Ewen C. D. Todd

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Cross Contamination

• Ewen C. D. Todd

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A Systems Approach to Minimize Escherichia coli
O157H7 Food Safety Hazards Associated With
Fresh- and Fresh-cut Leafy Greens
Production Primary Handling
Processing Packaging
Distribution Shelf-life
Minimizing an increase in levels

• Minimizing
• initial levels
• Composting (1)
• Internalization (2)
• Cross contamination (3)
• Processing water (4)

Reducing levels
Food Safety Objective (8)

• Physical Chemical
• Treatments (5)

• Survival Growth (6)

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Risk Analysis Model (7)
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Risk Assessment and Management of Leafy Greens

• Fernando Pérez-Rodríguez, Food Science and
  Technology, University of Córdoba, Córdoba,
  Spain.
• Martin Cole and Alvin Lee, National Center for
  Food Safety and Technology, Summit Argo, IL
• Tom Ross, Tasmanian Institute of Agricultural
  Research School of Agricultural Science
  University of Tasmania, Hobart, Australia
• Ewen Todd, Ewen Todd Consulting, Okemos, MI

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QRA Scheme of Production of Minimally Processed
Vegetables
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Leafy Green Processing Shredding and Washing
Conveyor
Shredder
Flume tank
Shaker table
Centrifugal dryer
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Sampling for Transfer 11 Flume Tank and 9 Shaker
Table Samples
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Leafy Green Processing (Lettuce and Spinach)

• Number of batches processed in a day 22 ( 3
  batches/h) contamination may occur at any stage
• Batch size 1000 kg
• Number of bags per batch 10,000
• Bag size 100 g

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Modeling Transfer

• Modeling cross contamination by E. coli O157H7
  during processing of leafy greens (spinach)
• Probabilistic model
• Two-dimensional model
• Uncertainty
• Variability
• Probability distributions describing transfer
  experimental data
• Contaminated product to Equipment
• Equipment to Non-contaminated product

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Cross Contamination Simulations

• The model was simulated by applying Latin
  Hypercube Sampling technique implemented with
  _at_Risk
• The simulation consisted in 10 uncertainty
  realizations and 1000 variability iterations
• The outputs were prevalence and concentration of
  E. coli O157H7 at the end of the processing line
  (bags)

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Modeling Transfer
Transfer (at low level) Maximum Mininum Mean Distribution
Spinach-Centrifuge 0.08 0.01 0.04 Beta
Spinach-Flume 0.24 0.00 0.06 Beta
Spinach-Shaker 0.12 0.00 0.06 Beta
Spinach-Water 52.65 0.00 10.78 Beta
Lettuce-Shredder 0.02 0.00 0.02 Log-Normal
Lettuce-Flume 0.02 0.00 0.01 Log-Normal
Lettuce-Shaker 0.02 0.00 0.01 Log-Normal
Lettuce-Conveyor 0.24 0.00 0.10 Log-Normal
Lettuce-Water 10.46 0.00 8.79 Beta
Equipment-Lettuce 18.83 9.90 15.33 Log-Normal
Transfer data expressed as a percentage ()
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Modeling Transfer
Beta distribution describing transfer
rates contaminated spinach?shaker
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Leafy Green Processing
Conveyor
Shredder
Flume tank
Shaker table
Centrifugal dryer
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Modeling Cross-contamination
ESTIMATING TRANSFER USING DISTRIBUTIONS Monte
Carlo Simulation
Risk
Tr()EB
Tr()AE
Product A (cfu/g)
Product B (cfu/g)
Transfer rate from Product A to Equipment
Tr()AE Transfer rate from Equipment Product B
Tr()EB
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Modeling Assumptions

• As contamination by E. coli O157H7 is sporadic
  event (Doyle Eriksson, 2007), it is assumed
  that only one contaminated batch would be in the
  processing line, and this variable was modeled as
  a stochastic process being an uncertainty source
• Transfer was expressed as transfer percentage
  () proportion of cells transferred from donor
  surface (food, water or equipment) to receptor
  surface (food, water or equipment) expressed in
• Transfer rate () (cfu receptor surface/ cfu
  donor surface)100
• Transfer rates for the modeling were estimated
  using experimental data obtained at low
  contamination levels
• Growth rate was determined as under some
  refrigeration after processing

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Cross-contamination Model
The analysis of iterations showed that E. coli
O157H7 was transferred to the product at very
low levels, average being 1-6 cfu/bag
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Managing Risk from Risk Assessment outputs
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A Systems Approach to Minimize Escherichia coli
O157H7 Food Safety Hazards Associated With
Fresh- and Fresh-cut Leafy Greens
Production Primary Handling
Processing Packaging
Distribution Shelf-life
Minimizing an increase in levels

• Minimizing
• initial levels
• Composting (1)
• Internalization (2)
• Cross contamination (3)
• Processing water (4)

Reducing levels
Food Safety Objective

• Physical Chemical
• Treatments (5)

• Survival Growth (6)

-

?
Risk Analysis Model (7)
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Generic Process Risk Assessment Model (Whiting,
2009)
Performance Objectives
Microbiological Criteria
Raw ingredients
Heating
Storage Trans. Periods
Consumption
Illness
Acceptable Level Of Protection
Performance Criteria (logs
inactivation) Process Criteria (C -
min) Product Criteria (pH, salt)
Food Safety Objective
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Food Safety Objectives

• Ho - ?R ?I FSO
• Ho initial contamination
• ?R sum of reductions
• ?I sum of increases
• FSO Food Safety Objective

