MXPA99011386A - Preferential heating of materials by use of non-ionising electromagnetic radiation - Google Patents

Abstract

Se presenta un método y aparato para el calentamiento preferencial de un material, los cuales se basan en la exposición del material a una radiación electromagnética de alta intensidad, pulsada, no ionizante. El método puede destruir microorganismos, esterilizar empaques, o bien esterilizar alimentos húmedos. Una modalidad. emplea radiación de microondas con duración de impulso de menos de 0.1 segundo con una potencia media de al menos 1 LW para esterilizar latas metálicas de extremo abierto antes del empaquetado.

Description

PREFERENTIAL HEATING OF MATERIALS USING NON-IONIZING ELECTROMAGNETIC RADIATION The present invention relates to the special heating of materials by non-ionizing electromagnetic radiation. The term "non-ionizing electromagnetic radiation" includes, for example, microwave radiation, and radio wave radiation. A particular, but not exclusive, use of the present invention is to preferentially heat microorganisms at temperatures that destroy microorganisms. This use of the present invention has several applications.

One application is the medical industry in which the invention can be employed, for example, to sterilize pharmaceutical products, packaging for pharmaceutical products, as well as surgical and other equipment. Another application that is particularly interesting for the applicant is the food processing industry. The term "food processing industry" encompasses the industry involved in the preparation and packaging of food products, including solid and liquid food products. It is a critical requirement of the food processing industry: (i) to sterilize food products after the packing of food products; or (ii) prepare and then pack food products under sterile conditions. An example of the first category is the widely used method of packaging beverages such as beer, which includes the pasteurization of beverages. Typically, a suitable package, for example metal or glass containers, is filled with beverages, the package is sealed, and the packaged beverages are then heated to a temperature comprised between 65 and 70 ° C for 15 minutes. This method, while effective, has numerous disadvantages including substantial capital and operating costs. Another example of the first category is the known method of spice sterilization. Typically, a suitable package is filled with spices, the packaging is sealed and then ethylene oxide is permeated through the high pressure packing and comes into contact and destroys microorganisms in the spices. While ethylene oxide is an efficient means to destroy bacterial spores and other microorganisms that present spices, it is toxic and therefore the removal of residual ethylene oxide at low levels is critical. Inevitably, this includes careful control of the method which in turn increases operating costs.

An example of the second category is the packaging of beverages under aseptic conditions. Typically, the beverages are prepared and taken to a filling station under sterile conditions, the filling equipment is kept under sterile conditions, the packaging is sterilized and transported to the filling station under sterile conditions, and the beverages are filled into the Packaging and packing is sealed under sterile conditions. An important factor in the aseptic packaging of food products is the sterilization of the packaging. Known technologies for sterilizing packaging in the food processing industry include: (i) chemical sterilization, such as for example hydrogen peroxide and chlorine; (ii) UV radiation; (iii) gamma radiation; and (iv) steam sterilization. There are advantages and disadvantages to each of the options and the adequacy of these (and other) technologies of a given situation depends on the packaging, the food product, and the food preparation. A particular object of the present invention is to offer an alternative to known technologies for sterilizing packaging for the food processing industry. A more general object of the present invention is to offer an alternative to sterilization technologies known in the food processing industry and other industries. In accordance with the present invention, a method of preferential heating of the material comprising exposure of the material to electromagnetic non-ionizing pulsed, high intensity radiation is offered. The present invention is based on an experimental work performed with microwave radiation, pulsed, high intensity. It was found in the experimental work that a high intensity pulsed microwave radiation represents a particularly effective means of destroying microorganisms.

