EP1725846A1

EP1725846A1 - Time temperature indicator (tti) system

Info

Publication number: EP1725846A1
Application number: EP05722847A
Authority: EP
Inventors: Xavier Varlet-Grancher
Original assignee: Sun Chemical Corp
Current assignee: Sun Chemical Corp
Priority date: 2004-02-09
Filing date: 2005-02-09
Publication date: 2006-11-29
Also published as: WO2005078402A1; JP2007525664A

Abstract

Provided is a time temperature indicator (TTI) system/device for monitoring a thermally sensitive product, such as foodstuff, food additives, chemicals, biological, materials, drugs, cosmetics, and so forth, which are handled and stored at temperatures between about 2°C and about 40°C. The TTI system of the present invention is activated by contacting with each other a reactive ink layer comprising microorganisms, for instance, yeasts, in a water-based vehicle printed on a plastic film and an adhesive layer comprising an activator, specific for the microorganisms, printed on another plastic film. The activated TTI that is affixed to the product to be monitored indicates the time temperature history of the product by the color change of the color indicator, contained in the TTI system, caused by fermentation of sugars by the microorganisms.

Description

TIME TEMPERATURE INDICATOR (TTI) SYSTEM

FIELD OF THE INVENTION

The Invention relates to a system for visually and irreversibly indicating the cumulative history of time and temperature exposure of thermally-sensitive products. More specifically, the invention relates to Time Temperature Indicators/Integrators (TTIs). The TTI system of the invention operates based on biochemical reactions through anaerobic respiration by microorganisms. The invention is adapted for use with thermally sensitive products, such as foodstuff, food additives, chemicals, biological materials, drugs, cosmetics, and so forth, which are handled and stored at temperatures between about 2°C and about 40°C.

BACKGROUND OF THE INVENTION

Thermally-sensitive products generally go through life cycles starting at manufacturers/producers and ending at consumers, as depicted in Figure 1. At each stage of their life cycles, rigorous thermal controls are often put in place so as to preserve certain qualities, such as microbiological, biological, organoleptic, physical, chemical, and nutritional qualities, and so forth, until the products are consumed by consumers. Thus, TTIs complete the Hazard Analysis and Critical Control Point (HACCP) system enforced by governmental agencies.

A Time-Temperature Indicator or Integrator (TTI) can be defined as a device that can show an easily readable, time-temperature dependent change that reflects the full or partial temperature history of the thermally sensitive product to which it is affixed. In other words, TTIs are integral systems allowing irreversible visual indication of the combined action of temperature and time on the products, unlike an expiration date (ED) and a best-consumed-before-date (BCBD), both of which take in account only a single parameter, i.e., time. TTIs thus offer a means for assessing and controlling thermal cycles and storage conditions of the products, in addition to the benefit provided by ED and BCBD.

TTIs are put in place during the preparation of thermally sensitive products at the time of production to help consumers see if the product is still fresh at the time of sale and at home. The TTIs must therefore evolve with the products on which they are placed so as to reflect correctly the freshness of the products. Thus, the TTIs must have the same life cycle as the products. At the end of the life cycle (or "cold chain"), the TTIs inform the consumers of not only the time-temperature history of the TTI in relation to ED and/or BCBD, but also of the necessity of not breaking the cold chain himself.

There may often be a situation where a product, after manufactured, is transported, perhaps, over a long distance under a non-refrigerated condition, and then kept in a refrigerator that is not working well. Figure 2 shows the evolution of the TTI under ideal conditions (A: the color change matches with the ED) and when the product has undergone thermal shocks (B: the color change is faster, which indicates that the product has been exposed to temperatures beyond the permissible limits).

The principle of TTI operation may be a mechanical, chemical, electrochemical, enzymatic or microbiological irreversible change usually expressed as a visible response, in the form of a mechanical deformation, color development or color change. The rate of change is temperature dependent, increasing at higher temperatures similarly to most physicochemical reactions. The visible response thus gives a cumulative indication of the storage conditions to which the TTI has been exposed. The extent to which this response corresponds to a real time-temperature history depends on the type of the indicator and the physicochemical principles of its operation. In the last decade, various types of TTI have been developed and are being used commercially to track the time and temperature history of various products.

One prevalent class of TTI is a diffusion-based indicator (TTI Type I). This type of TTI indicates a temperature history of a product based on the diffusion of a colored chemical (e.g., fatty acid esters, phthalates, certain polymers) from the reservoir through a wick. Within this class, four (4) types of TTI are known , of which three types are commercially available (Freeze Watch, Stop! Watch and MonitorMark™, from 3M Innovative Properties Company, St. Paul, MN) (see U.S. Patents 3,954,011; 5,120,137; 5,667,303; 6,244,208; and 6,435,128; U.S. patent application publication 2003/0053377; and international patent publication nos. WO 94/12859; WO 96/28714; and WO 99/56098). One of the first significant applications of Type I TTI was the use by the World Health Organization (WHO) to monitor refrigerated vaccine products.

Another class of known TTI utilizes an enzymatic indicator (TTI Type II). For example, VITSAB® Time Temperature Indicator (NITSAB AB, Malmo, Sweden) is based on a color change caused by decrease in pH value as a result of a controlled enzymatic hydrolysis of a lipid substrate (see U.S. Patents 5,857,776; 4,043,871; 4,284,719; and 3,977,945). This type of TTI must be kept chilled before activation.

The third type (TTI Type III) of indicators is based on a chemical polymerization reaction, such as the polymerization of disubstituted diacetylene crystals (R-C=C-C=C-R), which results in a highly colored polymer. Commercially available TTIs are FreshCheck® indicator for food products and HEATmarker® indicator for vaccines (see U.S. Patents 3,999,946; 4,208,186; 4,228,126; 4,276,190; 4,735,745; 4,737,463; 4,812,053; 4,892,677; 4,917,503; 5,057,434; 5,709,472; 6,042,264; and 6,544,925, and EP patents EPO 930 487 Al and EPl 333 262). These TTIs must be kept in deep freeze (i.e., at -24°C) before use because the reaction will spontaneously occur under other conditions. This is a significant drawback in terms of handling and application of the TTIs.

A TTI system using microorganisms as an indicator for microbial spoilage of food products is described in U.S. Patent 2,950,202. Microbiological technology has been also used as an indicator for cold chain disruptions for perishable products, based on the growth of microorganisms that is measured by the visibility of certain bar codes (see international patent publication no. WO 0/025529). In these systems, microorganisms are usually dehydrated and contained in an air-tight bag together with dehydrated nutrients. The system is activated by breaking an inner pouch containing water, which rehydrates the system. Thus, this system cannot be conveniently manufactured on the spot by, for example, conventional printing processes.

