Method for processing poultry

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DESCRIPTION

Method of processing poultry.

The present invention relates generally to a method for processing poultry, comprising the phases of supplying live poultry, stunning live poultry in a stunning device, placing the poultry on product conveyors along a conveyor belt, slaughter of stunned poultry and removal of dead poultry feathers in a plucking device.

In the poultry processing industry, poultry such as hens, chickens, turkeys and the like are processed in slaughterhouses, among others, into products intended for human consumption. Examples of such edible products are, for example, breasts, fillets, thighs and products comprising edible organs, such as livers and hearts.

Before poultry can be processed, they are first stunned and then slaughtered. Stunning of poultry is effected, for example, by briefly exposing the poultry to an electric current or by placing the poultry in a room containing stun gas. The object of stunning the poultry, whether through an electric current or otherwise, is to render the poultry semi-unconscious, so that the poultry does not strain to free itself from the product conveyors. . Such stress can result in wing breakage and other damage to the poultry, reducing the value of the poultry.

The slaughter of the poultry is usually done through the neck cut, so that the poultry is bled to death. It is also possible to re-subject the poultry to an electrical current, through which the poultry is electrocuted, however, and subsequently slaughtered.

For the poultry processing industry it is of great importance to supply products that meet the specific wishes of the consumer. In particular, the consumer expects a great measure of quality in the products they buy. Within the structure of the present application, the term quality is defined and hereinafter used as the degree to which a product at a given time satisfies the needs, that is, the expectations and desires of a given consumer. One of the quality requirements that poultry meat must meet is that it must be sufficiently tender. The fact that it is tender is a characteristic of the meat that is experienced by the consumer after having prepared the meat in a normal way.

It is checked whether a meat is tender enough by carrying out so-called sensory measurements, using a technical or consumer panel. In this, a group of specially trained people are served a series of prepared pieces of meat, and they are asked to make a judgment on a series of characteristics of the meat, including if it is tender and to what degree. Finally, the people in the panel rate the products on a scale between very tender and very hard. This way of determining hardness is, however, a subjective method. An objective method of measuring hardness is the measurement of the so-called "shear force" or shear stress. The cutting force can be measured, for example, with a Warner-Bratzler instrument, in which case a scissor-shaped tool can be used to measure the force required to tear or cut a piece of meat. These measurements can then be re-calibrated using a sensory panel.

In addition to toughness, the moisture - firmness characteristics of poultry meat are also evaluated before, during and after cooking. Along with the visual characteristics of the meat (what it looks like) and the microbiological quality of the meat, the moisture-firmness characteristics of the meat have an influence on the degree of consistency of the meat as experienced by the consumer. A large loss of moisture during cooking (large loss during cooking) results in a dry product which, although the "shear force" value is the same, is experienced by the consumer as less tender.

A slightly tender product, with little moisture - firmness and / or a product that has experienced a loss of moisture due to a spontaneous release of the product (drip loss) or due to a loss of moisture as a result of cooking the product, is experienced by the consumer as a tough, fibrous product.

Next, a quality requirement that the consumer assigns to poultry meat is that the quality should be as constant a variant as possible. In other words, a consumer will not accept too great a difference in terms of quality, for example consistency, of the product.

Through experience it has been possible to verify over a considerable period of time that the fact that a meat product is tender is a characteristic that is substantially determined by the time passed after the death of the animal in which the meat is separated from the bone. This time is known, in practice, as the post-mortem deboning time, and will be used as such hereafter.

It is an empirically proven fact that, when post-mortem deboning times are short, that is, shortly after the death of a bird slaughtered for processing, the result is a hard product. At the same time, it is an empirically proven fact that, in addition to a hard product, there is also a large variation in consistency between different products that have the same post-mortem deboning time.

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The culmination in a hard end product, when deboning occurs too shortly after death, has its origin in the following motif. As long as the muscle remains connected to the skeleton of the poultry, it is impossible for the muscle to contract without limitations. A contraction of the muscles after the slaughter of the animal is caused by the so-called “Rigor Mortis” (RM).

Shortly after the death of an animal, a certain amount of energy is still present (stored) in its muscles. If a muscle is separated from the skeleton before the MRI has been extended, the muscle will contract severely under the influence of this residual energy that is still present in the muscle in question, and the muscle will stiffen. The supply of energy that is still present in the muscle is substantially present in the form of glycogen, which through intermediate products such as glucose, ends up being converted into lactic acid, and as a consequence, there is a drop in the pH of the muscles. As a result of this stiffness of the muscles, a piece of meat, after it has been prepared in the normal way, will be less tender, which is undesirable in order to avoid unwanted toughness if the slaughtered poultry is allowed to mature. for a long period. Such a maturation period easily occupies a period of between 6 and 24 hours, depending on the type of poultry. During the maturation period, the poultry is stored and the toughness of the meat will improve if the meat is deboned after the maturation period is over.

