ABSTRACT
Acknowledgments .............................................................................................................. 414
References .......................................................................................................................... 414
The heat treatment or pasteurization of milk derives its principles from the work of Louis
Pasteur (1822-1895). In 1864 he developed a method to prevent an abnormal fermentation in
wine by destroying the responsible organisms by heating the wine to 608C. Today, the heat treatment of milk and milk products is one of the most important operations in the dairy
industry. It is done to ensure safety from microbes and to increase the shelf life of the end
product. In addition, the heat treatment has an effect on the final product in terms of
chemical, physical, and organoleptic properties. The kinetics of these processes are an order
of magnitude lower than the bacterial inactivation, keeping these undesirable changes
minimal [1,2]. The mentioned effects depend on the combination of temperature and time
to which the product is subjected. The higher the temperature, the shorter the required time to
obtain a sufficiently safe product. In the dairy industry, the basic heat treatments can be
classified by four main types:
1. Thermization for inactivation of psychrotrophic microorganisms (e.g., 20 s at 658C). 2. Low pasteurization for inactivation of pathogenic microorganisms (e.g., 20 s at 728C). 3. High pasteurization for inactivation of all microorganisms (e.g., 20 s at 858C). 4. Sterilization (e.g., 30 min at 1108C) and ultrahigh temperature (UHT) treatment (e.g.,
5 s at 1408C) to destroy spores, such as Bacillus stearothermophilus and Bacillus sporothermodurans spores [3]. Recent research indicated that B. stearothermophilus
spores attach better to stainless steel walls than vegetative cells, stressing the need
for high processing temperatures [4,5].