Finally, the last type of TTI utilizes a combination of biochemistry (i.e., an enzymatic reaction) and electronics (see U.S. Patent 6,642,016 and EP 1 218533; commercially known as Time Temperature Biosensor™) to monitor the thermal cycle of the products. This particular technology requires special equipment and is expensive and not user friendly.

Most of commercially available TTIs have the disadvantages in requiring chilled or frozen storage, sometimes away from actinic radiation, before activation, or specific conditions for activation, or special preparation processes, such as preconditioned temperature, prior to affixation to packages. Furthermore, it is sometimes necessary to apply pressure manually to each indicator or even to remove an activation strip from the indicator, in order to determine the results. These extra steps are often tedious and cost more.

Thus, there is a need for a TTI system that can be activated at the site of application, i.e., at the time of manufacturing and packaging of the products, thereby obviating a need for the storage under special conditions prior to their use on the packages. Furthermore, there is a need for a TTI system that gives the time- temperature history of the products by a simple visual observation of the indicator on the package, without extra steps. Such systems will considerably simplify the monitoring process and lower the costs associated with the TTI system.

SUMMARY OF THE INVENTION

The present invention is based, in part, on a discovery by the present inventor that the integration of the preparation step, by on-site printing, of a TTI, using microorganisms, into the manufacturing process of the product packaging, can obviate disadvantages posed by previously available TTI technology. Accordingly, it is an object of this invention to provide an improved TTI system/device that is simple in operation and cost effective. Namely, it is an object of the present invention to provide a TTI system that can be easily incorporated into the manufacturing processes of the products to be monitored. It is another object of the invention to provide a TTI device that is easy to manufacture, store, activate and handle under normal conditions, i.e., without requiring freezing or refrigeration prior to the activation of the system, and without spilling, splattering or staining, and accurately gives a visual indication of cumulative thermal exposure of the products. It is another object of this invention to provide a TTI device that is safe for use with foodstuff, drugs, cosmetics, etc. It is another object of the invention to provide a TTI device for use with products adapted for refrigerated storage, for room temperature storage, or for non-freezing and non-refrigerated storage within certain temperature ranges (e.g., chocolates, wine, champagne, etc.). It is yet another object of this invention to provide a TTI device that is relatively thin and supple so as to allow its attachment to a wide variety of packaging configurations.

Accordingly, the present invention provides a TTI system comprising: (a) a first part comprising a microorganism; (b) a second part comprising an activator; and (c) a pH-sensitive color indicator, wherein the pH-sensitive color indicator is contained in at least one of the parts (a) and (b). The term "activator" used herein refers to any material that is a nutrient for the microorganism contained in the first part and promotes the growth of the microorganism, thereby leading to acid production. In a preferred embodiment, the activator comprises a carbon source, such as sugars.

In a specific embodiment, the present invention provides a TTI system comprising a two-part self-adhesive label, which comprises a first part containing a reactive agent, i.e., microorganisms and a color indicator in an appropriate water- based ink vehicle, printed on a transparent plastic film, and a second part comprising an aqueous adhesive layer containing an activator component, specific for the reactive agent, which is printed on a conventional pressure-sensitive, self- adhesive support film, wherein the two parts are kept separate until activation. Thus, the TTI system of the present invention is configured in an inactive state and is activated only at the time of its association with the product unit to be monitored, by bringing the reactive agent surface of the first part and the activator surface of the second part in contact. In a preferred embodiment, the first part further comprises a permanent conventional ink which matches with the final color of the indicator and is printed on a transparent plastic film around the perimeter of the microorganism- based ink. In another preferred embodiment, an aqueous adhesive used to coat the specific activator onto the self-adhesive support film is acrylic-based and has a pH in the range between about 7.5 and about 8.0. Yet in another preferred embodiment, the second part is protected on both sides with two sheets of silicone release liner. The silicone release liner sheets are removed at the time of activating the TTI and mounting it onto a packaging of the product.

In another specific embodiment, printing of the reactive agent and the activator is switched. Namely, the reactive agent is printed onto a self-adhesive ^• support film, whereas the activator is printed onto a transparent sheet. In this case, the present invention provides a TTI system comprising a two-part self-adhesive label comprising a first part comprising a transparent film substrate printed with a water-based contact adhesive that contains an activator, and a second part comprising a conventional pressure sensitive adhesive label that is printed with a reactive ink containing microorganism and a color indicator. In a preferred embodiment, the second part further comprises a conventional permanent ink that matches with the final color of the indicator.

In either of the specific embodiments described above, the pH-color indicator can be mixed with either the first part, or the second part or the both, in so far as it is contained at least one of these two (2) parts.

The present invention further provides a method for preparing the TTI system of the present invention, comprising (i) printing a first part comprising microorganisms; and (ii) printing a second part comprising an activator, wherein a pH-sensitive indicator is contained in at least one of the first and the second parts, and the first and the second parts are kept separate until activating the TTI system. The TTI system is then activated by (iii) contacting the first part and the second part with each other. The activated TTI system is then mounted on a product package or container. In a preferred embodiment, the first part is printed onto a transparent film. In another preferred embodiment, the second part is printed onto a transparent film. In yet another preferred embodiment, the first part is printed onto a self-adhesive label. In yet another preferred embodiment, the second part is printed onto a self-adhesive label.

The present invention also provides a method for monitoring a time- temperature history of a product, comprising: (i) activating the TTI system of the present invention by contacting the first and the second parts; (ii) affixing the TTI system onto a product to be monitored; and (iii) assessing a time temperature history of the product by comparing a final color of the color indicator with a reference color. In a specific embodiment, the product is adapted for refrigerated storage. In another specific embodiment, the product is adapted for room temperature storage. And yet in another specific embodiment, the product is adapted for non-freezing and non-refrigerated storage, but requires certain temperature ranges for storage (e.g., chocolates, wine, champagne, etc.).

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1 shows a schematic diagram of various steps of a product within a standard handling and transportation chain in which cumulative history of temperature should be monitored.

Fig. 2 shows a schematic diagram of the initial and the final state of a TTI label that reflects both time and temperature history of the label itself and, therefore, that of the product. In Fig. 2A, the temperature was kept in optimal conditions for a period of time, whereas in Fig. 2B, the temperature fluctuated, thereby exposing the TTI system and the product bearing the TTI system to a wide range of temperatures for different time periods.

Fig. 3 shows a cross sectional view of a cumulative TTI of the present invention in a preferred embodiment, represented in a non-joined state.