It is believed that microwave radiation, pulsed, high intensity caused a substantial net increase in potency in microorganisms which resulted in a sudden increase in temperature in microorganisms which destroyed the microorganisms. It was found in the experimental work that a high intensity pulsed microwave radiation could destroy microorganisms without substantially heating the surrounding environment also exposed to radiation. The parameters that are important for this preferential heating of microorganisms include the high intensity, pulsed power, the microwave absorption capacity of the surrounding environment, and the size of the microorganisms exposed to radiation. As for the third factor, generally, the speed of heat accumulation in a material is smaller with larger size of an object comprising the material. In general terms, when the size of two objects is equal, the relative absorption capacity of the objects will determine the magnitude of the preferential heating, and when the absorption capacity of the objects is the same, the relative size of the objects will determine the magnitude of preferential heating. In the context of the food processing industry, preferential heating with non-ionizing electromagnetic radiation, such as microwave radiation, makes it possible to sterilize the package by destroying microorganisms in the package without causing significant heating of the package which could adversely alter the chemical properties or other properties of the packaging. Again, in the context of the food processing industry, preferential heating with non-ionizing electromagnetic radiation makes it possible to sterilize wet food before or after food packaging. In this context, within the scope of the present invention is the high intensity pulsed non-ionizing electromagnetic radiation focus on the upper spaces of sealed containers containing beverages and containers containing jam in order to sterilize the spaces above the contents. The term "wet food" encompasses foods that have an aqueous activity (ie, the ratio between the pressure of water vapor in the food and the water vapor pressure) less than 1.0. Again, in the context of the food processing industry, the present invention is not limited to situations in which packaged food products exhibit "moisture". There is considerable flexibility in the selection of non-ionizing electromagnetic radiation characteristics (such as power, intensity, and wavelength) and the parameters that define the pulses (such as pulse duration, pulse frequency, profile) of pulse, work cycle and average power) to achieve an effective destruction of microorganisms. An important consequence of the flexibility is that it is possible to select operating parameters for non-ionizing, pulsed, high intensity electromagnetic radiation that are suitable for the characteristics of particular food products and particular packages. The intensity / pulse train time of the pulses can be any suitable profile.

Preferably, the pulse duration is less than one second. More preferably, the pulse duration is less than 0.1 seconds. More preferably, the pulse duration is less than 0. 01 seconds Generally speaking, it is preferable that the pulse duration be selected in such a way that there is sufficient exposure to cause significant heating of dry materials, such as packaging materials. Preferably, the average power of the microwaves is at least 1 kW. More preferably, the average power is at least 5 kw. The term "average power" is understood in the direction of the product of the peak power by the duty cycle. The term "peak power" is understood as referring to the maximum power of a pulse. The term "work cycle" is understood in the sense of the time duration of a pulse divided by the sum of the temporary pulse duration and the time between the pulses.

Preferably, the peak power of the radiation is 3 kW. More preferably, the peak power is at least 30 kW.

