PH color developing nano-particles responding to freshness of fresh fruits and application of pH color developing nano-particles in preparation of 4D intelligent printing labels

Abstract

The invention discloses pH developing nano-particles responding to freshness of fresh fruits and application of the pH developing nano-particles in preparation of 4D intelligent printing labels. A mixture of anthocyanin and hawthorn phenol-containing hydrolysis extracts is used for extracting phenolic substances from hawthorn pomace through a hydrolysis method, and the phenolic substances are mixed with specific purple cabbage anthocyanin; the color developing sensitivity is obviously improved; the zein nanoparticles are obtained by embedding the mixture, so that the problem of weak color developing sensitivity of the anthocyanin is solved; the mixture of the anthocyanin and the hawthorn phenol-containing hydrolysis extract and the zein nanoparticles have important application prospects in color development products responding to pH, fresh keeping of fresh fruits or prolonging of the shelf life of the fresh fruits and the like. According to the intelligent printing label prepared by loading the zein nanoparticles, the intelligent printing label is combined with a 4D printing technology, high-sensitivity indication of freshness change is realized through color change, and the shelf life of fresh fruits is remarkably prolonged.

Description

Technical Field

[0001] The present invention belongs to the field of food packaging, and in particular relates to a pH color-developing nanoparticle that responds to the freshness of fresh fruit and an application thereof in the preparation of a 4D smart printing label. Background Art

[0002] Smart printed labels have been developed that automatically respond to changes in the packaging environment. By observing the changes in the label, users can intuitively determine the freshness of fruits and vegetables and whether they are in suitable storage conditions, thereby reducing fruit waste. However, the widespread application of smart printed labels in the preservation industry is still severely limited by their monitoring sensitivity, especially when distinguishing between fresh and less-fresh fruit, and the "pain point" of low adaptability to the objects being preserved.

[0003] The Chinese invention patent with publication number CN118342779A installs inert metal and DC power supply positive and negative electrodes at the nozzle of a single-nozzle printer to cause the printing ink flowing through the nozzle to undergo water electrolysis reaction. Changing the applied voltage intensity causes the electrolyzed water to produce different amounts of hydrogen ions or hydroxides, which in turn causes the color of the printed products loaded with anthocyanins from different sources to show different colors as the voltage changes. These printed products are assembled into an array and used to monitor the freshness of meat; the Chinese invention patent with publication number CN117818157A uses 60 Using Co gamma rays to modify sapodilla gum, researchers used unmodified sapodilla gum and modified sapodilla gum loaded with garlic essential oil as printing inks. Using a dual-nozzle printer, they fabricated printed labels with an upper and lower layer. These labels respond to moisture from the fruit within the packaging by changing shape, enabling a more sustained release of the essential oil from the printed product and extending the shelf life of the fruit. This suggests that the sensitivity of smart printed labels is primarily related to the color developer composition and label structure. Therefore, there is a need to develop color developers and smart printed labels with higher sensitivity and greater adaptability to fresh-keeping products. Summary of the Invention

[0004] The purpose of the present invention is to develop a color developer and smart printing label with higher sensitivity and better adaptability to preservation objects, so as to realize the dual functions of monitoring the freshness of fruits and vegetables and preserving them.

[0005] The present invention adopts the following technical solutions:

[0006] The present invention provides a mixture of anthocyanidins and a hawthorn phenolic hydrolyzed extract, wherein the mass ratio of the mixture of anthocyanidins and the hawthorn phenolic hydrolyzed extract is 1:(1-4); the hawthorn phenolic hydrolyzed extract is obtained by soaking hawthorn pomace in a hydrolyzed solution for hydrolysis and fully drying, and the hydrolyzed solution is an acidic hydrolyzed solution, an alkaline hydrolyzed solution or an enzyme-containing hydrolyzed solution; preferably, the pH of the acidic hydrolyzed solution is 1-3; the pH of the alkaline hydrolyzed solution is 10-12; the enzyme-containing hydrolyzed solution contains cellulase and pectinase, and the mass ratio of the cellulase to the pectinase is 1:(1-2); and the mass-to-volume ratio of the hawthorn pomace to the hydrolyzed solution is 1:(1-4) g / mL.

[0007] Preferably, the pH of the acidic hydrolyzate is 2; the pH of the alkaline hydrolyzate is 12; the enzyme-containing hydrolyzate contains cellulase and pectinase, the mass ratio of the cellulase and pectinase is 1:1, and the total concentration of the cellulase and pectinase is 0.2 mg / mL; the mass volume ratio of the hawthorn pomace and the hydrolyzate is 1:3 g / mL.

