CA2362037A1 - Thermal history indicators - Google Patents

Abstract

A temperature history indicator means for affixing to goods. A temperature related phase change in a material within the indicator leads to an indicati on that a high temperature event has occurred. A preferred format has a water- soluble, lipid-insoluble dye immobilised within a lipid selected to have a melting point at a particular temperature and has all components made from edible materials. Upon melting, the dye dissolves in water present in a secondary phase or the goods themselves giving a visual indication. Another format has a primary reagent within a solid lipid and a secondary reagent he ld with a secondary phase such that melting of the lipid allows the primary reagent to react with the secondary reagent, providing an indication of a hi gh temperature event. Time-dependent formats are also considered.

Description

3 The present invention relates to the field of thermal 4 history indicators and time-temperature indicators. These are devices which display a physical change in response to 6 their temperature history and are typically attached to or 7 integrated with temperature sensitive goods in order to 8 provide a quality control and/or quality assurance 9 indicator.
il Many goods sold at the present time are temperature 12 sensitive. For example, fresh food produce needs to be kept 13 in a rigidly temperature controlled environment until it is 14 sold. This has implications for manufacturers, distributors, retailers and consumers.

17 Distributors are faced with the technological problem of 18 maintaining temperature of goods within a very tight 19 specification for local, national and international distribution of goods. As a result of this need, it is 21 necessary to verify that goods have been distributed under 1 the required conditions for reasons of quality control and 2 quality assurance.

4 Manufacturers and retailers have a duty of care to their customers. When dealing with produce that is temperature 6 sensitive, they must not only control and verify the 7 temperature under which goods are stored and processed 8 internally but will also want to receive proof that raw 9 materials and supplies have been looked after properly.
When mistakes in temperature regulation are not noted, goods 11 may be spoiled and unsellable or, worse, may lead to damage 12 to the consumer for which the vendor becomes liable.

14 Consumers also face problems related to the temperature control of goods they have purchased. To take an example, 16 milk can spoil extremely quickly if allowed to warm up for a 17 period of time. Consumers would benefit from a way of 18 finding out whether or not retailers are storing goods 19 appropriately. Furthermore, consumers would prefer to purchase goods which they believe have been stored correctly 21 prior to their purchase.

23 At the present time, businesses and retailers typically use 24 thermometers and thermocouples to monitor temperature throughout the food chain. Consumers will not usually 26 monitor temperature of their purchases.

28 Several organisations currently manufacture and sell time-29 temperature indicators. These are devices which can be attached to, or be incorporated in packaging and which 31 provide a visual indicator of the temperature history of the 32 label and, therefore, the produce to which it is attached.

2 The 3M Monitor Mark contains a dye which moves along a scale 3 when the indicator is above a certain melting point. This 4 suffers from the disadvantages of not being edible, not having a clear link between the length the dye has moved 6 along the scale and the temperature history of the product 7 and also requires to be kept below its freezing point before 8 use.

The Lifelines Fresh-Check Indicator uses time and 11 temperature sensitive polymers which gradually deepen in 12 colour. The product is considered to be off when an inner 13 ring made of temperature sensitive material becomes darker 14 than an outer ring. This suffers from the disadvantage that the range of thermal sensitivities which the polymer can 16 adopt are not continuous. Usually, different sensitivities 17 are achieved by varying the colour of the printed outer 18 ring. Care is also required by the user when deciding 19 whether the inner or outer ring is darker. This product also requires refrigeration before use and, indeed, must be 21 kept at a particularly cold temperature to ensure that the 22 sensor has not been triggered. Examples of relevant Patents 23 are US 5,709,472; US 4,892,677 and US 4,735,745.

VITSAB sell time temperature indicators in which an enzyme 26 reaction causes a solution to change from deep green to 27 bright yellow as a result of a controlled pH decrease. A
28 reference colour is printed nearby to enable a viewer to 29 establish whether temperature storage conditions have been violated. One useful benefit of this technology is that the 31 two solutions involved are separated by a divider which can 32 be manually broken, mixing the two solutions (See SE508602 1 and W09838112). This allows the label to be transported at 2 ambient temperature and to be activated only when. it is 3 ready for use. However, this tag is expensive and =ragile 4 and may leak; it is not clear whether the enzyme and chemicals involved are entirely non-toxic. Furthermore, as 6 the colour changes gradually, it becomes difficult for a 7 user to judge when the colour has reached the shade of the 8 reference colour.

These products have so far not been commonly used due to 11 their expense, supply problems with raw materials, 12 limitations to their applicability, toxicity, fragility, 13 sensitivity and the difficulty of manufacture.

The present invention aims to provide a time-temperature 16 indicator which:

18 - is flexible in its application and can be used in many 19 different op erating environments;

21 - can give permane nt, semi-permanent or non-permanent a 22 record;

24 - can respond also the passage of time as well as high to temperature events, for example to indicate when a 26 product has been stored at the stored too long, even if 27 correct temp erature;

29 - is simple use;
to 31 - is easy and cheap manufacture and use;
to WO 00/47964 PC'~/GB00/00398 2 - is reliable and has reproducible properties;

4 - is non-toxic, indeed is actually edible when required for 5 food applications;

7 - is adaptable for a plurality of environments;

9 - has an expiry recognition system that is adaptable, for instance not simply limited to a colour change;

12 - can be adapted to react quickly or slowly to temperature 13 changes ; and - can be understood regardless of the linguistic base of 16 the user.

18 According to a first aspect of the present invention, there 19 is provided a thermal history indicator for attachment to goods, the indicator comprising a temperature sensitive 21 material selected to melt at a predetermined temperature;
22 wherein melting of the temperature sensitive material leads 23 to provision to the user of an indication that the 24 temperature of the indicator has exceeded the predetermined temperature.

27 Preferably, the temperature sensitive material is edible.

29 Preferably also, the temperature sensitive material is a lipid.

1 The temperature sensitive material may provide a visual 2 image through -is shape and which melts at the particular 3 temperature, thereby losing its shape, destroying the visual 4 image and thereby indicating that the particular temperature has been exceeded.

7 The temperature sensitive material may be mounted on a 8 support, the support being adapted for mounting on goods.

The indicator may have a chamber within which the 11 temperature sensitive material is held, the chamber being 12 adapted such that the temperature sensitive material 13 obscures a visual indicator and configured such that melting 14 of the temperature sensitive material results in the visual indicator becoming visible.

17 Preferably, the chamber is hemispherical and adapted so that 18 the temperature sensitive material flows from the top to the 19 bottom of the hemispherical chamber on melting.
21 Preferably, the temperature sensitive material has a primary 22 reagent immobilised therein; the primary reagent is released 23 upon melting of the temperature sensitive material and the 24 released primary reagent provides an indication that the particular temperature has been exceeded.

27 The temperature sensitive material may be a lipid, the 28 primary reagent may be a water-soluble dye and the released 29 water-soluble dye may form a colour on contact with water in the goods to which the indicator is affixed, the formation 31 of the colour leading to a visual indication that the 32 particular temperature has been exceeded.

2 Preferably, the thermal history indicator has a secondary 3 phase located so that when the temperature sensitive 4 material melts, the primary reagent comes into contact with the secondary phase, wherein contact between the primary 6 reagent and the secondary phase leads to an indication that 7 the particular temperature has been exceeded.

9 Typically, the primary reagent interacts with the secondary phase itself in such a way as to produce a colour change.

12 Typically, the secondary phase has a secondary reagent held 13 therein, wherein the first reagent and secondary reagent 14 react giving a product which provides a visual indication.
16 Typically also, the first and secondary reagents are, in 17 either order, an enzyme and a substrate for the enzyme.

19 The temperature sensitive material and the secondary phase may be separated by a physical gap.

22 The temperature sensitive material and the secondary phase 23 may be separated by a temperature sensitive barrier.

The temperature sensitive barrier may have a gate which is 26 opened by a thermostat.

28 The temperature sensitive barrier may be a layer of material 29 which melts at a particular temperature.

1 The temperature sensitive material and the secondary phase 2 may be separated by a physical barrier which can be broken 3 and thereby made permeable by a user.

The indicator may have a means for urging molten temperature 6 sensitive material into contact with the secondary phase.

8 The thermal history indicator may be configured so that the 9 primary reagent diffuses through the secondary phase, thereby producing a temperature indication that varies with 11 time.

13 Preferably, the primary reagent is a water-soluble dye.

According to a second aspect of the present invention, there 16 is provided a data encoding image comprising a thermal 17 history indicator arranged such that the data encoded by the 18 data encoding image changes when the particular temperature 19 is exceeded.
21 Preferably, the data encoding image is a bar code.

