The present invention generally relates to pathogen detection devices and methods, and, in particular, to devices and methods for detecting food-borne pathogens and spoilage.
Food borne diseases as well as food spoilage remain a significant burden in the global food supply. In the U.S. alone there are 76 million cases of food-borne illnesses annually, which is equivalent to one in every four Americans, leading to approximately 325,000 hospitalizations and over 5000 deaths annually. According to the United States Government Accounting Office (GAO) and United States Department of Agriculture (USDA), food-borne pathogens cause economic losses ranging from $7 billion to $37 billion dollars in health care and productivity losses. Hazard Analysis and Critical Control Point (HACCP) regulations state that a hazard analysis on a food product must include food-safety analyses that occur before, during, and after entry into an establishment. There is a clear need to ensure that food transported from the processor to the consumer is as safe as possible prior to consumption. For example, the development of antibiotic resistance in food borne pathogens, the presence of potential toxins, and the use of growth hormones, all indicate a need for further development of HACCP procedures to ensure that safer food products are delivered to the consumer. There is also a need to monitor foods being handled by a consumer even after such food is purchased, partially used, and stored for future use.
Meat, for example, is randomly sampled at a processor for food borne pathogens. Generally, no further testing occurs before the meat is consumed, leaving the possibility of unacceptable levels of undetected food-borne pathogens, such as Salmonella spp. and Listeria spp., as well as spoilage bacteria, such as Pseudomonas spp. and Micrococcus spp. being able to multiply to an undesirable level during the packaging, transportation, and display of the product. Subsequently, the food product may be purchased by the consumer, transported, and stored in uncontrolled conditions that only serve to exacerbate the situation, all these events occurring prior to consumption.
Retailers generally estimate shelf life and thus freshness with a date stamp. This method is inaccurate for at least two reasons: first, the actual number of bacteria on the meat at the processor is typically unknown, and second, the actual time-temperature environment of the package during its shipment to the retailer is typically unknown. As an example, a temperature increase of less than 3° C. can shorten food shelf life by 50% and cause a significant increase in bacterial growth over time. Indeed, spoilage of food may occur in as little as several hours at 37° C. based on the universally accepted value of a total pathogenic and non-pathogenic bacterial load equal to 1×107 cfu/gram or less on food products. Food safety leaders have identified this level as the maximum acceptable threshold for meat products.
While many shelf-life-sensitive food products are typically processed and packaged at a central location, this has not been typical for the meat industry. The recent advent of centralized case-ready packaging as well as “cryovac” packaging for meat products offer an opportunity for the large-scale incorporation of sensors that detect both freshness and the presence of bacteria.
A number of devices are known that have attempted to provide a diagnostic test that reflects either bacterial load or food freshness, including time-temperature indicator devices. To date, none of these devices has been widely accepted either in the consumer or retail marketplace, for reasons that are specific to the technology being applied. First, time-temperature devices only provide information about integrated temperature history, not about bacterial growth. Thus it is possible, through other means of contamination, to have a high bacterial load on food even though the temperature has been maintained correctly. Wrapping film devices typically require actual contact with the bacteria. If the bacteria are internal to the exterior food surface, then an internally high bacterial load on the food does not activate the sensor. Ammonia sensors typically detect protein breakdown and not carbohydrate breakdown. Since bacteria initially utilize carbohydrates, these sensors typically have a low sensitivity in most good applications, with the exception of seafood.
Further, known devices and methods for detecting bacteria in food substances typically integrally incorporate the device in to a package at manufacture. Neither the provider nor the consumer is able to continue the monitoring with a repackaging of the food product. It is desirable to provide a device, food packaging, and associated methods for detecting at least a presence of bacteria in a perishable food product. Further, it is desirable for a consumer to be able to detect a presence of bacteria throughout the handling of the food product by the consumer.
The present invention may be directed to detecting at least a presence of bacteria in a perishable food product carried within a container or package prepared by a supplier of the food product or by a consumer handling the food product after purchase. Embodiments of the invention may provide a quantitative measure of bacterial load and detect the presence of bacteria in or on the food product. In addition, a sensor according to the teachings of the present invention may be safely consumed if mistakenly eaten.