At the same time, there will be less variation in the degree of hardness between different birds in the same flock. However, late deboning of the product has a number of drawbacks. Over the post-mortem deboning time delay, along with the hardness and difference that occurs, a number of different quality factors change, such as the color of the product, the degree of moisture - firmness in the product and the surface texture of the product, especially the texture of the product, all of which have potential repercussions for the further processing of the product. Also, as previously indicated, when deboning takes place at a late stage after the moment of death, the need arises for a maturation period in which the slaughtered bird must be stored for a certain time, so the muscle tissue to soften again under the influence of natural processes. However, this has some disadvantages, since expensive storage areas must be adapted and there is a risk that the meat will become infected while the slaughtered birds are in storage, since the possibility of infection increases with a longer storage period.

One possibility to reduce the maturation period, and therefore to achieve a shorter post mortem deboning time, while improving the quality range of the different products is the use of electrical stimulation or electrostimulation of the poultry slaughtered before of its boning.

Electrostimulation is a form of direct muscle tissue stimulation, in which muscle tissue is directly stimulated by applying an electrical voltage across a euthanized bird. As a result of this stimulation, the muscles are agitated and prompted to perform work. As work is done by the muscles, the glycolysis process in the muscles is accelerated. The glycogen that is still found present in the muscle is eventually converted, via intermediates such as glucose, into lactic acid. Therefore, the pH in the muscles is lowered. Therefore, through the stimulation of the muscles, the energy supply is expended more quickly, the stimulated muscle enters MRI earlier, and the hanging process will be accelerated. In this way, deboning can be carried out sooner after death without having to experience the consequent increase in hardness, and therefore it is easier to deboning earlier post-mortem, and in this way the drawbacks mentioned above are largely offset. .

The use of electrostimulation to achieve a more tender poultry meat is known from the publication of the American patent US-A-5,888,132.

US-A-5,888,132 discloses a device and method for processing poultry carcasses, especially electrical stimulation of poultry carcasses, in order to tenderize the meat by expelling the supply of stored biochemical energy present. in the muscle tissue, and producing accelerated maturation of the meat. In the known device and method, the poultry is suspended from product carriers, the product carriers advance through a conveyor, and the poultry is successively stunned, sprayed with water and slaughtered, after which the Poultry is transported along two electrically conducting bars across which there is an electrical voltage differential, so that the poultry is subjected to electrical stimulation. After electrical stimulation of the carcasses, they are plucked and subjected to subsequent processing operations, such as deboning and the like.

The electrically conducting rods of the known device are positioned in such a way relative to the carcasses that electrical stimulation takes place through the breast portion of the poultry. Here the channels are exposed to a constant electrical stimulation with an alternating voltage ranging from 100 to 250 V with a current intensity ranging from 130 to 500 mA for a period of between 8 and 13 seconds.

The patent US-A-5,888,132 also shows an electrical stimulation of the carcasses, dragging the carcasses through a bath containing a saline solution, an aqueous solution or dragging the head of a canal on a mesh or a charged metal net. , with the legs connected to the ground through the product carrier.

The use of electrostimulation to accelerate the maturation process is also known from the publication of the international patent WO-9819550.

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WO-9819550 describes a method to accelerate the maturation of the carcass of a slaughtered bird, thus avoiding a natural maturation period. The known method comprises the phase of electrical stimulation of the bird, with the euthanized bird exposed to a pulsed voltage for a continuous period. WO-9819550 also describes the cooling of the slaughtered poultry after its electrical stimulation. The slaughtered poultry is refrigerated to approximately 5 ° C, after which it is transported to a post-processing station for further processing of the poultry.

WO-9819550 also shows that it is desirable to carry out electrical stimulation of a euthanized bird as soon as possible after the moment of death, preferably after 90 seconds.

A subsequent use of electrostimulation to accelerate the ripening process is known from the publication of US-A-5,512,014.

US-A-5,512,014 describes a method and device for electrically stimulating poultry carcasses with a view to tenderizing meat and reducing the maturation period during poultry processing in a slaughterhouse. In the known method, the poultry is subjected to electrical stimulation some time after the neck has been cut, thus allowing the poultry to bleed sufficiently. The poultry is then stripped of its feathers, which is directed to a further processing line.

