FIELD OF THE INVENTION

The invention relates to a method for providing a pitaya-based edible time temperature indicator. The invention further relates to the edible time temperature indicator. The invention further relates to a food item comprising the edible time temperature. The invention further relates to a food item comprising the edible time temperature indicator. The invention further relates to a use of the time temperature indicator.

BACKGROUND OF THE INVENTION

Time temperature indicators are known in the art. For instance, Rahimah et al, “Betacyanin as Bioindicator Using Time-Temperature Integrator for Smart Packaging of Fresh Goat Milk”, The Scientific World Journal, 2020, describes determining the quality of fresh goat milk during storage at freezing temperatures (-20 ± 2°C) for 31 days and room temperature (25 ± 3°C) for 24 hours using a time-temperature indicator by utilizing a natural dye betacyanin. The observation criteria consisted of changes in bioindicator color, milk pH, and total microbes.

Ardiyansyah et al. “The potency of betacyanins extract from a peel of dragon fruits as a source of colourimetric indicator to develop intelligent packaging for fish freshness monitoring”, IOP Conference series, Volume 207, 1st International Conference on Food and Agriculture 2018 20-21, describes the development of a colourimetric matrix film to monitor fish freshness. This film is prepared by immobilizing betacyanin into glucaomannan-Polyvinyl alcohol matrix.

Tekin Esra et al. “Time temperature indicator film based on alginate and red beetroot (Beta vulgaris L.) extract: in vitro characterization”, Ukrainian Food Journal 2020, Vol. 9, No. 2, 30 June 2020, describes developing and characterizing a biodegradable time temperature indicator (TTI) film by incorporating red beetroot (Beta vulgaris L.) extract into alginate (A)/ polyvinyl alcohol (PVA) blend film.

Qin Yan et al. “Development of active and intelligent packaging by incorporating betalains from red pitaya (Hylocereus polyrhizus) peel into starch/polyvinyl alcohol films”, Food Hydrocolloids, part 100, 1 October 2019, describes the development of active intelligent packaging films based on starch/polyvinyl alcohol incorporated with betalains-rich red pitaya (Hylocereus polyrhizus) peel extract. SUMMARY OF THE INVENTION

Storage temperature may play an important role in food quality and safety. Improper storage temperature can cause spoilage of food, thereby reducing the food shelf life and potentially leading to (severe) illness if ingested. Visual and olfactory cues may, however, be unreliable for assessing food quality and safety.

The prior art may describe time temperature indicators (TTI) integrated into food packaging to monitor temperature fluctuations, and to thereby assist consumers in assessing food quality.

Generally, TTI's may be regarded as tags or devices that show an irreversible response based on mechanical, chemical or enzymatic activation. However, the TTIs described in the prior art may suffer from various drawbacks. For instance, prior art TTIs may comprise (organic and/or inorganic) compounds that may be toxic and can migrate into a food item from a food package. Further, TTIs may require specific operational conditions; for instance, prior art enzymatic TTIs may require temperatures (well) above room temperature. Such requirements may further hamper the use of a TTI for a varied set of food items, as different food items may have different temperature tolerances. In addition, prior art TTIs may be relatively expensive relative to the food items they are to be used for.

In short, prior art TTIs may be potentially harmful to consumers, inflexible with regards to operational conditions, and (too) expensive in view of the intended application.

Hence, it is an aspect of the invention to provide an alternative time temperature indicator which preferably further at least partly obviates one or more of above-described drawbacks. The present invention may have as object to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

In a first aspect, the invention may provide a method for providing a time temperature indicator. The time temperature indicator may especially be pitaya-based. Further, the time temperature indicator may especially be edible. The method may comprise providing an aqueous solution comprising 3 - 10 wt.% of a pitaya extract, especially a pitaya peel extract, especially wherein the aqueous solution has a pH in the range of 7-9. The method may further comprise combining the aqueous solution with a matrix material to provide a precursor combination, especially wherein the precursor combination comprises 1 - 10 wt.% matrix material (on dry weight basis), and especially wherein the matrix material is selected from the group comprising alginate, pectin, gelatin and xanthan gum. Especially, the time temperature indicator may comprise a film or an alginate bead, such as a film, or such as an alginate bead. The aqueous solution may especially comprise at least 80 wt.% water, such as 85 wt.%, especially 90 wt.% water. In embodiments, the aqueous solution may essentially consist of water, a base, and the pitaya extract. In particular, the water, the base, and the pitaya extract may account for at least 90 wt.% of the aqueous solution, such as at least 95 wt.%, especially at least 98 wt.%, including 100 wt.%.

The aqueous solution comprising the pitaya extract may over time (irreversibly) change color as a function of the temperature the pitaya extract is exposed to. In particular, the pitaya extract may turn from a purplish color to a yellowish color when exposed to higher temperatures. Surprisingly, the inventors have discovered that the time temperature response of the pitaya-extract may depend on the pH the pitaya extract is exposed to. Thereby, by adjusting the pH, the TTI of the invention may be tuned for the desired response in view of the specific food item it is applied to. In particular, the method may comprise selecting the pH of the aqueous solution such that the TTI has a time temperature response in the range of 4 - 60 °C, such as at (around) room temperature.

In addition, the TTI may in embodiments consist of edible components. In particular, both the pitaya extract and the matrix material may be safe for consumption. Hence, if a part of the TTI of the invention arranged in a food package would migrate to the food item, this would not pose health concerns. Further, the TTI may be comprised by a food item, thereby having the TTI essentially experience the same conditions as the food item, which may further increase how representative the TTI is of the food quality and safety. By arranging the TTI in the food item, the TTI may also contribute to the nutritional value of the food item, and may result in a reduction of waste relative to food packaging containing TTIs.

