阅读说明：本技术 一种可视化检测肉类新鲜度智能指示标签的制备方法及应用 (Preparation method and application of intelligent indication label for visually detecting freshness of meat ) 是由 邹小波 胡雪桃 石吉勇 李艳肖 李文亭 徐艺伟 李亚惠 于 2019-08-28 设计创作，主要内容包括：本发明涉及食品检测领域,涉及一种肉类新鲜度智能指示标签的制备方法及应用；步骤为：首先制备荧光碳量子点,和溴百里酚蓝一起溶于乙醇中,调整pH值,得到新鲜度指示剂；然后,将壳聚糖溶液、聚乙烯醇溶液和新鲜度指示剂混合,经超声去泡、干燥形成指示膜,再用低密度聚乙烯膜包裹,得到新鲜度智能指示标签；将标签与肉类共存后,记录不同储藏天数标签的可见光颜色图片组成可见光颜色比色卡,记录荧光颜色图片组成荧光颜色比色卡；待测肉类与标签共存后标签发生颜色变化,通过比色卡的颜色对比实现肉类新鲜度的可视化检测；本发明制备的标签安全环保,采用荧光纳米材料结合传统的颜色指示剂使指示标签颜色信号更加丰富,测定结果更加准确。(The invention relates to the field of food detection, in particular to a preparation method and application of an intelligent indicating label for meat freshness; the method comprises the following steps: firstly, preparing fluorescent carbon quantum dots, dissolving the fluorescent carbon quantum dots and bromothymol blue in ethanol, and adjusting the pH value to obtain a freshness indicator; then, mixing the chitosan solution, the polyvinyl alcohol solution and the freshness indicator, carrying out ultrasonic defoaming and drying to form an indicating film, and wrapping the indicating film by using a low-density polyethylene film to obtain an intelligent freshness indicating label; after the tags and the meat coexist, recording visible light color pictures of the tags on different storage days to form a visible light color colorimetric card, and recording fluorescence color pictures to form a fluorescence color colorimetric card; the color of the label changes after the meat to be detected and the label coexist, and the visual detection of the freshness of the meat is realized through the color comparison of the color comparison card; the label prepared by the invention is safe and environment-friendly, and the fluorescent nano material is combined with the traditional color indicator to enrich the color signal of the indicating label and make the determination result more accurate.)

1. A preparation method of an intelligent indication label for visually detecting freshness of meat is characterized by comprising the following steps:

step 1, preparing a freshness indicator; firstly, adding sucrose into water to obtain a sucrose aqueous solution, then adding the sucrose aqueous solution into ethanol, carrying out heating reaction under a vacuum condition, and after the reaction, centrifuging, filtering, and carrying out vacuum freeze drying to obtain the fluorescent carbon quantum dots; then, dissolving bromothymol blue and fluorescent carbon quantum dots in ethanol to obtain a bromothymol blue-carbon quantum dot indicator, and adjusting the pH value to obtain the visible light/fluorescent meat freshness indicator;

step 2, preparing an intelligent freshness indication label; firstly, adding chitosan into an acetic acid aqueous solution to obtain a chitosan solution; then mixing the chitosan solution, the polyvinyl alcohol solution and the meat freshness indicator prepared in the step 1, uniformly stirring to obtain a mixed solution, adjusting the pH value of the mixed solution, and performing ultrasonic defoaming and drying to form a freshness indicating film; and (4) wrapping the obtained indicating film by using a low-density polyethylene film to obtain the intelligent freshness indicating label.

2. The preparation method of the intelligent indicator label for visually detecting the freshness of the meat according to claim 1, wherein the mass concentration of the sucrose aqueous solution in the step 1 is 20-40%; the volume ratio of the sucrose aqueous solution to the ethanol is 3: 5-15; the heating reaction temperature is 150-300 ℃, and the time is 12-36 h.

