WO2006024848A1

WO2006024848A1 - Food spoilage sensor

Info

Publication number: WO2006024848A1
Application number: PCT/GB2005/003370
Authority: WO
Inventors: Sergey Anatoliyovich Piletsky; Seamus Patrick John Higson; Frank Davis
Original assignee: Cranfield University
Priority date: 2004-09-01
Filing date: 2005-08-31
Publication date: 2006-03-09
Also published as: GB0419335D0

Abstract

A sensor is disclosed which provides a visual indication of contamination or deterioration of food via loss of packaging integrity or internal spoilage processes. The sensor includes a redox anal pH-sensitive polymeric material, e.g. polyaniline, deposited inside packaging. Changes in the pH or in the chemical composition of food in the packaging or loss of integrity of the packaging produce a visible change in the colour of the polymeric material. The colour of the polymeric material is compared with the colour of a standard placed inside or outside of container. The suitability of food or drink for consumption or the occurrence of atmospheric contamination may therefore be rapidly and safely determined.

Description

FOOD SPOILAGE SENSOR

Field of the Invention

This invention relates to a visual assay or sensor for detecting food spoilage processes, e.g. due to decay or the loss of packaging integrity via ingress of atmospheric gases.

Background As food deteriorates, accompanying chemical changes take place. Often this is due to microbial growth and several by-products may be given off. This process can be reflected in, for example, a change in pH, production or loss of a redox active chemical, etc. Detection of such changes may give a measurement of the degree of deterioration. Typically, heat and pressure also develop during food deterioration but are difficult to measure and are more likely to be influenced by outside conditions than are measurements based on chemical composition..

Already there are commercial time-temperature labels which can be affixed to the outside of food containers and give a measure of the age and history of the product. These have the disadvantage that they only give a measurement of the product history, not the actual state of the contents. Also they can easily be removed and replaced by fresh labels to disguise product history whereas our label is integral with the packing materials and cannot be removed without repackaging the contents. US 6,723,285 describes a method where some of the food is mixed with a series of pH sensitive dyes within a separate container within the package and changes in the colour of this mixture reflect the state of the contents. US 2004-0106162 describes a sensor having a molecularly imprinted polymer membrane capable of selectively binding pathogens. The binding sites are fluorescent in the absence of pathogen, the fluorescence being quenched in the presence of pathogens, thereby giving an indication of contamination.

US 6,149,952 describes the use of a hydrophilic polymeric composition incorporated in the lining of a food container. The composition contains an indicator for detecting the presence or absence of a gas produced by contaminating bacteria.

Summary of the Invention

One aim of the present invention is to provide a simple and safe food deterioration sensor. At its most general, the invention provides a polymer having an observable property which changes upon interaction with solutes or vapours associated with food decay in order to give an indication of food deterioration. Many polymers are known to rapidly interact with solutes or vapours, leading to a marked change in conductivity or visible adsorption characteristics.

Thus, according to the invention, there is provided a food spoilage sensor having: a polymer in chemical communication with food contained in packaging, the polymer having an observable property that changes from an unspo'ilt state to a spoilt state upon chemical reaction between the polymer and one or more substances associated with food deterioration; and a control element having an observable property arranged to be unaffected by the food deterioration which matches the unspoilt state of the polymer; wherein the observable properties of the polymer and control element are comparable to provide a visual indication of food deterioration. Preferably, the observable property is the colour of the polymer, so food deterioration may be detected by directly observing the polymer. Polyaniline may be used as the polymer. It is especially suitable because it exists in a protonated conductive form (green) and a neutral non-conductive form (blue) . It is also capable of being oxidised or reduced.

In general, the polymers suitable for use in the invention preferably have a wide spectrum of adsorption which varies with environmental conditions. In other words, the observable property preferably changes gradually from the unspoilt state to the spoilt state, thereby giving a range of indication of quality. This makes the sensor more versatile than arrangements which only exhibit a simple transition from one colour to another, e.g. traditional dyes.

Whilst polyaniline is a useful example, there are other coloured conjugated polymers which may be used, e.g. substituted polyaniline, polythiophenes, polypyrroles, polyacetylenes, polyphenylene and polyphenylene vinylidine. The use of such coloured conjugated polymers in as food deterioration sensors is an independent aspect of the present invention.

