Teacher Professional Development Programme
Knowledge Enriching Series for
New Senior Secondary Technology and Living:
Food Science and Technology Strand
Item 1: Food Studies
Food Preservation II
Professor Peter CK Cheung
Food and Nutritional Sciences
The Chinese University of Hong Kong
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Outlines for Food Preservation I and II
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Purpose of food preservation
Factors causing food deterioration
Principles of food preservation
Thermal and non-thermal methods of
food preservation
Emerging methods of preservation
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Thermal methods of food
preservation
Methods of heat treatment
– Pasteurization
– Blanching
– Canning (commercial sterilization)
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Objectives of thermal treatment
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To eliminate pathogens
To eliminate or reduce spoilage
organisms
To extend the shelf-life of the food
To improve palatability of the food
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Mild heat treatment/ thermal processing
Blanching
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Heat treatment of vegetables in boiling, salted water to
inactivate enzymes, kill microorganisms and retain
color (chlorophyll)
Typical example: 100oC for 1 min to inactivate
peroxidase
Pasteurization
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Heat treatment of milk adequate to kill potential
harmful microorganisms Destroy pathogens
Purposes:
To reduce bacterial count
To inactivate enzymes
To extend shelf-life
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Different methods of pasteurization
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Low-temperature hold method (LHT): typical
conditions of 63oC for 30 min before cooled
to 7oC
High-temperature short-time (HTST): typical
conditions of 71.5oC and hold for at least 15
sec before cooled to 10oC
Ultrahigh-temperature (UHT): 138oC for at
least 2 seconds; extreme pasteurization that
kills all microorganisms for keeping milk in a
closed, sterile container at room
temperature
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Table 1 Some examples of convention pasteurization treatments
Product
Temperature
Time
Remark
Milk
62.8oC
30 min
LTH
Milk
71.7oC
15 sec
HTST
Milk
137.8oC
2 sec
UHT
Ice-Cream
71.1oC
30 min
LTH
Ice-Cream
82.2oC
16-20 sec
HTST
Grape Wines*
82-85oC
1 min
in bulk
Fruit Wines*
62.8oC
depends
bottled hot
Beer
60oC
depends
bottled hot
Dried fruits
65.6-85oC
30-90 min
Grape Juice*
76.7 oC
30 min
Apple Juice*
85-87.8 oC
30-60sec
bottled in bulk
Carbonated Drinks*
65.6
30 min
in common
Vinegar*
60-65.6
30 min
in bulk
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*depends on the acidity
Severe Heat treatment/ thermal processing
Sterilization (in Canning)
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Intensive heat treatment that kills all the
pathogens and microorganisms, including
their spores, in food.
Relatively long shelf-life (i.e., more than six
months) in a hermetically sealed container
without other supplementary preservation
measures.
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Sterilization (in Canning)
Intrinsic factors of food affecting
sterilization conditions:
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Heat penetration characteristics of food
pH of the food
Composition of food
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Sterilization of canned foods
Canning of food before sterilization
Vertical retort for sterilization of canned foods
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Sterilization (in Canning)
Commercial sterilization conditions:
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Temperature ranges from 116 - 121oC
Heating time (D values) : 12D concept
Thermal Death time (TDT)
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Sterilization of
Canned Foods
Table 2
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2 2
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Murano, 2003
Table 2. Overview of Mild and Severe Heat
Treatments
Mild Heat Treatment
Aims
Kill pathogens
Reduce bacterial count (food is
not sterile
Inactive enzymes
Severe Heat Treatment
Aims
Kill all bacteria
Food will be commercially sterile
Advantages
Advantages
Minimal damage to flavor, texture,
and nutritional quality
Long shelf life
No other preservation method is
necessary
Disadvantages
Disadvantages
Short shelf life
Food is overcooked
Another preservation method
Major changes in texture, flavor,
must be used, such as refrigeration and nutritional quality
or freezing
Examples
Pasteurization, blanching
Examples
Canning
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Low-temperature treatment/ cold
storage
Refrigeration/chilling
Freezing
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Chilling
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temperature between -1 to 8 oC
purpose: to reduce biochemical and
microbial changes => extend shelf life of
fresh and processed foods
characteristics: minimal sensory and
nutritional changes
in combination with fermentation,
irradiation, pasteurization, etc. as post
treatment
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Table 3
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Figure 3
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Chill injury
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tropical, subtropical (<10-15 oC) and some
temperate fruits (<5-10 oC)
caused by maintaining temp below a specific
optimum for the fruit in concern resulted in the
physiological changes as browning (surface
discoloration), un-ripening, blemishing (pitting,
collapse of tissue), etc.
