Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N31/00—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods
  • G01N31/22—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods using chemical indicators
  • G01N31/221—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods using chemical indicators for investigating pH value
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/02—Food

Definitions

• the field of this invention concerns the determination of food freshness, and, in particular, methods and devices for the detection of spoilage in food products.
• the spoilage and souring of perishable foods with time is an on-going problem for the consumer and food product provider alike.
• Deterioration in freshness is in large part due to the growth of microbes such as bacteria, yeasts, and fungi. To derive energy for their growth, these microbes break down food carbohydrates, proteins and fats. The breakdown process produces a variety of low molecular weight molecules capable of producing hydrogen ions that affect pH.
• Such molecules include carboxylic acids (e.g., lactic and acetic acids), aldehydes, nitrogen containing molecules including ammonia, trimethylamine and small diamines, and some sulfur compounds.
• microbes in milk and dairy products produce an increased amount of lactic acid and lactic acid derivatives resulting in sour and odorous milk, respectively.
• the generation of lactic acid and its derivatives creates a more acidic environment with a lower pH.
• U.S. Patent No. 5,306,466 by Goldsmith discloses a packaging method which includes a bar code design consisting of labeled antibodies bound to toxins.
• the bar code design is placed in contact with the food product, for example by printing it on a membrane in the packaging itself, and a competitive antibody-antigen reaction is used to detect spoilage.
• the antibodies on the membrane which react with the specific class of toxins accumulating in the food product, are released from the membrane, thereby destroying the design and providing a visual indication of toxin presence.
• this type of indicator is expensive because of the antibody cost, may not be safe to consumers, and has limited applicability.
• electrode systems and electrochemical or competitive assay techniques do not solve the consumer problem. These techniques often involve relatively lengthy or complex procedures, and may have limited applicability. Accordingly, there exists a need for relatively rapid, efficient, accurate, inexpensive and simple methods and devices for indicating spoilage in a variety of food products. Such methods and devices would simplify spoilage indication techniques while maximizing their accuracy, efficacy and applicability through the selection of indicators, buffers and barriers.
• TTI Time-Temperature indicators
• Jalinksi describe methods of monitoring a possible unfavorable temperature history of refrigerated foods.
• time temperature indicator with distinct end point label for food packaging indicating refrigerated storage
• U.S. Patent 5,182,212 and time temperature indicator with distinct end point dual system of active reagent, substrate and pH-sensitive dye for monitoring shelf-life of cooked packaged food, room temperature or refrigerated storage.
• U.S. Patent No. 5,085,802 Commercial TTI include the Life Line Monitor, the I- Point Time/Temperature Monitor, and the 3M Monitor Mark. The TTI approach is expensive and complicated at the retail consumer level and implementation will require much consumer education.
• an object of the invention is to provide a method of indicating food spoilage which is simple, accurate and inexpensive.
• Another object of the invention is to provide a food spoilage indicator device for placing in fluid contact with a food product.
• the present invention provides a method of detecting spoilage in food products using the described spoilage indicator device.
• the spoilage indicator device has a barrier sheet which is permeable to uncharged molecules less than 200 daltons in size and is substantially impermeable to larger uncharged and charged molecules.
• the barrier sheet is disposed in contact with the food product.
• the spoilage indicator device also includes a carrier which has been impregnated with a pH indicator material and buffer material.
• the pH indicator material is capable of producing a visually detectable change upon reacting with a reactant molecule produced in the food product when the food product is undergoing spoilage.
• the first planar surface of the carrier is separated from fluid contact with the food product by the barrier sheet.
• the spoilage indicator device also includes a transparent or translucent outer layer disposed on a second planar surface of the carrier. This outer layer protects the pH indicator material and buffer material impregnated within the carrier from contamination associated with the food packaging.
• the method of the present invention allows the desired reactant molecules produced by food product spoilage to traverse the barrier sheet separating the food product from the carrier and react with the pH indicator material in the carrier.
• the reactant molecule can be carried in a liquid phase, gas phase, acid or base and the pH indicator of the present invention is capable of reacting with the reactant molecule in each of these situations.
• the detectable change caused by the reaction of the reactant molecule with the pH indicator is a visible change in color which indicates a build-up of the reactant molecule in the food product which provides an indication of spoilage.
