ICAR AIEEA PG Dairy Technology 14 July 2023 Shift-1 Paper

Low-temperature extrusion (LTE) draws ice cream at $-12^\circ\text{C}$ to $-15^\circ\text{C}$ (compared to $-5^\circ\text{C}$ to $-6^\circ\text{C}$ in standard continuous freezers). Under the high shear and low temperature of LTE, ice crystals and air bubbles are broken down into exceptionally fine distributions, resulting in significantly smaller air cells and ice crystals that yield an ultra-smooth, creamy texture and superior thermal shock stability.

Option analysis:

• Much smaller size air bubbles: Correct, LTE produces mean air bubble diameters below $20\,\mu\text{m}$, nearly half that of conventional freezing.
• Larger ice crystal size: Incorrect, LTE significantly reduces ice crystal size.
• Lower percentage of water frozen: Incorrect, much more water ($70 - 80\%$) is frozen at extrusion compared to standard freezing ($50\%$).
• Higher drawing temperature: Incorrect, drawing temperature is substantially lower ($-12^\circ\text{C}$ to $-15^\circ\text{C}$).

Raw cow milk naturally contains inherent antimicrobial/protective factors such as lactoferrin (iron chelator), lysozyme (cell wall lysis), immunoglobulins (especially IgG1), and lactoperoxidase. Haemagglutinin (phytohaemagglutinin) is a plant lectin (found in legumes like raw kidney beans) and is not an inherent protective factor of bovine milk.

Option analysis:

• Lactoferrin: Inherent antimicrobial glycoprotein in milk that binds iron.
• Haemagglutinin: Correct, it is a plant-derived toxic lectin, not a milk constituent.
• IgG: Major protective immunoglobulin naturally present in bovine colostrum and milk.
• Lysozyme: Natural antibacterial enzyme present in milk that hydrolyzes peptidoglycan.

Increasing milk solids-not-fat (MSNF) increases total solids, increases mix viscosity due to proteins, and depresses the freezing point because of added lactose and soluble milk salts. However, higher MSNF does not enhance added flavourings; in fact, milk proteins bind volatile flavour compounds, often masking or dampening added delicate flavour notes.

Option analysis:

• Lowering of freezing point: Directly affected due to the colligative effect of lactose and soluble mineral salts.
• Increased viscosity: Directly affected because caseins and whey proteins hydrate and thicken the serum phase.
• Increased total solids: Directly affected since MSNF is a primary contributor to total solids.
• Enhance the flavouring used: Correct, increasing MSNF does not enhance added flavours (it tends to mask them).