NL8120506A - STERILIZATION PROCESS AND DEVICE. - Google Patents

Description

3 1 2 0 5 O C

N.0. 32023 1

Sterilization process and device.

BACKGROUND OF THE INVENTION

This invention relates to a sterilization process and apparatus for killing bacteria and similar organisms within a host material.

5 In United States Patent Specification 2,081,243, Macy describes an apparatus for pasteurizing only liquids, such as milk, by "slow and intensive pulses of an electric wirling current." He produces it through a breaker 3.3 times per second, the " interruptions literally cause the bacteria to explode. ”The temperature of the milk can also rise considerably through this process. The device is of the coaxial flow-through type and has a large number of parts.

Golden, 1,934,703, describes a trough-shaped electric sterilizer with an internal central electrode and a pair of external flux concentrator electrodes.

Smith, 1,975,805, describes a dry type sterilizer in which a high voltage on a pair of rotating electrodes coaxially spaced on opposite sides of a conveyor carrying the material to be sterilized acts on the material.

OVERVIEW OF THE INVENTION

A host material, or a number of guest materials, containing organisms to be killed are surrounded by a weak electrolyte within the sphere of influence of several electrodes.

Successive flow pulses of high density and varying polarity, each with a duration in the microsecond region, are generated about 120 times per second.

The organisms are electrocuted by the passage of the electric current through the host material and associated therewith through the organisms. Bacteria are not "exploded". The prior art explosive destruction mode also destroys the cellular structure of the host material substance, thereby reducing its quality.

The current pulses are formed by electronic switches, capable of providing a rapid rise in electric current, such as 35 controlled phase-controlled silicon rectifiers (SCRs).

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic electrical diagram of a single-phase AC-powered device for carrying out the process of this invention.

Figure 2 is a current / time waveform illustrating the operation of the circuit of Figure 1. The time axis is not to scale for the sake of clarity.

Figure 3 is a schematic electrical diagram of a device powered from a dual power source.

Figure 4 is a current / time waveform for the circuit of Figure 3; the time axis is not to scale.

Figure 5 is a schematic diagram of a circuit similar to that of Figure 1, but including a pair of capacitors.

Figure 6 is a waveform for the circuit of Figure 5; the time axis is not to scale.

Figure 7 is a circuit diagram in which the circuit of Figures 3 and 5 are combined.

Figure 8 is the waveform of the circuit of Figure 7; the time axis is not to scale.

Figure 9 is a perspective view of a single-phase processing device according to this invention.

Figure 10 is a similar view of a three-phase device.

Figure 11 shows a schematic three-phase circuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In Figure 1, the numeral 1 denotes an alternating current source. This can be the usual public electrical network with typically 120 volts effective, 230 volts effective or higher. It is the running electric current that performs the operation of this invention.

The voltage required to obtain the desired current depends on the spacing of the electrodes in the treatment cell, the conductivity of the electrolyte, and the nature of the material to be treated.

A typical current density is 1.25 amps effective per square inch of the material to be treated. This value can be changed as will become apparent in the following.

The treatment cell 2 typically has parallel spaced electrodes 3 and 4. These are connected to the power source 1 through oppositely polarized phase controlled rectifiers or thyristors 5 and 6.

In Figure 2, the dotted sinussoidal wave 8 represents a voltage cycle of the source 1. The pulse 9 drawn with a solid line represents the current. The current is limited to a short 40 time interval, for example 10% of each half wave. It is initiated by the triggering of the phase-controlled rectifiers, for example, by a unijunction circuit 13 of the relaxation oscillator type. Such a circuit is known and is illustrated in "Transistor Manual", G.E., seventh edition, 1964, p. 312-16.

5 For the sake of clarity, the time axis is not to scale in figure 2. The "on" duration of the current in the cycle is typically less.

It is desirable that the chosen rectifier type be able to turn on current very quickly, preferably within a few microseconds. A steep turn-on wave front is very effective at killing 10 unwanted organisms in a guest substance.

In Figure 3, elements 2, 3, 4, 5 and 6 are the same as in Figure 1. However, power source 1 has been replaced by power sources 10 and 11 of relatively high voltage. These supply a DC current and charge capacitors 12 and 14 through resistors 15 and 16. The time-15 constants of these resistor-capacitor combinations are equal and such that the capacitors can be fully charged fifty or more times per second. The capacitors have an equal capacity.

It is desirable that the rise time of the current pulse obtained upon discharge of the capacitors (one at a time) be extremely short. The inductance of the capacitor, rectifier and treatment cell must therefore be minimal. This is improved by using low-inductant capacitors. A capacity of 100 microfarad (IF) for each capacitor is suitable.

