Food Processing Technologies andMicrobiological Safety

Margaret Patterson and Mark Linton, Food MicrobiologyBranch, Agri-Food & Biosciences Institute, Belfast, UK

Email: margaret.patterson@afbini.gov.uk

mark.linton@afbini.gov.uk

Overview of Presentation

• What technologies are available as alternatives to traditionalthermal processing?

• What microbiological challenges do they present and how canthese be overcome?

• Traditional thermalpasteurisation andsterilisation treatments wellestablished worldwide.

• Proven to give assurance ofmicrobiological safety andshelf-life.

• Can alter quality.

Traditional thermal processing generallyworks well

Why seek alternative technologies?

• Consumers are more demanding than ever before

– about quality (sensory, nutrition)

- about price

- about environmental issues

- about convenience.

Microbiological safety taken for granted?

Challenge is to meet all these expectations.

New technologies can help meetconsumer demands

High hydrostatic pressure

Irradiation

Pulsed Electric Field

Ultrasound

UV light

Cold Plasma

Dense phase CO2

Ozone

Electrolyzed water

Chlorinedioxide

Oscillatingmagnetic fields

Pulsed light

Intelligentpackaging

Microwave

Ohmic heating

Heat v Non-thermal Technologies

Heat HPP PEF IRR

Processparameters

TemperatureTime

PressureTimeTemperature

TimeElectric field strengthPulse energyTemperature

DoseTemperature

Sporeinactivation

Yes, at hightemperatures

Generally no - butpossible - PATS(Pressure + heat)

No Yes at high doses

Positives Well established &trusted

Good quality retention.Many food applications.“Novel” products

Good quality retention Good microbialcontrol with minimalquality changes

Negatives Some loss ofproduct quality(sensory andnutritional)

Capacity – batch processNot suitable for dryfoods

Limited topumpable liquids;limited particulate size

Consumerresistance;Limited approvals.

Challenges

How to ensure safety and quality?

How to get acceptance/approval ?

How to get cost effectiveness?

Needs multidisciplinary approach – scientists, industry,Government/regulatory authorities, consumers.

Microbiological Challenges

• New concepts and new ways of thinking.

- Redefining “pasteurisation” beyond thermal.

“Any process, treatment or combination thereof, that is appliedto food to reduce the most resistant microorganism (s) ofpublic health significance to a level that is not likely to presenta public health risk under normal conditions of distribution andstorage”.

National Advisory Committee on Microbiological Criteria forFoods, 2004.

Microbiological challenges

How to demonstrate new technology is equivalent to traditionalthermal pasteurisation?

- What is the most resistant organism?

- How does the characteristics of the food itselfaffect effectiveness?

- Combination treatments may be beneficial(Hurdle approach).

- Processing conditions – microbiologicalrequirements v quality and cost considerations.

Determine resistant pathogen of concern that islikely to survive the process.

• Depends on intended use and technology used to process food.

• Pathogen with greatest resistance to one treatment may notbe most resistant to another type of treatment.

O Heat

57°C/13 min

• □Irradiation

1.5 kGy @ 20°C

High-pressure

350 MPa/10 min/20°C

Cluster analysis of 40 Salmonella isolates after heat, highpressure and irradiation

MeanIrradiation

Mean HighPressure

-6

-5

-4

-3

-2

-1

0

Group 1 Group 2 Group 3 Group 4 Group 5

MeanHeat

Inact

ivati

on

(log

N/N

o)

Determine resistant pathogen of concern that islikely to survive the process.

• Resistance can vary between species and within strains of thesame species.

Inactivation of pathogens pressure treated in10mM PBS (pH 7.0)

Pressure required for a 105

reduction in numbers(all with hold time 15 min/20oC)

Yersinia enterocolitica 275 MPa

Salmonella Typhimurium 350 MPa

Listeria monocytogenes 450 MPa

St. aureus 700 MPa

E.coli O157:H7 700 MPa

-7

-6

-5

-4

-3

-2

-1

0

1 2 3 4 5 6 7 8 9 10 11 12 13

Strain of Listeria monocytogenes

Log

10N

/N0

Variation in pressure (600 MPa/2 min/20°C)resistance of L. monocytogenes in cooked chicken

Consider impact of food matrix onsurvival of pathogens

• Substrate composition can affect survival

• pH.

• Water activity.

• Food composition.

High pressure inactivation (700 MPa/15 min/20oC) of E. coliO157:H7 in various substrates

Storage conditions can affect recovery andgrowth of surviving microorganisms

Combination treatments can be beneficial

High pressure (600 MPa/2 min/20oC) in combination with antilisterialagents on growth of L. monocytogenes during

storage (8oC) of cooked poultry meat

• Raw chicken treatments - untreated, + W. viridescens or + 2%sodium lactate.

• Chicken was cooked (80oC/ 1min).

• L. monocytogenes cocktail added (~104 cells/g).

• Half of samples pressure treated (600 MPa/2 min/20oC).

• Samples stored for 105 days at 4, 8 and 12oC.

