Daly, Clyde (c/- Meat and Livestock Australia Limited, Level 1 165 Walker Stree, North Sydney NSW, AU)
|1.||A method of controlling the reflex action of a recently slaughtered animal carcase, including the steps of applying pulses of electrical energy to the carcase, the pulses being applied in a waveform having a pulse frequency selected to be above 500hz and wherein each pulse has a duration of less than 200 gs.|
|2.||A method according to claim 1 wherein the pulse frequency is between 500hz and 3000hz.|
|3.||A method according to claim 1 or claim 2 wherein and each electrical pulse is of between 50, us and 200 sus in duration.|
|4.||A method according to claim 1 or 3 whereby the pulses are selected to be in the frequency range of between 500hz and 2000hz.|
|5.||A method according to claim 1 or 3 whereby the pulses are selected to be in the frequency range of between 1000hz and 2000hz.|
|6.||A method according to any one of the preceding claims wherein the pulse duration is less than four times the duration between each pulse.|
|7.||A method according to any one of the preceding claims whereby waveform parameters are selected to have minimal glycolysis and tetanus in the carcase while providing a desired degree of carcase immobilisation and be safe for human contact said parameters including, pulse duration, pulse frequency, pulse voltage, pulse current and pulse shape.|
Background of the Invention Immobilisation is used in the animal processing industry as an aid to worker safety.
Freshly slaughtered carcases have active nervous systems for some minutes after death and violent reflex action may be initiated by even small stimuli such as moving a limb into a new position, small knife incisions etc. Depending on species, the nerves can remain alive and active for periods in excess of 5 minutes. This nerve action can trigger spontaneous and/or continuous violent movement, which is potentially dangerous to anyone in close proximity, particularly when sharp implements are being used.
The two most common forms of carcase immobilisation are by mechanical restraint, where limbs are physically pined to prevent movement and electrical restraint, which uses an applied electrical energy to override nerve function and control the muscles. This invention relates to electrical means of restraining a carcase and the following is a background to electrical immobilisation (restraining) of a carcase.
Electrical immobilisation in the early stages of post mortem acts primarily on the nerves while they are still alive (and it is only the live nerves which create the problem).
In order to hasten work on the carcase, immobilisation of the nerves is often applied almost immediately after death.
There are two possible approaches in electrical immobilisation. Temporary immobilisation, when nerves are prevented from causing carcase movement only during application of electrical energy and permanent immobilisation which may have a temporary effect but also rapidly fatigues the nerves to the point where carcases can be safe to work on immediately the energy is removed. This may be substantially less than 5 minutes post mortem.
However, there are several disadvantages to electrical immobilisation depending on carcase type and species. The major disadvantages are:-
Muscle damage from excessive muscle contraction (muscle tetanus) during periods of elevated blood pressure following an animal stun-Uncontrolled or excessive electrical inputs can destroy some muscles.
Blood spotting or ecchymosis in and on the surface of the muscle due to burst blood vessels. Thought to be due to excessive muscle contraction and elevated blood pressure.
Excessive acceleration of the rigor process (glycolysis). The electrical inputs act like another technology, Low Voltage Electrical Stimulation, which accelerates the natural metabolic process where muscle uses up stored energy anaerobically and eventually dies (reaches rigor mortis). Excessive acceleration can lead to poor meat quality.
Earlier electrical immobilisation waveforms were low voltage mains frequencies, simple sinusoids with no electronic control. These techniques created an immobilisation effect which was uncontrolled as the electric current flowing through the carcase varied depending on carcase and contact resistance. The effect was variable and unless excessive voltage and application time was used there was little residual control (permanent nerve death).
Later immobilisation took the form of a continuous sequence of electronically controlled current pulses at frequencies up to several times the mains frequency.
Although this approach is far more effective than the sinusoid because the waveform is better shaped to immobilise nerves, it can also create excessive glycolysis and tetanus with undesirable consequences. The immobilisation effect is generally temporary at energies which do no damage, but even at these energies there can be an undesirable glycolytic effect. As the pulse frequency is increased up to several hundred pulses per second, the undesirable glycolytic and tetanus effects are lessened but not eliminated and there is still no significant permanent immobilisation effect.
From another aspect, the electrical energy applied to the carcase must be kept within a safe parameter range. There is a concern that if the energy applied is too high and has a dangerous waveform, it may render the carcase dangerous to abattoir staff.
It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.
Disclosure of the Invention Accordingly, the present invention provides a method of controlling the reflex action of a recently slaughtered animal carcase, including the steps of applying pulses of electrical energy to the carcase, the pulses being applied in a waveform having a pulse frequency selected to be above 500hz and wherein each pulse has a duration of less than 200 us.
Preferably, the waveform parameters are selected to have minimal glycolysis and tetanus in the carcase while providing a desired degree of carcase immobilisation and be safe for human contact.
Preferably, the pulse frequency is less than 3000hz. More preferably the pulse frequency is between 1000hz and 2000hz.
Preferably, each electrical pulse is of between 50 zits and 200 us in duration.