[0008] Preferably, the anthocyanin is purple cabbage anthocyanin. According to actual needs, it can also be replaced by other anthocyanins that have color differences within a pH range of 4 to 7, such as geranium pigment, morning glory pigment, etc.

[0009] Preferably, the hawthorn pomace is the pomace obtained after fresh hawthorn juice is squeezed with a juicer.

[0010] Preferably, the acidic hydrolyzate is an acidic methanol aqueous solution; and the alkaline hydrolyzate is an alkaline methanol aqueous solution.

[0011] Preferably, the acid hydrolysis is to soak the precipitate in an acidic methanol aqueous solution at 80-90° C. for 4-6 hours.

[0012] Preferably, the alkaline hydrolysis is to soak the precipitate in an alkaline methanol aqueous solution at 80-90° C. for 4-6 hours.

[0013] The enzyme-containing hydrolysis solution is an aqueous solution containing cellulase and pectinase, the hydrolysis pH is 4.5, and the hydrolysis time is 2 to 4 hours.

[0014] Furthermore, the hawthorn pomace needs to be cleaned and fat removed before being hydrolyzed.

[0015] Preferably, methanol or petroleum ether is used for cleaning and removing fat.

[0016] The present invention provides zein nanoparticles embedded with a mixture of anthocyanidins and hawthorn phenolic hydrolyzed extracts. The zein nanoparticles are nanoparticles in which the above mixture is embedded in zein. Preferably, the nanoparticles are prepared by an antisolvent precipitation method.

[0017] Furthermore, the preparation method of the zein nanoparticles is to dissolve the above mixture in an ethanol aqueous solution of zein, and then drop the mixture into an aqueous solution of sodium caseinate to obtain the zein nanoparticles.

[0018] Furthermore, the mass ratio of the mixture to zein is 1:(5-10); the volume ratio of the zein to the sodium caseinate aqueous solution is 1:(0.5-3); the mass concentration of the zein in the 70%-90% ethanol aqueous solution is 0.5-3%; and the mass concentration of the sodium caseinate aqueous solution is 1-3%.

[0019] Preferably, the zein nanoparticles are water-removing nanoparticles.

[0020] The present invention also provides applications of the above mixture and the above zein nanoparticles, wherein the applications are one or more of the following:

[0021] Application in color development, preferably, the color development is pH-responsive color development;

[0022] Application in extending the shelf life of fruits and vegetables;

[0023] Application in fruit and vegetable preservation;

[0024] Application in assessing the freshness of fruits and vegetables;

[0025] Application in the preparation of a color-developing product, preferably, the color development is pH-responsive color development, and the product is a color developer;

[0026] Application in the preparation of products that extend the shelf life of fruits and vegetables;

[0027] Application in the preparation of a product for preserving fruits and vegetables, preferably, the product is a preservative;

[0028] Application in preparing a product for evaluating the freshness of fruits and vegetables, preferably, the product is a smart printing label.

[0029] Preferably, the fruit is a climacteric fruit.

[0030] Preferably, the fruits are kiwi, mango and persimmon.

[0031] The present invention provides a smart printing label, which contains the above mixture or the above zein nanoparticles.

[0032] Furthermore, the smart printable label is double-layered, including layer A and layer B. Layer A contains ink A loaded with a developer, and layer B contains ink B loaded with a preservative. Ink A is formed by dispersing the above-mentioned zein nanoparticles in a polyvinyl alcohol solution; and ink B is formed by dispersing lemongrass essential oil and gelatinized starch in a polyvinyl alcohol solution.

[0033] Preferably, the smart printed label is in a tube or sheet shape.

[0034] Preferably, the smart printed label is tubular, with layer A on the outside.

[0035] Furthermore, the mass volume concentration of the zein nanoparticles in the polyvinyl alcohol solution is 0.4% to 0.6%, the mass volume concentration of the lemongrass essential oil in the polyvinyl alcohol solution is 0.3% to 0.6%, the mass volume concentration of the starch in the polyvinyl alcohol solution is 8% to 10%, and the mass volume concentration of the polyvinyl alcohol in the polyvinyl alcohol solution is 10% to 20%.

[0036] The present invention provides a method for preparing a smart printable label, which is prepared by any of the following methods (1) to (3):

[0037] (1) Ink A is placed in a mold to obtain film A, and then ink B is placed on film A to form a smart printed label;

[0038] (2) Ink A and ink B are respectively filled into the syringes of a dual-nozzle printer to print a smart printed label with a two-layer structure;

[0039] (3) Using ink A as the outer core and ink B as the inner core, a coaxial printer is used for coaxial printing to obtain a smart printed label;

[0040] The ink A is formed by dispersing the zein nanoparticles in a polyvinyl alcohol solution; the ink B is formed by dispersing lemongrass essential oil and gelatinized starch in a polyvinyl alcohol solution.

