2. THERMAL PROCESSING
Thermal processing is defined as the combination
of temperature and time required to eliminate a
desired number of microorganisms from a food
product.
The term "thermal" refers to processes involving
heat.
Heating food is an effective way of preserving.
The basic purpose for the thermal processing of
foods is,
to reduce or destroy microbial activity,
reduce or destroy enzyme activity,
and to produce physical or chemical changes,
to make the food meet a certain quality
standard.
3. TYPES OF THERMAL PROCESSING
There are three main temperature categories employed in thermal processing -
1. Blanching
2. Pasteurization
3. Sterilization
Mild processes-
• Blanching
• Pasteurization
More severe processes –
• Canning
• Baking
• Roasting
• Frying
BLANCHING STERILIZATION
PASTEURIZATION
CANNING ROASTING
BAKING
4. BLANCHING
The primary purpose of blanching is to destroy enzyme
activity in fruit and vegetables.
It is not intended as a sole method of preservation,
But as a pre-treatment prior to freezing, drying and canning.
Functions of blanching include:
1. Reducing surface microbial contamination
2. Softening vegetable tissues to facilitate filling into
containers
3. Removing air from intercellular spaces prior to canning
5. METHODS OF BLANCHING
Blanching is carried out at up to 100°C using
hot water
Blanching is carried out steam
Hot Water Blanchers
Includes various designs which hold the food
in hot water (70 to 100°C) for a specified
time, then moves it to a dewatering/cooling
section.
In this type the food enters a slowly rotating
drum, partially submerged in the hot water.
6. Steam Blanchers
This is the preferred method for foods with large
cut surface areas as lower leaching losses.
Normally food material carried on a mesh belt or
rotatory cylinder through a steam atmosphere,
residence time controlled by speed of the
conveyor or rotation.
Often poor uniformity of heating in the multiple
layers of food, so attaining the required time-
temperature at the centre results in overheating
of outside layers.
7. Pasteurization
Purpose of Pasteurization
Pasteurization is a relatively mild
heat treatment.
In which food is heated to <100°c.
It is widely used throughout the
food industry.
It can be used to destroy enzymes.
It can be used to destroy relatively
heat sensitive Micro-organisms
It is used to extend shelf life.
8. Pasteurization
Milk Pasteurization Temperature
Temperatures Time
63°C For 30 min (low
temperature long time
LTLT)
72°C For 15 sec (primary high
temperature short time,
HTST method)
89°C For 1.0 sec 90°C For 0.5
sec 94°C For 0.1 sec 100°C
For 0.01 sec
90°C For 0.5 sec
94°C For 0.1 sec
100°C For 0.01 sec
9. Conti..
The two groups of micro-organisms that
survive pasteurization temperatures used in
milk
1. Thermoduric: organisms that can survive
exposure to relatively high temperatures but
do not necessarily grow at these
temperatures E.g. Streptococcus and
Lactobacillus.
2. Thermophilic: organisms that not only
survive relatively high temperatures but
require high temperatures for their growth
THERMODURIC
THERMOPHILIC
10. Pasteurization Method
There are number of basic methods of
pasteurization.
1. Batch (holding) Method
In this method every particle (e.g.
milk) must be heated to at least
63°C.
and held for at least 30 minutes,
however this is not used commercially
these days.
11. Conti…
2. Pasteurization High-Temperature-Short-Time (HTST)
In this method the heating of every particle of milk to at
least 72°C.
and holding for at least 15 seconds.
Carried out as a continuous process.
Ultra Heat Treatment (UHT) a sterilization treatment,
can also be performed using higher temperatures and
shorter times e.g. 1 s at 135°C
12. Conti…
Typical Equipment employed for (HTST) method includes:
a. Plate heat exchanger (PHE)
b. Holding tube – sized to ensure the correct treatment time
is achieved
c. Holding tanks – for storage of the raw and pasteurised milk
d. Balance tank – to assist in maintaining full flow, and to
take returned milk if temperature not Achieved
e. Control and monitoring system.
13. Sterilization
Sterilization is a controlled heating process used to completely
eliminate all living micro-organisms, including thermo resistant
spores in milk or other food.
