Trends in Thermal Processing

Pasteurization and Commercial

Sterilization

Hosahalli S. Ramaswamy

Professor, Department of Food Science

McGill University, Canada

Food Processing and Safety –

Food Industry Meeting

MAC Campus, June 8, 2012

Presentation Outline

Public Safety – Food Microbiological Issues

Thermal Processing Principles

Focus on pasteurization and sterilization

Novel approaches in thermal processing

Non-Thermal Processing

Conclusions

Micro-organisms & Food

• Food Pathogens – public health concern

because they enter the human system through food

and cause various disease

• Food Poisoning Micro-organisms – these

are not pathogens but produce toxins in foods which

when ingested cause harm to public health

• Food Spoilage Microorganisms – these are

not of public health concern, but they cause spoilage

of foods

Common Food Pathogens

• Clostridium perfringens

• Salmonella, Bacillus cereus

• Escherichia coli O157:H7

• Listeria monocytogenes

• Shigella

• Staphylococcus

• Streptococcus faecalis, faecium

• Vibrio; Yersinia

• Clostridium botulinum (proteoletic)

Micro-organisms of Safety Concern

Bacteria Producing Exotoxins

• Clostridium botulinum

• Clostridium perfringens

• Staphylococcus aureus

• Bacillus cereus

Food Processing Objectives

Primary Objectives

Safety and Stability (Preservation)

Safety Concern

Eliminate or Disable Pathogens

Stability

Eliminate or Disable Spoilage Organisms

Inactivate enzymes

Suppress chemical reactions

Thermal Processing

Good Old Technology, Old is Gold

• To make the product safe & shelf-stable

• Objective is to reduce microorganisms of public health concern to a statistically small level

• Most serious & heat resistant (low acid)

Clostridium botulinum

Level: Survivor probability 1 in 1012

Botulinum Cook

• Create conditions that prevents the activity of spoilage bacteria

Vacuum Sealed Cans/Pouches (Prevents the growth of Obligate Aerobes

pH pH < 4.5

High Acid Foods

pH > 4.5

Low Acid Foods

Sterilization:

severe treatment

>110oC

Pasteurization:

mild treatment

< 100oC

Controls pathogenic &

Spooilage vegetative forms.

Spore formers in-active.

Shelf-stable products for

fruits & acidified

foods

Only pathogens

controlled.

Spores are active Provides Short-term

storage at refrigerated

conditions

Spores killed: Public health concern:

Clostridium botulinum; Bot Cook

- 12D Process is implemented.

Spoilage: Mesophiles are killed.

Heat resistant thermophiles are not

killed but controlled by storing the

product below 30oC

Thermal Processing Principle Overview

Pasteurization:

mild treatment

< 100oC

Pasteurization

Mild heat treatment

Destruction of pathogenic microorganims

Temporary shelf-life extension

Product refrigerated to control spoilage

Sterilization or Appertisation

More severe heat treatment

Control of pathogenic and spoilage bacteria

Shelf life extension & safety

Long term preservation

Product not fully sterile – it is a “misnomer”

Considered to be practically sterile because of stability

Pasteurization vs Sterilization

Pasteurization (CFIA) The processes is normally developed by a process authority.

The target organism depends on the product storage

temperature and safety parameters.

Targeting non-proteolytic Clostridium botulinum will control both spore and

non-spore formers in a refrigerated product.

Targeting L. monocytogenes prevents the growth of other non-spore formers but does

not prevent growth of spore formers.

The pasteurization must result in one of the following (CFIA):

a) A 5 log reduction of Listeria monocytogenes where:

D value at 65 C=1.18 minutes and; Z value = 6.7 C, or;

b) A 6 log reduction of non-proteolytic Clostridium botulinum where:

F value at 90 C = 10 minutes and; Z value = 10 C (F90 10 min process)

Comparison of Criteria

Sterilization

Pasteurization

Target micro-organism Clostridium botulinum

Target micro-organism Streptococcus faecalis

Reference temperature = 121C

Reference temperature = 70C

Characteristics: D121 = 0.25 min and z = 10C

Characteristics: D70 = 2.95 min and z = 10C

Estimated number of micro-organisms No = 1/g

Estimated number of micro-organisms No = 10

7/g

Number desired in final product N = 1/10

12g = 10

-12/g

Number desired in final product N = 1/10

6g = 10

-6/g

Treatment effectiveness n = log (1/10

-12) = 12

Treatment effectiveness n = log (10

7/10

-6) = 13

Minimum sterilization value at 121C

Fo = n x D = 12 x 0.25 = 3 min

Minimum pasteurization value at 70C

Pm = n x D = 13 x 2.95 = 38 min

Thermal Processing Objectives

Safety vs Quality

FROM A SAFETY ASPECT

Need to monitor the temperature and establish the process at:

coldest point in the container placed at the coldest location in the retort.

FROM A QUALITY POINT OF VIEW

Need to minimize the bulk cooking.

Product near or at the surface of the container will be cooked more than the product near the centre.