In the aforementioned methods, electrical stimulation takes place as a phase within a series of processes for the slaughtered birds. However, practice has shown us that the performance of the plucking process (pluckability), in which the slaughtered bird is stripped of its feathers, is affected by the previous electrical stimulation. In practice, post-electrostimulation stunning in the muscles of slaughtered poultry has been shown to make plucking considerably more difficult as a result of the feathers being more firmly attached to the skin. . Said reduction in pluckability in practice turns out to be a drawback of the known method.

Another drawback of the known methods is that the supply of the stored biochemical energy that is present in the muscle tissue of the slaughtered poultry is not completely eliminated during electrostimulation, so that a considerable increase in stiffness will occur. of muscle tissue. Therefore, there is still a need for a maturation period in which the slaughtered poultry is stored for a certain period to allow the muscle tissue to soften again under the influence of natural processes. However, this is a disadvantage as expensive storage areas must be provided, and there is a risk that the meat will become infected while storing the slaughtered poultry, with a probability of infection increasing as the time of storage increases. storage.

A first objective of the present invention is therefore to provide a method for processing slaughtered birds that eliminates the above-mentioned drawbacks.

According to a first aspect of the present invention, a method according to the invention is characterized by exposing the poultry, following the plucking device, to an electrical stimulation for at least a first period of stimulation.

By arranging for electrical stimulation of the poultry subsequent to plucking, a reduction in pluckability as a result of electrical stimulation is prevented in the first place. Also, the softening effect of plucking can be used. Because the plucking of poultry, and especially for the mechanical plucking of slaughtered poultry, has, like electrostimulation, a softening effect on the muscles of slaughtered poultry. As with electrostimulation, mechanical plucking puts the cells of the poultry muscles to work, and therefore ensures an acceleration of the maturation process, and consequently the faster establishment of the RM. Research has shown that by carrying out electrical stimulation of the poultry after plucking, the energy supply that is still present in the muscles can be further reduced. This results in a better final product, that is, more tender. Electrical stimulation of slaughtered poultry has the additional advantage that, apart from accelerating the maturation process, a further improvement in variety is achieved in relation to characteristics important for the quality of the meat product, of which the hardness is one of the most important characteristics.

Likewise, an acceleration in the ripening process in the manner indicated by the invention offers the advantage that deboning can be carried out in a phase that takes place shortly after death (post-mortem), while, without However, optimum hardness of the final product is maintained. At the same time, less storage capacity is required compared to known methods and production processes can take place online. Likewise, a profit of one day is obtained in the expiration period of the final product.

In a preferred embodiment of the method according to the invention, an electric current is applied through the carcass of the poultry, or at least through a part thereof, with an electrical contact that occurs in the chest part of the carcass, so that optimal flow through the carcass is achieved. In addition, the largest amount of meat and the most important part of the meat, which should have the least possible toughness, should be in the breast part. Likewise, the neck escapes from said stimulation, thus preventing the

ES 2 288 554 T3 distortion of the neck, which has advantageous consequences for the rest of the process. If the neck of the carcass is actually distorted as a result of electrical stimulation, the head and neck are much more difficult to remove.

In another preferred embodiment of the method according to the invention, the carcass is guided by the chest over at least one electrode connected to a power source, preferably an electrically conductive rail, with the legs of the carcass connected to the ground. through the product carrier. Thus, it is possible to ensure a substantially constant supply of energy to the chest and legs, while achieving optimal contact between the channel to be stimulated and the electrode.

In another preferred embodiment of the method according to the invention, a force is applied to the carcass in the direction of the rail, while it is driven along the rail. In particular, the carcass, at least while being driven along the rail, is obliquely at a substantially right angle to the direction of movement. The effect of these measures is that the carcass, in the second case under the influence of gravity, rests on the rail and remains in sliding contact with the rail while the carcass advances through it. Also, a transfer of energy is carried out safely. In a preferred embodiment of the method according to the invention, at least a first quiescent period of zero current is provided (t₂) after the first period of stimulation (ti), and a second period of stimulation (t₃) after the first period of rest (t₂), and during said second period of stimulation (t₃) the poultry is exposed to electrical stimulation in which an electrical voltage (v₁) through the poultry carcass, or at least through a part of it. By carrying out a second electrical stimulation after a first electrical stimulation followed by a period of zero current, it has been shown that the energy supply (biochemistry) still present in the muscles can be further reduced. In this way, the rigor mortis process that is established in the muscles of the slaughtered poultry is substantially accelerated, and a more tender product is obtained. Therefore, the period for further maturation of the poultry can be shortened.

