JP2008523391A - Food freshness sensor - Google Patents

Abstract

A sensor that detects the presence of bacteria in perishable foods includes a pH sensing solution, the pH sensing solution consisting of methyl red and bromothymol blue mixed with alkali to a constant pH value, a constant concentration When exposed to carbon dioxide, normal green color changes to orange. The solution is packed into a gas permeable container using a TPX (PMP) thin film that can effectively diffuse carbon dioxide through the container. When acidic carbon dioxide comes into contact with the solution to form carbonic acid, the pH level decreases, and bacterial growth is indicated by displaying the carbon dioxide concentration in the solution.

Description

  The present invention relates generally to pathogen detection devices and methods, and more particularly to food-borne pathogens and damage detection devices and methods.

  Like food damage, foodborne infections are a significant burden on the global food supply. In the United States alone, there are 76 million foodborne illnesses annually (equivalent to 1 in 4 Americans), approximately 325,000 hospitalized annually and over 5000 deaths. According to the US GAAP and the US Department of Agriculture (USDA), foodborne pathogens have caused US $ 7 billion to US $ 37 billion in economic losses in health and productivity losses . The Hazard Analysis Critical Control Point (HACCP) regulation states that food hazard analysis should include food safety analysis before, during and after entering the facility. There is clearly a need to ensure that the food transported from the manufacturer to the consumer is as safe as possible before consumption. For example, the development of resistance to food-borne pathogen antibiotics, the presence of potential toxins, and the use of growth hormones all ensure that HACCP procedures deliver safer foods to consumers. Indicates the need for further development. There is also a need to monitor food handled by consumers even after such food has been purchased, partially used, and stored for future use.

  For example, meat is randomly sampled for foodborne pathogens at manufacturing processors. In general, no further testing has been done before meat is consumed, such as unacceptable levels of undetected foodborne pathogens (Salmonella spp. And Listeria spp.), Etc. As well as spoilage bacteria (Pseudomonas spp. And Micrococcus spp.) Can propagate to undesirable levels while packaging, transporting and displaying the product. The food is then purchased by the consumer, transported and stored in an uncontrolled condition that exacerbates the situation, all of which can occur before consumption.

Retailers typically estimate shelf life, ie freshness, by date stamp. This method is not accurate for at least two important reasons. First, the real value of meat bacteria at the manufacturing processor is generally unknown, and second, the actual time-temperature environment during transport of packaged goods to retailers is generally unknown. . As an example, a temperature increase of less than 3 ° C. can shorten the shelf life of food by 50% and can significantly increase bacterial growth over time. Indeed, food damage is only a few at 37 ° C., based on the generally accepted value that the total load of pathogenic and non-pathogenic bacteria in the food is 1 × 10 ⁷ cfu / g or less. Can happen in time. Food safety leaders have confirmed that this level is the maximum acceptable threshold for meat products.

  Many foods that are sensitive to shelf life are generally processed and packaged in a central location, which is generally not the case in the meat industry. The recent emergence of intensive case-ready packaging and “cryovac” packaging for meat products gives the opportunity to incorporate sensors on a large scale that detect both freshness and the presence of bacteria.

  Many devices are known that have attempted to provide diagnostic tests that reflect bacterial load or food freshness, including time-temperature displays. To date, none of these devices have been widely accepted in the consumer or retail market because they are specific to the technology applied. First, the time-temperature device provides only information about the accumulated temperature history, not about bacterial growth. Thus, there may be a high bacterial load of food through other means of contamination, even though the temperature was correctly maintained. Wrapping film devices generally require actual contact with bacteria. If the bacteria are inside with respect to the outer food surface, the sensor is not activated even if the bacterial load inside the food is high. Ammonia sensors generally detect proteolysis rather than carbohydrate degradation. In general, these sensors are less sensitive in most normal applications except seafood, since bacteria initially utilize carbohydrates.

  Furthermore, known devices and methods for detecting bacteria in food materials generally incorporate the device integrally into the package at the time of manufacture. Neither suppliers nor consumers can continue to monitor with repackaging of food. It would be desirable to provide an apparatus, food packaging, and related methods for detecting the presence of bacteria in at least perishable foods. In addition, it is desirable for consumers to be able to detect the presence of bacteria during the time they are handling food.

