High Pressure Food Freezing Prof. Vinod Jindal 1 FST 151: FOOD FREEZING High Pressure Food Freezing Lecture Notes Prof. Vinod K. Jindal (Formerly Professor, Asian Institute of Technology) Visiting Professor Chemical Engineering Department Mahidol University Salaya, Nakornpathom Thailand

High Pressure Food Freezing Prof. Vinod Jindal 2 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.

High Pressure Food Freezing Prof. Vinod Jindal 3 Under high pressure, water shows an unusual freezing point depression to −22°C at 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.

High Pressure Food Freezing Prof. Vinod Jindal 4 Fig. 1 Phase diagram of water

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6 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.

High Pressure Food Freezing Prof. Vinod Jindal 7 In HPAF, an increase in pressure decreases the freezing and melting point of water to a minimum of -22 ◦ C at 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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9 Pressure transmitting medium? Water ? No applicability at sub-zero temperatures

High Pressure Food Freezing Prof. Vinod Jindal 10 Pressure transmitting medium? Water/ethanol ? % Ethanol in Water (v/v)Melting Temperature (°C) 24.8% % % % % % %-28.7 Organoleptic problems after treatment

High Pressure Food Freezing Prof. Vinod Jindal 11 [Source: International Association for the Properties of Water and Steam IAPWS] Thermophysical Properties

High Pressure Food Freezing Prof. Vinod Jindal 12 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.

High Pressure Food Freezing Prof. Vinod Jindal 13  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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High Pressure Food Freezing Prof. Vinod Jindal 16 Some Examples of Typical Freezing Curves

High Pressure Food Freezing Prof. Vinod Jindal 17 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.

High Pressure Food Freezing Prof. Vinod Jindal 18 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 )

High Pressure Food Freezing Prof. Vinod Jindal 19 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 )

High Pressure Food Freezing Prof. Vinod Jindal 20 Thank you for your attention