Fig. 4 shows a cross sectional view of a cumulative TTI of the present invention in another preferred embodiment, represented in a non-joined state.

Fig. 5 shows a cross sectional view of the TTI of Fig. 4, represented in a joined state (i.e., an activated state).

Fig.6 shows a schematic view of an example of a coating apparatus for manufacturing an indicator according to the present invention.

Fig. 7 shows a schematic view of a rotary UN screen-printing apparatus for manufacturing an indicator according to the present invention. Fig. 8 shows a schematic view of an apparatus that is an alternative to the laminator 62 and die 63 of Fig. 7.

Fig. 9 is a graph showing the effect of three different strains of the genus, Saccharomyces, i.e., FERMIROUGE®, FERMICRU® LS2 and FERMICRU®LNCB, on the rate of color change in one embodiment of the invention. The Y-axis represents the colorimetric value b* and the X-axis represents the time.

Fig. 10 is a graph showing the effect, on the rate of the color development, of the additive, K-Carrageenan, which is a linear anionic polysaccharide gum having hydrocoUoidal properties. The Y-axis represents the colorimetric value b* and the X- axis represents the time.

DETAILED DESCRIPTION OF THE INVENTION

A. The TTI System/Device of the Invention

The basic configurations of the TTI systems according to the present invention will be now explained in reference to the accompanying drawings.

The present invention provides a TTI system comprising: (a) a first part comprising a microorganism; (b) a second part comprising an activator; and (c) a pH-sensitive color indicator, wherein the pH-sensitive color indicator is contained in at least one of the parts, (a) and (b).

In one specific embodiment as shown in Fig. 3, the indicator device 10 includes a first part 20 and a second part 30, which are not in contact with one another in the inactivated state. The first part 20 includes a covering layer made of clear flexible printable, preferably a plastic, film 21. Suitable materials as the film 21 include polymeric materials such as polyesters, polycarbonates, polyethylene, polypropylene, biaxially oriented polypropylene, biaxially oriented polyethylene terephthalate, polyamides, polyurethanes, polyvinyl chlorides, and so forth. In a preferred embodiment, the material 21 is a transparent polypropylene film. The film layer 21 can be untreated or treated with, for example, polyvinylidenechloride copolymer or acrylic polymers on one or both surfaces to increase printability. Furthermore, the film layer 21 may be treated with antistatic, adhesive receptive coating, and so forth. The film layer 21 may be prepared by a co-extrusion of a variety of plastics.

On the underside of the film layer 21, a conventional permanent ink 22 is printed around the perimeter of a reactive ink 24. The reactive ink 24 and the conventional ink 22 may be printed onto the plastic film either simultaneously or sequentially in either order. However, it is preferable if the conventional ink is printed first to leave a space for the reactive ink to be printed later, for. easier handling and storage. The preference is that the permanent ink 22 matches the final color of the acid-base indicator (i.e., a color indicator; infra) included in the formulation of the reactive ink 24. Other information, such as a legend comprising instructions for use of the device, a particular message, or the indication for the proper interpretations of the device, can be also printed. In this case, a care must be taken so that the letters are printed in a reverse orientation and can be read from the other side of the film. A suitable printing process for the conventional ink 22 is offset, inkjet, flexo, silkscreen, gravure, folio or spray printing. Preferably messages are printed by offset and the ink 22 is printed by silkscreen.

The reactive ink 24 can be composed of a water-based vehicle, a pH-dye indicator (i.e., a color indicator or acid-base indicator; see infra) and a population of microorganism. The water-based vehicle may be selected from cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose, hydro-gels, gum arabic, or any other conventional water-based resins well known to one skilled in the art, including, but not limited to, natural polymers, such as rosin based resins, agar, acacia gums, alginates, carrageenans, guar gums, and xanthans, and synthetic polymers, such as polyamides, polyvinyl esters, polyvinyl acetals, polyvinyl ethers, epoxide resins, polyacrylic acid esters, polymethacrylic acid esters, polyesters, alkyd resins, polyacrylamide, polyvinyl alcohol, polyethylene oxide, polydimethyl acrylamide, polyvinyl pyrrolidone, polyvinyl methyl acetamide, polyurethane, polystyrene resin, styrene-maleic anhydride copolymer (SMA), styrene-(meth)acrylate ester copolymer resin or styrene-conjugated diene copolymer resin, butyral resin, xylene resin, coumarone-indene resin, as well as a mixture of or copolymer of those listed above. Suitable solvents include, but not by way of limitation, water, alkaline buffer such as Tris-HCl, sodium bicarbonate, and so forth. In a preferred embodiment, the water-based vehicle is hydroxyethyl cellulose (HEC). In another preferred embodiment, the water-based vehicle may be selected from screen printing blending paste SERIES 420-04 available from Printcolor Screen Ltd, Berikon, Switzerland, and other water-based varnishes. The pH of the ink is adjusted between about pH 7.8 and about pH 8.5 with sodium hydroxide. The adjustment of pH of the ink 24 is very important in relation to the reactive pH ranges of the color indicator used. For example, for a color indicator whose pH- reactive range is between 7.8 (blue) and 6 (yellow), then the pH of the reactive ink 24 should be at about 7.8 or higher, but lower than the pH level detrimental to the microorganism.

The reactive element of the reactive ink 24 is a population of microorganism.

The microbial species employed is preferably one that is not capable of inducing food poisoning, i.e. it is non-pathogenic. Even though the microorganism will not be in direct contact with foodstuff products or drug products, it is preferable to use a non-pathogenic microorganism to avoid any risk of contaminating food or drugs.

Another important criterion in selecting a microorganism is that it must be capable of growing over the temperature range conducive to spoilage. In this regard, it is preferable that the microorganism is an acid producing species that undergoes growth in temperature range of about 5°C to about 40°C when in contact with a suitable nutrient. As a result of its growth, the acid production increases in concentration to the point that it will change the color of the acid-base indicator within the ink 24. Any microorganisms that are not pathogenic and capable of growing and fermenting at the above-indicated temperature range may be used for the TTI of the present invention. Such microorganisms include, but are not limited to, non-pathogenic fungi, such as yeasts often used in bakery, brewery and oenology, and non-pathogenic bacterium often used in dairy, cereal and meat products, such as Lactobaάllus spp. (e.g., Lactobacillus bulgaricus, Lactόb cϊllus heleveticus, Lactobacillus casei, etc.), Propionϊbacterium spp. (e.g., Propionibacterium acidipropioniei, Propionibacteriumfreudenreichii, etc.), Bifidobacterium spp. (e.g., Bifidobacterium longum, Bifidobacterium bifidum, Bifidobacterium infantis, etc.), Leuconostoc spp. (e.g., Leiiconostoc mesenteroides, Leuconostoc carnosum, etc.), Streptococcus spp. (Streptococcus thermophilus, etc.), and Pediococcus spp. (e.g., Pediococcus acidilactici, Pediococcus pentosaceus, Pediococcus cerevisiae, etc.).