Preferably, the pulse duration is less than four times the duration of between each pulse.
Preferably, waveform parameters are selected to have minimal glycolysis and tetanus in the carcase while providing a desired degree of carcase immobilisation and be safe for human contact said parameters including, pulse duration, pulse frequency, pulse voltage, pulse current and pulse shape.
Brief Description of the Drawings Not withstanding any other forms that may fall within its scope, one preferred form of the invention will now be described by way of example only with reference to the accompanying diagrams in which: Fig 1 is a graphical representation of voltage vs time of an immobilisation waveform according to the prior art; and Fig. 2 is a graphical representation of voltage vs time of an immobilisation waveform according to the invention.
The Figures are for illustrative purposes only and are not to scale.
Preferred Embodiments of the Invention The invention aims to overcome the limitations mentioned in the prior art preamble above using a phenomenon whereby high frequency pulses prevent proper functioning of the nervous system (temporary immobilisation) without allowing the nerves to activate the muscle and create an increased rate of glycolysis.
It has been found that higher frequency pulses can more rapidly deplete the energy of the nerves and permanently deactivate the nerve reaction (permanent immobilisation) compared to lower frequencies. As can be seen in the Figures, the frequency of the pulses is relatively high in comparison with those commonly used. The waveform of the invention shown in Figure 2, uses pulses 1 having a frequency of between 500hz and 3000hz whereas the existing art uses a waveform having pulses 2 of below 200hz (Figure 1). The graphical representations shown are for illustrative purposes only and may not be to scale. In particularly preferred embodiment of the invention a waveform having a pulse frequency of less than 2000hz and of more than 1000hz is used.
However, as frequency is increased, more electrical pulses are applied for a given time period and consequently, all other things being equal, the effective energy transmitted to the carcase also increases.
Accordingly, increasing the frequency at the pulse widths considered necessary to stimulate the nervous system, may run the risk of exceeding safety limits set by the Safety Standards AS/NZS 60479.1 : 2002. Adding to this safety issue is the documented effect (J.
Patrick Reilly,'Electrical Stirnulation and Electro Pathology', Cambridge University Press (1992) ) wherein waveforms having insufficient rest time between pulses can tend to compound. Accordingly, it is advisable to have a rest period, where little or no energy is applied to the carcase, between the pulses of a duration greater than four times the duration of the pulses.
Furthermore, in addition to the safety issue, higher frequencies can present a problem because the waveform begins to act like direct current and the immobilisation effect due to the waveform diminishes. This becomes an increasing problem at high frequencies when the pulse width is comparable to the waveform period.
However, it has been found that pulse widths significantly less than currently used will still immobilise nerves. As such, the invention uses a waveform having a pulse
duration 3 of between 50 microseconds (lys) and 200 zits whereas the existing art uses pulses 4 of around 7 milliseconds (ms) to 10 ms. These shorter pulse durations have the effect of reducing the tendency of the waveform to simulate direct current. Moreover, the reduction in pulse duration provides for a reduction in the effective energy, somewhat offsetting the prior mentioned increase due to increased frequency.
In addition, the very high frequency pulses have a beneficial safety effect for the operator. As frequencies increase beyond several hundred pulses per second there is a rapid reduction in risk of cardiac interference should the operator be exposed to the electrical energy. This reduction in risk more than makes up for any increase in the effective energy of the waveform.
By choosing the parameters for the waveform which have minimal glycolysis and tetanus effects (various combinations of high pulse frequencies, narrow pulse shapes, low currents) but still create some degree of temporary immobilisation, both temporary and permanent immobilisation can be achieved.
Therefore, it is a particular feature of the invention that by increasing the frequency of pulses, a high rate of neuron fatigue can be achieved without resorting to the use of high voltage spikes or other current manipulations which lead to undesirable glycolytic effects and safety issues.
Different production systems demand different degrees of both temporary and permanent immobilisation and until now no technology offered this control.
By changing such things as frequency, pulse width and duration of application, control can be exercised over the relative degrees of both temporary and permanent immobilisation. For instance, a high rate of neuron fatigue will provide for a permanent immobilisation, whereas temporary immobilisation can be achieved by minimising neuron fatigue. Of course of major impact to the effectiveness of the method will be the voltage and current applied. Both can be adjusted dependant upon the immobilisation and safety requirements and animal type, breed and size. It is also possible to apply a bipolar voltage waveform instead of the uni-polar waveform shown in the Figures.
It will be appreciated that the waveform can be applied to the carcase in any suitable known manner, e. g. by the use of applied electrodes or slip rails.
It will be appreciated that the invention provides a flexible method of permanently or temporarily immobilising a recently slaughtered animal carcase. Whereby electrical waveform characteristics of applied electrical energy can be tailored to the particular
situation e. g. particular carcase size or characteristics to give a safe working environment while maintaining a high degree of meat quality due to minimisation of muscle tetanus or glycolysis. In all these respects, the invention represents practical and commercially significant improvement over the prior art.
Although the invention has been described with reference to specific examples it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.