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How do microwaves compare to ionizing irradiation waves?
Microwaves are much lower energy and longer wavelengths
What is the frequency range of microwaves?
What was the first microwave?
Why are we limited in wavelength for microwave use?
Because the same range is used for communications and it would interfere
What frequency do industrial microwaves commonly operate at?
What frequency do home microwaves operate at?
How do microwaves react with metals?
They are reflected
How do microwaves react with pastic and glass?
They pass through
What is 'loss factor'?
Degree of absorption of microwaves
What material has a high loss factor?
What material has a low loss factor?
Why are microwaves efficient sources of heat transfer?
They pentrate and release their energy throughout the product- thus largely overcome slower process of heat conduction
How do salts contribute to microwave heat exchange?
Salts contribute by electrophoretic heating
How are microwaves used to heat up water?
Water molecules try to align with the wave which changes direction 915,000,000 (for 915 MHz) per second, this causes intermolecular friction resulting in the product heating up rapidly
What foods is a lower frequency microwave used for?
What are the limitations of microwaves?
Temperatures do not rise above 100°C for moisture containing foods
What is suscepter packaging?
Converts microwaves into inrared
What foods is Ohmic heating beneficial for?
Fluids containing particulates
How does Ohmic heating work?
- Product is placed between plates (electrodes) and exposed to an alternating current (50-60 Hz)
- Electric current tries to pass through the product and the resistance encountered heats the product
What do products require for Ohmic heating to be effective?
A minimum and controlled amount of ionic content (salt) to partially conduct
Why do foods need salt to conduct ohmic heating?
Particulates containing salt heat more rapidly, tansfering their heat to the fluid- avoids center-point (cold point) lag
What is the main benefit of Ohmic heating?
Avoids excessive surface heating (burn-on) which reduces quality
What is pulse electric field processing?
- Pulses of 15,000-30,000 V/cm2
- Kills vegetative bacteria
What is PEF an alternative for?
Low temperature alternative to heat pasteurization
What is the benefit of PEF processing?
Less effect on delicate flavor constituents
How does PEF processing work?
Strong electric pulses produced between two plates disrupt the porosity of cell memebranes (bacteria/tissue) with little heating
Why is PEF processing not a complete process?
- Enzymes are not destroyed
- Need blanching
- Refrigeration is required
What is PEF processing used for?
- Juice pasteurization
- Enhance juice extraction from fruit tissue
Food packaging alone cosumes over ___% of all packaging materils used
Aside from preservation, what other roles does packaging serve?
What does specialized packaging machinery do?
What are some desirable features associated with an ideal package?
- Sanitary and Rugged
- Moisture/Fat protection
- Gas/Odor protection
- Light protection
- Resistance to impact
- Tamper resistance
- Ease of opening
- Low weight
- Pouring feature
- Re-sealing capabiity
- Ease of disposal
- Special Features
Why is it important for packages to provide light protection?
Reduce product autoxidation/color fading
Why is it important for packaging to have low weight?
How are containers/packages classified?
What is primary packagin?
Comes into contact with food
What is secondary packaging?
Often provides for rigidity, printing, or grouping into larger units
What is an alternative classification system for packaging?
What is an example of rigid packaging?
What is an example of semi-ridig packaging?
- Squeeze bottle
- Tetra brick
What is an example of flexible packaging?
What is hermetic packaging?
A hermetic package, by definition, is impermeal to fases and vapors
What is an example of a hermetic package?
Cans, Bottles, Tetra brick
What is the downside of many flexible packages?
Many flexible packages are semi-permeable to gasses, susceptible to pinholes and their seals may be imperfect
What are some common packaging materials?
- Plastic/Metal/Paper/Laminates combos
What is the 'tin can' originally made of?
Steel with a thin coating of tin to prevent rusting
What are tin cans made of now?
Base steel usually coated with chrome
Why do some cans include speciaized internal coatings?
For acid and other corrosive food products, such as pineapple
What is the rate of manufacturing and sealing cans?
What is the can's seal made up of?
Five metal folds, sealed by epoxy
Why are cans ribbed?
So the can can survive the retort pressure changes
What is the most popular material for 2 piece cans?
Why is aluminum often used for cans?
Light and resistant to atmospheric corrosion and malleable
What do aluminum cans need to maintain their shape?
Internal pressure (soft drinks/beer)
What is the convenience of aluminum cans?
What is aluminum foil used for in pther types of packaging?
Used as a laminate to provide gas/vapor barrier in other packaging materials such as the retort pouch
Why is aluminum a very preferred material for all packaging?
Economical to recycle
What is an advantage of glass packaging?
Chemically inert and transparent
What are the disadvantages to glass packaging?
Brittle and heavy
How can glass breakage be reduced substantially?
Adding coatings to glass
How do you make glass?
Combine sand, soda ash, and limestone and heat to 1500°C and blow mold
What is the disadvantage of glass in retorts?
Susceptible to mechanical and thermal shock
What has brought glass back as a major packaging contender
Why is paper often used for packaging?
Cheap and versatile
Why is paper packaging often waxed?
To prevent loss of strength due to moisture ingression
What is the most predominant form of pastic in the food industry?
Wraps, films and packages
What are the two types of plastic polymers that can be produced?
Homo or Hetero
How is plastic packagin formed?
Can be melted and blown into containers and formed into films
What are some typical films?
What is cellophane?
What is nylon made of?
What is mylar made of?
What was the original saran made of?
What are some very specific properties we can obtain with plastic films?
- Moisture or gas barriers
- Selective permeability's (water vapor, O2, CO2)