M. Borissenko
July, 2002
PASTEURIZATION
Named after its
inventor Louis Pasteur the process of pasteurization is an integral
part of the dairy industry. The initial discovery demonstrated that
organisms responsible for the spoilage of wine could be inactivated
by applying heat. This process has since been also applied to milk
where it remains the single most important step in the manufacturing
of dairy products.
The definition
of pasteurization is as follows:
"The heating
of every particle of milk or milk product to a specific temperature
for a specified period of time without allowing recontamination of
that milk or milk product during the heat treatment process."
The process of
pasteurization is performed for two main reasons. Firstly, the prime
purpose of pasteurization is to destroy potentially pathogenic microbes
present in milk thus rendering the milk or milk product safe for human
consumption. The secondary purpose of pasteurization is to extend
the shelf life of the milk or milk product. It is not only organisms
but also enzymes, which are involved with spoilage, and these are
also inactivated by pasteurization.
The Pasteurization
Marketing Ordinance (PMO) is a regulatory body founded by the US Public
Health Service, in conjunction with the US Food and Drug Agency (FDA)
and other agencies and institutions. It is the governing body that
states limits and compliance standards for pasteurization in the United
States of America. It should be pointed out that this is the accepted
world standard in regard to pasteurization. The PMO has given the
following statement regarding health reasons for pasteurization.
The public health
value of pasteurization is unanimously agreed upon by health officials.
Long experience conclusively shows it value in the prevention of disease
which may be transmitted through milk.
Pasteurization
is the only practical, commercial measure which, if properly applied
to all milk, will destroy all milk-borne disease organisms.
It has been demonstrated
that the time-temperature combinations specified by this ordinance,
if applied to every particle of milk, will devitalize all milk-borne
pathogens. Compilations of outbreaks of milk-borne disease by the
US Public Health Service over many years indicate that the risk of
contracting disease from raw milk is approximately 50 times as great
as from milk labeled "pasteurized"
The extent to
which micro-organisms and enzymes are inactivated is directly proportional
to the degree (temperature) and duration (time) of pasteurization.
Thus the higher the temperature and the longer the duration the greater
the effect of killing micro-organisms and inactivating enzymes.
The two most
heat stable pathogens found in fresh milk are Mycobacterium tuberculosis
and Coxiella burnetti. The first being the bacterium causing tuberculosis
and the second being the causative bacterium responsible for Q fever.
The minimal degree (temperature) and duration (time) requirements
for pasteurization of milk are based on thermal death time studies
on these two organisms. To ensure the safety of all dairy products
these temperature and time combinations are highly regulated. For
milk and colostrum the temperature and duration of pasteurization
has been established by the PMO and is as follows:
Milk Pasteurization
- PMO Guidelines
Temperature Time
63C (145F) 30 min.
72C (161F) 15 sec
89C (191F) 1.0 sec
90C (194F) 0.5 sec
94C (201F) 0.1 sec
96C (204F) 0.05 sec
100C (212F) 0.01 sec
As must be apparent
the higher the temperature utilized the shorter the time required
to destroy all potentially pathogenic microbes. It should be pointed
out that for diary products containing 10% or more fat, or if they
contain added sweeteners the PMO guidelines stipulate that the specified
temperature shall be increased by 3C (5F).
The process of
pasteurization has since it's inception undergone many improvements.
In the beginning milk and other fluids were simply boiled and unfortunately
many of the nutrients and bio-active substances were adversely affected.
For a growing number of milk and colostrum manufacturers the preferred
method of sanitizing milk and colostrum is by flash pasteurization
- also know as High Temperature Short Time (HTST) pasteurization.
By incorporating this method to sanitize or kill microbial contamination
the biological integrity of the milk and colostrum is maintained and
any loss of bioactivity is minimized.
Flash pasteurization
is performed using a continuous plate and tube or heat exchange system.
This counter current method ensures that the temperature of the product
is elevated to the exact required temperature: held there for the
required time and then swiftly lowered in the shortest possible time.
Thus the milk and colostrum is heated to 72C in the shortest time
possible - held at that temperature for a minimum of 15 seconds and
immediately cooled. In this way complete destruction of microbial
growth and inactivation of enzymatic activity is achieved. Microbiological
testing is performed to assure sanitation and product safety. Of significant
importance is the fact that this method ensures that maximal biological
activity and nutritional benefits are retained.
