Question

Discoloration of milk powder during storage is due to______\

• A. Caramalization
• B. Lactose crystallization
• C. Maillard reaction
• D. Autooxidation

Hint:

Maillard browning is a chemical reaction between reducing sugars (lactose) and amino acids (lysine residues on milk proteins) that occurs during storage, leading to brown melanoidin pigments.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
During storage, milk powder can undergo physical and chemical changes that lead to quality degradation.
One of the most common defects is brown discoloration, accompanied by a loss of solubility, the formation of off-flavors, and a decrease in nutritional value.
This non-enzymatic browning is driven by chemical reactions between the sugar and protein components present in the milk powder.

Step 2: Detailed Explanation:
Milk powder contains high levels of lactose (a reducing sugar) and milk proteins rich in lysine (which has free amino groups).
The primary pathway responsible for browning in milk powder during storage is the Maillard reaction.
The reaction begins with the condensation of the carbonyl group of lactose with the free $\epsilon$-amino group of lysine residues on milk proteins, forming a reversible Schiff base.
This base undergoes the Amadori rearrangement to form lactulosyl-lysine.
In the intermediate and final stages of the reaction, these Amadori compounds undergo dehydration, fragmentation, and polymerization with other nitrogenous compounds.
This leads to the formation of insoluble, high-molecular-weight brown pigments called melanoidins.
The rate of this reaction is accelerated by high storage temperatures and elevated water activity (moisture content) in the powder.
Caramelization also causes browning, but it requires high temperatures to degrade sugars in the absence of amino compounds, which does not occur during standard storage.
Therefore, the Maillard reaction is the primary cause of discoloration during storage.

Step 3: Final Answer
The discoloration of milk powder during storage is caused by the Maillard reaction.