CA1153254A - Method and devices for detecting defrosting processes, even temporary - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE:
A process for detecting a defrosting, even temporary, of products, wherein an aqueous saline solution is kept sepa-rate from a colouring agent by a diaphragm which is broken, at the moment of freezing, by effect of the increase in volume of the solution. The solution, which has been chosen according to the eutectic point thereof, dissolves when the temperature reaches a pre-determined value, allowing thus the diffusion of the colouring agent in the solution. There are also described devices, for effecting said process.

Description

~53Z54 The present invention relates to a method and devices suitable for signalling the defrosting, even temporary, of pro-ducts that have to be preserved at temperatures below 0C.
~any products, or instance in the food, chemical and pharma-ceutical fields, must be stored at low temperatures. A possible defrosting, even if accidental and temporary, may damage these products or modify the characteristics thereof without the con-sumer becoming aware of this fact, since the exterior appear-ance, if the products are subsequently refrozen, may remain unchanged.
If the possible consequences of the use of the damaged pro-ducts are considered~ there can be well understood the utility of a method and/or of devices that can signal a defrosting occurred, even if temporarily, in an irreversible way and by indications that anyone can easily detect and understand.
In particular case of foodstuffs, such as frozen foods, said means, besides giving sure and immediately detectable indications, have to be extremel~ inexpensive so as to allow the application thereof also to products of large consumption without affecting the production costs.
There are available means suitable for signaJ.ling when a frozen product is brought to temperatures higher than the pre-scribed one, but such means are scarcely effective because either they have such a quick action that they detect also variations in temperature occurred for a period of time so short as not to affect the productr or give indications not ; easily intelligible, in that they are based on a continuous relationship between exposure temperature and time of permanence at that temperature~ without providing really effective signals relating to the changes the product has undergone.
- Still with reference, by the way of example, to the par-~`

~;3254 ticular case o ~rozen ~oods, it is to be noted that for per-fectly preserving the product an uninterrupted continuity of the so called "cold chain" is essential.
In fact, recent studies proved that an insufficient stan-dard temperature or occasional and recurring variations in temperature bring about phenomena of re-crystallization of the water present in the product cells, causing the subsequent development o bigger and bigger crystals which can make the cells themselves breakf allowing sub-strata and enzymes to get into contact among them, producing thus those alternations that were prevented by cold. Since cold does not stop the enzymatic activity, but just makes it slower, it is evident that an increase even partial in temperature, especially if recurrent, may give rise to conditions capable of deteriorating the quality of the product.
On the other hand, the frozen product has a certain degree of thermical inertia due to the stored refrigerating units, and to the mass, and is as wéll protected against sudden environ-mental variations in temperature.
Said protection is granted by the insulation the packing provides, so that even if the product is kept at unsuitable temperature for very short periods (such might be the case, e.g., during transport operations), this fact will not affect the quality thereof.
~;; Whence the necessit~ of a defrosting signalling device which is not to signal at once the outside variation in tem-perature, but rather to be sensitive, to some extent, to the life cycle o the ~rozen product from the inside of the packing, and to register not each single slight increase in temperature but, instead, the total amount of the repeated variations in temperature or of the long periods marked by an unsuitable tem-~ S3254 perature.
The detecting device must therefore be provided with a lag time liable, among other things, to be chosen, taking into account the possible occurring of those sudden slight changes in temperature which even the best cold chain is not in condition to avoid.
To this end, the present invention provides a method and the relevant devices to detect and signal when products which need to be preserved at a low temperature, are possibly kept, even temporarily, at an unsuitable temperature.
An essential feature of the invention is the exploi-tation of the chemico-physical characteristics of an aqueous saline solution, the eutectic point of which may be used to supply the calibration temperature of the device according to the invention. In fact, there is applied the principle according to which, at a temperature lower than the eutectic point, an aqueous saline solution is wholly in a solid state (e.g. ice plus solid salt).
Such a temperature, which is different for each of ~20 the chosen solutions or mixtures of solutions, may be used as a calibration temperature of the device.
The freezing characteristics of these saline solutions will be explained in more details hereinafter.
By utiliziny the above-mentioned charaateristics of aqueous saline solutions, there is provided the combination of an aqueous saline solution having a known eutectic point (EP), with a colouring detecting agent,preferably treated,so that it will not dissolve in the liquid solution before a pre-arranged tlme has elapsed. Before the freezing a diaphragm is inter-posed between the solution and the colouring agent, preventingtheir mutual contact.
In the course of the temperature drop below 0, the .~ ~
~J 3 . - . . :: - : -. ' . -: : -diaphragm is broken or removed by efEect of the increase in volume of water separating from the salt present in the solu-tion, but, because of the solid state in which the solution itself is, as soon as it reaches and surpasses the temperature corresponding to the EP, there is no mixing between the solu-tion and the colouring agent.
If a temporary permanence at a temperature higher than the E.P occurs, the solution dissolves and touches the colouring agent, so that, after a pre-determined period of time due to the treatment the colouring agent has undergone, the solution gets coloured and it will keep the colour assumed, in a per-manent way, even when a subsequent re-freezing process occurs.
It is to be noted that, by the words <~septum)> or diaphragm)> mentioned in the speciication, it is meant any means which, under the action of the increase in volume of the aqueous saline solution, mav break, teat, get a hole in it or be shoved out of its seat.
According to the present invention, there is provided a process for detecting and signalling a defrosting, even temporary, o~ products, wherein an aqueous saline solution and a colouring agent are separated by a diaphragm mounted within a rigid container, the part of the container containing the solu-tlon being full and closed, the increase in volume of the solutlon when thls one is freezing applies a strength on the diaphragm which is broken or displaced by the action of this strength at the moment of freezing when the solution and the colouring agen-t cannot mix with each other because of their ph~vsical states, and wherein any increase in temperature beyond a temperature corresponding to the eutectic point of the solution produces a visible and irreversible interaction between the solution and the colouring agent.
The present invention also proposes a device for _ ~153ZS4 detecting and signalling a defrostin~, even temporary, of proclucts. This device comprises a rigid container, a diaphragm mounted within the container for keeping separated from each other an aqueous saline solution and a colouring agent both contained in the container, the part of the container containing the solution being full and closed, the increase in volume of the solution when this one is freezing applies a strength on the diaphragm which is broken or displaced by the action of this strength at the moment of freezing when the solution and the colouring agent cannot mix with each other because of their physical states, and wherein any increase in temperature beyond a temperature corresponding to the eutectic point of the solution produces a visible and irreversible interaction between the solution and the colouring agent.
The present invention, and particularly the devices for putting this process into practice, will be now described in detail, by mere way of non-limiting example, with particular reference to the attached igures wherein: -Flg. 1 represents the section of a device for effect-ing the process according to the invention, wherein the solu-tion and the colouring agent, both held in a rigid container, are kept separate by a breakable septum.
Fig. 2 represents the section of a device for effect-ing the process according to the lnvention wherein the colour-ing agent is held in a breakable container soaked in the solu-tion.
Fig. 3 represents the section of a device for effect-ing the process accordlng to the invention, wherein the solu-tion and the colouring agent are kept separate by a removable septum.