3. The preparation method of the intelligent indicator label for visually detecting meat freshness according to claim 1, wherein in the step 1, the dosage ratio of bromothymol blue to carbon quantum dots to ethanol in the bromothymol blue-carbon quantum dot indicator is 0.1-1 mg: 1-2 mg: 10-20 mL.

4. The method for preparing the intelligent indicator label for visually detecting the freshness of the meat according to claim 1, wherein the pH value is adjusted to 6.0-7.6 by hydrochloric acid or sodium hydroxide in step 1.

5. The preparation method of the intelligent indicator label for visually detecting the freshness of the meat according to claim 1, wherein the dosage ratio of the chitosan to the acetic acid aqueous solution in the step 2 is 1-2 g: 50-100 mL; the volume concentration of the acetic acid aqueous solution is 1-5%; the concentration of the polyvinyl alcohol solution is 10-50 mg/mL.

6. The preparation method of the intelligent indicator label for visually detecting the freshness of the meat according to claim 1, wherein the dosage ratio of the chitosan solution, the polyvinyl alcohol solution and the meat freshness indicator in the step 2 is 5-10 mL: 5-10 mL: 1-5 mL.

7. The preparation method of the intelligent indicator label for visually detecting the freshness of the meat according to claim 1, wherein the pH value of the mixed solution in the step 2 is adjusted to 6.0-7.6 by hydrochloric acid or sodium hydroxide; the drying temperature is 40-60 ℃, and the drying time is 10-30 h.

8. The method for detecting the freshness of the meat by using the intelligent freshness indicating label prepared by the method according to any one of claims 1 to 7, which is characterized by comprising the following steps:

(1) sticking the freshness intelligent indication label in a fresh meat packaging bag, and storing the freshness intelligent indication label and fresh meat in the same space for m days, wherein m is a positive integer;

detecting the TVB-N values of the meat stored for different time by a Kjeldahl method to be used as a basis for judging the freshness of the meat; when the TVB-N value is more than 15mg/100g, the meat is not fresh, the storage days at the moment are recorded as N days, wherein N is a positive integer less than or equal to m; namely, the meat with the storage period of 1-n-1 day is a fresh product, and the meat with the storage period of n-m days is an unrifted product;

observing the visible light color change of the indicating label in the storage process, regularly recording visible light pictures of the freshness intelligent indicating label in different storage time, simultaneously irradiating the freshness intelligent indicating label by using a handheld ultraviolet lamp, and recording a fluorescent picture of the intelligent indicating label changing along with the storage time; arranging the visible light color pictures from small to large according to preservation days, and sequentially marking as V1, V2 … …, Vn … … and Vm to form a visible light color colorimetric card for intelligently indicating freshness; arranging the fluorescent color pictures from small to large according to preservation days, and sequentially marking as F1, F2 … …, Fn … … and Fm to form a fluorescent color colorimetric card for intelligently indicating freshness;

(2) sticking the prepared intelligent freshness indicating label in a packaging bag of a meat sample to be detected, storing the meat sample to be detected in the same space, and obtaining a visible light color picture and a fluorescent color picture of the intelligent freshness indicating label in the packaging bag; and (3) comparing the observed visible light color picture and the observed fluorescence color picture with the visible light color colorimetric card and the fluorescence color colorimetric card obtained in the step (1) respectively, and realizing the visual detection of the freshness of the meat through color comparison.

9. The use according to claim 8, wherein in step (1) the V1 is an indicator tag visible light picture stored for 1 day, V2 is an indicator tag visible light picture stored for 2 days, … …, Vn are indicator tag visible light pictures stored for n days, … …, Vm are indicator tag visible light pictures stored for m days; the visible light color colorimetric card consists of V1, V2 … …, Vn … … and Vm.

10. Use according to claim 8, wherein in step (1) the F1 is an indicator label fluorescence picture for 1 day of storage, F2 is an indicator label fluorescence picture for 2 days of storage, … …, Fn is an indicator label fluorescence picture for n days of storage, … …, Fm is an indicator label fluoresceable picture for m days of storage; the fluorescent color colorimetric card consists of F1, F2 … …, Fn … … and Fm.

