Thermal Processing of Food and Food Preservation
Transcript of Thermal Processing of Food and Food Preservation
Thermal Processing of Food and Food Preservation
Chris Domenico
Territory Manager, North America
5/11/2021
Agenda
Introduction
Microbiology
Thermal Process Types
• Blanching
• Pasteurization
• Canning
Bacteria
• Growth
• Equipment
“D-value” / z-value
Log Reduction
“F0 value”
Lethality
Close
Bringing four global brands together to deliver Science for a Safer World.
The world’s leading
proficiency testing provider,
delivering confidence in
your product testing.
Protecting your brand with
globally recognised supply
chain assurance solutions.
Delivering quality assurance
through globally trusted
testing and certification
programmes for banned
substances.
A leading software provider
of food safety, supplier
quality and compliance
management software.
3
4
LGC ASSURE offers a connected suite of
solutions that intelligently analyse the safety,
quality and authenticity of your goods and
services, alongside evolving value drivers such
as health, environmental, human welfare and
ethical impact.
Intelligent assurance for you and your supply network
5
SOFTWARE PLATFORM
Comprehensive platform covering all aspects of food
industry compliance
About Safefood 360°
• SaaS solution
• Web Access
• 30+ Modules
• Compliant with Global Standards
DOMAIN EXPERTISE
World class knowledge of food safety and compliance
provided by a team of experienced food industry experts
• IT developers led by Food Safety experts
• Experienced team
• Food Safety Product – not an IT project
• Backed by LGC ASSURE
7
Food Preservation Timeline
Cooking Over Fire:
Smoke Preservation
Dried Foods:
Solar Drying
Jam:
Pulverization/Boiling
Curing:
Preservative - Salt
Refrigeration:
Stored Foods to Inhibit
Microorganism growth
Canning: Heat
Application/Reduced
O₂
Pasteurization:
Heating/Cooling –
Reduction of harmful
bacteria
Vacuum Packing: Food
Packed in Oxygen-free
Plastic Bags
Chemical Preservatives: Stop
Microbial Growth, Retain
Flavor/Texture, Prevent
Adverse Chemical Changes
500,000 BC
1400 AD 1800 AD
2000 AD
8
Microbiology
Food Preservation:
A competition between the human species and microorganisms
• We attempt to preserve the food
• Microorganisms attempt to destroy food
10
Bacteria
Bacteria are single celled microorganisms that multiply rapidly (e.g., 1x every 8 minute)
12
Types of Thermal Processing
Frying
Roasting
Baking
Canning
Pasteurization
Severe Processes
Blanching
Mild Processes
13
Blanching
Primary Purpose:
• Destruction of enzyme activity in fruit and vegetables
• Not a primary method of processing
• Pretreatment prior to freezing, drying, and canning
Reduce surface microbial contamination
Soften vegetable tissues to facilitate filling into containers
Remove air from intercellular spaces prior to canning
14
Blanching: Caution
Over blanching
• Over blanching causes quality loss due to overheating
Under blanching
• Causes quality loss due to increased enzyme activity because enzymes are activated
and substrates released by heat
15
Pasteurization
Process
• Relatively mild heat treatment
• Food is heated to <212° F (100° C)
• Widely used in the food industry
• Typically a CCP in various HACCP processes
• Used to destroy enzymes and relatively heat
sensitive micro-organisms
Non spore
forming bacteriaYeast Mold
Extend Shelf Life
Several Days –
Several Months
16
Pasteurization
Purpose
• Pasteurization is normally used
for the destruction of all
disease causing organisms
(e.g. pasteurization of milk) or
the destruction or reduction in
the number of spoilage
organisms in certain foods, e.g.
vinegar.
17
Pasteurization
Methods
• Some liquid foods (e.g.
beer and fruit juices) are
pasteurized after filling
into containers
Water is used reduce
thermal shock
Metal and plastic
containers may
be pasteurized
using steam-air
mixtures or hot
water
Packaged Foods Liquid Foods
18
What is Thermal Processing?
A food sterilization technique in which the application of heat, at a specific
temperature for a specific time, destroy microorganisms and enzymes.
19
Commercial Sterility
The destruction of all viable microorganisms of public health significance
and those capable of reproducing under normal non-refrigerated conditions
of storage and distribution.
Heat Resistant : Pathogen
Clostridium Botulinum
Heat Resistant : Non-Pathogenic
Bacillus Stearothermophilis
Clostridum Thermosaccharolytom
20
Processing
Types
In Package Sterilized
Aseptic
The product is packed into containers and the
container of product is then sterilized.
The product and the package are sterilized
separately and then the package is filled with the
sterile product and sealed under specific
conditions.