[0041] Preferably, in the dual-nozzle printer, the printing parameters are set to 0.8mm outer nozzle diameter, 0.8mm inner nozzle diameter, 0.3-0.5Mpa inner core extrusion pressure, 15-20mm / s printing speed, 0.8mm printing nozzle height and 60%-100% filling ratio to obtain a smart printed label printed by dual nozzles.

[0042] Preferably, in the coaxial printer, the printing parameters are set to 1.8mm outer nozzle diameter, 0.6-1.2mm inner nozzle diameter, 0.3-0.5Mpa inner core extrusion pressure, 15-20mm / s printing speed, 1.8mm printing nozzle height and 60%-100% filling ratio to obtain coaxially printed smart printed labels.

[0043] Preferably, the mold is a glass square dish with a length, width and height of 3 to 20 cm.

[0044] The present invention provides a method for using a smart printed label, wherein the smart printed label or the smart printed label prepared by the above method is placed in a sealed container together with fresh fruit; preferably, as the fresh fruit becomes corrupted, the smart printed label gradually changes from blue-purple to pink; the smart printed label extends the shelf life of the fresh fruit by 2 to 5 days.

[0045] The beneficial effects of the present invention are as follows:

[0046] (1) The mixture of anthocyanidins and hawthorn phenolic hydrolyzed extract of the present invention, the specific extraction process of hawthorn phenolic substances combined with the specific mass ratio of anthocyanidins can significantly improve the color development sensitivity; the present invention also provides zein nanoparticles encapsulating this mixture, which solves the weak color development sensitivity of anthocyanidins themselves by utilizing the hawthorn phenolic hydrolyzed extract and nano-encapsulation technology, and at the same time, improves the economic utilization value of hawthorn pomace; the mixture of anthocyanidins and hawthorn phenolic hydrolyzed extract and zein nanoparticles of the present invention have important application prospects in color development products that respond to pH and in preserving fresh fruits or extending the shelf life of fresh fruits.

[0047] (2) The present invention comprises a smart printable label containing the aforementioned zein nanoparticles. Using zein nanoparticle-loaded ink A and preservative-loaded ink B, the smart printable label combines freshness monitoring and preservation functions. The smart printable label, produced using a coaxial printer, can more sensitively display the different freshness levels of fruit and extend the shelf life of the fruit by 2 to 5 days. This smart printable label expands the application scope of printed labels and improves the sensitivity of smart printable label monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is the effect of different mass ratios of red cabbage anthocyanins and hawthorn pomace polyphenol complexes on color sensitivity.

[0049] Figure 2 Effects of different mass ratios of zein and sodium caseinate on the particle size (A), ξ-potential (B) and color development (C) of the prepared nanoparticles.

[0050] Figure 3Comparison of labels prepared by traditional method, dual-nozzle printing and 4D coaxial printing for freshness monitoring and preservation of kiwifruit (A), green mango (B) and persimmon (C) during storage. DETAILED DESCRIPTION

[0051] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0052] Example 1 Effects of different hydrolysis methods on the composition of hawthorn phenolic hydrolysis extract

[0053] 1. Experimental Methods

[0054] 1 kg of fresh hawthorn pomace was stirred with 6 L of 50% (v / v) methanol (pH 7) at 25°C for 1 hour, then centrifuged at 2100 × g. The precipitate was washed three times with 12 L of 70% (v / v) methanol (pH 7). The precipitate was collected at 300 g, and 900 mL of petroleum ether was added to the precipitate. The precipitate was then centrifuged at 2100 × g for 10 minutes to remove fat. The resulting precipitate was then subjected to acid hydrolysis, alkaline hydrolysis, and enzymatic hydrolysis.

[0055] The acid hydrolysis was carried out by soaking the precipitate in 1.5 L of 70% (v / v) methanol aqueous solution (pH=2) at 85° C. for 5 h.

[0056] Alkaline hydrolysis refers to soaking the precipitate in an alkaline methanol aqueous solution (pH=12) at 85°C for 5 h.

[0057] Enzymatic hydrolysis involves mixing the centrifugal precipitate with water at a mass-to-volume ratio of 1:3 g / mL. A complex enzyme, comprising cellulase and pectinase, is added at a 1:1 (w / w) ratio, resulting in an enzyme concentration of 0.2 mg / mL in the precipitate-water mixture, while maintaining a pH of 4.5. The mixture is then immersed in a 40°C water bath for 3 hours.

