SCHROOT, Joyce, Henrika (Paalbergweg 25, AD Hoenderloo, NL-7351, NL)
GROENEWEG, Bastiaan, Rinke, Anthony (Dwarsweg 50, CG Rockanje, NL-3235, NL)
VAN DEN BOSCH, Henricus, Franciscus, Maria (Schoolstraat 17, NL- 5438 AC Gassel, NL)
VAN DER VOORT, Aart-Jan (Churchillweg 1, JA Wageningen, NL-6707, NL)
DE BRUIN, Martijn, Willem (Roerdomp 36, CB Kockengen, NL-3628, NL)
DE HEIJ, Wouter, Bernardus, Cornelius (Mennonietenweg 68, AB Wageningen, NL-6702, NL)
SCHROOT, Joyce, Henrika (Paalbergweg 25, AD Hoenderloo, NL-7351, NL)
GROENEWEG, Bastiaan, Rinke, Anthony (Dwarsweg 50, CG Rockanje, NL-3235, NL)
VAN DEN BOSCH, Henricus, Franciscus, Maria (Schoolstraat 17, NL- 5438 AC Gassel, NL)
VAN DER VOORT, Aart-Jan (Churchillweg 1, JA Wageningen, NL-6707, NL)
DE BRUIN, Martijn, Willem (Roerdomp 36, CB Kockengen, NL-3628, NL)
| Claims 1. A process for defining the respiration of a food product especially vegetables or fruit, in which a sample with a predetermined weight of the food product is enclosed in a gas tight container, the temperature and the gas composition in the container is set to defined values, and the respiration rate of the food product is defined under these set circumstances by measuring the change of concentration of oxygen, nitrogen and or carbon dioxyde in the container during a fixed time. 2. A process according to claim 1 , characterized in that the defined respiration rate is stored in a computerized data base. 3. A process according to claim 1 and 2, characterized in that the gas composition in the container is adjusted by regulating the oxygen, nitrogen and/or carbondioxyde content of the gas composition. 4. A process according to any one of the preceding claims, characterized in that the temperature in the container is set to the intended storage temperature of the food product. 5. A process according to any one of the preceding claims, characterized in that the gas composition in the container is defined for optimal storage of the food product at a defined temperature. 6. A process for packaging a food product in a plastic film material, in which the respiration rate of the food product is defined in accordance to anyone of the claims 1 -5, characterized in that based upon the gas transfer rate (GTR) of the plastic film material, the weight of the food product to be included in each package and the surface area of the plastic film material to be used in the package, the optimal gas transfer rate of the package is defined in view of the registered respiration rate of the food product and the gas transfer rate of the package is adjusted either by selecting the correct quality of the plastic film material and/or applying at least one gas transfer hole in the plastic film material. 7. A process according to claim 6, characterized in that the packaging is done in a process in which starting from a blank film material a bag is made which is subsequently filled with the food product and in which a perforation unit is provided for applying the required number and/Or size and distribution of gas transfer holes in the plastic film material. 8. A process according to claim 6 or 7, characterized in that the optimal gas transfer rate of the plastic film material is defined by the optimal oxygen transfer rate (OTR), and/or the optimal carbondioxyde transfer rate (CTR) of the plastic film material or a combined value resulting from the optimal OTR and CTR. 9. A process according to claim 5 and anyone of the claims 6-8, characterized in that the package is filled with the optimal gas composition for a given storage temperature. 10. A process according to claim 10, characterized in that the gas composition of the package is adjusted by adding oxygen and/or nitrogen and/or carbondioxyde to the gas composition inside the package. |
The invention relates to a process for defining the respiration of a food product especially vegetables or fruit.
It has already been known that food products especially vegetables or fruit , when packed in plastic film material, should not be sealed off completely form the surrounding atmosphere, but that some exchange of gas products between the inside and the outside of the package should be allowed. When this exchange of gaseous substances between the inside and the outside of the package is regulated in the right way, the quality of the product over time is improved as well as the appearance and conservation time. In view of this known phenomena it has already been proposed make a package of plastic film material which allows a defined gas exchange. In view thereof the plastic film material may be provided with additional perforations in order to have the optimal gas exchange.
The required gas exchange between the inside and the outside of the package is dependent upon a number of parameters such as the nature of the food product, the weight of food product contained in the package and the surface area ov the film material used in the package.
The definition of the optimal gas exchange however still remains a difficult and complicated issue and was based upon trial and error approaches. As an illustration of the complications encountered it can be stated that the same type of agricultural product has not always the same respiration characteristics. Under respiration characteristics there is understood the adsorption or desorption of oxygen, nitrogen and carbon dioxide of the product involved, and this is not a fixed value of the product but may be dependent upon the time and place of the harvesting of the product. The same applies when the size of the package is changed during the packaging process, because another quantity of the food product should be contained in the package, and because of this change two important parameters, weight and surface area, are changed at the same time.