23 According to a third aspect of the present invention there 24 is provided a temperature history indicator comprising a cylinder, a piston and an indicator which can be viewed 26 through a window, the cylinder having therein a material 27 that changes volume with temperature thereby driving the 28 piston, the piston being linked to the indicator such that 29 motion of the piston is coupled to motion of the indicator, wherein motion of the indicator changes the part of the 31 indicator which can be seen through the window, wherein a 32 first portion of the indicator can be viewed through the 1 window at a first temperature and a second portion of the 2 indicator can be viewed through the window at a second 3 temperature, the first and second portions of the indicator 4 having visually different information thereon and thereby indicating that a temperature change has taken place.

7 Preferably, the temperature history indicator is adapted so 8 that motion of the piston is irreversible.

According to a fourth aspect of the present invention there 11 is provided an indicator for providing temperature sensitive 12 visual images on goods, the indicator comprising lipid 13 formed into a visual image, the lipid being selected to melt 14 above a particular temperature, thereby destroying the visual image.

17 An example embodiment of the present invention will now be 18 described with reference to the following Figures in which:

Figure 1 is a plan view and elevation of a temperature 21 history indicator;

23 Figure 2 shows a plan view and elevation of another 24 embodiment of a temperature history indicator;
26 Figure 3 shows a plan view and elevation of a further 27 embodiment of a temperature history indicator;

29 Figure 4 shows a plan view and elevation of a time-temperature indicator;

1 Figure 5 shows a plan view and elevation of a 2 temperature indicator having a thermostat controlled 3 gate mechanism;

5 Figure 6 shows a plan view and elevation of a yet 6 further embodiment of a temperature history indicator;
7 and;

9 Figure 7 is a graph of phenol red diffusion through 10 agar strips of different agar concentrations and 11 different thicknesses.

13 The invention herein disclosed is adapted to monitor 14 temperature-time transformations of products (e. g. foods, pharmaceuticals, hormones, micro-organisms, vaccines, 16 electrical goods, patients, animals), processing techniques, 17 living environments (homes and abodes), working 18 environments, leisure environments, transport, distribution 19 systems etc. The applications are almost limitless and the technology will be of value wherever temperature and time 21 permanent records are required.

23 The technology is based around coupling phase transitions of 24 materials to the provision of a record. Phase transitions such as solid to liquid, liquid to gas, solid to gas, liquid 26 crystal to liquid and the like take place at defined 27 temperatures and provide a dramatic change in the structure 28 of a material. Some basic prior art has coupled phase 29 transitions to indicators; for example, a pop-up indicator is disclosed in US 4, 356, 790 wherein a biased spring moves 31 once a material against which it presses is melted.

1 In the present invention, there are provided a primary 2 reactant which is capable directly or through a reaction 3 with another component, of acting as an indicator.

In one embodiment, the primary reactant simply disperses 6 when the primary immobilising phase undergoes a phase 7 transitions. In another embodiment, there are two chemical 8 components, the primary and secondary reactants, which can 9 together undergo a chemical reaction which results in a change, such as an colour change, that functions as an 11 indicator. However, the primary reactant is immobilised 12 within a material, known as the primary immobilising phase, 13 and thereby kept separate from the secondary reactant until 14 such time as the primary immobilising phase undergoes a phase transition which releases the primary reactant. The 16 secondary reactant may simply be water; for instance, a 17 dyestuff may be used as primary reactant which is colourless 18 in a lipid-based primary immobilising phase but has colour 19 when in contact with water (the water acting as secondary reactant or secondary immobilising phase).

22 The primary immobilising phase is chosen to undergo a phase 23 transition at a desired temperature and/or to otherwise 24 break down and release the primary immobilising phase with time. The phase transition may for example be melting, 26 sublimation, evaporation, formation or breakdown of liquid-27 crystal phase etc. The preferred transition is melting.
28 The secondary reactant may also be immobilised in a 29 secondary immobilising phase.

1 When the primary and secondary reactants meet and undergo a 2 reaction, a colour, smell or other indicator is provided 3 that can be sensed by an observer.

Considerations relating to the primary immobilising phase, 6 secondary immobilising phase (if present) and indication 7 mechanism will now be presented in turn, followed by more 8 detailed examples.

Primary immobilising phase 12 A key development in the present invention is the use of 13 lipids as the primary immobilising phase (PIP). Although 14 any appropriate material with defined (sharp or broad) phase transitions may be used (e. g. waxes and hydrocarbons), data 16 and experimental results disclosed herein show that lipids 17 are ideal materials for use in time-temperature indicators 18 for two important reasons. Firstly, a great many different 19 lipids can be readily purchased or manufactured with different melting points. Therefore, it is easy to tune the 21 trigger temperature of the system by selecting a different 22 lipid. Secondly, lipids are safe to use and are generally 23 edible. Further benefits are that they are readily and 24 cheaply available, can be readily modified and derivatised, have physical and chemical characteristics compatible with 26 time-temperature indicators and are hydrophobic.
27 Hydrophobicity is of great benefit as, in an indicator 28 format in which the secondary reactant is kept in an aqueous 29 phase, the primary immobilising phase will not dissolve nor readily allow unwanted mixing of the primary and secondary 31 reactants.

1 Because of the normal operating environments for this 2 technology and their broad range of chemical and physical 3 properties and safety, lipids (fats, oils, conjugates, 4 mixtures of etc.) and their derivatives are extensively used (singly or mixtures) herein. Within this document and the 6 appended claims, the term lipid includes all waxes, esters 7 of fatty acids, simple and compound lipids. Upon melting, 8 the primary reactant (PR) or reactants (PRs) are released.
9 The PR can itself be the indicator of change or can further react with another component (below). Table 1 shows the 11 melting temperatures of example hydrocarbons and similar 12 organic molecules, which although not all lipids, could be 13 used as PIPS with melting transitions from around 0 to 20°C.
14 Table 2 shows the equivalent properties of fatty acids.
16 Table 1. Examples of PIPS - Melting Transitions from around 17 0 to 20°C

Compound Melting Temperature (C) 1-bromotetradecane 4.5 1-bromotridecane 6.0 2-cyclopentene-6-tridecenoic 6.0 acid 5-decanol 8.7 1,13-dibromotridecane 8-10 6-dodecanone 9 5-dodecenoic acid 1-1.3 Glycerol 2-9, 12- 8.9 octadecadienoate 9-henicosene 3 1-hexadecene 4.1 2-methylheptadecane 5.7 6-methylheptanoic acid 0 Methanoic acid 8.4 Methyl dodecanoate 5.1 Methyl tridecanoate 5.8 2-nonenoic acid 0.3 8-nonenoic acid 5 11,14-octadecadienoic acid 4.5-5.5 9-octadecen-2,4,6-triynedioic 0 acid 9-octyl-9-heptadecanol 8-9 2-(octylthio)ethanol 0 Methyl 5-oxodecanoic acid 5 Tetradecane 5.9 6-tridecynoic acid 7.5-8.5 Tridecane -5.5 Tetradecane 5.9 Pentadecane 10 Hexadecane 18.2 2,5-undecadiyn-1-of 1.2-1.5 4-undecanone 4-5 5-undecanone 2 Table 2. Examples of PIPS - Fatty Acid Melting Points Systematic Name of Fatty Acid mp (C) Methyl Ester mp Fatty Acid (C) Methanoic 8.4 -Ethanoic 16.6 -Propanoic -20.8 -Butanoic -5.3 -Pentanoic -34.5 -80.7 , Hexanoic -3.2 -69.6 Heptanoic -7.5 -55.7 Octanoic 16.5 -36.7 Nonanoic 12.5 -34.3 Decanoic 31.6 -12.8 Undecanoic 29.3 -11.3 Dodecanoic 44.8 5.1 Tridecanoic 41.8 5.8 Tetradecanoic 54.4 19.1 Pentadecanoic 52.5 19.1 Hexadecanoic 62.9 30.7 Heptadecanoic 61.3 29.7 Octadecanoic 70.1 37.8 Nonadecanoic 69.4 38.5 Icosanoic 76.1 46.4 Henicosanoic 75.2 -Docosanoic 80.0 51.8 Tricosanoic - 79.6 53.9 Tetracosanoic 84.2 57.4 Pentacosanoic 83.5 59.5 Hexacosanoic 87.8 63.5 Heptacosanoic 87.6 64.6 Octacosanoic 90.9 67.5 Nonacosanoic 90.4 68.8 Tricontanoic 93.6 71.5 2 When for example glycerides are used, depending on the 3 crystalline form, there are different melting points as 4 shown in Table 3.

2 Table 3. Examples of PIPS - Monoglyceride Melting Points _Glycerol-1 -.- MP (3 (C) Mp (3' (C) Mp a (C) alkanoate Decanoata 53 49 27 Undecanoate 56.5 52 36.5 Dodecanoate 63 59.5 44 Tridecanoate 65 61 50 Tetradecanoate 70.5 67.5 56 Pentadecanoate 72 69 62 Hexadecanoate 77 74 66.5 Heptadecanoate 77 74.5 70 Octadecanoate 81.5 79 74 A broad range of melting points similarly exists for di- and 6 triglycerides - which are equally valuable for this 7 technology.