[0058] After acid, alkaline, and enzymatic hydrolysis, the extract was centrifuged at 3000 × g for 15 min and washed three times with 1.5 L of 70% (v / v) methanol-water solution (pH = 7). The supernatant was collected. The pH of the supernatant was adjusted to 7 and concentrated to a final volume of <200 mL using a rotary evaporator (vacuum pressure -0.1 MPa, water bath temperature 45°C, and treatment time 12 h). The extract was then freeze-dried to obtain a phenolic hawthorn hydrolyzed extract, i.e., hawthorn pomace polyphenols. The composition and content of total phenols, flavonoids, and major phenols were determined after each hydrolysis step.

[0059] 2. Experimental Results

[0060] The composition and content of total phenols, flavonoids and main phenols obtained by each hydrolysis method are shown in Table 1. It can be seen from Table 1 that acidic hydrolysis can obtain higher total phenols and flavonoids contents, and the phenol contents obtained by different hydrolysis methods have significant differences.

[0061] Table 1 Composition and content of total phenols, flavonoids and main phenols obtained by each hydrolysis method

[0062]

[0063] Note: Total phenolic content is expressed as mg gallic acid equivalent / kg fresh hawthorn pomace; flavonoid content is expressed as mg rutin / kg fresh hawthorn pomace.

[0064] Example 2 Sensitivity of mixtures of hawthorn phenolic hydrolyzed extracts and anthocyanins obtained by different hydrolysis methods

[0065] 1. Experimental Methods

[0066] According to the method of Reference Example 1, hawthorn phenolic hydrolyzed extract was prepared by different hydrolysis methods (acidic hydrolysis, alkaline hydrolysis and enzymatic hydrolysis), and purple cabbage anthocyanins and hawthorn phenolic hydrolyzed extract were mixed at mass ratios of 1:1, 1:2, 1:3 and 1:4, respectively, wherein the mixture did not contain hawthorn phenolic hydrolyzed extract as a control, and the color development at different pH was tested.

[0067] 2. Experimental Results

[0068] The experimental results are as follows Figure 1 As shown by Figure 1 It can be seen that each hydrolysis method has more sensitive test results than the control group, but the sensitivity of acidic hydrolysis is significantly improved compared with the other two hydrolysis methods. Among them, when the mass ratio of anthocyanin and hawthorn phenolic hydrolyzed extract is 1:3, the color development effect is the most sensitive.

[0069] Example 3 Preparation of developer nanoparticles

[0070] 1. Experimental Methods

[0071] According to the method of Example 1, a phenolic hydrolyzed extract of hawthorn was prepared by acidic hydrolysis. Anthocyanidins and the phenolic hydrolyzed extract of hawthorn were mixed in a ratio of 1:3 to obtain a mixture of anthocyanidins and hawthorn phenolic hydrolyzed extract. Nanoparticles were prepared by an antisolvent precipitation method. The mixture of anthocyanidins and hawthorn phenolic hydrolyzed extract was dissolved in an 80% (v / v) ethanol aqueous solution of zein at a mass ratio of 1:9. The mixture was then dropwise added to an aqueous sodium caseinate solution at a volume ratio of zein to sodium caseinate of 1:0.5, 1:1, 1:2, and 1:3, respectively, to form zein nanoparticles encapsulating the mixture of the phenolic hydrolyzed extract of hawthorn and anthocyanidins. A control without sodium caseinate (i.e., without the addition of sodium caseinate solution) was used to measure the particle size distribution, average particle size, PDI, and zeta potential of the different nanoparticles.

[0072] 2. Experimental Results

[0073] The experimental results are as follows Figure 2 As shown, Figure 2 A represents the particle size distribution at the volume ratio of each zein to sodium caseinate aqueous solution; Figure 2 B is the average particle size, PDI and zeta potential, Figure 2 C represents the color rendering. Figure 2 It can be seen that when the above volume ratios of zein and sodium caseinate are included, relatively stable nanostructures are formed, but when the volume ratios of zein and sodium caseinate aqueous solution are 1:2 and 1:3, the stability is the highest and the particle size distribution is the most concentrated.

