Progress in food Progress in food dehydration dehydration Joseph S. Cohen and Joseph S. Cohen and Tom C.S. Yang Tom C.S. Yang - - Trends Food Sci. Trends Food Sci. Technology.6, 20-25 Technology.6, 20-25 Lab. of Food & Biomaterial Chemistry Lee Si Yeon
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Progress in food dehydration Joseph S. Cohen and Tom C.S. Yang - Trends Food Sci. Technology.6, 20-25 Lab. of Food & Biomaterial Chemistry Lee Si Yeon.
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Progress in food Progress in food dehydrationdehydration Joseph S. Cohen and Tom C.S. YangJoseph S. Cohen and Tom C.S. Yang - -Trends Food Sci. Technology.6, 20-25Trends Food Sci. Technology.6, 20-25
Lab. of Food & Biomaterial Chemistry
Lee Si Yeon
IntroductionIntroduction
Dehydration is the oldest method of food preservation.
Almost as old as open-air drying.Usage :meat, fish.Advantages :added flavor, formed bactericidal properties. Disadvantages :difficult to control, slow.
3. Convection drying3. Convection drying
Hot air is to pass over the product, which has been placed in open trays.
Usage :low-value products.Advantages :continuous process.Disadvantages :difficult to control.
4. Drum drying4. Drum drying
Products have been placed on the surface of a heated drum.
contact with hot gas→liquid is rapidly evaporated →final product.
Usage :liquids, instant tea, coffee.Advantage :spherical product.Disadvantages :quality loss, not all materials can be dried in this way
6. Fluidized-bed drying6. Fluidized-bed drying
Usage :small uniform particle, small vegetables.
Advantages :usually batch operation, uniform
drying, maintain constant temperature, rapid.Disadvantages :restriction on particle size.
7. Freeze drying7. Freeze drying
Principle. :under high vacuum, frozen water removed
from a food.Four rate-limiting step.1. the external transfer of heat to the outer
surface of the material from the heat source. 2. the internal transfer of heat within from
the heat source. 3. the external mass transfer of water vapor
from the surface.4. internal mass transfer within the material.☞During the drying cycle, the thickness of dried layer increased, sublimation rate decrease.
Usage :value-added products, fruit pieces, instant
coffee.Advantages :continuous operation, no restriction on
particle size, no heat demage.Disadvantages :slow, expensive.
Freeze Drying
8. Other drying methods.8. Other drying methods.
1. Explosive puffing -Combination of high temperature and high
pressure. -Usage : small particle, honeycombo
structure. -Advantage : rapid. -Disadvantage : High heat.
Fig. 4 Schematic diagram of an experimental ultrasonic dryer.
ConclusionConclusion
In the future, it is probable that other novel drying techniques will be developed and become available for specialized purpose.
Furthermore, current techniques will also probably be further refined to make them more economical and will also be explored for use with other food products.