Patent Application
20070176773
The invention relates to a sensor according to the preamble of claim 1.
The invention also relates to a method according to claim 11, a system according to claim 23 and use according to claim 32.
In a package, the most stringent demands for many kinds of packaged foodstuffs include a hermetic seal, low oxygen content and sufficiently low storage temperature of the foodstuff package. If the protective gas of a gas-filled package leaks out from the package, oxygen which is a deleterious agent as to the extended acceptable quality of most products can enter the package, whereby the prolonged aging time gained by the initial protective gas filling is lost. Also in vacuum packages, the access of oxygen into the package is undesirable. In addition to the integrity and storage temperature of the package, a high quality of the raw material used is an essential factor particularly in unheated products as to the preservation of the sensory and microbiological quality. With the spoilage of a product, the microbial activity releases a large number of volatile compounds and compounds remaining in the product, whereby the quality and quantity of such compounds are determined by the character and chemical composition of the foodstuff product in combination with the microbial species causing spoilage. The compounds thus generated on one hand can affect the sensory acceptability of the foodstuff quality and on the other hand serve as quality indicators of the microbiological quality of a foodstuff product. The composition of the compounds formed in spoilage depends on the type of the foodstuff and, in the decay of poultry products for instance, different kinds of sulfur compounds (e.g., hydrogen sulfide, dimetylsulfide and dimetyldisulfide) are typically found.
Prior-art applications of RFID technology into packaging comprise theft detectors and identification tags.
Sensors employed in these applications are ultimately disposed of or deactivated in a controlled fashion, whereby these sensor embodiments lack the ability of detecting cumulative effects such as spoilage in the interior of a foodstuff package.
Conventional indicators developed to react on an increasing amount of compounds released by foodstuff decay or on increasing oxygen content in the package utilize a visible change of color. The primary function of such indicators is to help a consumer assess the quality of the product at the instant of purchase or at home. On the other hand, it would be an advantage in the wholesale or retail stage to secure the hermetic seal of packages and quality of products in the packages already prior to offering the product to a consumer.
From patent publication WO 95/33991 is known an embodiment wherein the indicator includes an electronic circuitry and a display typically integrated with the indicator construction. Alternatively, the indicator may include an output channel for taking the sensor signal over a galvanic connection to an external measurement device. This kind of an indicator with a dedicated display is necessarily an expensive solution. Moreover, passing a sensor signal to an external device over a conductor line is a very clumsy technique of retrieving information on individual foodstuff packages.
Among others, patent publications U.S. Pat. No. 5,443,987, WO 9821120, EP 0666799, U.S. Pat. No. 4,169,811 and WO 9904256 disclose indicators based on displaying a change in the indicator color or visual look at the spoilage of the product and/or change in the oxygen content of the package.
From patent publication U.S. Pat. No. 5,663,072 is known an arrangement wherein an addition of suitable chemicals is utilized in the assessment of the condition of a meat package from the absorption or reflection properties of the package itself under exposure to electromagnetic radiation. However, the compatibility of such chemicals with foodstuffs may be problematic and, furthermore, the measurement method is rather inaccurate.
As none of the hydrogen sulfide indicators known in the art are readable by RF techniques, they cannot be placed inside a foodstuff package so as to be noninvasively readable without breaking/touching the package.
Patent publication WO 01/25472 discloses an arrangement wherein a sensor readable by RF techniques is used for measuring a temperature-time integral, e.g., in order to estimate the spoilage of foodstuffs. In this system, the properties of the RF sensor placed outside the packages change cumulatively as the resistance of a biologically active material connected to the sensor varies with temperature. Inasmuch as the sensor itself is of a biologically active type, it cannot be placed inside a foodstuff package. Hence, the sensor monitors a variable (ambient temperature integral) that is known to correlate with spoilage but makes the sensor unsuitable for measuring the actual spoilage phenomenon. As a result, this embodiment is not able to identify situations in which the raw materials of the packaged product have already been defective as to their quality thus inducing a faster decay than normally expected.
It is an object of the present invention to eliminate the problems hampering the prior-art techniques and to provide an entirely novel type of sensor and method for indicating the condition of perishable products such as foodstuffs in particular.