High pressure (600 MPa/2 min/20oC) in combination with antilisterialagents on growth of L. monocytogenes during storage (8oC) of cooked

poultry meat

0

1

2

3

4

5

6

7

8

9

10

0 10 20 30 40 50 60 70 80 90 100 110

Lo

g10C

FU

/g

Storage time (days)

Untreated control

limit of detection

High pressure (600 MPa/2 min/20oC) in combination withantilisterial agents on growth of L. monocytogenes during storage

(8oC) of cooked poultry meat

0

1

2

3

4

5

6

7

8

9

10

0 10 20 30 40 50 60 70 80 90 100 110

Lo

g10C

FU

/g

Storage time (days)

Untreated control

2% lactate only

limit of detection

High pressure (600 MPa/2 min/20oC) in combination withantilisterial agents on growth of L. monocytogenes during storage

(8oC) of cooked poultry meat

0

1

2

3

4

5

6

7

8

9

10

0 10 20 30 40 50 60 70 80 90 100 110

Lo

g10C

FU

/g

Storage time (days)

Untreated control

HPP only

2% lactate only

limit of detection

0

1

2

3

4

5

6

7

8

9

10

0 10 20 30 40 50 60 70 80 90 100 110

Lo

g10C

FU

/g

Storage time (days)

Untreated control

HPP only

Weissella viridescens only

2% lactate only

limit of detection

High pressure (600 MPa/2 min/20oC) in combination withantilisterial agents on growth of L. monocytogenes during storage

(8oC) of cooked poultry meat

High pressure (600 MPa/2 min/20oC) in combination withantilisterial agents on growth of L. monocytogenes during storage

(8oC) of cooked poultry meat

0

1

2

3

4

5

6

7

8

9

10

0 10 20 30 40 50 60 70 80 90 100 110

Lo

g10C

FU

/g

Storage time (days)

Untreated control

HPP only

Weissella viridescens only

Weissella viridescens + HPP

2% lactate only

limit of detection

High pressure (600 MPa/2 min/20oC) in combination withantilisterial agents on growth of L. monocytogenes during storage

(8oC) of cooked poultry meat

0

1

2

3

4

5

6

7

8

9

10

0 10 20 30 40 50 60 70 80 90 100 110

Lo

g10C

FU

/g

Storage time (days)

Untreated control

HPP only

Weissella viridescens only

Weissella viridescens + HPP

2% lactate only

limit of detection

2% lactate + HPPbelow level of detection

Summary of poultry study

• HPP (600 MPa/2 min) alone gave < 3.3 log kill of L. monocytogenesin cooked chicken.

• W. viridescens extended lag phase of Listeria that survived pressuretreatment to ~ 35 days.

• 2% sodium lactate + pressure kept Listeria numbers below 50CFUg-1

throughout storage.

Ref: Effect Of high pressure, in combination with antilisterial agents, on the growth ofListeria Monocytogenes during extended storage of cooked chicken. FoodMicrobiology 28 (2011), pp. 1505-1508

HPP and the microbiological quality and safety ofcarrot juice during refrigerated storage

HPP and survival of L. monocytogenes in carrot juice

• Fresh carrot juice reported to have antilisterial activity.

• Active compound is not known.

• Activity lost when juice is heat treated.

• Effect of HPP on activity not known.

Effect of high pressure on the microbiological qualityof carrot juice

• Freshly squeezed carrot juice.

• Pressure treated at 500 MPa and 600 MPa for 1 min at 20oC, orleft untreated as control.

• Samples stored at 4, 8 and 12oC for up to 22 days.

Total viable counts in untreated and pressure-treated carrot juice during storage at 4oC

0

1

2

3

4

5

6

7

8

9

10

0 2 4 6 8 10 12 14 16 18 20 22

Lo

g1

0C

FU

ml-1

Storage Time (days)

Control

500 MPa/1 min/20ºC

600 MPa/1 min/20ºC

Effect of high pressure (500 MPa/1 min/20°C) on the survival ofListeria monocytogenes in carrot juice during storage at 4°C

0

1

2

3

4

5

6

7

8

9

10

0 2 4 6 8 10 12 14

Lo

g1

0C

FU

ml-1

Storage time (days)

Control

Heat treated (90ºC for 20 s)

HPP only

limit of detection

HPP only – all belowlevel of detection

Summary of carrot juice study

• Pressure treatment ≥500 MPa for 1 min at 20oC significantlyreduced the microbial load in carrot juice.

• There was little subsequent microbial growth in the juiceduring 22 days storage at 4oC.

• Inoculation studies with Listeria monocytogenes showed thatthe normal antilisterial effect of carrot juice was significantlyenhanced by high pressure.

• Carrot juice also enhanced the lethal effect of pressure onEscherichia coli.

Ref: The effect of high hydrostatic pressure on the microbiological quality andsafety of carrot juice during refrigerated storage (2011). Food Microbiology30: 205-212.

ConclusionsIdentify best technology solution on a case by case basis.

• Substitute for existing method

• Use new method to solve old problem.

• Create new market for a new product

Conclusions

• Wide range of technologies available.

• No one technology is suitable for all foods.

• Need to identify which gives best opportunity - on a case bycase basis.

• Multidisciplinary approach required for success.

Acknowledgements

My thanks to the AFBI high pressure team:

Mark LintonAideen MackleMalachy ConnollyAndrew Fulton

and

to the Department of AgricultureAnd Rural Development for funding the work