Lecture 17: Microwave, Radio Frequency, Ohmic Heating, PEF, PL Flashcards
how to microwaves compare to telecommunication range
MW are longer
how can MC be generated?
by oscillating electric fields
what are restrictions of MW?
- interference w/ radar communications
- only some frequencies are permitted
what types of MW interactions are used to heat foods?
- dipole rotation: flip flop rotation of dipole molecules, like water
- ionic polarization: back and forth vibration of ionic salts like NaCl
what factors does MW heating depend on?
- MW frequency
- thermo physical properties of foods
- dielectric properties
define the dielectric constant
ability of material to absorb MW
define the loss factor
ability of material to dissipate MW
what go the dielectric properties of MW heating depend on?
product composition
temp
MW properties
how is penetration of MW energy related to depth of product?
penetration decreases exponentially w/ depth
shorter frequency of MW = ____ penetration
higher/lower
higher
what does the MW penetration depth depend on?
state of the product (eg. ice vs water)
how is penetration depth related to dielectric constant?
inversely related
what are some applications of MW?
- heating: pasteurization and sterilization
- tempering, thawing
- drying
- MW osmotic drying
- vacuum MW drying
what are some advantages of MW processing?
- volumetric heating
- decreased processing time
- instant control and clean process
- selective E absorption by polar molecules
- can be combined with other E sources and chemicals
what are problems with WM processing?
- lack of penetration depth in large samples
- lack of flavour development and browning due to wet environment cooking
- non-uniform heating due to non-uniform field strength
what can MW blanching be used for?
to inactivate enzymes
how does MW blanching compare to conventionally bleached products?
MW products are higher quality
what is fouling? what effects can this cause?
occurs at contact surface due to over heating of proteins, CHO, etc…
can cause reduced heat transfer and formation of off flavours
why does fouling occur in conventional heat exchangers, but not in MW?
conventional heating: surface is hot to transfer heat to fluids
MW: heats food directly, not indirectly by the surface. Since the surface is cooler than the product, there is no fouling
what is MW pasteurization used for?
milk
orange juice
apple juice
what are benefits of MW pasteurization?
- processing temp can be lower than conventional pasteurization
- better quality retention
- incr destruction of microorganisms and enzymes
what are thermal effects of MW processing?
explained by interactive effects of time and temp combinations based on some models
what are non-thermal effects of MW processing?
occurs in temperatures not low enough to cause any inactivation
what are enhanced thermal effects of MW processing?
when the observed effect is greater than can be explained by time and temp combinations
