Question

What is the ideal transmittance of incident light at 500 nm for packaging materials used for liquid milk?

• A. Not more than 2%
• B. Not more than 8%
• C. Not more than 5%
• D. Not more than 11%

Hint:

To prevent riboflavin-mediated photo-oxidation of milk, the package must act as a barrier to visible light, restricting transmittance to $\le 8\%$ at $500\text{ nm}$.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Milk is a highly light-sensitive product.
Exposure to light (especially ultraviolet and short-wavelength visible light) triggers the photodegradation of riboflavin (Vitamin B2).
This reaction produces singlet oxygen, which oxidizes milk lipids and proteins, leading to objectionable "light-activated" off-flavors.

Step 2: Detailed Explanation:
To protect liquid milk from light-induced quality deterioration, the packaging materials (such as co-extruded LDPE pouches or plastic bottles) must incorporate light-blocking pigments (typically titanium dioxide for white opacity and carbon black for complete light blocking).
According to dairy packaging standards and research, to prevent riboflavin degradation and the development of oxidized off-flavors, the transmission of light through the packaging material must be minimized.
Specifically, at the critical wavelength of $500\text{ nm}$ (close to the absorption peak of riboflavin), the ideal light transmittance of the packaging material must be not more than 8%.
Therefore, option 2 is the correct standard limit.

Step 3: Final Answer:
The ideal transmittance of incident light at 500 nm for liquid milk packaging materials is not more than 8%.