Question

The main purpose of thermization is to __________.

• A. to extend storage of raw milk prior to processing
• B. to substitute for pasteurization
• C. to substitute for boiling
• D. to destroy all pathogenic organisms

Hint:

Thermization is a low-intensity thermal process (\(63\text{--}65^\circ\text{C}\) for \(15\text{ s}\)) designed strictly to arrest psychrotrophic growth and preserve raw milk quality; it is not a legal substitute for pasteurization.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Thermization is a sub-pasteurization thermal treatment applied to raw milk, typically at temperatures ranging from \(63^\circ\text{C}\) to \(65^\circ\text{C}\) with a holding time of \(15\) seconds.
Unlike pasteurization, which is a regulatory public health measure designed to eliminate pathogenic microorganisms, thermization is an industrial quality control measure.
Its primary objective is to restrict the growth of psychrotrophic bacteria during storage in silo tanks without causing significant heat damage to milk constituents.

Step 2: Detailed Explanation:
In modern dairy operations, raw milk is often stored at low temperatures (\(4^\circ\text{C}\) or below) for several days before final processing.
Although refrigeration prevents the multiplication of mesophilic and thermophilic bacteria, it permits the slow growth of psychrotrophic species, such as Pseudomonas, Achromobacter, and Flavobacterium.
These psychrotrophic contaminants synthesize highly heat-stable extracellular lipases and proteases during their growth phase.
Since these enzymes are not inactivated by standard pasteurization, they persist into finished dairy products, where they break down milk fat and casein, leading to defects such as bitter off-flavors, rancidity, and age-gelation.
Applying a thermization step immediately upon the arrival of raw milk at the processing plant kills the vegetative cells of these psychrotrophic bacteria.
This prevents the production of the damaging enzymes, thereby preserving milk quality and safely extending its permissible storage period by \(3\) to \(4\) days.

Step 3: Final Answer:
Thus, the main purpose of thermization is to extend the storage period of raw milk prior to processing.