Preparation method and application of nanoemulsion capable of indicating food freshness

Abstract

The present invention belongs to the field of food packaging, and in particular to a method for preparing a nanoemulsion with a function of indicating the freshness of food and its application in food freshness detection. The steps are: preparing a buffer solution with a pH of 2‑12, adding a natural pigment to the buffer solution, recording the colorimetric situation of the pH-sensitive natural pigment at different pH values, and screening to obtain the pH-sensitive natural pigment; dissolving a solid particle emulsifier in ultrapure water, stirring and dissolving to form an emulsifier aqueous phase; using vegetable oil as a carrier, adding a pH-sensitive natural pigment to the vegetable oil, stirring to obtain a pH-sensitive natural pigment oil phase; mixing the pH-sensitive natural pigment oil phase with the emulsifier aqueous phase, and forming a crude emulsion through the first homogenization; and then using a high-pressure homogenizer to perform secondary treatment on the crude emulsion to obtain a nanoemulsion. The present invention will contain a pH-sensitive natural pigment and put it into an oil phase to be wrapped therein, thereby improving the stability of the pigment and making visual detection more accurate.

Description

Technical Field

[0001] The invention belongs to the field of food packaging, and in particular relates to a method for preparing a nanoemulsion with the function of indicating the freshness of food and an application of the nanoemulsion in food freshness detection. Background Art

[0002] During the storage process, food will spoil at different levels due to uncontrollable factors such as enzymes and environmental factors (temperature, humidity, oxygen, microorganisms, etc.), posing a threat to consumers' health. Traditionally, the identification of food spoilage is often achieved through physical, chemical and microbiological methods, but the above methods have the disadvantages of being time-consuming and expensive. Therefore, it is of great significance to develop a technology that can detect the freshness of food in real time.

[0003] Smart food packaging is one of the technologies that can currently indicate food quality in real time. That is, through the sensors inside the packaging, the intrinsic quality information of the food is visualized, so that consumers can know the deterioration of the food in a short time. Food spoilage will produce a lot of volatile gases, including acidic gases (such as hydrogen sulfide) and alkaline gases (such as biogenic amines). The gas sensors in the food packaging can quickly react with volatile gases to generate signals, thereby showing the quality of the food. At present, most of the gas sensors reported at home and abroad are based on pH colorimetry, that is, the indicator film is prepared using pH-sensitive pigments for the detection of food spoilage.

[0004] Natural pigments are natural ingredients mainly extracted from animals, plants and microorganisms. They have certain biological activity, no side effects, and high safety. In food production, they are often used as colorants. In addition, some natural pigments are sensitive to pH, and the color of the pigment will change at different levels under different pH. For example, purple potato anthocyanins appear red under acidic conditions, purple under neutral conditions, and blue under alkaline conditions. Therefore, there are studies that use this property to make sensors using natural pigments as pH indicators, giving the sensor the ability to respond to alkaline gas ammonia, so as to indicate food corruption. However, the current disadvantage is that natural pigments are extracted from nature, the color is unstable, and they are sensitive to environmental factors (light, temperature, metal ions, additives, etc.), and are easily degraded, resulting in inaccurate indication results. Therefore, improving the stability of natural pigments is critical for the detection of food corruption. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention aims to solve one of the problems and proposes a method for preparing a nanoemulsion that can indicate the freshness of food. The method comprises dispersing a pH-sensitive natural pigment in vegetable oil, adding a solid particle emulsifier aqueous phase, homogenizing and emulsifying to obtain a crude emulsion, and then placing the crude emulsion in a high-pressure homogenizer to prepare an "oil-in-water" Pickering nanoemulsion. The prepared nanoemulsion can effectively improve the stability of the pH-sensitive natural pigment, avoid degradation of the pigment due to environmental influences during storage, and achieve the purpose of real-time detection of freshness.