In addition, a pulse-forming network 33 can be placed in series with the treatment cell 2 to increase the rate of change of the current rise, dl / dt, thereby obtaining improved results.

The network 33 is particularly effective when air bubbles or insulating material are present in the host material. These form 30 capacitive areas. Fourier analysis of the wavefront shows that by increasing dl / dt there is generally more energy at higher frequencies. This results in good current conditions through the capacitive areas.

Operating voltages of 1000 volts or more can be produced by the power sources 10 and 11. It is noted that these are connected to the capacitors with opposite polarity.

Figure 4 shows the current waveform as a function of time. It is noted that the current pulses are extremely sharp and of very short duration. The on-off ratio is typically a small portion of 40 1%.

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According to this invention, alternating current is used to prevent polarization and deposition effects in cell 2. So both net positive and negative flows are equal.

Figure 5 shows the schematic for an improved modification of Figure 1. Elements 1 to 6 are the same or similar to the equally numbered elements in Figure 1. Elements 12 'and 14' are similar or similar to elements 12 and 14 of figure 3.

The new element 18 is a diode, typically a solid state diode, which stops conducting at the maximum value of the voltage wave-form 10 in Figure 6. Thus, the peak voltage charge is held in the capacitor 12 'and the current pulse 21 upon discharge. is proportional to the peak voltage of the waveform 8. The current continues at a reduced amplitude 9 'as in Figures 1 and 2.

The diode 19 behaves in the same manner with respect to the capacitor 14 *, but with opposite polarity, and forms the current pulse 21 ".

Figure 7 combines the circuits of Figures 3 and 5. Analogously to these circuits, current pulses 22 and 22 'of high amplitude and opposite polarity are formed as shown in Figure 8. The reduced current 9' is also present.

A common return connection 20 is provided in Figure 7.

As before, the use of power sources 10 'and 11' allows current pulses of relatively large amplitude to be produced. The reasons for large and small pulses of current when performing the process of this invention are given later herein. Again, a pulse-forming network 33 can be placed in series with the treatment cell to increase the value of dl / dt. These networks use inductors and capacities and are known in the field of power sources operating with laser flash tubes.

Figure 9 illustrates in perspective as a base a single-phase treatment cell 2. The shape is that of a hollow rectangular parallelepiped. In the figure, the two ends are drawn in phantom so that the interior is visible.

The electrodes 3 and 4 are the same as those shown schematically in the earlier schematic circuit diagrams. The electrodes are normally simply attached to the adjacent inner wall of the parallelopipid sides. However, they can be moved closer together when the internal electrical resistance of the cell is high. 40 An electrolyte 24 fills the cell 2. For solid guest material, such as a shellfish or crustacean 25, the electrolyte may consist of a salt-containing liquid such as seawater. Normally many things can be present for treatment at the same time; For the sake of clarity, only one is shown in Figure 9.

The electrodes are formed from materials that are inert to the electrolytes and the host materials to be processed. One such material is carbon, which may have a "U" channel-shaped stainless steel edge contact to which connecting wires are attached. Other successful electrode materials include stainless steel, tantalum and titanium. 10 The guest material to be treated can be handled in batches in rectangular baskets. For best results, these baskets should be non-conductive except for the two sides that are parallel to the treatment cell electrodes, which sides must be electrically conductive.

Alternatively, a slow flow hydraulic configuration can be used, in which material enters at one end of the cell and exits at the other end.

A preferred embodiment of a treatment cell for a three-phase device is shown in Figure 10. Part of the outer container shell 27 is cut away to show the internal construction and the front end is cut for the same purpose.

The purpose of a three-phase cell is to arrange three electrodes in a symmetrical configuration so that the electrical flux charges between the electrodes are substantially uniform over the working areas.

In Figure 10, the segmented electrodes 28, 29 and 30 occupy much of the volume of the outer container 27. This allows parallel electrode surfaces to be presented from one electrode to the other. This is typically a flow-through embodiment. The electrolyte and the material to be treated flow through each of the three channels, as indicated by the arrows in the channel visible in the cutaway part of the container.

The electrodes are composed of the same or similar materials as those used in the single-phase device described above.

The central cylindrical surface 31 is of an electrically insulating material, such as a plastic or vitrified refractory material. This prevents a flow of electrolyte in the central region between the electrodes where the flux charges would otherwise be higher than desired.

Figure 11 schematically shows an electrical three-phase circuit.

