Risk based control of Listeria monocytogenes Professor Francis - - PowerPoint PPT Presentation

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Risk based control of Listeria monocytogenes

Professor Francis Butler School of Agriculture, Food Science & Veterinary Medicine UCD, Belfield, Dublin 4, Ireland

www.ucd.ie/foodandhealth

Microbial Quantitative Risk Assessment Network of Ireland

Network Co-ordinator Professor Francis Butler (UCD)

01/11/07 to 31/10/12

www.ucd.ie/microbialrisknetwork/

Statistical Process Monitoring (TASK 3)

Pork

(Salmonella)

Beef

(VTEC)

Powdered Infant Formula

(Chronobacter)

Cheese

(Listeria) Risk model development (TASK 4) Refrigeration (TASK 5) Staphylococcus Model (TASK 6) Meat Dairy

Scientific Programme

1 2 3 4 5 5 10 15 20 25 5 10 15 20 25 30 35

W e e k l y n u m b e r p

• s

i t i v e T e n W e e k R

• l

l i n g P

• s

i t i v e

Week ek

Salmonella control in pork

Risk based control of Listeria monocytogenes

• Regulatory Framework

– EU COMMISSION REGULATION No 2073/2005 – Microbiological criteria for foodstuffs – RTE foods able to support the growth of Listeria monocytogenes – RTE foods unable to support the growth of Listeria monocytogenes

RTE foods unable to support the growth of Listeria monocytogenes

• Requirements
• 100 CFU/g limit throughout the shelf-life of the product

RTE foods unable to support the growth of Listeria monocytogenes

0.9 0.92 0.94 0.96 0.98 1 3 3.5 4 4.5 5 5.5 6 6.5 7 Aw pH

Safe Ph ≤ 4.4

RTE foods unable to support the growth of Listeria monocytogenes

0.9 0.92 0.94 0.96 0.98 1 3 3.5 4 4.5 5 5.5 6 6.5 7 Aw pH

Safe Safe Ph ≤ 4.4 Aw ≤ 0.92

EC 2073/2005 Micro Criteria

0.9 0.92 0.94 0.96 0.98 1 3 3.5 4 4.5 5 5.5 6 6.5 7 Aw pH

Safe Safe Safe Ph ≤ 4.4 Aw ≤ 0.92 Ph ≤ 5 and Aw ≤ .94

EC 2073/2005 Micro Criteria

0.9 0.92 0.94 0.96 0.98 1 3 3.5 4 4.5 5 5.5 6 6.5 7 Aw pH

Safe Safe Safe Cheddar

EC 2073/2005 Micro Criteria

0.9 0.92 0.94 0.96 0.98 1 3 3.5 4 4.5 5 5.5 6 6.5 7 Aw pH

Safe Safe Safe Soft cheeses

Journal of Food Protection, Vol. 70, No. 9, 2007, Pages 2172–2198

Listeria monocytogenes contamination (≥100 CFU/g) detected in various ready-to-eat products

Consequences of the EU Micro Criteria

• Most cheeses have to be considered to be able to

support the growth of Listeria monocytogenes

– 100 cfu/g measured in the market place during their shelf life if ”the manufacturer is able to demonstrate, to the satisfaction

• f the competent authority, that the product will not exceed

the limit 100 cfu/g throughout the shelf-life”

• Or

– Absence in 25 g (zero tolerance) before the food has left the immediate control of the food business operator

Interesting linkages with the concept of Food Safety Objectives

• An FSO is 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

– 100 cfu/g measured in the market place

• Performance objective is a level that must be met at

earlier steps in the food chain

– “The operator may fix intermediate limits during the process that should be low enough to guarantee that the limit of 100 cfu/g is not exceeded at the end of the shelf life”

SOME OF THE RISK BASED CONSEQUENCES OF “ZERO TOLERANCE”

Consequences of the EU Micro Criteria

• Cheeses able to support the growth of Listeria

monocytogenes

– Absence in 25 g (zero tolerance) before the food has left the immediate control of the food business operator – Sampling plan

• N – sample size = 5
• C – no of positive samples = 0

Probability of accepting a batch: n = 5, c = 0

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.05 0.1 0.15 0.2 Probability of acceptance Proportion positive

Operating characteristic curve

Simulation of number positives, prevalance = 0.5%

Simulation of number positives, prevalance = 2%

Risk based approach

• “The operator may fix intermediate limits during the process that

should be low enough to guarantee that the limit of 100 cfu/g is not exceeded at the end of the shelf life”

• In practice hard to do

PMP modelling of Listeria growth

1 2 3 4 5 6 7 20 40 60 Log CFU Days 4 Deg 5 Deg

pH 5.2 NaCl 5.1%

Probability of growth of L. monocytogenes during the early stages of cheesemaking

0.93 0.94 0.95 0.96 0.97 0.98 0.99 1 0.4 0.9 1.4 1.9 2.4 2.9 3.4 3.9

log10 cfu/ml inoculum size water activity

Upper line (──) corresponds to probability of growth = 0.9; middle line (―—) corresponds to probability of growth = 0.5; lower line (-----) corresponds to probability of growth = 0.1

Concluding perspectives

• Acceptance sampling is a blunt instrument

– Temptation is to minimise sampling

• Determination of risk based performance objectives

challenging

• Difficult to „prove‟ always less than 100 cfu/g
• Microbial Quantitative Risk Assessment Network of

Ireland here to help

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