• the device of the present invention includes a barrier sheet composed of the hydrophobic materials polyethylene or polyvinyl chloride with a thickness in the range of 10 to 15 microns.
• the carrier layer of the spoilage indicator device consists of a paper and has a thickness in the range of 15 to 20 microns.
• the pH indicator material of the spoilage indicator device is selected from the group consisting of phenol red, cresol red and w-cresol purple.
• the buffer material of the spoilage indicator device should be effective within the pH 8-10 range and preferred buffer systems consist of amino acids with the most preferred buffer systems consisting of lysine or glycine.
• the transparent (translucent) outer layer of the spoilage indicator device has a thickness in the range of 5 microns to several millimeters and may be composed of various materials depending upon the position of the device.
• the outer layer consists of a gas-impermeable material selected from the group consisting of polyester, cellulose acetate, polyolefin, polypropylene polystyrene, polyvinylidene chloride and glass.
• the outer layer consists of the gas-permeable materials polyvinyl chloride or polyethylene.
• fluid refers to liquid or gaseous states
• carrier means a device or portion of a device which provides a physical separation between one location and another or between the device and the product;
• reactant molecule means any molecule produced in a food product causing spoilage, or a product of a secondary reaction of a molecule produced in the food product causing spoilage, which can react with the selected pH indicator in the device of the invention
• indicator means any material which can react with the reactant molecule to produce a detectable, e.g., visual change, either through a direct or intermediate reaction
• spoilage means any reduction in freshness of a food product making it less palatable or dangerous for consumption by the animal, e.g., human, that would normally eat the food product;
• carrier means any material which entraps or holds an indicator; e.g., paper, other fibrous or cellulosic materials and the like.
• buffer means any material which maintains pH reasonably constant when additional acid and base is added.
• FIG 1 is an enlarged cut-away side view of the spoilage indicator device, showing a barrier sheet disposed on a first surface of the carrier containing a pH indicator material and buffer material;
• FIG 2 is a cut away of another embodiment of the spoilage indicator device, wherein the device has a sealed outer surface.
• the present invention features methods and devices for providing a visibly detectable indication of food spoilage.
• the spoilage indicator device contains a barrier sheet which allows passage of uncharged reactant molecules of a predetermined size but segregates out charged and larger uncharged molecules.
• the barrier sheet is in contact with the food product and is contiguous to the first planar surface of the carrier which has been impregnated with a pH indicator material and buffer material.
• the barrier sheet protects the carrier from potential contamination
• the pH indicator material provides a visually detectable change, a color change, upon reaction with the reactant molecules which indicates spoilage.
• the present invention also contains an outer layer that separates the second planar surface of a carrier from the ambient atmosphere or the fluid phase of the food product.
• the present invention is based on the further recognition that such a device can be placed in a food product package without contaminating the food.
• Reactant molecules produced by food products undergoing spoilage exist in liquid and gaseous forms and impact the pH of the fluid phase of the food product.
• Reactive molecules produced by food spoilage include acids, bases, aldehydes, sulfur compounds, and their derivatives.
• reactant molecules resulting from spoilage include carboxylic acids, such as acetic or lactic acids; acid derivatives such as acetylaldehyde, basic molecules containing nitrogen such as ammonia, and amines (e.g., trimethylamine and small diamines having a molecular weight of less than about 200 daltons) and sulfur containing molecules such as hydrogen sulfide.
• carboxylic acids such as acetic or lactic acids
• acid derivatives such as acetylaldehyde
• basic molecules containing nitrogen such as ammonia
• amines e.g., trimethylamine and small diamines having a molecular weight of less than about 200 daltons
• sulfur containing molecules such as hydrogen sulfide.
• the barrier sheet of the present invention is selected to allow the desired reactant molecule to pass through while retaining the pH indicator and buffer materials and excluding larger, unwanted molecules.
• the desired reactant molecules produced by food product spoilage are allowed to traverse the barrier sheet separating the food product from the carrier and react with the pH indicator material in the carrier.
• the detectable change caused by the reaction of the reactant molecule with the pH indicator is a visible change in color which indicates a build-up of the reactant molecule in the food product which provides an indication of spoilage.
• suitable barrier materials must be permeable only to uncharged molecules less than 200 daltons in size and substantially impermeable to larger uncharged molecules.
