Manufactured & Traditional Dairy Products

Microcrystalline cellulose (MCC) is prepared by acid hydrolysis of native cellulose to remove amorphous regions, leaving crystalline microfibrils that are practically water-insoluble. In ice cream mixes, it forms an insoluble colloidal dispersion rather than a true molecular solution.

Option analysis:

• Guar gum: Cold-water soluble galactomannan polysaccharide.
• Sodium alginate: Readily soluble in warm water forming a viscous sol.
• Microcrystalline cellulose: Correct, virtually insoluble in water; functions via mechanical thixotropic network formation of dispersed microcrystals.
• Carboxymethyl cellulose: Chemical etherification renders CMC highly soluble in both cold and hot water.

Dry ice (solid carbon dioxide) has a sublimation temperature of $-78.5^\circ\text{C}$ and sublimes directly into cold gas without leaving any liquid residue, providing high latent heat of sublimation ($571\text{ kJ/kg}$) that maintains ice cream far below its softening point during long-distance transit.

Option analysis:

• Use of ice and salt mixture: Cannot sustain temperatures below $-15^\circ\text{C}$ for long journeys and leaves corrosive brine.
• Use of liquid nitrogen: Extremely cryogenic ($-196^\circ\text{C}$), expensive, and boils off rapidly without specialized vacuum-jacketed tanks.
• Use of dry ice: Correct, solid $CO_2$ sublimes cleanly, sustains deep freezing temperatures, and is ideally suited for insulated shipping containers.
• Use of glycol chiller: Requires continuous electrical power/compressors, unsuitable for passive long transit containers.

Overrun represents the volume of air incorporated into the ice cream during freezing. By definition, $\%\,\text{Overrun} = \frac{\text{Weight of unit volume of mix} - \text{Weight of unit volume of ice cream}}{\text{Weight of unit volume of ice cream}} \times 100$. In dairy factory operations, the overrun is directly monitored and indicated by routinely weighing a known fixed volume cup (e.g., weight per litre) of frozen ice cream drawn from the freezer.

Option analysis:

• Ammeter reading in the freezer: Measures motor load indicating ice cream stiffness and viscosity, not overrun.
• Whipping time in freezer: Measures residence time, does not directly measure the volume expansion.
• Weight/litre of ice cream mix: Mix density is constant (approx. $1.08 - 1.12\text{ kg/L}$) regardless of overrun.
• Weight/litre of ice cream: Correct, as more air is incorporated, the weight per litre of the finished ice cream decreases proportionately.