It can be achieved by,
1. Moist heat
2. Dry heat
3. Filtration
4. Irradiation
5. Chemical methods
The aim of sterilization is the destruction of all bacteria
including their spores.
14. Conti…
Food products filled in sealed
containers are exposed to
temperatures above 100°C.
Temperatures above 100°C, usually
ranging from 110-121°C depending
on the type of product,
Heat must be reached inside the
product.
Products are kept for a defined
period of time at temperature
levels required for the sterilization
It depending on type of product and
size of container.
MOIST HEAT
IRRADIATED FRUIT
DRY HEAT
15. Food irradiation
Irradiation is the process of exposing
fresh food to low amount of gamma-rays
or x- rays to sterilize and prolong its life.
It carries enough energy to free electrons
from atoms or molecules, thereby ionizing
them.
Irradiation can kill microorganisms,
insects and parasites
16. Why Irradiated Food?
Prevention of food borne illness
effectively eliminates microbes; Salmonella and E. Coif
Preservation
Destroy/ inactivate organisms that cause spoilage and
decomposition.
Control of insects
Destroys insects e.g imported fruits.
Delay of sprouting and ripening
Lengthen the longevity of products e.g: potatoes.
Sterilization
Useful for patients in the hospital especially with
impaired immunity.
17. Types of Radiation and Their Sources-
1. Non-Ionizing radiation
Non-ionizing radiation has less energy than ionizing
radiation; it does not possess enough energy to
produce ions.
Examples:- Visible light, Infrared, Radio waves,
Microwaves, and Sunlight
2. Ionizing radiation
There are several types of ionizing radiation
a. Alpha radiation
b. Beta radiation
c. Photon radiation
d. Neutron radiation
18. Ionising radiation sources
According to the Codex General Standard for Irradiated
Foods, ionizing radiations recommended for use in food
processing are
1. Gamma rays produced from radioisotopes cobalt-60 and
cesium-137
Cobalt-60 is produced in a nuclear reactor via neutron
bombardment of highly refined cobalt-59 (59-Co) pellets, while
cesium-137 is produced as a result of uranium fission. - Both
cobalt-60 and cesium-137 emit highly penetrating gamma rays
that can be used to treat food in bulk or in its final packaging.
2. Electron beams and X-ray generated from machine
sources
A major advantage of machine-sourced ionising radiation is that
no radioactive substance is involved in the whole processing
system. - Powered by electricity - Suitable only for foods of
relatively shallow depth
19. Application of Food Irradiation
Control of sprouting and germination.
Shelf-life extension of perishable foods.
Delaying ripening and aging of fruits and
vegetables.
Destruction of parasites.
Control of food borne diseases
20. Advantages-
1. Irradiation leaves no radioactivity or toxic residues on the treated product.
2. Irradiation is an efficient, continuous, automated process requiring less
treatment time.
3. Irradiation will not contaminate the environment while chemical vapor from
fumigation will.
4. Irradiation delivers a superior product to the consumer because the efficacy
of the process permits the fruit to be picked at the optimal ripeness.
Disadvantages-
1. It reduces small amount content of several key nutrients.
2. It is ineffective against viruses.
3. Capital cost is more.
21. The sterilization process
The sterilization process in the canned
product can be subdivided into three phases.
a. Phase 1 = (heating phase) heating medium
(water or steam) the product temperature is
increased from ambient to the required
sterilization temperature
b. Phase 2 = (holding phase) temperature is
maintained for a defined time.
c. (Phase 3 = (cooling phase) the temperature
in the can is decreased by introduction of
cold water into the autoclave.
22. Sterilization Equipment
Autoclaves or retorts
In order to reach temperatures above 100°C
(“sterilization”), the thermal treatment has to be
performed under pressure in pressure cookers, also called
autoclaves or retorts.
In autoclaves or retorts, high temperatures are generated
either by direct steam injection, by heating water up to
temperatures over 100°C or by combined steam and water
heating.
23. Thermal Death Rate Kinetics
Of Microorganism
Factors affecting heat resistance of microorganism
Age of cell, younger cell are less heat
resistance
Initial concentration of spore or cells more the
number greater the heat treatment
The medium in which growth has occurred a
more nutritious medium increases heat
resistance
Moisture content dry food tend to require more
serve heat treatment during sterilization
pH of medium cell or spore have great heat
resistance at or natural pH values.