9 Table 4. Examples of PIPS - Triglyceride Melting Points Chain Melting Long Spacing Point x 10-(-C) m length a ~3' (3 a (3' (3 8 -51.0 -18.0 10.0 - - 22.7 9 -26.0 4.0 10.5 - 25.3 24.9 10 -10.5 17.0 32.0 30.2 27.7 26.5 11 2.5 27.0 31.0 32.7 29.8 29.6 12 15.0 34.5 46.5 35.6 32.9 31.2 13 24.5 41.4 44.5 37.8 ' 34.2 34.0 14 33.0 46.0 58.0 41.0 37.3 35.7 39.0 51.5 55.0 42.9 39.2 39.2 16 45.0 56.5 66.0 45.8 42.5 40.8 17 50.0 60.5 64.0 X48.5 43.8 43.5 18 54.7 64.0 73.3 50.6 47.0 45.1 19 59.0 65.5 71.0 53.1 48.1 48.2 20 62.0 69.0 78.0 55.8 50.7 49.5 21 65.0 71.0 76.0 58.5 53.2 52.7 22 68.0 74.0 82.5 61.5 56.0 54.0 2 Other phase transitions associated with other materials are 3 not, however, excluded. An alternative example would use 4 solvents (e. g. water) or solutions in which the particular solutes defined the melting point.

7 Many different lipid systems have been investigated as the 8 melting phase. Fatty acids, monoglycerides, diglycerides and 9 triglycerides are all effective. Care must be taken to retain the appropriate crystalline form (especially the di 11 and triglycerides).

13 Mixtures of lipids, non-lipids and lipids with non-lipids 14 are also envisaged for the PIP. These may/may not include other non-lipid components.

17 Secondary immobilisina phase 19 In embodiments where there is a secondary reactant (SR), a secondary immobilising phase may be provided. The secondary 21 immobilising phase (SIP) can be any material which can form 22 a matrix to entrap the secondary reactant (SR) or reactants 23 ( SRs ) .

1 The secondary immobilising phase is often solvent based.
2 Although lipids may form the matrix, typically a permeable 3 matrix is used which entraps water. For example polymer 4 based materials can be used, where polysaccharide based materials are preferred because time dependent 6 biodegradation of these materials can be built in if 7 desired(discussed further below).

9 A broad range of polymeric - especially polysaccharide systems - have been evaluated for this phase. A readily 11 gelling phase is preferred that can readily entrap a 12 solvent/solution with a small polysaccharide to 13 solvent/solution ratio. Mixtures of these polymers, their 14 derivatives and hydrolysis products are also valuable.
Protein gels (like gelatine) work well, although potential 16 problems with BSE favour the use of other gelling materials 17 from plants in particular - like polysaccharides.

19 Alginic acid, pectin, starch and agar gels have been used successfully, although other polysaccharides can equally be 21 used. Mixtures can also be used. Agar forms very rigid gels, 22 can entrap large volumes of water and other materials, can 23 be blended with for example gelatinised starch, can be 24 sterilised and can contain antimicrobiological agents.
26 A preferred embodiment uses a lipid as primary immobilising 27 phase and a water containing medium as secondary 28 immobilising phase wherein the primary reactant is a water 29 soluble chemical trapped within the primary immobilising phase .

1 In several of the examples given below, agar gel is 2 preferred as secondary immobilising phase. When using a 3 gel, the choice of material is important. Agar poorly 4 withstands freeze-thaw cycles (largely independently of concentration), as syneresis occurs. In circumstance where 6 there may be multiple freezer-thaw incidents, it is 7 preferable to use other polysaccharides like iota 8 carrageenan, locust bean and xanthan gums. These we have 9 found to be very successful.
il Indication mechanism 13 The main trigger which activates the indicator is melting of 14 the PIP. Phase transition of this phase (typically melting, i.e. a solid-liquid transition) releases the reactant which 16 leads to a permanent irreversible change that functions as 17 an indicator. This can be a colour, smell, texture 18 difference etc. If, for example, a lipid is used it can melt 19 and liberate a dye/colour. In a preferred embodiment, non-lipid soluble colours are used which have little colour when 21 particulate in the lipid PIP but are coloured once dissolved 22 in an aqueous SIP. A PR is chosen which can freely dissolve 23 in whatever SIP is chosen.

Although the PR may be a dye or indicator, it may be any 26 chemical species. This can further react with another 27 compound or compounds to indicate a permanent and preferably 28 irreversible change.

The PR may also be a biochemical species like an enzyme or 31 enzyme substrate or a biologically important molecule like 32 a protein, lipid, carbohydrate, mineral, vitamin or element.

2 The PR could be a micro-organism, cellular structure or 3 organism or a substance metabolised by these living species 4 ( for example a sugar which could be metabolised by a yeast 5 and coupled to a colour change). A micro-organism could be 6 released on melting of the PIP an d then grow, with the 7 growth coupled to a colour change reaction by techniques 8 known to those skilled in the art.

10The PR may itself be a solvent (like water) and the PIP may 11be in the form of an emulsion.

13The PR may also be particulate or made from materials such 14as to create a particular structure which is obvious as a 15consequence of PIP passing through phase transition.
a 17The PR may be a volatile material wh ich is entrapped by the 18PIP. For example an odorous material which is only obvious 19upon phase transition of the PIP.

21The SR may be an immobilised solvent (e. g. water), solution, 22colloid or suspension. Equally, the SR may be one or more 23of: chemical; molecule; biochemical (including enzymes and 24substrates); organism, microorganism or tissue or substrate 25thereof in some combination.

27A~r~lication One 29The simplest application of this te chnology is to monitor 30defrosting, warming and heating of products such as meat, 31meat products, poultry etc., although any food, 32pharmaceutical, apparatus, environment etc. would be 1 appropriate. In this example, the indicator is applied 2 directly to the actual product to be monitored.

4 An appropriate lipid or suitable edible or non-edible material is chosen as PIP with the desired melting point. If 6 for example the transition through 13°C is required, oleic 7 acid is appropriate.

9 A fat insoluble or soluble dye (or appropriate material) is used as PR and is blended into the lipid. No SIP or SR is 11 required. The preferred option is to use a fat soluble food 12 dye which forms a particulate nature when dispersed in fat.
13 This can then be applied directly to frozen meat (spray, 14 stamp, print etc) in the form of lettering or shapes. If oleic acid is used on frozen meat etc., it instantly freezes 16 and the letter/shape is permanent until the sausage 17 defrosts. Therefore, a visible indicator which may be even 18 be words, such as "SAFE" can be displayed harmlessly on the 19 product and will be destroyed when the temperature of the produce exceeds the melting temperature for a significant 21 period of time.

23 In a related embodiment, an organisation's brand or any 24 other sort of identifier or advertising could be written directly onto a product such as a meat, but disappear during 26 the cooking process as it melts.

28 Alternatively, a thin film of the lipid is applied to the 29 cut of meat etc. below this temperature, the lipid remains intact as a thin film. If the meat is frozen, it is very 1 easy to stamp or brush a small film of the lipid onto the 2 meat directly.

4 In practice, we have found this to work effectively and well with the following three approaches being particularly 6 successful for, by way of example, applying triglycerides as 7 melt indicators on the surface of meat products such as 8 sausages. It is important to be careful not to modify the 9 crystalline structure of the lipid in a manner which undesirably alters the lipid melting characteristics.

12 ~ Melting and stamping 14 ~ Dissolving in appropriate solvent - hexane was especially valuable 17 ~ Dispersing in a 'gluing' medium. Polysaccharides and 18 gelatine are especially valuable in this respect.

If the meat is wet, the lipid film can be stamped, brushed 21 etc. onto an edible base - rice paper is preferred. Onto 22 this base, another thin film is applied but this time the 23 film contains an/the indicator which may be an edible 24 material (like food colour, above) which becomes obvious when the trigger temperature has been exceeded. If printed 26 on the rice paper, the sandwich disc is then applied to the 27 meat. The transition may be a visible transformation, a 28 smell (i.e. a volatile compound is entrapped), a texture 29 etc. Lettering or shapes printed using the lipid-dye mixture on the rice paper lose their image upon melting providing a 31 useful indication that the product is no longer safe to eat.

2 Food colours have been found to be particularly suitable as 3 PR in this application as they are freely water-soluble and 4 form small particles within the lipid phase without any discernible colour.

7 When the meat is heated, the lipid melts and the food colour 8 interacts with the water from the meat and a visible smear 9 is obvious. The meat can of course be eaten without any harm from the indicator, although the indicator shows that it has 11 been heated above a safe storage regime.