• the barrier material must be chemically inert and non- contaminating to the food product.
• Preferred barrier materials include, but are not limited to, low- or medium- density polyethylenes, polyvinyl chlorides and other water resistant or hydrophobic materials meeting Food and Drug Administration standards for food wrappings.
• the barrier sheet has a thickness in a range of 10 to 15 microns.
• the barrier sheet extends beyond the contours of the carrier to form a totally sealed package. This type of device is particularly useful if liquids are to be use since it will protect the carrier against contamination by splashing.
• Various carriers for entrapping an indictor material are known to those of ordinary skill in the art.
• Examples of such carriers include paper (e.g., untreated cellulose), polyamides, cellulose acetate, gels, foams, glass fibers and resins such as ion-exchange resins.
• a transparent polyester layer can be adhered to the carrier to stiffen it and make it easier to cut and handle. This layer can also be used as the outer layer.
• the first planar surface of the carrier is contiguous to the barrier sheet and has been impregnated with a pH indicator material and buffer material.
• the carrier material must be capable of uniformly absorbing the pH indicator material and buffer material and must also allow the reactant molecules access to the pH indicator.
• the carrier material As the carrier material will be observed visually and/or photometrically, the material must allow for a good contrast between the acid and basic colors of the absorbed pH indicator. In addition, the carrier material should be non-reactive with the pH indicator and buffer and possess minimal fixed charge and little ash content. As a result, porous, inert materials are preferred carrier materials.
• the carrier generally has a thickness in the range of 15 to 25 microns.
• the preferred carrier material is a paper, specifically, low-lint, high density, facial tissue-type paper. In addition, other similar personal care-type "tissues" may also prove equally satisfactory.
• the preferred pH indicator material has a pK close to the pK range of the food product and produces a substantial color change in response to very small changes in hydrogen concentration (e.g. less than 10 -7 M [H + ]).
• the preferred pH indicator material is sensitive enough to produce detectable changes when the reactant molecules are in a concentration of approximately 0.01% by volume in the fluid surrounding the food product.
• Specific examples of preferred indicator materials include but are not limited to, phenol red (phenolsulfonephthalein), -cresol purple (w-cresolsulfone-phthalein), cresol red ( ⁇ -cresolsulfonephthalein) and mixtures thereof. All the preferred indicators are characterized by a strong change in color and an increase in color intensity moving from pH 7-7.5 to pH greater than 8.
• pH indicator materials as well as the pH ranges within which they are effective and what color changes occur, are shown in Table 1.
• the preferred indicators are in bold.
• buffer/indicator combinations As pH indicators with a pK greater than 7.0 do not exhibit stable basic colors unless buffered, the use of appropriate buffer/indicator combinations is essential to maintain stable initial colors. In order to achieve stable initial colors, buffer concentrations of 0.01 to 0.05 M or buffer/indicator molar ratios of 20 to 200 (typically 50) are required. At such buffer/indicator ratios, the response of the spoilage indicator device to acid or basic volatiles is predominately that of the buffer. Raising the indicator concentration enough to significantly affect the buffer ratio will obscure color change and lowering buffer concentration significantly decreases initial color stability.
• the preferred buffers for general use include lysine and glycine.
• Additional amino acid derivatives which may also be of use as a buffer system include; N,N-(Bis-2-hydroxyethyl)glycine; l,5,(4)dimethylimidazole; 2- amino-2-methyl- 1 ,3 ,-propanediol; 2-amino-2-ethyl- 1 ,3,propanediol, diethanolamine; ethanolamine,2-(cyclohexylamino)ethane sulfonic acid and 2-amino-2-methyl- 1 -propano.
• Borate buffers also appear equally suitable in principle to lysine and glycine but are not as preferred for food applications.
• carbonate buffers are suitable for use in carbonated beverages.
• the spoilage indicator device of the present invention also includes an outer layer which is transparent, translucent and/or has at least a translucent or transparent portion through which an underlying layer, such as the carrier, can be observed visually and/or photometrically.
• the outer layer is normally disposed directly on the second planar surface of the carrier material.
• the outer layer can have a thickness ranging from 0.07 to 2.5 mm.
• both layers are composed of a material permeable to reactant molecules in order to increase the diffusion area of the device.
• the preferred materials for the outer layer include, but are not limited to, polyvinylchloride and polyethylene.
