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FOSC302 > Microwave and ohmic heating > Flashcards

Microwave and ohmic heating Flashcards

1
Q

impact of microwaving on microrganisms is similar to?

A

traditional methods

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2
Q

how is heat generated by microwaving

A

the molecules become excited and movement causes friction which generates heat

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3
Q

describe thermal gradients of traditional vs microwave

A

traditional have a large heat gradient as food is heated from outside in which varies the nutritional and textural properties of food
-microwave is more homogenous as food is heated from within the product

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4
Q

define microwaves

A

very short wave lengths of electromagnetic energy

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5
Q

frequency of microwave ovens

A

2450 MHZ (home)
900mhz (commercial)

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6
Q

type of electric fields microwaves produces

A

rapid oscillating fields
-2 waves 90 degrees between them
-1 electric, 1 magnetic

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7
Q

how do the waves generate friction

A

placing a dipole product between the waves results in product changing in orientation to match the fields which generates movement and friction

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8
Q

explain the dipole in water

A

oxygen is negative, hydrogen is positive

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9
Q

other polar molecules in food include…

A

protein and carbohydrates

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10
Q

what determines the dielectric constant of a food

A

number of dipoles and changes induced by the electric field

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11
Q

what is the dielectric constant

A

measure of the ability of a material to store electromagnetic radiation

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12
Q

what is the dielectric loss factor

A

measure of the abiliity of a material to dissipate electrical energy into heat

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13
Q

what is penetration depth

A

ability of wavelength to penetrate food

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14
Q

what is a limitation to having a food than can convert electrical to heat energy really fast

A

it stops penetration so cooking may be uneven and cold spots can occur

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15
Q

explain how cold spots occur

A

when overlapping of the waves occurs

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16
Q

what is the amount of electromagnetic energy depnedant on

A

loss factor of material

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17
Q

types of heat transfer in food

A

convection and conduction

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18
Q

will a product with a low loss factor be heated

A

no,
glass, plastic adn paper are transparent to microwaves

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19
Q

what type of material reflect microwaves

A

metals

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20
Q

lower wave power generates _____ loss factor

A

higher

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21
Q

3 components to a microwave

A

microwave generator (magnetron)
wave guides
metal chamber

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22
Q

purpose of microwave generator/magnetron

A

convert electricity into electromagnetic waves

23
Q

purpose of wave guides

A

aluminium tubes that guide the waves into the chamber

24
Q

purpose of metal chamber

A

used in batch operations, to place the food product into

25
Q

main problem with when energhy transfer rates are too high

A

non-uniform heating

26
Q

what else can result in uneven heating

A

variation in moisture and composition of food

27
Q

effect of dissolved salt in food

A

hinders microwaves

28
Q

what can microwaves be used ot limit

A

browning
case hardening
sensory damage

29
Q

how can microwaves be used in baked products

A

prevent furthur colour change but ensure baking by having them at the end of tunnel ovens

30
Q

how can microwaves improve pasta processing

A

reduce drying time from 8h to 90 mins
reduce bacterial counts by 15x

31
Q

advantages of microwaves for conventional thawing

A

faster
less storage space required
no drip loss
lower labour requirements
more hygenic
better control

32
Q

major advantage to ohmic heating

A

heating takes place volmetrically and the product does not experiance a large temp gradient during heating

33
Q

advantage of ohmic heating over microwave

A

depth of oenetration is not limtied and the extent of heating is determined by the electrical conductivity throughout tge product and resistance time

34
Q

how long does it take to heat to sterilisation and cool a product using ohmic heating

A

less than 90 sec to get to 140C and 15 mins to cool

35
Q

quality benefits of ohmic heating

A

better nutritonal retenion
less softening of delicate particulates

36
Q

principles of ohmic heating

A

a food of electrical conductivty is placed between two electrodes with a field strenght betweeen them resulting in energy generation

37
Q

what is the critical property that affects energy generation rate

A

s: electrical conductivity

38
Q

what does the electrical conductivity of solid foods depend on

A

temperature and voltage gradient

39
Q

describe ohmic heating process for viscous foods

A

enter continous-flow ohmic heating system through a feed pump hopper
twin-pisotn positive displacement metering pump minimises particle damage
product flows past a series o felectrodes in heating column to reach sterilising temp
product enters holding tube
then flows into tubular coolers andholding tanks before being aseptically filled

40
Q

ohmic heating processes (4)

A

pastuerisation
aseptic processing
pre-heating
hygenic production

41
Q

objectives of each heating processes

A

pasteurisation: inactivate vegetative microorgansism/ extend shelf life
Asepetic processing: inactivate microbial spores, commercially sterile
pre-heating: heat during processing stage
hygenic production: heating and inactivation of vegetative microorganisms

42
Q

typical food application for each heating process

A

aseptic processing: pumpable particulate (ready made sauces etc)
pasteurisation: pumpable particulate for fruit and high acid foods
pre heating: in-can sterilisation products
hygienic production: ready meals

43
Q

typical food products produced by ohmic heating

A

high acid: pasta sauce, fruit compote, pie fillings
low acid: tortellini in sauce, vege curries

44
Q

things to consider about particulate of processing product

A

size, shape, concentration, density conductivity, specific heat capacity

45
Q

size of particulates and things to consider

A

less than 25mm, flexible and elongate
-needs to clear electrodes, size to eat

46
Q

particulate concentration considerations

A

20-70%, higher conc can be processed if particualtes are pliable, small and varied shape
-lower conc require more viscous solution to maintain dispersion

47
Q

particulate density considerations

A

only an issue if significantly different from one another

48
Q

carrier medium considerations

A

needs to be able keep particulates in suspension
-changes due things like gelatinisation can result in uneven heating

49
Q

what are ohmic heating rates dependant on

A

electrical conductivity of food

50
Q

process and installation cost comparison for ohmic heating, freezing and retorting for low acid

A

installation
freezing: 4.4M
retorting: 3.2 M
ohmic: 19.2M
10 year cost
freezing: 1.12/kg
retorting:1.44/kg
ohmic: 0.94/kg

51
Q

process and installation cost comparison for ohmic heating, freezing and retorting for high acid

A

installation
freezing: 1.1M
retorting: 3.9 M
ohmic: 9.6M
10 year cost
freezing: 0.36/kg
retorting:0.36/kg
ohmic: 0.63/kg

52
Q

is ohmic better for high acids foods

A

cost: not better
quality: way better

53
Q

advantages ohmic heating

A

fresh tasting: shorter process time
not hot surfaces that can damage product
high particulate solutions can be processed
particulates remain firm

FOSC302 (14 decks)

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