24. DEHYDRATION
Foods dehydration refers to
Dehydration is one of the oldest methods of
food preservation, and many cultures still
dry food in the sun.
The nearly complete removal of water that
causes minimum or ideally no change in
food properties. Foods are dried to the
final moisture content 1-5%. Stability over
1 year at room temperature.
Concentration processes that remove only
part of water are not considered as
dehydration processes.
Drying is usually accomplished by the
evaporation of water, but any method that
decreases the amount of water activity in
food is a form of drying.
25. Contd……..
The drying process removes enough moisture
from food to greatly decrease these
destructive effect.
The moisture content of fresh foods ranges
from 20% to 90%. Foods require different
levels of dryness for safe storage,
The dryness of air is measured in terms of
relative humidity (RH).
If air is at 100% relative humidity, it has
absorbed 100% of the water it can hold at
that temperature.
26. PURPOSES OF DRYING
To avoid or eliminate moisture which may lead to
corrosion and decrease the product stability.
To improve or keep the good properties of a material,
eg: flow ability, compressibility.
To reduce the cost of transportation of large volume
materials(Liquids).
To make the material easy or more suitable for handling
Preservative
The final step in: Evaporation, Filtration, Crystallization
27. TYPES OF DRYING
1. Direct: Convective Drying
Drying is established through direct contact between the
product and the gas heating medium. Material reaches
steady state temperature.
2. Indirect Drying
Established from heated surface in contact with the product.
The heating medium and product are separated by wall.
Material reaches steady state temperature near liquid boiling
point for contact rate drying.
3. Radiation
Heat transfer established by radiation from energy source.
There is no contact from heated surface or medium and
product
28. MECHANISM OF DRYING
Liquid diffusion: If the wet solid is at a temperature
below the boiling point of the liquid
Vapor diffusion: If the liquid vaporizes within material
Condensation diffusion: If drying takes place at very low
temperature and pressure,Eg:Freeze drying
Surface diffusion: (possible although not proven)
Hydrostatic pressure differences: When internal
vaporization rates exceed the rate of vapor transport
through the solid to the surroundings
Combination
29. CHOICE OF METHODS OF DRYING
Choice of methods of drying depends on-
Product is sensitive to heat or not
Nature of solvent to be removed
Process is to be carried out under aseptic conditions
Quantity of products to be dried.
Available source of heat
Cost involved
30. THE EFFECTS OF
DEHYDRATING ON FOODS
The main principle of drying is the evaporation of water, using
higher than normal temperatures. As the water evaporates
there is an increase in the concentration of solutes in the
product. This increase can physically damage the food. This
damage can be seen in the changed physical appearance of
dried apples.
31. DRYING CAUSES
Denaturation of proteins
A general loss of structure
Browning reactions
Changes occur in:
1. Color
2. Flavor
3. Texture
4. Viscosity
5. Reconstitution Rate
6. Nutritional Value
7. Storage Stability
32. 1. Dehydrator
This is a quick, simple
method for drying your food.
Dehydrators are designed to
dry food uniformly and
efficiently while maintaining
the highest food quality.
Dehydrators like
the Snackmaster are built
with ventilation and a fan to
provide air circulation while
drying.
2. Oven Drying
Using an oven to dry food is
the fastest option, taking
between 4 to 12 hours
depending on the food.
To dry your food, heat the
oven to 140° F. Because an
oven does not get the best
air circulation, you will
need to crack the door
open 2 or 3 inches to
encourage airflow and
allow the moisture to
escape.
Can also improve
circulation by placing a fan
near the opening of the
oven.
33. 3. Microwave
A microwave works
for small amounts
of foods like herbs
or leafy vegetables.
It is not really a
feasible method for
other types of
foods. If we do use
a microwave, we
will place our herbs
or leaves between
two paper towels
and heat for 2 or 3
minutes, adding 30
second increments
as needed.
4. Sun Drying
Drying your food with the sun
requires direct exposure to
sunlight and will take 3 or 4 days
to completely dry the food.
This method works in warmer,
dry climates.