[0074] Example 4 Preparation of Smart Printing Labels

[0075] (1) Stir 1 kg of fresh hawthorn pomace with 6 L of 50% (v / v) methanol (pH = 7) at 25°C for 1 h, then centrifuge at 2100 × g. Wash the pellet three times with 12 L of 70% (v / v) methanol (pH = 7). Add 900 mL of petroleum ether to the pellet at 300 g, and centrifuge at 2100 × g for 10 min to remove fat. Soak the pellet in 1.5 L of 70% (v / v) methanol (pH = 2) at 85°C for 5 h. Centrifuge at 3000 × g for 15 min, then wash three times with 1.5 L of 70% (v / v) methanol (pH = 7), and collect all the supernatants. The supernatant was adjusted to pH 7 and concentrated to a final volume of <200 mL using a rotary evaporator (vacuum pressure -0.1 MPa, water bath temperature 45°C, and treatment time 12 h), followed by freeze-drying to obtain a hawthorn phenolic hydrolyzed extract. The red cabbage anthocyanins and hawthorn phenolic hydrolyzed extract were mixed uniformly in a mass ratio of 1:1 (w / w) to obtain a color developer.

[0076] (2) 450 mg of zein and 50 mg of a color developer were dissolved in 45 mL of 80% (v / v) ethanol and stirred magnetically for 12 h. Under continuous stirring, 20 mL of the color developer solution was gradually added dropwise to 60 mL of a 2% (w / w) sodium caseinate solution to form color developer-loaded nanoparticles. The resulting color developer-loaded zein nanoparticles were then freeze-dried.

[0077] (3) The 0.6% (w / w) developer obtained in step (2) was added to a 15% (w / w) polyvinyl alcohol solution and uniformly dispersed under magnetic stirring at 200 r / min to obtain a mixed solution A; lemongrass essential oil and 8% (w / w) gelatinized potato starch were added to the 15% (w / w) polyvinyl alcohol solution and stirred for 1 hour to obtain a mixed solution B. Smart printing labels were prepared using different methods:

[0078] Traditional method: 25 mL of mixed solution B was poured into a glass square dish, which was then placed in a fume hood and allowed to stand for 24 hours. Then, 25 mL of mixed solution A was poured into the glass square dish again and allowed to stand in a fume hood for 24 hours to obtain a smart printed label prepared by the traditional method.

[0079] Dual-nozzle printing method: Mixed solution A and mixed solution B were filled into syringes respectively, and printed using a dual-nozzle printer. The printing parameters were set to 0.8 mm outer nozzle diameter, 0.8 mm inner nozzle diameter, 0.3 MPa inner core extrusion pressure, 15 mm / s printing speed, 0.8 mm print nozzle height, and 80% fill ratio, to obtain a dual-nozzle printed smart printed label.

[0080] Coaxial printing method: Mixed solution A was used as the outer core and mixed solution B was used as the inner core, and printing was performed using a coaxial printer. The printing parameters were set to 1.8 mm outer nozzle diameter, 1.0 mm inner nozzle diameter, 0.3 MPa inner core extrusion pressure, 15 mm / s printing speed, 1.8 mm printing nozzle height and 80% filling ratio to obtain a coaxially printed smart printed label.

[0081] The labels prepared by the three methods contained the same quality of lemongrass essential oil.

[0082] Example 5 Preparation of Smart Printing Labels

[0083] (1) 1 kg of fresh hawthorn pomace was stirred with 6 L of 50% (v / v) methanol-water solution (pH = 7) at 25°C for 1 h, then centrifuged at 2100 × g. The centrifuged precipitate was washed three times with 12 L of 70% (v / v) methanol-water solution (pH = 7). 900 mL of petroleum ether was added to the precipitate at 300 g, and the precipitate was centrifuged at 2100 × g for 10 min to remove fat. The precipitate was soaked in 1.5 L of 70% (v / v) methanol-water solution (pH = 2) at 85°C for 5 h. After centrifugation at 3000 × g for 15 min, the precipitate was washed three times with 1.5 L of 70% (v / v) methanol-water solution (pH = 7), and the supernatant was collected. The pH of the supernatant was adjusted to 7 and concentrated to a final volume of < 200 mL using a rotary evaporator (vacuum pressure -0.1 MPa, water bath temperature 45°C, and treatment time 12 h), followed by freeze-drying. The purple cabbage anthocyanin and the extracted hawthorn phenolic substances are evenly mixed in a mass ratio of 1:2 (w / w) to obtain a color developer.

[0084] (2) 450 mg of zein and 45 mg of a color developer were dissolved in 45 mL of 80% (v / v) ethanol and stirred magnetically for 12 h. Under continuous stirring, 20 mL of the color developer solution was gradually added dropwise to 60 mL of a 2% (w / w) sodium caseinate solution to form color developer-loaded nanoparticles. The resulting color developer-loaded zein nanoparticles were then freeze-dried.