Technical Field

The invention relates to the field of food detection, in particular to a preparation method and application of an intelligent indication label for meat freshness.

Background

With the improvement of the awareness of food safety, people pay more and more attention to the quality and safety of meat. Due to the incomplete cold chain system, meat is influenced by conditions such as external environment, microorganisms and the like in the processes of storage, transportation, processing and sale, and the meat contains rich nutrient components, so that the microorganisms in the meat are easy to grow and reproduce, the sensory quality and the physicochemical quality of the meat are changed under the enzymolysis effect of the meat and the decomposition effect of the microorganisms, and finally the freshness of the meat is reduced. If the rotten pork is not detected in time, the health of people is seriously damaged. Therefore, how to track and detect the freshness of meat is a very important and urgent task.

The freshness of the meat is evaluated mainly according to the sensory characteristics of the meat, the nature and the content of decomposition products, the amount of microorganisms and the like, and established detection methods comprise a sensory analysis method and a physicochemical analysis method. Although the sensory analysis method does not need instruments and equipment, the detection result completely depends on the subjective judgment and experience of an inspector, and the analysis result has subjectivity and sidedness. The physical and chemical analysis method mainly comprises the steps of measuring physical properties (pH value, viscosity, conductivity and the like) and chemical properties (ammonia gas, volatile basic nitrogen (TVB-N), microorganisms and the like) of meat, such as the content of the volatile basic nitrogen (TVB-N) detected by a Kjeldahl method, the quantity of spoilage microorganisms detected by a microbiological method and the like. Although the physicochemical analysis method can accurately determine the freshness of the meat, the method has the disadvantages of complicated operation process, long pretreatment time, sample damage and incapability of realizing rapid and nondestructive detection of the freshness of the meat.

The meat freshness indicating label utilizes acid-base indicator dyes (such as bromocresol blue, methyl red, bromocresol green and the like) to react with volatile components generated by meat to change the color of the indicating label, so that the freshness of meat products is detected. This freshness indicator label has the function that need not to destroy meat and its packing and can detect meat quality and freshness, and the consumer only needs to observe the fresh degree of meat in the indicator label colour just knows the packing. However, the existing freshness indicating label can only realize freshness detection according to visible light color change, but the detection label has low sensitivity and high detection limit. Therefore, it is necessary to prepare a visible light/fluorescence dual-signal indicator of freshness and an intelligent indicating label, so as to realize visible light/fluorescence visual detection of the freshness of meat.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention develops the intelligent indicating label for the freshness of the meat, and the intelligent indicating label can visually track and monitor the freshness change condition of the meat in the processes of transportation, storage, processing and sale in real time and can ensure the quality and safety of the meat when being eaten by consumers. The method comprises the steps of firstly preparing a visible light/fluorescent meat freshness indicator, then preparing a green and safe intelligent freshness indicating label, establishing visible light colors and fluorescent color colorimetric cards with different freshness degrees by using the prepared intelligent indicating label, and finally judging the freshness degree of the meat by comparing the colors of the intelligent indicating label and the colorimetric card in the actual meat. The invention can realize real-time, visual and rapid monitoring of freshness of meat in the processes of transportation, storage, processing and sale, and can overcome the defects of complex operation, long time consumption, sample damage and the like of the traditional detection method.