If the humidity is too high, the
food will spoil before is dry.
After 2 days, turn the food over
to dry on the other side.
The food will need to be brought
in every night.
Once it has dried, you can put
the food either in the freezer at
0° F or the oven at 175° F for 30
minutes to kill any bacteria that
might have been collected while
outside.
34. 5. Air Drying
Air drying takes place in a warmer area
indoors, such as an enclosed porch or a
sun room where there is a lot of
ventilation and air circulation.
This method is common with herbs and
peppers. For even drying, hang the food
up on a string so the air can easily flow
around it.
35. Freezing
There are different methods of commercial
freezing available, but they are all based on two
concepts.
Very low temperatures inhibit growth of micro-
organisms and limit enzyme and chemical activity.
The formation of ice crystals draws available
water from the food, also preventing growth of
micro-organisms.
36. Treatment prior to freezing
Blanching of some fruits and most vegetables to
inactivate peroxidase, catalase and brown enzymes,
reduce cellular oxygen, reduce microbial numbers and
improve color
Addition of or dipping into ascorbic acid or sulphur
dioxide solutions to retain color and reduce browning.
37. Methods of Freezing
The freezing methods are classified as two methods
1. FAST FREEZING
Quick or fast freezing occurs at –25ºC or less.
Ice crystals are small and do not damage food
cells.
2. SLOW FREEZING
Slow freezing occurs at -24ºC or above.
Ice crystals are big and damage the food cells
causing loss of texture, nutrients, color & flavour
on thawing.
38.
39. AIR BLAST FREEZING
Either still air or forced air is used. Air is re-
circulated over food at between -30ºC and -40ºC
at a velocity of 1.5–6.0 m/s. In batch equipment,
food is stacked on trays in rooms or cabinets.
Continuous equipment consists of trolleys stacked
with trays of food.
Air freezer or cold storage is the simplest method
with the lowest investment costs. It is most
suitable for large or unprocessed products;
however it is the slowest freezing method. Forced
air freezer is the improved version of cold storage
and it is using convection to circulate cold air in
the freezing room.
40. ADVANTAGES
It can be suitable for any types of products.
This process can freeze irregular shaped
foods, including those which have already
been packaged, e.g. battered fish pieces.
It is the cheapest freezing method, air blast
freezers are used on a wide range of
products.
DISADVANTAGES
High manpower needed for operation
Slow freezing.
41. CARTOON/
BOX FREEZING
Cartoon freezers, also called box freezers are mechanically
complicated freezers
Products already packaged and placed in boxes are sorted,
transported and stored mechanically by automated mechanism,
placing them on shelves in storage with cold blasts of air.
These boxes are then left for usually longer amounts of time, whole
mechanism is automated and needs very limited man power
however it is not suited for many types of products.
Airflow ensures uniform product cooling, shorter dwell times and
energy saving. Throughputs from 3,500 Kg/hr to 35,000 Kg/hr.
42. ADVANTAGES
• Needs very limited man power
• Using belts is the extremely accurate
control of transportation process
DISADVANTAGES
• Maintenance requirement, difficulty of
cleaning or belt marks left on the
product
43. IMMERSION FREEZING
Immersion method is the fastest freezing method
It is commonly used as a pre-treatment of large products in order
to create a frozen layer before the product is exposed to longer
freezing time, in order to avoid dehydration.
Traditionally foods were immersed in solutions of salt and ice for
several hours, e.g. brine, freezing of fish at sea. However, modern
methods of freezing have meant that this process is rarely used.
Refrigerants are now sprayed directly onto the food.
Direct immersion in refrigerants [(glycols, glycerol, sodium
chloride, calcium chloride, and mixtures of salt and sugars)].
The challenge with this method is that the solution becomes
quickly diluted with the product which can change the process
speed and efficiency.
44. PLATE FREEZING
The food is prepared as normal, then packed between flat,
hollow, refrigerated metal plates.
These are adjusted to press tightly on the food and reduce
any air gaps.
The plates may be horizontal or vertical, the latter being
used for many bulky products, such as blocks of fish for fish
fingers.
This system is ideal for freezing large blocks of product, but
cannot easily freeze irregular shaped items.