21
Thermal Processing
Canned Foods
• Canned foods are processed so that they are shelf stable
• They should be ‘commercially sterile’
• That means if any microbes survive the processing, they should not be capable of growing
(and therefore spoiling the contents) under the normal storage conditions of the can
28
Thermal Process
Equipment
In order to reach temperatures above sterilization (100°C), the thermal treatment has
to be performed under pressure in pressure cookers (e.g. Retorts)
*Sanitizer such as Chlorine used to sterilize water
30
Thermal Process
Containers
Type Description
Glass Jars • Glass jars are sometimes used for meat and
vegetable products but are not common due to their
fragility
• Glass jars consist of 2 parts: Glass body and a metal
lid
• The seaming panel of the metal lid has a lining of
synthetic material (compound)
31
Thermal Process
Pouches
Type Description
Retortable Pouches • Containers made of either:• Laminates of synthetic material only
• Laminates of aluminum foil with synthetic materials
• Thermo-stabilized laminated food pouches have a
seal layer - usually PP (polypropylene) or PP-PE
(polyethylene) – and the outside layers are usually
made of polyester (PETP) or nylon.
• PE or PP permits the heat-sealing of the lid made of
the same laminate onto these containers, which can
then be subjected to intensive heat treatment (125°C
or above
Cleaning prior to closure Seaming of cans
32
Thermal Process
Container Close
• Rigid containers are delivered to
processing plants with the lids separate
• Dirt/dust must be removed prior to
filling
• Small scale: hot water
• Industrial scale: steam cleaning
• After filling with product the can is
mechanically sealed tightly
(Doubleseam)
• Closed cans consist of multiple layers
which must overlap sufficiently and all
curves need to be smooth to avoid
small cracks
33
Thermal Process
Death Rate Curve (D Value)
• At slightly elevated temperatures, most
microbes will grow and multiply quickly
• At relatively high temperatures,
microbes will be destroyed• Due to variation most microbes will be killed
relatively quickly, others survive much longer
• If a population of microbes is held at a
constant high temperature, the number of
surviving spores or cells plotted against time
(on a logarithmic scale) can be plotted on a
graph. This is referred to as the ‘death rate
curve’
34
Thermal Process
Death Rate Curve (D Value)
• This graph is a straight line – it is referred to as the
Logarithmic order of death
• Logarithms refers to the power to which a base must be
raised to produce a given number• For example, if the base is 10, then the logarithm of 1,000 -
written log 1,000 or log10 (1,000) - is 3 because 10³= 1,000
• The “death rate curve” is a straight line when plotted
using a logarithmic scale• This means that if in some time period the number was reduced
from 1000 to 100 (divided by ten, sometimes referred to as “1 log
reduction”), then if you had held the microbes at the same
temperature for twice that time period, the number would have
been reduced to 1 (divided by 100, or “2 log reductions”)
35
Thermal Process
Log Reduction
• The time period for each “log reduction” is
referred to as the decimal reduction time or D
value (D-value = Decimal Decay Time)
• For example, the D-value of Bacillus
stearothermophillus, a common spoilage
microorganism at 121°C, is about 4 minutes.
This means if you had cans of food product
each containing 1000 of these spore and you
held the product at a constant temperature of
121°C
• After 4 minutes (1 D-value) there would
be 100 surviving spores in each can (1
log reduction)
• After 8 minutes (2x D-value) there
would be 10 spores surviving in each
can (2 log reductions)
• After 12 minutes (3x D-value) there
would be 1 spore surviving in each can
(3 log reductions)
• If this food product,
which began with
1000 spores of
Bacillus
stearothermophillus,
was held for 16
minutes at 121°C, it
would result in 4 log
reductions (0.1 spores
per can)
• After 20 minutes
there would only
be 1 spore per
100 cans
• The higher the microbial load,
the longer it will take to reduce
the numbers to an acceptable
level
• It is theoretically impossible to
destroy all cells – therefore we
reduce the probability of
spoilage to an acceptable small
number
• This information refers to
holding the product at a constant
temperature as the destruction
of microbes is temperature
dependent
36
Thermal Process
Thermal Death Time (TDT)
• If D-value versus time is plotted, the graph looks
similar to the one previously
• This one is called the Thermal Death Time
(TDT) curve
• The straight line graph means that if you change
the temperature by a certain amount, the D-value
will change by a factor of 10
• If you changed it by twice that amount, the
D-value will change by a factor of 100
• The change in temperature to cause a factor of
10 change in D-value is referred to as the z-value
• z-value for Bacillus stearothermophillus is 10°C
• D-value for Bacillus stearothermophillus is
121°C for 4 minutes
• If you held this microbe at 111°C (10°C, or one
Z-value, less than 121°C), D-value would be 40 minutes
• In other words, for Bacillus stearothermophillus, 4 minutes at 121°C will have the same effect (one log reduction in spores) as
40
minutes at 111° C, which would have the same effect as 400 minutes at 101°C
It is obvious why using high processing temperatures is an advantage!