Retort Temperature Distribution - Very important as it affects the retort performance

- It can compromise safety

- It can compromise quality

- Must be assessed by a process authority

Large temperature fluctuations warrant modifications to the

retort equipment or loading practice

Two major issues in temperature distribution

1) Temperature stability with respect to Time Controller / System limitations

2) Temperature stability with respect to Space Distribution / Loading pattern limitations

125

122 122

125

119

124

126 127

124

123

Spatial Retort Temperature Distribution

Local mean temperatures

during cook time

119

124

126

123

Average local retort temperatures as a function of time

Time

T

e

m

p

Transient Temperature Distribution

Quality Optimization in Thermal

Processing

• All techniques used improve the heat transfer to the product which reduces the cooking time and hence improve the quality in thermally processed foods

x

TkAq q = h A

Quality Optimization: 1) Increase T

Rel

ativ

e D

val

ue

Temperature

Nutrient

Microbial Spore

Vegitative bacteria

Illustration of high temperature short time (HTST)

heating principle

Bot cook

Nutrient Destruction

90%

50%

10%

5%

3%T1 T2 T3 T4

Temperature (C )

Rel

ativ

e ti

me

t1

t2

t3

t4

Rotary Processing

mg

Axial Rotation

(Continuous Operation)

End over end rotation

(Batch Operation)

Two modes of agitation/rotation

q = h A

Steristar rotary retort (Courtesy Malo Inc.)

End-over-

end

Agitation

processing,

steam/air

or steam

A cutaway view of the continuous rotary

turbo cooker (FMC)

Aseptic processing

Aseptic

Environment

Fillin

g &

Sea

ling

Aseptic Product

Sterilization Sterilization

q = h A

Thin Profile Process

Retort Pouch

Outer

layer

Middle

layer

Inner

layer

Outer layer: strength and

printability

Middle layer: barrier

properties

Inner layer: heat sealing,

food contact

x

TkAq

Semi-Rigid Plastic Containers

Light weight, easy storability, thin profile,

easy end use preparation and disposal, microwavable

Slow filling and sealing, labor intensive

Microwave Heating: Two Modes

Ionic Polarization Dipole Rotation

Novel Methods of Heating

Applications

Heating, Reheating and Cooking

Pasteurization and Sterilization

MW Tempering and Thawing

MW Blanching

Enhancing reaction kinetics

Microwave assisted extraction

Ohmic heating

VR

Food Product

Electrode

Electrode

An electrical circuit analogue

Also called Direct resistance heating Joule effect heating Electro-conductive heating Electro-resistive heating Principle Heat generation occurs when an electric current is passed through an electrically conducting food product.

Novel Heating Techniques….

Typical Time Temperature Profiles

under Ohmic Heating Conditions

0

10

20

30

40

50

60

70

80

90

0 5 10 15 20 25

Time (min)

50v

60v

70v

80v

100v

Tem

pera

ture

(oC

)

~

Advantages of Ohmic Heating

Very rapid heating

No need for a heat transfer surface

Gentle handling of particulates

No moving parts

Quiet operation

Easy process control

Better energy conservation than MW

Easier tailoring of particle/liquid heating

Easy adaptability to Aseptic Processing of Particulates

High Pressure Processing

l An emerging and Novel

technology

l Gaining tremendous

popularity

HP Characteristics and

Advantages

Results in fresh-like

product

Environmentally

friendly (less wastage)

Process Independent of

product shape and size

Can destroy

microorganisms and

inactivate enzymes

High Pressure Application Areas

• Pasteurization: Juices, milk

• Sterilization: High and low acid foods

• Texture modification: Fish, egg, proteins, starches

• Functional changes: Cheese, yogurt , surimi

• Specialty processes: Freezing, thawing,

fat crystallization, enhancing

reaction kinetics

Equipment

Avure

STANSTED

NC Hyperbaric

HP Dynamics Inc

ACB

High Pressure Pilot Plant at McGill

High Pressure Processing

Pasteurization

and

Sterilization

HP Pasteurization

Well studied Guidelines have been developed (USDA - FDA)

Processes now must demonstrate 5 log reduction in

pressure resistant pathogens

Examples: Listeria monocytogenes,

E. coli 0157:H7, Salmonella sp.

1 min at 500 - 550 MPa adequate for juices

Safe - shelf stable high quality product

HP Sterilization

Shelf-stable product

Spores of both spoilage and public health concern

need to destroyed, requires high pressure and high

temperature

High pressure accelerates the destruction kinetics.

Permits the use of lower processing temperatures:

Quality advantage

Most unique feature: Adiabatic heating

Temperature change ( T) due to adiabatic compression

Substance (25 C) T ( C) per 100MPa

Water ~ 3

Mashed potato ~ 3

Orange juice ~ 3

2%-fat milk ~ 3

30%-fat Cheese ~ 5 ^

Salmon ~ 3.2

Water/glycol (50/50) 4.8 ~ 3.7 *

Beef fat ~ 6.3

Olive oil 8.7 ~ 6.3 *

Soy oil 9.1 ~ 6.2 *

^ Observed by Shao and Zhu (2002). * T decreases as pressure increase.

T 3-5°C/100MPa for high moisture foods Large T for fat-rich foods

HP sterilization: Principle

Pack and

Bring initial

temperature

to 90C

Load sample

and quickly

pressurize

chamber to 700

MPa

Compression

heating

increases

sample

temperature

to 125C

Hold until

sterility is

achieved: 1-

5 min

Depressurize.

Sample cools to

90C

instantaneously

Delivery of target

lethality - Safe

product

Rapid heating &

cooling - High

quality product

Effect on HP treatment on

quality

Salami, before and after

Effect on HP treatment on

quality

Milk and strawberry, before and after

Effect on HP treatment on

quality

Cheese and Milk, before and after

Effect on HP treatment on quality

Salmon, Chicken, beef and pork before and after

Thank you