Fig. 4 represents the section of a device for effect-ing the process according to the invention, wherein there is ~1~;32S4 used a separating pierceable element.
Fig. 5 represents the section of more than one devices for effecting the process according to the invention, joined together and calibrated for different defrosting temperatures.
Fig. 6 represents the view from above of a particular perfected embodiment of a device for effecting the process according to the invention.
Fig. 7 represents a vertical section of the device of figure 6, when open.
Fig. ~ represents a freezing diagram of an aqueous saline solution.
In order to give a better understanding of the present invention, the freezing diagram of Figure 8 illustrates the freezing characteristics mentioned in the preamble of the disclosure for an aqueous saline solution used for carrying out the method according to the present invention.
Examining the freezing diagram of Figure 8 for an aqueous saline solution, it can be noted that, taking an aqueous solution with a weight percentage of salt, for instance Cb, with the lowering of temperature from ta to tb~ the solution does not frèeze up to poing B. Once point B is reached, if the outside ~ ~ .
temperature is lower than tb~ some ice begins to separate from the solution, said process resulting in an increase in the concentration o the saline solution. This occurs as long as, once the temperature o the whole solution has reached te, almost all the water has separated from ice and all salt has .
crystallized.
;~ ~ At point E of the curve (eutectic point), there coexist equal proportions of water, ice and solid salt. Below point E, there coexist only ice and solid salt (solid eutectic).
The hatched part in Fig. 8 shows the area wherein solution and ice form at the same time.

.