13 Examr~le 1 To 1g of oleic acid at room temperature (where it is a 16 liquid), 10mg of patent blue was added. The dye was 17 dispersed by thorough mixing whereupon the particles are 18 dispersed throughout the lipid. Shapes and letters were 19 drawn and written onto frozen sausages, frozen burgers and egg shells for eggs previously stored in a refrigerator. The 21 mixture rapidly solidifies on the surface and can be happily 22 stored in the freezer (meat) or refrigerator (egg) without 23 any change. However, upon defrosting, the lipid melts and 24 the image is lost. In addition, the food dye stains the meat (blue) indicating that it has defrosted. It has to be noted 26 that this is a natural event when the food is legitimately 27 defrosted for food use, and the food can be eaten as normal.

29 For foods that are refrigerated, the rice paper disc approach is most appropriate and can successfully indicate a 31 temperature transition. Using the same lipid and dye, the 32 defrosting of burgers has been successfully monitored.

2 Example 2 4 Discs of rice paper were soaked in oleic acid and the excess lipid was drained away. The discs were cooled to 5°-C. To the 6 surface of this phase, shapes (or lettering) of oleic acid 7 containing patent blue (as above) were applied. Many 8 technologies can be used for this purpose, e.g. painting, 9 stamping, spraying, ink jet printing. The discs were cooled and then placed on the surface of sausages and burgers 11 within the refrigerator. Nothing happens until the meat 12 products are removed from the cool environment, whereupon 13 the lipid melts and a permanent record of the thermal 14 exposure is obvious.
16 Example 3 18 Commercial triglycerides were obtained from a number of 19 suppliers. Two products, one with a peak melting temperature (established by differential scanning calorimetry) of ~65°-C
21 and another with a peak melting temperature of -74°C were 22 applied to food products including sausages. Application was 23 achieved in three ways:

By dissolving in solvent (especially hexane) and applying 26 the solution in a form of a shape to the surface of the 27 sausage. Reactants like dyes were also applied to the 28 sausage surface in this way, where they were immobilised in 29 the lipid. The sausages were heated at different temperatures and the core temperature was monitored with 31 respect to melting of the surface lipid layer. Colony counts 32 of surface and core microorganisms were also made as a 1 function of the cooking time. These data are presented in 2 the following tables:

4 Table 17 - Averaae core temperature of collagen cased S sausaaescooked at 100°-C for up to 1.20 hours in a 6 convection oven Time Average core (mins) temperature (mean of 2) 10 44.5 84.5 88.5 10 Table 18 Average core temperature of collaaen cased sausages 11 cooked at 80°-C for up to 3 hours in a convection oven Time Average core (mins / temperature hours) (mean of 2) 10 mins 27.5 20 mins 41.5 30 mins 47.5 40 mins 59.5 50 mins 63.5 1.10hours 70.5 1.20hours 70.5 1.30hours 70.5 1.40hours 74 1.50hours 75.5 2.00hours 78 2.10hours 78.5 2.20hours 78.5 2.30hours 79.5 2.40hours 79.5 2.50hours 80 3.00hours 80 2 Table 19 - Averaae core temperature of collaaen cased 3 sausages cooked at 100°C for u~ to 1 hour in a convection 4 oven Time Average core (mins) temperature (mean of 2) 89.5 7 Bacterial Analvsis of Sausages 9 10 g sample was taken into 90 ml diluent. Serial dilutions 10 were made (1:10 to 1:10000), and duplicate plates were made.

2 Before cooking:

4 Dilution 1:100 was selected Number of colonies / plate 297 and 44 6 The average 171 7 Therefore 171 x 10 x 100 - 171000 CFU/g 9 After cooking: (after 30 mins) 10(Internal temperature 80-C) il 12Dilution 1:10 was selected 13Number of colonies / plate 46 and 36 14The average 41 15Therefore 41 x 10 x 10 4100 CFU / gram 17The number of bacteria dropped sharply after sausages were 18cooked at 100-C for about 30 mins. The availability of 19bacteria in the cooked sausages was due to the fact that no 20food is free from micro-organisms u nless the food is 21sterilised to over 121-C for at least 15 mins.

23Table 20 - Averaae times when fat was melted on sausages 24cooked at 80-C in a convection oven Average time Remarks (mins ) Fat in test tube - 10 Fat started melting Melted fat on 25.5 at 8 mins sausage Fat started melting Fat in solvent on 32.5 at 20 mins sausage Solvent evaporated Fat in solvent in 5.5 at 13 mins tube Fat started melting at 30 mins 3 Table 21 - Averaae times when fat T,aas melted on sausaaes 4 cooked at 100--°C in a convection oven Average time Remarks (miris) Melted fat on 11 Fat started melting sausage at 8 mins Fat in solvent on 12 Fat started melting sausage at 10 mins Fat in gelatine 16 Fat started melting on sausage at 12 mins Table 22 Time when fat melted on sausages cooked at 100°-C
in a convection oven. The fat was mixed with solvent, starch, carrac~eenan and aelatine Average time (mins) Fat in solvent on 19 sausage Fat in starch on 20 sausage Fat in carrageenan on 20 sausages Fat in gelatine on 20 sausage 1 Table 23 - Time when fat with starch and gelatine at 2 different concentrations were melted- on cellulose cased 3 sausages cooked at 100°-C in a convection oven Conc Average (%) time (mins) Starch on sausages 3 18 Gelatine on sausages 3 22 6 These results show that lipid applied directly to the 7 surface of sausages can be used to provide visible images 8 which are destroyed by heating in conditions appropriate for 9 the safe cooking of sausages.
11 Examx~le 4 - process monitoring.

13 The technology described above can also be adapted to 14 monitor temperature transfer in food products to assess the effectiveness of processing operations (and related 16 industrial processes).

18 Small wells are created within little block of high melting 19 temperature fats. A paste of lipid (which may be the same lipid as the block of high melting temperature fat or a 21 different material) containing food colour (e. g. patent 22 blue) was inserted. Into the recess of the small blocks, 23 colouring free lipid was applied. These fat blocks were 24 placed in raw meat pies and the pies were heated. Upon 1 cutting open, only those pies exposed to temperatures above 2 the melting point of the lipids contained dye stains -3 showing where temperature penetration occurred.

5 Note that lipid mixtures and mixtures with other products 6 (e. g. carbohydrates, proteins etc) can also be used for this 7 purpose.

9 Example Five 11 Figure 1 shows a plan view of and cross section through an 12 indicator according to the present invention. An indicator 13 1 comprises an enclosure 2 with transparent bubble-shaped 14 window 3 within which there is frozen lipid 4. Coloured card 5 makes a backing. When the lipid 4 melts, its runs 16 down from the bubble shaped window 3, revealing the coloured 17 card which indicates there has been an overtemperature 18 event. The lipid is absorbed into absorbent material 6 19 thereby preventing it reobscuring the card. Importantly, this construction will function at all orientations.

22 Abt~lication Two - Packaging type temperature transition 23 indicators.

In this application, temperature transition indicators 26 adapted for application to packaging of temperature 27 sensitive items is disclosed.

29 Examr~le Six 31 A dyestuff, Patent blue (10mg), was added to 1g of oleic 32 acid (although other appropriate lipids, combinations, 1 mixtures etc. can be used) at room temperature (where oleic 2 acid is a liquid). The particles are dispersed throughout 3 the lipid by thorough mixing. The dye/food colour must be 4 water but not fat soluble, since this means that no obvious colour is apparent in the lipid but simply discrete 6 particles.

8 Into small plastic petri-dish type plates, 1o agar solutions 9 were poured. Gelatine and other polysaccharide systems were also found to be effective, as were polysaccharide mixtures.
11 The agar simply serves as an example. Agar was removed form 12 the centre of the agar plates, and the plates were then 13 cooled below 5°-C.

Small volumes of the lipid containing the water soluble dye 16 were pipetted into the agar free region of the petri dishes.
17 The lipid cools on contact with the cold dish. The plates 18 were immediately refrigerated whereupon the lipid was 19 immobilised. In this embodiment, a physical gap separates the dye containing lipid from the agar.

22 As well as circular set pools of lipid, other geometric 23 forms can and have been readily produced.

In an alternative embodiment, lipid without dye is pipetted 26 into the agar free region. When cooled and solidified, a 27 well is made in this lipid and lipid containing the dye is 28 pipetted into this well. In this embodiment, the dye-free 29 lipid forms an interface layer between they dye containing lipid and the agar.

1 In both embodiments, the lipid containing the water soluble 2 dye is solidified. It is separated from the agar either by a 3 physical gap or an interface which acts as a physical 4 barrier and responds to temperature. The preferred method S is to use a lipid as an interface layer.

7 In all systems, when the melting point of the lipid is 8 exceed, the lipid containing the water soluble dye melts and 9 runs into the agar. The dye diffuses into the agar and the colour becomes obvious. Any colour may be used provided that 11 it is water soluble.

13 The rate of colour development throughout the agar is time 14 dependent and can be modified by the gel composition -including agar concentration, adjuncts etc.

