Question

Which of the following can be used as an index of heat treatment of milk

• A. Urea content
• B. Lactose content
• C. Lactulose content
• D. Formic acid content

Hint:

Lactulose is a key chemical marker in milk analysis:
- It is absent in raw milk and formed only by heat-induced isomerization of lactose.
- Its concentration directly reflects the thermal severity, distinguishing pasteurized, UHT, and sterilized milks.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Thermal processing of milk (such as pasteurization, UHT treatment, or sterilization) alters its chemical composition.
Measuring these heat-induced chemical changes allows analytical laboratories to determine the severity of the heat treatment and verify the processing category of commercial milk samples.

Step 2: Detailed Explanation:
Let us analyze the chemical indicators used to monitor heat treatment in milk:
-Lactulose Formation:
Lactulose is a synthetic disaccharide composed of galactose and fructose.
It is not naturally present in raw milk.
However, when milk is heated, lactose undergoes isomerization (the Lobry de Bruyn-Alberda van Ekenstein transformation) to form lactulose.
The concentration of lactulose formed is directly proportional to the temperature and duration of the heat treatment:
- Pasteurized milk contains virtually no lactulose (\(< 10\ \text{mg/L}\)).
- UHT milk contains moderate levels (\(10\) to \(250\ \text{mg/L}\)).
- In-container sterilized milk contains very high levels (\(> 250\ \text{mg/L}\)).
Therefore, lactulose content is used internationally as a chemical index to verify heat treatments and differentiate between UHT and sterilized milk.
-Other Options:
- Urea and lactose contents do not change predictably with heat.
- Formic acid is produced only under extreme, excessive heating conditions, making it less useful for monitoring standard heat treatments.

Step 3: Final Answer:
Lactulose content is used as a chemical index of the heat treatment of milk, which corresponds to Option (C).