Emerging Technologies in Pasteurisation
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The thermal treatment of foodstuffs is carried out, inter alia, to the destruction of microorganisms and to inactivate enzymes. By this heating above all, the durability of the products is increased and the consumption due to a drastic reduction of bacteria, germs, spores, etc is harmless. The thermal pasteurization and sterilization of foods is based on tried and tested concepts, the D-value and z-value, performed . D-value (decimal reduction time) indicates how long a particular microorganism must be maintained at a predetermined temperature level in order to achieve a reduction in the number of microorganisms by 90% or a logarithmic cycle.The z-value shows the dependence of the D value of the temperature.
- Figure 1 D value of certain microorganisms in the pasteurization or sterilization of a specific temperature level
- Figure 2 Z-value of certain microorganisms in the pasteurization or sterilization to a certain temperature level
In principle, the higher the temperature, the lower the time required (D value) to achieve the desired reduction and vice versa. Thus, different time-temperature combinations come to the same result, thus reducing sterilization effect. Sterilization and pasteurization on the basis of the D-value is still a successful concept, which is mainly due to the fact that in the food industry, a safety margin is used, which does increase the elimination of microorganisms and thus food safety, but increases the thermal load and thus the quality will be reduced. An even gentler thermal treatment of food would direct heating of the product through the use of direct steam or of ET, such as MW or RF .
- Figure 3 Comparison between different methods of Pasteurisation/Sterilisation
Conventional Pasteurisation of Fruit preparation
The fruit preparations produced are made from fruit, sugar and other additives. The fruits are stored frozen and thawed prior to processing . After thawing the fruits they are mixed with sugar and other additives and again cooled to -10 ° C. Subsequently, the pasteurization of fruit preparations in batch mode occurs. In principle, the pasteurization is performed so that the fruit preparation is heated (indirectly) to 92 ° C with steam as the heating medium, and then cooled again to 35 ° C by cold water before being packaged and subsequently stored at 10 ° C. On the one hand there are systems in which the heating and cooling is carried out in the same container , on the other hand plants are used in which the heating and subsequent cooling is carried out in separate containers. In principle, carried the cooling of 92 ° C hot fruit preparation over two steps. In a first step (cooling zone 1) the fruit preparation is cooled by cold water from a cooling tower of 92 ° C to 55 ° C. In a second step (cooling zone 2) the fruit preparation is cooled by cold water from a NH3 refrigeration system from 55 ° C to 35 ° C .
- Figure 4 Flowsheet showing pasteurization of fruit preparations
Potential ET for the pasteurisation and their evaluation
Since the specific energy consumption of conventional thermal pasteurization or sterilization methods by large heat recovery potential may be very low (preheating of the feed with the heat from the already heat treated feed), appropriate ET for the reduction of find thermal load on the product by lowering the process temperature levels without the required process time is increased significantly.The process time (cycle time) depends on the thermal pasteurization greatly on the process temperature. In principle, lower temperatures in the thermal pasteurization could well be used, but means a lower temperature, a longer cycle time and this is often undesirable because certain throughput must be achieved.
PASTEURIZATION - ULTRA HIGH PRESSURE METHOD
Principle and procedure of the UHP process
The conventional thermal pasteurization of food products is carried out in the destruction of microorganisms and to inactivate enzymes. By this heating above all, the durability of the products is increased and the consumption due to a drastic reduction of bacteria, germs, spores, etc. harmless. On the other hand, the quality is reduced by the thermal load of the product.In contrast to conventional pasteurization, the process is non-thermal and offers high-quality, fresh-tasting products that are microbiologically safe beyond that and have a long shelf life. UHD for pasteurization or in the production of food was first in Japan, then in the United States and in Europe already industrially in the production and processing of jams, fruit juices, guacamole (avocado), meat products (eg ham), fish (eg oysters), soups and other precooked ready meals etc.
Most UHD systems used in industry work in batch mode, but there are also semi-continuous systems. The selection of the plant or process depends on the product to be treated as solid foods or foods that contain large, solid pieces, only in batch mode can be processed while other liquids and pumpable products in a semi-continuous system can be treated. The industrially used UHD systems, which are designed for batch operation, consist of a pressure vessel with a capacity of about 35-350 liters, a druckübertragendem medium (usually water) and one or more pumps to generate pressure. To be treated, already packaged product is placed in the pressure vessel, which is closed and subsequently filled with the druckübertragendem medium.
The pressure is then increased either further through the pump the medium in the pressure chamber or by the reduction of the volume of the pressure chamber, for example, by a bolt (piston).The pressure is uniformly transmitted to the pressure transmitting medium, and thereby also to the product. By the transfer of the isostatic pressure, the entire product is subjected to the same pressure level at the exact same time and thus there are no significant changes in product shape. After the required treatment time during which the product must be subjected to a certain pressure, the pressure in the chamber is reduced to open the pressure chamber and the product can be removed from the pressure vessel.
In UHP treatment of liquid or pumpable foods, the pressure chamber can be filled completely with the product and the product itself will be characterized for the pressure-transmitting medium. If this is the case, according to the UHP treatment is an aseptic packaging in order to exclude recontamination of the product may be required. By a possible series circuit of pressure vessels, comprising a container which is filled with liquid food, a container in which the UHP treatment is carried out and a container for emptying, with simultaneous operation of the container is a semi-continuous process can be carried out .
Processes used in UHP process pressures are usually between 50 and 1000 MPa (~ 500-10,000 bar) . With pressure chambers, which are made of a block, the application of the UHP process is limited to a capacity of 25 liters and an applied pressure of 400 MPa. For the processing of larger volumes and for the application of higher pressures prestressed wire wound vessel for safe, long-term and reliable performance must be used. The same applies to the bracket, which are used for the support of the lid and the bottom of the chamber. Due to the necessary windings but increase the system cost. A second technological barrier exists at 680 MPa, because there is this pressure, at least according to technological level in 2005, no pressure chambers, which can be used in industry .
- Figure 5 UHP Process
Literature: Ulrike Herzog (2012)Möglichkeiten des Einsatzes von „Emerging Technologies“ in der Lebensmittelindustrie zur thermischen Energieverbrauchs-senkung und zur Einbindung von Solarthermie