Food or edible material: processes – compositions – and products – Direct application of electrical or wave energy to food...
Reexamination Certificate
1999-11-03
2001-05-15
Bhat, Nina (Department: 1761)
Food or edible material: processes, compositions, and products
Direct application of electrical or wave energy to food...
C426S241000, C426S665000, C422S022000, C422S033000, C422S295000, C422S296000, C099S451000, C099S473000
Reexamination Certificate
active
06231908
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates a method of preserving a food product, wherein the food product is forced through a treatment system having an entrance and an exit while a pressure difference of at least 10 MPa is substantially maintained between the entrance and the exit, wherein the product is subjected to a varying electric and/or magnetic field, and to an apparatus for preserving food products, comprising at least one treatment system having an entrance and an exit, a high-pressure generating means for forcing a product through the treatment system, while substantially maintaining a pressure difference of at least 10 MPa between the entrance and the exit, and means for generating a varying electric and/or magnetic field and for subjecting the product to the varying electric and/or magnetic field. “Entrance” and “exit” are herein to be understood as to describe the part where at least part of the treatment occurs. Prior to the entrance, there will be pressurising means, and prior to the pressurising means there will be a storage of food product which is to be preserved. Hence, the foodproduct to be preserved will go from storage, pressurising means, entrance, a phase of high pressure, pressure reduction, to an exit.
Such a method and apparatus are disclosed in International patent application WO 97/43914. Ultra-high pressure (UHP) preservation is a technique which allows micro-organisms in food products to be destroyed, or at least inactivated, without substantially increasing the temperature of the product. Thus, the disadvantages of heat treatments such as pasteurisation and sterilisation, often affecting the quality (taste, nutrients) of the product, are avoided. The pressures involved in UHP-preservation are extremely high, typically several hundred MPa. The method described allows a continuous process which especially in the food industry is particularly advantageous.
In the known apparatus, the treatment system includes one treatment chamber having a load impedance, wherein the means for generating the varying field has a characteristic impedance matched to the load impedance in order to obtain an optimal energy transfer from the generating means to the treatment chamber. However, an unwanted effect of the varying field is that the food product is also heated up during the treatment. Under normal operation, the heating of the product can reach 30° C. or more. Heating the product causes a decrease of the load impedance of the treatment chamber and this impedance change results in a temperature dependent mismatch of the load impedance and the characteristic impedance of the generating and subjecting means. This unwanted effect results in an energy transfer between the generating means and the treatment chamber which is temperature dependent.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome the problems of the prior art and to provide a method and apparatus for preserving food products which allow an even better preservation without increasing the required pressure.
It is another object of the present invention to provide a method and apparatus for preserving food products which allow a thorough inactivation of micro-organisms while maintaining the advantages of a continuous treatment.
Accordingly, these and other objects are met by a method of the above-mentioned kind which, according to the present invention, is characterized in that a treatment system with a plurality of treatment chambers is used, wherein the treatment chambers are electrically connected to reduce impedance variations of the treatment system during the preserving of the food product, and wherein the treatment chambers are series connected for the food product flow.
By subjecting the product to a varying electric and/or magnetic field in this manner load impedance variations caused by temperature increase of the food product during the preservation treatment can be minimised, so that the energy transfer between the generating means and the treatment system is significantly reduced. This guarantees an improved control of the preservation treatment.
In a preferred embodiment of the invention four treatment chambers are used, the treatment chambers being electrically connected in a Wheatstone bridge configuration. In this manner a compensation of the load impedance variation of the treatment chambers is obtained in a simple manner resulting in a load impedance of the treatment system which is less dependent of the food product temperature.
A dual treatment is achieved which even more efficiently inactivates both micro-organisms and spores. In order to obtain a sufficient UHP-effect the pressure difference between the entrance end and the exit end of the tube is preferably at least 100 MPa, possibly at least 300 MPa. However, due to the synergy between the pressure treatment and the electric field treatment, for the same degree of inactivation the required pressure is less than the one applied in the prior art process. Forcing the product through the treatment system and the step of subjecting the product to a varying electric field are preferably carried out simultaneously. In this way, the food product is subjected to two different treatments simultaneously, resulting in an optimal synergy of the two treatments. It is, however, also possible to apply the two steps one after the other.
In the method of the present invention, the varying electric field may be applied directly or be induced by a varying magnetic field, independently of the way the varying magnetic field is generated. A suitable method of generating a varying magnetic field for preserving food products is described in Dutch patent application PCT/EP99/0672 of the same Applicant. Alternatively, a varying magnetic field may be used instead of the varying electric field, or a combination of a magnetic and an electric field may be applied.
The present invention further provides an apparatus for preserving food products of the above-mentioned kind, characterized in that the treatment system comprises a plurality of treatment chambers which are electrically interconnected to reduce impedance variations of the treatment system and which are series connected for the food product flow.
Additionally, the present invention provides a food product which is preserved by the above-mentioned method.
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“Inactivation ofBacillus subtilisendospores by UHP in combination with other treatments”, Heinz et al. IFT Annula Meeting 1995; Dep. of Food Scie., Univ. of Tech, D-14195 Berlin Germany p. 268.*
“The heat is off”, Byrne, Food Engineering International, (1993) 18(1) p. 34-38.
Lelieveld Hubertus Leonardus
Volanschi Alexandru
Bhat Nina
Farrell James J.
Lipton division of Conopco, Inc.
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