Dairy Chemistry & Milk Constituents

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: $\text{C}_{12}\text{H}_{22}\text{O}_{11} + \text{H}_2\text{O} \to 4\text{ CH}_3\text{CH(OH)COOH}$).

Chemistry of milk salts and ash analysis:

• Statement (I) is false: Ashing milk at $550^\circ\text{C}$ completely volatilizes organic counter-ions (citrates, lactates), converts organic phosphorus of caseins and phospholipids into inorganic phosphates, and partially volatilizes chlorides. Therefore, ash represents only the oxidized mineral residue after combustion and does NOT represent the true native salt equilibrium or ionic composition in fluid milk.
• Statement (II) is true: According to Sommer and Hart's classical salt balance theory, the heat stability of milk depends critically on the ionic ratio between polyvalent cations and polyvalent anions:
  $$\text{Salt Balance Ratio} = \frac{\text{Ca}^{2+} + \text{Mg}^{2+}}{\text{Citrate}^{3-} + \text{Phosphate}^{3-}}$$

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).