The goal of the invention is achieved by virtue of placing into a foodstuff package a remote readable sensor based on an electric resonant circuit whose detector element sensitive to the variable to be measured is selected to be responsive to cumulative decay of a product thus making it possible to indicate the decay process in a direct and reliable fashion.
Accordingly, the essential component in an embodiment of the invention is a disposable sensor adapted to be locatable inside a foodstuff package so as to be remotely readable by RF techniques for indication of quality of a packaged foodstuff (in a sealed air-filled package, protective atmosphere package or vacuum package) by virtue of directly reacting with compounds generated in the atmosphere of the foodstuff package due to the microbiological decay of the foodstuff (particularly with hydrogen sulfide, other sulfur compounds and the like compounds capable of changing the resistance of a silver thin film).
The sensor according to the invention may also react so as to be responsive to increased oxygen content in the atmosphere of the package due to a leak or break in the package.
More specifically, the sensor according to the invention is characterized by what is stated in the characterizing part of claim 1.
Furthermore, the method according to the invention is characterized by what is stated in the characterizing part of claim 11, the system according to the invention is characterized by what is stated in the characterizing part of claim 23 and the use according to the invention is characterized by what is stated in the characterizing part of claim 32.
The invention offers significant benefits.
With the help of the electronic remotely-readable foodstuff package sensor according to the invention, the use of smart packages can be promoted in quality control from a production plant via a transportation chain to the warehousing and retail steps.
The quality control operations can be implemented in a predictive and effective fashion so that spoiled products can be discarded prior to offering them to consumers. By virtue of remote read/identification, quality control may be accomplished already in the production plant or, alternatively, for instance as a standard operation incorporated with the initial handling of goods at the firm's receive section, whereby spoiled goods can be reliably identified irrespective of the location of the spoilage sensor. In a possible alternative or complementary step, product quality control may also be carried out at the cash terminal counters.
A further advantageous benefit of the invention is that a consumer has no chance of seeing the “tripping” of the spoilage indicator, whereby spoiled products already placed on displays in a shop can be inconspicuously picked away from among the overall inventory of displayed products. Also a final quality control at the cash terminal can be used to prevent customers from receiving spoiled products.
By virtue of the invention, also the conventions related to the “Use by” date can be refined to represent more accurately the actual freshness of foodstuff products.
In the following, the invention will be examined with the help of exemplifying embodiments illustrated in the appended drawings in which
a shows an embodiment of the sensor according to the invention viewed from the direction of the device coil;
b shows the sensor of
c shows the sensor of
Referring to
As shown in
A reader device 24 is used for measuring the impedance of sensor 22 as a function of frequency. The frequency range swept in this application covers a band (7-9 MHz) centered about the sensor circuit resonant frequency. The reader device processor computes the resonance full-width half-value of the frequency-response impedance curve of the sensor circuit. Based on this information, it is further possible to derive the value of the sensor's variable resistor assuming that the properties of the sensor is coil remain constant.
Referring to
In this fashion, a change in the properties of sensor 22 due to a resistance change of resistor 12 is detected by way of computing the resonant circuit quality factor of sensor 22 and, if the quality factor falls below a predetermined value, the reader device 24 can issue an alarm. The sensor 22 is placed inside a foodstuff package, wherein its active element 12 communicates directly with the foodstuff or a solution/gas enclosing the same. Hence, the perishable foodstuff can directly affect the properties of sensor element 12 so as to cumulatively change its measured value by oxidation or corrosion.
In
Based this technique, the invention provides a disposable spoilage sensor that can be placed in a foodstuff package so as to be remotely readable without opening/touching the package. The remote read technique makes it possible to generate an unambiguous “Accept/Reject” signal. Additionally, the sensor according to the invention allows the condition of a foodstuff/package to be checked, e.g., individually identifiably by unit or case in a production plant, warehouse and/or retail shop without touching the packages. In a retail shop, an individual package can be checked by means of a remote reader device incorporated with a chilled display cabinet or cash register counter.
The function of a sensor according to the invention responsive to a spoilage-indicating compound formed in the microbiological decay of a foodstuff (typically hydrogen sulfide or the like sulfur compound or any compound reacting with a silver thin film) is based on a change in the conductivity (resistive loss) of a silver-containing material when the silver moiety is converted into silver sulfide in the presence of hydrogen sulfide. The sensor is implemented by fabricating a resonant LC circuit from the silver-containing material such that the quality factor of the circuit changes in the presence of sulfur compounds (particularly hydrogen sulfide) as the silver particles are converted into silver sulfide.
