Non-thermal Technologies
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Food Safety Management of Novel Technologies

• Practical issues to be considered by
• - Consumers
• - Processors
• - Buyers
• - Regulatory authorities
• - International Trade

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Management of Microbial Hazards

• Setting Food Safety Objectives (FSOs)
• Use of Performance Criteria
• Use of Process criteria
• Use of HACCP and Good Hygiene Practices

International Commission on Microbiological
Specification for foods (ICMSF) Guidelines (2001)
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Food Safety Objectives

• Specifiy goals which can be incorporated into the
  design of control measures during processing.
• Measure effectiveness/adequacy of control
  measures.
• Links risk management with risk assessment.
• Allows comparison between different control
  measures.
• - useful when considering novel processing
  technologies.

Stewart et al (2002), Innov..Fd Sci Emerg,
Technol. 3 105-112.
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Theoretical Example Cooked poultry meatHazard
Listeria monocytogenes
FSO Performance Process
Criteria Criteria
To achieve level of lt100/g at point of-sale
A 6D reduction
Heat 2 min_at_70oC
Ionising radiation 3.25 kGy_at_ 10oC
HPP 10 min _at_ 600 MPa/20oC
Adapted from Stewart et al (2002), Innov. Fd Sci
Emerg, Technol. 3 105-112.
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Microbiological Process Criteria

• Resistance of pathogens
• Influence of food matrix
• Validating the process
• Define the critical limits

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Pressure resistance of some foodborne pathogens
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Determine resistant pathogen of concern that is
likely to survive the process.

• Depends on intended use and technology used to
  process food.
• Pathogen with greatest resistance to one
  treatment may not be most resistant to another
  type of treatment.

• Use strains with high, but not abnormal,
• resistance?

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Variation in pressure resistance between strains
of E. coli O157H7
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Consider impact of food matrix on survival of
pathogens

• Substrate can affect survival
• Food composition
• pH
• Water activity

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Substrate can affect extent of pressure
inactivation
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Validate efficacy of process

• Vary critical factors to determine margin of
  safety.
• For example
• - Incubation and enumeration
  conditions
• - Injury and recovery
• Use appropriate statistical design

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HPP cooked poultry meat

• Aim Use HPP to extend the shelf-life of
  MAP/vacuum packaged cooked chicken meat to 30
  days with storage at 8oC.
• Hazard Growth of psychrotrophic Clostridium
  botulinum (and toxin production).

Performance criteria
Process criteria
FSO
Heat Cook at 90oC for 10 min (or equivalent)
A 6 log reduction in psychrotrophic C. botulinum
spores
absence of neurotoxin at point-of-consumption
HPP equivalent? or Heat HPP equivalent?
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Ongoing work

• Inoculation studies with Clostridium botulinum
  spores.
• Spores added to raw meat, which is cooked and
  then pressure treated.
• Microbiological quality, including toxin
  production, monitored during extended storage at
  8oC.

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Summary

• Increasing consumer demand for high quality foods
  that are free from additives, fresh tasting,
  convenient, microbiologically safe and with an
  extended shelf-life
• New food processing technologies, often
  non-thermal, being developed to meet this
  demand.
• Need to establish food safety control measures
  equivalent to traditional heat processing.
• Many factors can interact to influence the
  process criteria. These must be considered in
  order to produce high quality, microbiologically
  safe products.

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Acknowledgements
Thanks to The Food Preservation team Mark
Linton Alan McKay Malachy
Connolly Aideen Mackle Gareth
Ridgway The Department of Agriculture
Rural Development. The Agri-Food
Biosciences Institute