In another preferred embodiment of the method according to the invention, the carcass, during the first period of stimulation (t₁) and the second period of stimulation (t₃), it is exposed to a pulsed alternating voltage (v₁). The administration of a pulse current has been shown to be very effective. When using a pulsed current, the channels are exposed to a voltage pulse with a pulse time and a subsequent period of zero current with an assigned relaxation time. Preferably, the pulse time goes up to about 0.5 seconds, and the relaxation time goes up to about 1 second.

Preferably, during electrical stimulation of the poultry, a thin film of water is applied to the point where electrical contact occurs, for example the breast of the poultry, and the electrode is also moistened. In this way, a very good result is achieved, while avoiding a local (over) heating of the poultry skin, and therefore a possible unwanted loss of color.

Another important criterion when evaluating the quality of meat from slaughtered animals, especially slaughtered poultry, is the development in toughness. One of the aspects of the invention is the view that from the data gathered regarding the toughness, especially the development in toughness, of the meat at different points in the production process offers the possibility of fine tuning this process on the basis of the data.

In particular, for further optimization of the processing process, it is important that the different production phases are carried out at the right time (time) and, where applicable, for the most appropriate duration.

The purpose of this is, once again, to produce a product of the highest possible quality, in particular a product as tender as possible, with which the minimum possible variation in the factors that determine quality is also achieved.

In order to achieve this objective, the invention according to a second aspect thereof provides a method for processing poultry that additionally comprises the phase of controlling the process parameters, especially the time and duration of the execution of the process phases in a mechanized work process of slaughtered animals, especially poultry, which consists in that the hardness of a given portion of meat is evaluated before the due process phase and, after this evaluation, the important process parameters for the particular process phase are placed at an optimal value.

If the slaughtered animals are poultry, the breast meat is preferably chosen to be evaluated. The evaluation can be carried out before deboning, or before filleting or before chilling or hanging and, if desired, before electrical stimulation of the slaughtered bird.

In particular, evaluation is important for refrigeration, since after all, the duration of refrigeration - which precedes filleting - has a great influence on the quality (hardness) of the product that is finally obtained. Prolonged refrigeration can improve hardness, but requires a large amount of energy, and therefore increases the final price; With the proposal of the invention, an optimal cooling duration can be established, and therefore the corresponding savings can be achieved.

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At the same time, the assessment of hardness before electrical stimulation is an advantage. As described above, electrical stimulation of slaughtered poultry has a positive influence on the toughness and toughness development of the poultry. This influence can be further increased if, prior to electrical stimulation, the (instantaneous) hardness of the poultry is known and, on the basis of these data, the electrostimulation process can be controlled so that an optimal effect can be achieved.

Therefore, the combination of measuring the hardness during the different phases of the process, controlling the different phases of work on this basis and, in particular, electrically stimulating the slaughtered birds, is an especially suitable way of producing a very tender product with a very short maturation period, also obtaining a very low variety in the characteristics important for the quality of the product.

Hardness can be determined by measuring the diffuse reflection coefficients of this kind for radiation with different wavelengths determined in the visible and near infrared zone, comparing the measurement values ​​obtained in this way with those obtained from a similar determination carried out in species that have a known hardness measurement and deriving from there a variable that characterizes the hardness in question.

In this context, for example, two reflection coefficient determinations can be carried out for radiation wavelengths in the visible light spectrum, combined with two in the near infrared spectrum.

Information regarding hardness would also be obtained by subjecting the meat part to a concentrated impact, of a predetermined duration and intensity, from a flow medium, while carefully observing the evolution of the deformation of the surface resulting in the meat. Air can be used as the working medium.

A preferred model of the invention is that with which a definitive measurement variable is obtained, representing the hardness, combining a series of determinations according to claim 34, carried out at different radiation wavelengths, with, at least a determination according to claim 35.

Preferably, the mode of procedure in this case is that the measurement variables are regularly determined from the new meat specimens of known hardness in the way indicated in claims 34 and 35 respectively, and in this way a bank of data in which the correlation between the results of the determinations according to this claim and the hardness experienced in practice is established.

A specific device to implement the proposed method can be made with a nozzle for the directed and controlled discharge of a current impact of a medium, a detection device, interacting with it, to provide an electrical output signal that represents the scheme of behavior of the impression formed on the meat to be evaluated, and a process circuit for sampling characteristic parts of the detection signal obtained. Here the process circuit is configured to analyze the initial formation, the maximum size and the relaxation of the parts of the signal that represent the impression to be evaluated.