One sensor for detecting a presence of bacteria in a perishable food may include a pH sensitive solution of bromothymol blue and methyl red mixed with an alkaline solution, by way of example, resulting in a pH value and a generally green color changing to a generally orange color responsive to exposure to a concentration of carbon dioxide. The solution is packaged in a gas permeable container using a TPX (PMP) thin film that allows an effective diffusion of carbon dioxide through the container. The pH level drops when acidic carbon dioxide comes into contact with the solution resulting from a formation of carbonic acid making the solution an indicator of carbon dioxide concentration and thus bacterial growth.
Another embodiment may include a sensor for detecting a presence of bacteria from a perishable food product, wherein the sensor may include a sealed container having a gas permeable wall formed from a TPX (PMP) thin film and a transparent portion for viewing its contents. A pH sensitive solution is carried within the container and may have a generally green color changing to a generally orange color responsive to a 0.5% concentration of an acidic gas generated outside the container in a bacteria detection range between one million and ten million bacteria. The pH sensitive solution may be carried between first and second gas-permeable wall portions of the container for permitting a desirable diffusion of the carbon dioxide between the wall portions.
A sensor may also include a pH sensitive mixture carried within a container with the mixture including bromothymol blue and methyl red mixed with an alkaline resulting in a pH value between 6 and 8. Yet further, the sensor may include the pH sensitive mixture of bromothymol blue and methyl red mixed with an alkaline resulting in a generally green color changing to a generally orange color responsive to exposure to a 0.5% concentration of an acidic gas, wherein the bromothymol blue comprises a % wt/volume between 0.02 and 0.08, the methyl red comprises a % wt/volume between 0.001 and 0.005, dissolved in an alkaline amount ranging between 0.5 mM and 1.5 mM.
One embodiment of the invention may comprise an aqueous pH indicator in a gas permeable envelope such that CO2 gas (produced by bacteria as they grow) diffuses into the container and reacts with the solution to reduce the pH:
CO2+H2O⇄H2CO3⇄H++CO3− −
As the pH of the aqueous solution drops, due to the formation of carbonic acid, the pH indicator changes color thereby providing a visual indication of the drop in pH and therefore the presence of bacteria.
Extensive research and development has resulted in a desirable format for one embodiment of the invention including a sensor. In order to maximize the diffusion of carbon dioxide into the sensor, a two-sided design was selected that permits diffusion of gas from both sides of the sensor. This permits a rapid color change that minimizes the time a sensor is in an “uncertain zone,” where color changes are gradual and not produced in a step-styled change as is the case for embodiments of the present invention. To further improve free diffusion of gas to both sides of the sensor, it may also be desirable to place the sensor in a spaced relation to a wall of a food package in which the food product is carried.
Each component was selected and optimized to achieve the highest performance and longest shelf life at the lowest cost to manufacture. The sensor may comprise:
Features and benefits of the present invention will become apparent as the description proceeds when taken in conjunction with the accompanying drawings in which:
The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are described. This invention may, however, be embodied in many different forms and should not be construed to be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.
Referring initially to
As herein described by way of example for one embodiment of the invention, carbon dioxide is used as a generic indicator of bacterial growth and for quantitatively estimating a 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 a formation of carbonic acid, making a pH value an indicator of carbon dioxide concentration and thus of a bacterial load.
For embodiments of the invention as herein described, the sensor 10 includes the solution 20 having a pH value between 6 and 8. Further, an embodiment includes the pH sensitive solution having bromothymol blue and methyl red mixed with an alkaline solution of sodium hydroxide. One embodiment includes the bromothymol blue in a 0.05% wt/volume and the methyl red in a 0.0035 wt/volume dissolved in 1 mM sodium hydroxide for providing a pH value of approximately 6.8. By way of example, test results have resulted in effective solutions 20 with the bromothymol blue having a % wt/volume between 0.02 and 0.08, the methyl red having a %wt/volume between 0.001 and 0.005, dissolved in an alkaline solution of sodium hydroxide ranging between 0.5 mM and 1.5 mM for providing the pH value of the solution ranging between 6 and 8.