~153254 The dotted part shows the area wherein ice and solid eutectic coexist.
The part contained between the diaphragm and the ordinate te shows the area wherein solution and salt are present at the same time.
Some possible saline solutions for use in the method and device according to the present invention with their respec-tive eutectic points are listed in tahle A.
With reference to Fig. 1, an aqueous saline solution 4, of proper concentration, is contained in a rigid holder made of non-deformable, non-toxic material, resistant to low tempera-tures, such as polystyrene.
Holder 1 is hermetically sealed by a cover 2, made of transparent rigid material, e.g. polystyrene of the crystalline type.
The aqueous solution is separate from the colouring agent 5 by a wall 3 made of fragile material, e.g. a foil of glass film (breakable septum).
While the saIine solution takes up entirely the ~` 20 avaiIable room, the colouring agent (for instance a food dye -~ suitably packed) does not, allowing the aqueous solution (which, during the freezing or deep-freezing process has increased in volume), to exert a pressure on the diaphragm until it breaks it.
The colouring detecting agent is preferably treated ~ :
~ by means of techniques deriving from the micro-encapsulation i ~ .
~ methods or the like, so that it takes on a granulous appearance.
1 .
Each granule is covered by a membrane, the chemical nature and thickness of which make possible the contact between the colouring agent and the chosen aqueous saline solution, in the . liquid state, only after a pre-determined period of time has elapsed. Said period of time is directly proportional to the .~ ,.
- 6a -membrane thickness and inversely proportional to the temperature at which the contact between the liquid aqueous saline solution and the granulous detecting agent takes place, and is referred to as Lag time.
Therefore, during the freezing cycle, the solution, after breaking the diaphragm, comes in contact with the colouring agent but, either because it silidifies quickly, or because of - -' - 6b -' ~1~i3~5~

the presence o the protecting memb~ane, it does not take any colour.
In case o defrosting, after a proper pre-determinable period of time, the solution dissolves the membrane which coats the granules and takes on a colour irreversibly;
Fig. 2 represents a variation of the device according to the invention. It consists of a rigid container 6, hermetically closed by a transparent cover 7, holding the aqueous saline solution 8. The colouring agent 10, properly treated, is con-tained in a fragile capsule 9 which is broken b~ sol~tion 8while the same is reezing.
In this case, the prevlousl~ mentioned breakable septum consists o the ragile capsule 9.
Fig. 3 is a further variation o the device according to the invention~
In it the container consists o a capsule 11 made of rigid material, filled by the aqueous saline solution 12 and provided with a well 13 having a hole c~osed b~ a pressure diaphragm 14.
During the freezing the solution 12, by expanding displaces diaphragm 14 removing it from its seat and making possible, during a subsequent defrosting, the contact with the colouring agent 15 contained in the well.
; According to a Eurther variation (fig~ 4), the separating ;~wall 16 (breakable septum) may b~ made of deformable material, properly stretched, in contact with polnted or cutting elements . ~
17, and it may divide the container 18 into two compartments.

When the aqueous saline solution contained in the upper ~ compartment reeæes~ the increase in volume thereof makes wall ; ~16 tear~ because it is pushed against the pointed elements 17.

After which the solution, in case of defrosting, can come in contact (when in the liquid state) with the colouring agent ~;3254 contained in the lower compartment.
As it can be noted from the above, the devices for effecting the process according to the invention may be calibrated in accordance with a pre-determined temperature (e.g. next to the limit temperature of a single product) according to the type of the aqueous saline solution used, said temperature corresponding to the eutectic point o the solution itself.
However, it is also possible to combine two or more devi-ces, each of which having its particular solution di~ferent from that o the others, having colouring agents of different colours and being calibrated for different temperatures.
Besides, there may be combined two or more devices containing the same saline solution but with different colouring agents treated in a different way, so that the colouring is provided after different periods o permanence at temperatures higher than the calibration one.
One such version o the device (fig. 5) provides the outer envelope 19 subdivided into several independent compartments each with its own colouring agent 20 separated by a breakable septum 21 from the solution 22r which may be different as well.
So the device according to the invention will be able to signal different degrees of defrosting, or the permanence at too high temperatures or different times. A simpli~ied version of the ;~ above multiple devicef suitable ~or detecting di~ferent times ~ of permanence at a temperature higher than that of calibration, `~ may consist of a rigid envelope identical to the one described in fig. 1, provides with a breakable septum separating the aqueous saline solution from the detecting colouring agent.
The latter consists o a mixture of two or more different colouring agents, each o which has been treated so as to give colour to the liquid solut;on to which it may come in contact, .

