Novel techniques: electro-technologies Flashcards
Electro technologies for thermal processing include: (5)
MW, RF, ohmic, PEF, PL
MW are part of the _____ spectrum. They are (longer/shorter) waves, and can be generated by:
EM (electro-mag)
longer
oscillating electric fields
Why are frequencies used for MW restricted? Which ones are permitted?
interfere w/ radar communications
915MHz for INDUSTRIAL applications
2450MHz for DOMESTIC applications
The 3 factors that affect MW heating:
- frequency
- dielectric properties of food
- thermo-physical properties of food
How do MW induce heating in food? (2) (on molecular level)
oscillating field will cause electronic/dielectric heating:
- dipole rotation - dipole molecules flip flop repeatedly
- ionic polarization - vibration of ionic salts
True/False: MW used for domestic applications have longer wavelengths than industrial MW
False; higher frequency so shorter wavelength
diaelectric properties of foods are assessed by what 2 parameters?
What factors affect it?
dielectric constant - ability to ABSORB MW
loss factor - ability to DISSIPATE MW
depends on: temp, MW properties, product composition
What happens to penetration of MW as depth increases?
decrease exponentially
What are some applications of MW?
heat/reheat pasteurize/sterilize cooking temper/thaw drying enhance other processes: (extraction, osmotic drying, finnish drying, etc)
What affects penetration depth? (3)
frequency
state
dielectric constant
the higher the frequency, the (higher/lower) the penetration depth.
Higher penetration occurs for a (solid/liquid) state
The higher the dielectric constant, the (higher/lower) the penetration depth.
lower
solid
lower
What feature makes MW good for drying?
selective energy absorption by polar molecules (water is very polar)
What are the advantages of MW?
volumetric heating (evenly heat) faster easy controls/clean up targets polar molecules can combine w/ other energy/chemicals
What are some problems with MW? (4)
lack of penetration in large sample
uneven heating in heterogenous sample (or uneven field strength)
wet environment - no browning, no maillard, no crispness
measurement difficulties
Volumetric MW heating is only possible with: (2)
homogenous product: liquid or semisolid
uniform field strength
A major safety concern with MW heating is:
uneven heating: cool spots lead to inadequately processed/cooked food
What are the various temperature distribution studies done with MW?
frozen products
family size containers
hedge-hog system (when MW off)
What highly energy intensive step in vegetable processing can be replaced by MW? Why is this better? (4)
blanching
less affluent (water, steam)
effective on enzymes (enhanced!)
can air-cool afterwards
better quality
Why would microwave pasteurization give higher quality? (2)
do not require heated surface (heat food directly)
so no fouling (over heating of proteins/carbs)
= HIGHER QUALITY
can use lower temp
How do MW kinetics compare to thermal kinetics?
equal, or enhanced (not conclusive)
Aside from thermal effects, what else could possibly contribute to MW kinetics? (2)
non-thermal (effects observed at lower temps) enhanced thermal (effects at high temp that is GREATER than can be explained by just thermal alone)
True/False: MW kinetics have an instant CUT.
False. Need to integrate.
Experimentally, were any non-thermal effects found for MW?
No
What property makes MW particularly useful for thawing
deep penetration of MW for ice