Preferably, a film of the polymer is deposited on the inside of the packaging or vessel containing the food. The packaging is preferably transparent or may have a window for the polymer film to be viewed from outside the packaging. The polymer may be encased or covered by a porous barrier element if physical contact between the food and the polymer is undesirable. The barrier element may be a gas-permeable membrane. The gas-permeable membrane is preferably made from any porous hydrophobic polymer; Teflon® is preferred. Other examples include porous polyethylene, polypropylene or polystyrene.

The control element may be formed from either the same polymer or may include a dye of similar, e.g. substantially identical, colouration to the unspoilt state of the polymer. If the same polymer is used, the control element is preferably deposited on the outside of the vessel or packaging. Thus, as the food spoils in any way, the polymer inside the packaging reacts, leading to a colour change, whereas the control element outside is unaffected. The polymer and control element may be easily visually compared, e.g. by locating the control element adjacent to the polymer. This then provides a simple, sensitive visual test for the condition of the packaged food.

Preferably, the polymer is attached directly to the packaging material. Preferably, the polymer is insoluble and stable, so fabrication and filling of the food container is simplified and there is no danger of potentially contaminating the food, e.g. by using carcinogenic dyes .

When packaged, the sensing polymer and control element are preferably identical in colour. Therefore any spoilage within the food will cause the sensing polymer to change colour, which change is easily visualised by comparison with the control element, thereby warning the consumer not to buy or consume the food. The absence of any difference between the colour of sensing polymer and control element will indicate that the product is suitable for consumption.

The sensor may also be used to detect loss of packaging integrity. In other words, the polymer may be sensitive to the ingress of oxygen or other gases capable of spoiling food into an inert or evacuated environment. For example, the observable property of the polymer may change when it is oxidised. Thus, in one embodiment polyaniline in its reduced form (leucoemeraldine) may be deposited onto the inside of a package which is either evacuated or filled with an inert gas (e.g. nitrogen) . Loss of integrity will allow the ingress of oxygen and oxidation of the polymer will occur, which leads to a colour change. This process can be used also to monitor natural ageing processes in food and drinks in order to identify the expiry time.

This form of sensor lends itself to mass fabrication due to the simplicity and inexpensiveness of the materials and methods used, and is particularly advantageous because it gives an easy visual response rather than one which requires measurement equipment to be interpreted.

Brief Description of the Drawings

Fig. 1 shows a sensor according to one embodiment of the present invention; and

Fig. 2 shows a photograph comparing a protonated polyaniline sheet with a neutral polyaniline sheet.

Detailed Description Embodiment 1

Fig. 1 shows a first embodiment of the present invention. A film consisting of green polyaniline is deposited in a circular spot 1 on the inside of a food package (not shown) . The film may be deposited using any of a variety or techniques, e.g. chemical deposition, stencilling, screen printing or spraying of an aqueous dispersion. The packaging material can be conventional, e.g. polyethylene or polypropylene. A control sample e.g. of the same polymer or some other dye with identical green colouration is deposited in an annular ring 2 on the outside of the food package, i.e. isolated from the environment containing the food. The spot 1 and ring 2 are deposited so as to appear next to each other (one inside the other) to a user viewing the package from outside. Foodstuff, e.g. chicken, is packaged inside the food package. If the chicken were to decompose in any way, products such as amines would be released which would deprotonate the polyaniline, causing a change from green to blue. This could be easily seen visually, especially by comparing the polymer spot 1 with the control ring 2. If contact between the foodstuff and the polyaniline inside the package is undesirable or is to be minimised, a gas-permeable membrane (e.g. Teflon®) could be placed between the polyaniline and the food.

Embodiment 2

In a second embodiment of the invention, a film of neutral blue polyaniline is deposited (e.g. using one of the techniques described above) on the inside of a transparent or translucent bottle. A control material is deposited on the outside. The bottle is then filled with milk. As the milk turns sour, lactic acid is released which will cause a transition to the green form which can be easily visualised. Other species such as ascorbic acid will also lead to colour changes due to oxidation/reduction reactions.

Embodiment 3

A third embodiment describes a use of the above- mentioned sensor to detect loss of packaging integrity. Loss of integrity allows the ingress of oxygen. This causes oxidation of the polymer to occur, which leads to a colour change. This process can be used also to monitor natural ageing processes in food and drinks in order to identify the expiry time.

The present invention will now be further described in detail by reference to the following examples, which are intended to illustrate some of the possibilities, but are not intended to limit the scope of the invention.

