Question

Pasteurized milk at filling is generally saturated with about _____ ppm of oxygen, but if no additional oxygen can gain access, its content falls and the rate of adverse reactions slows or stops.

• A. 1.2
• B. 2.4
• C. 3.6
• D. 8

Hint:

The solubility of oxygen in milk at cold storage temperatures (4\(^\circ\text{C}\)) is approximately 8 to 9 ppm. Standard plastic and cardboard packaging must provide a barrier to prevent additional oxygen ingress during shelf life.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Dissolved oxygen in milk can promote oxidation reactions, leading to the degradation of vitamins (such as vitamin C and folic acid) and the development of off-flavors during storage.
The concentration of dissolved oxygen is governed by temperature, agitation, and exposure to air during processing and packaging.

Step 2: Detailed Explanation:
Let us analyze the dissolved oxygen levels in milk:
- At typical cold filling temperatures (around 4\(^\circ\text{C}\)), milk exposed to air in storage tanks and piping absorbs oxygen up to its saturation limit.
- This saturation concentration is approximately 8 to 9 ppm (parts per million or mg/L) of dissolved oxygen.
- When the pasteurized milk is sealed in an airtight container (such as glass bottles or barrier cartons) that prevents further oxygen ingress, the dissolved oxygen is rapidly consumed.
- It is used up through ascorbic acid oxidation and the respiration of residual bacteria, falling to near zero within a few days.
- Once the dissolved oxygen is depleted, further oxidative degradation slows down or stops.
Therefore, pasteurized milk at filling is saturated with approximately 8 ppm of oxygen.

Step 3: Final Answer:
Pasteurized milk at filling is generally saturated with about 8 ppm of oxygen. Hence, the correct option is (D).