45. FLUIDISED BED
FREEZING
Vertical jets of refrigerated air are blown
up through the product, causing it to float
and remain separated. This is a
continuous process which takes up to 10
minutes. The product, e.g. peas, beans,
chopped vegetables or prawns, move
along a conveyor belt.
46. CRYOGENIC FREEZING
Liquid nitrogen or carbon dioxide is sprayed
directly onto small food items such as soft fruit
and prawns.
Due to the liquids’ extremely low temperatures
(-196ºC) and -78ºC respectively) freezing is almost
instant. The nitrogen gas is removed by fans.
Liquid carbon dioxide is used for larger products.
47.
48. LIQUID CARBONDIOXIDE
FREEZING
When the CO2 gas is released to the atmosphere at -70 °C,
half of the gas becomes dry-ice snow and the other half
stays in the form of vapor.
This unusual property of liquid carbon dioxide is used in a
variety of freezing systems, one of which is a pre-freezing
treatment before the product is exposed to nitrogen spray
49. SPIRAL BELT FREEZER
In this case, the belt is bent around a central supporting
structure, maximizing the belt surface in a limited
space.
The spiral belt freezer can be a good solution for gentle
products as it minimizes product damage at transfer
points.
This technology also presents the advantage of very
large amount of square meters on a limited footprint
allowing high capacity and continuous production with
limited man power.
However the spiral belt freezer still presents the
disadvantages of the belt.
50.
51. ADVANTAGES
OF FREEZING
Many foods can be frozen
Natural color, flavor, and nutritive
value retained. Texture usually
better than other methods of food
preservation.
Foods can be frozen in less time than
they can be dried or canned.
Simple procedures.
Adds convenience to food
preparation.
Proportions can be adapted to needs
unlike other home preservation
methods.
Kitchen remains cool and
comfortable.
DISADVANTAGES
OF FREEZING
Changes in colour (loss of natural colour
constituents, chlorophyll pigments,
development of off colour)
Changes in texture (loss of cloud
destruction of gels, denaturation,
toughening) Changes in flavour (loss of
natural flavour, development of off -
flavour, rancidity)
Changes in nutrients, such as ascorbic
acid in fruits and vegetables, unsaturated
lipids, essential amino acids.
Initial investment and cost of maintaining
freezer is high.
Storage space limited by capacity of
freezer.
52. Refrigeration
Refrigeration and freezing are probably the
most popular forms of food preservation
In the case of refrigeration, the idea is to slow
bacterial action to a crawl so that it takes food
much longer (perhaps a week or two, rather
than half a day) to spoil but freezing, the idea is
to stop bacterial action altogether. Frozen
bacteria are completely inactive.
Refrigeration and freezing are used on almost
all foods: meats, fruits, vegetables, beverages,
etc.
Refrigeration has no effect on a food's taste or
texture. Freezing has no effect on the taste or
texture of most meats, has minimal effects on
vegetables, but often completely changes fruits
(which become mushy). Refrigeration's minimal
effects.
53. Method of refrigeration
1. Mechanical-Compression Refrigeration Systems
The most widely used refrigeration cycle method
is mechanical compression.
It has applications in both air conditioning and
commercial and industrial refrigeration.
these types of systems transfer heat by
mechanically compressing refrigerant into a low-
pressure, cold liquid and expanding it into a
high-pressure, hot gas.
Refrigerants are substances that can boil at a
wide range of temperatures with the application
or removal of pressure.
54. 2. Absorption Refrigeration
Heat is also transferred in absorption
refrigeration systems by compressing and
expanding refrigerant.
These systems rely on the process of absorption
and heat, instead of an electrically powered
mechanical compressor, to move the refrigerant
from the low-pressure side to the high-pressure
side.
Residential HVAC chillers often use ammonia as
the refrigerant and water as the absorbent.
55. Conti…
The water is located in a component called
the absorber, where it sucks ammonia from
the low-pressure side of the system and
removes heat while absorbing it.
A pump sends the water-ammonia solution to
a generator, which boils it, separating the
ammonia from the water before sending it to
the high-pressure side.
In addition to the process of absorption, heat
is also used to move the refrigerant
throughout the system. The heat can derive
from hot water, steam, natural gas or other
fuel sources.
