Preparation and application of sulfur dioxide/carbon dioxide sensitive intelligent labelTechnical Field
The invention discloses a preparation method and application of an SO2/CO2 sensitive intelligent label, which are applied to the field of storage and fresh-keeping and logistics transportation of fruits and vegetables.
Background
The quality and variety structure of the fruit and vegetable products are continuously optimized in China, which is the first country of global fruit and vegetable yield, but the reasons of cold chain, transportation condition, insufficient fresh-keeping measures and the like are caused. The research of the comprehensive evaluation system for enhancing the freshness of foods such as fruits and vegetables and the storage environment condition has important social and economic benefits. Taking grapes as an example, most international grape antistaling agents are SO2, but the grape is bleached due to too high concentration of SO2, and the grape is rotten and deteriorated due to too low concentration of SO2. Therefore, the concentration of SO2 in the package directly affects the shelf life of fruits and vegetables such as grapes.
The intelligent food packaging technology is a novel packaging technology which is emerging in the food industry at home and abroad in recent years. By monitoring the environmental changes in the package and the characteristic changes of the package, the quality, safety and other information of the package during storage and transportation are obtained. Compared with the traditional package, the intelligent package can actively communicate the quality and the safety of the food with the producer, the seller and the consumer, and the technology has very important significance on the food safety and the nutritive value. The food label with the diagnosis or detection function mainly comprises a time-temperature indication label, a freshness indication label, an oxygen indication label, a CO2 indication label, a packaging leakage label, a pathogenic bacteria indication label and the like.
The measurement of the content of SO2 is an essential link for evaluating the storage environment of fruits and vegetables such as grapes. SO2 is acidic under a wet condition, has a large influence on the pH value of a closed environment, and an indicator for measuring the content of SO2 has potential use value in the package of fruits such as fruits and vegetables. The existing instrument for measuring the SO2、CO2 content is mostly precision equipment, and has the advantages of high price, complex operation, poor portability, narrow application range and non-visual measurement result. The intelligent labels for directly measuring the SO2、CO2 content are lacking in the market, most of the color-developing agents of the intelligent labels are organic matters such as bromocresol purple, methyl red and the like, and skin contact and swallowing are harmful to human bodies, SO that potential safety hazards exist.
In the sulfur dioxide detection device and the sulfur dioxide detection method (application publication number: CN 112362625A), a detection instrument comprises a reaction chamber, an ultraviolet light emission source and an ultraviolet detector, wherein a condensation system and a quartz tube are arranged in the reaction chamber, and the quartz tube is communicated with the external environment. By using a semiconductor laser generator as a light source for generating deep ultraviolet laser light. [ high-precision nitrogen oxide and sulfur dioxide detector ] (application publication number: CN 112414961A) respectively pumps background gas and gas to be detected into a long-optical-path absorption cell cavity through an air pump, drives a deuterium lamp light source to emit ultraviolet light, gas sample molecules and ultraviolet light beams interact in the long-optical-path absorption cell, utilizes a spectrometer to split the ultraviolet light beams, converts optical signals into electric signals, sends the electric signals to a control and processing unit, and the control and processing unit calculates the concentration of SO2 in the gas to be detected according to an established absorbance-concentration relation model. Compared with the invention, the two sulfur dioxide detection devices are high in price and complex in operation. The invention uses the label to replace the instrument, and has low cost and simple operation.
[ Method for detecting sulfur dioxide in wine ] (application publication number: CN 104165878A) a macroscopic planar zinc oxide nanomaterial is prepared as an adsorption material for headspace solid phase extraction, and after the enrichment of sulfur dioxide in wine, the method is combined with a surface enhanced Raman spectroscopy technology to detect the sulfur dioxide in wine. [ method for rapidly detecting sulfur dioxide residue in a sulfur fumigation traditional Chinese medicine ] (application publication number: CN 112113950A) discloses a method for rapidly detecting sulfur dioxide residue in a sulfur fumigation traditional Chinese medicine, wherein a Si@Ag@PEI composite film substrate is prepared, a headspace extraction method is adopted to adsorb sulfur dioxide of a target object, and finally a surface enhanced Raman spectroscopy technology is adopted to detect, so that sulfur dioxide residue in a sample to be detected is calculated. Both the above two inventions enrich sulfur dioxide by preparing adsorption materials, and finally detect by adopting a surface enhanced Raman spectroscopy technology, so that the sulfur dioxide content can be accurately measured, but the sulfur dioxide content cannot be intuitively judged. According to the invention, the sulfur dioxide content can be intuitively, simply, conveniently and accurately judged by observing the color development degree of the label from red to white.