Mechanisms: membrane lipid structure/enzyme
conformational changes, loss of
compartmentalization
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Chill Injury after long time storage
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Freezing and frozen-food storage
food temp below freezing point
„ water forms ice (change in state)
„ for almost all kinds of food (fruit – whole,
puree, concentrates; vegetables, seafood,
meat, baked food, ready-to-eat prepared
food)
How does freezing preserve food?
„ low temperature
„ low water activity
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Figure 4
(Fellows, 2000)
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Figure 5
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Figure 6a
Figure 6c
Figure 6b
Figure 6d
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Delgado and Rubiolo, 2005
Changes in food during frozen storage
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Recrystallization
Freezer burn (dehydration)
Residual chemical (lipid oxidation) and
enzymatic reaction (plant originpolyphenoloxidase, lipoxygenase; animal
origin- proteolytic and lipolytic enzymes
Colloidal substance/physical change (starch
syneresis; emulsion breakdown)
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Mechanisms of migratory recrystallisation in
foods during frozen storage
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caused by fluctuation of storage temp.
heat entering a freezer => melting of ice crystal on
food surface nearest to heat source => ice crystal
reduces in size => vapour pressure increases Vs
inside of freezer => migration => dehydration near
the region of the heat source => when temp falls
=> no recrystallisation of water vapor, but migrated
and joined with other ice crystals => bigger size=>
quality loss as in slow freezing
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Figure 7
(Brennan et al., 1990)
Freezer burn
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loss of moisture from food to storage
environment
characterized by: lighter colour (microscopic
cavity previously occupied by ice can
change the wavelength of reflected light)
foods with large surface area/volume ratio
e.g. IQF
minimized by packaging
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Freezer Burn of Red Meat
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Moisture removal
Product concentration
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Evaporation; distillation; ultrafiltration; dialysis
Dehydration
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Sun drying; Drum drying
Freeze drying; Smoking; Spraying drying
Controlling factors: temperature, humidity,
pressure, and portion size
Deterioration: color, flavor, textural changes due
to enzymatic activities; non-enzymatic reaction
(Maillard browning); oxidative spoilage by fat
oxidation
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Figure 8
Murano, 2003
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Freeze Drying: the Sublime Solution
www.ofd.com
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Commercial
freeze drying
equipment
www.ofd.com
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Non-thermal methods of
food preservation
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Acidity control
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Control of pH of a food through the use of
acidulants
High-acid foods (pH < 4.6)
Spore-forming bacteria generally do not
grow in foods having pH values of 4.5 and
less
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Table 3 Examples of acidulants used in the food processing industry. Acetic acid is
present in vinegar, while the acid salt sodium acetate can be used as an additive to decrease a
food’s pH. Citric acid is present in citrus fruits; malic acid is a component of apples; and all of
these acids also can enhance food flavor. Sodium benzoate and calcium propionate are acid
additives that are effective antimicrobial agents. One type of inorganic acid, namely phosphoric,
is used extensively in foods and beverages.
Acid
Comment
Acetic
Provides flavor, decreases pH
Sodium acetate is salt form present in vinegar
Benzoic
As sodium benzoate, effective antimicrobial agent
Occurs naturally in cranberries
Citric
Provides flavor, decreases pH, acts as chelating and sequestering agent
Occurs naturally in citrus fruits
Lactic
Provides tartness
Malic
Provides flavor
Occurs naturally in apples
Phosphoric
Provides flavor and tartness in beverages
Enhances juiciness in meats (as phosphate)
Propionic
As calcium propionate, effective antimicrobial agent
Produced in some cheeses
Tartaric
Present in baking powder as potassium tartrate salt
Occurs naturally in grapes
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Use of packaging
Packaging functions
Control of packaging atmosphere
For fresh
meat
For small
goods
For cheese
For dairy
For produce
For seafood
For poultry
For
convenience
For anything!
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Packaging functions
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Preserve spoilage of color, flavor, odor, and
texture
Prevent contamination by biological, physical,
chemical hazards
Prevent loss or absorption of water and oxygen
Prevent tampering (neckbands/shrink-film sleeves)
Communicate information with
ingredients/nutrition facts
Facilitate marketing
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Controlling packaging atmosphere
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Vacuum –no entry/escape of air, carbon
dioxide, water
Modified Atmosphere Packaging
(MAP) – gas flush (nitrogen and inert
gases)
Active packaging – sachet: oxygen (iron
oxide); carbon dioxide (calcium
hydroxide); water, ethylene (potassium
permanganate), ethanol
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Aseptic packaging
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Independent sterilization of both foods
and packaging material with assembly
under sterile environmental conditions
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Tetra Aseptic packages
(Source: Tetra Pak Inc.)
