Food Preservation: Why, How, and Methods: 20 MCQs with answers

C · Keeping food safe for a long time while preserving colour, taste, value and texture

Food preservation means keeping food safe for a long time so that it does not spoil and its colour, taste, value and texture remain preserved. Refrigeration alone protects food only for a short period, so it is not full preservation.

C · Microorganisms, enzymes, and insects, worms and rats

The source names three causes of spoilage: microorganisms (bacteria, yeast, mould), enzymes naturally present in plants and animals, and insects, worms and rats that damage food by eating it and making holes.

B · Moisture and suitable temperature

Microorganisms generally need moisture, warmth, and usually oxygen and nutrients from the food to multiply. Very low temperature slows them down rather than helping them grow.

C · Heat increases microorganism growth

Summer temperatures provide the warmth that speeds up microorganism growth, so food spoils faster. Cold winter temperatures slow down microorganism activity considerably.

B · By removing moisture

Dehydration removes water or moisture from food. Microorganisms need moisture to survive and multiply, so removing it prevents their growth and keeps food safe for longer.

D · Pickling

Pickling preserves food using salt, oil, vinegar and spices. Salt draws moisture out of the food and out of microorganisms, while oil helps seal out air that many microorganisms need.

D · Removing water content

A high concentration of sugar outside a microorganism's cells draws water out of those cells by osmosis. Without enough water, microorganisms cannot survive or multiply — the same basic principle as using salt.

D · By reducing temperature

Freezing turns water into ice and comes much closer to fully stopping microorganism activity than refrigeration, which only slows it down.

A · True

Refrigeration does not completely stop food spoilage; it only slows down the growth of microorganisms, whereas freezing turns water into ice and comes much closer to fully stopping microorganism activity.

B · Refrigeration slows microorganisms but does not stop them, so food still spoils eventually

Cold temperatures slow down, but do not fully stop, the activity of microorganisms. That is why refrigerated food eventually spoils, just much more slowly than food left at room temperature.

C · Heating kills existing microorganisms and the airtight seal keeps new ones out

Canning is a two-step defence: heating the food first kills the microorganisms already present, and sealing the container airtight then prevents new air and new microorganisms from getting in.

D · Inactivating enzymes

Enzyme activity can be stopped by changing temperature and moisture conditions. Boiling peas for a few minutes makes their enzymes inactive, preventing over-ripening and spoilage.

A · It removes the moisture microorganisms need, using only sunlight and air

Microorganisms need moisture to survive and multiply. Sun-drying removes most of the moisture from food and can be done using only sunlight and air, without any modern technology or equipment.

B · Both A and R are true, and R correctly explains A.

Salt draws moisture out of the food and out of any microorganisms present, and oil helps seal out air that many microorganisms need. Together they create conditions where most microorganisms cannot easily survive or multiply, which is exactly why pickle keeps for months.

D · It destroys many microorganisms, but some can survive and grow again later

High temperature destroys many microorganisms and enzymes and helps prevent food spoilage, but some microorganisms can survive high temperatures and may grow again later.

B · To supply food where crops cannot grow

Many foods cannot be grown in deserts and cold regions. Preserved food helps provide nutritious and varied diets to people in these areas — this is the 'supply food where crops cannot grow' reason for preservation.

C · It inactivates enzymes and kills microorganisms, extending the food's shelf life.

The correct option is true because boiling peas inactivates enzymes and kills microorganisms, which are essential for preventing spoilage.

C · The method is effective as it uses osmosis to draw moisture out of microorganisms.

The correct option is true because using high concentrations of sugar creates an osmotic environment that draws moisture out of microorganisms, preventing their growth.

D · Heating the food and sealing the container airtight.

The correct option is true because canning requires both heating to kill microorganisms and sealing the container to prevent new ones from entering.

C · Refrigeration only slows down microorganisms, while freezing nearly stops their activity.

The correct option is true because refrigeration slows down microorganism activity, while freezing nearly stops it by turning water into ice, making it less available for microbial growth.