high pressure food freezing prof. vinod jindal 1 fst 151: food freezing high pressure food freezing...
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High Pressure Food Freezing Prof. Vinod Jindal
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FST 151: FOOD FREEZING
High Pressure Food Freezing Lecture Notes
Prof. Vinod K. Jindal(Formerly Professor, Asian Institute of Technology)Visiting ProfessorChemical Engineering DepartmentMahidol UniversitySalaya, NakornpathomThailand
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Application of High Pressure Technology to Freezing and Thawing of Foods
With the recent increasing impact of high-pressure technology on food processing, there has been a lot of research dealing with the potential applications of high-pressure effects on ice-water transitions.
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Under high pressure, water shows an unusual freezing point depression to −22°C at 207.5 MPa. In addition to the conventional ice I, various solid phases with a higher density than liquid water (ice II to ice V) exist in the pressure range between 210 and 500 MPa, as visualized in Fig. 1.
This has led to the development of several high-pressure freezing and thawing processes.
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Fig. 1 Phase diagram of water
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According to the path followed by the process in the phase diagram of water, three different types of high-pressure freezing processes can be distinguished in terms of the way in which the phase transition occurs.
These include high-pressure assisted freezing (HPAF), high-pressure shift freezing (HPSF) and high-pressure induced freezing (HPIF). It is generally accepted that HPSF processes are the most advantageous.
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In HPAF, an increase in pressure decreases the freezing and melting point of water to a minimum of -22◦C at 207.5 MPa. Thus, the ice nucleation rate subsequently increases at a much lowered temperature causing ice formation to occur.
In case of HPSF, the sample is cooled under high pressures without causing freezing. Once the pressure is released the sample freezes instantly resulting in the formation of more uniform ice crystals.
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Pressure transmitting medium?
Water ?• No
applicability at sub-zero temperatures
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Pressure transmitting medium?Water/ethanol ?
% Ethanol in Water (v/v) Melting Temperature (°C)24.8% -10.627.0% -12.229.5% -14.032.4% -16.036.1% -18.940.5% -23.646.3% -28.7
• Organoleptic problems after treatment
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Density
950
1000
1050
1100
1150
-25 -5 15 35
Temperature (°C)
Dens
ity (k
g/m
3)
240 MPa
0.1 MPa
Specific Heat
3
3.2
3.4
3.6
3.8
4
4.2
-25 -5 15 35
Temperature (°C)
Spec
ific h
eat (
J/g°
C)
0.1 MPa
240 MPa
Thermal Conductivity
0.55
0.6
0.65
0.7
0.75
-25 -5 15 35
Temperature (°C)
Ther
mal
cond
uctiv
ity
240 MPa
0.1 MPa
[Source: International Association for the Properties of Water and Steam IAPWS]
Thermophysical Properties
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The benefits of high pressure freezing techniques are:
• Increased rate of freezing • Higher density ice polymorphs • Smaller ice crystal formation • Uniform crystal formation
Polymorphs have different stabilities and may spontaneously convert from a metastable form (unstable form) to the stable form at a particular temperature.
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Homogeneous crystallization and smaller crystalls (PSF) Shorter phase transition times by higher T (PAF & PSF) Enzymathic inactivation - quality of products (less browning)
Microbial inactivation & permeabilization
Texture maintenance: positive V by liquid-ice III
1. HPLT processing – Effects of HPLT on foods
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Blast air Pressure Shif t Freezing
(G 400)
CELL
I CE
I CE
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Some Examples of Typical
Freezing Curves
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Figure 1.8 Time-temperature profiles for freezing a meat sample in a blast freezer system at -25ºC temperature and 4.5 m/s air speed.
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Figure 2: Effect of the sample thickness (L = 6mm, 13 mm, 26 mm) on temperature histories of the beef mince slabs frozen in an air blast freezer. (International Journal of Engineering and Technology, Vol. 3, No.2, 2006, pp. 182-190)
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Figure 3: Experimental temperature histories of the beef mince slab (L = 13mm) covered with different types of packaging films.
(International Journal of Engineering and Technology, Vol. 3, No.2, 2006, pp. 182-190)
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Thank you
for
your attention