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Figure 7a Tetra Brik ®
aseptic packaging material
layers (Source: Tetra Pak
Inc.)
Figure 7b Illustration of
roll-fed packaging
material being formed
into Tetra Briks.
(Source: Tetra Pak Inc.)
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Fellows, 2000
Figure 8 Aseptic packaging
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Minimal processing of foods
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Non-thermal methods with no
substantial increases in product
temperature
Preserve foods with greater retention
of and/or insignificant detrimental
effect on nutritional and sensory
quality
Higher consumer appeal and premium
prices
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Table 4. Examples of novel processes that may have
applications for minimal processing of foods
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Electro-heating (radiofrequency, microwave
and ohmic heating)
High pressure
processing (HPP)
High voltage electrical
discharge
High intensity light
Ultrasound
Modified atmosphere
packaging
Jet impactation
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Gamma radiation
Lasers and masers
Microfiltration
X-rays
Cryogenic thermal
shock
Immobilised enzymes
Active packaging
Ozone
Nitrous oxide
(Fellows, 2000)
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Theory of Food Irradiation
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Ionization of water byγrays and electrons to produce
ions and free radicals
Radiolysis: subsequent reactions caused by products
of ionization to destroy micro-organisms, insects and
parasites in irradiated food
Figure 10
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Rate of destruction of micro-organisms by radiation
Resistance to irradiation: viruses>spore forming bacteria>vegetative cells
and non-spore forming bacteria>insects and parasites
Figure 11
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Table 5
Applications of food irradiation
Application
Dose range
(kGy)
Examples of foods
Countries with commercial
processing
Sterilization
7-10
Herbs, spices
Belgium, Canada, Croatia, Czech
Republic, Denmark, Finland, Israel,
Korea (Rep.), Mexico, South Africa,
USA, Vietnam
Up to 50
Long term ambient storage of meat
(outside permitted dose)
None
Sterilization of packaging
materials
10-25
Wine corks
Hungary
Destruction of pathogens
2.5-10
Spices, frozen poultry, meat,
shrimps
Belgium, Canada, Croatia, Czech
Republic, Denmark, Finland, France,
Iran, Netherlands, South Africa,
Thailand, Vietnam
Control of moulds
2-5
Extended storage of fresh fruit
China, South Africa, USA
Extension of chill life from
5 days to 1 month
2-5
Soft fruit, fresh fish and meat at 04℃
China, France, Netherlands, South
Africa, USA
Inactivation/control of
parasites
0.1-6
Pork
--
Disinfestation
0.1-2
Fruit, grain, flour, cocoa beans, dry
foods
Argentina, Brazil, Chile, China
Inhibition of sprouting
0.1-0.2
Potatoes, garlic, onions
Algeria, Bangladesh, China, Cuba
Adapted from Ley (1987), Guise (1986a), Goresline (1982), Anon (1985), Loaharanu (1995) and Wilkinson
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and Gould (1996).
Table 6 Advantages and limitations of Gamma Radiation
Advantages
Limitations
Examples of commercial
applications and products
„Well
„High
„Fruit
established and understood
„Excellent
„Suitable
penetration into foods
for sterilization
capital cost
„Localized
risks from radiation
„Herbs
and spices
consumer
understanding
„Packaging
for non-microbial
applications (e.g. sprout inhibition)
„‘Politics’
„Meat
„Permitted
„Changes
„Suitable
in some countries
„Poor
and vegetables
of nuclear energy
and fish
in flavor due to
oxidation
„Reliable
„Little
„Difficult
to detect
loss of food quality
„Suitable
for large-scale production
„Low energy costs
„Insecticidal
„Improvement
in flavor in some
foods (e.g. strawberries)
„Suitable
for dry foods
(Fellows, 2000)
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Recommended basic references
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Food Processing Technology: Principles
and Practice by P. Fellows (2000), 2nd
edition, CRC Press.
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Food Processing Handbook by J.G.
Brennan (2006), Wiley-VHC
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Understanding Food Science and
Technology by Peter S. Murano (2003),
Thomson Wadsworth
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Advanced reading for
Emerging Preservation Technologies
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New trends in food processing by Senorans et al.
in Critical Reviews in Food Science and Nutrition,
43(5):507-526 (2003)
Tasks of food technology in the 21st century by M.
Karel in Food Technology 54(6):56-64 (2000)
Applications and potential of ultrasonic in food
processing by Knorr et al. in Trends in Food
Science & Technology 15:261-266 (2004)
Advances in the use of high hydrostatic pressure
for processing cereal grains and legumes by
Estrada-Giron et al. in Trends in Food Science &
Technology 16:194-203 (2005)
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