Processing of Food Commodities

In colloidal chemistry, a foam is defined as a dispersion of gas bubbles in a liquid or continuous solid matrix. Whipped cream is produced by vigorously whipping air into heavy cream ($30 - 40\%$ milk fat), entrapping air bubbles stabilized by a partially coalesced fat globule membrane network at the air-water interface, making it a classic food foam.

Option analysis:

• Foam: Correct, gas (air) dispersed in a liquid/semi-solid matrix.
• Aerosol: Liquid or solid particles dispersed in a gas phase (like fog or smoke).
• Sol: Solid particles dispersed in a continuous liquid phase.
• Emulsion: Liquid droplets dispersed in another immiscible liquid (unwhipped cream is an emulsion, but whipped cream is a foam).

Milk and cream are natural oil-in-water (O/W) emulsions where fat droplets are dispersed throughout a continuous aqueous serum phase. During the churning of cream into butter, phase inversion takes place: the fat globule membranes rupture, allowing liquid fat to become the continuous phase embedding microscopic droplets of moisture and air, making butter a classic water-in-oil (W/O) emulsion.

Option analysis:

• Oil in water emulsion: Describes milk, cream, and mayonnaise.
• Water in oil emulsion: Correct, butter and margarine are water-in-fat emulsions with continuous lipid phase.
• Oil in oil form: Non-existent colloidal phase.
• Water in water form: Non-existent colloidal phase.

Khoya (khoa) is an indigenous partially desiccated whole milk product. The yield of khoya depends on the total solids and fat content of the raw milk: cow milk ($3.5 - 4.0\%$ fat, $8.5\%$ SNF) typically yields $17 - 19\text{ kg}$ khoya per $100\text{ kg}$, whereas buffalo milk ($6.0 - 7.0\%$ fat, $9.0\%$ SNF) yields $21 - 23\text{ kg}$ khoya. On an average mixed milk basis, $100\text{ kg}$ of milk yields approximately $20\text{ kg}$ of finished khoya.

Option analysis:

• $12$: Underestimate, represents yield of chhana or paneer from cow milk.
• $20$: Correct, standard average yield of khoya from $100\text{ kg}$ whole milk.
• $32$: Far too high.
• $42 - 45$: Highly excessive.