A system for evaluating the toughness of a piece of meat from a slaughtered animal, especially slaughtered poultry, which uses the methods described above, comprises means for comparing the results of the respective measurements obtained from a directed evaluation with those that are have been obtained during a series of determinations that have been previously conducted and to, on this basis, provide a measurement value representing the hardness. This measurement value can then be used to control the product process.

The foregoing aspect and other aspects, characteristics and advantages of the present invention will be illustrated in greater detail below, with reference to the drawing and with reference to the following description of examples of a method according to the invention, in which:

Fig. 1 is the drawing of a diagrammatic design of a poultry processing plant, indicating the places where the method according to the invention can be used to advantage;

Fig. 2 is a block diagram representation of a device for implementing the proposed method;

Fig. 3 reproduces a graph that indicates the behavior scheme of the surface deformation that is formed during the implementation of the method;

Fig. 4 is a diagrammatic representation of a first model of a device according to the invention;

Figs. 4 and 5 are diagrammatic representations of a second model of the invention;

Fig. 6 shows in a diagram a third model of the invention, and

Fig. 7 illustrates a fourth model of the invention.

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In the operation of the process in a slaughterhouse to form pieces of poultry fit for human consumption, the following steps are generally carried out. First, a flow of live poultry, for example in cages, is created to a stunning device. In the stunning device, the poultry is brought into a state of semi-unconsciousness or unconsciousness, which allows the poultry to be hung by the legs in product carriers that are known per se and that advance through a conveyor. The poultry can be stunned by using a controlled gas environment, in which the birds lose consciousness, among others due to oxygen deficiency, or by administering an electric shock. Typically, the moment the fowl begins to regain consciousness, the neck of the fowl is cut so that the fowl is slaughtered and completely bled out. The poultry is then de-feathered in a plucking device provided for this purpose, and the poultry can then be processed in downstream processing stations, such as evisceration devices for the collection of organs, devices division to cut the poultry carcass into pieces and deboning devices to separate the meat from the carcass bones. However, when deboning the carcass, the following should be taken into account. Shortly after the death of an animal, an energy supply is still present in the muscles. This energy supply is spent slowly, it is the so-called maturation or hanging of the meat. This maturation period easily occupies a period of between 6 and 24 hours. During maturation, there is a stiffness, and therefore a shortening, of the muscles, rigor mortis. If a muscle is separated from the skeleton before rigor mortis has occurred, the muscle will become severely contracted, which cannot be prevented by a connection to the bones, and the muscle will become rigid.

The result of this is that a stiff muscle, after having been prepared by a consumer in the normal way, will be perceived by this consumer as a very tough meat product. Therefore, if a bird is deboned shortly after the moment of death, a hard product is obtained. At the same time, it is an empirical fact that, in addition to a hard product, there is also a large variation in hardness between different products that have the same short postmortem deboning period.

One possibility to shorten the maturation period and thus achieve a shorter postmortem deboning time is to use electrical stimulation of the slaughtered poultry prior to deboning.

The present invention is based on the idea that the effect of an electrical stimulation of the slaughtered poultry to shorten the maturation period in order, therefore, to achieve shorter deboning periods, is favorably influenced if the bird is plucked before its electrical stimulation. By ensuring that the electrical stimulation of the poultry occurs after plucking, the least plucking caused by electrical stimulation is avoided. Likewise, the effect of less hardness of plucking is used. The plucking of poultry and, in particular, the mechanical plucking of slaughtered poultry, has a lower hardness effect on the muscles of slaughtered poultry, due to the fact that the muscle cells of the slaughtered poultry poultry go to work.

Research has revealed that by carrying out electrical stimulation after plucking, the energy supply that is still present in the muscles can be eliminated to a greater extent, resulting in a more tender end product.

The administration of an electrical stimulation according to a first preferred model of a method according to the invention is carried out in the following way.

Poultry suspended in product carriers, with said product carriers advancing on a conveyor, is moved forward and, while being transported, is pulled by the head through a bath containing either a saline solution or an aqueous solution. The legs of the carcass are connected to the ground through the product carrier, so that the poultry is subjected to an electrical stimulation (flow throughout the body). Another possibility is that the carcasses advance along two electrically conductive bars, with said electrically conductive bars positioned relative to the carcasses such that electrical stimulation takes place through the chest portion of the carcass.

Another very favorable possibility is a combination of the possibilities just mentioned, that is, grounding the carcass legs through the product carrier and advancing the carcass, across the chest, on an electrically conductive rail. connected to a power source or on a strip-shaped electrode. In order to ensure contact between the carcass chest and the rail (or the strip-shaped electrode), a force is applied on the carcass in the direction of the rail while it is directed along the rail. In particular, the carcass, at least while being driven along the rail, assumes an oblique position substantially at right angles towards its direction of movement, which can be achieved, for example, by positioning the rail in such a way relative to the track of the product carriers that the carcass, under the influence of gravity, leans on the rail while traveling on it. Consequently, the channel remains in sliding contact with the rail, a very optimal flow through the body is achieved, and electrical stimulation can be carried out very effectively.

