Dehydration Flashcards
Is it possible to decrease water content of a food product to 0%
No
When sun drying, the moisture content is reduced to
10-35%
Why is sulfur dioxide often listed as an ingredient in dried fruit?
Sulfur protects against enzymatic browning and may cause allergic reactions (headache, coma, death) in some individuals
What are the advantages of freeze drying?
- Does not subject the food to high heat
- Does not alter flavour, colour, or structure of the food
- Freeze dried products can be easily reconstituted
What is the disadvantage of freeze drying?
Costly
All heat transfer is governed by the 1st law of thermodynamics, which states
Energy cannot be created nor destroyed. It can only be converted into other forms of energy
Microwave ovens heat foods by converting __________ energy to __________ in water molecules
Radiant; kinetic
Industrial heating processes include __________, __________ and __________
Canning, pasteurization and evaporation
In the food industry changes in phase of __________ are important, since a large proportion of the mass of most foods consists of __________
Water; water
A pressure cooker can cook foods faster because
It can achieve higher temperature
The drying efficiency increases when there is sufficient __________ to carry away moisture
Air flow
What are the major considerations for all food manufacturers when choosing processing equipment for their plants?
Cost of the equipment, cost of operating, cost of maintaining, available space in the plant, how to clean the equipment, technical support from the manufacturer, types and range of products to be produced
Heat processing for __________ time at __________ temperature contributes to better retention of nutritional and sensory qualities
Short; high
Application of heat may be detrimental to __________ or __________ attributes in some products
Nutritional or sensory
Define wet steam
Any steam less than 100% quality
TRUE or FALSE?
Cooling is not the addition of “cold” it is the removal of heat from food
TRUE
Define commercial sterilization
There might be a few spores of microorganisms left in the can/food, but they are so damaged that they cannot cause any problem
Explain why a fluidized bed drier is advantageous over tunnel drier
It has the porous plate, so air is flown from top and bottom thus drying will be faster
Ideally, refrigeration of perishables starts at the time of __________ or slaughter and is maintained throughout transportation, warehousing and storage prior to ultimate use
Harvest
TRUE or FALSE?
The principal requirements for effective refrigerated storage are controlled low temperature, air circulation, humidity control and modification of gas atmospheres
TRUE
TRUE or FALSE?
Refrigerated storage permits exchange of flavours between many foods. Butter and milk will absorb odours from fish and fruits
TRUE
The more salt, sugar, minerals or proteins in a solution the __________ its freezing point
Lower
The freezing point of pure water is __________, but actually water does not begin to freeze at __________. Instead, it generally becomes __________ to a temperature several degrees below __________ before some stimulus such as crystal nucleation or agitation initiates the freezing process
0 degrees C, 0 degrees C, supercooled, 0 degrees C
TRUE or FALSE?
Repeated freezing and thawing cycles are very detrimental to stored foods
TRUE
There are three basic freezing methods in commercial use: Freezing in air (give one example: ____________________); freezing by indirect contact with the refrigerant (give one example: ____________________); freezing by direct immersion in a refrigerating medium (give one example: ____________________).
Air blast freezing; plate freezing; liquid nitrogen
Although refrigeration and cool storage reduces the rate of food deterioration, with most foods, it will not prevent deterioration to anywhere the same degree as does __________, dehydration, irradiation, fermentation or freezing.
Heat
When refrigerated storage is to be for prolonged periods, various techniques are used to maintain quality, for example: eggs in the shell are sprayed with a thin edible __________ to prevent __________ and __________ loss.
Oil; H2O; CO2
TRUE or FALSE?
Low temperature separation and concentration processes employing selective membranes are not applicable in food industry
FALSE
The liquid whey is forced through an ultra-filtration membrane to concentrate the __________ above the membrane. The filtrate then can be forced through a reverse osmosis membrane to concentrate __________
Protein; lactose
Concentration processes that expose food to 100 °C or higher can cause major organoleptic changes such as cooked flavour and __________ of colour
Darkening
Sugar and salt in concentrated solution have __________ osmotic pressure which can draw water from microbial cells or to prevent normal diffusion of water into these cells
High
TRUE or FALSE?
Two foods with the same water content can have very different water activity values
TRUE
The major factors affecting food deterioration include
Microorganisms, enzymes, insects, parasites, rodents, inappropriate temperature, oxygen, light, physical damage, lengthy storage time
