4.3.preservation by dehydration and irradiation

Question 1

how can the deterioration of food products be slowed?

Answer 1

-by processing foods by the removal or reduction in the water content (dehydration)
-through irradiation to change the chemical structure, thereby extending shelf life

Question 2

how can reducing water content extend the shelf life of foods?

Answer 2

-prevents the growth of vegetative microbial cells, germination of spores, and toxin production by molds and bacteria.
-A decrease in water activity decreases the growth rate.

Question 3

what are the 3 methods to reduce water content?

Answer 3

dehydration, crystallization, and addition of solutes

Question 4

what can inadequate hygiene conditions cause?

Answer 4

-when it occurs during drying, transport, and storage can cause contamination by molds, which can result in the formation of mycotoxins

Question 5

name methods of dehydration?

Answer 5

-tunnel drying
-roller drying
-sun/solar drying
-Fluidised bed/ warm air drying
-spray drying
-freezedrying

Question 6

tunnel drying explanation and example?

Answer 6

-Layers of food are dried on trays, which are stacked on trucks programmed to move semi continuously through an insulated tunnel. Able to dry large quantities of food in a relatively short time
-eg.Crops ,vegetables

Question 7

roller drying explanation and example?

Answer 7

Product is dried through conduction , by contact with a heated surface; roller or drum.
eg. Milk powder, powder egg

Question 8

sun/solar drying explanation and example?

Answer 8

-Using direct sunlight tro dry food, but can have several implications in terms of hygiene.
-eg.Tomatoes and Fish

Question 9

Fluidised bed/ warm air drying explanation and example?

Answer 9

-where warm AIR is blown upwards directly underneath the food, causing it to flow and remain separated. This procedure is suitable for small items.
-eg.fruits

Question 10

Spray drying explanation and example?

Answer 10

-A dispersion of pre-concentrated food (40–60% moisture) is first ‘atomized’ to form fine droplets and then sprayed into a counter-current flow of heated air at 150–300ºC in a large drying chamber.
-eg.Milk, eggs, tea, spices

Question 11

freeze drying explanation and example?

Answer 11

-Used for high-quality dried products, which contain heat-sensitive components. The absence of air and low temperature prevents deterioration due to oxidation or chemical modification of the product. It also gives very porous products, which results in high rehydration rates.
-Coffee, Vitamins

Question 12

what is food irradiation?

Answer 12

a technology that improves the safety and extends the shelf life of foods by reducing or eliminating microorganisms and insects.

Question 13

examples of food that undergo irradiation?

Answer 13

Beef , pork and poultry
Crustaceans and molluscs
Fresh fruits and vegetables
Salad leaves
Seeds for sprouting (e.g. alfalfa sprouts)
Eggs
Spices and seasonings

Question 14

what are the 3 methods of irradiation and explain them

Answer 14

-gamma rays- are emitted from either radioactive form of cobalt and cesium
-x rays -produced by reflecting a high-energy stream of electrons off a target substance (usually one of the heavy metals) into food
-electrobeam-A stream of high-energy electrons propelled

Question 15

what symbol identifies foods that have been irradiated?

Answer 15

Radura symbol- green dot in centre, 2 leaves below and green dashes in a circle around it
-important as some people have concerns and don’t eat irradiated foods as they think its unsafe

Question 16

dehydration advantages and disadvantages

Answer 16

+- affects organoleptic properties of food- Moisture lost, food is dried, texture and visible changes. Flavour often concentrated
-can be significant loss of nutrient
+Can be done cheaply, using natural sources (is less safe and hygienic tho)
+improves shelf life due to removal of water
+consumers generally don’t have a negative view of it

Question 17

irradiation advantages and disadvantages?

Answer 17

+has little affect on organoleptic properties
+doen’t effect nutrient content
-expensive process
+can be done in large quantities
+increases shelf life of food
-sometimes negative consumer opinion-Some concerns over eating food treated with radiation. Concerns over safety