The pitaya extract may further be relatively cheap. In particular, although pitaya may already be relatively cheap, the pitaya extract may especially be a pitaya peel extract. In general, although pitaya pulp may be consumed, the pitaya peel may often be discarded as waste. Hence, the pitaya extract may be obtained from a product which may generally be considered a waste product, which may be both financially and ecologically attractive.

Hence, the invention may provide an edible TTI which may be sensitive even under room temperature and cheap enough for food items used on a daily basis. The TTI may be based on a heat-sensitive dye extracted from (red or) purple pitaya, which may be rich in betacyanins, such as betanin. In particular, by manipulating the pH, the pitaya dye can be tuned to turn yellowish over time as a function of temperature, even at a temperature below 23 °C.

In specific embodiments, the invention may provide a method for providing a pitaya-based edible time temperature indicator, the method comprising: providing an aqueous solution comprising 3 - 10 wt.% of a pitaya extract, wherein the aqueous solution has a pH in the range of 7-9; and combining the aqueous solution with a matrix material to provide a precursor combination, wherein the precursor combination comprises 1 - 10 wt.% matrix material, wherein the matrix material is selected from the group comprising alginate, pectin, gelatin and xanthan gum.

In further embodiments, the invention may provide a method for providing a pitaya- based edible time temperature indicator, the method comprising providing an aqueous solution comprising 3 - 10 wt.% of a pitaya extract, wherein the aqueous solution has a pH in the range of 7-9; and combining the aqueous solution with a matrix material to provide a precursor combination, wherein the precursor combination comprises 1 - 10 wt.% matrix material, wherein one or more applies of (a) the matrix material comprises alginate, wherein the time temperature indicator comprises an alginate bead; and (b) the matrix material is selected from the group comprising alginate, pectin, gelatin and xanthan gum, wherein the time temperature indicator comprises a film.

The invention may herein primarily be described in the context of food, such as with regards to food packaging and food items. It will be clear to the person skilled in the art, however, that the invention is not limited to food, and that the time temperature indicator may also be used for non-food applications.

Hence, the invention may provide a method for providing a time temperature indicator (TTI). The term “time temperature indicator” may herein especially refer to an item or a substance of which an (observable) parameter changes over time as a function of the temperature the item or the substance is exposed to. Such a time temperature response may reflect the response of spoilable goods to temperature over time. In particular, spoilable goods, such as food items, may spoil faster at a higher temperature, but the mere exposure to a higher temperature does not imply that the good is spoiled. For instance, an apple may keep well for 1-2 months when stored at 7°C, but may spoil in about a week when stored at 25 °C. Hence, a TTI that does not undergo a visible change at 7°C would not be indicative of spoilage at a low temperature, such as in a fridge, whereas a TTI that instantaneously reacts to 25 °C would not be indicative of spoilage at room temperature. A TTI is ideally indicative of the time the good has spent at different temperatures, particularly with regards to the rate at which the good spoils at such temperatures.

In particular, in embodiments, the time temperature indicator may undergo a visible change over time as a function of the temperature the time temperature indicator is exposed to, especially a (visible) change in color. The time temperature indicator may especially be a pitaya-based time temperature indicator. In particular, in embodiments, the time temperature indicator, especially the alginate bead, or especially the film, may comprise a pitaya extract.

The term “pitaya” may herein especially refer to fruit of the genera Stenocereus and Hylocereus. Hence, in embodiments, the pitaya extract may be an extract of fruit of a species selected from the genera Stenocereus and Hylocereus, especially from the genus Stenocereus , or especially from the genus Hylocereus. The term “pitaya” may herein also be referred to as “dragon fruit”.

The term “pitaya extract” may herein especially refer to an extract of a pitaya, i.e., the pitaya extract may comprise one or more compounds obtained from a pitaya. In embodiments, the pitaya extract may especially be a pitaya pulp extract, i.e., an extract of pitaya pulp. In further embodiments, the pitaya extract may especially be a pitaya peel extract, i.e., an extract of a pitaya peel. The pitaya extract may especially be an extract of a pitaya with purple or red pulp, especially purple pulp, i.e., the pitaya extract may be obtained from a pitaya with purple or red pulp. The pitaya extract may especially be an extract of a ripe pitaya, especially a ripe pitaya with purple or red pulp. In particular, unripe pitayas may have a green or yellow pulp rather than a purple or red pulp.

In embodiments, the method may comprise obtaining the pitaya extract from a pitaya. In particular, the method may comprise one or more of solvent extraction, distillation, pressing and sublimation, especially solvent extraction. In further embodiments, the method may comprise solvent extraction from a pitaya with water as solvent.

Hence, the method may comprise obtaining a pitaya extract from a (fresh) pitaya. For instance, water and the fresh (red, or purple) pitaya pulp and/or peel may be homogenized in a food blender at low speed, such as around 1700 rpm, and then centrifuged, for example for 15 minutes at 7400 rpm. In embodiments, the supernatant may be filtered as particulates may remain despite the centrifugation, such as by using a filter paper. The (filtered) supernatant may comprise the pitaya extract. Hence, in embodiments, the pitaya pulp and/or peel may be homogenized, centrifuged, and optionally filtered, to provide the pitaya extract.

In further embodiments, the method may comprise providing the pitaya extract from (frozen) dried pitaya (powder). For instance, 2 grams of dried pitaya powder may be mixed in 50 ml of water. The mixture may be (magnetically) stirred, such as with a speed of 600 rotations per minute at 60 °C for two hours. The mixture may then be centrifuged, such as for 15 minutes at 7400 rpm. The supernatant may be then filtered (see above), for example by using a filter paper. The (filtered) supernatant may comprise the pitaya extract. Hence, in embodiments, dried pitaya powder may be mixed in water, optionally stirred, centrifuged, and optionally filtered, to provide the pitaya extract.