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Setting the FSO

• Food safety objective (FSO) the maximum
  frequency and/or concentration of a hazard in a
  food at the time of consumption that provides or
  contributes to the Appropriate Level of
  Protection (ALOP)
• There is no one way to set a FSO by an assessor
  because it is a decision made by managers in the
  context of scientific and other parameters
• A possible FSO for E. coli O157H7 is 10-4/g
  based on the FDA Juice HACCP regulation 1 cfu
  in 10 kg

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Flow Chart for Production of Leafy Greens
Farms
Harvest Clear cut
Initial Number Ho
Transport In Bins
Reduction of Hazard ?R
Dump tank
Sanitizer Tank
Rinse Tank
Potential Increase ?I
Shredder
Food Safety Objective FSO
De-watering Centrifuge
Irradiation/testing/ Ultrasound/chilling
Consumption
Distribution,Retail Storage in Home
Packaging
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Possible Decontamination Strategies

• Testing. Increased testing and removal of
  possible contaminated product the more samples
  tested, the more the contaminated product is
  likely to be discovered and removed
• Chilling. Regardless of atmosphere and E. coli
  O157 inoculation level, populations of the
  pathogen decreased only when the temperature was
  7C
• Ultrasound with chlorine. High power ultrasound
  (HPU) for 120 sec in the presence of 200 ppm
  chlorine at 10 or 20C inactivated 1.3 or 0.5 log
  E. coli O157/g, respectively, more than 200 ppm
  chlorine without HPU
• X-ray irradiation. A 5-log reduction likely
  achievable at a dose of 0.2 kGy with a X-Ray
  irradiator

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Example of Achieving a FSO in Leafy Greens
Ho - ?R ?I FSO
lt 1/10kg
14 Days Shelf-Life 12oC 1 log Increase 5oC 1
Log Decrease
3.0 9.2 MPN/g generic E.coli (Valentin-Bon et
al, 2008) Worst case 10/g Testing to
eliminate highly contaminated lots 15 x 25 g
samples -2.63 1 cfu/400g (S.D.0.8)
200 ppm chlorine plus high power ultrasound 2.43
Log reduction (S.D.0.67)
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Ho - ?R ?I FSO

• ?R sum of reductions
• in leafy green processing/distribution,
  reductions through
• washing and sanitizer (W/S)
• ultrasound (U)
• chill storage (C)
• ?R Rw/s Ru Rc
• ?I I Growth at 12ºC

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Ho Rw/s Ru Rc ?I FSO
Possible Inputs to Achieve FSO
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Scenario 1 log cfu/g
Ho -1 Rw/s 0 Ru
0 Rc 0 ?I 1
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Scenario 2 log cfu/g
Ho -1 Rw/s 1.86 Ru
0 Rc 0 ?I 0
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Scenario 3 log cfu/g
Ho -1 Rw/s 1.86 Ru
0.57 Rc 0 ?I 0
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Scenario 4 log cfu/g
Ho -2.52 Rw/s 1.86 Ru
0.57 Rc 0 ?I 0
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Scenario 5 log cfu/g
Ho -2.52 Rw/s 1.86 Ru
0.57 Rc 1 ?I 0
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Scenario 6 log cfu/g
Ho -4.09 Rw/s 1.86 Ru
0.57 Rc 0 ?I 0
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Scenario 7 log cfu/g
Ho -4.09 Rw/s 1.86 Ru
0.57 Rc 1 ?I 0
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Interventions Original Contaminated Batch
FSO -4 log cfu/g
Frequency ()
E. coli O157H7 (Log cfu/g)
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Interventions Effect Cross-contaminated Batch
FSO -4 log cfu/g
0 log (1 cfu/g)
Frequency ()
E. coli O157H7 (Log cfu/g)
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FSOs and POs (van Schothorst et al., 2009)

• ALOP expression of the level of protection in
  relation to food safety that is currently
  achieved
• It is not an expression of a future or desirable
  level of protection
• FSO the maximum permissible level of a
  microbiological hazard in a food at the moment of
  consumption
• Maximum hazard levels at other points along the
  food chain are called Performance Objectives
  (POs)
• PO the maximum frequency and / or concentration
  of a hazard in a food at a specified step in the
  food chain before consumption that provides or
  contributes to an FSO or ALOP, as applicable

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FSOs and POs (van Schothorst et al., 2009)

• Industries may have to validate that their food
  safety system is capable of controlling the
  hazard of concern, i.e., to provide evidence that
  control measures can meet the targets
• In addition, industry must periodically verify
  that their measures are functioning as intended
• To assess compliance with FSOs and POs, control
  authorities rely on inspection procedures (e.g.,
  physical examination of manufacturing facilities,
  review of HACCP monitoring and verification
  records, analysis of samples) to verify the
  adequacy of control measures adopted by industry

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FSOs and POs (van Schothorst et al., 2009)

• Safe food is produced by adhering to GHPs, GMPs,
  GAPs, etc., and implementation of food safety
  risk management systems such as HACCP, but the
  level of safety that these food safety systems
  are expected to deliver is usually not in
  quantitative terms
• Establishment of FSOs and POs provides the
  industry with quantitative targets to be met
• Although FSOs and POs are expressed in
  quantitative terms, they are not Microbiological
  Criteria (MCs) which are defined as the
  acceptability of a product or a food lot, based
  on the absence/presence or number of
  microorganisms including parasites, and/or
  quantity of their toxins/metabolites, per unit(s)
  of mass, volume, area or lot
• MCs are designed to determine adherence to GHPs
  and HACCP (i.e., verification) when more
  effective and efficient means are not available

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Generic Process Risk Assessment Model
Performance Objectives
Microbiological Criteria
Raw ingredients
Heating
Storage Trans. Periods
Consumption
Illness
Acceptable Level Of Protection
Performance Criteria (logs
inactivation) Process Criteria (C -
min) Product Criteria (pH, salt)
Food Safety Objective