Lactose is a disaccharide with chemical formula $\text{C}_{12}\text{H}_{22}\text{O}_{11}$, giving a molecular weight of approximately $342.3\text{ g/mol}$. Lactic acid has the chemical formula $\text{C}_3\text{H}_6\text{O}_3$, giving a molecular weight of $90.08\text{ g/mol}$. The ratio is $\frac{342.3}{90.08} \approx 3.8 \approx 4$ times higher. (Homolactic fermentation theoretically yields 4 moles of lactic acid from 1 mole of lactose: $\text{C}_{12}\text{H}_{22}\text{O}_{11} + \text{H}_2\text{O} \to 4\text{ CH}_3\text{CH(OH)COOH}$).

$\alpha$-Lactalbumin acts as the regulatory 'specifier' subunit (B protein) of the lactose synthase enzyme complex in the mammary gland. It complexes with galactosyltransferase (A protein), lowering its $K_m$ for glucose by ~1000-fold and thereby promoting lactose synthesis: $\text{UDP-galactose} + \text{glucose} \xrightarrow{\text{lactose synthase}} \text{lactose} + \text{UDP}$.

Consequences of the advanced Maillard reaction in heated milk systems:

• Melanoidins are high-molecular-weight brown nitrogenous polymers responsible for browning Colour $\to$ (II).
• Hydroxymethylfurfural (HMF) and associated carbonyl volatiles contribute to caramel-like cooked Flavour $\to$ (I).
• Cross-linked protein aggregates formed by advanced glycation cross-links decrease protein Solubility $\to$ (IV).
• Early Maillard condensation involves blocking the $\epsilon$-amino group of essential lysine to form lactulosyl-lysine/lysine-sugar complexes, directly destroying available lysine and impairing Nutrition $\to$ (III).