56. 3. Evaporative Cooling
Unlike the mechanical-compression and absorption
refrigeration systems discussed above, evaporative
cooling doesn’t use the traditional refrigeration cycle.
Instead, these units, often called swamp coolers, cool
warmer outdoor air by blowing it over water-soaked
pads as it enters the home.
The water absorbs the heat from the air and
evaporates. The cooler air is channeled into the home
and the warm air out of it.
Evaporative coolers can reduce air temperature by
15° to 40°F but are best suited for dry climates, such
as those in the south-western U.S. They’re also less
costly to install and use about a quarter of the energy
of central air conditioners.
57. 4. Thermoelectric Refrigeration
Thermoelectric refrigeration systems are
unique from the three other types of
refrigeration in that no refrigerant or water
is used. These systems use an electric
current and a thermocouple.
A thermocouple is made up of two different
metal wires that are united at both ends.
Insulation separates the rest of the wires
from each other. When the current is
directed on the thermocouple, one end will
become hot and the other cool.
58. Cont…
Reversing the current’s direction has the effect
of swapping the cold and hot junctions. The hot
end will typically be placed outside of the area
to be cooled with a heat sink attached to it to
keep it the same temperature as the surrounding
air.
The cold side, which is below room temperature,
is placed in the area to be cooled, attracting
heat out of the air.
This type of refrigeration is generally used for
small cooling loads that can be difficult to
access, such as electronic systems.
59. Chemical method for food
preservation
The purpose of using a chemical agent as a
preservative is to retard food spoilage caused
by microorganisms the WHO has estimated
that 20% of the world’s food is lost by this
type of spoilage.
Partial prevention of this spoilage can be
achieved through the use of refrigeration,
drying, freezing and fermentation.
The use of chemical additives or preservatives
will prolong the shelf life of the food even
further
60. Conti…
Chemical preservatives
• Interfere with the cell membranes of microorganisms,
• their enzyme activity or then genetic mechanisms.
Preservatives may also serve
• as antioxidants,
• as stabilizers,
• firming agents
• as moisture retainers.
Chemicals that function to preserve the food are generally added after
the food has been processed and before it is packaged.
61. Conti…
Certain preservatives have been used
either accidentally or intentionally for
centuries, and include sodium chloride
(common salt), sugar, acids, alcohols and
components of smoke.
In addition to preservation, these
compounds contribute to the quality and
identity of the products, and are applied
through processing procedures such as
salting, curing, fermentation and smoking.
62. CLASSES OF PRESERVATIVES
Chemical preservatives may be grouped into two
classes.
1. Class I preservatives
2. Class II preservatives.
63. CLASS I PRESERVATIVES
The first one includes the use of sugar, salt, spices,
acetic acid(vinegar) and alcohol, and is referred to as
class I preservatives and is considered to be relatively
safe to humans.
Sugars and salt in high concentrations have high osmotic
pressure and draw water from microbial cells or prevent
normal diffusion of water into these cells resulting in a
preservative condition.
64. PRESERVATION BY SALT
Salt acts as
preservative when
its concentration is
increased above 12
%.
Salt levels of about
18 to 25% solution
will generally
prevent all growth of
microorganisms in
foods.
PRESERVATION BY SUGAR
Sugar in high concentrations
acts as a preservative due
to osmosis.
Sugars attracts all available
water and water is
transferred from the
microorganisms into the
concentrated sugar syrup.
65. CLASS II PRESERVATIVES
The second group includes the use of benzoic
acid, sulfur dioxide, nitrates and nitrites and
a variety of neutralizers, firming agents and
bleaching agents and referred to as class II
preservatives
66. SULPHUR DIOXIDE AND SULPHITES
Sulphur dioxide and its derivatives have been widely
used in foods as a food preservative. It serves both as
an antioxidant and reducing agent.
Sulphur dioxide gas (SO2) is one of the oldest known
fumigant and a wine preservative.
Sulphites are effective in producing more SO2 ions at
ph values less than 4.0.
Sulphites inhibit microbial growth by reacting with the
energy rich compounds like adenosine tri phosphate
67. BENZOIC ACID AND RELATED COMPOUNDS
It was the first chemical preservative permitted in
foods by the FDA, and it continues to be widely
used in large number of foods.
