[PPT] - A consumer risk assessment model of Salmonella in Irish fresh pork PowerPoint Presentation

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A consumer risk assessment model of Salmonella in Irish fresh pork sausages: Transport and refrigeration modules

Dr. Ursula Gonzales Barron

Ilias Soumpasis

Dr. Grainne Redmond
Prof. Francis Butler

Biosystems Engineering, UCD School of Agriculture, Food Science and Veterinary Medicine University College Dublin, Ireland

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Background

 Between 10-30% of all cases of foodborne

salmonellosis had pork and pork products incriminated as the actual source.

 In Ireland, a pork product that merits

attention is the fresh pork sausage for being a raw comminuted product that is widely consumed.

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Background

 From an Irish consumption database, a

person eats on average 90 g of sausages per week 12 800 tons of sausages would be consumed each year.

 A risk assessment model estimated that on

average 4.0% (95% CI: 0.3 – 12.0%) of the pork cuts produced in Ireland would be contaminated with Salmonella spp.

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Objective

 To develop a consumer risk assessment model

for estimating the exposure and risk of salmonellosis associated with Irish fresh pork sausages.

 Second-order model is underpinned by:



Predictive microbiology data of Salmonella in sausage



Irish data of Salmonella prevalence and numbers in fresh pork sausages at retail



Temperature profiles of the refrigerated product



Consumer surveys on transport and refrigeration conditions



An Irish consumption database.

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Methodology

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Structure of the consumer model

Prevalence data (Prev) Salmonella concentration at t0 (λ0) in a pack Transport & Refrigeration Retail Temperature profile (T(t)) Time (t) Cooking Growth parameters (Tmin, µ, Nmax, ho) Salmonella concentration (λR) Dynamic Baranyi’s model D-value, Ea Dynamic exponential death model Salmonella concentration (λC)

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Initial concentration of Salmonella in fresh pork sausage at retail (λ0)



MPN data of Salmonella from Mattick et al. (2002)

Pack

Sausage replicate Mean (MPN/g)

1 2 3 4 5 6 1 1-1-1 (110) 2-0-1 (140) 1-1-1 (110) 1-1-1 (110) 1-1-1 (110) 2-0-1 (140) 120 2 2-0-0 (90) 2-1-0 (150) 2-0-0 (90) 2-0-0 (90) 2-0-0 (90) 2-2-0 (210) 120 3 1-1-1 (110) 2-0-0 (90) 2-0-1 (140) 1-2-0 (110) 2-0-0 (90) 2-0-0 (90) 115 4 2-0-0 (90) 1-1-1 (110) 1-0-1 (70) 1-0-0 (40) 1-0-1 (70) 1-0-1 (70) 75 5 1-0-1 (70) 1-0-1 (70) 1-0-1 (70) 2-0-0 (90) 1-0-0 (40) 2-0-0 (90) 72 6 1-0-0 (40) 1-0-1 (70) 1-0-1 (70) 1-0-0 (40) 1-0-1 (70) 1-0-0 (40) 55 7 1-0-1 (70) 1-0-0 (40) 1-0-1 (70) 1-0-1 (70) 1-0-0 (40) 1-0-0 (40) 55 8 0-1-0 (30) 1-0-0 (40) 1-0-0 (40) 1-0-0 (40) 1-0-0 (40) 0-1-0 (30) 37 9 0-0-0 (<30) 0-0-0 (<30) 0-0-0 (<30) 0-0-0 (<30) 0-0-0 (<30) 0-0-0 (<30) <30 10 0-0-0 (<30) 0-0-0 (<30) 0-0-0 (<30) 0-0-0 (<30) 0-0-0 (<30) 0-0-0 (<30) <30

Posterior distribution for the uncertainty around MPN Variability in initial λ0 from contaminated packs

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Modelling initial concentration (λ0)



For every triplet (every sausage tested), a likelihood function l(x|λ) or conditional probability of observing the positive tube counts X={xi} given true Salmonella concentration λ was calculated.



Out of ni serial dilution analysis tubes, the numbers of positive tubes xi are independent random variables distributed as Binomial (ni, pi) with,

df v p

i i

/ exp 1

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Modelling initial concentration (λ0)

 Likelihood function l(x|λ)  Each triplet (sausage tested) produced a

likelihood function

i i i

x n i x i i i m i

df v df v x n x l / exp / exp 1 |

1

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For instance, pack #4: l(x|λ)

0.0 0.1 0.2 0.3 0.4 0.5 50 100 150 200 250 300 350 400 450

Concentration of Salmonella in fresh raw sausages (CFU/g)

Sausage 1: X={2, 0, 0}

Uncertainty

90 MPN/g

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For instance, pack #4: l(x|λ)

0.0 0.1 0.2 0.3 0.4 0.5 50 100 150 200 250 300 350 400 450

Concentration of Salmonella in fresh raw sausages (CFU/g)

Sausage 1: X={2, 0, 0} Sausage 2: X={1, 1, 1}

Uncertainty

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For instance, pack #4: l(x|λ)

0.0 0.1 0.2 0.3 0.4 0.5 50 100 150 200 250 300 350 400 450

Concentration of Salmonella in fresh raw sausages (CFU/g)

Sausage 1: X={2, 0, 0} Sausage 2: X={1, 1, 1} Sausages 3,5,6: X={1, 0, 1}

Uncertainty

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For instance, pack #4: l(x|λ)

0.0 0.1 0.2 0.3 0.4 0.5 50 100 150 200 250 300 350 400 450

Concentration of Salmonella in fresh raw sausages (CFU/g)

