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Pathogen Reduction Dialogue Pathogen Reduction Dialogue Panel 3 Panel 3
Microbial Testing for Control Microbial Testing for Control VerificationVerification
Robert L. BuchananU.S. Food and Drug AdministrationCenter for Food Safety and Applied
NutritionMay 7, 2002
Microbiological TestingMicrobiological Testing
Microbiological testing important food safety tool
Technologically-based, statistically-based tool
Right tool for the right job
Microbiological TestingMicrobiological Testing
One of the most apparent, but poorly understood parts of food microbiology
Different types of microbiological testing Safety of “batches” * Process control * Investigational sampling Surveillance
Microbiological TestingMicrobiological Testing
Effective use requires a clear understanding of the goals, assumptions, and characteristics of testing programs
Microbiological TestingMicrobiological Testing
“Within batch testing” vs. “Between batch testing”
Different goals, assumptions, and techniques
Microbiological TestingMicrobiological Testing
“Within Batch Testing”: Demonstrate the safety of a single lot of food
Microbiological TestingMicrobiological Testing Within-batch testing
detailed “snapshot” of an operation assumes no prior knowledge of the
process focus on establishing safety (or
quality) of the batch provides only limited capability to
do trend analysis of performance over time
can be used nationally to acquire “state of industry”
Microbiological TestingMicrobiological Testing Effective within certain ranges
of contamination frequency or levels of contamination Above or below those ranges,
becomes increasingly ineffective When acceptable defect rate is
less than 1%, the number of samples needed becomes a limiting factor
Microbiological TestingMicrobiological Testing
“Between Batch Testing”: Demonstrate that a food safety system/process is continuing to function as intended
Microbiological TestingMicrobiological Testing
“Between-batch testing” not designed to assure batch safety
which is assumed to be safe if validated process is “in control”
assumes intimate knowledge of process
requires prior analysis for performance and variation
requires sampling over time can also be used nationally to assess
“state of industry”
Microbiological TestingMicrobiological Testing
“Between-batch testing” Much easier to demonstrate
that a process is not functioning within a specification than to prove that something (e.g., a pathogen) is not present
Sampling for Process Sampling for Process VerificationVerification Microbiological contamination
typically flows with a process A microbiological sample taken
within a process provides a measure that integrates all the preceding steps in a process
Sampling for Process Sampling for Process VerificationVerification The status of a multiple step
process is the summation the initial level of contamination and all the steps that increase or decrease the level of contamination
Microbial Status = Ho + Microbial Status = Ho + I + I + RR
Sampling for Process Sampling for Process VerificationVerification Sampling of end products integrates the
effects of the entire food safety system For investigations of cause, benefits to
taking samples at multiple locations
Process Control StatisticsProcess Control Statistics
The basis for process control evaluations is the collection of microbiological data over time
Typically arrayed graphically as a control chart
0.00.20.40.60.81.01.21.41.61.8
0 10 20
Sample Number
Log
(cf
u/g)
Process Control StatisticsProcess Control Statistics
First step is to conduct a process control study (baseline study) An “under control” process is run for a
period of time to access its “capabilities” and establish:
Central tendency (mean or median performance)
Variance Also used to establish limits (control
values) Often use 3
Process Control StatisticsProcess Control Statistics
Loss of process control is then assessed by determining if “defect rate” has become greater than what would be expected by “chance alone”
Approach can be used with either “variables” (quantitative data) or “attribute” (+/- or binned quantitative data) sampling plans
Example: Moving Window Example: Moving Window SumSum One of simplest for
attribute sampling plans
+ - + - - - - + - - - - - + - -
Moving Window SumMoving Window Sum
Example: Making red marbles
ReceiveBlue Marbles
Paint MarblesRed*
Package Marbles
*Defect rate = 10%
Moving Window SumMoving Window Sum
Based on the probability of finding more than an expected number of “defective” responses within a specified window of samples
Moving Window SumMoving Window Sum
Is this process under control?(Sampling rate = 1 per 1000)
Moving Window SumMoving Window Sum
When is control of this process lost?(Sampling rate = 1 per 1000)
Operating Characteristics
0
20
40
60
80
100
0 10 20 30 40 50 60 70
Actual % Positive
Pro
ba
bili
ty o
f P
as
sin
g (
%)
99%90%80%
Impact of StringencyImpact of Stringency
JuiceJuiceHACCPHACCP
Juice HACCPJuice HACCP
Key feature: 5-D (99.999%) performance
standard Restricted to juice after it has
been expressed Verification of this requirement
is via process validation and review of process records
Goal: Limit risk to >10-5/year
Juice HACCPJuice HACCP
Microbiological testing not required based on ineffectiveness of
testing at low defect rates
treatment affects all juice
processes are validated and reliable
A pple Juice
Microbiological TestingMicrobiological Testing Simplified example
Assume 1 enteric bacteria per ml 5-D treatment reduces to 1 per 10,000
mL To detect survivor, need
1 10-L sample 10 1-L samples 100 100-mL samples 1000 10-mL samples 10,000 1-mL samples
Juice HACCPJuice HACCP Key exemption: Citrus Juices
Processors of citrus juices may count surface treatments of the fruit as partially or totally fulfilling 5-D treatment
Based on the underlying assumption that the nature of citrus fruit is such that contamination is restricted to the fruit’s surface
Juice HACCPJuice HACCP
These citrus juice processors have an additional HACCP verification requirement of periodic testing for E. coli Two 10-ml juice samples/1000
gal/day Once per week if produce <1000
gal
Juice HACCPJuice HACCP
Data evaluated using process control statistics using a 7-sample window
One positive sample requires process review
Two positive samples require diversion to 5-D after extraction until cause identified
Juice HACCPJuice HACCP Designed to verify that the original
assumption is still valid, i.e. pathogens are restricted to the surface of the fruit Internalized pathogens will not be
treated Potential for growth at least in
some fruit Within range for effective detection Requirement takes into account
potential for chance contamination
Microbiological TestingMicrobiological Testing
Microbiological testing can be an integral part of any integrated program for verifying the effectiveness of food safety control measures