It is used in acidic foods, these act essentially as a
mould and yeast inhibitor.
It is more effective against yeasts than against
moulds.
Sodium benzoate, sodium salt of benzoic acid, is
very effective as it is nearly 180 times more soluble
in water than benzoic acid when dissolved in water.
68. SORBIC ACID AND RELATED COMPOUNDS
Sorbic acid and related compounds have
antimicrobial properties they are available as
sorbic acid , potassium sorbate, sodium
sorbate or calcium sorbate.
LACTIC ACID
This acid is the main product of many food
fermentations; it is formed by microbial degradation
of sugars in products such as sauerkraut and pickles.
The acid produced in such fermentations decreases
the pH to levels unfavourable for growth of spoilage
organisms such as putrefactive anaerobes and
butyric-acid-producing bacteria.
Yeasts and moulds that can grow at such pH levels
can be controlled by the inclusion of other
preservatives such as sorbate and benzoate.
69. CARBON DIOXIDE
Carbon dioxide is used as a solid (dry ice)
in many countries as a means of
lowtemperature storage and transportation
of food products.
Beside keeping the temperature low, as it
sublimes, the gaseous CO2 inhibits growth
of psychrotrophic micro-organisms and
prevents spoilage of the food (fruits and
vegetables, etc.)
Carbon dioxide is used as a direct additive
in the storage of fruits and vegetables
70. Chemical changes during
Processing and storage of food
Chemical changes during Processing of food
1. Some anti-nutritional factors like trypsin
inhibitors get inactivated by heat
2. Denaturation of proteins by heating
3. Loss of vitamins
4. Non Enzymatic Browning
5. Starch degradation
6. Loss of pigments
71. TRYPSIN INHIBITOR
Trypsin is an enzyme involved in the breakdown of
many different proteins.
A trypsin inhibitor (TI) is a protein that reduces the
biological activity of trypsin.
Trypsin inhibitor is present in various foods such as
soybeans, grains, cereals and various additional
legumes.
Trypsin inhibitor is heat liable, therefore by exposing
these foods to heat, the trypsin inhibitor is removed
and the food subsequently becomes safe to eat.
72. DENATURATION OF PROTEIN
If a protein loses its shape, it ceases to perform that
function. The process that causes a protein to lose
its shape is known as denaturation.
In this the destruction of its quaternary , tertiary
structure of protein to give primary structure.
Conversely, protein denaturization can also cause
the formation of softer textures. For example, the
protein collagen, which is the major component of
the connective tissue in meat, has a tough, chewy
texture
73. LOSS OF PIGMENTS
The main foods containing pigments. There are
three families of pigments found in fruit and
vegetable plants.
Chlorophyll – green pigment
Carotenoids –pigments ranging from yellow to
deep red, and the flavonoids;
Anthocyanins – red, blue or purple pigments
according to the pH, and
Anthoxanthin – white pigment.
74. The pigment chlorophyll is responsible for
photosynthesis and can be found in many
fruits and vegetables such as cabbage,
broccoli, kiwi fruit and green apples.
Chlorophyll is a fat-soluble pigment and
thus, may leach from fruit and vegetables
if they are cooked in a medium containing
fat e.g., stir-frying . As well as the cooking
medium, the chlorophyll pigment may be
affected by the length of cooking
CHLOROPHYLL
75. The carotenoid pigments are found in fruits such as lemons,
oranges, strawberries, and vegetables such as peppers,
carrots and sweet potatoes.
Similar to chlorophyll, carotenoids are also fat-soluble
colorants, which means cooking methods involving the use
of fats may also cause leaching of the pigment
Cooking methods, which expose fruits and vegetables
containing carotenoids to the atmosphere for long periods
of time e.g., boiling without a lid, will therefore cause the
depletion of the pigment, resulting in paler coloured food.
CAROTENOID
76. Anthocyanins are found in fruits such as
blueberries, cherries and red plums, and
vegetables such as red potatoes and
aubergine, whilst anthoxanthins are found
in fruits such as apples, and vegetables
such as cauliflower, onions and potatoes.