17 The benefit of this approach being that if the dye 18 containing lipid is placed next to the agar (which contains 19 99~ water), although the lipid has not melted, the dye still diffuses from the lipid into the agar and generates a 21 colour. Hence, instead of relying upon a gap in space to 22 separate the agar from the dye containing lipid, a dye free 23 lipid interface can be used very effectively. This has been 24 especially useful when making laminates of the technology where the agar layer is coated with dye free lipid and 26 cooled to solidify the lipid. To the lipid layer, a lipid 27 layer containing water soluble dye is painted and the system 28 is cooled. Hence no interaction between the lipid containing 29 the dye and the agar can occur because of the lipid interface.

1 The interaction of lipid and agar can also be optimised by 2 design - for example by applying the lipid to a small mound 3 on the dish which forces the lipid-dye mixture to run 4 towards the agar when melted.
6 To extend the life of the agar, it is necessary to use 7 preservatives as it gets readily infected by bacteria and 8 moulds. Alternatively, sterile production may be employed.

An example implementation is shown in plan and cross-11 sectional views in Figure 2. Indicator 10 consists of a 12 petri dish 11 which has a block of lipid 12 containing a 13 water-soluble, lipid-insoluble dye. Agar gel 13 surrounds 14 the lipid block separated by, in this example, a physical gap 14. A preferred embodiment would use a dye free lipid 16 layer. Upon raising to a temperature where the lipid block 17 12 melts, the dye is released into the agar gel, becoming 18 visible.

Figure 3 shows an improved embodiment in plan view, cross-21 section and end view before the final construction stage.
22 Sensor 20 is made from a base 21 to which is clipped a cover 23 22, using clips 23. Lipid block 24 is positioned so that 24 when it melts, lipid runs onto spike 25 and thereby into contact with agar blocks 26 where indication takes place as 26 above .

28 Example Seven - use of chemical reaction to enhance 29 indication.
31 The dye diffusion as described above is 'passive' diffusion 32 of a water soluble dye into water (in the agar) to generate 1 colour. The resulting (typically visual) indication can be 2 enhanced and made more striking by designing a system 3 wherein the primary reactant reacts with a secondary 4 reactant present in a secondary immobilising phase.
6 Agar as secondary immobilising phase has also be produced 7 containing 1-5o sodium bicarbonate or containing given 8 molarities of sodium hydroxide as secondary reactant. In 9 place of the patent blue in the lipid, phenol red, cresol red, phenolphthalein (typically 10) and other pH indicators 11 have been used as primary reactant. These readily develop a 12 colour upon the contact with the alkali in the agar after 13 the primary immobilising phase (the lipid) has melted. Other 14 chemical colour generating systems have been employed where one reactant resides in the agar and one in the lipid.
16 Systems responsive to pH, silver nitrate interacting with 17 chloride systems, acid (e. g. HC1) reacting with bicarbonate 18 to generate carbon dioxide, dye binding of protein etc. have 19 been evaluated. Other systems are not excluded.
21 The pH sensitive systems are especially attractive in view 22 of the different colours that can be easily formed. This 23 effect can be multiplied by using different indicators in 24 different lipids (with different melting points).
26 The key to this approach is, therefore, the provision of a 27 water soluble reactant (which may only be water) acting as 28 secondary reactant in the agar phase (secondary immobilising 29 phase) and a water soluble reactant acting as primary reactant (which may just be a dye) in the solidified lipid 31 (primary immobilising phase). The two reactants meet upon 32 lipid melting.

2 The version of the system where a circle of agar surrounds a 3 lipid containing dye (with perhaps a dye free lipid 4 interface rather than a gap) is easy to manufacture.
5 However, the laminate approach is easier still to prepare.
6 These are made as follows:

8 Pour an agar plate (1% with respect to agar and sodium 9 bicarbonate) about 0.5mm thick. Immediately cool to 5°-C.
10 Onto this apply a thin film of oleic acid - which freezes 11 immediately as the agar is less than 5°-C. The oleic acid may 12 be painted on, although it is easier to spray it uniformly.
13 Immediately cool to 5°-C. Onto this solid lipid film apply a 14 thin film of oleic acid containing 1o cresol red- which also 15 freezes immediately as the lipid interface and agar base are 16 less than 5°-C. When the system is placed at room temperature 17 both lipid phases melt and the dye comes into contact with 18 the agar and a red colour develops.

20 In a trial, Agar plates (1 0) containing water or 1 o sodium 21 bicarbonate are prepared. From the centre small holes were 22 cut in the agar and oleic acid (mp 13.4°-C) containing Congo 23 red dye, cresol red or phenolphthalein.

25 No colour generation within the agar was identified upon 26 storage at 5 or 10°-C. However at 15-°C there was slow 27 generation of colour (<5 minutes). At 25°-C this was very 28 fast (<1 minute) .

30 The polysaccharide gels (variable concentrations) made of 31 water and polysaccharide or containing alkali (like 10 32 sodium bicarbonate) were stored at refrigeration temperature 1 for up to sixteen weeks and were found to exhibit no change 2 in performance with respect to their ability to operate in 3 the time-temperature devices.

Clearly, the embodiments of Figures 2 and 3 can be used to 6 apply this example in practice.

8 Example Eiaht This Example details a biochemical approach where an enzyme 11 or substrate as primary reactant is immobilised in a lipid 12 primary immobilising phase, with a secondary reactant which 13 undergoes a reaction with the primary reactant in the agar.

In one experiment, mushrooms were purchased from a local 16 shop and freeze dried. The mushrooms were then pulverised to 17 a powder and dispersed throughout oleic acid. Agar ( 1 0 ) was 18 prepared containing 1°s tyrosine and the indicators were 19 configured as described above. Upon melting, the polyphenoloxidase (PPO) from the mushrooms reacts with the 21 tyrosine in the agar and generates a pink colour. This 22 embodiment contains only edible materials and so is likely 23 to be well regarded by the public. The functionality has 24 been further confirmed using commercial PPO.
26 Hence, as well as the chemical-chemical indication system 27 described above, a biochemical approach can also be used.
28 These can essentially be any enzyme-substrate processes that 29 provides a suitable indication.

1 It will be clear to one skilled in the art that 2 immunological systems and diagnostic systems may be made 3 using the same approach.

Microorganisms (MOs) have also been immobilised in the lipid 6 phase. Upon melting the MOs come into contact with the agar 7 phase and may thereupon grow and as a consequence produce 8 colour/gas etc. products which may be detected by methods 9 known to those skilled in the art.
11 Application Three 13 As well as providing packaging indicators which respond to 14 temperature, it would be desirable to provide indicators which respond also to the passage of time, thereby 16 recognising that certain categories of product, such as 17 foodstuffs, will go off with time even if maintained at 18 their optimum temperature.

The present invention therefore provides in one embodiment 21 an indicator to show time specific changes which contains a 22 water holding medium. This may be an inert material (like 23 for example sponge) although gelling agents are preferred.
24 Examples include proteins (like gelatine), synthetic polymers like 'hydrogel', polysaccharides, and similar 26 materials. Polysaccharides are preferred because of their 27 effectiveness and relatively low cost.

29 Exam,~le Nine 31 Polysaccharide solutions containing one or more 32 polysaccharide were prepared and poured into wells to make 1 strips of gel. The gels were allowed to set and the 2 following experiments were conducted but serve as examples 3 only.

Tyke of Gelling Agent 7 Many polymers and polysaccharides (e. g. agar, carrageenan, 8 locust bean gum xanthan, waxy-, normal- and high amylose 9 starches and gelatine) were investigated for their gel strength and ability to support molecular diffusion of water 11 soluble dyes. These polymers were dissolved in water and 12 dilute alkali solutions (since the diffusion was often based 13 on a pH indicator diffusing through the gel and colouring as 14 it diffused). The polymers were stored at freezing, refrigeration and ambient temperatures and their properties 16 were investigated.

18 Agar and carrageenan (singly or in combination) were 19 preferred media for refrigeration and room temperature use.
For sub zero temperatures, locust bean gum and xanthan were 21 preferred (singly or in combination), as they did not 22 exhibit extensive syneresis as a consequence of freeze-thaw 23 cycles .