In further embodiments, the pitaya extract may comprise (pure) freeze-dried pitaya extract. The term “pure” with respect to pure freeze-dried pitaya extract may refer to the absence of conservatives and additives.

In embodiments, the pitaya extract may at least comprise one or more betacyanins, especially (about) 0.1 - 2 wt.% of one or more betacyanins (on dry weight basis), such as 0.15 - 1 wt.%, especially 0.2 - 0.5 wt.%. In embodiments, the pitaya extract may comprise at least 0.1 wt.% of one or more betacyanins, especially at least 0.15 wt.%, such as at least 0.2 wt.%. In further embodiments, the pitaya extract may comprise at least 0.25 wt.% of one or more betacyanins, such as at least 0.3 wt.%.

The pitaya extract may further comprise other compounds extracted from the pitaya, such as one or more compounds selected from the group comprising vitamins, minerals, and anti -oxidants. Essentially, the pitaya extract may consist of water and compounds extracted from pitaya, including at least one or more betacyanins.

In embodiments, the pitaya extract may have a color in the CIELAB color space, as defined in ISO standard 11664 part 4. In the CIELAB color space color may be expressed using three values: L* for perceptual lightness, and a* and b* for the four unique colors of human vision: red, green, blue, and yellow. In particular, L* may denote the lightness of the color which ranges between 0 to 100 where 0 denotes black and 100 denotes white, whereas a* and b* values may range from -128 to +128. The positive value of a* denotes red tones while the negative value denotes green tones. The positive values of b* denotes yellow tones while negative value denotes blue tones.

In further embodiments, the pitaya extract, especially when fresh, may have a color defined by the CIELAB color space parameters L*, a* and b*. Especially, L* may be selected from the range of 20 - 60, such as from the range of 25 - 55, especially from the range of 30 - 50. In further embodiments, a* may be selected from the range of 40 - 90, such as from the range of 45 - 85, especially from the range of 50 - 80. In further embodiments, b* may be selected from the range of -20 - 20, such as from the range of -15 - 15, especially from the range of -10 - 10.

In particular, the color of the pitaya extract may be determined using a UV-Vis Spectrometer HACH DR6000, which has a preset CIELAB program providing CIELAB values. Optionally, the pitaya extract may be diluted prior to measuring, such as an 80 times dilution, and the dilution factor can be entered into the spectrometer for calculation of the CIELAB values. In embodiments, the time temperature indicator may be an edible time temperature indicator. In particular, the time temperature indicator may be devoid of any compounds that are (considered) toxic and/or unsafe for (human) consumption. It will be clear to the person skilled in the art that the toxicity of a compound may depend on the intended consumer of the food item. For instance, if the food item comprises a feed item, such as dog food, there may be different compounds/sub stances to avoid than when the food item is intended for human consumption.

The method may comprise providing an aqueous solution comprising 2 - 15 wt.% of a pitaya extract (on dry weight basis), especially 2.5 - 10 wt.%, such as 3 - 5 wt.%. If the aqueous solution comprises low concentrations of the pitaya extract, the TTI response may be poorly observable, or even unobservable. Hence, in embodiments, the aqueous solution may comprise at least 2 wt.% of the pitaya extract, especially at least 2.5 wt.%, such as at least 3 wt.%. In further embodiments, the aqueous solution may comprise at least 3.5 wt.% of the pitaya extract, such as at least 4 wt.%, especially at least 4.5 wt.%. If, however, the aqueous solution comprises high concentrations of the pitaya extract, the aqueous solution may become rather viscous, which may complicate the handling, especially filtering, of the aqueous solution and the TTI formation. Hence, in embodiments, the aqueous solution may comprise at most 12 wt.%, such as at most 10 wt.%, especially at most 7 wt.%. In further embodiments, the aqueous solution may comprise at most 5 wt.%, such as at most 4.5 wt.%, especially at most 4 wt.%. In particular, it appears that the range of 3-5 wt.%, especially about 4 wt.%, may be beneficial with regards to color and (lack of excessive) viscosity.

The phrase “an aqueous solution comprising X wt.% pitaya extract, and similar phrases, especially indicate that the pitaya extract on dry weight basis constitutes X wt.% of the (total) aqueous solution. For instance, if the aqueous solution consists of water and 5 wt.% pitaya extract, and has a weight of 1 kg, the dried in pitaya extract would have a weight of 50 g. Similarly, herein indicated wt.% of matrix material with respect to the precursor combination are especially on dry weight basis.

In embodiments, the aqueous solution may have a pH selected from the range of 6- 10, such as from the range of 6.5-9.5, especially from the range of 7-9. In further embodiments, the pH may especially be selected from the range of 7-8. Especially, the method may comprise adjusting the pH of the aqueous solution to a value in the range of 6-10, especially to a value in the range of 7-9, such as to a value in the range of 7-8, dependent on a desired TTI response, especially dependent on a food item the TTI will be applied to. In particular, if the pH value is too low, the pitaya extract may be insufficiently sensitive with regards to temperature, especially with regards to room temperature, for a TTI. However, if the pH value is too high, the pitaya extract may be oversensitive and may change color too quickly and/or at too low temperatures. In particular, values in the range of 7-9, especially in the range of 7-8, may be suitable for goods, especially food items, that may spoil at temperatures close to room temperature.

In further embodiments, the method may comprise selecting the pH of the aqueous solution (in the range of 7-9) based on a predetermined time temperature criterium. In particular, the method may comprise adjusting the pH of the aqueous solution to a value in the range of 6-10, such as in the range of 7-9, especially in the range of 7-8, based on a predetermined time temperature criterium. The predetermined time temperature criterium may especially relate to a (target) food item. In particular, in embodiments, the predetermined time temperature criterium may comprise one or more of: (i) a maximum temperature, (ii) a (corresponding) maximum temperature-dependent storage time, and (iii) a target food item. In further embodiments, the time temperature criterium may comprise a plurality of maximum temperatures and corresponding maximum temperature-dependent storage times.