[ Efficient CO2 gas detector ] (application publication No. CN 205749433U) discloses an efficient CO2 gas detector comprising a sealing device and a housing. Through the dual filter screen of installation in the air filter device, can effectually filter unnecessary dust and impurity that contain in the air, improve the purity degree of air, and then be favorable to the accuracy of instrument detection CO2. [ an O2、CO2 rapid test tube ] (application publication No. CN 205786537U) discloses an O2、CO2 rapid test tube comprising an O2、CO2 rapid test tube body and an isolation layer. The content of O2、CO2 is detected simultaneously, so that guarantee is provided for the life safety of coal mine workers. The invention has high cost for the detection equipment of the CO2, is inconvenient to carry, and lacks an intelligent tag capable of detecting the CO2、SO2 at the same time. The invention is convenient to carry, simple and convenient to use and wide in application prospect.
[ PH sensitive type freshness detection intelligent label, preparation method and application ] (application publication number: CN 110954534A) uses bromocresol purple/methyl red as a color developing agent, and uses polyvinyl alcohol/methyl cellulose as a film forming substrate to prepare the bromocresol purple/methyl red composite pH sensitive type intelligent label, which is used for accurately monitoring and detecting the freshness of food materials such as livestock, poultry, aquatic products and the like in real time so as to ensure the quality of the food. The color developing agent is bromocresol purple and methyl red, and skin contact and swallowing are harmful to human bodies, so that potential safety hazards exist. The invention is different in that the natural pigment indicator is used, so that the safety is high.
In summary, the existing apparatus for precisely measuring the content of SO2、CO2 has high price, narrow application range and needs a certain technical support; the reported labels can only detect CO2, and no intelligent labels with double responses to SO2、CO2 gas exist yet; most of the chromogenic substances are artificially synthesized pigments, such as bromocresol purple, methyl red and other organic matters, and skin contact and swallowing are harmful to human bodies, so that potential safety hazards exist. The invention selects natural pigment as an indicator to prepare the SO2/CO2 sensitive intelligent label. When SO2 is measured (the concentration is 0 ppm-25 ppm), the color of the label is changed from dark red to light as the content of SO2 is gradually increased; when CO2 was measured (0% -100% by volume), the label exhibited a dark red-pink-bluish violet-reddish brown color change as the CO2 content was gradually reduced. The intelligent label can be used for rapidly detecting the content of SO2、CO2 in fruit and vegetable packages such as grapes, longan and lotus roots and judging the suitability of the fruit and vegetable packaging environment, SO that the purpose of predicting the shelf life is achieved.
Disclosure of Invention
In order to achieve the above object, the present invention discloses the following technical contents:
The invention firstly discloses an SO2/CO2 sensitive intelligent label which is characterized by comprising the following components: a PLA (polylactic acid) base material layer 2 at the bottom layer and a natural pigment adhesion layer 1 at the upper layer; the natural pigment adhesion layer is one or more of beet red, rose red, lac red, radix Arnebiae red, purple cabbage, morning glory red and purple sweet potato red. The PLA substrate layer is made of a PBAT/PLA modified material; the smart tag is a full component degradable material.