In a preferred embodiment, the microorganisms used for the present invention are yeasts. Suitable yeast strains are those commonly used in oenology, brewery or bakery and belong to genus Saccharomyces. Some examples include, but are not limited to, Saccharomyces cerevisiae, Saccharomyces uvarum, Saccharomyces pastorianus, and Saccharomyces bayanus. Different strains of these microorganisms are commercially available by many suppliers under various tradenames. In a preferred embodiment, the type of yeast to be used for the TTI of the invention is Active Dry

Yeast (ADY) or Instant Dry Yeast (IDY). ADY is an yeast that has been dehydrated, as is IDY, to prolong the storage stability of the yeast. However ADY and IDY are distinct in that the former needs to be rehydrated in lukewarm water to activate it.

IDY was developed 30 years ago to replace ADY which needs to be pre-soaked in water containing sugar for its activation. IDY is often used in bakery and does not require prior rehydration. Suitable concentrations of microorganism in the reactive ink for the present invention are at least about 10⁸ colony forming unit per 1 ml of the ink (i.e., 10⁸ CFU/ml), and preferably at least about 10⁹ CFU/ml. The reaction of the TTI system of the present invention employing microorganisms is based upon anaerobic respiration of the yeast that produces acids as a product of its glucose fermentation. The reaction occurs only when the first and the second parts of the TTI system are made in contact with each other via contact adhesive/glucose. The acids are produced at a rate which is dependent upon the storage temperature of the TTI system and, therefore, that of the product to which the TTI system is affixed. Hence, the TTI systems of the present invention are most useful for a type of product whose shelf life is known at a fixed temperature. Any temperature fluctuations during storage will bring about a faster (or slower) color change than expected as a result of a pH drop. The reactive system (i.e., the part comprising reactive inks) of the invention is preferably maintained in an anhydrous state until its activation by bringing the first and the second parts together and attaching it to the packaging. The reactive ink 24 being water-based must be dried thoroughly to remove traces of residual water while a great care must be taken to ensure that the drying system does not raise the temperature above 60°C, which would otherwise kill the microorganisms.

The ink 24 comprises also a pH-dye indicator (or color indicator or acid-base indicator). The acid-base indicators suitable for the TTI system of the present invention should be able to indicate the pH range of about 3.0 and about 8.5, more preferably between about 3.5 and about 8.0 and most preferably between about 4.0 and about 7.5 and include, but are not limited to, bromocresol green, methyl red, alizarin red, chlorophenol red, bromocresol purple, bromothymol blue, brilliant yellow, and so forth. In a preferred embodiment, the color indicator is bromothymol blue which has a distinct color transition from blue (at about pH 7.8) to yellow (at about pH 6.0). In another preferred embodiment, the acid-base indicator is chlorophenol red, with a pH transition range between 4.8 (Yellow) to 6.0 (violet). A wide variety of dyes suitable for the TTI of the invention can be found in "The

Sigma- Aldrich Handbook of Strains, Dyes and Indicators", 1991, 2nd ed., available from Sigma- Aldrich, Milwaukee, WI. The pH-sensitive color indicator can be incorporated either in the reactive ink 24 or the adhesive layer 31 (infra), or both. Preferably, the amount of the color indicator is at least about 0.05%, at least about 0.1%. at least about 0.2%, at least about 0.5%, at least about 1%, or at least about 2%, by weight of the reactive ink or the adhesive layer.

In the Figure 3, the second part 30 includes a conventional self adhesive label comprising planar support film 32, pressure-sensitive adhesive layer 33, and silicone release liner 34a. The adhesive layer 31 contains an activator and is printed upon the film 32 and release liner 34b covers the adhesive layer 31. Suitable support material for the film 32 include, but not by way of limitation, polymeric materials, such as polyesters, polycarbonates, polyethylene, polypropylene, biaxially oriented polypropylene, biaxially oriented polyethylene terephthalate, polyamides, polyurethanes, polyvinyl chlorides, and so forth. In a preferred embodiment, the planar support film 32 is a white polypropylene film. The film layer 32 can be untreated or treated with, for example, polyvinylidenechloride copolymer or acrylic polymers on one or both surfaces to increase printability. Furthermore, the film layer 32 may be treated with antistatic, adhesive receptive coating, and so forth. The film layer 32 may be prepared by a co-extrusion of a variety of plastics.

The adhesive layer 33 can be formed with solvent- or water-based self- adhesives, UV or other radiation curable adhesives or pressure sensitive adhesives. In a preferred embodiment, pressure-sensitive adhesives are most suitable. The adhesive layer 33 allows attachment of the TTI system/device to a container or packaging of the product.

The bottom layer 34a is a release liner, placed under the adhesive layer 33, that is removed prior to the attachment of the TTI device to the packaging of the product being monitored. The adhesive layer 31 is formulated with an activator component that will be used as nutrients for the microorganism in the reactive ink 24 of the first part. The nutrients to be used for the TTI of the invention should be those which promote the growth of the microorganism, thereby leading to acid production. In a very basic formulation, the minimum medium required as an activator is a carbon source. The carbon sources suitable for the present invention include, for example, monosaccharides, such as glucose, levulose, mannose and galactose; disaccharides, such as sucrose, lactose and maltose; and the polysaccharides, such as starch, inulin and dextrin.

In a preferred embodiment, glucose is used as a carbon source for the microorganism. The quantity of glucose included in the adhesive layer 31 should be adjusted so that the metabolic pathway of the microorganism is directed to a fermentation process, instead of aerobic respiration, thereby leading to the acid production.

In a specific embodiment, the concentration of the activator is preferably at least about 10%, more preferably at least about 15%, and most preferably at least about 20%, by weight of the adhesive layer 31. The adhesive in the adhesive layer 31 is aqueous and preferably based on the acrylic technology available from Forbo Swift or Kiwo (Kissel & Wolf). Preferably, the pH of the adhesive in the layer 31 should be adjusted to between about 7.5 and 8.5, more preferably between about 7.8 and about 8.3, and most preferably about 8.0. This adhesive must also be dried carefully so that a certain level of water is retained. The preferable moisture content of the adhesive layer is between 10% and about 50%, and more preferably between about 15% and about 40%, and most preferably between about 20% and about 30%. This is important for the activation of the microorganism when the first and the second components are brought together in contact to each other. The adhesive layer may also contain certain additives, for example, K- Carrageenan, to increase the water retention of the layer. κ-Carrageenan is a linear anionic polysaccharide gum having hydrocoUoidal properties and is water-soluble. Carrageenans occur in certain species of red seaweeds and have a common structural feature of being linear polysaccharides with alternate 1,3-linked β-D- galactopyranosyl and 1,4-linked α-D-galactopyranosyl units. To increase the water retention of the adhesive layer, other hydrocoUoidal materials as well as microcapsules containing water may be also added to the activator.

