Food or edible material: processes – compositions – and products – Direct application of electrical or wave energy to food... – Involving dielectric heating or passage of electric current...
Reexamination Certificate
2001-09-24
2004-08-10
Yeung, George C. (Department: 1761)
Food or edible material: processes, compositions, and products
Direct application of electrical or wave energy to food...
Involving dielectric heating or passage of electric current...
C426S521000
Reexamination Certificate
active
06773736
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method for treating products, which may contain cellular material of eukaryotic and or prokaryotic origin, in particular micro-organisms, located in a device comprising two electrodes onto where voltage cycles are imposed by an auxiliary electric source such that in the device and in the product electrical fields are created for a short period of time.
A prior art method of this type is known as the Pulsed Electric Field (PEF) process.
BACKGROUND OF THE INVENTION
Many biological systems, such as micro-organisms, comprise a cell membrane to regulate its energy balance. Cell membranes consist of a lipid double layer whereby the lipids are made of a polar head and a fatty acid tail. Metabolic processes are regulated by said cell membrane. Physical damage of the cell membrane may lead to inactivation of the system or to an increase of the exchange of mass transport through the membrane such as inter-cellular material and/or compounds present in the bulk of the product. In the case of micro-organisms damage to the cell membrane may lead to inactivation of the organism such that the cell division process will be interrupted or its functional abilities to produce metabolic compounds is affected
Damage to the cell membrane of micro-organisms may be caused by bringing the micro-organisms into a high electric field. An sufficiently high externally imposed potential difference across the micro-organism is believed to lead to damage of the cell membrane as it leads to the inactivation of the micro-organisms as such. A treatment based on PEF can performed by using a pulsed DC voltage source. The above mentioned PEF process relies on the use of high voltage pulses to generate a pulsating electric field of in a product of such a short duration that the heating of the bulk product is restricted.
A very simple system in which the PEF-method is applied is described in U.S. Pat. Nos. 5,393,541 and 5,447,733. Both related publications illustrate a system comprising a container which is filled by product to be treated and a metal electrode which is lowered into the container. The container itself forms the other electrode and both electrodes are connected to a power supply delivering pulses of at 2 kV or more with a duration of typically two microseconds.
Another embodiment of a chamber for treating fluid products according to the PEF-method is described in U.S. Pat. Nos. 4,695,472 and 4,838,154. In this embodiment two flat electrodes are positioned opposite each other with a flow channel in between. Both electrodes are connected to a power source which during operation generates pulses. In this configuration a pulsed electrical field is produced within the product inside the channel in agreement with the PEF-method. As described, in both patents the product is subjected to high electric field pulses each having a minimum field strength of at least 5 kV/cm and each having a duration of at least about one micro-second. Preferably a duration in the range from about 5 to about 100 micro-seconds.
A further example of a system in which a PEF-method is performed is described in U.S. Pat. Nos. 5,235,905, 5,776,529 and an article with the title “Inactivating Micro-organisms Using a Pulsed Electric Field Continuous Treatment System” by Bai-Lin Qin published in IEEE Transactions on Industrial Applications, Volume 34, nr. 1, 1 February 1998, pages 43/49. This prior art system comprises a socalled coaxial treatment chamber. During operation electrical pulses are supplied to both electrodes such that electrical field strengths in the range of 35 to 55 kV/cm are developed. Preferred pulse duration's are less than 100 milliseconds, more preferably in the range of 0.1 to 100 microseconds and even more preferably in the range of approximately 0.2 to 10 micro-seconds.
A system comprising a series of tubular treatment chambers is described in U.S. Pat. No. 5,690,978. Each chamber has electrically conducting end-sections, which act as electrodes separated by a non-conducting intermediate section. During operation a pulsed electric field is developed in the treatment chamber with a typical pulse duration time of three microseconds at an applied electric field strength of E=30 kV/cm whereas the temperature reaches a maximum T=36° C.
In all these prior art systems the medium to be treated has to be in physical and electrical contact with both the electrodes during the treatment.
A different mode of treatment is described in an article with the title “Inactivation of Yersinia enterocolitica Gram-Negative Bacteria using high voltage pulse technique” by Piotr, Lubicki et al published as record of the industry application conference (IAS, Orlando, Oct. 9/12, 1995, Volume 2, Number 30, pages 1338-1344, Institute of Electrical and Electronics Engineers ISBN 0-7803-3009/9, page 1339, column 1, lines 3-24). In this article a treatment device is described comprising a cylindrical electrode system including a rod shaped inner electrode inside a cylindrically shaped outer electrode. The inner electrode is connected to a source of high voltage pulses and the outer electrode is electrically grounded. The product to be treated is contained between both electrodes in a helical shaped glass tube and the remaining space within the electrode system is filled with water.
During operation a pulsed electrical field is developed between the electrodes where the rise time of each pulse is between 500 and 1300 nanoseconds and the voltage has a peak value equal to 45, 60 or even 75 kV. The article, however, does not provide any information about the electrical field strength within the product to be treated nor the processing temperatures of the product. In the article it is stressed that “in order to cause electroporation of a cell membrane, the voltage magnitude must be high enough to induce suitable value of transmembrane potential for breakdown of the membrane, and at the same time, duration of the voltage pulse must be at least higher then the relaxation time of a bacteria suspension”. The product to be treated in the described model is a solution of NaCl in water for which ∈=0.7 nF/m with an electrical conductivity between 0.8 and 1.2 S/m. The relaxation time is therefore between 0.6 and 0.9 nanoseconds. In other words, the above mentioned rise time of 500 to 1300 ns is indeed significantly larger than the relaxation time of the product to be treated. It is furthermore indicated that “there is no remarkable effect of increasing rise time within the range of 500 to 1300 ns”.
OBJECT OF THE INVENTION
An objective of the invention is now to provide another method for treating suitable products, which may contain micro-organisms by developing pulsed electrical fields within the product by a different coupling. More specific it is an objective of the invention to provide a method for mild preservation of products where direct contact between the product and the electrodes is not required and where a different phenomenon is exploited to produce a substantial electrical field inside a product.
THE INVENTION
In agreement with these objectives, the invention now provides a method for treating products by bringing the product into a treatment device containing two electrodes onto which a rapidly changing high voltage difference is imposed. The two electrodes are connected to an electronic circuitry such that the device and the product are subjected to a time dependent voltage. The time dependence of the imposed voltage is primairily characterised by the rise time of the voltage which is in duration shorter than the so-called relaxation time of the product. The relaxation time has to be understood as the time necessary to obtain a complete separation of charges in a product from the moment an external voltage difference is induced over a product column. The charges in a food product may be the result of a mineral salt content of e.g. NaCl or KCl. In foodstuffs of sufficiently high water content the NaCl molecules are dissolved as Na+ and Cl− ions. The relaxat
Bartels Paul Vincent
De Winter Edwin Johannus Gerardus
Mastwijk Hendrikus Cornelis
Ato B.V.
Yeung George C.
Young & Thompson
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