Q73: In freshly made milk powder, lactose is non-crystalline and exists... - Chemistry of Dairy Products - ICAR AIEEA PG Dairy Science 14 July 2023 Shift-1 Paper | Agrigyan

In liquid milk at room temperature ($20^\circ\text{C}$), mutarotation equilibrium yields approximately $37.3\%\text{ }\alpha$-lactose and $62.7\%\text{ }\beta$-lactose. The ratio of $\alpha$-lactose to $\beta$-lactose is $37.3 / 62.7 = 1.0 : 1.68$. In conventional spray drying, water removal is so rapid (droplets dry in milliseconds) that lactose molecules cannot orient themselves into an organized crystal lattice. Consequently, lactose solidifies into an amorphous, metastable glassy state ('lactose glass'), precisely capturing and freezing the pre-existing liquid equilibrium ratio of $1.0 : 1.68$.

Option analysis:

• $1.0 : 1.68$: Correct. Ratio of $\alpha$- to $\beta$-lactose at room temperature ($37.3\% : 62.7\%$).
• $1.0 : 2.2$: Incorrect.
• $2.2 : 1.0$: Incorrect.
• $1.0 : 1.42$: Incorrect.