In it, the unit 35 receives the conventional three-phase, or poly-40 phase, power and transforms it to a higher or lower voltage 8120506 6 as needed to obtain effective energization of the. treatment cell 27. Windings connected in delta configuration as well as in "Y" configuration are shown in unit 35 in a general view of a transformer. Both connection modes of the windings 5 can be used. The transformer also isolates the device according to the invention from the electrical network for safety reasons.

Three conductors run from the output of the unit 35 to the control circuit 36. It is provided with three separate single-phase control circuits, as shown in Figures 1, 3, 5 or 7. These 10 separate circuits are controlled in conjunction such that each of the three phases are controlled in the same way.

The output of the control circuit 36 is individually connected to the electrodes 28, 29 and 30 of the three-phase treatment cell 27 for electrically energizing it.

The circuits, arrangement and operating parameters of this invention "electrocute" the unwanted organisms. Bacteria are not "exploded", contrary to the prior art. Importantly, the cellular structure of the host material is not altered by the operation of this invention. This was determined by optical microscopy.

It will be understood that a significant change in the cellular structure is undesirable in the value of the host material as a food.

Numerous materials can be treated, including shellfish or shellfish, fish, fruits, vegetables, poultry and meat. The main advantage of the treatment is to reduce the number of bacteria or other organisms in the host material, thereby extending the time before decay occurs, and the time prior to which a fragrant flavor is retained. Very important reductions in the number of bacteria can be achieved with this operation.

The preferred editing mode was developed as indicated by the successive schematic accompanying figures.

First there was phase control. When it became apparent that by increasing the conductivity of the electrolyte, thereby shortening the necessary duration of the conducting periods, the sterilization effect was greatly improved, a further development step arose.

That was the pulse discharge. With sufficient capacitance in two storage capacitors, a very significant killing effect was created on the Bacte-40 calling population.

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A third step involves the impulse discharge followed by a conduction angle, such as 22 and 9 'in Figure 8. This gives a maximum sterilization effect with minimal heating of the material.

Using the embodiment of Figure 1, the results for shrimp were: control sample 1,600,000 bacteria / gram average of treated samples 201,250 bacteria / gram

Bacteriological tests performed by an independent laboratory-10 torium

Using the embodiment of Figure 3, the results in shrimp were:

Control sample 2,000,000 bacteria / gram Average of treated samples 150,000 bacteria / gram

Using the embodiment of Figure 5 or 7, the results for shrimp were: control sample 350,000,000 bacteria / gram 20 average of treated samples 320,000 bacteria / gram

Dito were the results for scallops: control sample 40,000 bacteria / gram mean of treated samples zero * * (At or below the laboratory test resolution)

It is possible to establish a treatment procedure for each substance to be treated. This is based on the substance to be treated, its initial state, the desired degree of sterilization, and the parameters of the device used. The latter include the circuit used and the configuration of the treatment cell. It is unlikely that the treatment procedure should be varied during a processing procedure with a particular host material.

Certain examples of the parameters giving the above test results can be given.

Using the circuit arrangement of Figure 5 and the cell of Figure 9, the current was 1.5 amperes per square centimeter (amp / cm 2), which was thus 60 amp / cm 2 peak. The treatment time was about 3 seconds. The electrolyte was salt water and the electrode spacing was 7 cm.

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The parameters were the same for scallop processing.

it has been found that a live lobster can be electrocuted while reducing the number of bacteria. This is a fast, effective and humane method of processing, better than using boiling water.

The invention is effective for processing materials containing pathogenic multicellular organisms.

For example, in certain raw fish, such organisms can exist which, when consumed by humans, can be quite dangerous. One is the dibothriocephalus latus, a worm found in whitefish.

Another example is trichin-contaminated pork, which causes trichinosis in humans.

As discussed previously, the use of alternating current with rapid rise times allows currents to flow through void areas in the host and through shellfish shells or shells. In an electrical sense, these are capacities, making alternating currents run smoothly.

In general, tap water can be used as an electrolyte 20 as an alternative to sea water. Tap water conductivity can be increased if required by adding certain amounts of ionizable chemical salts, or even by acidic or basic chemicals.

For maximum effectiveness, the electrolyte has a conductivity slightly lower than that of the host material to be treated. This ensures that the stream is concentrated to the host material to a nominal degree. When using the invention, the greater the peak amplitude of the current, the shorter the processing time. If a reduced degree of sterilization is desired, it is obtained by a shorter processing time or a reduced flow amplitude.

Regarding the voltage, the greater the distance between the electrodes and / or the lower the conductivity of the electrolyte, the more voltage is required to obtain a given amperage.

