Q.73.Pasteurization of milk is carried oul by
(A) boiling for 5 min
(B) heating at 63C for 15 min
(C) heating at 72°C for 30 min
(D) heating al 63C: for 30 min

You’re asking about the correct method of pasteurization of milk and want an SEO‑friendly article around this MCQ. I’ll include title, slug, meta description, focus key phrase, and then the explanation.

Correct Answer

(D) Heating at 63 °C for 30 min

This is the classic LTLT (Low Temperature Long Time) pasteurization method. Milk is heated to 63 ∘C63∘C and held at that temperature for 30 minutes, then rapidly cooled. This kills pathogenic bacteria (like Mycobacterium tuberculosis, Brucella, Salmonella) while preserving most nutrients and flavor.

Why Option (A) Is Incorrect: Boiling for 5 min

• Boiling reaches around 100 ∘C100∘C, much higher than pasteurization temperatures.

• Although it destroys most microorganisms, it is closer to sterilization than pasteurization.

• Boiling for 5 minutes significantly alters taste, can cause protein denaturation, and may lead to loss of heat‑sensitive vitamins (e.g., vitamin C, some B vitamins).

• Pasteurization is defined as controlled sub‑boiling heating, not boiling.

So, boiling for 5 minutes is not the standard or correct pasteurization procedure.

Why Option (B) Is Incorrect: 63 °C for 15 min

• 63 ∘C63∘C is the correct temperature for LTLT, but the holding time is too short.

• Established LTLT conditions are 63 ∘C63∘C for 30 minutes, which ensure adequate destruction of pathogenic bacteria based on thermal death time studies.

• Reducing the time to 15 minutes may allow survival of more heat‑resistant pathogens, compromising safety.

Therefore, 63 ∘C63∘C for 15 minutes does not meet standard pasteurization criteria.

Why Option (C) Is Incorrect: 72 °C for 30 min

• 72 ∘C72∘C is the hallmark temperature for the HTST (High Temperature Short Time) method, but the time is wrong in this option.

• Standard HTST pasteurization is 72 ∘C72∘C for 15 seconds, not 30 minutes.

• Holding milk at 72 ∘C72∘C for 30 minutes is unnecessarily severe, damaging flavor and quality more than needed without additional safety benefit.

So, while the temperature matches HTST, the time given in this option is not correct for pasteurization.

Why Option (D) Is Correct: 63 °C for 30 min

• This matches the classical LTLT pasteurization standard:

  • Temperature: 63 ∘C63∘C

  • Time: 30 minutes

• Provides sufficient log reduction of common milk pathogens while minimizing changes in taste and nutritive value.

• It is widely used in smaller dairies, batch processes, or where continuous HTST plants are not installed.

Thus, heating milk at 63 ∘C63∘C for 30 minutes is the scientifically established and exam‑correct answer for this MCQ.