In order to achieve the above object, the present invention specifically comprises the following steps:

step 1, preparing a freshness indicator; firstly, adding sucrose into water to obtain a sucrose aqueous solution, then adding the sucrose aqueous solution into ethanol, carrying out heating reaction under a vacuum condition, and after the reaction, centrifuging, filtering, and carrying out vacuum freeze drying to obtain the fluorescent carbon quantum dots; then, dissolving bromothymol blue and fluorescent carbon quantum dots in ethanol to obtain a bromothymol blue-carbon quantum dot indicator, and adjusting the pH value to obtain the visible light/fluorescent meat freshness indicator;

step 2, preparing an intelligent freshness indication label; firstly, adding chitosan into an acetic acid aqueous solution to obtain a chitosan solution; then mixing the chitosan solution, the polyvinyl alcohol solution and the meat freshness indicator prepared in the step 1, uniformly stirring to obtain a mixed solution, adjusting the pH value of the mixed solution, and performing ultrasonic defoaming and drying to form a freshness indicating film; wrapping the obtained indicating film with a low-density polyethylene film to obtain an intelligent freshness indicating label;

preferably, the mass concentration of the sucrose aqueous solution in the step 1 is 20-40%; the volume ratio of the sucrose aqueous solution to the ethanol is 3: 5 to 15.

Preferably, the heating reaction in the step 1 is carried out at the temperature of 150-300 ℃ for 12-36 h.

Preferably, the fluorescence emission peak of the fluorescent carbon quantum dot in the step 1 is 450-480 nm, blue fluorescence is displayed, and the fluorescent carbon quantum dot has excellent fluorescence characteristics.

Preferably, in the bromothymol blue-carbon quantum dot indicator in the step 1, the dosage ratio of bromothymol blue to carbon quantum dots to ethanol is 0.1-1 mg: 1-2 mg: 10-20 mL.

Preferably, the pH value is adjusted to 6.0-7.6 by hydrochloric acid or sodium hydroxide in the step 1.

Preferably, the dosage ratio of the chitosan to the acetic acid aqueous solution in the step 2 is 1-2 g: 50-100 mL; the volume concentration of the acetic acid aqueous solution is 1-5% (v/v).

Preferably, the concentration of the polyvinyl alcohol solution in the step 2 is 10-50 mg/mL.

Preferably, in the step 2, the dosage ratio of the chitosan solution, the polyvinyl alcohol solution and the meat freshness indicator is 5-10 mL: 5-10 mL: 1-5 mL.

Preferably, the pH value of the mixed solution is adjusted to 6.0-7.6 by hydrochloric acid or sodium hydroxide in the step 2.

Preferably, the drying temperature in the step 2 is 40-60 ℃ and the time is 10-30 h.

The detection of the freshness of the meat slices to be prepared by the intelligent freshness indicating label comprises the following steps:

s1, manufacturing a meat freshness intelligent indication colorimetric card; sticking the prepared intelligent freshness indication label in a fresh meat packaging bag, and storing the prepared intelligent freshness indication label and fresh meat in the same space for m days, wherein m is a positive integer;

detecting volatile basic total nitrogen (TVB-N) stored for different time by a national standard method (Kjeldahl nitrogen determination method), judging the freshness of the meat, and when the TVB-N value is more than 15mg/100g, indicating that the meat is an stale product, and recording the storage days as N days, wherein N is a positive integer less than or equal to m; at the moment, the meat stored for 1-n-1 days is a fresh product, and the meat stored for n-m days is an unrifted product;

observing the visible light color change of the indicating label in the storage process, and regularly recording the visible light pictures of the freshness intelligent indicating label at different storage time; meanwhile, a handheld ultraviolet lamp is used for irradiating the intelligent freshness indicating label, fluorescent pictures of the intelligent indicating label changing along with preservation time are recorded, visible light color pictures are arranged from small to large according to preservation days and are sequentially recorded as V1, V2 … …, Vn … … and Vm, and a visible light color colorimetric card for intelligently indicating freshness is formed; arranging the fluorescent color pictures from small to large according to preservation days, and sequentially marking as F1, F2 … …, Fn … … and Fm to form a fluorescent color colorimetric card for intelligently indicating freshness;

s2, visually detecting the freshness of the meat;

sticking the intelligent freshness indicating label prepared in the step (2) in a packaging bag of a meat sample, and storing the meat sample in the same space for storage to obtain a visible light color picture and a fluorescent color picture of the intelligent freshness indicating label in the packaging bag; and comparing the observed visible light color picture and the observed fluorescence color picture with the visible light color colorimetric card and the fluorescence color colorimetric card obtained in the step S1 respectively, and realizing the visual detection of the freshness of the meat through color comparison.