Effects of c~el strip concentration and dimensions 26 Polysaccharide solutions were made with 1,2,3,4 and 5%
27 polymer in water and 1o sodium bicarbonate (heating is 28 usually required). The solutions were poured into small 29 plastic troughs which were 0.5, 1.0, 2.0 or 4.Omm deep, 0.5, 1cm, 1.5 or 2cm wide and 5cm long. Results are shown in the 31 following tables:

Table 5 Aaar concentration and phenol red 2 diffusion at different strip thickness Thickness(mm) Agar conc 0.5 1 2 4 1 2.663 2.375 1.95 2.625 2 2.513 2.2 2.613 2.375 3 2.4 2.213 2.413 2.363 4 2.013 1.975 2.138 2.375 2.163 2.213 2.275 3.038 4 Table 6 - Aaar concentration and cresol red 5 diffusion at different strip thickness Thickness(mm) Agar cons 0.5 1 2 4 1 2.538 2.888 2.5 2.588 2 2.213 2.5 2.4 2.588 3 2.25 2.063 2.225 2.413 4 1.788 1.738 1.775 1.713 5 2.06 1.975 1.725 1.875 Table 7 Aaar concentration and phenol red 8 diffu~ion at different strip sizes Thickness 0.5 Strip size 1 2 3 4 1 2 3 4 Agar conc 1 2.75 2.8 3 2.1 2.5 2.5 2.4 2.1 2 2.55 2.65 2.5 2.35 2.75 2.35 1.9 1.8 3 2.65 2.65 2.4 1.9 2.35 2.25 2 2.25 4 2.25 2.1 1.9 1.8 2.25 2.25 1.65 1.5 5 2.5 2.25 1.9 2 2.3 2.3 2.25 2 SUBSTITUTE SHEET (RULE 26) Thickness Strip size 1 2 3 4 I 1 2 3 4 Agar conc 2.2 2.1 1.55 2 2.6 2.7 2.6 2.6 2 3 2.5 2.2 2.75 2.5 2.45 2.5 2.05 3 2.75 2.25 2.5 2.15 2.5 2.5 2.05 2.4 4 2.25 2.1 2.1 2.1 2.75 2.4 2.25 2.1 5 2.35 2.35 2.5 1.9 3.25 3.25 2.9 2.75 Table 8 - Aaar concentration and cresol red diffusion at different strip sizes Thickness 0.5 Strip size 1 2 3 4 1 2 3 4 Agar conc 1 2.55 2.55 2.55 2.5 3.15 2.9 2.75 2.75 2 2.6 2.35 2.1 1.8 2.75 2.75 2.45 2.05 3 2.3 2.2 2.5 2 2 2.1 2 2.45 4 2.2 1.75 1.65 1.55 2 1.8 1.65 1.5 5 2.1 2.1 2 2.05 2.15 1.85 1.9 2 Thickness Strip size 1 2 3 4 1 2 3 4 Agar conc 1 2.65 2.6 2.5 2.25 2.75 2.7 2.55 2.35 2 2.65 2.5 2.35 2.1 2.7 2.5 2.75 2.4 3 2.55 2.35 2 2 2.7 2.25 2.6 2.1 4 2.1 1.9 1.5 1.6 1.8 1.75 1.55 1.75 5 1.85 1.75 1.65 1_65 2 1.8 1.85 1.85 SUBSTITUTE SHEET (RULE 26) Table 9 Incubation time and phenol red diffusion of different strip thickness of agar concentrations Thickness (mm) ~

Agar cons days 0.5 1 2 4 1 0.5 0.5 0.5 0.5 3 1.5 1.5 1.5 1.5 4 2.15 2.163 1.575 2.133 5 2.663 2.375 1.95 2.625 Thickness (mm) Agar cons days 0.5 1 - 2 4 1 0.5 0.5 0.5 0.5 2 1.3 1.225 1.463 1.225 2~ 3 1.738 1.7 2.15 1.55 4 2.088 2.05 2.4 2.013 5 2.513 2.2 2.613 2.375 Thickness (mm) Agar cons days 0.5 1 2 4 1 0.5 0.5 0.5 0.5 30 3 1.513 1.588 1.563 1.475 4 1 .813 1 .913 2.138 1 .963 5 2.4 2.213 2.413 2.363 Thickness (mm) Agar cons days 0.5 1 2 4 1 0.5 0.5 0.5 0.5 2 0.988 1.15 1.288 1.288 40 3 1.5 1.55 1.675 1.75 4 1 . 888 1 . 888 ~ . 1 2 . 1 1 25 ~ 3 5 2.013 1.975 2.138 2.375 SUBSTITUTE SHEET (RULE 26) Thickness(mm) Agar conc days 0.5 1 2 4 1 0.5 0.5 0.5' 0.5 2 1.138 1.313 1.225 1.875 5% 3 1.588 1.613 1.763 2.525 4 1.913 2.175 1.938 2.7 5 2.163 2.213 2.275 3.038 2 Table 10 Incubation time and cresol red diffusion 3 of different strip thickness of aaar at different 4 concentrations Thickness(mm) Agar cone days 0.5 1 2 4 1 0.5 0.5 0.5 0.5 3 1.5 1.5 1.5 1.5 4 2 2.038 1.95 1.98 5 2.538 2.888 2.5 2.583 Thickness(mm) Agar cone days 0.5 1 2 4 1 0.5 0.5 0.5 0.5 2 1.25 1.3 1.238 1.35 3 1.575 1.875 1.913 1.963 4 2.05 2.3 2.325 2.363 5 2.213 2.5 2.4 2.588 SUBSTITUTE SHEET (RULE 26) Thickness(mm) Agar conc days 0.5 1 2 4 1 0.5 0. 0.5 ~.5 3% 3 1.363 1.25 1.5 1.588 4 2.05 1.95 1.788 2.063 5 2.25 2.063 2.225 2.413 Thickness(mm) Agar cons days 0.5 1 - 2 4 1 0.5 0.5 0.5 0.5 2 0.625 1 0.825 0.813 4 0 3 0 . 838 1 . 1 1 . 1 1 . 1 63 4 1.363 1.313 1.463 1.638 5 1.788 1.738 1.775 1.713 Thickness(mm) Agar conc days 0.5 1 - 2 4 1 0.5 0.5 0.5 0.5 2 1.1 1.05 0.875 0.888 50 3 1.438 1.463 1.163 1.05 4 2.05 1.863 1.563 1.863 5 2.06 1.975 1.725 1.875 Table 11 - Diffusion of phenol red at different strip sizes and thickness of Gum locust bean and um xanthan Strip size 1 2 3 4 1 2 3 4 Agar cons 1 2 1.65 1.25 1.25 2.25' 1.15 1 1 2 2 1.25 1.25 1 1.75 1.4 1.15 1.25 SUBSTITUTE SHEET (RULE 26) Thickness Strip size 1 2 3 4 i ~ 2 3 4 Agar conc 1.75 1.4 1 1 2 1.65 1.25 i.25 1 1 .25 1 1 1 1 1 1 1 2 .1 Table 12 Diffusion of cresol red at different strip sues and thickness of Gum locust bean and Gum xanthan Thickness 0.5 1 Strip size 1 2 3 4 1 2 3 4 Agar conc 3 2.25 1 1 1.1 1.1 1 1 1 1 .75 1 . 1 . 1 . 1 1 .6 1 1 .35 2 1 1 1 .6 .4 Thickness Strip size 1 2 3 4 1 2 3 4 Agar conc 1.2 1.15 1.15 1.15 1.4 1.1 1.1 1 Table 13 - Diffusion of phenol red and incubation time of different strip thickness with different carraaeenan conc.
Thickness (mm) Carr. cons days 0.5 1 2 4 1 0.5 0.5 0.5 0.5 2 1 1.238 1.088 1.175 1% 3 1.35 1.238 1.175 1.275 4 1.763 1.438 1.475 ..75 5 2.05 1.913 1.738 1.75 SUBSTITUTE SHEET (RULE 26) Thickness (mm) Carr. cone days 0.5 1 2 4 1 0.5 0.5 0.5 0.5 2 0.9 0.938 1 0.888 20 3 1.375 1.325 1.613 1.275 4 1.925 1.55 1.663 1.525 5 2.013 1.638 1.85 1.525 Thickness (mm) Carr. cone days 0.5 1 2 4 1 0.5 0.5 0.5 0.5 2 0.75 0.988 0.925 0.788 3% 3 1.638 1.213 0.988 1.15 4 1 .763 1 .313 1 .188 1 .163 5 1.975 1.475 1.288 1.188 Thickness (mm) Carr cone days 0.5 1 2 4 1 0.5 0.5 0.5 0.5 2 0.8 0.75 0.888 0.65 4g 3 1.5 1.1 1.625 1.13 4 1.538 1.25 1.838 1.25 5 1.988 1.588 1.975 1.25 Thickness (mm) Carr. cone days 0.5 1 2 4 1 0.5 0.5 0.5 0.5 2 0.638 0.613 0.525 0.563 3 0.825 0.938 0.8 0.675 4 1.088 1.125 0.9 0.9 5 1.088 1.125 0.9 0.9 SUBSTITUTE SHEET (RULE 26) Table 14 - Diffusion cf cresol red and incubation 2 time of different strip thickness with different carraaeenan cone.
Thickness (mm) Carr. cone days 0.5 1 2 4 1 0.5 0.5 0.5 0.5 2 0.975 1 1.1 1.238 3 1.275 1.2 1.3 1.325 4 1.638 1.363 1.4 1.538 5 1.85 1.725 1.522 1.563 Thickness (mm) Carr. cone days 0.5 1 2 4 1 0.5 0.5 0.5 0.5 2 1 .388 1 .313 1 .125 1 2$ 3 1.65 1.563 1.263 1.35 4 1.913 1.813 1.725 1.488 5 2.025 1.863 1.938 1.65 Thickness (mm) Carr. cone days 0.5 1 2 4 1 0.5 0.5 0.5 0.5 2 1.063 1.063 1.125 1.125 30 3 1.063 1.063 1.2 1.188 4 1.375 1.275 1.463 1.188 5 1.375 1.338 1.463 1.25 SUBSTITUTE SHEET (RULE 26) Thickness (mm) Carr cons days 0.5 1 2 4 1 1 0.5 0.5 0.5 0.5 2 0.963 1.088 0.813 1.038 4% 3 0.963 1.163 1.013 0.963 4 1.288 1.288 1.1 1.1 5 1 .788 1 .288 1 .125 1 .138 Thickness(mm) Carr. conc days 0.5 1 2 4 1 0.5 0.5 0.5 0.5 2 0.863 0.65 0.6 0.55 50 3 0.963 0.85 0.713 0.625 4 1.175 1.363 0.85 0.75 5 1.175 1.363 0.85 0.75 Table 15 Diffusion of phenol red and carraaeenan concentration at different strip sizes with different thickness Thickness 0.5 Strip size 1 2 3 4 1 2 3 4 Carr. cons 3.15 2.15 1.45 1.45 1.9 2.5 1.75 1.5 1 2.9 2.15 1.5 1.5 2.25 1.6 1.35 1.35 2 2.75 1.9 1.85 1.4 2.25 1.4 1.25 1 3 2.9 2.15 1.4 1.5 1.85 1.5 1.5 1.5 4 1.75 0.9 0.9 0.8 1.65 1.1 0.9 0.8 SUBSTITUTE SHEET (RULE 26) Thickness i Strip size 1 2 3 4 1 2 3 4 Carr. Conc 1.9 1.5 1.9 1.65 1.75 1.75 1.75 1.75 2 2 2 1.75 1.65 2.25 1.5 1.5 0.85 3 1.6 1.35 1.1 1.1 1.5 1 1.25 1 4 3 2.15 1.5 1.25 1.65 1.35 1 1 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 Table 16 - Diffusion of cresol red and carrac~eenan concentration at different strip sizes with different thickness Thickness 0.5 Strip size Carr. conc 2.5 2.1 1.65 1.15 1.8 1.-9 1.6 1.6 2 2.75 2.25 1.7 1.4 2.5 1.65 1.65 1.65 3 2.25 1 .15 1 .05 1 .05 1 .85 1 1 .1 1 .1 4 2 1.6 1.25 1.25 2 1 1 1.15 5 1 .65 1 .25 0.9 0.9 2 1 1 .15 1 .15 .15 Thickness Strip size 1 2 3 4 1 2 3 4 Carr.conc 1 1.6 1.5 1.5 1.5 1.75 1.5 1.5 1.5 2 2.5 1.75 1.75 1.75 2.25 1.55 1.4 1.4 3 2.15 1 .4 1 .15 1 .15 2 1 1 1 4 1.5 1.1 0.9 1 1.55 1 1 1 5 1 0.8 0.8 0.8 1.05 0.65 0.65 0.65 SUBSTITUTE SHEET (RULE 26) 1 By way of example, Figure 7 shows the results of table 5 in 2 graph form.

