Question

The water activity value for Skim Milk Powder is approximately:

• A. 0.995,
• B. 0.94,
• C. 0.2,
• D. 0.9

Hint:

Dehydrated food powders (like milk powder or instant coffee) are dried to a water activity range of \(0.15\text{ to }0.30\) to prevent chemical degradation (like Maillard browning) and microbial spoilage.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Water activity (\(a_w\)) measures the vapor pressure of water in a food system relative to pure water, representing the amount of "free" water available to support chemical reactions and microbial growth.

Step 2: Detailed Explanation:
- Skim Milk Powder (SMP) is a dehydrated dairy product with a very low moisture content, typically between \(3.0\%\) and \(4.0\%\).
- Because most of its water has been evaporated during spray drying, the remaining water molecules are tightly bound to proteins and lactose.
- This results in a very low water activity value, approximately 0.2.
- This low water activity level prevents the growth of all bacteria, yeasts, and molds (which require \(a_w > 0.60\) to grow) and slows down chemical degradations, ensuring the powder remains shelf-stable for long periods.

Step 3: Final Answer
The water activity of Skim Milk Powder is approximately 0.2.