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

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/foodandhealth

www.ucd.ie/microbialrisknetwork/

Scientific Programme Statistical Process Monitoring (TASK 3) Pork Beef Cheese Powdered Infant Formula (Salmonella) (VTEC) (Listeria) (Chronobacter) Risk model Refrigeration Staphylococcus development (TASK 5) Model (TASK 6) (TASK 4) Meat Dairy

Salmonella control in pork 25 5 T P p 20 4 R e o W n o o n s e u s 15 3 l i e m i l W t k b t i 10 2 e i l e i n e v y r v g 5 1 k e e 0 0 0 5 10 15 20 25 30 35 Week ek

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 1 Ph ≤ 4.4 0.98 0.96 Aw Safe 0.94 0.92 0.9 3 3.5 4 4.5 5 5.5 6 6.5 7 pH

RTE foods unable to support the growth of Listeria monocytogenes 1 Ph ≤ 4.4 0.98 Aw ≤ 0.92 0.96 Aw Safe 0.94 0.92 Safe 0.9 3 3.5 4 4.5 5 5.5 6 6.5 7 pH

EC 2073/2005 Micro Criteria 1 Ph ≤ 4.4 0.98 Aw ≤ 0.92 Ph ≤ 5 and Aw ≤ .94 0.96 Aw Safe 0.94 Safe 0.92 Safe 0.9 3 3.5 4 4.5 5 5.5 6 6.5 7 pH

EC 2073/2005 Micro Criteria 1 Cheddar 0.98 0.96 Aw Safe 0.94 Safe 0.92 Safe 0.9 3 3.5 4 4.5 5 5.5 6 6.5 7 pH

EC 2073/2005 Micro Criteria 1 Soft cheeses 0.98 0.96 Aw Safe 0.94 Safe 0.92 Safe 0.9 3 3.5 4 4.5 5 5.5 6 6.5 7 pH

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 of 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 Operating characteristic curve Probability of acceptance 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 0.05 0.1 0.15 0.2 Proportion positive

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 7 6 5 Log CFU 4 3 4 Deg 5 Deg 2 1 0 pH 5.2 0 20 40 60 NaCl 5.1% Days

Probability of growth of L. monocytogenes during the early stages of cheesemaking 1 0.99 water activity 0.98 0.97 0.96 0.95 0.94 0.93 0.4 0.9 1.4 1.9 2.4 2.9 3.4 3.9 log 10 cfu/ml inoculum size 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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