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FOSC302 > Microwave and ohmic heating > Flashcards

Microwave and ohmic heating Flashcards

(53 cards)

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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

Study These Flashcards
A

convert electricity into electromagnetic waves

23
Q

purpose of wave guides

Study These Flashcards
A

aluminium tubes that guide the waves into the chamber

24
Q

purpose of metal chamber

Study These Flashcards
A

used in batch operations, to place the food product into

25
main problem with when energhy transfer rates are too high
non-uniform heating
26
what else can result in uneven heating
variation in moisture and composition of food
27
effect of dissolved salt in food
hinders microwaves
28
what can microwaves be used ot limit
browning case hardening sensory damage
29
how can microwaves be used in baked products
prevent furthur colour change but ensure baking by having them at the end of tunnel ovens
30
how can microwaves improve pasta processing
reduce drying time from 8h to 90 mins reduce bacterial counts by 15x
31
advantages of microwaves for conventional thawing
faster less storage space required no drip loss lower labour requirements more hygenic better control
32
major advantage to ohmic heating
heating takes place volmetrically and the product does not experiance a large temp gradient during heating
33
advantage of ohmic heating over microwave
depth of oenetration is not limtied and the extent of heating is determined by the electrical conductivity throughout tge product and resistance time
34
how long does it take to heat to sterilisation and cool a product using ohmic heating
less than 90 sec to get to 140C and 15 mins to cool
35
quality benefits of ohmic heating
better nutritonal retenion less softening of delicate particulates
36
principles of ohmic heating
a food of electrical conductivty is placed between two electrodes with a field strenght betweeen them resulting in energy generation
37
what is the critical property that affects energy generation rate
s: electrical conductivity
38
what does the electrical conductivity of solid foods depend on
temperature and voltage gradient
39
describe ohmic heating process for viscous foods
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
ohmic heating processes (4)
pastuerisation aseptic processing pre-heating hygenic production
41
objectives of each heating processes
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
typical food application for each heating process
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
typical food products produced by ohmic heating
high acid: pasta sauce, fruit compote, pie fillings low acid: tortellini in sauce, vege curries
44
things to consider about particulate of processing product
size, shape, concentration, density conductivity, specific heat capacity
45
size of particulates and things to consider
less than 25mm, flexible and elongate -needs to clear electrodes, size to eat
46
particulate concentration considerations
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
particulate density considerations
only an issue if significantly different from one another
48
carrier medium considerations
needs to be able keep particulates in suspension -changes due things like gelatinisation can result in uneven heating
49
what are ohmic heating rates dependant on
electrical conductivity of food
50
process and installation cost comparison for ohmic heating, freezing and retorting for low acid
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
process and installation cost comparison for ohmic heating, freezing and retorting for high acid
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
is ohmic better for high acids foods
cost: not better quality: way better
53
advantages ohmic heating
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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