The term "organism" has been used in a general sense herein. The term includes bacteria, yeast, viruses, parasitic worms, insect larvae and eggs, and bacteria spores. Generally, any living organism within the host material is subjected to current pulses 40 and is electrocuted. These living organisms encompass the region 8120506-9 of micro- inherent in this invention is the concept of phase control; that is, sending a current pulse through the host medium for only a short period of each half cycle of the incoming alternating current. This is as shown in Figure 2.

The addition of pulse discharges from capacitors, such as 12 and 14 of Figure 3, improves the killing effect of the operation on unwanted organisms while reducing power dissipation. See figure 4.

10 It has been found that a combination of the two current wave forms has a superior killing effect better than both individually. This has been achieved with the device of Figure 5 and illustrated by the waveforms of Figure 6, provided with parts 21 and 9 '. When a greater killing effect is needed, the device of Figure 7 and the wave-form of Figure 8 are used. The current pulse 22 has a greater amplitude than in Figure 6.

8120506

Claims (14)

A method for killing organisms residing in a host material, comprising the following method steps: a) immersing the guest material in an electrically conductive liquid, b) sending an electric current through both the host material and the liquid, in the form of successive strong pulses of opposite electrical polarity, each of said pulses having a duration in the microsecond region, with a repetition rate greater than approximately 50 pulses per second, c) running this current for a period of maximum a few seconds. An apparatus for killing organisms residing in a host material comprising: a) an electrically non-conductive container (2 or 27) for receiving the host material, b) an electrically conductive liquid (24) within said container and comprising the host material, c) electrodes (3, 4 or 28, 29, 30) arranged symmetrically within said container and making contact with said liquid, and d) a pulsating electric source (1, 5, 6, 13, etc. .) connected to said electrodes to send electric current through the host material and in conjunction therewith through the organisms, in the form of short pulses of successively opposite polarity. The device of claim 2, wherein: a) the electrically conductive liquid is tap water. The device of claim 2, wherein: a) the electrically conductive liquid is sea water. The device of claim 2, wherein: a) said equally spaced electrodes, one of the other. The device of claim 2, wherein said pulsating electric source comprises: a) a source of alternating current power (1), 35 b) a pair of thyristors (5, 6) oppositely poled and connected to said alternating current source of power, c ) an electrical connection from both said thyristors to said one electrode (3), and d) an electrical connection from the other said electrode (4) to said source of alternating current power. 8120506 The device of claim 6, further comprising: a) an oscillating trigger means (13) connected to each of the thyristors (5, 6) to pull each thyristor into conduction near the end of each half cycle of the alternating current source -5 may (1). The device of claim 7, wherein said oscillating trigger means comprises: a) a unijunction relaxation oscillator. The device of claim 2, wherein said pulsating electric power source comprises: a) a source of alternating current power (1), b) a pair of thyristors (5, 6) connected in reverse polarity to said source of alternating current power via the same manner polarized diodes (18, 19), and c) a pair of capacitors (12 ', 14') connected to said thyristors for accumulating oppositely polarized electric charges, and also connected to said electrodes (3, 4. through said thyristors to pass said current pulses through said host material and said organisms. The device of claim 2, wherein said pulsating electric source comprises; a) a pair of oppositely polarized DC power sources (10, 11), b) a capacitor (12, 14) connected separately over each said DC power source, c) oppositely polarized thyristors (5, 6) connected to said capacitors and to a from said electrodes, and d) a reverse connection (20) from said other electrode (4) to said DC power sources. The device of claim 10, further comprising: a) a diode (18, 19) connected to each of said oppositely polarized thyristors, having the same polarity as that of said thyristors, and b) a source of alternating current power (1 ) connected to both said diodes and to said reverse connection. The device of claim 2, wherein said pulsating electric source comprises; a) a pulse-forming network (33) disposed between the source (5, 6, etc.) and said electrodes (3, 4) in order to change the rate of current flow with respect to the time (dl / dt) of the to improve pulses 8120506 V- from said source. The device of claim 2, wherein said container comprises: a) a cylindrical outer casing (27), 5 b) a plurality of equally protruding and equidistant electrodes (28, 29, 30) spaced together within said casing, and c) connecting each of said plural electrodes to a multi-phase pulsed electric source (35, 36). The device of claim 2, wherein said pulsating electric source comprises; a) a multiphase source of alternating electrical electrical energy (35), b) multiple nature circuits (36) individually connected to a phase of said multiphase source, and c) a connection of each of said plurality of control circuits to a separate electrode of a container (27) provided with multiple electrodes (28, 29, 30). 8120506