PASTEURIZATION AND BLANCHING
• PURPOSE OF THE PROCESSES
• DESCRIPTION OF PROCESSING SYSTEMS
• ESTABLISHMENT OF THE
PASTEURIZATION PROCESS
• DETERMINATION OF BLANCHING
PROCESS
• PROCESSES FOR PRODUCT QUALITY
IMPROVEMENT
• SUMMARY
Vocabulary
• pasteurization blanching
• mild \severe \batch-type \continuous
• brucellosis tuberculosis Salmonella Listeria
• enzyme inactivation
• plate heat exchanger\ \a flow diversion
valve (FDV) \cooling medium\ \high temp.short-time (HTST) \ \ultra-high-temperature
(UHT) \\conveyor tunnel
• The processes that utilize
relatively mild thermal treatments
to achieve the desired results are
pasteurization and blanching. Both
processes apply thermal treatment
to food products in an effort to
improve the stability of the
product during storage.
• Although the magnitude of the
thermal processes is similar,
application of the processes involves
two distinctly different types of food
products. Pasteurization is most often
associated with liquid foods, while
blanching is most often associated
with solid foods.
• The magnitude of thermal
treatment used for both processes is
not sufficient to establish storage
stability at room temperature. The
criteria utilized in establishing
these modest thermal treatments are
rather specific and are different for
different food commodities.
Purpose of Pasteurization Processing
• Pasteurization is a mild thermal process
applied to a liquid food to increase the
product shelf life during refrigeration
and to destroy vegetative pathogens
(brucellosis and tuberculosis),
Salmonella and Listeria.
• In fruit juice ,to inactivate enzymes
Purpose of Blanching Processing
• In fruits and vegetables to inactivate
enzymes.
• To removes air from intercellular spaces
of a fruit or vegetable
• Before canning raw fruits and vegetables
and the more severe thermal processes
associated with commercial sterilization.
DESCRIPTION OF PROCESSING
SYSTEMS
• batch-type operation pasteurization
• continuous high temperature, short-time
(HTST) pasteurization system
• rotary hot water system blanching system
• Steam blanchers
Batch Pasteurization System
Batch-type operation
• The vessel containing the product has a
jacket where a heating medium is introduced.
• The liquid product in the vessel is mixed to
ensure uniform temperature rise until the
desired temperature is reached.
• The same jacket is utilized during cooling of
the product by introducing a cold medium
and cooling the product contact surface.
Batch-type operation
• Batch pasteurization systems can be
relatively inexpensive and will vary in
capacity from small vessels to
relatively large vessels. The primary
disadvantage of these systems is the
inefficiency associated with batch
processing.
HTST Pasteurization System
system six essential components
• Three of the six components are heat
exchangers (regeneration, heating,
cooling).
• Timing pump
• Flow diversion valve
• Holding tube
Heat exchangers
• The regeneration, heating, and cooling
sections of the pasteurization system are
heat exchangers. Most often, plate heat
exchangers are used. The plate heat
exchanger is divided into three sections,
with the middle section serving as the
regeneration component, while the sections
of the plate heat exchanger on either side
are used for heating and cooling.
Plate heat exchangers
• Plate heat exchangers are ideal for
pasteurization systems with these
configurations. The heat exchange
component of the system is very compact.
Plate heat exchangers provide very
efficient heat transfer from one lowviscosity liquid to another.
Ultra-high-temperature (UHT)
pasteurization
• When temp. exceeding the boiling point of
water is used for pasteurization, It is ultrahigh-temperature (UHT) pasteurization, The
systems requires pressure control in regions
where the product is elevated to temperatures
above the boiling point of water. In these
systems, the pressure control would be
maintained throughout the time that the
product is in the holding tube.
The timing pump
• The timing pump is a critical component
of the pasteurization system. This pump
must be positive displacement and must
be set at a flow rate to ensure an
established mass flow rate of product
through the system as long as the system
is operating in forward flow.
The flow diversion valve
• The FDV is controlled by a temp.-sensing
device located at the exit of the heating
section. If temp. is below the desired
temp., the valve diverts flow to the
entrance point. As soon as the established
temp. is reached, the flow diversion valve
changes and the product moves forward
through the holding tube. This control
device ensures safety of product.
The holding tube
• A holding tube has a known-diameter pipe
designed to provide an established
residence time for product at the
pasteurization temp., the critical time/temp
relationship needed for pasteurization is
achieved by the residence time requirement
in the holding tube. the length of holding
tube ensures the necessary residence time
of product.
Plate Heat Exchanger
Rotary Hot Water Blanching System
Rotary Hot Water Blanching System
Waterfall Hydroblanching System
Pure Steam Blanching System
Steam Blanching System with Water
Tank Inlet
Steam Blanching System with Rotary Inlet
Steam & Water Blanching System
Individual Quick Blanching(IQB)
ESTABLISHMENT OF THE
PASTEURIZATION PROCESS
• The impact of pasteurization is defined by a
time/temp. relationship applied to the food
product. There are two considerations.