The present invention relates to the detection of the presence of at least bacteria in perishable foods in containers or packages prepared by food suppliers or consumers who handle foods after purchase. Embodiments of the present invention provide quantitative measurement of bacterial load in or on food and detection of the presence of bacteria. Furthermore, the sensor according to the invention is safely digested if eaten by mistake.

  One sensor for detecting the presence of bacteria in perishable foods includes, by way of example, a pH sensing solution consisting of methyl red and bromothymol blue mixed with an alkaline solution to a constant pH value. However, generally the green color turns orange when exposed to concentrated carbon dioxide. This solution is packed in a gas permeable container using a TPX (PMP) thin film that can effectively diffuse carbon dioxide through the container. When acidic carbon dioxide comes into contact with this solution to form carbonic acid, the pH level drops, so this solution displays the carbon dioxide concentration and thus bacterial growth.

  In another embodiment, a sensor may be included to detect the presence of bacteria from perishable foods. The sensor may comprise a sealed container having a gas permeable wall formed by a TPX (PMP) thin film and a transparent portion for viewing the contents. The pH sensing solution is placed in a container, usually green, and generally orange in response to 0.5% acid gas generated outside the container in the bacterial detection range of 1 million to 10 million bacteria Changes to. A pH sensing solution may be placed between the gas permeable first and second wall portions of the container to allow the desired diffusion of carbon dioxide between these wall portions.

  The sensor may also include a pH sensing mixture within the container, the mixture including methyl red and bromothymol blue mixed with alkali to a pH value of 6-8. Furthermore, the sensor may include a pH sensitive mixture consisting of methyl red and bromothymol blue mixed with alkali, and generally green will turn to approximately orange when exposed to 0.5% concentration of acidic gas. In this case, bromothymol blue is 0.02 to 0.08 wt / vol%, methyl red is 0.001 to 0.005 wt / vol%, and amounts in the range of 0.5 mM to 1.5 mM. Dissolved in alkali.

In one embodiment of the present invention, a gas permeable covering is used so that CO ₂ gas (generated as bacteria grow) diffuses into the vessel and reacts with the solution to lower the pH as shown below. May contain an aqueous pH indicator.

CO ₂ + H ₂ O⇔H ₂ CO ₃ ⇔H ⁺ + CO ₃ ⁻⁻

  When the pH of the aqueous solution is lowered due to the formation of carbonic acid, the pH indicator changes color to visually indicate a drop in pH, ie the presence of bacteria.

  Extensive research and development has resulted in a desirable configuration of one embodiment of the present invention that includes a sensor. In order to maximize the diffusion of carbon dioxide into the sensor, a two-sided configuration was chosen that allows gas diffusion from both sides of the sensor. This allows for quick color changes and minimizes the time that the sensor is in the “indeterminate zone”. In this “indeterminate zone”, the color change occurs gradually and does not change stepwise as in the embodiment of the present invention. In order to further improve the free diffusion of gas to both sides of the sensor, it is also desirable to place the sensor at regular intervals relative to the walls of the food package containing the food.

Each component was selected and optimized to achieve the highest performance and maximum shelf life at the lowest manufacturing cost. The sensor
1. an initial pH of the pH indicator and sensor solution;
2. A permeable membrane encapsulating the solution;
3. Manufacturing the sensor by sealing the solution between the two layers of the thin film;
Can be included.
The features and advantages of the present invention will become apparent from the following description of the accompanying drawings.

  The invention will now be described in more detail with reference to the accompanying drawings, in which embodiments of the invention are shown. However, while the invention is described in many different forms, it should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.

