Transcript Chapter 5. Pasteurisation File

By: Mohmmed Sabah
Book: Food processing tecnology Page 263
2013
Pasteurisation
• Pasteurization: is a relatively mild heat treatment, in which
food is heated to below 100 ºC. In low acid foods (pH>4.5, for
example milk) it is used to minimize possible health hazards
from pathogenic micro-organisms and to extend the shelf life
of foods for several days.
• In acidic foods (pH <4.5, for example bottled fruit) it is used to
extend the shelf life for several months by destruction of
spoilage micro-organisms (yeasts or moulds) and/or enzyme
inactivation
1- Three main types of pasteurization used today:
1- Lower Temperature/Longer Time (e.g. milk at 63 °C for
30 min, less often used)
2- High Temperature/Short Time (e.g. milk at 71.7 °C for
15 s)
3- Ultra High Temperature (or flash pasteurization) (e.g.
Milk at 100 °C for 0.01 s
The time-temperature treatment used in pasteurization
depends on:
(1) the heat resistance of the particular vegetative or
pathogenic microorganisms the process is designed to
destroy.
(2) the sensitivity of product quality to heat. The hightemperature and short-time (HTST) method involves a
comparatively high temperature for a short time (e.g., 72 °C
for 1 s for milk), whereas the low temperature and longtime procedure involves relatively low temperatures for
longer times (e.g., 63 °C for 30 min for milk).
• Optimization of the pasteurization process
depends on the relative destruction rates of
organisms as compared to quality factors, but
generally the HTST process results in
maximum product quality.
Methods of Pasteurization
There are two basic methods, batch or continuous.
continuous
Batch Pasteurization System
3. Equipment
3.1 Pasteurization of packaged foods
Some liquid foods (for example beers and fruit juices) are
pasteurized after filling into containers. Hot water is
normally used if the food is packaged in glass, to reduce
the risk of thermal shock to the container (fracture caused
by rapid changes in temperature). Maximum temperature
differences between the container and water are 20 ºC for
heating and 10 ºC for cooling.
• Metal or plastic containers are processed using
steam–air mixtures or hot water as there is little
risk of thermal shock. In all cases the food is
cooled to approximately 40 ºC to evaporate
surface water and therefore to minimize external
corrosion to the container or cap, and to
accelerate setting of label adhesives.
Time–temperature relationships for pasteurization. The
hatched area shows the range of times and temperatures used
in commercial milk pasteurization.
3.2 Pasteurization of unpackaged liquids
• Swept surface heat exchangers or open boiling pans are used
for small-scale batch pasteurization of some liquid foods.
However, the large scale pasteurization of low viscosity liquids
(for example milk, milk products, fruit juices, liquid egg, beers
and wines) usually employs plate heat exchangers.
• Some products (for example fruit juices, wines) also require
de-aeration to prevent oxidative changes during storage. They
are sprayed into a vacuum chamber and dissolved air is
removed by a vacuum pump, prior to pasteurization.
Pasteurized Foods
• The
most common pasteurized food is milk
• Originally
designed to eliminate
Mycobacterium tuberculosis and Coxiella
burnetti
• Fruit
juice
• Spoilage
yeast and bacteria, E. coli
O157:H7
• Beer
• Spoilage
bacteria and yeast
Pasteurized Foods
• Liquid
egg
• Salmonella
and spoilage bacteria
• Honey
• Spoilage
• Meat
yeast
surfaces (steam, hot water)
• E.
coli O157: H7, Salmonella,
Campylobacter
Milk Pasteurization
Time/Temperature Combinations
• High
72oC
Temperature Short Time (HTST) 15 sec @
• Low Temperature Long Time (LTLT) 30 min at 63oC
• These
pasteurization time/temperatures are
considered to be equivalent.
• Heat treatments are established on the basis
of safety first (elimination of pathogens) and
spoilage (extension of shelf life) second.
Plate heat exchanger
4. Effect on foods
• Pasteurization is a relatively mild heat treatment and
even when combined with other unit operations (for
example irradiation and chilling there are only minor
changes to the nutritional and sensory characteristics
of most foods. However, the shelf life of pasteurized
foods is usually only extended by a few days or
weeks compared with many months with the more
severe heat sterilization. Minimizing post processing
contamination is essential to ensure an adequate shelf
life.
4.1 Vitamin loss
• In fruit juices, losses of vitamin C and carotene are minimised by
deaeration. Changes to milk are confined to a 5% loss of serum
proteins and small changes to the vitamin content
Vitamin losses during
pasteurization of milk
Holder