• The first is the necessary time/temp. to
achieve the desired result of the process.
• The second is the configuration of the
equipment required to achieve the
established process.
Milk pasteurization
• Minimum pasteurization processes are based on
the occurrence of several microbial pathogens in
milk. These pathogens include Brucella abortis,
Myobacterium tuberculosis, and Coxiella burnetti.
The impact of these pathogens on human health is
recognized in the form of tuberculosis and q fever.
The minimum pasteurization process has been
established as 63℃ for 30 minutes. This process is
based on D63 = 2.5 minutes and a Z of 4.1℃.
The minimum pasteurization process
• The process of 30 minutes at 63℃ represents a
12-D process in that the population is reduced
by 12 times the D-value of 2.5 minutes. an
initial population of 100 pathogens would be
reduced to a probability of l0-10 by the
minimum pasteurization process. On the other
hand, it must be recognized that the
populations of these pathogens in raw milk are
much below l00, resulting in the probability of
survival being significantly less.
• An additional factor that must be
considered is that most pasteurization
processes exceed the minimum for
pathogens in order to achieve the
extended product shelf life achievable
by reducing the populations of product
spoilage microorganisms.
Survival Curve for Pathogen in Milk
• The process of 63℃ for 30 minutes is a typical
process for batch pasteurization of a liquid food
product like milk. Most pasteurization processes
for liquid foods are accomplished in continuous
HTST processes. To determine the HTST process
equivalent to 63℃ for 30 minutes, the concept of
lethal rate as introduced in Chapter 2 can be
utilized. As indicated in Chapter 2, lethal rate is
defined by Eq. (2.5) (here as 3.1) as follows:
• By accepting the reference temp. as 63℃ as
well as pasteurization temp. of 63℃, the lethal
rate is equal to 1. The temp. rise and cooling
occur rapidly at time zero and the end of 30
minutes.
• The key factor to recognize at this point is that
the minimum requirement for pasteurization
when considering the impact on a pathogen is
a minimum of 30 minutes at the pasteurization
temp.
• The lethal rate curve illustrates that the area
of the curve is equal to 30 minutes. This
represents the holding time at the desired
pasteurization temperature.
• Any additional impact of the thermal
process, prior to the time the product
reaches pasteurization temperature, and
after the 30 minutes of holding at the
desired temperature, is additional process
that is in excess of the minimum
requirement.
LD Equation
Lethal Rate Curve for Batch Pas.
• A temperature of 71.5℃ is quite often
utilized in HTST pasteurization of milk. If
the lethal rate associated with this higher
temperature is determined as illustrated in
Eq. (3.2): Where the reference temperature
is maintained at 63 and the Z of 4.1 is
utilized, the lethal rate is 120.
• The lethal rate of 120 is shown on the
vertical axis, the process time on the
horizontal axis. For example, if the lethal
rate curve represent l5 seconds of process
time, the area under the curve represents
1,800 seconds or 30 minutes. The area
under curve is 30 minutes. These show that
a HTST pasteurization process of 7l.5℃ for
l5 seconds is equivalent to a pasteurization
process of 63℃ for 30 minutes.
Lethal Rate Curve for HTST Batch Pas.
Velocity Profile in Holding Tube
Design the holding tube
• The holding tube must be designed to be of
sufficient length to accomplish the desired
residence time as established by the
minimum process.
Two key factors
• The length of the holding tube
• The velocity of the fastest moving particle within
the product flow stream.
• The velocity of product within the holding tube
will be a function of the flow characteristics.
• Laminar: the velocity of the fastest moving
particle will be 2 times the mean velocity
• Turbulent: the velocity of the fastest moving
particle will be 1.2 times the mean velocity
DETERMINATION OF
BLANCHING PROCESS
• The typical minimum time/temperature
relationships for blanching are based on
inactivation of enzymes within the product.
Due to the variety of fruits and vegetables
and the different enzyme systems within
these products, blanching processes are
quite variable in requirements.
• The impact of thermal energy on enzymes
has been expressed in terms of decimal
reduction times (D) and thermal resistance
constants (Z) for many enzyme systems. For
example, peroxidase has D121 equal to 3
minutes and Z equal to 37.2℃. Based on
these thermal resistant characteristics, a
reduction of enzyme activity to .01% would
require 12 minutes at 121℃.
• In most cases, blanching is accomplished
using water at near its boiling point of l00℃
or at steam-produced atmospheric pressure
at l00℃. In order to achieve the process
described for peroxidase, a time in excess of
12 minutes would be required.
blanching
• The temperature at surface of particle increases
rapidly but slowly at the center of the particle. The
temperature at center is a function of thermal
conductivity of the product. Since the enzyme
system to be inactivated by the blanching process
will be as active at the center as compared to the
surface, the blanching process must be
accomplished based on time after the product
particle center reaches the desired b1anching
temperature.
• What is the purpose of pasteurization and
Blanching?
• Describe the batch pasteurization and the
continuous pasteurization system.
• Describe the batch blanching and the
continuous blanching system
• What are the relationships between them?