  Referring first to FIGS. 1 and 2, by way of example, a sensor 10 of the present invention for detecting the presence of bacteria from a perishable food 12 includes a sealed container 14 having opposed gas permeable walls 16,18. The gas permeable walls 16, 18 are formed from a TPX (PMP) transparent film for viewing the pH sensing solution 20 in the container 14. In one embodiment, the pH sensing solution 20 generally has a green color to a 0.5% concentration of acidic gas generated outside the container 14 due to food 12 damage in the bacterial detection range of 1 million to 10 million bacteria. In response, it turns orange. With continued reference to FIGS. 1 and 2, the desired gas diffusion 22 of the carbon dioxide gas 24 released from the food product 12 is allowed to pass through the container 14 and the solution 20 so that the pH sensing solution 20 is located on the opposite wall 16 of the container. , 18 between. Although not necessarily required, the sensor 10 is expected to be placed in the package 26 with the food item 12 being monitored. As described above, in order to maximize the diffusion of the carbon dioxide gas 24 into the sensor 10, a two-sided configuration that allows gas diffusion from both sides of the sensor was selected. This allows for quick color changes and minimizes the time that the sensor is in the “indeterminate zone”. In this “indeterminate zone”, the color change occurs gradually and no step-like change occurs as in the embodiment of the present invention. In order to further improve the free diffusion of gas to both sides of the sensor 10, the sensor is spaced at a distance from the wall 27 of the package 26 containing the food 12 or the surface 13 of the food package itself as shown in FIG. It is also desirable to arrange

  As described above for one embodiment of the present invention by way of example, carbon dioxide is used as a general indicator of bacterial growth to quantitatively estimate the level of bacterial contamination present in the food product 12. As is well known, when carbon dioxide comes into contact with a solution, the pH drops as a result of the formation of carbonic acid, and this pH value indicates the carbon dioxide concentration and thus the bacterial load.

  In the embodiment of the invention described herein, the sensor 10 includes a solution 20 having a pH value of 6-8. In addition, one embodiment includes a pH sensing solution, the pH sensing solution comprising methyl red and bromothymol blue mixed with an alkaline solution of sodium hydroxide. In one embodiment, 0.0035 wt / vol% methyl red and 0.05 wt / vol% bromothymol blue dissolved in 1 mM sodium hydroxide to a pH value of about 6.8. Including. As an example, the effective solution 20 obtained from the test results can be dissolved in an alkaline solution of sodium hydroxide in the range of 0.5 mM to 1.5 mM to bring the pH value of the solution in the range of 6-8. 0.001-0.005 wt / vol% methyl red and 0.02-0.08 wt / vol% bromothymol blue.

  In the embodiment of sensor 10 shown in FIG. 2, the walls 16, 18 are made from a thin film having a thickness 28 of about 0.001 inch. As will be appreciated by those skilled in the art who are aware of the advantages of the present invention, an antifreeze such as ethylene glycol may be added to solution 20 along with a suitable modifier of the mixture to achieve the desired pH value. In one embodiment where test data is presented here, a 1.4 mil thick transparent film of TPX (PMP) film was used as the facing sheet sealed near the outer periphery 30. In one embodiment, as shown in FIG. 1, a container 14 having a size of about 1 inch X 1 inch 32 was used. In the embodiment presented here as an example, heat was applied to seal the perimeter 26 of the facing membrane sheet.

Studies on solution 20 may also find products in the pH range that are initially dark green (similar to traffic light green) but produce an orange-red (generally recognized hazard color) at the associated microbial load. It was conducted. As an example, although potentially effective in some situations, the initial formulation was too sensitive and proved undesirable for the actual application in question as a freshness detector (0.5% CO ₂ and about Color change at 5 × 10 ⁵ CFU / g). In a preferred embodiment comprising a formulation containing 0.003% methyl red and 0.05% bromothymol blue dissolved in 1 mM NaOH, the pH at the start is 6.8 and 0.5% CO Green changed to orange at ₂ concentrations. Of course, certain applications may require modifiers to the formulation (eg, antifreeze agents such as ethylene glycol may be added to the active formulation to prevent freezing at low temperatures). Furthermore, as an example, the Chemical Safety Data Sheet (MSDS) for the chemicals used at the concentrations presented here show that these formulations at the suggested concentrations are harmless if humans accidentally eat them. Is shown. As an example, as shown in FIG. 3, the spectrum (360-720 nm) of solution 20 of the pH formulation at room temperature on day 1 (hatched plot) and day 60 (solid line plot) is shown in the desired formulation. In contrast, the shelf life was excellent.

  For container 14, a wide variety of transparent thin films were available on the market. However, the conditions of the membrane holding the aqueous solution are very clear, and we have conducted virtually controlled studies and experiments on the optimal material for the sensor. Desirable conditions include: high gas permeability; available thin film (<2/1000 inch); relatively high carbon dioxide gas permeability; high transparency; high flexibility; heat sealable material; selected from: not soiled by the pH indicator formulation; and relatively low manufacturing costs.