• FIG. 1 shows a cut-away view of an embodiment of the spoilage indicator device 110.
• Device 110 has a carrier 114 with a first surface 115 directed toward food product 126.
• Carrier 114 has a pH indicator material and buffer material 120 entrapped within it.
• First surface 115 of carrier 114 is separated from contact with food product 126 and its surrounding juices 128 by a barrier 118.
• Spoilage indicator device 110 as shown also includes a transparent or translucent outer layer 116 disposed on a second surface 117 of carrier 114. Such an outer layer 116 protects the pH indicator material and buffer material 120 entrapped within the carrier 114 from contamination associated with the food packaging.
• the barrier layer 118 is disposed directly on the first surface 115 of carrier 114 and may continue beyond the contours of the carrier 1 14 to form the wrap or food packaging, thereby eliminating additional layers between the carrier 114 and the food. Similarly, outer layer 116 may continue beyond the contours of carrier 114 in the form of a tape or label.
• the device may have a barrier sheet 218 wrapped around carrier 214, covering both first and second carrier surfaces 215 and 217.
• barrier sheet 218 also extends beyond the contours of the carrier 214 to form a totally sealed package. This type of device is particularly useful if liquids are to be use since it will protect against contamination by splashing.
• FIG. 2 further shows the outer layer 216 is sealed with a food-package grade, water- and cold-insensitive tape 219.
• the tape 219 adheres to the outer layer 216 and to the wrap or food packaging layer 212 if used separately. It is advantageous that tape 219 is provided with a transparent or translucent window 221 to observe the detectable changes of the pH indicator material 220. Alternatively, tape 219 itself is transparent or sufficiently translucent to allow an observer to view a detectable change in the pH indicator material 220 through the tape 219.
• the spoilage indicator device includes cresol red as the pH indicator and lysine as the buffer impregnated within a paper carrier for detecting lactic acid and other reactant molecules produced by the spoilage of milk.
• the carrier's first planar surface is separated from fluid contact with the food product by a barrier sheet composed of polyvinyl chloride and an outer layer composed of Saran Wrap (see Example 7).
• the spoilage indicator device includes phenol red as the pH indicator and lysine as the buffer impregnated within a paper carrier for detecting acetic acid and other reactant molecules produced by the spoilage of citrus juices.
• the carrier is separated from fluid contact with the food product by a barrier sheet composed of polyethylene film and an outer layer composed of Saran Wrap (see Example 4).
• the spoilage indicator device also includes a "window" or a transparent or translucent layer which allows visualization of the pH indicator from outside the packaging. This window could be a cellulose acetate, poly vinylidene chloride, polyester or glass outer layer disposed on a second planar surface of the carrier.
• the spoilage indicator device of the present invention can be placed such that the pH indicator is in fluid contact with the food product and/or its surrounding fluid phase.
• fluid contact with the food product includes either liquid or gaseous contact.
• the pH indicator device can be placed in a variety of ways known to those skilled in the art so long as its placement allows reactant spoilage molecules to contact and to traverse a barrier sheet. Therefore, the spoilage indicator device may be placed in a bottle cap or other part of a liquid containing package without fear of contamination.
• the response of the spoilage indicator to different concentrations of sodium bicarbonate in 0.1 M phosphate buffer were tested.
• the spoilage indicator device used PVC as an inner layer and 0.01% cresol red plus 0.01% m-cresol purple in 0.05M Lysine buffer, pH 9.05, as indicator. Detection was carried out in the gas phase at room temperature. The color of the sensor changes from purple, P, to colorless 0, with increasing bicarbonate
• the CO2 concentration is related to pH by the following formula:
• Example 2 shows that the spoilage inicator device is sensitive to bicarbonate concentration.
• the barrier sheet was composed of PVC cling wrap (thickness 11.4 microns)
• the carrier was composed of EX-L Kimwipe tissue paper (thickness -18 microns)
• the indicator material used was 10 microliters of 0.02% cresol red
• the buffer material used was 0.01M lysine ( pH 9.45)
• the outer layer was composed of polyvinylidene chloride (Saran) cling wrap (thickness - 7 microns).
• the spoilage indicator device was located 2.5 cm above the test liquid for gas phase detection of the reactant molecules.