The invention further discloses a preparation method of the SO2/CO2 sensitive intelligent label, which is prepared by adopting a natural pigment as a color developing agent and adopting a degradable material PLA as a base material, and comprises the following specific steps of:
(1) Preparation of an indicator solution: dissolving natural pigment in distilled water according to the mass ratio of 0.8-3% to obtain an indicator solution; the natural pigment is one or more of beet red, rose red, lac red, lithospermum red, purple cabbage, morning glory red and purple sweet potato red;
(2) Preparation of the pigment adhesion layer: preparing a mixed solution of the indicator solution in the step (1) and a 3% chitosan solution according to the mass ratio of 0.5-1.0%; weighing trehalose with the mass ratio of 1.0-2.0%, pouring the trehalose into the mixed solution, and uniformly stirring; weighing starch with the mass ratio of 2.0-5.0%, pouring the starch into the mixed solution, and stirring for 5-10 minutes; dripping 1.5-2% of glycerol, stirring, mixing, and heating in water bath at 80deg.C for 20-30 min to obtain pigment attachment solution;
(3) Preparation of intelligent labels: taking out the mixed solution obtained in the step (2), and cooling for 10 minutes. Uniformly coating the solution on a PLA film with the thickness of 0.04-0.08mm by using a coating machine, and drying for 48 hours at normal temperature; putting the film into a constant temperature and humidity box with the temperature of 30 ℃ and the relative humidity of 60 percent, and drying for 16-24 hours; and standing and drying the film for 24 hours at normal temperature to obtain the intelligent label.
The invention further discloses application of the SO2/CO2 sensitive intelligent label prepared by the method in the aspect of rapidly detecting the change of the SO2、CO2 gas content in the fruit and vegetable packaging environment; the color reaction refers to the color difference DE change of the pigment caused by the reaction of the SO2、CO2 gas content in the storage environment of fruits and vegetables. Judging the gas content of SO2 according to the color change of the intelligent label, and gradually fading the label from dark red to colorless, wherein the corresponding gas content of SO2 is 0 ppm-25 ppm. And judging the content of CO2 gas according to the color change of the intelligent label, wherein the label is changed from blue-violet, pink and red in sequence, and the corresponding volume fraction of CO2 is 0% -100%. The fruits and vegetables of the invention are respectively: fruits such as grape, longan, etc.; vegetables such as lotus root, bamboo shoot, etc.
The invention cures natural pigment on the intelligent label, and the specific application method is as follows:
The intelligent label is used as a rapid detection indication label of SO2/CO2 content: placing the detection product and the intelligent label into a sealing box/bag, or placing the intelligent label into the detection product, and judging the content of SO2/CO2 within 5min according to the color change condition of the label; or b, using the smart label as a packaged smart indication card: the intelligent label is stuck in the package for use, is not in direct contact with food, and judges the content of SO2/CO2 according to the color change of the intelligent label, and the suitability of the packaging environment of fruits and vegetables is judged, SO that the purpose of predicting the shelf life is achieved.
The intelligent label mainly solves the problem of rapid detection of the content of SO2/CO2 in a fruit and vegetable storage environment, and focuses on examining the corresponding relation between the color change identifiable by naked eyes and the content of SO2/CO2, and has the main difficulty of preparation of the intelligent label and convenience and sensitivity of application in fruit and vegetable packaging.
The preparation method and the application effect of the SO2/CO2 sensitive intelligent label disclosed by the invention have the following positive effects compared with the prior art:
(1) The SO2/CO2 sensitive intelligent label can cause obvious change of the color of the label through the specific reaction of the pigment and SO2、CO2 gas in the fruit and vegetable storage environment. The aim of simply, real-time and accurately monitoring the freshness and shelf life of fruits and vegetables is fulfilled. Natural pigments are widely available and readily available. Therefore, the intelligent label can be used as an indicator and compounded on a biodegradable material to prepare the intelligent label for detecting the SO2/CO2 gas content in the fruit and vegetable package.
(2) The SO2/CO2 sensitive intelligent label can also be applied to food packaging and used as a test paper for rapidly detecting the gas content of SO2/CO2.
(3) The intelligent label prepared by the invention can intuitively measure the gas content of SO2/CO2, can be matched with the existing food package for use, is safe and healthy, has reliable results, and is convenient and practical.