A resonant LC circuit made from a silver-containing material can be realized by way of, e.g., sputtering a thin film of silver. Typically, the thickness of the thin film is 10 to 500 nm. The optimal thickness of the thin film is in the range of 15-50 nm.
The change of resistance in a resonant LC circuit can be detected using similar electronic techniques as those employed for reading concurrent intrusion detectors or 13.5 MHz RFID tags.
The function of an oxygen-responsive sensor can be based on the change of conductivity or capacitance (permittivity) in a suitable material (e.g., a metal, metal oxide, redox indicator dye or conductive polymer) in the presence of oxygen. Such an oxygen-responsive sensor can be realized, e.g., as a thin-film sensor having a thin film element made from iron. To prevent oxidation during the storage of the sensor and in the foodstuff packaging phase, the sensor can be protected by a foil of controlled oxygen permeability. Also in this kind of an oxygen-responsive sensor, the change of its properties can be detected using such electronic techniques as are employed for reading concurrent intrusion detectors or 13.5 MHz RFID tags.
The invention is elucidated in the following exemplary embodiment.
Chicken strips (weight about 115:5 g) were packaged in 210 ml sealed containers (material HDPE) filled with protective gas (80% CO2/20% N2) and stored at controlled temperatures of +5.5° C. and +8° C. In order to analyze volatile metabolic compounds, a 5 ml gas sample was sucked from the gas spaces of each container using a gas-tight syringe and was further injected into gas-tight sealed head-space vials (volume 22 ml) in a clean room space. The hydrogen sulfide contents in the gas space of each container were determined by gas chromatography using a sulfur-selective detector.
The hydrogen sulfide content in the gas space that increases as a function of storage time and temperature (Table 1) is indicative of the freshness of chicken strips.
The effect of hydrogen sulfide on silver thin-film resistors of different thicknesses was measured in a measurement chamber of relatively high gas-tightness equivalent to a foodstuff package and maintained at a controlled temperature +4° C. (±0.02° C.). Nitrogen was used as the protective atmosphere in the chamber. The measurement equipment comprised generally an RLC bridge, while for lower resistance values a four-terminal resistance meter was employed.
In
In
In
The effect of hydrogen sulfide on 50 nm thick silver thin-film resistors was measured in a measurement chamber of relatively high gas-tightness equivalent to a foodstuff package and maintained in a chilled cabinet (+6° C.). A mixture of nitrogen and carbon dioxide that typically is employed as a protective gas in sealed meat product packages was used as the protective atmosphere in the chamber. Hydrogen sulfide was added in steps into the reaction chamber. A digital four-terminal resistance meter was used for measurements.
In
The effect of compounds released during spoilage on 50 nm thick silver thin-film resistors was examined by placing the silver thin-film resistor together with an aliquot (50 g) of chicken strips into a container (volume 120 ml, material HDPE). At the packaging instant, the recommended remaining shelf life of the chicken strips was 5 days. The protective gas filing in the container was a mixture of nitrogen and carbon dioxide (40%/60%). The container with the chicken strips therein was stored in a chilled cabinet. The resistance of the silver thin-film resistor as a function of time was measured using a digital four-terminal resistance meter as the measurement device. Simultaneously with the progress of the test on the package incorporating a sensor, sensory evaluation of the smell, particularly the sulfurous smell, released by chicken strips packaged in similar containers was performed.
In
RF technology can be utilized for implementing a plurality of foodstuff package sensors based on different responsive materials. In Table 2 are given examples on sensor materials with compounds affecting their properties so as to indicate the freshness status of a package and/or a packaged product. In addition to the compounds mentioned in Table 1, a change in the electrical properties of a sensor may also be caused, e.g., by ethanol, organic acids or volatile amines. The sensor may also be implemented using other materials than those mentioned in Table 2, such as aluminum or copper, for instance. As the resistive properties of the sensor materials listed in the latter table change in a cumulative fashion due to product spoilage, they can be used, e.g., as the cumulatively changing resistive circuit element 12 of
| Number | Date | Country | Kind |
|---|---|---|---|
| 20012243 | Nov 2001 | FI | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FI02/00911 | 11/15/2002 | WO | 6/23/2004 |