[0085] (3) The 0.4% (w / w) developer obtained in step (2) was added to a 15% (w / w) polyvinyl alcohol solution and uniformly dispersed under magnetic stirring at 200 r / min to obtain a mixed solution A; lemongrass essential oil and 10% (w / w) gelatinized potato starch were added to the 15% (w / w) polyvinyl alcohol solution and stirred for 1 hour to obtain a mixed solution B. Smart printable labels were prepared using different methods.

[0086] Traditional method: 25 mL of mixed solution B was poured onto a glass plate, which was then placed in a fume hood and allowed to stand for 24 hours. Then, 25 mL of mixed solution A was poured onto the glass plate again and allowed to stand in a fume hood for 24 hours to obtain a smart printed label prepared by the traditional method.

[0087] Dual-nozzle printing method: Mixed solution A and mixed solution B were filled into syringes respectively, and printed using a dual-nozzle printer. The printing parameters were set to 0.8 mm outer nozzle diameter, 0.8 mm inner nozzle diameter, 0.3 MPa inner core extrusion pressure, 15 mm / s printing speed, 0.8 mm print nozzle height, and 80% fill ratio to obtain a dual-nozzle printed smart printed label.

[0088] Coaxial printing method: Mixed solution A was used as the outer core and mixed solution B as the inner core, and printing was performed using a coaxial printer. The printing parameters were set as 1.8 mm outer nozzle diameter, 0.8 mm inner nozzle diameter, 0.35 MPa inner core extrusion pressure, 20 mm / s printing speed, 1.8 mm printing nozzle height, and 100% filling ratio to obtain a 4D printed label.

[0089] The labels prepared by the three methods contained the same quality of lemongrass essential oil.

[0090] Example 6 Preparation of Smart Printing Labels

[0091] (1) 1 kg of fresh hawthorn pomace was stirred with 6 L of 50% (v / v) methanol-water solution (pH = 7) at 25°C for 1 h, then centrifuged at 2100 × g. The centrifuged precipitate was washed three times with 12 L of 70% (v / v) methanol-water solution (pH = 7). 900 mL of petroleum ether was added to the precipitate at 300 g, and the precipitate was centrifuged at 2100 × g for 10 min to remove fat. The precipitate was soaked in 1.5 L of 70% (v / v) methanol-water solution (pH = 2) at 85°C for 5 h. After centrifugation at 3000 × g for 15 min, the precipitate was washed three times with 1.5 L of 70% (v / v) methanol-water solution (pH = 7), and the supernatant was collected. The pH of the supernatant was adjusted to 7 and concentrated to a final volume of < 200 mL using a rotary evaporator (vacuum pressure -0.1 MPa, water bath temperature 45°C, and treatment time 12 h), followed by freeze-drying. The purple cabbage anthocyanin and the extracted hawthorn phenolic substances are evenly mixed in a mass ratio of 2:1 (w / w) to obtain a color developer.

[0092] (2) 450 mg of zein and 65 mg of a color developer were dissolved in 45 mL of 80% (v / v) ethanol and stirred magnetically for 12 h. Under continuous stirring, 20 mL of the color developer solution was gradually added dropwise to 60 mL of a 2% (w / w) sodium caseinate solution to form color developer-loaded nanoparticles. The resulting color developer zein nanoparticles were then freeze-dried to obtain the final color developer zein nanoparticles.

[0093] (3) The 0.5% (w / w) developer obtained in step (2) was added to a 15% (w / w) polyvinyl alcohol solution and uniformly dispersed under magnetic stirring at 200 r / min to obtain a mixed solution A; lemongrass essential oil was added to the 15% (w / w) polyvinyl alcohol solution and stirred for 1 hour to obtain a mixed solution B. Smart printing labels were prepared using different methods:

[0094] Traditional method: 25 mL of mixed solution B was poured into a glass square dish, which was then placed in a fume hood and allowed to stand for 24 hours. Then, 25 mL of mixed solution A was poured into the glass square dish again and allowed to stand in a fume hood for 24 hours to obtain a smart printed label prepared by the traditional method.

[0095] Dual-nozzle printing method: Mixed solution A and mixed solution B were filled into syringes respectively, and printed using a dual-nozzle printer. The printing parameters were set to 0.8 mm outer nozzle diameter, 0.8 mm inner nozzle diameter, 0.3 MPa inner core extrusion pressure, 15 mm / s printing speed, 0.8 mm print nozzle height, and 80% fill ratio to obtain a dual-nozzle printed smart printed label.

[0096] Coaxial printing method: Mixed solution A is used as the outer core and mixed solution B is used as the inner core, and printing is performed using a coaxial printer. The printing parameters are set to 1.8 mm outer nozzle diameter, 1.2 mm inner nozzle diameter, 0.4 MPa inner core extrusion pressure, 20 mm / s printing speed, 1.8 mm printing nozzle height and 100% filling ratio to obtain a coaxially printed smart printing label.