The method may further comprise combining the aqueous solution with a matrix material to provide a precursor combination. The term “precursor combination” may especially refer to a combination of the aqueous solution and the matrix material. The precursor combination may especially be suitable to provide the time temperature indicator (also see below). Hence, the method may further comprise providing the time temperature indicator from the precursor combination.

The term “matrix material” may herein especially refer to one or more compounds that may form a matrix in which a second material, such as the pitaya extract, may be embedded. Hence, in embodiments, the precursor combination may especially have a gel-like structure.

If too little matrix material is added the time temperature indicator, especially the alginate bead, or especially the film, may be fragile and break easily. However, too much matrix material may increase the viscosity of the solution, which may complicate handling of the solution and may prevent molding of the TTI in a desired shape, such as in a bead or a film. Hence, in embodiments, the precursor combination may comprise 0.5-15 wt.% of matrix material (on dry weight basis), especially 0.8 wt.% - 10 wt.%, such as 1 - 5 wt.% matrix material In particular, in embodiments, the precursor combination may comprise at least 0.8 wt.% of matrix material, such as at least 1 wt.%, especially at least 2 wt.%. In further embodiments, the precursor combination may comprise at most 10 wt.% of matrix material, such as at most 7 wt.%, especially at most 5 wt.%, such as at most 4 wt.%.

In embodiments, the matrix material may comprise a gelling agent, especially a hydrogel. In further embodiments, the matrix material may be selected from the group comprising alginate, pectin, gelatin, chitosan, cellulose, agarose, guar gum, agar, carrageenan, dextran and xanthan gum, especially from the group comprising alginate, pectin, gelatin and xanthan gum.

In specific embodiments, the precursor combination may comprise 2-8 wt.% of alginate, especially 2.5 wt.% - 7 wt.%, such as 3 - 5 wt.% alginate. In further embodiments, the precursor combination may comprise at least 2 wt.% of alginate, especially at least 2.5 wt.%, such as at least 3 wt.%. In further embodiments, the precursor combination may comprise at most 8 wt.% of alginate, such as at most 7 wt.%, especially at most 6 wt.%, such as at most 5 wt.%.

In further embodiments, the precursor combination may comprise 2-10 wt.% of pectin, especially 3 wt.% - 8 wt.%, such as 4 - 6 wt.% pectin. In further embodiments, the precursor combination may comprise at most 8 wt.% pectin, such as at most 6 wt.%, especially at most 5 wt.%. In further embodiments, the precursor combination may comprise at least 1 wt.% of pectin, especially at least 2 wt.%, such as at least 3 wt.%. In further embodiments, the precursor combination may comprise at least 4 wt.% of pectin, especially at least 5 wt.%. In further embodiments, the precursor combination may comprise at most 10 wt.% of pectin, such as at most 8 wt.%, especially at most 6 wt.%. In further embodiments, the precursor combination may comprise at most 5 wt.% of pectin, such as at most 4 wt.%.

In further embodiments, the precursor combination may comprise 2-10 wt.% of gelatin, especially 3 wt.% - 8 wt.%, such as 4 - 6 wt.% gelatin. In further embodiments, the precursor combination may comprise at most 8 wt.% gelatin, such as at most 6 wt.%, especially at most 5 wt.%. In further embodiments, the precursor combination may comprise at least 1 wt.% of gelatin, especially at least 2 wt.%, such as at least 3 wt.%. In further embodiments, the precursor combination may comprise at least 4 wt.% of gelatin, especially at least 5 wt.%. In further embodiments, the precursor combination may comprise at most 10 wt.% of gelatin, such as at most 8 wt.%, especially at most 6 wt.%. In further embodiments, the precursor combination may comprise at most 5 wt.% of gelatin, such as at most 4 wt.%.

In further embodiments, the precursor combination may comprise 2-10 wt.% of xanthan gum, especially 3 wt.% - 8 wt.%, such as 4 - 6 wt.% xanthan gum. In further embodiments, the precursor combination may comprise at most 8 wt.% xanthan gum, such as at most 6 wt.%, especially at most 5 wt.%. In further embodiments, the precursor combination may comprise at least 1 wt.% of xanthan gum, especially at least 2 wt.%, such as at least 3 wt.%. In further embodiments, the precursor combination may comprise at least 4 wt.% of xanthan gum, especially at least 5 wt.%. In further embodiments, the precursor combination may comprise at most 10 wt.% of xanthan gum, such as at most 8 wt.%, especially at most 6 wt.%. In further embodiments, the precursor combination may comprise at most 5 wt.% of xanthan gum, such as at most 4 wt.%. In further embodiments, the matrix material may comprise alginate. The term “alginate” may herein especially refer to a member of a family of linear unbranched copolymers comprising (1,4)- linked -D-mannuronic acid (M) and -L-guluronic acid (G) residues covalently linked in different sequences/blocks.

In embodiments wherein the matrix material comprises alginate, the method may further comprise dropwise adding the precursor combination to a second aqueous solution, especially wherein the second aqueous solution comprises a divalent cation, especially calcium. In particular, the precursor combination may form an alginate bead in the second aqueous solution. The alginate bead may encapsulate part of the aqueous solution comprising the pitaya extract. The term “alginate bead” may herein also refer to a plurality of alginate beads.

Alginate may gel (or “gelate”) when exposed to divalent cations, such as when exposed to divalent calcium. Hence, in embodiments, the second aqueous solution may comprise a divalent cation, especially calcium. In particular, the second aqueous solution may comprise a salt comprising the divalent cation, especially the calcium, such as a salt comprising calcium chloride.