The top layer 34b of the second component is a release liner, applied over the adhesive layer 31, which is removed prior to the activation of the TTI to bring the first part 20 and the second part 30 in contact with each other. The release liner 34b should have tack properties compatible with that of the adhesive layer 31 for optimal protection and release of the adhesive layer 31 before the activation of the system.

Shown in Fig. 4 is a cross sectional view of the cumulative TTI of the present invention in another preferred embodiment represented in a non-joined state. In this alternative embodiment, the locations of the reactive component and the activator component are switched. Namely, a reactive ink 25 is printed on a self adhesive label 310 and the adhesive 31 containing the activator is printed on a transparent film 21. The indicator device 100 includes a first part 200 and a second part 300, which are not in contact with one another in the inactivated state. The first part 200 includes a covering layer made of clear flexible imprintable plastic film 21. Suitable support materials as the film 21 are the same as those described for Figure 3. In a preferred embodiment, the support material is a transparent polypropylene film. The layer 21 can be untreated or treated on one or both surfaces to increase printability. The film 21 may be prepared by a co-extrusion of a variety of plastics. The adhesive layer 31 is formulated with an activator component that will be used as nutrient by the microorganism in the reactive ink 25. In a preferred embodiment, glucose is used as a carbon source for the microorganism. The quantity of glucose included in the adhesive layer 31 should be adjusted so that the metabolic pathway of the microorganisms is directed to a fermentation process, instead of aerobic respiration, thereby leading to the acid production. The adhesive in the adhesive layer 31 is aqueous and preferably based on the acrylic technology available from Forbo Swift or Kiwo (Kissel & Wolf). The bottom layer 34b of the first part (i.e., the activator part) is a release liner, applied over the adhesive layer 31, that is removed prior to the activation of the TTI by bringing the part 200 and the part 300 together in contact with each other. The release liner 34b should have tack properties compatible with that of the adhesive layer 31 for optimal protection and release of the adhesive layer 31 before the activation of the system.

The second part 300 includes a conventional self adhesive label 310 comprising, from the bottom up, a silicone release liner 34a, a pressure-sensitive adhesive layer 33, and a planar support film 32. A conventional permanent ink 22 is printed on the film layer 32 in the perimeter of the reactive ink 25. The reactive ink

25 and the conventional ink 22 may be printed onto the plastic film either simultaneously or sequentially in either order. However, it is preferable if the conventional ink is printed first, leaving a space for the reactive ink to be printed later, for easier handling and storage. The preference is that the permanent ink 22 matches the final color of the indicator (i.e., a color indicator; infra) included in the formulation of the reactive ink 25. Other information such as a legend comprising instructions for the use of the device, a particular message, or the indication for the proper interpretations of the device, can be printed. A suitable printing process for the conventional ink 22 is offset, inkjet, flexo, silkscreen, gravure, folio, or spray printing. Preferably messages are printed by offset and the ink 22 is printed by silkscreen. The reactive ink 25 is composed of a water-based vehicle, a pH-dye indicator and a population of microorganism, exactly the same as described for the reactive ink 24 of Figure 3. In a preferred embodiment, the water-based vehicle is hydroxyethyl cellulose (HEC). In another preferred embodiment, the water-based vehicle is selected from screen-printing blending paste SERIES 420-04 available from PRINTCOLOR Screen Ltd, Berikon, Switzerland. The pH of the ink is adjusted between about pH 7.8 and about pH 8.5 with sodium hydroxide. The reactive element of the reactive ink 25 is a population of microorganism as described for the reactive ink 24 of Figure 3. The ink 25 comprises also a pH-dye indicator as described for the ink 24. In a preferred embodiment, the color indicator is bromothymol blue which has a distinct color transition from blue (at about pH 7.8) to yellow (at about pH 6.0). In another preferred embodiment, the acid-base indicator is chlorophenol red, with a pH transition range between 4.8 (Yellow) to 6.0 (violet). As described for Fig. 3, the pH-sensitive color indicator can be incorporated either in the reactive ink 25 or the adhesive layer 31 (supra), or both. Preferably, the amount of the color indicator is at least about 0.05%, at least about 0.1%. at least about 0.2%, at least about 0.5%, at least about 1%, or at least about 2%, by weight of the reactive ink or the adhesive layer.

In another embodiment of the present invention, the self adhesive label 310, in Figures 3 and 4 can be replaced by any suitable support material including, but not by way of limitation, polymeric materials, such as polyesters, polycarbonates, polyethylene, polypropylene, biaxially oriented polypropylene, biaxially oriented polyethylene terephthalate, polyamides, polyurethanes, polyvinyl chlorides, and the like.

The part 30 in Figure 3 and the part 300 in Figure 4 as well as the part 20 in Figure 3 and the part 200 in Figure 4 may be stored in rolls or in a folded state until the time of the activation of the TTI system. The TTI device may be delivered to the final end-users as two separate rolls or folds of the part 30 or 300 and the part 20 or 200 to be affixed upon the part 30 or 300, at the time of activating the TTI system and starting the monitoring.

Fig. 5 shows the TTI device represented in a joined state (activated) and is affixed to the object 40 (product) to be monitored. Placing the part 200 comprising the adhesive 31 containing glucose and the part 300 containing the reactive ink 25 in contact with each other activates the indicator device 100. In a preferred embodiment, the product 40 is in container (e.g., drug bottles) or in packaging (e.g., food packaging) and the TTI device of the present invention is affixed to the containers or to the packaging, rather than directly onto the products themselves.

In another embodiment, the packaging material itself for the product can serve as the planar support film 32 in the embodiments shown in Fig. 3 and Fig. 4. In this case, the pressure-sensitive adhesive layer 33 and the silicone release liner 33 are not necessary. Either the adhesive layer 31 containing the activator (in the case of Fig. 3 configuration), or the layer with the reactive ink 25 and the conventional permanent ink 22 (in the case of Fig. 4 configuration) can be directly printed onto a surface of the packaging material specifically reserved for this purpose. Then, the part 20 (in Fig. 3 configuration) or 200 (in Fig. 4 configuration) is placed on the top of the part 30 or 300, respectively, so that the activator surface and the reactive ink surface become in contact with each other and the TTI is activated.