Sausage 1: X={2, 0, 0} Sausage 2: X={1, 1, 1} Sausages 3,5,6: X={1, 0, 1} Sausage 4: X={1, 0, 0}

Uncertainty

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0.0 0.1 0.2 0.3 0.4 0.5 50 100 150 200 250 300 350 400 450

Concentration of Salmonella in fresh raw sausages (CFU/g)

Sausage 1: X={2, 0, 0} Sausage 2: X={1, 1, 1} Sausages 3,5,6: X={1, 0, 1} Sausage 4: X={1, 0, 0} Uncertainty distribution f(λ|X)

Uncertainty

Each sausage from a pack was stuffed from same mix, and assuming no clustering 

| |

6 1 i s

x l X f

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Modelling variability in initial concentration (λ0)

 Uncertainty around the 10 distributions of

within-pack Salmonella concentration fj(λ|X) (j=1…10) was propagated to a log-normal distribution using Bootstrap.

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Estimating growth parameters of Salmonella in raw pork sausage



Data from Ingham et al. (2009), where Salmonella Typhimurium, Heidelberg, Infantis, Hadar and Enteritidis were inoculated in fresh bratwurst.



Square-root or Belehradek-type equation

min max

T T b T

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 10 15 20 25 30 35 40 45 50

Temperature (°C)

Raw bratwurst Broth pH=5.9, Aw=0.97

(log CFU/h)

R2=0.77

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Estimating Salmonella growth Y(t) in raw sausage

 Dynamic microbial growth (Y(t)) was estimated

using Baranyi and Robert’s differential equation

max max

exp 1 exp 1 1 Y Y t T t Q Y dt d

t T Q dt d

max

ln , q Q Y Y

max

1 1 ln q T LP T h

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Temperature profile (T(t)) of sausages during transport



Transport time (tT) from retail purchase to cold storage modelled from Irish consumers’ survey



tT ~ InvGaussian(36.037, 38.761)



Internal temperature of the sausage pack (T(t)) was modelled with one-directional transient heat transfer equations with



T0 = product’s initial temperature (T at retail) = Normal(5,0.8)



hT = convective heat transfer coefficient (11.0 W/m2 C)



α (k/(ρcp)) = thermal diffusivity of pork sausage (1.41x10-7 m2/s)



k = thermal conductivity of pork sausage (0.48 J/m-s- C)



T∞= Tamb + 3 C

2 4 6 8 10 12 5 10 15 20 25

Refrigeration time (h) Temperature (°C)

Tavg=4.2°C

 In every

iteration (sausage pack)

 Tavg is sampled

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T(t) of a refrigerated sausage pack

 In every

iteration (sausage pack)

Time after purchase (h)

2 4 6 8 10 12 14

Y(t) (log CFU/g) Temperature (°C)

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Results: Prevalence



The probability that a random pork sausage pack has Salmonella was estimated to be around 0.046 (95% CI: 0.032-0.064)

X <= 0.0638 97.5% X <= 0.0322 2.5% 10 20 30 40 50 60 10 20 30 40 50 60 70 80 90

Prevalence of Salmonella Typhimurium in fresh sausage packs (x10-3)

Mean = 0.0467

Probability density function

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Results: Initial Salmonella concentration



Uncertainty in λ0 from MPN



Superimposed: mean of the raw data from 10 packs

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 50 100 150 200 250 300

Concentration of Salmonella Typhimurium in contaminated fresh pork sausage packs (CFU/g)

Mean = 69.7 CFU/g

St. dev = 49.5 CFU/g

95% CI = 15 - 200 CFU/g

Cumulative density function

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Results: Transport

 Because of the short transport time (E(tR)=40 min);

the contaminated sausage packs did not suffer a noticeable increase in Salmonella concentration.

 At the end of transport, the expected value of the

Salmonella concentration YT was still low at 1.85 log CFU/g (95% CI of 1.21 – 2.35 CFU/g).

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Results: Refrigeration



Growth was observed in some sausage packs (iterations)



The likelihood of having packs with high levels of Salmonella (>3 log CFU/g) increased when the average temperature of the sausage exceeded ~ 5 C

1 2 3 4 5 6 7 8 9

5

5 10 15

Average temperature of sausage during refrigeration (°C) Salmonella concentration in pork sausage prior to cooking (log CFU/g)

X <= 1.30 2.5% X <= 2.76 97.5% 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1 2 3 4 5 6 7 8

Mean = 1.89 log CFU/g

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Results: Refrigeration



The likelihood of finding hazardous levels of Salmonella (>3 log CFU/g) increased when the cold storage time exceeded ~ 30 h Freq(YR>3))~0.77% 95% CI: 0.41-1.80%

1 2 3 4 5 6 7 8 9 30 60 90 120 150

Refrigeration time (h) Salmonella concentration in pork sausage prior to cooking (log CFU/g)

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Conclusions

 Salmonella has a low prevalence (4.6%) in sausage packs and when

present, levels are relatively low (product to be cooked).

 Salmonella concentration in sausages prior to cooking was mainly

driven by the initial Salmonella load at retail (R=0.77), and storage time (R=0.43) had by far a stronger effect than the average temperature of the sausage packs (R=0.17).

 Salmonella concentration in sausages from contaminated packs

were on average low prior to cooking (E(YR) = 1.89 log CFU/g; 95% CI: 1.30-2.76 log CFU/g).

 However, out of 100 sausage packs initially contaminated, a

maximum of 2 packs would be expected to have hazardous Salmonella levels higher than 1000 CFU/g prior to cooking.

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Acknowledgments

 Irish Department of Agriculture, Fisheries and Food