Hence, in embodiments, the second aqueous solution may comprise 5 - 500 mM of divalent cation, such as 9 - 450 mM, especially 22 - 270 mM, such as 45 - 180 mM, especially 65-135 mM. In further embodiments, the second aqueous solution may comprise at least 22 mM of calcium, such as at least 45 mM, especially at least 65 mM. In further embodiments, the second aqueous solution may comprise at most 270 mM calcium, such as at most 180 mM, especially at most 135 mM. In particular, with low concentrations of divalent cation, the gelation may be rather slow, which may result in diffusion out of the pitaya extract. However, a high concentration of divalent cation may lead to an increased viscosity, which may complicate handling and the providing of a desired shape for the TTI.

In embodiments, the second aqueous solution may comprise 0.1 - 5 wt.% calcium chloride, especially 0.25 - 3 wt.%, such as 0.5 - 2 wt.%. In further embodiments, the second aqueous solution may comprise at least 0.25 wt.% calcium chloride, such as at least 0.5 wt.%, especially at least 0.75 wt.%. In further embodiments, the second aqueous solution may comprise at most 3 wt.% calcium chloride, such as at most 2 wt.%, especially at most 1.5 wt.%.

The method may, in embodiments, especially comprise leaving the alginate bead in the second aqueous solution for a time period sufficient to form a (rigid) shell. The time may be selected in view of the second aqueous solution, especially based on the cation, or especially based on a salt comprising the cation, such as described in Lee and Rogers, International Journal of Gastronomy and Food Science, 2012, which is hereby herein incorporated by reference. In embodiments, the method may comprise leaving the alginate bead in the second aqueous solution for at least 50 seconds, such as at least 70 seconds, especially at least 100 seconds, such as at least 200 seconds. In particular, the alginate bead may be left in the second aqueous solution until the bead’s elastic properties remain (essentially) constant.

In embodiments wherein the matrix material comprises alginate, the precursor combination may especially comprise at least 2.5 wt.% alginate, such as at least 3 wt.% alginate.

In further embodiments, the method may comprise retrieving the alginate bead from the second aqueous solution, and especially rinsing the alginate bead, such as with water.

In particular, the alginate bead may form the time temperature indicator, i.e., the alginate bead may be the time temperature indicator. Such embodiments may be particularly beneficial as the presence of alginate and/or the divalent cation appears to increase the temperature sensitivity of the TTI, enabling to tune the time temperature response of the TTI by varying the wt.% of alginate and/or divalent cation in the precursor material besides varying the pH of the aqueous solution.

In further embodiments, the time temperature indicator, especially the alginate bead, may comprise (at least part of) the matrix material, especially the alginate. Further, the time temperature indicator, especially the alginate bead, may comprise (at least part of) the pitaya extract.

In further embodiments, the alginate bead may have a color defined by the CIELAB color space parameters L*, a* and b*. Especially, L* may be selected from the range of 20 - 60, such as from the range of 25 - 55, especially from the range of 30 - 50. In further embodiments, a* may be selected from the range of 40 - 90, such as from the range of 45 - 85, especially from the range of 50 - 80. In further embodiments, b* may be selected from the range of -20 - 20, such as from the range of -15 - 15, especially from the range of -10 - 10.

In particular, the color of the alginate bead may be determined by obtaining an image using a digital camera in a LED light box, and by subsequently analyzing the color of the image using Adobe Photoshop software with CIELAB as color model. For instance, the color of the alginate bead may be determined by obtaining an image with an iphone 7 camera, using the Pro Camera app, with ISO standard set to (about) 33, in a LED light box providing a white background and, for example, 2x20 white LED strips, especially a DUCLUS5030, such as commercially offered in February 2020.

In further embodiments, the matrix material may comprise one or more of pectin, gelatin and xanthan gum. In such embodiments, the method may further comprise casting the precursor combination to provide a film. In particular, the film may form the time temperature indicator, i.e., the film may be the time temperature indicator.

In further embodiments, the time temperature indicator, especially the film, may comprise (at least part of) the matrix material, especially one or more of pectin, gelatin and xanthan gum, such as two or more of pectin, gelatin and xanthan gum. Further, the time temperature indicator, especially the film, may comprise (at least part of) the pitaya extract.

In embodiments, the matrix material may especially comprise two or more of pectin, gelatin and xanthan gum. The combination of two or more of pectin, gelatin and xanthan gum may provide films that are more robust with regards to handling and/or color stability.

In embodiments, the film may be cast at a temperature selected from the range of - 5 - 15 °C, such as from the range of 0 - 10 °C. A temperature in this range may be suitable for the setting of the film.

In further embodiments, the film may have a color defined by the CIELAB color space parameters L*, a* and b*. Especially, L* may be selected from the range of 20 - 60, such as from the range of 25 - 55, especially from the range of 30 - 50. In further embodiments, a* may be selected from the range of 40 - 90, such as from the range of 45 - 85, especially from the range of 50 - 80. In further embodiments, b* may be selected from the range of -20 - 20, such as from the range of -15 - 15, especially from the range of -10 - 10.

In particular, the color of the film may be determined by obtaining an image using a digital camera in a LED light box, and by subsequently analyzing the color of the image using Adobe Photoshop software with CIELAB as color model.

In a second aspect, the invention may provide a time temperature indicator. The time temperature indicator may especially be edible. Further, the time temperature indicator may especially be pitaya-based. The time temperature indicator may especially comprise 2 - 15 wt.% of a pitaya extract, such as 2.7 - 10 wt.%, especially 3-10 wt.%. In embodiments, the time temperature indicator may comprise 0.5 - 10 wt.% of matrix material, especially 1 - 5 wt.% of matrix material, especially wherein the matrix material is selected from the group comprising alginate, pectin, gelatin and xanthan gum. In further embodiments, the time temperature indicator may a pH selected from the range of 6-10, especially from the range of 7-9, such as from the range of 7-8. Especially, the time temperature indicator may comprise a film or an alginate bead, such as a film, or such as an alginate bead.