B. Methods for Preparing the TTI

The present invention further encompasses a method for preparing the TTI system/device of the present invention. Accordingly, the present invention provides a method for preparing a TTI system comprising: (i) printing a first part comprising a microorganism; (ii) printing a second part comprising an activator; and (iii) contacting the first part and the second part with each other, wherein either the first part or the second part, or both contain a pH-sensitive color indicator. The preferred embodiments described in Figs. 3, 4 and 5 may be advantageously constructed by means of apparatus 50, 60, 62 and 63, as schematically illustrated in Figs. 6-8. Apparatus 50 shown in Fig. 6 is a coating printer that deposits a layer of reactive ink 24 or 25 upon the parts 21 or 310, respectively, that has been already printed with the conventional ink 22. The coating printing process includes pumping, blending, injecting and finally printing the ingredients for the reactive ink 24 or 25. One skilled in the art will know how to set up various parameters for the coating printer, such as speed, temperature, hot air flux, grammage, etc., appropriate for printing of a given reactive ink in accordance with the specification thereof (e.g., composition, viscosity, etc.). The resulting part 20 or 300 is then rolled or folded and stored until it is used in combination with the part 30 or 200, respectively, at the time of activation and affixation of the TTI device 100 onto the product.

A second embodiment of an apparatus for providing indicators according to the present invention is illustrated schematically in Fig. 7. Apparatus 60 is particularly suited for providing the TTIs fabricated in accordance with the embodiment described with respect to Figs. 4 and 5. Apparatus 60 is a rotary UV screen-printing apparatus for printing the part 200. A roll of the silicone release liner 34b is unwound and passes through the rotary UV screen printing apparatus 60 that deposit a layer of the adhesive 31 formulated with glucose activator. A roll of transparent clear, flexible, and printable plastic film 21, is simultaneously unwound. The film 21 and the release liner 34b are bonded with the adhesive 31 while passing through a laminating tool, a part of the machinery. The part 200 thus formed passes under an ultraviolet illuminator 61. The part 200 is then lead to a laminator 62. The part 200 thus obtained can be die-cut into lengths of several strips of the part 200 divided by perforations therebetween to be separated later, as illustrated in Fig. 7. Alternatively, the part 200 of the indicator can be prepared as a long tape and wound in a roll as represented in Fig. 8. These processes are likewise applicable to preparing the part 30 of Fig. 3.

Thus, the TTI device of the present invention can be manufactured and delivered to end-users as two rolls of part 20 or 200 and 30 or 300, respectively.

In one preferred mounting method (not shown), the part 20 or 200 is first unwound by an unwind assembly, and the release liner 34b is removed from part 30 or 200, respectively. The part 20 or 200 is then placed upon the part 30 or 300. In a second step, the resulting activated device 10 or 100 is affixed to the object (product) 40 to be monitored, by peeling the release liner 34a from part 30 or 300 with a second unwind assembly and affixing the part 30 or 300 to the product 40 at a place reserved for the TTI device. In another preferred mounting method (not shown), the part 30 or 300 is first affixed to the object 40 to be monitored. The part 20 or 200 is then unwound in an unwind assembly and the release liner 34b is removed. The part 20 or 200 is then placed precisely just upon the part 30 or 300, respectively, affixed to the product 40.

One skilled in the art will be able to make appropriate modifications to preparing the parts 20/200 and 30/300 and mounting the activated TTIs to the products, considering cost efficiency and convenience of the manufacturing processes.

C. Methods for Monitoring Products

The present invention also provides a method for monitoring a thermally sensitive product comprising: (i) activating the TTI system of the present invention by contacting the first and the second part of the TTI system; (ii) affixing the activated TTI system on the product; and (iii) assessing a time temperature history of the product based on a color change of the pH-sensitive color indicator. In a preferred embodiment, the TTI system of the present invention also comprises a conventional permanent ink which matches with a final color of the color indicator. The permanent ink (see supra; also see 22 in Figs. 3 and 4) serves as a reference color for assessing a color change of the indicator.

EXAMPLES

The following examples illustrate the TTI system of the present invention. These examples should not be construed as limiting. All percentages are by weight and all temperatures are in centigrade, .unless otherwise indicated.

Example 1-3

According to the first preferred embodiment described in Fig. 3, a TTI device 10 was prepared as follows: Part 20 comprises a reactive ink 24 and a conventional ink 22 both printed on a film 21. The conventional reference ink 22 consists in VFP MPI Yellow (VFP Screen Printing Inks, Saint-Christol-lez-Ales, France) in order to match the final color of the TTI device which corresponds to the Pantone 129C reference. It was printed with a 90 mesh stencil with a KAIROS S20 machine (KAIROS, Paris, France). A space of 1 cm² was reserved for the reactive ink to be printed. The film 21 used was a Label-Lyte LL536 film (ExxonMobil Chemical Films, Rueil-Malmaison, France) which is a transparent, biaxially oriented polypropylene (BOPP).

The reactive ink 24 was prepared by mixing a vehicle made of hydroxylethyl cellulose (HEC) 4%, a mixture of yeast strain and an acid-base indicator. The solution of hydroxylethyl cellulose was prepared by mixing 8 g of HEC (FLUKA Chemie GmbH, Buchs, Switzerland) with 4 ml of 0.1 M NaOH and 188 ml of deionized water filtered on 0.2 μm Nalgene filter (Nalge Limited, Hereford, United Kingdom) to provide 200 ml of clear, substantially bacteria-free 4% HEC solution with a final pH of 9. The yeast-based reactive ink 24 was prepared by mixing 1 g of bromothymol blue indicator (Acrδs Organics France, Noisy Le Grand, France), 10 g of dry yeast strain LAP F (Laffort Oenologie, Bordeaux, France) and 100 g of 4% HEC. AU the components were mixed with 40 ml of carbonate buffer pH 9 (0.71 M NaHCθ3 and Na₂C0₃ diluted with deionized water to 100 ml volume). The reactive ink 24 was then printed onto the film 21 in the reserved area and air dried.

In the examples 1-3, the TTI devices were prepared in accordance with the present invention. The adhesive 31 of the part 30 were formulated in the examples as described in Table 1, wherein the components used are as follows: Syncol 534 adhesive (FORBO Swift Adhesives, Blois, France), Kiwoprint D158 adhesive (Kissel + Wolf GmbH, Wiesloch, Germany), D(+)-Glucose (Sigma- Aldrich Chimie S.a.r.l., Lyon, France) and Tego Foamex 1495 (Tego Goldschmidt France, St.-Quentin-en- Yvelines, France).

