Fish Microbiology and Quality Assurance (2+2)

Unit 4 - Food preservation techniques and microorganisms

4.2.1 Pasteurization
Pasteurization refers to use of heat at the range of 60~80^oC for a few minutes for the elimination/ destruction of all disease causing microorganisms, and reduction of potential spoilage organisms. Pasteurization is commonly used in the preservation of milk, fruit juices, pickles, sauces, beer etc.
Pasteurization process which is commonly employed in milk preservation can be achieved by heating the milk at 63^oC for 30 min, called low temperature long time (LTLT) process; or 72^oC for 15 sec, called high temperature short time (HTST) process. This process destroys most heat resistant non-spore forming pathogens (Ex. Mycobacterium tuberculosis), all yeasts, molds, Gram negative bacteria and most Gram positive bacteria.

Organisms surviving pasteurization
The pasteurization treatment does not bring about complete removal or destruction of microorganisms and some organisms survive pasteurization process. The surviving organisms are of two types;

• Thermoduric microorganisms
• Thermophilic microorganisms.

Thermoduric microorganisms are those which can survive exposure to relativity high temperature but do not grow at these temperatures. Example: The non-spore forming Streptococcus and Lactobacillus sp can grow and cause spoilage at normal temperature. So, milk need to be refrigerated after pasteurization to prevent spoilage.
Thermophilic organisms are those that not only survive high temperature treatment but require high temperature for their growth and metabolic activities. Example: Bacillus, Clostridium, Alicyclobacillus, Geobacillus etc.