Preferably, in step S1, V1 is an indicator tag visible light picture stored for 1 day, V2 is an indicator tag visible light picture stored for 2 days, … … and Vn are indicator tag visible light pictures stored for n days, and … … and Vm are indicator tag visible light pictures stored for m days; the visible light color colorimetric card consists of V1, V2 … …, Vn … … and Vm.

Preferably, in step S1, the F1 is an indicator label fluorescent picture stored for 1 day, the F2 is an indicator label fluorescent picture stored for 2 days, … …, Fn is an indicator label fluorescent picture stored for n days, … …, Fm is an indicator label fluoresceable picture stored for m days; the fluorescent color colorimetric card consists of F1, F2 … …, Fn … … and Fm.

Compared with the prior art, the invention has the beneficial effects that:

(1) the invention firstly prepares a visible light/fluorescence double-signal indicator (bromothymol blue-carbon quantum dot indicator), the indicator generates the change of visible light color and fluorescence color by reacting with volatile components generated by meat decay, and the monitoring of the freshness of meat products can be realized by utilizing the change of the visible light color and the fluorescence color; compared with a single visible light indicator, the indicator also has fluorescence indicating property, the fluorescence indicating signal changes sensitively, the freshness of the meat can be accurately detected, and the detection limit is low.

(2) The intelligent indicating label prepared by the invention is synthesized by polyvinyl alcohol and chitosan, and can be placed in a food package to realize the intelligent indicating label of meat freshness; compared with other intelligent indicating labels, the indicating label is non-toxic, low in cost, high in stability, good in film forming property, antibacterial property and biocompatibility, is an excellent degradable green material, and accords with the sustainable development trend in food processing.

(3) The method for visually detecting the freshness of the meat, which is established by the invention, can effectively judge fresh or stale meat according to the change of visible light color and fluorescent color of the indication label in the processes of transportation, storage, processing and sale of the meat, and can realize real-time and rapid monitoring of the meat; the fluorescent nano material is combined with the traditional color indicator, so that the color signals of the indicating label are richer, and the measuring result is more accurate; the freshness of the meat can be judged by naked eyes, an expensive detection instrument is not needed, the detection cost is low, and the operation is simple and convenient.

Drawings

Fig. 1 (a) is a uv-vis spectrum curve and a fluorescence spectrum curve of the carbon quantum dot and bromothymol blue-carbon quantum dot indicator in example 1; (b) the middle left picture is a visible light picture of the carbon quantum dots, and the right picture is a fluorescence picture of the carbon quantum dots; (c) the middle left picture is a visible light picture of the bromothymol blue-carbon quantum dot indicator, and the right picture is a fluorescence picture of the bromothymol blue-carbon quantum dot indicator;

in fig. 2, (a) is a visible light picture of the smart indicator prepared in example 1 under visible light, and (b) is a fluorescent picture of the smart indicator prepared in example 1 under ultraviolet light.

FIG. 3 is a visible light picture and a fluorescent picture of the freshness intelligent indicator label prepared in example 1 and after meat storage; (a) the visual light pictures of the intelligent freshness indication label for 1 day, 3 days, 5 days, 7 days, 10 days, 15 days and 20 days of pork storage are respectively displayed from left to right; the figure (b) is a fluorescent picture of the intelligent freshness indication label for 1, 3, 5, 7, 10, 15 and 20 days of pork storage from left to right.

Fig. 4 (a) is a visible light picture of the intelligent freshness indicator label in example 1 after coexistence of 3 types of pork to be detected; (b) the fluorescent pictures of the intelligent freshness indicating label in example 1 and 3 pork to be detected coexisted are shown.

Detailed Description

The invention is described in more detail below with reference to the figures and examples, but the scope of the invention is not limited thereto.