Another option is to direct an air stream towards the carcass while it is directed over the rail or, for example, use a second rail (non-conductive) at the rear of the carcass, so that the carcass is clamped between the rails while it is driven on the rail with electrical conductivity.

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During electrical stimulation of the poultry, it is advantageous to apply a thin film of water to the place where electrical contact takes place, for example the breast of the poultry. If the electrode is also moistened, a very optimal result is achieved, and local (over) heating of the poultry skin is avoided and therefore possible unwanted discoloration is avoided.

The channels are subsequently exposed to electrical stimulation with an alternating pulse voltage Vi of 100 V and a frequency F₁ 50 Hz for a first period of stimulation t₁ about 90 seconds.

Research has revealed that the administration of a direct current is less effective than a pulsed current. When using a pulsed current, the channels are subjected to a current pulse with an associated pulse time and a subsequent zero voltage period with a corresponding relaxation period. It is preferable that the impulse time is about 0.5 seconds, while the relaxation time should be about 1 second.

In a second preferred model of a method according to this invention, in which the slaughtered poultry is exposed to electrical stimulation in basically the same way as in the first preferred model, after electrical stimulation over the first period of stimulation t, a rest period t is provided₂, during which period of rest the poultry is not exposed to an electric current, and after the period of rest t₂ a second period of stimulation is provided t₃, during which period of stimulation the poultry is exposed to electrical stimulation that is fully consistent with electrical stimulation over the first period of stimulation t₁. In this way, as research has shown, the energy supply (biochemistry) that is still present in the muscles can be eliminated to a greater extent. Therefore, the rigor mortis process is accelerated substantially.

For a person skilled in this matter, it will be clear that the models that have been discussed are not limited to the indicated durations. Depending on the circumstances, it is perfectly conceivable that the stimulation periods t₁ and t₂are longer or shorter, for example 2.5 minutes or 4.5 minutes. Also, periods of rest can be longer or shorter. It is also perfectly conceivable that after the second period of stimulation t₂ a second rest period is used t₄ followed by a third period of stimulation t₅, in order to further eliminate the energy supply in the muscles.

As discussed above, the use of electrical stimulation in slaughtered poultry has an accelerating effect on meat maturation. Therefore, it is possible to separate the meat from the bone in which it is attached sooner after the moment of death, in which case the final quality of the final product is still guaranteed. In particular, deboning is possible after electrical stimulation after a maturation period of between two and three hours post-mortem.

During the process for the processing of poultry in a slaughterhouse, a decision must be made as to when the maturation process has progressed sufficiently so that the aforementioned quality of the final product is capable of being guaranteed. A first option is to proceed with further processing of the poultry after this maturation period. However, it is also possible to decide on the point at which further processing can proceed on the basis of the changing parameters of the meat during the maturation period, and therefore during the transport of the poultry (online) .

A first possible parameter on which a decision can be based is the acidity or pH of the meat. As discussed above, during the meat maturation process the energy supply that is still present in the muscle is consumed. This energy supply is used by the muscle to contract (contraction) and to relax (relaxation), for which the muscle requires calcium and adenosine triphosphate (ATP). Muscle contraction takes place at the moment in which, as a result of a signal from the nervous system, a large amount of calcium is released into the muscle fiber, which leads to a large number of contractions, thereby reducing the amount of ATP. It is simple that it is still possible for a cell to synthesize new ATP through an anaerobic process, glycolysis. The glycogen in the muscles is eventually converted, through intermediates such as glucose, into lactic acid, which results in the pH of the muscles falling during the maturation process. By measuring the pH just after the completion of the electrical stimulation or shortly thereafter, a prediction can be made on the basis of known data regarding the appropriate point at which the subsequent process can begin.

A second option is to measure in the muscle the degree of depletion of the amount of stored energy present, in order to base the decision to take on this.