In embodiments, the time temperature indicator may comprise a precursor combination consisting of an aqueous solution and a matrix material. In embodiments, the aqueous solution may especially comprise 2 - 15 wt.% of a pitaya extract, especially 3-10 wt.% of a pitaya extract. In further embodiments, the precursor combination may comprise 0.5 - 10 wt.% of matrix material, especially 1 - 5 wt.% of matrix material, especially wherein the matrix material is selected from the group comprising alginate, pectin, gelatin and xanthan gum. In embodiments, the aqueous solution may have a pH selected from the range of 6-10, especially from the range of 7-9, such as from the range of 7-8.

The time temperature indicator may especially be obtainable using the method of the invention.

In embodiments, the matrix material may comprise alginate. In such embodiments, the time temperature indicator may especially comprise an alginate bead.

In further embodiments, the matrix material may comprise one or more, especially two or more, of pectin, gelatin and xanthan gum. In such embodiments, the time temperature indicator may especially comprise a film.

In a further aspect, the invention may provide a food package comprising the (edible) time temperature indicator according to the invention. The food package may further comprise a food item. The time temperature indicator may especially be configured to be representative of spoilage of the food item.

In embodiments, the time temperature indicator may be arranged on the inside of the food package. Such arrangement may further relate (or “match”) the conditions the time temperature indicator and food in the food package are exposed to. In further embodiments, the time temperature indicator may comprise a film arranged on the food package, especially inside of the food package.

In further embodiments, the food package may comprise a reference label, wherein the reference label relates the color of the time temperature indicator to a (spoilage) status of the food item. The combination of the time temperature indicator and a reference label may aid a consumer in identifying whether the food item in the food package is good for consumption, which may reduce food waste and may prevent ingestion of spoiled food items.

In a further aspect, the invention may provide a food item comprising the time temperature indicator according to the invention. The time temperature indicator may especially be configured to be representative of spoilage of the food item.

The food item may especially be a perishable food item, such as a food item that spoils at room temperature. In embodiments, the food item may be selected from the group comprising meat, fruit, vegetables, nuts, and dairy products. In particular, in embodiments, the food item may comprise a food item intended for (long-term) storage in a fridge or freezer, such as a frozen food item.

In a further aspect, the invention may provide a use of the time temperature indicator as an indicator for temperature exposure, especially temperature exposure over time. Especially, the use may comprise associating, such as attaching, the time temperature indicator to a (food) item to determine the (time-dependent) exposure of the item to a (high) temperature.

In a further aspect, the invention may provide a use of the time temperature indicator as a freshness indicator, especially as a freshness indicator for a (food) item. In particular, the time temperature indicator may be representative of the freshness of an associated (food) item. Especially, the use may comprise use of the time temperature indicator as a spoilage indicator, especially as a spoilage indicator for a (food) item. In particular, the time temperature indicator may be representative of whether an associated (food) item is likely to be spoiled and/or to spoil soon.

The time temperature indicator may be part of or may be applied in e.g. food packages, food items, feed packages, feed items, storage monitoring systems.

The embodiments described herein are not limited to a single aspect of the invention. For example, an embodiment describing the method may, for example, further relate to the time temperature indicator, which may be obtainable using the method. Similarly, an embodiment of the time temperature indicator may further relate to embodiments of the food package and the food item.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which: Fig.l schematically depicts an embodiment of the method. Fig. 2A-D schematically depict experimental results obtained using embodiments of the time temperature indicator. The schematic drawings are not necessarily on scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Fig. 1 schematically depicts an embodiment of the method for providing a pitaya- based edible time temperature indicator 100. The method may comprise obtaining a pitaya extract 11, especially a pitaya peel extract, from a pitaya 10. The method may further comprise providing an aqueous solution 110 comprising 3 - 10 wt.% of the pitaya extract 11. In embodiments, the aqueous solution 110 may have a pH in the range of 7-9, especially in the range of 7-8. The method may further comprise combining the aqueous solution 110 with a matrix material 130 to provide a precursor combination 140, especially wherein the matrix material 130 is selected from the group comprising alginate, pectin, gelatin and xanthan gum. The precursor combination 140 may especially comprise 1 - 5 wt.% matrix material 130.

In embodiments, the matrix material 130 may comprise alginate. In such embodiments, the method may comprise dropwise adding the precursor combination 140 to a second aqueous solution 120, especially wherein the second aqueous solution 120 comprises 45 - 180 mM of a divalent cation, especially calcium, such as an aqueous solution 120 comprising 0.5 - 2 wt.% calcium chloride. In particular, the precursor combination 140 may form an alginate bead 101 in the second aqueous solution 120. The alginate bead 101 may comprise part of the aqueous solution 110.

In embodiments, the method may comprise leaving the alginate bead 101 in the second aqueous solution 120 for at least 50 seconds.

In further embodiments, the method may comprise retrieving the alginate bead 101 from the second aqueous solution 120, and especially rinsing the alginate bead 101 with water.

In particular, the alginate bead 101 may be an embodiment of the time temperature indicator 100, i.e., the time temperature indicator 100 may comprise the alginate bead, especially consist of the alginate bead, such as of a plurality of alginate beads 101.

In further embodiments, the matrix material 130 may comprise two or more of pectin, gelatin and xanthan gum. In such embodiments, the method may further comprise: casting the precursor combination 140 to provide a film 102, especially casting at a temperature selected from the range of 0 - 10 °C.

In particular, the film 102 may be an embodiment of the time temperature indicator 100, i.e., the time temperature indicator 100 may comprise the film, especially consist of the film 102.