The thermal stability
of immunoglobulin preparations has long been the focus of many research
studies. It has been observed that flash pasteurization incorporating
high temperature short time (HTST) - 72C for 15 seconds has a minimal
effect on protein denaturization and reduction in bioactivity. The
following exemplifies the thermal stability of IgG in flash pasteurization.
Thermal Destruction
of Immunoglobulins During Processing of Colostrum
Pasteurisation
is a critical quality parameter used during the manufacture of dairy
products. Data collected during processing has shown that minimal
loss due to denaturization of immunoglobulins occurs when colostrum
is pasteurized (Table 1.).
Table 2. D-Value
of IgG in Bovine Colostrum
Temperature (oC)
D-Value (sec)
70 13,038
72 6,456
74 3,960
78 1,122
82 414
D-value = time
required to inactivate 90% of the IgG
If a second pasteurization
step is a requirement of further processing, research has shown that
65oC for 30 minutes has no effect on the activity of IgG. Previous
research conducted at 72oC for 15 seconds found a reduction in IgG
activity of approximately 0.5-10%. However, this reduction is likely
to be dependent on the precise system into which the Colostrum is
incorporated and the interactions of the components within this system.
For example, salt causes IgG to become less susceptible to denaturization
and aggregation during heat treatment. Further in a recent investigation
it has been reported that IgG values will be only very slightly affected
by HTST pasteurization at 72C for 15 seconds. In fact what was observed
was an approximate drop of 2% in quantified IgG value which is well
within the standard error of the assay used in the measurement.
Further antigen
binding studies have shown that the bioactivity of antibodies is little
affected by the process of flash pasteurization. In determining D-values
, the time required to reduce the antigen binding activity of IgG
(antibody) by 90% was determined (Table 2.)
Table 2. D-Values
IgG antibody/antigen binding in bovine colostrums
Temperature (oC)
D-Value (seconds)
69 8504
72 1387
77 285
81 152
D-value = time to inactivate 90% of the IgG antibody binding to antigen
Thus modern dairying
technology has developed to the point where the process of pasteurization,
though effective in neutralizing any potential microbial health hazard,
has very little negative effect on the bioactivity, biofunctionality,
and nutritional composition of the various components found in milk
and colostrums.
REFERENCES:
University of
Guelph, Pasteurization module, http://www.foodsci.uoguelph.ca/dairyedu/pasteurization.html
17/05/02
University of
Saskatchewan, College of Agriculture, Agricultural Science II, Module
9 Processing of Milk and Derived Products, AGRIC 112.3 www.ag.usask.ca/academic/notes
29/05/02.
Dominguez E.,Perez
MD, Calvo M. Effect of Heat Treatment on the Antigen-Binding Activity
of Anti-Peroxidase Immunoglogulins in Bovine Colostrum. (1997) Journal
of Dairy Science. Dec; 80 (12): 3182-7.
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mutans and Streptococcus sobrinus in Bovine Milk Fermented with Lactobacillus
Strain GG or Treated at Ultra-High Temperature. (2002) Oral Microbiological
Immunology. Feb; 17 (1): 9-15.
Chen CC, Tu YY,
Chang HM. Thermal Stability of Bovine Milk Immunoglobulin G (IgG)
and the Effect of Added Thermal Protectants on the Stability. (2000)
Journal of Food Science. Vol. 65, No.2: 188-193.
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A, Losso JN, Kitts DD, and Nakai S. (1995). Stability of Bovine Immunoglobulins
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Thermal Destruction
of Microorganisms - Thermal Lethality Determinations - Dairy Science
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Mainer G, Dominguez
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66:131-137.
International
Dairy Foods Association - Regulation and Food Safety - Current Systems
for Thermal Processing. www.idfa.org/reg/fda/fedhaccp.htm. 11/06/02
Grade "A"
Pasteurized Milk Ordinance. 1999 Revision. U.S. Department of Health
& Human Services. Public Health Services, Food and Drug Administration,
Washington DC, United States of America
Dairy Heat Treatment
- Discussion Paper 35. Ministry of Agriculture and Forestry, Wellington,
New Zealand.
Nutraplex 415
Product Safety Program www.symbiotics.com/nutrplex.htm
Korhonen H. Immune
Milk Preparations - Novel Means for Prevention and Treatment of Human
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