In the initial postmortem period, a muscle tries to maintain a solid balance between adenine nucleotides; the ATP level remains constant; the ATP level remains constant or drops slightly. If stored glycogen decreases, ATP formation through glycolysis also decreases. ATP is dephosphorylated into adenosine diphosphate (ADP) and adenosine monophosphate (AMP). From two ADP molecules, an ATP molecule and an AMP molecule are formed. In order to allow this reaction to occur, AMP is virtually directly deaminated to inosine monophosphate (IMP). IMP can no longer be converted back to ATP. Finally, IMP is systematically converted to inosine and finally to hypoxanthine. A parameter to measure the progress of this process is the so-called R value, which is an important parameter for the progress of rigor mortis. The R value is the

ES 2 288 554 T3 ratio of adenine nucleotides (ATP, ADP and AMP) and their decomposed products (IMP, inosine and hypoxanthine). Choosing a certain value for the R-value, at which the meat will have acceptable toughness, can help decide the point at which the poultry can continue to be processed.

The method of electrical stimulation of poultry slaughtered after the poultry has been plucked has been discussed in depth previously. Practice has shown us that, in methods known in the prior art, an electrical stimulation has a negative effect on the pluckability of the poultry if the electrical stimulation precedes plucking.

As a solution to avoid this adverse effect of electrical stimulation, in addition to the execution taking place after the poultry has been plucked, a short electrical stimulation can also be carried out immediately before plucking. As a consequence, the subcutaneous muscles have practically no opportunity to become stiff, and the pluckability of the poultry is practically unaffected. In this regard, a period of about 50 seconds post-mortem should be considered.

As described above, another important criterion when evaluating the quality of meat from slaughtered animals, especially slaughtered poultry, is the development of toughness. A view of this can be obtained through the data collected regarding toughness, especially the development of toughness in meat at different points in the production process, thus offering the possibility of fine-tuning this process based on the data obtained. .

Another option to decide on the point at which further processing can be carried out on the basis of changing the meat parameters during the maturation period, and therefore during the transport of the poultry (in line), is described below with reference to Figures 1 and 7.

A modern poultry processing plant according to the prior techniques, in Fig. 1 which is characterized in its entirety by a reference numeral 100, comprises a delivery and unpacking station 102, the so-called slaughter line 104, the plucking line 106, the prep list 108, the refrigeration line 110 and, finally, a deboning and filleting line 112, where the meat of the slaughtered poultry is separated from the bones. Each of these "lines" contains a combination of workstations, all of which are known per se and are therefore not further explained.

A first place where it can be interesting to obtain data relating to the toughness of the meat of the poultry to be processed is position A, that is, directly before plucking. There a first quantity of data is obtained, relative to the quality of the poultry supplied.

A second position of interest is position B, directly after the "dressing" operation, that is, after the carcass has been separated into parts but has not yet been deboned or filleted. Also in position C, before cooling, an assessment of the toughness of the meat can provide interesting data on the basis of which subsequent processes can be fine-tuned. A determination at position D -that is, during cooling- and position E -after cooling- allows to obtain additional data, and the same can be said for positions F, G and H, that is, on the line of deboning and filleting, whether adjustable or the period and / or instants of bleeding, the period and / or instants of heating, and / or the periods and / or instants of plucking need to be adjusted.

By far the most interesting is the evaluation at position C, since here the toughness of the meat is evaluated before the carcass is separated into pieces (deboned, filleted) and the data obtained here can more widely influence the duration of the subsequent process, especially the duration of refrigeration and any intermediate storage before filleting and deboning. If, for example, the evaluation reveals that no intermediate storage is necessary to obtain a satisfactory hardness in the final product, the duration of the process can be suitably regulated, whereby significant savings can be achieved.

A device with which the evaluation can be performed is shown in a diagrammatic representation in Figs. 2 and 3. A piece of meat to be evaluated is indicated by the number 120; the housing 121 of the device that acts next comprises a spray nozzle 122 which, through an electric valve 126 which is regulated from a control circuit 124, is connected to a pressure source 128 of the medium used, for example air. Another suitable medium can also be used, possibly a liquid. The impression 132 formed by the action of the discharged jet 130 on the surface 120a of the piece of meat 120 is "seen" by a suitable detector 134, also housed in the housing 121. This detector 134 may comprise, for example, a radiation sensitive detector 138, which interacts with converters 136 that transmit light discharges that are reflected by the background of the "print" 132 and, after reflection, fall on the detector. 138; the operating time that passes between the transmission of an imposed by the converters 136 and the return received after reflection and by the detector 138 is therefore a measurement of the "depth" of the print 132, since the distance between the sensing device and the surface 120a is, after all, known. It is also conceivable to use a system that operates in the way known from modern cameras, and that can determine the distance between an image plane and an object plane.