In view of these complications thers ia a need ot have a reliable method for defining the respiration characteristics of a food product in order to have a reliable value which gives an indication of these respiration characteristics which can be used in defining the gas exchange needed for a given package to be used. According to the invention this is obtained by means of a process in which a sample with a predetermined weight of the food product is enclosed in a gas tight container, the temperature and the gas composition in the container is set to defined values, and the respiration rate of the food product is defined under these set circumstances by measuring the change of concentration of oxygen, nitrogen and or carbon dioxyde in the container during a fixed time.
Other characteristics and advantages of the invention will become clear from the following description reference being made to the annexed drawing In which there is schematically shown an installation for performing the process according to the invention.
In the drawing there is shown a so-called respiration meter 1. Basically this comprises a container with a door, which can be closed in a gas tight manner, so as to form a completely isolated space with no exchange of gas with the environment. In this container there a installed a number of metering systems for measuring the temperature and the concentration of oxygen, nitrogen and/or canbondioxyde in the gas present inside the container. Such metering systems are generally known in the art. The respiration meter 1 is further provided with a heat exchanging unit which allows the heating or cooling of the content of the container in a controlled and accurate way. Moreover it is also possible to include a system for regulating the humidity level in the container and a metering device for defining that level.
The container is connected to a mixing device 2 which is further connected to a supply of oxygen 3, nitrogen 4 and carbondioxyde 5. In the mixing device 2 any composition of gas mixtures consisting of oxygen, nitrogen and/or carbondioxyde can me bade and supplied to the container in order to accurately control the initial gas composition inside of the container. The different gas concentration metering systems are further electrically connected to a computer system 6 in which the measured value can be stored and used in further calculations.
In order to define the respiration characteristics of the a food product, especially of vegetables or fruit, a standard sample of the food product is prepared. With standard sample is meant a sample which is representative of the average quality of the whole of the food product for which the respiration characteristics must be defined and a defined quantity expressed in weight. This sample is put in the container and its door is closed. Subsequently the temperature in the container is regulated to a temperature at which the respiration characteristics of the food product must be defined. Normally this temperature is equal to the expected storage temperature of the food product, but in fact any other temperature is applicable as well, provided the food product will not be damaged or modified by such
temperature. This can be important for defining the optimal storage temperature of a food product. Normally the gas composition in the container is equal to the standard environmental conditions, but if needed also the inside pressure can be controlled as well. Once the temperature in the container has reached a fixed an constant value the concentration of the oxygen, nitrogen and/or carbondioxyde is measured and stored in the computer system. Subsequently the temperature is kept constant and after a defined period of time the concentration of oxygen, nitrogen and /or carbon dioxide is once more measured and the obtained data are also transferred to the computer system. This process can be repeated several times each time after a
predetermined time period has elapsed and the measured values are each time transmitted to the computer system. Based upon the received data the computer system can calculate one or more numerical values which are representative for the respiration characteristics of the food product involved.
It is known that the conservation of a food product can be improved if the food product is packed in a substantially sealed package with a controlled gas
composition, especially the concentration of oxygen, nitrogen and/or carbondioxyde. When using such modified gas composition in the package is also important to know the respiration characteristics of the food product in these circumstances. For that purpose the mixer 2 can be used in order to fill the container with the required gas composition. This can be done by flushing the container with the required gas composition fed by the mixing device and introducing the sample of the food product while flushing, whereupon the door of the container is closed. Once the temperature is set to the required value, the proceeding as described above can be repeated and the respiration characteristics of the food product in these circumstances defined.
In a preferred embodiment of the process according to the invention the computer system 6 and the data collected from the respiration meter 1 are directly coupled to a packaging machine, in order to monitor the respiration characteristics of the package to be made. Preferably the packaging machine is of the type described in European patent specification EP-B-1 332 089 in which there is described a machine in which a plastic film material is provided with perforations and subsequently shaped into bags, filled with food products and sealed. As generally known in the art, it is important that the packaging material has a defined degree of gas exchange with the environment or respiration in order to optimize the conservation of the food product in the package.
The required respiration of a package made of plastic film material is defined by a number of parameters.
First at all there are the respiration characteristics of the food product as defined before, and data representative for this parameter are stored in the computer system 6. Based upon these data the optimal respiration for a given quantity can be calculated.
A second parameter is the film material. Dependent upon the chemical and physical composition of the film material this has a defined gas permeability especially with respect to oxygen, nitrogen and carbondioyde, the three gases mainly defining the conservation quality. This parameter is a fixed value for each individual plastic film material and as such indicated by the supplier of this type of material and can also be stored in the computer system 6 for the different type of plastic film materials which will be used for the packaging of the food products. The above mentioned two parameters are fixed values in so far as these values are independent of the quantity of the food product to be packed, and to some extent only dependent upon the nature of the food product and the nature of the plastic film material. Each package to be prepared will have a defined weight and the value of the above defined respiration characteristics of the food product must be modified in function of the weight.