4 The above results as a whole show that:
6 Diffusion of water soluble dyes from one end of the gel to 7 the other is slower as concentration is increased.

9 Depth or width, for the same amount of dye applied at one end, do have some effect on the rate of dye diffusion. As 11 the depth and width increase the rate of diffusion is 12 reduced.

14 Length is very important as the diffusion occurs over many days. Typically it takes 5 days for dye dispersed in a 16 liquid fat (e. g. 1o with respect to cresol red or 1% with 17 respect to phenol red) to diffuse from one end to the other 18 of a 3cm gel strip (2mm deep and 0.5cm wide) prepared in 10 19 sodium bicarbonate solution and stored at 5°-C. Hence time dependence and self life dependence could be determined 21 using this approach.

23 At higher temperatures, the rate of diffusion is increased.
24 For example, for the above experiment it would occur at 3 rather than 5 days if stored at 25°-C.

27 Geometry is not a rate limiting effect on diffusion, as the 28 gels may be stored under any orientation and the diffusion 29 occurs at the same rate. Spirals of the matrix have also been made and work very effectively.

1 The gels prepared in 1o sodium bicarbonate (2o with respect 2 to polysaccharide) were stored at refrigeration temperatures 3 for up to 16 weeks and no microbiological storage was 4 detected. The gels must, however, not be allowed to dry out.

6 A modification of these gels strips has been to incorporate 7 gelatinised maize starch with agar gels in the ratios from 8 25:750 to 75:250 (although any other ratios are not excluded 9 nor combinations of gels containing one or more hydrolysable 10 material) with a total solids concentration of 0.5 to 50.
11 Before the gels set, thermostable alpha-amylase (e.g. 0.1 to 12 1mg ml) was added. Thin strips were cut (as above) and were 13 stored at room temperature. It was found that the rate of 14 diffusion could be increased where the enzyme was present as 15 it slowly hydrolysed the starch component of the matrix.
16 Other polysaccharides with other appropriate hydrolytic 17 enzymes may be used (e.g. xanthan and xanthanase, pectin and 18 pectinase etc.).

20 Figure 4 shows a practical example of an indicator in plan 21 view and side elevations. Indicator 30 comprises a gel 22 strip 31 upon which is immobilised water-soluble, lipid-23 insoluble gel in a matrix of frozen lipid 32.

25 A~nlication four - Triaaerable indicators.

27 When manufacturing the product as described in the second 28 application above, the sensors as made must be transported 29 below the trigger temperature. This can make manufacture 30 difficult. To avoid this problem, the lipid phase can be 31 immobilised as a solid or liquid in a discrete compartment.
32 When activation is required, the product is cooled to below 1 the trigger temperature whereupon the lipid (now solid) 2 containing compartment is ruptured. Mechanical rupture has 3 proved very successful although other triggering processes 4 are not ruled out. When the temperature exceeds the melting point of the lipid, it melts and moves towards the agar 6 phase and colour development occurs.

8 Example Ten Agar (1g) containing sodium bicarbonate (1%) was prepared as 11 described above (3). Oleic acid containing cresol red or 12 phenol red indicator (1%) was sealed in a small plastic or 13 metal pouch and placed in a ring cut within the agar. The 14 temperature was cooled to 5°-C whereupon the pouch was pierced. The contents remained in the pouch until the 16 temperature exceeded 13.4--°C whereupon the lipid (containing 17 cresol red) began to run out of the pouch and into the agar 18 phase and colour developed.

In general, this application uses lipid and gel phases which 21 are partitioned with barriers that are broken after cooling 22 and the product becomes active. We have built many designs 23 where the trigger is:

Mechanically ruptured by physical force (pressure, rotation 26 etc . ) 28 Activated by material contraction upon cooling Activated by enzymatic hydrolysis of lipid or gelling phases 31 or a separating phase.

i Activated by ripping out a barrier or film.

3 Activated by hydrating the gelling phase (pregelatinised 4 starch is especially valuable) or a separate barrier phase 6 Many other activation processes are possible and will be 7 readily apparent to one skilled in the art.

9 Apx~lication Five 11 These technology allow the interesting idea of preparing 12 barcodes which have an appearance which is time-temperature 13 sensitive. Once the time-temperature transition has taken 14 place, probably when the product in question has expired, the bar code reading changes. For example, individual lines 16 or the whole bar code disappear. Alternatively colour may 17 appear. This allows the creation of a system whereby 18 expired product cannot be bar-code read or can give a 19 different signal to a bar code reader allowing, for example, defectively stored supplies to be immediately identified and 21 not accepted. Example constructions are as follows:

23 Lipid melting has been used to reveal or disguise part or 24 all of the barcode.
26 The bars of the bar code have been printed with thermo-27 sensitive materials like lipids which, melt at a defined 28 temperature and reveal temperature exposure.

Lipid containing a water soluble reactant has been placed in 31 close contact with a thin gel phase above or below the 32 barcode itself. Upon melting, the lipid makes contact with 1 the gel and colour development occurs. This leads to the 2 loss of visibility of the discrete lines.