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Either way: device 134 provides, at its output 140, an electric current, the behavior diagram of which represents the evolution of the formed impression 132. This voltage is supplied to suitable process circuits 142, 144 (possibly analog converters / digital, interface circuits, memory stores, etc.), the realization of which is not a subject of the invention. It is conceivable to store evaluation results on a series of standard test pieces as standard in a memory on circuit 144 and produce an evaluation result using an effective comparator. Circuit 144 has three outputs: one, 144a, feeds the evaluation result in a form suitable for printer 146; and the second, 144b, feeds the evaluation result in a form suitable for screen 148, and the third, 144c, feeds the evaluation result in the form of a parameter variable to a central control unit (not drawn specifically), through which the global periods are established in the different lines of work of the plant.

It should be noted that, in fact, the printer 146 and the screen 148 may be sufficient: in this case an operator can read directly from the evaluation results and, on this basis, fine-tune the process.

Fig. 3 shows the graphical representation of the behavior scheme of the output voltage of the detector 138 which represents the depth d, that is to say in the shape of the line of the curve 150. At the moment T1, the "radiation pulse" starts. and the depth d of the formed impression begins to increase to the value d_max at time T2. After this the depth remains more or less constant until time T3, the moment when the "radiation pulse" ends. The depth is then reduced again to a residual value, indicated by^dbeef^.

For the evaluation of the hardness, the line of the curve between the points a and b of the same, that is to say, between the times T1 and T2 and, in fact, the value of the angle a are of interest. This can be easily determined by differentiating the detector output voltage between times T1 and T2. Also of interest is the maximum print depth, which is derived from the maximum value of the output voltage. If, at time T3, that is, at time c of curve 150, the radiation pulse stops, the meat begins to recover and the printing depth d falls again to a residual value d_beef, which is reached after moment T4, at point d of the curve. Here too, the value of the angle β is of interest, the value of which can be easily determined. Therefore, the evaluation of curve 150 does not require very highly developed electronic elements.

Determining in advance, for a large number of pieces of meat of known hardness, the curve represented in Fig. 3, with its corresponding variables, and storing all this in a memory, a comparison of the measurement result with these "data calibration ”it is possible to make a diagnosis, with a high degree of accuracy, on the toughness of the meat.

Figs. 4 to 6 show diagrammatically some illustrative models according to the invention by which a determination is made on the meat of a slaughtered animal that is still suspended from a conveyor track. Fig. 4 shows a transport hook 155 which is guided along a track 154 already from which an already plucked channel 156 hangs, with said channel, in the place of the measuring device, supported against the stop bar 158. The device contains the aforementioned nozzle 160, connected through control valve 162 to a pressure source, symbolically indicated by arrow 164; the detection part located near the nozzle 160 is not visible in this figure, but it can be carried out in the manner explained in relation to Fig. 2. The measurement result obtained is represented on the monitor 166 connected to the elements. electronic evaluation and process 168. Within the circle 170 is represented, on an enlarged scale, the impression 172 formed in the meat, as discussed above.

Fig. 5a refers to the case where the carcass 180, with the legs 182 suspended from the usual suspension hook 184, has not yet been plucked, so that the negative influence of the feathers present must be overcome. For this purpose, use is made according to this figure of a kind of "shaving" bar 186 with rotating knives 188, which are represented on an enlarged scale at 189. All this is supported by a suitable support 190, in which the different device units are also housed.

Fig. 5b shows how, after this "cleaning-shaving", the evaluation is carried out in the manner explained with reference to Fig. 4: the apparatus used is the same in both cases.

Fig. 6 shows a model that roughly matches that of Fig. 4, but has been adapted to carry out an evaluation on a poultry that has not yet been plucked. For this purpose, there is a second nozzle 200; Through this nozzle, a gentle jet of air is directed over the point 202 to be evaluated on the breast part of the poultry, so that the feathers 204 present here are pushed aside and the evaluation can be carried out using the device according to what is indicated in Fig. 4.

Finally, Fig. 7 shows how the device can be easily used to evaluate pieces of meat from slaughtered poultry, for example breast fillets 300a-300d, which are guided by means of the conveyor track 302 along the evaluation device. 304. Also here the evaluation device comprises the nozzle 306 and still visible behind it in this figure is a part of the detection device 308, made according to the detection device which has been explained with reference to Fig. 2.

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For a person skilled in this field, it will be clear that the scope of the present invention is not limited to the models described above, but that different changes and modifications can be made hereinafter without deviating from the scope of the invention as defined in the appended claims.

In this way, it is possible, for example, to apply the data collected concerning the hardness of the slaughtered birds independently of the electrical stimulation of the slaughtered birds, and it is also possible to apply the electrical stimulation of the slaughtered birds independently of the data previously collected mentioned.