[0097] The labels prepared by the three methods contained the same quality of essential oil.

[0098] Example 7: Application of intelligent printed labels to monitor freshness and preserve kiwifruit during storage

[0099] 1. Experimental Methods

[0100] The smart printed labels prepared by the three methods in Example 4 were cut into squares with a length and width of 3 cm and 3 cm respectively. 1 kg of kiwifruit and the prepared smart printed labels were added to a sealed plastic box and stored at 25°C. The sensory changes of the kiwifruit and the labels during storage were observed.

[0101] 2. Experimental Results

[0102] Figure 3 Figure A compares the freshness monitoring and preservation of kiwifruit during storage using three smart printed labels. The results demonstrate that, in terms of freshness monitoring, smart printed labels produced using the traditional and dual-nozzle printing methods can distinguish between kiwifruit in a corrupted and uncorrupted state. In comparison, the smart printed label produced using the coaxial printing method not only distinguishes between corrupted and uncorrupted kiwifruit but also more accurately indicates the freshness level of the kiwifruit during storage, exhibiting visually observable color changes at different freshness stages. Furthermore, compared to smart printed labels produced using the traditional and dual-nozzle printing methods, the smart printed label produced using the coaxial printing method extends the shelf life of kiwifruit by five days.

[0103] Example 8: Application of intelligent printed labels to monitor freshness and preserve green mango during storage

[0104] 1. Experimental Methods

[0105] The smart printed labels prepared by the three methods in Example 5 were cut into squares with a length and width of 3 cm and 3 cm respectively. 500 g of green mango and the prepared smart printed labels were added to a sealed plastic box and stored at 25°C. The sensory changes of the green mango and the labels during storage were observed.

[0106] 2. Experimental Results

[0107] Figure 3 Figure B compares the freshness monitoring and preservation of green mangoes during storage using three smart printed labels. The results demonstrate that, in terms of freshness monitoring, the smart printed labels produced using the traditional and dual-nozzle printing methods can distinguish between spoiled and unspoiled green mangoes. In comparison, the smart printed label produced using the coaxial printing method not only distinguishes between spoiled and unspoiled green mangoes but also more accurately indicates their freshness level during storage, with visible color changes depending on their freshness level. Furthermore, the smart printed label produced using the coaxial printing method extends the shelf life of green mangoes by three days compared to the traditional and dual-nozzle printing methods.

[0108] Example 9: Application of intelligent printed labels to monitor freshness and preserve persimmons during storage

[0109] 1. Experimental Methods

[0110] The smart printed labels prepared by the three methods in Example 6 were cut into squares with a length and width of 3 cm and 3 cm respectively. 800 g of persimmons and the prepared smart printed labels were added to a sealed plastic box and stored at 25°C. The sensory changes of the persimmons and labels during storage were observed.

[0111] 2. Experimental Results

[0112] Figure 3Figure C shows a comparison of three smart printed labels used to monitor and preserve the freshness of persimmons during storage. The results show that, in terms of freshness monitoring, the smart printed labels prepared using the traditional and dual-nozzle printing methods can distinguish between persimmons that are in a corrupted and uncorrupted state. In comparison, the smart printed label prepared using the coaxial printing method not only distinguishes between corrupted and uncorrupted persimmons but also more accurately indicates the freshness level of the persimmons during storage, with visible color changes depending on the freshness level. Furthermore, the smart printed label prepared using the coaxial printing method extends the shelf life of persimmons by two days compared to the smart printed labels prepared using the traditional and dual-nozzle printing methods.

[0113] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the solution. Although the present invention has been described in detail with reference to the preferred embodiments, ordinary technicians in this field should understand and can modify or replace the technical solution of the present invention based on the understanding of this solution without departing from the purpose and scope of the technical solution of the present invention, which should be covered by the scope of the claims of the present invention.