Drawings
Color difference (Δe) changes in the response of the fig. 1 label to different SO2 gas concentrations;
Color difference (Δe) changes in the response of the fig. 2 label to different CO2 gas concentrations;
FIG. 3 SO2/CO2 is a schematic diagram of a sensitive smart tag architecture;
in the figure, 1 is a natural pigment adhesion layer; 2 is a PLA substrate layer.
Detailed Description
The invention is described below by means of specific embodiments. The technical means used in the present invention are methods well known to those skilled in the art unless specifically stated. Further, the embodiments should be construed as illustrative, and not limiting the scope of the invention, which is defined solely by the claims. Various changes or modifications to the materials ingredients and amounts used in these embodiments will be apparent to those skilled in the art without departing from the spirit and scope of the invention. The raw materials (PBAT/PLA modified material, namely, poly (terephthalic acid-adipic acid-butylene glycol)/polylactic acid, natural pigment) and other reagents used in the invention are all commercially available.
Examples
(1) Preparation of an indicator solution: 2.5g of morning glory red natural pigment is dissolved in 200ml of distilled water to obtain an indicator solution;
(2) Preparation of the pigment adhesion layer: preparing a mixed solution of the indicator solution in the step (1) and a 3% chitosan solution according to the mass ratio of 0.5%; weighing trehalose with the mass ratio of 1% and pouring the trehalose into the mixed solution, and uniformly stirring; weighing 3% of starch by mass, pouring the starch into the mixed solution, and stirring for 5 to 10 minutes; dripping 1.5% glycerol, stirring, mixing, and heating in water bath at 80deg.C for 20-30 min to obtain pigment attachment solution;
(3) Preparation of intelligent labels: taking out the mixed solution obtained in the step (2), and cooling for 10 minutes. Uniformly coating the solution on a PLA film by using a coating machine, and drying the PLA film at normal temperature for 48 hours, wherein the thickness of the PLA film is 0.04 mm; putting the film into a constant temperature and humidity box with the temperature of 30 ℃ and the relative humidity of 60% for drying for 24 hours; and standing and drying the film for 24 hours at normal temperature to obtain the intelligent label.
Examples
(1) Preparation of an indicator solution: 1g of purple cabbage and 1g of morning glory red natural pigment are dissolved in 200ml of distilled water to obtain an indicator solution;
(2) Preparation of the pigment adhesion layer: preparing a mixed solution of the indicator solution in the step (1) and a 3% chitosan solution according to the mass ratio of 0.5%; weighing trehalose with the mass ratio of 1.5%, pouring the trehalose into the mixed solution, and uniformly stirring; weighing 3% of starch by mass, pouring the starch into the mixed solution, and stirring for 5 to 10 minutes; dripping 1.0% of glycerol, stirring, mixing, and heating and stirring in a water bath at 80deg.C for 20-30 min to obtain pigment attachment solution;
(3) Preparation of intelligent labels: taking out the mixed solution obtained in the step (2), and cooling for 10 minutes. Uniformly coating the solution on a PLA film with the thickness of 0.06mm by using a coating machine, and drying for 48 hours at normal temperature; putting the film into a constant temperature and humidity box with the temperature of 30 ℃ and the relative humidity of 60% for drying for 18 hours; and standing and drying the film for 24 hours at normal temperature to obtain the intelligent label.
Examples
(1) Preparation of an indicator solution: 1g of purple sweet potato red and 1.2g of morning glory red natural pigment are dissolved in 200ml of distilled water to obtain an indicator solution;
(2) Preparation of the pigment adhesion layer: preparing a mixed solution of the indicator solution in the step (1) and a 3% chitosan solution according to the mass ratio of 0.5%; weighing trehalose with the mass ratio of 1% and pouring the trehalose into the mixed solution, and uniformly stirring; weighing 3% of starch by mass, pouring the starch into the mixed solution, and stirring for 5 to 10 minutes; dripping 1.5% glycerol, stirring, mixing, and heating in water bath at 80deg.C for 20-30 min to obtain pigment attachment solution;
(3) Preparation of intelligent labels: taking out the mixed solution obtained in the step (2), and cooling for 10 minutes. Uniformly coating the solution on a PLA film by using a coating machine, and drying the PLA film at normal temperature for 48 hours, wherein the thickness of the PLA film is 0.05 mm; putting the film into a constant temperature and humidity box with the temperature of 30 ℃ and the relative humidity of 60% for drying for 24 hours; and standing and drying the film for 24 hours at normal temperature to obtain the intelligent label.
