Unit Operations in Food Processing Questions and Answers

Answer: C

The most suitable laminate is BOPP/LDPE.

Dry fruits are low-moisture products: their packaging must keep moisture out so that they stay crisp, while showing the product and resisting handling. Biaxially oriented polypropylene has a very low water-vapour transmission rate, good clarity, stiffness and printability, and the LDPE inner layer provides the heat seal. The laminate is cheap and widely used for nuts and dry fruits.

Polystyrene is brittle and a poor moisture barrier, so PS/LDPE is unsuitable for flexible pouches. PET/LDPE and Nylon/LDPE offer higher oxygen barrier or puncture strength at greater cost; nylon in particular absorbs moisture and is the usual choice for vacuum packs of meat and cheese, not for dry snacks.

Answer: A

The correct sequence is slaughtering and bleeding → scalding → defeathering → eviscerating → chilling.

After the bird is killed and bled, it is dipped in hot water (scalding) to loosen the feather follicles. Only then can the feathers be removed cleanly by the rubber-fingered pickers (defeathering). The carcass is then opened and the viscera removed (eviscerating), and finally it is chilled quickly to limit bacterial growth.

Defeathering before scalding tears the skin because the feathers are still held firmly. Eviscerating before defeathering or scalding exposes the body cavity to dirt and scald water, and scalding after evisceration would contaminate the opened carcass.

Answer: C

The one not used as an ethylene absorber is calcium hydroxide.

Calcium hydroxide reacts with carbon dioxide to form calcium carbonate, so it is used as a CO₂ absorber in packaging, for example for coffee and for produce that releases CO₂. It does not remove ethylene.

Potassium permanganate oxidises ethylene and is the most common scavenger, usually carried on an inert porous support such as silica gel, alumina or zeolite in sachets. Activated carbon, often with a palladium catalyst, adsorbs and breaks down ethylene. These are standard ethylene-control materials.

Answer: A

The suitable mix is O₂ = 0; CO₂ = 50; N₂ = 50.

The pink colour of cured meat comes from nitrosyl myoglobin, which fades quickly when exposed to oxygen and light, and oxygen also promotes rancidity of the fat. Cured meats are therefore packed with oxygen excluded. Carbon dioxide is included because it dissolves in the meat and inhibits aerobic spoilage bacteria and moulds, and nitrogen, an inert filler, prevents pack collapse as CO₂ dissolves.

The 50% oxygen mixes suit fresh red meat, where oxygen keeps the bright red oxymyoglobin, but they would discolour cured meat. Pure nitrogen excludes oxygen but gives no antimicrobial effect, so it protects the product less well.

Answer: A

It is Thermal conductivity.

Fourier's law gives the heat flow by conduction as q = -kA(dT/dx). The constant k, the rate of heat flow through unit thickness of material per unit area normal to the flow, per unit time, for unit temperature difference, is the thermal conductivity, measured in W/m K.

Enthalpy is the total heat content of a substance. Thermal diffusivity is conductivity divided by density times specific heat and measures how fast temperature spreads. Specific heat is the heat needed to raise unit mass by one degree. None is defined per unit thickness and area.