• the indicator material, cresol red is violet (V) at a pH > 9 and yellow (Y) at a pH ⁇ 8.
• the barrier sheet of the device was composed of PVC
• the carrier material used was EX-L Kimwipe tissue paper (thickness ⁇ 18 microns)
• the indicator material used was 0.01% cresol red plus 0.01% w-cresol purple
• the buffer material used was 0.05M lysine (pH 9.05)
• the outer layer was composed of Saran Wrap. The device was placed above the orange juice for gas phase detection and was monitored at room temperature.
• the color of the indicator material was noted to change from purple (P) to colorless (O) to yellow (Y) as spoilage progressed and acidity increased.
• the barrier sheet was composed of Cling Wrap polyethylene film
• the carrier material used was EX-L Kimwipe tissue paper (thickness -18 microns)
• the indicator material used was 0.01% phenol red
• the buffer material used was 0.05M Lysine/NaOH (pH 8.6)
• the outer layer was composed of Saran Wrap.
• the device was initially positioned above the citrus juices and then the vials were turned upside down to put the device in direct contact with the food product. The experiment was conducted with both fresh and aged juices at both room temperature and 10°C.
• the spoilage indicator device can differentiate between food and aged orange juice.
• the barrier sheet was composed of PVC film
• the carrier material used was EX-L Kimwipe tissue paper (thickness -18 microns)
• the indicator material used was 0.01% cresol red plus 0.01% r ⁇ -Cresol purple
• the buffer material used was 0.05 M lysine (pH 9.16)
• the outer layer was composed of Saran Wrap. The device was placed above the food product at room temperature for gas phase detection of the reactant molecules.
• the color of the indicator material was noted to change from bluish purple (P) to yellow (Y) as spoilage progressed and acidity increased.
• the device was noted to be more sensitive to the spoiling aged juices rather than the meats. Significant changes of color are indicated in bold.
• the barrier sheet was composed of Cling- Wrap polyethylene film
• the carrier material used was EX-L Kimwipe tissue paper (thickness -18 microns)
• the indicator material used was 0.01% cresol red plus 0.01% -cresol purple
• the buffer material used was 0.05 M lysine (pH 9.4)
• the outer layer was composed of Saran Wrap.
• the device was positioned above the food product for gas phase detection of the reactant molecules.
• the color of the indicator material was noted to change from purple (P) to yellow
• the barrier sheet was composed of PVC film
• the carrier material used was EX-L Kimwipe tissue paper (thickness -18 microns)
• the indicator material used was cresol red 0.02%
• the buffer material used was 0.05 M lysine (pH 9.4)
• the outer layer was composed of Saran Wrap.
• the barrier sheet was composed of PVC .
• the carrier material used was EX-L Kimwipe tissue paper (thickness -18 microns)
• the indicator material used was cresol red 0.02%
• the buffer material used was 0.05 M lysine (pH 9.4)
• the outer layer was composed of Saran Wrap. The device was placed above the milk at room temperature for gas phase detection of the reactant molecules.
• the response time of the spoilage indicator device to the spoilage of meat, chicken and fish at both room temperature and 10°C was assessed using a borate buffer.
• the barrier sheet of the device was composed of PVC
• the carrier material used was EX-L Kimwipe tissue paper (thickness -18 microns)
• the indicator material used was cresol red 0.01%
• the buffer material used was 0.025 M Borax (pH 9.36)
• the outer layer was composed of Saran Wrap.
• the device was placed above the meat for gas phase detection of the reactant molecules.
• the response of the spoilage indicator device to different concentrations of soda water was assessed.
• the barrier sheet was composed of PVC
• the carrier material used was EX-L Kimwipe tissue paper (thickness -18 microns)
• the indicator material used was phenol red 0.02%
• the buffer material used was 0.025 M lysine (pH 8.42)
• the outer layer was composed of Saran Wrap.
• the device was placed above the soda water for gas phase detection of the reactant molecules. The color of the indicator material was read at 15 minute intervals at room temperature.

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• 1997
  • 1997-11-04 WO PCT/US1997/020097 patent/WO1998020337A1/en not_active Application Discontinuation
  • 1997-11-04 AU AU51671/98A patent/AU5167198A/en not_active Abandoned
  • 1997-11-04 EP EP97946515A patent/EP0951644A4/de not_active Withdrawn

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