Table 1

Example 1 & 2 Example 3 wt % Kiwo D158 Syncol 534 Adhesive 74 87 Glucose 10 10 Deionized Water 12 - NaOH 1 M 3 1 NaOH 0.1 M - 1 Tego Foamex 1495 1 1

The adhesive 31 of the part 30 was printed on a self adhesive label MACscreen (MACtac, Morangis, France).

The two resulting parts of the TTI devices were then stuck together and transferred to a Friocell 55 incubator (MMM Medcenter GmbH, Grafelfing, Germany) maintained at 12°C (Examples 1 and 3), or to a BE400 Memmert incubator (MEMMERT, GmbH, Schwabach, Germany) maintained at 40°C (Example 2). The colorimetric values in the L*a*b* space were followed using a spectrophotometer Minolta CM-503i (Konica Minolta Photo Imaging France S.A.S., Roissy C.D.G., France). The times were measured from initial activation of the TTI system, when the two parts are brought together, until the color change of the acid-base color indicator occurs. Under these conditions, the indicator composition of Examples 1-3 changed from a blue color to a greenish yellow within the times as indicated in Table 2.

Table 2

Example 4

The following example illustrates the second preferred embodiment obtained by reversing the order of the two reactive components and replacing the ink vehicle and the pH-dye indicator. According to the second preferred embodiment described in FIG. 4, a new time temperature indicating device 100 was prepared as follows: Part 300 comprises a reactive ink 25 printed on a conventional self adhesive label 310, for example, MACscreen (MACtac, Morangis, France); and part 200 comprises a layer 31 of an adhesive containing an activator printed on a film, for example, biaxially-oriented polypropylene (BOPP).

In Example 4, a reactive ink 25 was prepared by mixing a water-based vehicle, a pH-dye indicator and a population of microorganism. The water-based vehicle selected in that particular embodiment is a water-based, screen printing blending paste SERIES 420-04 available from PRINTCOLOR Screen Ltd, Berikon, Switzerland. The reactive element of the reactive ink 25 is a population of microorganism, preferably yeast strains. The commercially available yeast strains used for the indicator device are described in Table 3 and their concentrations expressed in colony-forming unit (CFU) per gram of dry weight of yeast. The ink 25 comprises also a pH-dye indicator. The acid-base indicator is preferably chlorophenol red, with a pH transition range between 4.8 (yellow) to 6.0 (violet).

Table 3

An indicator solution was prepared by mixing 0.2 g of chlorophenol red (FLUKA Chemie GmbH, Buchs, Switzerland) in 10 ml of IM NaOH. A yeast solution was made by dissolving 1 g of LAP G yeast strain (Laff ort Oenologie, Bordeaux, France) in 9 ml of deionized water that had been filtered through 0.2-μm Nalgene filter (Nalge Limited, Hereford, United Kingdom), in order to have a final concentration of 10⁸ CFU/g of the ink. The yeast-based reactive ink 25 was prepared by mixing 3 ml of chlorophenol red indicator solution and 0.3 ml of the yeast solution in the water-based screen printing blending paste SERIES 420-04 (PRINTCOLOR Screen Ltd, Berikon, Switzerland) to the final total weight of 30 g. The reactive ink 25 was then printed on a Label-Lyte Lithor LTL247 film (ExxonMobil Chemical Films, Rueil-Malmaison, France), which is a super white opaque, high gloss, cavitated biaxially-oriented polypropylene (BOPP).

The adhesive 31 of the part 200 formulated was a Swift E311 adhesive (FORBO Swift Adhesives, Blois, France) with 10% (w/w) of D(+)-Glucose (Sigma- Aldrich Chimie S.a.r.l., Lyon, France) and 2% of Tego Dispers 750W (Tego Goldschmidt France, St.-Quentin-en-Yvelines, France). It was then screen-printed on a transparent Propafilm™ RH50 (UCB Surface Specialties, Dijon, France) which is a biaxially-oriented polypropylene (BOPP) film coated with an aqueous dispersion of polyvinylidene chloride (PVdC) copolymer on the both sides.

The thus prepared part 200 and part 300 were then stuck together as shown in Fig. 5 and transferred to a BE400 Memmert incubator (MEMMERT, GmbH,

Schwabach, Germany) maintained at 30°C. The colorimetric values in the L*a*b* space were obtained using a spectrophotometer Minolta CM-503i (Konica Minolta Photo Imaging France S.A.S., Roissy C.D.G., France). Under these conditions, the indicator composition of Example 4 changed its color from violet to beige yellow within 336 hours. Example 5

In the following example, feasibility of using different yeast strains was tested and the minimum number of cells required for the color reaction was determined in liquid media. Three parameters were evaluated: 7 yeast strains, 2 concentrations of yeast and 2 concentrations of glucose. The growth media were only glucose solutions in water (minimum media) supplemented by the color indicator CPR (chlorophenol red). The term "Yeast -" refers to a solution of glucose without yeast. The term "GLU-" refers to water inoculated with yeast strain LS2. All tubes were placed in anaerobic conditions by adding 3 drops of sterile paraffin oil (GIFRER BARBEZAT, Decines, France) at the top, and incubated at 30°C in a BE400 Memmert incubator (MEMMERT, GmbH, Schwabach, Germany). Results are shown in Table 4.

Table 4

An inoculum with 10⁶ yeast cells per 10 ml of glucose solution (i.e., 10⁵ CFU/ml) was not enough to give clear color changes. At this concentration, there was no growth of the yeast either in a 20% glucose solution or in a 35% glucose solution. With an inoculum with 10⁹ yeast cells per 10 ml of glucose solution (i.e., 10^s CFU/ml), there was consumption of glucose, acidification of the medium and, therefore, a color shift from violet to deep yellow. In the reference tests GLU - and Yeast -, the color stayed violet. This demonstrated that the color changes were due to the fermentation of glucose by the yeast and that there was neither contamination with other organisms (see Reference Yeast -) nor the yeast growth in water (see Reference GLU -). AU the strains were able to ferment the glucose (even in very high concentration) under anaerobic conditions and induce the color change of the color indicator, with a minimum level of inoculums with 10⁸ cells per ml. Based on these results, we showed that the system is available in liquid configuration, with all the yeast strains used, and the minimum level of yeast concentration was determined to be 10⁸ cells per ml.

Example 6

The following example demonstrates that the variation in rate of reaction depends on the yeast strains used. According to the second preferred embodiment of the present invention, the TTI devices were prepared in the same way as in Example 4 except that the yeast strains used were Fermirouge®, Fermicru® LS2 and Fermicru® LVCB (DSM Food Specialties Beverage Ingredients, Montpellier, France).