Examples
(1) Preparation of an indicator solution: 1.5g of morning glory red natural pigment is dissolved in 200ml of distilled water to obtain an indicator solution;
(2) Preparation of the pigment adhesion layer: preparing a mixed solution of the indicator solution in the step (1) and a 3% chitosan solution according to the mass ratio of 0.5%; weighing trehalose with the mass ratio of 1.5%, pouring the trehalose into the mixed solution, and uniformly stirring; weighing 3% of starch by mass, pouring the starch into the mixed solution, and stirring for 5 to 10 minutes; dripping 1.0% of glycerol, stirring, mixing, and heating and stirring in a water bath at 80deg.C for 20-30 min to obtain pigment attachment solution;
(3) Preparation of intelligent labels: taking out the mixed solution obtained in the step (2), and cooling for 10 minutes. Uniformly coating the solution on a PLA film with the thickness of 0.08mm by using a coating machine, and drying for 48 hours at normal temperature; putting the film into a constant temperature and humidity box with the temperature of 30 ℃ and the relative humidity of 60% for drying for 24 hours; and standing and drying the film for 24 hours at normal temperature to obtain the intelligent label.
Examples
An SO2/CO2 -sensitive smart tag, comprising: a natural pigment adhesion layer 1 with the upper layer thickness of 0.07mm and a PLA substrate layer 2 at the bottom layer; the natural pigment (indicator) is one or more of beet red, rose red, lac red, radix Arnebiae red, purple cabbage, morning glory red and purple sweet potato red (preferably morning glory red); the PLA substrate layer is made of a PBAT/PLA modified material; the smart tag is a full component degradable material. The SO2/CO2 sensitive intelligent label provided by the invention mainly detects the change condition of the fruit and vegetable storage environment by specifically reacting pigment with SO2、CO2 gas in the fruit and vegetable storage environment, thereby causing obvious change of the color of the label. The fruits and vegetables respectively refer to: fruits such as grape, longan, etc.; vegetables such as lotus root, bamboo shoot, etc.
Examples
Comparative experiments
| Comparison | Gas response | Volume of | Timeliness of | Safety of |
| The utility model is that | Two kinds of SO2、CO2 | Small, can be used as part of a package | Timely color change along with gas concentration | Natural pigment and tag full component degradable |
| Conventional device | One of SO2 and CO2 | Large, in use, the probe is inserted into the package | Requiring sampling for determination | Chemical synthesis has potential safety hazard |
Theory: the SO2/CO2 sensitive intelligent label is prepared by taking natural pigment as a color developing agent and taking degradable material PLA as a base material, has double response to SO2、CO2 gas, is small in size and convenient to use, can be used independently, can also be used as a part of packaging materials, and can realize timely and rapid detection of the content of SO2、CO2 gas in a fruit and vegetable packaging environment through macroscopic color change. The label has the advantages of wide sources, safety, environmental protection, convenient use and the like.
Examples
Application: and (3) adhering the intelligent label to the inner surface of a PE (polyethylene) grape fresh-keeping bag, filling fresh Kyoho grape into a refrigerator at 0 ℃, and putting a sulfite slow-release preservative into the refrigerator. Along with the gradual increase of SO2 gas, the color of the label shows obvious color change, and the concentration of SO2 gas is detected in time, SO that the shelf life of the grape is predicted.
Examples
Application: and placing the intelligent label and the fresh-cut lotus roots into a sealing box/bag, and judging the content of SO2/CO2 within 5 minutes according to the color change condition of the label. Along with the gradual increase of SO2 gas, the color of the label shows obvious color change, and the gas concentration is detected in time, SO that the shelf life of the fresh-cut lotus roots is predicted.