~153254 after dierent periods o time.
The diferent colouring agents may also be packaged in one or more elements consisting of subsequent layers, so that they may dissolve one after the other, but with ever increasing different delays.
It is to be noted that one of the main features of the invention consists in the fact that the granules of the colouring agent are coated by a mèmbrane which delays the melting thereof in an aqueous saline solution.
The advantages said feature involves are twofold: first, it permits to avoid the inconveniences due to the fact that, according to the concentration, in the interval between the freezing point and the eutectic point of a saline solution there remains a liquid solution which, on coming in contact with the colouring agent, can make the detecting agent change its colour.
In the second place, since to each period (even if short) of permanence of the device at a temperature higher than that expected, corresponds a decrease in the lag time, it follows that the devices according to the invention memoriæe the pos- . .
sible sudden changes in temperature, reducing more and more the margin of delay or which the device had been calibrated, until .
the i~reversible colouring takes place. This phenomenon happens because the solution in the liquid state attacks the ~ranules ~: containing the colouring agent each time it is in contact with them, and ceases to do so when it is restored to its former solid state.
~:~
. After these more or less prolonged attacks, the.re is reached a point when the colouring~agent begins to diffuse, and the detecting agent to change its col.our.
3~ Said phenomenon takes place at the same time the lag time e~ds and is very important because while short single increases _ g _ .

~5;3254~
in temperature may not affect and damage the product, they can be harmful if repeated.
For the sake of a better understanding, there now follows a non-limiting example of an application of the process according to the invention.
The device used in the example described hereinafter has been specially devised for frozen foods:
EXAMPLE
The device shown in fig. 6 and used for the experiment consists of a container 23 having the shape of a square paralle-piped with a base of 22 mm and height of 8,8 mm.
Said container 23 consists of a base 24 closed by a cover 25 which can be inserted by pressure (fig. 7).
The edges of base 24 and cover 25 are such shaped as to fit the one into the other. On the bottom of base 24 of container 23, there is a depression, whose side walls 31 are 15,40 mm long. In tha middle of said depression, there is a square well 28, with a side of 5 mm and a depth of 2 mm.
~ he walls of the well are equidistant from inner walls 20- - 27 of the cover in order to favour a well-timed diffusion of the :
~ ~ coiouring agent all over the solution.
- The cover is provided with a circular central portion 29, inwardly protruding, having oblique ~aceted sides 30.
The thickness o~ portion 29 has been studied in such a way that the gas pocket, which forms when the liquid solution enters the well of the detecting agent, be spread around the basis of the cover as homogeneously as possible, and that the faceted sides prevent the particular characteristics inside the device to be seen (before use and after dissolution of the solution).
The inner edges of the cover are round, so as to favour a better spreading of the gas pocket.

'' ~
' ~ - 10 -~3254 The breakable septum (not shown in the figure) consists of a thin glass having 20 mm side and a thickness ranying from 0,130 to 0,145 mm.
The square shape was chosen for the glass in that it was found the least expensive of all.
The breakable septum is stuck on the lower edge 26 of the cover by means of a layer of silicone rubber of the t~pe Silastic RTV 734 (Trademark).
A triple result is thus obtained:
a) by means of the pressure itting between cover and basis it is possible to arrange the diaphragm in the desired position, and to let some of the glue penetrate along the touching edges of the cover and the basis, helping thus the tightness of the device;
b)~ the glue should be applied between the lower edge 26 of the cover and the glass; in fact, it is necessary to make the glass lean directly on the rigid base 24 at the moment the container is closed, without any deformable material being put in between. The reason for this lies in the fact that if the ~ . .

2~0 layer of glue were applied between the glass and base 24 it - would become~deformed, allowing thus the septum to shift fo~llowing the increase in vo~ume of the solution (when it Preezes?j without the breaking thereof taking plaae. On the contrary, if the septum is stuck on the rigid bottom of the container, an increase in volume of the above solution will no doubt cause the breaking of the septum.
c) the diaphragm therefore, besides being glued, is clamped between the basis and the cover, making thus the above breaking more effective.
Thè size of wall 31, which, together with the lower : . . -~ edge 26 of the cover holds the b~eakable septum, is such as to ; allow the diaphragm, by effect of the pressure of the freezing C ' ~ ' ' 11_ .

'' ~1~;3254~

solution, to bend so much that it surpasses the breading limit.
The device is made of materials such as opaque white polystyrene of the crystalline type (transparent) ~or the cover 25.
The reason why these materials have been chosen is their non-toxicity at low temperatures and their low cost.
As solution, there has been chosen a 19,7 % ammonium chloride (NH Cl) aqueous saline solution, and as detecting agent the food dye E 124 (red), microencapsuled so that it can pro-, ~ ~

/

~: :::.: : /
~ / t .,: : / :

~ - lla -: .

