Heat processing techniques like pasteurization and appertization are used to destroy microorganisms in food. [1] Pasteurization exposes food to heat for a shorter time at lower temperatures from 60-80°C to eliminate pathogens or extend shelf life. [2] Appertization subjects food to higher heat processing to achieve commercial sterility, making the food microbiologically stable at room temperature for a long shelf life. [3] Factors like heat penetration rate, microbial resistance as measured by D-value and Z-value, and food composition impact the effectiveness of heat treatments.

1. Heat Processing
• Pasteurization and Appertization –
• Pasteurization – Foods are exposed to thermal
processing for different reasons, often
destruction of microrganisms not the main
objective.
• However, this is inevitable useful side effect.

2. Back ground /Discovering the value of
heat
• Value of heat as a preservative go to French
chef, distiller and confectioner, Nicolas Appert.
• In 1975 French gov. Offered a prize of
12000francs to any one who develop the new
method of food presevation.
• Apart from this prize, he also experimented on
packing of foods in Glass bottles, sealing them
and then heating them in boiling water.

3. Background
• He described this technique in 1811 in a book
called “ art of conserving all kinds of animal and
vegetable matter for several years.”
• A similar technique was used by Englishman in
1807 to preserve fruits.
• British patents describing the use of iron or metal
containers were issued to Durand and de Heine in
1810 and the firm of Donkin and Hall established
a factory for the production of canned foods in
London around 1812.

4. EARLY/ APPERT AIR CONTACT VIEW AND
pasteur,s work
• Appert held the view that air contcat was the
cause of spoilage and the success of this
technique was due to the exclusion of air from
the product.
• This view persisted for another 50 years until
Pasteur,s work established the relationship
between microbial activity and putrefaction.

5. Pasteurization and Appertization
Today, two types of heat processes employed to destroy the
M.O in food, PASTURIZATION and APPERTIZATION.
PASTEURIZATION -
Heat processes typically in the range of 60 -80 c for upto few
minutes. This is used for 2 purposes. FIRST is the elimination
of a specific pathogen or pathogens associated with a prduct.

6. pasteurization
This type of pasteurization is often a legal
requirement introduced as a public health
measure when product has been
frequently implicated as a vehicle of
illness. e.g; milk, egg, ice cream mix, all
these products have a much improved
safety record as a result of pasteurization.

7. pasteurization
• Second reason for pasteurization a product is
to eliminate a large proportion of potential
spoilage organisms, thus extending its shelf
life. This is normally the objective when acidic
products such as beers, fruit juices, pickles
and sauces are pasteurized.

8. pasteurization
• Pasteurization by means of steam, hot water,
dry heat or electric current.
• In market milk 62.8 c for 30 min or 71.7 c for
15 sec.
• 137.8 c for 2 sec in ultrapasteurised for
coxiella burnetti
• In ice cream 71.1 for 30 min or 82.2 for 20 sec.

9. Pasteurization with low Ph and aw
On its own the contribution of pasteurization to extension of shelf-
life can be quite small, particularly if the pasteurized food lacks
other contributing preservative factors such as low pH or aw.
Spore forming and some Gram positive vegetative species in
genera Enterococcus, Microbacterium and Arthrobacter can
survive pasteurization temperatures.
Reffrigerated storage is often an additional requirement for an
acceptable shelf life.

10. APPERTIZATION
A process where the only organisms that survive
processing are non-pathogenic and incapable of
developing within the product under normal conditions
of storage. As a result appertized products have a long
shelf life even when stored at ambient temperatures.
The term was coined as an alternative to the still
widely used description “ commercially sterile which
was objected to on the grounds that sterility is not a
relative concept.

11. APPERTIZATION
Appertized or coomercially sterile food is not
necessarily sterile - completely free from viable
organisms. It is however free from organisms capable of
growing in the product under normal storage
conditions.
Canned in temperate climate is not a matter of concern
even if the viable spores of thermophile are present as
the organism will not grow at the prevailing ambient
temperature.

12. FACTORS AFFECTING HEAT RESISTANCE
THERMAL DEATH TIME – Cells and spores of microorganisms differ
widely in their resistance to high temperatures.
In a colony/sample, A small number of cells have low resistance
Most of the cells have a medium resistance
And small number have higher resistance
Conditions of growth may favour one or the other of these groups.

13. Heat penetration
• Conduction – heat passeses from molecule to
molecule
• Convection – heat is transfered by movements
of liquids or gases.

14. D-value
• D-value refers to decimal reduction time is the time
required at a certain temperature to kill 90% of the
organisms being studied. Thus after a colony is reduced
by 1 D, only 10% of the original organisms remain. The
population number has been reduced by one decimal place
in the counting scheme. Generally, each lot of a
sterilization-resistant organism is given a unique D-value.
When referring to D values it is proper to give the
temperature as a subscript to the D. For example, a
hypothetical organism is reduced by 90% after exposure to
temperatures of 300 degrees Fahrenheit for 2 minutes,
thus the D-value would be written as D300F = 2 minutes. D-
value determination is often carried out to measure a
disinfectant's efficiency to reduce the number of microbes,
present in a given environment

15. What is a Z-value?
•
A Z-value is defined as the number of degrees
(Celsius or Fahrenheit) required to change a D-
value by one factor of ten. In the practical
sense, it is a measure of how susceptible a
spore population is to changes in
temperature. For example, if the Z-value of a
population is 10 degrees, then increasing the
sterilization temperature 10 degrees will result
in a log reduction of the D-value.