In accordance with the present invention, an apparatus is provided for preferentially heating a material, comprising a device for generating high intensity, pulsed, non-ionizing electromagnetic radiation. Preferably the apparatus comprises a device for directing radiation in the material. More preferably, the steering device comprises a device for focusing the radiation. In accordance with what has been described above, a preferred but non-exclusive application of the present invention is to destroy the microorganisms by preferential heating. In this application, it is preferable that the apparatus further comprises a device for directing a high intensity, pulsed microwave radiation in a sterilization region. The sterilization region can be any region that must be a weak environment. By way of example, the sterilization region may be a chamber for sterilizing an empty package for food products. In this example, the apparatus further comprises a transport device, for example a conveyor belt, to move the empty package towards the chamber and outside the chamber, whereby the package is exposed to a high intensity, pulsed radiation, in the camera. The present invention is further described by way of example with reference to the accompanying drawing which is a schematic diagram of a preferred embodiment of an apparatus for sterilizing packaging for the food processing industry prior to filling the package with the food product and sealing. As indicated above, the present invention focuses particularly, but not exclusively, on the use of high intensity, pulsed, non-ionizing electromagnetic radiation, such as microwave radiation for destroying microorganisms. It is understood that the following description in connection with the sterilization of open, unfilled packages for the food processing industry is only one example. With reference to the figure, alternating current electricity is supplied to a DC power supply source, which may include a transformer, and then to a pulsating or switching circuit to produce pulses in a duty cycle of required intensity. Alternating current electricity can be supplied from any suitable source, such as 60 Hz AC, 600 Hz AC, three phase CE, and single phase AC. The pulses are supplied to the microwave activation device, such as a magnetron that produces pulses of high intensity microwave radiation in a prescribed working filter, and then the pulsed high intensity microwave radiation is transferred to a waveguide in an applicator to a treatment chamber or tunnel In a suitable form of treatment chamber or tunnel (not shown), the package, such as metal plates with open ends, is placed on a conveyor belt that carries the packing in vertical positions through the chamber or tunnel in such a way that the package is exposed to several impulses of microwave radiation, pulsed, of high intensity, which heat the microorganisms in the packaging at temperatures that destroy the microorganisms. this, it is observed that in situations in which the packaging is metal cans, since the metals reflect the microwaves, it is important to ensure that the relative positions of the applicator and the cans are selected such that the high intensity pulsed microwave radiation is directed through the open ends on the inside of the cans. The preferred embodiment of the present invention illustrated in the figure has considerable advantages compared to known chemical sterilization technologies, UV radiation, gamma radiation, and steam sterilization to sterilize packaging. As an example, capital and operating costs are relatively low compared to the capital and operating costs involved in known technologies. In addition, there is no risk of leaving chemical residues in the packaging - which is a concern in the case of chemical sterilization, particularly when the chemicals in question, such as hydrogen peroxide, are poisonous. In addition, the use of non-ionizing electromagnetic radiation makes it possible to avoid chemical changes to the packaging which is a concern with the use of UV and gamma radiation. For example, it is possible to destroy microorganisms without generating heat levels in the package that could alter the chemical properties of the package - which is a concern in the case of steam sterilization. In addition, the penetration power of high intensity microwave radiation is such that there is a high level of safety that regions of non-metallic packaging will not prevent exposure - which is a concern in the case of UV radiation in addition, the modality preferred is adapted to high speed sterilization and, therefore, is suitable for high performance applications which are frequently found in industries such as, for example, the food processing industry. The aforementioned advantages of the preferred embodiment are also generally applicable to the use of high intensity microwave radiation, pulsed in other situations in the food processing industry and in other applications. In a series of experiments, a DC power of 8 kW was supplied to a pulsating switch that produced a pulsed microwave of 3 kW at a duty cycle of 25% with pulses of seconds in duration and 0.025 seconds between pulses. The production of pulsed microwaves was made through an S-band magnetron operating at 2.460 GHz. The microwaves were focused on yeast spores in a 50 micron thick microwavable plastic film. The density of the yeast spores was estimated at 108 to 1010 / square centimeter. The yeast spores were exposed for a total of 2 to 5 seconds. The quantitative evaluation of the results determines that the spores were totally destroyed and that a minimum heating of the supporting substrate was observed. The experiment established that the invention could sterilize a surface of a material, such as packaging material, with minimal effect on the material. Many modifications can be made to the preferred embodiment described above without departing from the spirit or scope of the present invention. For example, while the preferred embodiment described in relation to the figure includes a pulsating switch, it can readily be seen that the present invention is not limited to this and that it extends to other suitable pulsed networks. Furthermore, while the preferred embodiment includes a magnetron, it can be readily observed that the present invention is not limited to this and extends to any other suitable means for generating microwaves. Possible alternatives include solid state devices, cliptrons and gyros.

Claims (11)

1. CLAIMS A method for the preferential heating of a material, which includes the exposure of the material to a high intensity, pulsed, non-ionizing electromagnetic radiation.
2. A method for the destruction of microorganisms comprising the exposure of microorganisms to electromagnetic non-ionizing, pulsed, high intensity radiation in order to destroy the microorganisms without substantially heating the surrounding environment that is also exposed to radiation.
3. A method for sterilizing a package, comprising exposing the package to electromagnetic radiations of high intensity, pulsed, non-ionizing in order to destroy microorganism without causing a heating of the package that negatively alters the chemical or other properties of the package.
4. A method for sterilizing wet food before or after food packaging, which involves exposing the package to non-ionizing, pulsed, high intensity electromagnetic radiation in order to destroy microorganisms without heating the package that negatively alters the chemical properties or of another type of packaging.
5. 5. The method defined in any one of the preceding claims, wherein the duration of each radiation pulse is less than 0.1 seconds.
6. 6. The method defined in any of the preceding claims, wherein the average power of the radiation is at least one kW.
7. The method defined in any of the preceding claims, wherein the peak power of the radiation is at least 3 kW.
8. The method defined in any of the preceding claims, wherein the radiation is a microwave radiation.
9. 9. An apparatus for preferentially heating a material, comprising a device for generating non-ionizing, pulsed, high intensity electromagnetic radiation. The apparatus defined in claim 9, further comprising a device for directing radiation to the material. The apparatus defined in claim 10, wherein the addressing device comprises a means for focusing the radiation.