The pitaya 10 may especially be a pitaya 10 with (red or) purple pulp, i.e., in embodiments, the pitaya extract 11 may be obtained from a pitaya 10 with (red or) purple pulp. Further, the pitaya extract 11 may comprise an extract of one or more species selected from the group comprising the genera Stenocereus and Hylocereus.

The time temperature indicator 100 may especially be tuned (or “calibrated”) for a particular food item 20. Hence, in embodiments, the method may comprise selecting the pH of the aqueous solution 110 in the range of 7-9, especially in the range of 7-8, based on a predetermined time temperature criterium, especially wherein the predetermined time temperature criterium is based on the food item 20. In further embodiments, the predetermined time temperature criterium may comprise one or more of: (i) a maximum temperature, (ii) a maximum temperature-dependent storage time, and (iii) a target food item 20.

Fig. 1 further schematically depicts an embodiment of a time temperature indicator 100, especially of a time temperature indicator 100 comprising a precursor combination 140 consisting of an aqueous solution 110 and a matrix material 130. In embodiments, the aqueous solution 110 may comprise 3 - 10 wt.% of a pitaya extract 11, and may especially have a pH selected from the range of 7-9. The precursor combination 140 may comprise 1 - 5 wt.% of matrix material 130. The matrix material 130 may especially be selected from the group comprising alginate, pectin, gelatin and xanthan gum.

The time temperature indicator 100 may especially comprise an alginate bead 101 or a film 102.

In embodiments, the matrix material 130 may comprise alginate, and the time temperature indicator 100 may comprise an alginate bead 101.

In further embodiments, the matrix material 130 may comprise two or more of pectin, gelatin and xanthan gum, and the time temperature indicator 100 may comprise a film 102.

Fig. 1 further schematically depicts a food package 30 comprising the time temperature indicator 100. In particular, Fig. 1 schematically depicts an embodiment of a food package 30 comprising a food item 20, wherein the food item 20 comprises the time temperature indicator 100, wherein the time temperature indicator 100 comprises an alginate bead 101. Fig. 1 further schematically depicts an embodiment of the food package 30, wherein the food package 30 comprises the time temperature indicator 100, especially wherein the time temperature indicator 100 is arranged on an outside surface of the food package 30, or especially wherein the time temperature indicator 100 is arranged inside of the food package 30, and especially wherein the time temperature indicator 100 comprises a film 102.

Fig. 1 further schematically depicts an embodiment of the food item 20 comprising the time temperature indicator 100, wherein the time temperature indicator 100 comprises an alginate bead 101. In further embodiments, the food item 20 may also comprise a film 102 as time temperature indicator.

Experimental

Pitaya extract - A freeze-dried pitaya extract was locally purchased. The freeze- dried pitaya extract did not contain preservatives or other additives. Generally, betacyanin may be extracted with solvents such as water, ethanol, and methanol. The freeze-dried pitaya extract was dissolved in each of these solvents to assess the suitability of these solvent for a pitaya-based time temperature indicator. The pitaya powder was added to the solvents and vortexed for 5 min to ensure proper mixing before being left to rest for an hour. The sample with water as a solvent had a bright purple color, whereas the samples made with methanol and ethanol as solvents exhibited a light pink shade. Hence, water was deemed to extract the color from the pitaya powder more effectively than ethanol and methanol. Further, water as a solvent may also be beneficial with regards to providing an edible time temperature indicator. In particular, with regards to the present invention, the extraction may be performed with a solvent considered safe for consumption, such as water and ethanol, especially with water. Unless specified otherwise, water was used as solvent for the experiments described hereinafter.

Aqueous solution - pitaya extract - With water as solvent, three concentrations of the pitaya extract in an aqueous solution were tested: 3 wt.%, 4 wt.%, and 5 wt.%. At 3 wt.% pitaya extract, the aqueous solution displayed a light purple color, whereas the color difference between the 4 wt.% and 5 wt.% was almost invisible to the naked eye. However, the 5 wt.% sample was more viscous and difficult to filter. Hence, unless specified otherwise, aqueous solutions with 4 wt.% pitaya extract were used for subsequent experiments.

Aqueous solution - pH - NaHC0 ₃ was added to prepared aqueous solutions to adjust their pH to 5, 6, 7 and 8.

Alginate bead - The alginate bead was provided by dropwise addition of the precursor combination into a second aqueous solution comprising 1 wt.% calcium chloride. Specifically, the precursor combination was dropped into the second aqueous solution using a syringe from a height of 1.2 cm (from the surface of the second aqueous solution), wherein the syringe had a needle with dimensions of 0.6*30mm. The second aqueous solution was stirred at 400 rpm at room temperature, which may contribute to the formation of spherical alginate beads. Hence, in embodiments, the method may comprise stirring the second aqueous solution. Alginate beads were used to encapsulate the dye to be used as a time temperature indicator. Precursor combinations with 1, 2 and 3 wt.% alginate were used to make alginate beads. The beads formed with the 1 and 2 wt.% concentration were relatively fragile and difficult to handle. Hence, unless specified otherwise, the alginate beads used for the experiments herein were provided with 3 wt.% alginate in the precursor combination. Similarly, unless specified otherwise, the alginate beads were left in the second aqueous solution for 100 seconds; after 100 seconds the elastic properties of the alginate beads were (essentially) constant. After obtaining the alginate beads from the second aqueous solution, the beads were washed with water and subsequently dried (using tissues).

Film preparation - Initial attempts to cast the films consisted of mixing each of the matrix materials pectin, gelatin and xanthan gum separately with the aqueous solution at different concentrations (2 wt.%,3 wt.%,4 wt.%,5 wt.%) and letting them set at 7°C. Pectin, gelatin and xanthan gum were selected as these are edible gelling agents.

