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4) Food Processing > Lecture 17: Microwave, Radio Frequency, Ohmic Heating, PEF, PL > Flashcards

Lecture 17: Microwave, Radio Frequency, Ohmic Heating, PEF, PL Flashcards

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1
Q

how to microwaves compare to telecommunication range

A

MW are longer

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2
Q

how can MC be generated?

A

by oscillating electric fields

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3
Q

what are restrictions of MW?

A
  • interference w/ radar communications

- only some frequencies are permitted

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4
Q

what types of MW interactions are used to heat foods?

A
  1. dipole rotation: flip flop rotation of dipole molecules, like water
  2. ionic polarization: back and forth vibration of ionic salts like NaCl
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5
Q

what factors does MW heating depend on?

A
  1. MW frequency
  2. thermo physical properties of foods
  3. dielectric properties
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6
Q

define the dielectric constant

A

ability of material to absorb MW

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7
Q

define the loss factor

A

ability of material to dissipate MW

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8
Q

what go the dielectric properties of MW heating depend on?

A

product composition
temp
MW properties

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9
Q

how is penetration of MW energy related to depth of product?

A

penetration decreases exponentially w/ depth

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10
Q

shorter frequency of MW = ____ penetration

higher/lower

A

higher

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11
Q

what does the MW penetration depth depend on?

A

state of the product (eg. ice vs water)

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12
Q

how is penetration depth related to dielectric constant?

A

inversely related

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13
Q

what are some applications of MW?

A
  1. heating: pasteurization and sterilization
  2. tempering, thawing
  3. drying
  4. MW osmotic drying
  5. vacuum MW drying
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14
Q

what are some advantages of MW processing?

A
  • 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
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15
Q

what are problems with WM processing?

A
  • 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
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16
Q

what can MW blanching be used for?

A

to inactivate enzymes

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17
Q

how does MW blanching compare to conventionally bleached products?

A

MW products are higher quality

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18
Q

what is fouling? what effects can this cause?

A

occurs at contact surface due to over heating of proteins, CHO, etc…

can cause reduced heat transfer and formation of off flavours

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19
Q

why does fouling occur in conventional heat exchangers, but not in MW?

A

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

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20
Q

what is MW pasteurization used for?

A

milk
orange juice
apple juice

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21
Q

what are benefits of MW pasteurization?

A
  • processing temp can be lower than conventional pasteurization
  • better quality retention
  • incr destruction of microorganisms and enzymes
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22
Q

what are thermal effects of MW processing?

A

explained by interactive effects of time and temp combinations based on some models

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23
Q

what are non-thermal effects of MW processing?

A

occurs in temperatures not low enough to cause any inactivation

24
Q

what are enhanced thermal effects of MW processing?

A

when the observed effect is greater than can be explained by time and temp combinations

25
Q

compare MW destruction kinetics to conventional kinetics

A

conventional

  • has instant come up and come down time
  • significant inactivation during hold time

MW:

  • mostly non-instantaneous heating
  • no hold time
  • complete inactivation test during come up and down periods
26
Q

why is MW tempering and thawing a significant application?

A

due to large penetration depth for MW in ice

27
Q

what is “runaway heating” in MW tempering?

A

when rapid heating under MW results in quick melting of surface ice

28
Q

describe MW drying and osmo/MW

what is it ideal for?

A

MW: adds heat and vaporizes water
air: carries water vapour

ideal for finish drying and osmotic drying

29
Q

describe the role of MW and vacuum in VMD process

A

MW: expels water due to rapid heating
vacuum: removes moisture

30
Q

what are 3 common MW packaging materials?

A
  1. transparent materials
  2. reflectors
  3. receptors of suceptors
31
Q

describe transparent MW packaging materials

A

transmits MW energy to heat the product directly

32
Q

describe reflector MW packaging

A

completely reflect MWs, so they can produce product from exposure to MW

33
Q

describe receptor or suceptor MW packaging

A

can convert MW energy to IR

receptors on inside of package can create an oven inside the package (eg. crisping fries, pop corn)

34
Q

what is RF heating?

A

radio frequency heating

35
Q

describe RF heating

A
  • alternative to MW heating

- uses high penetrative power

36
Q

what are advantages of RF heating?

A
  • rapid
  • uniform
  • high penetration depth
  • high efficiency
  • short residence time
  • no heat transfer surfaces
37
Q

what is the main limitation of RF heating?

A

higher initial capital investment

38
Q

what are non-food and food applications of RF heating?

A

non-food: lumber, paper, textiles, plastics

food: drying biscuits, snack foods

39
Q

why is RF better for cooking meat products than MW?

A

MW is more common in domestic use

RF has

  • higher penetrative power than MW and more homogenous heating
  • better for aseptic processing and industrial applications
40
Q

what is the principle of Ohmic heating?

A
  • heat is generated via electric current passing through an electircally conducting food product
41
Q

what are other names for ohmic heating?

A

direct resistance
joule effect
electroconductive
electoresistant

42
Q

in ohmic heating, heating rate is proportional to…. (4)

A

electrical power
electrical voltage
electrical conductivity
salt content

43
Q

in ohmic heating, how can you match electrical conductivity?

A

by matching salt content

44
Q

what is ohmic heating ideal for?

A

asceptic processing

45
Q

what are advantages of ohmic heating?

A
  • rapid heating
  • don’t need heat transfer surface
  • no moving parts
  • quiet operation
  • easy process control
  • better E conservation
46
Q

what is a limitation of ohmic heating?

A

electrode corrosion due to stainless steel contact

47
Q

how can you minimize corrosion in ohmic heating?

A

high frequencies

48
Q

what does PEF stand for?

A

pulse electric field

49
Q

what are the principle of PEF?

A

preserving fluid foods via high voltage electrical pulses between 2 electrodes w/ food in between them

50
Q

compare PEF with ohmic heating

A

similar, except PEF has higher voltage and shorter cycles

51
Q

what foods is PEF usually used in?

A

liquid foods

52
Q

what three things effect microbial inactivation in PEF?

A
  1. electric field strength
  2. time of treatment
  3. temp of medium
53
Q

in PEF, when pH decreases, how does this affect microbial destruction?

A

dec pH = incr microbial destruction

54
Q

what are limitations of PEF?

A
  • no inactivation of bacterial spores (need to combine with temp)
  • good only for homogenous foods
  • not good w/ viscous fluids or foods w/ electrical conductivity
55
Q

describe pulsed light processing

A
  • intense and short duration pulses of white light
  • effective when light can access all important volumes and surfaces
  • can decontaminate food, package and contact surfaces

4) Food Processing (18 decks)

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