Chapter 17
Food Protection with High
Temperatures, and Characteristics
of Thermophilic Microorganisms
The use of high temperatures to preserve food is based on their destructive effects on microorganisms. By high temperatures are meant any and all temperatures above ambient. With respect to food
preservation, there are two temperature categories in common use: pasteurization and sterilization.
Pasteurization by use of heat implies either the destruction of all disease-producing organisms (e.g.,
pasteurization of milk) or the destruction or reduction in the number of spoilage organisms in certain
foods, as in the pasteurization of vinegar. The pasteurization of milk is achieved by heating at one of
the following time/temperature combinations:
145
◦ F (63
◦ C) for 30 minutes (low temperature, long time [LTLT])
161
◦ F (72
◦ C) for 15 sec (primary high temperature, short time [HTST] method)
191
◦ F (89
◦ C) for 1.0 sec
194
◦ F (90
◦ C) for 0.5 sec
201
◦ F (94
◦ C) for 0.1 sec
212
◦ F (100
◦ C) for 0.01 sec
These treatments are equivalent and are sufficient to destroy the most heat resistant of the nonsporeforming pathogenic organisms—Mycobacterium tuberculosis and Coxiella burnetti. When six
different strains of M. avium subsp. paratuberculosis were added to milk at levels from 40 to 100,000
cfu/ml followed by pasteurization by LTLT or HTST, no survivors were detected on suitable culture
media incubated for 4 months.
26
Milk pasteurization temperatures are sufficient to destroy, in addition, all yeasts, molds, Gramnegative bacteria, and many Gram positives. The two groups of organisms that survive milk pasteurization are placed into one of two groups: thermodurics and thermophiles. Thermoduric organisms are
those that can survive exposure to relatively high temperatures but do not necessarily grow at these
temperatures. The non-sporeforming organisms that survive milk pasteurization generally belong to
the genera Streptococcus and Lactobacillus, and sometimes to other genera. Thermophilic organisms
are those that not only survive relatively high temperatures but require high temperatures for their
415
Food Protection with High
Temperatures, and Characteristics
of Thermophilic Microorganisms
The use of high temperatures to preserve food is based on their destructive effects on microorganisms. By high temperatures are meant any and all temperatures above ambient. With respect to food
preservation, there are two temperature categories in common use: pasteurization and sterilization.
Pasteurization by use of heat implies either the destruction of all disease-producing organisms (e.g.,
pasteurization of milk) or the destruction or reduction in the number of spoilage organisms in certain
foods, as in the pasteurization of vinegar. The pasteurization of milk is achieved by heating at one of
the following time/temperature combinations:
145
◦ F (63
◦ C) for 30 minutes (low temperature, long time [LTLT])
161
◦ F (72
◦ C) for 15 sec (primary high temperature, short time [HTST] method)
191
◦ F (89
◦ C) for 1.0 sec
194
◦ F (90
◦ C) for 0.5 sec
201
◦ F (94
◦ C) for 0.1 sec
212
◦ F (100
◦ C) for 0.01 sec
These treatments are equivalent and are sufficient to destroy the most heat resistant of the nonsporeforming pathogenic organisms—Mycobacterium tuberculosis and Coxiella burnetti. When six
different strains of M. avium subsp. paratuberculosis were added to milk at levels from 40 to 100,000
cfu/ml followed by pasteurization by LTLT or HTST, no survivors were detected on suitable culture
media incubated for 4 months.
26
Milk pasteurization temperatures are sufficient to destroy, in addition, all yeasts, molds, Gramnegative bacteria, and many Gram positives. The two groups of organisms that survive milk pasteurization are placed into one of two groups: thermodurics and thermophiles. Thermoduric organisms are
those that can survive exposure to relatively high temperatures but do not necessarily grow at these
temperatures. The non-sporeforming organisms that survive milk pasteurization generally belong to
the genera Streptococcus and Lactobacillus, and sometimes to other genera. Thermophilic organisms
are those that not only survive relatively high temperatures but require high temperatures for their
415