The yeast solutions were prepared with 2 g of each yeast strain mixed in 10 ml of deionized water which had been filtered through 0.2 μm Nalgene filter (Nalge Limited, Hereford, United Kingdom), in order to have a final concentration of 5 x 10⁸ CFU per gram of the ink. Each of yeast inks 25 was formulated and printed on Label-Lyte LH536 biaxially oriented polypropylene (BOPP), a white opaque film (ExxonMobil Chemical Films, Rueil-Malmaison, France) with bar-coater (24 μm).

The adhesive 31 was formulated in the same way as in Example 4 except that it contained 20%, rather than 10%, of glucose. The two resulting parts of the TTI devices were then stuck together and transferred to a BE400 Memmert incubator (MEMMERT, GmbH, Schwabach, Germany) maintained at 30°C. The colorimetric values in the L*a*b* space were measured using a spectrophotometer Minolta CM- 503i (Konica Minolta Photo Imaging France S.A.S., Roissy C.D.G., France).

As shown in Fig. 9, the results presented a similar general trend of the plot of b* colorimetric value versus the time for the 3 strains. The curves were superimposable with one another. The differences in b* value among the 3 strains were maintained along the time. The starting part of each curve (for the first 24 hours) showed an increase of the b* value, which corresponds to an equilibration of the pH between the layers of the reactive component and the activator. After the equilibration, followed was a linear increase of the b* value, reflecting a color change from violet to beige yellow due to the acidification of the media. The above- described example demonstrates that the present invention is suitable to provide a TTI system/device for use with products adapted for a room temperature or a higher temperature storage for a long period.

Example 7

The following example demonstrates that the use of a special additive in the adhesive 31 can improve the formulation by allowing retention of a greater amount of water. According to the second preferred embodiment of the present invention, the TTI systems/devices were prepared in the same manner as in Example 4 except that the adhesive 31 was composed of 10% glucose (Sigma-Aldrich Chimie S.a.r.l., Lyon, France) and 0.5% κ-carrageenan (Sigma-Aldrich Chimie S.a.r.l., Lyon, France) mixed in Laminelle Screenprinting Adhesive J0672 (COATES SCREEN, Orpington, United Kingdom) as an additive. The adhesive was printed on a sheet of transparent Propafilm™ RH50 (UCB Surface Specialties, Dijon, France) using a hand-coater (24 μm).

The reactive ink 25 was prepared in the same way as in Example 4 using

Fermicru® LS2 yeast strain (DSM Food Specialties Beverage Ingredients, Montpellier, France). The resulting two parts of the TTI devices were then joined together in correct orientations and transferred to a BE400 Memmert incubator

(MEMMERT, GmbH, Schwabach, Germany) maintained at 30°C. The colorimetric values in the L*a*b* space were measured using a spectrophotometer Minolta CM- 503i (Konica Minolta Photo Imaging France S.A.S., Roissy C.D.G., France). Under these conditions, the TTI systems of Example 7 changed the color from violet to beige yellow within 42 days, as shown in Fig. 10.

EQUIVALENTS

Those skilled in the art will recognize, or be able to ascertain many equivalents to the specific embodiments of the invention described herein using no more than routine experimentation. Such equivalents are intended to be encompassed by the following claims.

All publication and patents mentioned in this specification are herein incorporated by reference in their entireties into the specification.

Claims

What is claimed is: 1. A time temperature indicator (TTI) system comprising:

(a) a first part comprising a microorganism;

(b) a second part comprising an activator; and

(c) a pH-sensitive color indicator, wherein the pH-sensitive color indicator is contained in at least one of the parts (a) and (b).

2. The TTI system of claim 1 further comprising a permanent ink having a reference color that matches with a final color of the pH-sensitive color indicator.

3. The TTI system of claim 1 further comprising a water-based vehicle.

4. The TTI system of claim 3, wherein the water-based vehicle comprises carboxy methyl cellulose, hydroxy ethyl cellulose, hydroxypropyl cellulose, hydro- gels, gum arabic, rosin, agar, acacia gums, alginates, carrageenans, guar gum, xanthan, polyamide, polyvinyl ester, polyvinyl acetal, polyvinyl ether, epoxide resin, polyacrylic acid ester, polymethacrylic acid ester, polyester, alkyd resin, polyacrylamide, polyvinyl alcohol, polyethylene oxide, polydimethyl acrylamide, polyvinyl pyrrolidone, polyvinyl methyl acetamide, polyurethane, polystyrene resin, styrene-maleic anhydride copolymer, styrene-(meth)acrylate ester copolymer, styrene-conjugated diene copolymer, butyral resin, xylene resin, or coumarone- indene resin, or a mixture or copolymer thereof.

5. The TTI system of claim 1, wherein the second part further comprising an adhesive.

6. The TTI system of claim 5, wherein the adhesive is an acrylic adhesive.

7. The TTI system of claim 1, wherein the activator comprises a carbon source.

8. The TTI system of claim 7, wherein the carbon source is glucose.

9. The TTI system of claim 1, wherein an amount of the activator is at least about 10% by weight of the first part

10. The TTI system of claim 1, wherein the microorganism is a yeast.

11. The TTI system of claim 10, wherein the yeast is Instant Dry Yeast or Active Dry Yeast.

12. The TTI system of claim 10, wherein a concentration of yeast is at least about 10⁸ CFU/ml of the first part.

13. The TTI system of claim 1, wherein the pH-sensitive color indicator is reactive to a pH range between about 3.0 and about 8.5.

14. The TTI system of claim 1, wherein the first part further comprises a transparent film.

15. The TTI system of claim 1, wherein the second part further comprises a transparent film.

16. The TTI system of claim 1, wherein the first part comprises a pressure- sensitive self-adhesive.

17. The TTI system of claim 1, wherein the second part comprises a pressure sensitive self-adhesive.

18. The TTI system of claim 1, wherein either the first or the second part is a part of a packaging or a container of a product.

19. A method for monitoring a thermally sensitive product comprising:

(i) activating the TTI system of claim 1 by contacting the first part (a) and the second part (b);

(ii) affixing the activated TTI system on the product; and

(iii) assessing a time temperature history of the product based on a color change of the pH-sensitive color indicator.

20. A method for preparing a TTI system comprising:

(i) printing a first part comprising a microorganism;

(ii) printing a second part comprising an activator; and

(iii) contacting the first part and the second part with each other, wherein either the first part or the second part, or both contain a pH-sensitive color indicator.