Examples Spoilage of meat

A sheet of commercial Melinex plastic was rolled up into a tube and then placed into a solution of IM aniline hydrochloride in 0. IM HCl. An equal volume of 0.3 M ammonium persulphate was added and the solution rapidly turned green. After 20 minutes the plastic was removed and rinsed with 0.1 M HCl, a green film of emeraldine form polyaniline had been grafted to the plastic. A piece of this was then placed in a sealed tube along with some cooked ham. After a few days at room temperature the polymer had changed to a deep blue, indicating deprotonation, due to amines released by the decomposing meat. The resulting sheet is shown on the right in Fig. 2. The polyaniline has been converted from its initial green form into the blue form by the decomposing meat.

Spoilage of milk A piece of the previous plastic was dipped in 1% ammonia solution for a few seconds, removed and dried, converting it to the blue (deprotonated) form. This was then immersed in milk in a sealed bottle. After two days at room temperature the polymer had changed to a dark green, indicating protonation, due to lactic acid released by the souring milk. The resulting sheet is shown on the left in Fig. 2. Here the polyaniline has been converted from its initial blue form into the green form by the spoiling milk.

Claims

CLAIMS :

1. A food spoilage sensor having: a sensing polymer arranged in use to be in chemical communication with food contained in packaging and having an observable property that changes from an unspoilt state to a spoilt state upon chemical reaction between the polymer and one or more substances associated with food deterioration; and a control element having an observable property arranged to be unaffected by food deterioration, the observable property of the control element being arranged to match that of the unspoilt state of the polymer; wherein the observable properties of the sensing polymer and control element are comparable to provide a visual indication of food deterioration.

2. A sensor according to claim 1, wherein the observable property is the colour of the sensing polymer and control element and the indication of food deterioration is a direct visual comparison.

3. A sensor according to claim 1 or 2, wherein the observable property of the sensing polymer changes gradually from the unspoilt state to the spoilt state to give a measure of the extent of food deterioration.

4. A sensor according to any of claims 1 to 3, wherein the one or more substances associated with food deterioration include one or more chemicals associated with food decay that alter the pH of the sensing polymer.

5. A sensor according to any preceding claim, wherein the one or more substances associated with food deterioration include atmospheric gases which indicate loss of packaging integrity.

6. A sensor according to any preceding claim, wherein the chemical reaction is oxidation of the polymer.

7. A sensor according to any preceding claim, wherein the polymer is depositable as a film on the inside of the packaging.

8. A sensor according to any preceding claim wherein the control element includes the same material as the sensing polymer, the control element being arranged in use to be chemically isolated from the food.

9. A sensor according to any of claims 1 to 7, wherein the control element includes a dyed material having substantially the same colour as the unspoilt state of the polymer.

10. A sensor according to any preceding claim, wherein the control element is locatable on the outside of the packaging.

11. A sensor according to any preceding claim, wherein the control element is located adjacent the polymer to aid visual comparison.

12. A sensor according to any preceding claim, wherein the polymer is a conjugated polymer.

13. Use of a conjugated polymer in packaging to detect deterioration of food contained in the packaging, the polymer having an observable property that changes from an unspoilt state to a spoilt state upon chemical reaction between the polymer and one or more substances associated with food deterioration.

14. Use according to claim 13, wherein the polymer is polyaniline.

15. A food packaging method including: depositing a film of a polymer on the inside of a packaging material for containing food, the polymer having an observable property that changes from an unspoilt state to a spoilt state upon chemical reaction between the polymer and one or more substances associated with food deterioration; depositing a control element on the packaging material, the control element having an observable property arranged to be unaffected by food deterioration which matches the unspoilt state of the polymer; and packaging food in the packaging material.

16. A food package having: packaging containing food; a sensing polymer deposited on the packaging in chemical communication with food contained in packaging and having an observable property that changes from an unspoilt state to a spoilt state upon chemical reaction between the polymer and one or more substances associated with food deterioration; and a control element having an observable property arranged to be unaffected by food deterioration, the observable property of the control element being arranged to match that of the unspoilt state of the polymer; wherein the observable properties of the sensing polymer and control element are comparable to provide a visual indication of food deterioration.

17. A food package according to claim 16, wherein the sensing polymer is on the inside of the packaging and the control element is on the outside of the packaging.

18. A food package according to claim 17 including a porous barrier element preventing physical contact between the sensing polymer and the food.

19. A food package according to claim 18, wherein the porous barrier element is a gas-permeable membrane of Teflon® or the like.