37
Heat Resistance of Micro-organisms
Factors
• A range of factors affect the heat resistance of micro-
organisms. The most important are:
38
Thermal Processing
Design
• Design of Heat Sterilization Processes
• Take account of the type of microorganism - determined largely by food conductions (acidity)
• Result in an acceptable low probability of survival of spores
• Be effective in every part of the food
Low Acid Foods (pH>4.5)
Clostridium Botulinum is the bacteria of
greatest concern to the low acid food industry
for several reasons:
➢ When it grows it can produce a deadly
toxin (Botulism)
➢ C. Botulinum is ubiquitous (can be found
in soil and water practically anywhere in
the world)
➢ It grows well in the environment created in
canned products (pH>4.5, aw>.85, No
oxygen in can)
- C. Bot is anaerobic and so can survive and grow in a
sealed can
- The destruction of C. Bot is a minimum requirement of
heat sterilization
- Referred to as the “12D” process – the product
must be treated for 12 times the D-value of the
microbe.
- For C. Bot this is a process equivalent to about
2.5 minutes at 121°C (commonly known as the
“botulinum cook”)
39
Thermal Processing
Design
• Design of Heat Sterilization ProcessesTake account of the type of microorganism - determined largely by food conductions (acidity)
Result in an acceptable low probability of survival of spores
Be effective in every part of the food
High Acid Foods (pH<4.5)
• Anaerobic pathogens cannot grow or
produce toxins
• Spoilage microorganisms are quickly
killed at temperatures of about 90°C
• Minimum treatment applied to high acid
foods often involves ensuring every part
of the product reaches a temperature of at
least 95°C
- In acid foods (where pH is close to 4.5) Clostridium
butyricum can cause spoilage
- It is not killed by processes commonly used for acid
foods and can cause swelling / bursting of the cans in
about 2 weeks
40
Thermal Processing
The “F0 Value”
• Sterilizing value
• The amount of heat treatment applied to a food product can be measured using the F-value-concept
• The F0 value is a measure of the “sterilizing value” of a process.
• It can be thought of as the time required at a temperature of 121°C to reduce microbial numbers by the
same amount as the actual process being considered
121°C is the reference temperature
on which F0 is based
• Temperature is not constant throughout the process
• It provides a basis for comparing different heat sterilization procedures
if two processes have the same F0 value, they provide the same level of
sterilization
Aim of thermal process: heat penetration
achieved at the “cold point” of the can, where
heat arrives last
41
Thermal Processing
The “F0 Value”
• The required level of heat treatment (F0 of the process) may vary with factors
• such as pH and carbohydrate level, and type and expected level of
• contamination with microoganisms
Chemical additives may also assist
inhibition of micro-organisms (salt,
alcohol, nitrite)
Some products require additional
processing to achieve the required
level of cook (for quality reasons)
42
Thermal Processing
The Lethality Factor “L”
• Given that the F0 is based on a constant reference temperature (121°C), but the product is mostly at a different
temperature, how can the F0 be calculated?
L-valueThe time @
121.1°C
Equivalent in sterilizing value to
one minute at some other
temperature
• One minute at some temperature will contribute “L” minutes worth of F0.
• The L-value is dependent on the z-value of the micro-organism being considered, but for most purposes z=10°C
• L-value can be calculated from the formula or can be read from a table
L = 10(T-121.1)/z
43
Thermal Processing
The Lethality Factor “L”
• Example:
A product is held at a temperature of 118°C for a period of 12 minutes. Ignoring other
heating and cooling periods, what is the F0 value of this process? From the formula, the
L-value for 118°C is 0.490. That is each minute at 118°C contributes 0.490 minutes to the
F0 value. Therefore, the F0 value of this process = 12 x 0.490 = 5.9 minutes.
In a real retort process the temperature of the product is not constant – it slowly heats up,
will stay at a constant temperature for some time, then cool down again. The period when
the product is heating and cooling contribute significantly to the severity of the process.
To calculate the F0 value of such a process, the contribution of the varying temperatures
must be converted to an equivalent F0 value. This is achieved based on the L-value, as
indicated previously.
44
Thermal Processing
Affecting Factors
• A number of factors affect the rate at which a product heats inside a
container