Film; xanthan gum - Precursor combinations comprising matrix material consisting of xanthan gum at these concentrations (2 wt.%,3 wt.%,4 wt.%,5 wt.%) increased the viscosity of the aqueous liquid to a jam-like consistency complicating, especially preventing, the film from being cast.

Film; pectin - Precursor combinations comprising matrix material consisting of pectin were able to be cast but the precursor combination did not set in the fridge to form a film.

Film; gelatin - Precursor combinations comprising matrix material consisting of gelatin were able to be cast as a film. At 2, 3, and 4 wt.% the film formed was soft and could be torn easily. At 5 wt.%, a firmer gel was obtained. In particular, the color of the film turned from purple to red when kept at room temperature for two days indicating the film with gelatin is more sensitive to temperature than the aqueous liquid as such.

Film; gelatin and pectin - pectin and gelatin were used together in various concentration ratios to form the films. In particular, precursor combination comprising 5 wt.% of gelatin and pectin each produced a film with high mechanical strength and flexibility. The color of the film was stable; even when kept in the fridge for a month, the color had only turned slightly pink. It appears that pectin contributes to retaining the purple color.

Color measurements - Color measurements were performed using UV-Vis Spectrometer HACH DR600 with a program which gave Commission Internationale de FEclairage colour space coordinates (CIELAB). The aqueous solution was diluted 80 times to get accurate measurements in the spectrometer, which dilution factor was indicated in the spectrometer. Changes in the pH may lead to color change in the aqueous solution. For instance, the initial color of solution may change from purple to violet as the pH of the dye increases. A substantial color change to violet was seen after pH 7. As the pH increases from 7 and approaches 8, the color of the dye shifts to darker shades of violet.

Temperature dependent color-change; aqueous solution - the color change of the aqueous solution at various pH values was assessed at different temperatures: 4°C, 23°C, 40°C and 60°C. Samples were taken at regular intervals for UV-Vis spectroscopy analysis by measuring the absorbance of the pigment at 535 nm, which was the maximum absorption peak of the prepared aqueous solution. Fig. 2A-D schematically depicts the absorption A (in a.u.) versus the time (in h for 2A-2B, and in m for 2C-2D) at different temperatures, wherein line L5 indicates the response for the aqueous solution at pH5, L6 for pH6, L7 for pH7 and L8 for pH8, and wherein Fig. 2A corresponds to a temperature of 4°, Fig. 2B to a temperature of 23 °C, Fig. 2C to a temperature of 40 °C, and Fig. 2D to a temperature of 60 °C. In particular, Fig. 2A-D indicate both that the color change occurs faster at a higher pH and at a higher temperature. There appears to be little difference between a pH of 5 or 6 with regards to time temperature response, but for higher pH values the color change appears to occur more readily. Further, the rate of color change at all pH values is dependent on the temperature the aqueous solution is exposed to. Hence, the color of the aqueous solution exhibits a time temperature response, which may be modulated via the pH of the aqueous solution.

Temperature dependent color-change; alginate beads -alginate beads formed with aqueous solution at pH 7 and pH 8 were subjected to temperatures of 4 °C, 23 °C and 40 °C for 4 days. The results are summarized in table 1 :

Wherein ++ corresponds to a purple color, + to a pink color, +/- to a reddish brown color, - to an orange color, and - to a yellow color. In particular, the results of table 1 demonstrate that also for the alginate beads the color change due to temperature depends on the pH.

The term “plurality” refers to two or more. Furthermore, the terms “a plurality of’ and “a number of’ may be used interchangeably.

The terms “substantially” or “essentially” herein, and similar terms, will be understood by the person skilled in the art. The terms “substantially” or “essentially” may also include embodiments with “entirely”, “completely”, “all”, etc. Hence, in embodiments the adjective substantially or essentially may also be removed. Where applicable, the term “substantially” or the term “essentially” may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. Moreover, the terms ’’about” and “approximately” may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. For numerical values it is to be understood that the terms “substantially”, “essentially”, “about”, and “approximately” may also relate to the range of 90% - 110%, such as 95%-105%, especially 99%- 101% of the values(s) it refers to.

The term “comprise” also includes embodiments wherein the term “comprises” means “consists of’.

The term “and/or” especially relates to one or more of the items mentioned before and after “and/or”. For instance, a phrase “item 1 and/or item 2” and similar phrases may relate to one or more of item 1 and item 2. The term "comprising" may in an embodiment refer to "consisting of but may in another embodiment also refer to "containing at least the defined species and optionally one or more other species".

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

The devices, apparatus, or systems may herein amongst others be described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation, or devices, apparatus, or systems in operation.

The term “further embodiment” and similar terms may refer to an embodiment comprising the features of the previously discussed embodiment, but may also refer to an alternative embodiment.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim.

Use of the verb "to comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, “include”, “including”, “contain”, “containing” and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.

The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In a device claim, or an apparatus claim, or a system claim, enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

The invention also provides a control system that may control the device, apparatus, or system, or that may execute the herein described method or process. Yet further, the invention also provides a computer program product, when running on a computer which is functionally coupled to or comprised by the device, apparatus, or system, controls one or more controllable elements of such device, apparatus, or system.

The invention further applies to a device, apparatus, or system comprising one or more of the characterizing features described in the description and/or shown in the attached drawings. The invention further pertains to a method or process comprising one or more of the characterizing features described in the description and/or shown in the attached drawings. Moreover, if a method or an embodiment of the method is described being executed in a device, apparatus, or system, it will be understood that the device, apparatus, or system is suitable for or configured for (executing) the method or the embodiment of the method, respectively.

The various aspects discussed in this patent can be combined in order to provide additional advantages. Further, the person skilled in the art will understand that embodiments can be combined, and that also more than two embodiments can be combined. Furthermore, some of the features can form the basis for one or more divisional applications.