Claims

1. A mixture of anthocyanidins and hawthorn phenolic hydrolyzed extract, characterized in that: The mass ratio of the mixture of anthocyanidins and hawthorn phenolic hydrolyzed extract is 1:(1-4); The hawthorn phenolic hydrolyzed extract is obtained by soaking hawthorn pomace in a hydrolyzate to hydrolyze it and then fully drying it. The hydrolyzate is an acidic hydrolyzate, an alkaline hydrolyzate or an enzyme-containing hydrolyzate. Preferably, the pH of the acidic hydrolyzate is 1 to 3; the pH of the alkaline hydrolyzate is 10 to 12; the enzyme-containing hydrolyzate contains cellulase and pectinase, the mass ratio of the cellulase to the pectinase is 1:(1 to 2), and the total concentration of the cellulase and the pectinase is 0.1 to 0.3 mg / mL; the mass volume ratio of the hawthorn pomace to the hydrolyzate is 1:(1 to 4) g / mL; Preferably, the pH of the acidic hydrolyzate is 2; the pH of the alkaline hydrolyzate is 12; the enzyme-containing hydrolyzate contains cellulase and pectinase, the mass ratio of the cellulase and pectinase is 1:1, and the total concentration of the cellulase and pectinase is 0.2 mg / mL; the mass volume ratio of the hawthorn pomace and the hydrolyzate is 1:3 g / mL.

2. A zein nanoparticle embedded with a mixture of anthocyanidins and a phenolic hydrolyzed extract of hawthorn, characterized in that: The zein nanoparticles are nanoparticles in which the mixture according to claim 1 is embedded in zein. Preferably, the nanoparticles are prepared by an antisolvent precipitation method.

3. The zein nanoparticles according to claim 2, characterized in that The preparation method of the zein nanoparticles is as follows: dissolving the mixture according to claim 1 in an ethanol aqueous solution of zein, and then dripping the mixture into a sodium caseinate aqueous solution to obtain the zein nanoparticles.

4. The zein nanoparticles according to claim 3, characterized in that The mass ratio of the mixture according to claim 1 to zein is 1:(5-10); the volume ratio of the zein to the sodium caseinate aqueous solution is 1:(0.5-3); the mass concentration of the zein in the 70%-90% ethanol aqueous solution is 0.5-3%; the mass concentration of the sodium caseinate aqueous solution is 1-3%.

5. Use of the mixture according to claim 1 or the zein nanoparticles according to any one of claims 2 to 4, characterized in that: The application is one or more of the following: Application in color development, preferably, the color development is pH-responsive color development; Application in extending the shelf life of fruits and vegetables; Application in fruit and vegetable preservation; Application in assessing the freshness of fruits and vegetables; Application in the preparation of a color-developing product, preferably, the color development is pH-responsive color development, and the product is a color developer; Application in the preparation of products that extend the shelf life of fruits and vegetables; Application in the preparation of a product for preserving fruits and vegetables, preferably, the product is a preservative; Application in preparing a product for evaluating the freshness of fruits and vegetables, preferably, the product is a smart printing label.

6. A smart printing label, characterized in that: Contains the mixture according to claim 1 or the zein nanoparticles according to any one of claims 2 to 4.

7. The smart printing label according to claim 6, characterized in that: The smart print label is double-layered, including layer A and layer B, wherein layer A contains ink A loaded with a developer, and layer B contains ink B loaded with a preservative, wherein ink A is obtained by dispersing the zein nanoparticles according to any one of claims 2 to 4 in a polyvinyl alcohol solution; The ink B is formed by dispersing lemongrass essential oil and gelatinized starch in a polyvinyl alcohol solution.

8. The smart printing label according to claim 6, characterized in that: The mass volume concentration of the zein nanoparticles in the polyvinyl alcohol solution is 0.4% to 0.6%, the mass volume concentration of the lemongrass essential oil in the polyvinyl alcohol solution is 0.3% to 0.6%, the mass volume concentration of the starch in the polyvinyl alcohol solution is 8% to 10%, and the mass volume concentration of the polyvinyl alcohol in the polyvinyl alcohol solution is 10% to 20%.

9. A method for preparing a smart printing label, characterized in that: Prepared by any of the following methods (1) to (3): (1) Ink A is placed in a mold to obtain film A, and then ink B is placed on film A to form a smart printed label; (2) Ink A and ink B are respectively filled into the syringes of a dual-nozzle printer to print a smart printed label with a two-layer structure; (3) Using ink A as the outer core and ink B as the inner core, a coaxial printer is used for coaxial printing to obtain a smart printed label; The ink A is formed by dispersing the zein nanoparticles according to any one of claims 2 to 4 in a polyvinyl alcohol solution; and the ink B is formed by dispersing lemongrass essential oil and gelatinized starch in a polyvinyl alcohol solution.

10. A method for using a smart printing label, characterized in that: The smart printed label according to any one of claims 6 to 8 or the smart printed label prepared by the method according to claim 9 is placed in a sealed container together with fresh fruit; preferably, as the fresh fruit changes from fresh to corrupt, the smart printed label gradually changes from blue-purple to pink; the smart printed label extends the shelf life of the fresh fruit by 2 to 5 days.

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