~,53ZS4 vide a lag time o one hour.
This colouring agent has been chosen both because it is of a food kind (even though such a requisite is not indispensable, being the substance isolated inside the detecting agent), and because, among the more than 5~ colauring agents of various types experimented, it is readily soluble in ammonium chloride, is not light-sensitive and its colour is bright red.
As a variation there has been experimented also yellow E102 which supplied results similar to those supplied by the previous one.
The choice of the solution of ammonium chloride, solution which is non-toxic at the used concentration and quantity, is due to the fact that the E.P. thereof is of 15,8C, while in the majority of countries rozen products are kept at the maximum temperature o 18C.
If it is kept at this temperature, the ammonium chloride is in the solid state and snow-white.
The high concentration chosen tl9t7 % equal to the eutectic concentration) makes the freezing point very near to the eutectic ~20 point, therefore with a minimum interval during which, in the cooling phase, the liquid saline solution is in contact with the coloured detecting agent.

, ~ .

~ , ,

3~54 SOME SALINE SOLUTIONS AN~ THEIR RESPECTIVE EUTECTIC POINTS

Disodic maleate 0,4 C
Sodium sulphate 1,1C
Monosodic citrate 2,1 C
Potassium nitrate 2,9C
Magnesium sulphate 4,0 C
Trisodic citrate 6,9 C
Potassium chloride 10,7C
Disodic citrate 12,0C
Potassium bromide 13,0C
Ammonium chloride 15,4C
Dipotassic citrate 15,6C
Sodium nitrate 18,5C
Sodium chloride 21,8C
Sodium bromide 28,0C
Magnesium chloride 33,6C
Potassium carbonate . 36,5C
Tripotassic citrate 40,0C

TABLE A
' :: 13 ~ `.

Claims (11)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for detecting and signaling a defrost-ing, even temporary, of products, wherein an aqueous saline solution and a colouring agent are separated by a diaphragm mounted within a rigid container, the part of the container containing said solution being full and closed, the increase in volume of the solution when this one is freezing applies a strength on the diaphragm which is broken or displaced by the action of this strength at the moment of freezing when the solution and the colouring agent cannot mix with each other because of their physical states, and wherein any increase in temperature beyond a temperature corresponding to the eutectic point of the solution produces a visible and irreversible interaction between the solution and the colouring agent.

2. A process for detecting and signalling a defrost-ing, even temporary, of products according to claim 1, wherein the temperature corresponding to the eutectic point of the saline solution is taken as a calibration temperature for carrying out said process.

3. A process for detecting and signalling a defrost-ing, even temporary, of products according to claim 1, wherein the colouring agent comprises colouring parts covered with a delaying coating in such a way to produce a delaying action in said visible and irreversible interaction.

4. A process for detecting and signalling a defrost-ing, even partial or temporary, of products according to claim 3, wherein the delay produced by said delaying coating depends on the intrinsic characteristics of said coating of the coloring parts with respect to the characteristics of the saline solution, and on the thickness of the coating with respect to the dimensions of said parts.

5. A process according to claim 3 or 4, wherein said coating is laid by means of a microencapsulation method.

6. A device for detecting and signalling a defrost-ing, even temporary, of products, said device comprising a rigid container, a diaphragm mounted within said container for keeping separated from each other an aqueous saline solution and a colouring agent both contained in said container, the part of said container containing said solution being full and closed, the increase in volume of the solution when this one is freezing applies a strength on the diaphragm which is broken or displaced by the action of this strength at the moment of freezing when the solution and the colouring agent cannot mix with each other because of their physical states, and wherein any increase in temperature beyond a temperature corresponding to the eutectic point of the solution produces a visible and irreversible interaction between the solution and the colouring agent.

7. The device of claim 6, wherein said aqueous saline solution is chosen in relation with a predetermined calibration temperature, the temperature corresponding to the eutectic point of the chosen solution being said calibration temperature, and wherein said colouring agent is formed of colouring parts covered with a delaying coating for delaying the visible and irreversible interaction.

8. The device of claim 7, wherein said parts covered with a delaying coating comprise granules coated according to a micro-encapsulation method.

9. The device of claim 6, 7 or 8, wherein there is provided a plurality of rigid containers, each of said con-tainers containing a saline solution having an eutectic point different from that of the solutions contained in the other containers, and detecting devices of different colours, each of which being associated with one of the containers and compris-ing a colouring agent covered with a delaying coating and processed in such a manner to provide a same delaying action produced by said coating in the visible and irreversible interaction.

10. The device of claim 6, 7 or 8, wherein there is provided a plurality of rigid containers, each of said containers containing the same aqueous saline solution, and a different colouring agent processed in such a manner to provide a pre-determined and different delay before the visible and irreversible interaction is produced.

11. The device of claim 6, 7 or 8, wherein said colouring agent comprises the combination of two or more different colouring agents, each of which has been processed to provide a different delay before the visible and irrevers-ible interaction is produced.