  As a result of extensive evaluation, it was found that a TPX film having a high transparency rating and a thickness of 1.4 / 1000 inches satisfies all the above criteria. In one embodiment of the sensor 10, as described above, by way of example, two 1.4 mil thick, 1 inch square transparent TPX films are cut out, one square is placed on top of the other square, and the pulse With the production of a square sensor by sealing 3 sides using a heat sealer, adding 0.5 ml of the formulation to the formed container 14 and sealing the last side. If leakage occurs at the corners, a double seal on each side will eliminate the leakage problem.

  The sensor 10 is now ready for use, has a stability of 2 months at room temperature, and the expected shelf life exceeds 1 year at refrigerated temperatures. Of course, many parameters such as the shape, size, capacity, etc. of the added indicator described in the manufacturing method can vary depending on the application. In the sealing method, heat can be used as described above. Alternatively, an adhesive or other binder may be applied.

  The table in FIG. 4 shows data representing the performance of sensors manufactured as described above. Bacterial concentrations are given in colony forming units / gram (CFU / g). By way of example, the sensor 10 described above reflects one embodiment of the present invention that has collected data. After cooking, the microbial population was introduced on the surface of the cooked chicken. Cooked chickens took about 1.5 times longer to reach a high microbial load, but the sensor performance was good for both raw and cooked chickens.

  From the above description, those skilled in the art will envision many variations and other embodiments of the invention. As an example, the present invention can also be applied to the preparation of sensors that change color from green to blue in response to ammonia. Alternative pH indicators can be selected such that when the pH increases as a result of hydroxide ion formation and becomes alkaline, another color change occurs. Therefore, it should be understood that the invention should not be limited to the specific embodiments described, and that variations and embodiments are within the scope of the claims.

It is a schematic sectional drawing of embodiment of this invention effective in detecting the damage of a foodstuff. 1 is a partial cross-sectional view of one embodiment of a sensor according to the present invention. The spectrum (360-720 nm) of the solution of the pH formulation at room temperature on day 1 (hatched plot) and day 60 (solid line plot) is shown, reflecting the excellent shelf life of the formulation. FIG. 4 is a table showing the effect on biochemical and microbiological parameters of cultured chickens that have been cooked or stored raw at 10 ° C.

Explanation of symbols

10 Sensor 12 Food 14 Container 16, 18 Gas permeable wall 20 pH sensing solution 22 Gas diffusion 24 Carbon dioxide gas 26 Package 27 Wall

Claims (30)

