Preferential heating of materials by use of non-ionizing...

Details Preferential heating of materials by use of non-ionizing... Preferential heating of materials by use of non-ionizing...

2000-02-14

2001-06-19

Leung, Philip H. (Department: 3742)

Electric heating

Microwave heating

With diverse device

C219S702000, C219S715000, C422S021000, C426S241000

Reexamination Certificate

active

06248986

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to preferential heating of materials by non-ionising electromagnetic radiation.
The term “non-ionising electromagnetic radiation” is understood to include, by way of example, microwave radiation and radio wave radiation.
One particular, although by no means exclusive, use of the present invention is to preferentially heat micro-organisms to temperatures that destroy the micro-organisms.
This use of the present invention has a large number of applications.
One application is the medical industry in which the invention may be used, by way of example, to sterilise pharmaceuticals, packages for pharmaceuticals, and surgical and other equipment and implements.
Another application, which is of particular interest to the applicant, is the food processing industry.
The term “food processing industry” is understood to cover industry involved in preparing and packaging food products, including solid and liquid food products.
It is a critical requirement of the food processing industry:
(i) to sterilise food products after the food products have been packaged; or
(ii) to prepare and thereafter package food products under sterile conditions.
One example of the first category is the widely used method of packaging beverages, such as beer, which comprises pasteurising the beverages. Typically, suitable packaging (such as metal or glass containers) is filled with the beverages, the packaging is sealed, and the packaged beverages are thereafter heated at a temperature of 65-70° C. for 15 minutes. This method, whilst effective, has a number of disadvantages including substantial capital and operating costs.
Another example of the first category is the known method of sterilising spices. Typically, suitable packaging is filled with spices, the packaging is sealed, and thereafter ethylene oxide is permeated through the packaging at high pressure and contacts and destroys micro-organisms on the spices. While ethylene oxide is an efficient means of destroying bacterial spores and other micro-organisms carried by the spices, it is toxic and therefore removal of residual ethylene oxide to low levels is critical. Inevitably, this involves careful control of the method which in turn increases operating costs.
An example of the second category is packaging beverages under aseptic conditions.
Typically, beverages are prepared and conveyed to a filling station under sterile conditions, the filling equipment is maintained under sterile conditions, packaging is sterilised and transported to the filling station under sterile conditions, and the beverages are filled into the packaging and the packaging is sealed under sterile conditions.
An important factor in aseptic packaging of food products is the sterilisation of the packaging.
Known technologies for sterilising packaging in the food processing industry include:
(i) chemical sterilisation, such as hydrogen peroxide and chlorine;
(ii) UV radiation;
(iii) gamma radiation; and
(iv) steam sterilisation.
There are advantages and disadvantages with each option and the suitability of these (and other) technologies in any given situation depends on the packaging, the food product, and the food preparation.
SUMMARY OF THE INVENTION
A particular object of the present invention is to provide an alternative to known technologies for sterilising packaging for the food processing industry.
A more general object of the present invention is to provide an alternative to known sterilisation technologies in the Food processing industry and other industries.
According to the present invention there is provided a method of preferential heating of a material which comprises exposing the material to high intensity, pulsed, non-ionising electromagnetic radiation.
The present invention is based on experimental work carried out with high intensity, pulsed, microwave radiation.
It was found in the experimental work that high intensity, pulsed, microwave radiation is a particularly effective means of destroying micro-organisms. It is believed that the high intensity, pulsed microwave radiation caused a substantial net increase in energy in the micro-organisms which resulted in a sudden temperature increase in the micro-organisms that destroyed the micro-organisms.
It was also found in the experimental work that high intensity, pulsed microwave radiation could destroy micro-organisms without heating substantially the surrounding environment that was also exposed to the radiation.
The parameters that are important to this preferential heating of micro-organisms include the high intensity, pulsed energy, the microwave absorptivity of the surrounding environment, and the size of micro-organisms exposed to the radiation. With regard to the third factor, generally, the rate of heat build-up in a material is slower with larger size of an object that comprises the material. In general terms, where the size of 2 objects is the same, the relative absorptivity of the objects will determine the extent of preferential heating, and where the absorptivity of the objects is the same, the relative size of the objects will determine the extent of preferential heating.
In the context of the food processing industry preferential heating with non-ionising electromagnetic radiation, such as microwave radiation, makes it possible to sterilise packaging by destroying micro-organisms on the packaging without causing significant heating of the packaging that would alter adversely the chemical or other properties of the packaging.
Again, in the context of the food processing industry, preferential heating with non-ionising electromagnetic radiation makes it possible to sterilise moist food prior to or after the food has been packaged. In this context, it is within the scope of the present invention to focus high intensity, pulsed non-ionising electromagnetic radiation onto the head spaces of sealed beverage containers and jam jars to sterilise the head spaces.
The term “moist food” is understood to cover food having a water activity (ie. the ratio of vapour pressure of water in food to the vapour pressure of water) of less than 1.0.
Again, in the context of the food processing industry, the present invention is not limited to situations in which the food products being packaged are “moist”.
There is considerable flexibility in the selection of the characteristics of non-ionising electromagnetic radiation (such as power, intensity, and wavelength) and the parameters that define the pulses (such as pulse duration, pulse frequency, pulse profile, duty cycle and average power) to achieve effective destruction of micro-organisms. An important consequence of the flexibility is that it is possible to select operating parameters for the high intensity, pulsed, non-ionising electromagnetic radiation that suit the characteristics of particular food products and packaging.
The intensity/time pulse train of the pulses may be any suitable profile. It is preferred that the pulse train be rectangular.
Preferably the pulse duration is less than 1 second.
More preferably the pulse duration is less than 0.1 seconds.
More preferably the pulse duration is less than 0.01 seconds.
In general terms it is preferred that the pulse duration be selected so that there is insufficient exposure to cause significant heating of dry materials, such as packaging materials.
Preferably the average power of the microwaves is at least 0.1 kW.
More preferably the average power is at least 1 kW.
More preferably the average power is at least 5 kW.
The term “average power” is understood to mean the product of the peak power and the duty cycle.
The term “peak power” is understood to mean the maximum power of a pulse.
The term “duty cycle” is understood to mean the time span of a pulse divided by the sum of the pulse time span and the time between pulses.
Preferably the peak power of the radiation is at least 1 kW.
More preferably the peak power of the radiation is at least 3 kW.
More preferably the peak power is at least 30 kW.
Preferably the pulse frequency is less than 100 pulses per secon

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