Furthermore the weight of the food product to be packed has a relationship with the shape and the size of the package to be used and therefore also to the surface area of the plastic film material which in the ultimate package will be available for gas exchange or respiration between the inside and the outside of the package. The applicable value of permeability of the film material must be modified in function of the surface area of the film material present in the ultimate package.
In the computer system 6, the optimal respiration characteristics for a given quantity of food product has been defined. Based upon all these data as described above it is possible to calculate the difference between the optimal respiration rate of the package and the real respiration rate of the package without any additional perforation. Based upon this difference the number and size of the perforations can be calculated and supplied to the perforation device used in the packaging machine.
The complete calculation can be done by the computer system in which all the data are stored, In this way it becomes even possible to have a nearly on-line control of the packaging machine. This is possible in that immediately before the packaging of a new food product is started, a standard sample of that food product is put in the respiration mater and its respiration characteristics defined. As soon as this has been finished, a task which can be done at the moment that the previous packaging operation is running out, the new packaging operation can be started as all data required are present in the computer system. In another embodiment of the process according to the invention, it is possible to control the packaging process to such an extent that the gas composition inside the package is optimized.
As explained above the respiration meter has the capacity of defining the optimal conditions for the conservation of the food product with respect to the surrounding gas atmosphere at a given temperature.
In order to perform this in the packaging machine it is necessary to have a gas supply system 8 which is connected to gas mixing device 9 in which the required gas composition is prepared and this gas is injected in the package at the moment the latter will be closed. The required gas composition is also calculated by means of the computer system 6.
In the mixing device 9 a gas composition containing primarily oxygen, nitrogen and carbondioxyde will be prepared in the right relative amounts. The carbondioxyde is supplied from a container 10, whereas preferably the oxygen and nitrogen are originating from the environmental air. This air is supplied to a dust filter 11 and from the latter to a membrane separator 12 in which oxygen and nitrogen are separated and as almost pure gases supplied to the mixing device 9. In this way it is possible to have a relatively cheap supply of oxygen and nitrogen with a degree of purity which is sufficient for this type of applications. Is is of course also possible to have a more common supply of gases from three separate containers containing oxygen, nitrogen and carbondioxyde respectively.
It will be obvious that the invention is not restricted to the described embodiment of the process and to the process as described, but that within the wording of the claims modifications can be applied without departing from the scope of protection of these claims.
In order to further elucidate the invention a mathematical example will be given how the invention can be used in practise.
Example
A food product is put in the gas tight container at the desired conservation temperature and the desired oxygen xoncentration. Subsequently the oxygen concentration is measured during a defined time period and from the reduction of the oxygen concentration the respiration rate is calculated in the following way o, d(pQ 2 ) d(pQ 2 )
RR =— or RR = f(V 0 ,M,R,T, )
M - R - T dt dt in which
Vo2 is the volume of oxygen in the respiration mater in m 3 ,
M the mass of the product in kg,
R the gas constant (8.3 J/kg/K),
T the temperature in °K
d(p0 2 ) the change of the partial oxygen pressure p0 2 over a defined period of time (Pa/s).
Using these units the respiration rate is expressed as Mol/kg/s. In stead of seconds it is also possible to use as time unit hours or days.
In the following example hours are chosedn as time unit: Example:
Oxygen volume in the respiration meter: V 0 2 = 3 10 '3 m 3 ,
Mass of product : M = 2 kg
Gas constant R = 8.3 J/kg/K
Temperature: T = 278 K (= 5 °C),
Partial oxygen presseure decrease per hour: d (p02) / dt = ( 6 kPa - 5 kPa) / 1 hour = 1000 Pa/hour
Respiration rate RR = 6.5 10 "4 Mol/kg/hour = 0.65 mMol/kg/hour:
For the conservation in a plastc film material of 2 kg of this product with an optimal partial oxygen pressure of 5 kPa the transmission rate of the film material must be such that the enters the package is exactly equal to the quantity which uses the product for respiration:
OTR A-(p0 2amb -p0 2 )
ψ 2,amb v 21 = RR · M or
R T
OTR = f(RR,M,A,p0 2amb ,p0 2 ,R,T)
with the Oxygen transmission rate' OTR (m/s=24*3600*10 6 cc/m2/day) and a surface area A (m 2 ). p0 2 , a mb is the partial oxygen pressure in the environment whereas R, T RR and M are given data as disclosed above.
Example in which the time unit is hours: With
Respiration rate RR = 0.65 mMol/kg/uur,
Mass of product M = 0.5 kg product,
Film surface A = 0.1 m 2 ,
partial pressure environment oxygen (21%) p02amb = 21 kPa,
Partiale oxygen pressure in the package p0 2 = 5 kPa,
Gas constant R = 8.3 J/kg/K
Temperature: T = 278 K (= 5 °C),
Optimal 'oxygen transmission rate' OTR = 5 10 "4 m/uur = 12000 cc/m /dag.
As this is a very high value for a unperforated plastic film mateiral additional perforation scan be applied until the optimal OTR is reached.