Both anthocyanins and anthoxanthins are
water-soluble pigments and thus may
leach into cooking water during soaking or
prolonged heating.
ANTHOCYANIN & ANTHOXANTHINS
77. STARCH DEGRADATION
The polysaccharide starch is present in all plant seeds
and tubers, which means it can be found in many foods
such as pasta, rice, bread, potatoes and oats.
When foods containing starch are cooked, the heat can
break the glycosidic bonds linking the glucose units
together and effectively break-up the polysaccharides
to release the glucose monosaccharides. This imparts a
natural sweetness to the cooked food.
Any foods that contain starch e.g., rice, pasta, bread,
potatoes, wheat and oats. The cooking methods that
may result in starch degradation are boiling, baking,
roasting, frying, grilling and steaming.
78. Loss of Vitamins
Vitamin A
Vitamin A is found in foods like spinach, methi,
carrots etc. Vitamin A dissolves easily in fats
and oils. So, when food is fried in oil, vitamin A
comes out from the food and goes into oil
Vitamin B
Vitamin B being water soluble, goes out of the
rice and washes away with the water. After
washing rice, it is soaked in water.
A lot of water used to cook rice and the extra
water thrown away contains some dissolved
vitamin B.
79. Vitamin C
Vitamin C is an important nutrient which is easily
destroyed by cooking. During cutting of vegetables
and fruits some vitamin C is lost. Vitamin C is also
lost when vegetables and fruits are washed after
cutting and exposing cut vegetables to air for long
periods before cooking
80. Non Enzymatic Browning
Non‐enzymatic browning involves a set of chemical reactions
that take place during the preparation.
1. Caramelization
It is a non-enzymatic reaction that occurs when
carbohydrates or sugars in food are heated.
It turn golden brown and form new flavors when
exposed to high temperatures.
As the food is heated, the sucrose in the food melts and
starts to boil.
The temperature at which this occurs is known as the
caramelization temperature, which (depending on the
types of carbohydrates present in the food), is
generally between 110–180 degree celsius.
81.
82. MAILLARD REACTION
It is the chemical reaction which occurs between amino
acids and reducing sugars in the presence of heat that
results the browning of food while forming new flavor
Any foods that contain both protein and carbohydrate
e.g., meat, biscuits, bread, coffee and nuts.
83. Chemical changes during
storage
Chemical changes during storage of food
Absorption of moisture by hygroscopic
components of food
Enzymatic browning
Lipid oxidation
Flavour and odor change
84. Absorption of moisture by
hygroscopic components of food
Hygroscopy is the phenomenon of
attracting and holding water molecules
from the surrounding environment, which
is usually at normal or room temperature.
This is achieved through either absorption
or adsorption.
Examples include honey, glycerine ,
ethanol, methanol, concentrated sulfuric
acid, and concentrated sodium hydroxide
(lye
85. Lipid oxidation
Fats , when come in contact with air (O2) produce
undesirable characterstics.
There are two major oxidation that occur during
storage are-
1. Auto-oxidation
2. Photo-oxidation
86. 1. Auto-oxidation-
It occur in the presence of oxygen and generation of free
radicals .
It initiated when a hydrogen atom is abstracted in the
presence of initiators such as light , heat or oxygen.
In this three steps are involved during radical formation-
1. Chain initiation
2. Chain propagation
3. Chain termination
2. Photo-oxidation
The singlet oxygen interact with polyunsaturated fatty acids
to form hydroperoxide which initiate the auto-oxidation
reaction in the presence of UV- radiation.
87. Effect of lipid oxidation on
food
1. Off – flavors in food
2. Reduced nutritional quality
3. Bad taste and smell
88. BROWNING REACTION
Enzymatic browning is a chemical process which
occurs in fruits and vegetables by the enzyme
polyphenoloxidase, which results in brown pigments.
89. Flavor and odor change
It occur mainly due to the lowering in the ph of
the stored food , to prevent the growth of
microorganism.
When we store food before storing we add some
preservatives which leads to lowering in ph of the
food, and helps in increase the shelf-life of the
food.
Some examples are such as soda, bottled lemon
juice, pickles, jelly, salad dressing, soy sauce etc.
The common use preservative is sodium benzoate.
This leads to odor change of food .
