Question

Presence of excess fat in casein during drying may result in -

• A. high adhesive strength
• B. low adhesive strength
• C. brittleness
• D. browning

Hint:

Milk fat acts as a hydrophobic impurity in industrial casein. It disrupts the continuous protein binder film, significantly reducing the adhesive strength of the casein glue.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Industrial casein is a major milk-byproduct used extensively as an adhesive, sizing agent, and binder in paper coating, glues, and plywood manufacturing.
The quality of industrial casein is determined by its purity, with fat, ash, and moisture being the primary impurities.
During the manufacturing and drying process, any residual milk fat retained in the casein curd behaves as a contaminant that interferes with its adhesive properties.

Step 2: Detailed Explanation:
Industrial casein is produced by coagulating skim milk using acids or rennet, followed by washing and drying the curd.
If the skim milk is not thoroughly separated and contains residual milk fat, this fat becomes concentrated within the casein curd.
During the drying process, the fat melts and spreads over the surface of the casein particles, creating a hydrophobic layer.
When the casein is subsequently dissolved in alkaline solutions to prepare adhesives, this residual fat cannot form a homogeneous chemical solution.
Instead, the fat exists as dispersed droplets that disrupt the continuous, cohesive protein film required for strong adhesion.
This disruption reduces the contact area and chemical bonding between the adhesive and the substrate (such as paper or wood fibers).
Consequently, the presence of excess fat in casein significantly lowers its adhesive strength.
Other defects, such as browning or brittleness, are primarily caused by excessive heat during drying or high lactose levels, rather than fat content.

Step 3: Final Answer
The presence of excess fat in casein during drying results in low adhesive strength.