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Electromagnetic Radiation Applications in Food Processing
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Electromagnetic radiation
applications in Food Processing
Alistair Grandison
Modules FB2EFP, FBMFP1,
FBMFP2
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• Some refs for Modules FB2 EFP and FBM FP1 – EM processing and novel processes
• Food Processing Handbook (2011) J.G.Brennan & A.S.Grandison(ed.), Wiley-VCH (on line
access available)
•
• Ramaswamy, H. and Marcotte, M. (2006) Food Processing : Principles and applications.
Taylor & Francis, London
•
• Barbosa-Canovas, G.V. et al. (1998) Nonthermal preservation of food, Marcel Dekker, New
York.
•
• Fellows, P.J., Food Processing Technology: principles and practice, 3rd Ed., Woodhead
Publishing Ltd., Cambridge, 2009
•
• Brennan J.G., Butters, J.R., Cowell, N.D and Lilly, A.E.V., Food Engineering Operations, 3rd
edition, Elsevier Applied Science, London,1990 – out of print now unfortunately
•
• “Electromagnetic Radiation Properties of Foods and Agricultural Products” N N
MOHSENIN; 1984; Gordon & Breach
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What is EM radiation?
Is it a wave form?
OR
Does it consist of particles?
Answer - Well yes and no really to both questions!!
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Speed of light (3 x 108 ms-1) c = F λ
(F=frequency, Hz; λ=wavelength, m)
Consider EM radiation to be stream of photons – a photon is a
“quantum” of energy which possesses no resting mass, but
contains energy and momentum.
Energy of photon increases with F:
Energy of photon (J) Ep = hF
(where h=Plank’s constant, 6.63 x 10-34 Js).
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Listed below are the approximate wavelength, frequency, and energy limits
of the various regions of the electromagnetic spectrum.
Wavelength (m) Frequency (Hz) Energy (J)
Radio > 1 x 10-1 < 3 x 109 < 2 x 10-24
Microwave 1 x 10-3 - 1 x 10-1 3 x 109 - 3 x 1011 2 x 10-24- 2 x 10-22
Infrared 7 x 10-7 - 1 x 10-3 3 x 1011 - 4 x 1014 2 x 10-22 - 3 x 10-19
Optical 4 x 10-7 - 7 x 10-7 4 x 1014 - 7.5 x 1014 3 x 10-19 - 5 x 10-19
UV 1 x 10-8 - 4 x 10-7 7.5 x 1014 - 3 x 1016 5 x 10-19 - 2 x 10-17
X-ray 1 x 10-11 - 1 x 10-8 3 x 1016 - 3 x 1019 2 x 10-17 - 2 x 10-14
Gamma-ray < 1 x 10-11 > 3 x 1019 > 2 x 10-14
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Chemical analysis of foods by EM
• UV – e.g. proteins absorb at 280 nm
• Visible range – many colorimetric assays
• IR – e.g. Dairylab/Lactoscope
• Much research into non-invasive analysis
of foods – both chemical analysis and
texture
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Sorting & Grading etc. – usually
based on reflectance
• Ripeness – red/green tomatoes
• Removal of e.g. blackened peas and
beans or blemished fruit and vegetables
• Detection of fruit pips – e.g. cherries
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Wavelengths used for processing
• Solar drying
• UV sterilisation – e.g. packaging materials
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Wavelengths used for heat
processing
• Infra red
• Dielectric principle • - Microwaves
• - Radiofrequency
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Stefan’s law Rate of energy emission from a radiating body:
Q = σ ε A T4
(Js-1
) (m2)(K
4)
σ = Stefan’s constant = 5.7 x 10-8
Js-1
m-2
K-4
ε = Emissivity (1 for black body ; 0 for perfectly reflecting or
transmitting material)
A = surface area; T = Absolute temp.
The net rate of heat transfer between two bodies:
Q = ε σ A (T 4
1 - T 4
2 )
Where T1 (K) is the temperature of the emitter and T2 (K) is the
temperature of the absorber
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INFRA RED HEATING
IR energy produced by radiant heaters:
Electrical – Ni/Cr/Fe alloy filaments in metal or ceramic
sheath (500-10000 C surface temp); or W sheathed in quartz (up
to 30000 C)
Gas (up to 9000 C).
Radiant energy converted to heat directly on absorption by
directly increasing molecular motion of molecules (not dielectric
effects).
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Depth of penetration D
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Approximate depth of penetration of IR
radiation
(λ approx. 1μm)
Material Depth (mm)
Ice 30
Bread 7-12
Dough 4-6
Raw potato 6
Apple 4
Tomato paste 1
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To avoid interference with radio and telecommunications only
certain permitted frequencies – major ones are:
Microwave – 2450 and 915 (896 in Europe) MHz
Dielectric – 27.12 MHz
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Rate of heating derived from power developed in
the “dielectric” (P0)
P0 = 55.61 x 10-14 E2 . F . εr . tan δ
E = electrical field strength
F = frequency
εr = relative dielectric constant
tan δ = loss tangent
The term εr . tan δ is known as the “loss factor” (referred to as ε″r
in some publications) depends on composition of food, and varies
with temperature and frequency.
E and F are properties of machinery.
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e1
21
)tan.(2
r
D = Depth of penetration (distance at which power
falls to
th incident power):
D ≈
e.g. for water at 950C : D=29.5cm at 915 MHz; D=4.8
cm at 2450 MHz).
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Characteristics of radiofrequency
• Very fast heating (one tenth conventional)
• Penetrative
• Local overheating minimised
• Working space reduced
• Clean, continuous, automatic
• No surface browning
• Directional
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Microwaves
• Rapid, in-depth heating
• Compact, flexible processing lines
• Material heated inside insulating
packaging
• Disadvantage – expensive in terms of
equipment and energy
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