A sensor for detecting the presence of bacteria in perishable foods,
A sealed container having a gas permeable wall formed from a TPX (PMP) film and a transparent portion for viewing the contents therein; and a pH sensing solution in said container;
The pH sensing solution changes from normal green to approximately orange in response to a 0.5% concentration of acidic gas generated outside the vessel in a bacterial detection range of 1 to 10 million bacteria, The pH sensing solution is placed between the first gas permeable wall portion and the second gas permeable wall portion of the container so that carbon dioxide is admitted to the first gas permeable wall portion and the second gas permeable wall portion. A sensor characterized by being able to diffuse between walls.   The sensor according to claim 1, wherein the acid gas includes carbon dioxide.   The sensor according to claim 1, wherein the pH sensing solution has a pH value of 6-8.   The sensor of claim 1, wherein the pH sensing solution comprises methyl red and bromothymol blue mixed with an alkaline solution.   The sensor of claim 4, wherein the alkaline solution comprises sodium hydroxide.   A solution containing 0.0035 wt / vol% methyl red and 0.05 wt / vol% bromothymol blue dissolved in an alkaline solution of 1 mM sodium hydroxide to a pH value of about 6.8. 4. The sensor according to 4.   0.001 to 0.005 weight / volume% of the methyl red dissolved in an alkaline solution in the range of 0.5 mM to 1.5 mM to adjust the pH value of the solution to 6 to 8 and 0.02 to 0.08 5. A sensor according to claim 4, comprising weight / volume% of said bromothymol blue.   The sensor of claim 1, wherein the thickness of the thin film is 0.001 inch.   The sensor of claim 1 further comprising an antifreeze.   The sensor of claim 9, wherein the antifreeze comprises ethylene glycol.   The sensor of claim 1, wherein the container is formed from a 1.4 mil thick transparent film.   The first gas permeable wall portion and the second gas permeable wall portion are formed of a TPX (PMP) film that is a sheet facing each other, and the facing sheet is sealed near the outer periphery of the sheet. The sensor according to claim 1, wherein the pH sensing solution is sealed in the container.   The sensor of claim 12, wherein the size of the container is about 1 inch by 1 inch.   13. A sensor according to claim 12, wherein heat is applied to seal the perimeter of the facing sheets. A sensor for detecting the presence of bacteria in perishable foods,
A container having a gas permeable wall; and a pH sensitive mixture in said container;
The pH sensing mixture comprises methyl red and bromothymol blue mixed with an alkaline mixture to a pH value of 6-8, and the pH sensing mixture is exposed to 0.5% concentration acid gas A sensor that changes from normal green to almost orange.   The sensor according to claim 15, wherein the gas permeable wall comprises a TPX (PMP) thin film.   The container includes a first sheet and a second sheet facing each other made of a TPX (PMP) thin film, and the first sheet and the second sheet facing each other are sealed in a vicinity of an outer periphery thereof, so that the pH sensing mixture is combined with the first sheet. The sensor according to claim 16, which is held between the second sheet and the second sheet.   The sensor of claim 16, wherein the thickness of the thin film is about 1 mil.   16. A sensor according to claim 15, wherein the container comprises a transparent portion for viewing the contents contained in the container.   16. A sensor according to claim 15, wherein the acid gas comprises carbon dioxide obtained from a bacterial range of 1 million to 10 million bacteria.   The pH sensing mixture is placed between a first gas permeable wall portion and a second gas permeable wall portion of the container, and the first gas permeable wall portion and the second gas permeable wall portion. The sensor according to claim 15, wherein carbon dioxide can diffuse between them.   The sensor according to claim 15, wherein the alkaline mixture comprises a sodium hydroxide solution.   16. The composition of claim 15, comprising 0.0035 wt / vol% of the methyl red and 0.05 wt / vol% of the bromothymol blue dissolved in 1 mM sodium hydroxide to a pH value of about 6.8. The sensor described.   0.001-0.005 wt / vol% methyl red and 0.02-0.08 wt dissolved in an alkaline amount ranging from 0.5 mM to 1.5 mM to obtain a pH value of the mixture. The sensor according to claim 15, comprising: / volume% of the bromothymol blue. A sensor for detecting the presence of bacteria,
The sensor comprises a pH sensing mixture, the pH sensing mixture comprising methyl red and bromothymol blue mixed with alkali to a pH value of 6-8, the pH sensing mixture having a concentration of 0.5%. When exposed to acid gas, normal green color changes to approximately orange color, and 0.001 to 0.005 wt / vol% of the methyl red dissolved in an alkaline mixture in the range of 0.5 mM to 1.5 mM and 0. A sensor comprising 02 to 0.08 wt / vol% of the bromothymol blue.   26. The sensor according to claim 25, wherein the mixture is a solution in a gas permeable container, and the gas permeable container is formed of a TPX (PMP) thin film through which the acidic gas can diffuse.   The container has a first sheet and a second sheet facing each other made of a TPX (PMP) thin film, and the first sheet and the second sheet facing each other are sealed in a vicinity of an outer periphery thereof, and the first sheet and the second sheet are sealed. 27. The sensor of claim 26, holding a pH sensing mixture therebetween.   26. A sensor according to claim 25, wherein the alkaline mixture comprises a sodium hydroxide solution.   26. The composition according to claim 25, comprising 0.0035 wt / vol% of the methyl red and 0.05 wt / vol% of the bromothymol blue dissolved in 1 mM sodium hydroxide to a pH value of about 6.8. The sensor described.   In order to estimate the level of bacterial contamination present in perishable foods, the acidic gas contains carbon dioxide which functions as a general indicator of bacterial growth, and when the carbon dioxide comes into contact with the mixture, the pH is lowered, and at that pH 26. The sensor according to claim 25, wherein the bacterial load is displayed by displaying a carbon concentration.