For the embodiment of the sensor 10 illustrated with reference again to
With regard to the solution 20, studies involved a pH range finding to yield a product with an initial color of rich green (similar to traffic light green) while also producing an orange-red color (typically accepted danger color) at a relevant microbial load. By way of example, while potentially useful for some situations, an initial formulation proved to be too sensitive and thus not desirable for a practical application of interest as a freshness detector (color change at 0.5% CO2 and approximately 5×105 CFU/g). One desirable embodiment including a formula containing 0.05% bromothymol blue, 0.003% methyl red dissolved in 1 mM NaOH provides a starting pH of 6.8 and yielded a green to orange color change occurring at a 0.5% CO2 concentration. Of course modifications to the formulation may be required for certain applications (e.g. antifreeze agents such as ethylene glycol may be added to the active formulation to prevent freezing at lower temperatures). Further, the Material Safety data Sheet (MSDS) of the chemicals used at the concentrations herein presented, by way of example, indicate that such formulations at the concentrations presented would not be harmful to a human if consumed in error. By way of example, and as illustrated with reference to the plot of
With regard to the container 14, a wide variety of transparent thin films were available in the marketplace. However, requirements for a film that will hold the aqueous solution are very specific and a substantial regimen of research and experimentation into optimal material for the sensor was undertaken. Desirable requirements included features selected from: a high gas permeability; thin film available (<2/1000 inch); relatively high carbon dioxide gas permeability; a high transparency; high flexibility; a heat sealable material; high flexibility; unstained by the pH indicator formulation; and a relatively low cost for manufacturing.
After extensive evaluation, it was determined that a TPX film thickness of 1.4 one thousandths of an inch with a high transparency rating meets all the above criteria. One embodiment of the sensor 10, and as above described, includes the manufacture of a square sensor, by way of example, by cutting two squares of TPX 1.4 mil thick, transparent film 1″ square, placing one square on top of the other, using a pulsed heat sealer to seal three sides, adding 0.5 ml of formulation to the formed container 14, and sealing the final side. If leaks occur at the corner, double seals on each side will solve the leaking issue.
The sensor 10 is now ready for use and has stability for at least two months at room temperature and a predicted shelf life in excess of one year at refrigerated temperatures. Naturally many parameters described in the manufacturing process may be varied dependent of application such as shape, size, volume of indicator added. The method of sealing may be heat as described above alternatively glue or other bonding agent may be applied.
With reference to
Many modifications and other embodiments of the invention will come to mind of one skilled in the art now having the benefit of the teachings presented in the foregoing descriptions. By way of example, this invention may also be applied to preparing a sensor responsive to ammonia with the color change being green to blue. Alternative pH indicators may be selected that would provide alternative color changes as the pH increased to the alkaline as a result of the formation of hydroxide ions. Therefore, it is understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of claims supported by this disclosure.
This application claims the benefit of U.S. Provisional Application No. 60/633,750 filed Dec. 7, 2004 for “Food Freshness Sensor,” and is a Continuation-in-Part of application Ser. No. 10/659,222 filed Sep. 10, 2003 for “Food-Borne Pathogen and Spoilage Detection Device and Method,” and Ser. No. 10/799,312 for “Food Borne Pathogen Sensor and Method,” filed on Mar. 12, 2004, both of which have a priority claim to U.S. Provisional Patent Application Nos. 60/411,068 filed on Sep. 16, 2002, 60/421,699 filed on Oct. 28, 2002, and 60/484,869 filed on Jul. 3, 2003, the disclosures of which are hereby incorporated by reference herein in their entirety, and all commonly owned.
Number | Date | Country | |
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60633750 | Dec 2004 | US | |
60411068 | Sep 2002 | US | |
60421699 | Oct 2002 | US | |
60484869 | Jul 2003 | US |
Number | Date | Country | |
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Parent | 10659222 | Sep 2003 | US |
Child | 11295136 | Dec 2005 | US |
Parent | 10799312 | Mar 2004 | US |
Child | 11295136 | Dec 2005 | US |