4 The lipid may be replaced with other melting materials.
6 The barcode may be printed directly onto the product or 7 packaging material. When the product has been heated up 8 above the melting point of the material it melts and the 9 code is lost.
11 Figure 5 shows an example triggerable indicator which can be 12 used with the bar code concept. Indicator 40 has a PIP, for 13 example a lipid block 41 which contains, as before, a water-14 soluble, lipid-insoluble dye. When it melts, it may contact agar block 42 giving a visual colour change as described 16 above. Another agar block 43 is separated from the lipid 17 block 41 by a gate 44. The gate may have a plurality of 18 bars which block corresponding gaps in an adjacent wall, 19 meaning that the gate has to move only the width of one bar to allow lipid/agar mixing. The gate is activated by a 21 locking thermostat 45 which may, for example, by a 22 bimaterial strip which bends with temperature and, 23 optionally, a latch mechanism. Warming the device to a 24 temperature causes the lipid block to melt giving an indication when the PR interacts with the first agar block 26 42. At a second temperature the thermostat allows the lipid 27 block 41 to interact with agar block 43. The benefit of 28 this device is that it can indicate both a short high 29 temperature event (colour change in agar block 42) and have the capacity to indicate a longer high temperature event 31 (through diffusion of dye in agar block 43).

1 Key benefits of the invention as described herein are that 2 it provides a permanent and irreversible record that a 3 temperature-time event has occurred. The technology can be 4 activated at the point of manufacture or post manufacture by for example a consumer. This has the added advantage in that 6 the products can be manufactured at ambient temperatures if 7 required and shipped as such rather than under 8 refrigeration.

Figure 6 shows a cross-section through a further embodiment 11 of the present invention. Indicator 50 comprises a cylinder 12 51 filled with a lipid 52 which contracts linearly with 13 decrease in temperature. Change in volume of the lipid 52 14 drives a piston 53, the motion of which is opposed by a spring 54. The piston is attached by a joining member 55 to 16 a card 56 which can be viewed through a window 57 in a 17 further card 58. At low temperature, one part of card 56 is 18 visible. At high temperature, the lipid expands, and the 19 piston moves, lining the window 57 up with a region of card 56 which displays a message, or indicates a colour, to show 21 that a particular temperature has been exceeded. A ratchet 22 and pawl may be added to the piston in order to make the 23 change in indication irreversible. Card 56 may simply be a 24 bicoloured card, with e.g. green (indicating "safe" food product) visible at low temperatures and red (indication 26 "hazardous" food) visible at high temperatures.

28 By using these time-temperature indicators on products, 29 con sumers will be able to verifythat produce they purchase has been stored correctly prior to their purchase and will 31 be able to check they look afterit properly and do not use 32 it once it is no longer fit. Manufacturers, distributors 1 and retailers will be able to use the time-temperature 2 indicators for internal quality control and quality 3 assurance and will also better trust that materials 4 protected by this technology have been supplied to them in 5 the correct conditions with all due care. The bar code 6 concept allows rapid verification of the quality of 7 supplies.

9 As the invention can provide a dramatic visible change, it 10 will give clear indication to consumers and, as it may be 11 constructed of edible materials, it has the benefit of being 12 able to be attached to actual fresh product directly instead 13 of merely to its packaging. It will also therefore be 14 considered safe and natural by consumers.
16 Further modifications and variations will be clear to one 17 skilled in the art and may be made within the scope of the 18 invention herein disclosed.

Claims (39)

1. A thermal history indicator for attachment to goods, the indicator comprising a reactant and a primary immobilising phase, wherein the primary immobilising phase is a temperature sensitive material selected to melt at a predetermined temperature; wherein melting of the temperature sensitive material leads to the provision of an indication by the reactant that the temperature of the indicator has exceeded the predetermined temperature.

2. A thermal history indicator as claimed in any preceding Claim which is mounted on a support, the support being adapted for mounting on goods.

3. A thermal history indicator as claimed in Claim 2, wherein the support is rice paper.

4. A thermal history indicator as claimed in Claim 2, wherein the support is a petri dish.

5. A thermal history indicator, the indicator comprising a reactant and a primary immobilising phase, wherein the primary immobilising phase is a temperature sensitive material selected to melt at a predetermined temperature; wherein melting of the temperature sensitive material leads to the provision of an indication by the reactant that the temperature of the indicator has exceeded the predetermined temperature and wherein the thermal history indicator is applied or attached directly to the surface of the goods.

6. A thermal history indicator as claimed in Claim any one of the preceding Claims wherein the primary reactant is dispersed within the immobilising phase.

7. A thermal history indicator as claimed in Claim 6, wherein the reactant dispersed within the primary immobilising phase is applied to the goods to provide a visual image through its shape, wherein the primary immobilising phase melts at a particular temperature, thereby losing its shape, destroying the visual image and thereby indicating that the particular temperature has been exceeded.

8. A thermal history indicator as claimed in any one of the preceding claims wherein the reactant is a water soluble dye.

9. A thermal history indicator as claimed in any one of the preceding claims wherein the reactant is a micro-organism.

10. A thermal history indicator as claimed in any one of the preceding claims wherein the reactant is an odorous material.

11. A thermal history indicator as claimed in any one of the preceding Claims, wherein the primary immobilising phase is a lipid.

12. A thermal history indicator as claimed in any one of the preceding Claims which is edible.

13. A thermal history indicator as claimed in any one of the preceding Claims, wherein the reactant forms a colour on contact with the goods to which the indicator is affixed, the formation of the colour leading to a visual indication that the particular temperature has been exceeded.

14. A thermal history indicator as claimed in any one of the preceding Claims, wherein the primary reactant forms a smell on contact with the goods to which the indicator is affixed, the formation of the smell leading to a visual indication that the particular temperature has been exceeded.

15. A thermal history indicator as claimed in Claim 3 which is applied to the goods via stamping.

16. A thermal history indicator as claimed in Claim 3, which is applied to the goods via ink jet printing.

17. A thermal history indicator as claimed in claim 3 which is applied to the goods as a thin film.

18. A thermal history indicator as claimed in any one of the preceding Claims which is applied to eggs.

19. A thermal history indicator as claimed in any one of the preceding Claims, wherein the thermal history indicator also comprises a secondary reactant located so that when the phase transitional, material undergoes a phase transition, the primary reactant comes into contact with the secondary reactant, which leads to an indication that the particular temperature has been exceeded.

20. A thermal history indicator as claimed in Claim 19, wherein contact between the primary and secondary reactant produces a colour change.

21. A thermal history indicator as claimed in Claim 19, wherein the first and secondary reagents are, in either order, an enzyme and a substrate for the enzyme.

22. A thermal history indicator as claimed in Claim 19, wherein the first and secondary reagents are, in either order, a water soluble dye and water.

23. A thermal history indicator as claimed in any one of Claims 19-22, wherein the secondary reactant is immobilised within a secondary immobilising phase.

24. A thermal history indicator as claimed in Claim 23, wherein the secondary immobilising phase forms a matrix to entrap the secondary reactant.

25. A thermal history indicator as claimed in Claims 23-24, wherein the secondary immobilising phase is a polysaccharide.

26. A thermal history indicator as claimed in Claims 23-24, wherein the secondary immobilising phase is agar.

27. A thermal history indicator as claimed in Claims 23-24, wherein the secondary immobilising phase is gelatin.

28. A thermal history indicator as claimed in Claims 23-24, wherein the secondary immobilising phase is lipid.

29. A thermal history indicator as claimed in Claims 23-28, wherein contact between the primary reactant and the secondary immobilising phase, leads to an indication that the particular temperature has been exceeded.

30. A thermal history indicator as claimed in Claims 23-29, wherein contact between the primary reactant and the secondary immobilising phase produces a colour change.

31. A thermal history indicator as claimed in any of Claims 23-30, wherein the primary reactant and the secondary immobilising phase are separated by a physical gap.

32. A thermal history indicator as claimed in any of Claims 23-30, wherein the primary reactant and the secondary immobilising phase are separated by a temperature sensitive barrier.

33. A thermal history indicator as claimed in Claim 32, wherein the temperature sensitive barrier is in the form of a gate which is opened by a thermostat.

34. A thermal history indicator as claimed in Claim 32, wherein the temperature sensitive barrier is a layer of material which melts at a particular temperature.

35. A thermal history indicator as claimed in any one of Claims 23-30, wherein the primary reactant and the secondary immobilising phase are separated by a physical barrier which can be broken and thereby made permeable by a user.

36. A thermal history indicator as claimed in any of Claims 23-35, wherein the primary reactant diffuses through the secondary immobilising phase, thereby producing a temperature indication that varies with time.

37. A temperature history indicator comprising a cylinder, a piston and an indicator which can be viewed through a window, wherein motion of the piston is opposed by a spring, the cylinder having therein a material that changes volume with temperature thereby driving the piston, the piston being linked to the indicator such that motion of the piston is coupled to motion of the indicator, wherein motion of the indicator changes the part of the indicator which can be seen through the window, wherein a first portion of the indicator can be viewed through the window at a first temperature and a second portion of the indicator can be viewed through the window at a second temperature, the first and second portions of the indicator having visually different information thereon and thereby indicating that a temperature change has taken place.

38. A temperature history indicator as claimed in claim 26 adapted so that motion of the piston is irreversible.

39. A temperature history indicator as claimed in Claim 7, wherein the visual image is a bar code.