[0006] In order to achieve the above technical objectives, the present invention provides a method for preparing a nanoemulsion capable of indicating the freshness of food, and the specific steps are as follows:

[0007] S1. Screening pH-sensitive natural pigments; preparing a buffer solution with a pH of 2-12, adding a natural pigment to the buffer solution, recording the colorimetric conditions of the pH-sensitive natural pigments at different pH values, and screening to obtain pH-sensitive natural pigments;

[0008] S2. Preparation of an emulsifier aqueous phase: dissolving a solid particle emulsifier in ultrapure water, and dissolving by magnetic stirring in a hot water bath to form an emulsifier aqueous phase; the solid particle emulsifier includes clay, silicon dioxide, titanium dioxide, starch, cellulose, citrus pectin or β-cyclodextrin (β-CD);

[0009] S3, preparation of pH-sensitive natural pigment oil phase: using vegetable oil as a carrier, adding the pH-sensitive natural pigment selected in S1 into the vegetable oil, and dispersing it evenly by magnetic stirring to obtain a pH-sensitive natural pigment oil phase;

[0010] S4, preparation of nanoemulsion: the pH-sensitive natural pigment oil phase obtained in S3 is mixed with the emulsifier water phase prepared in S2, and firstly homogenized at room temperature to form a crude emulsion; then the crude emulsion is subjected to a secondary treatment using a high-pressure homogenizer to obtain a nanoemulsion.

[0011] Preferably, the buffer solution with a pH of 2-12 in S1 is composed of citric acid solution, disodium hydrogen phosphate solution, and sodium dihydrogen phosphate solution; the molar concentration range of the citric acid solution is 0.01mol / L to 0.1mol / L, the molar concentration range of the disodium hydrogen phosphate solution is 0.02mol / L to 0.2mol / L, and the molar concentration range of the sodium dihydrogen phosphate solution is 0.02mol / L to 0.2mol / L; and the chromaticity value is an RGB system or a LAB system.

[0012] Preferably, the pH-sensitive natural pigments in S1 include curcumin, alizarin, and cochineal red.

[0013] Preferably, the mass concentration of the solid particle emulsifier in the water phase in S2 is 1% to 2%; the water bath heating temperature is 45° C. to 60° C., and the stirring speed is 100 r / min to 150 r / min.

[0014] Preferably, the mass concentration of the pH-sensitive natural pigment in the vegetable oil in S3 is 0.1% to 1%; and the magnetic stirring speed is 80 r / min to 100 r / min.

[0015] Preferably, the mass ratio of the pH-sensitive natural pigment oil phase to the emulsifier water phase in S4 is 1-2:8-9.

[0016] Preferably, the conditions for the first homogenization in S4 are: a rotation speed of 10000 rpm / min to 12000 rpm / min, and a time of 1 to 2 min.

[0017] Preferably, the processing condition of the high pressure homogenizer in S4 is 25-35 MPa, and the homogenization is performed 2-4 times.

[0018] The food freshness nanoemulsion prepared by the method is used for indicating food freshness.

[0019] A nanoemulsion capable of indicating the freshness of food is specifically used for detecting the freshness of meat products in food intelligent packaging, and the specific steps are as follows:

[0020] The nanoemulsion prepared in the above S4 is compounded with the gas sensor substrate in the smart packaging, mixed and formed for use; then the gas sensor carrying the nanoemulsion is stored in a fresh-keeping box together with the meat product. As the storage time of the meat product increases, the gas sensor containing the nanoemulsion will change color, and the longer the storage time, the more obvious the color change; at regular intervals, the chromaticity value of the gas sensor is measured, and at the same time interval, the volatile nitrogen content of the meat product is measured, and a colorimetric relationship is established between the chromaticity value of the sensor and the volatile nitrogen content of the sample to achieve visual detection; finally, consumers can judge the corresponding volatile nitrogen content by the color of the sensor, and then determine whether the meat product is rotten or spoiled.

[0021] Due to the presence of enzymes and microorganisms, animal food will decompose its own protein during the process of spoilage and produce ammonia and amine alkaline nitrogen-containing gases. This type of gas substance is volatile, and the higher the content, the more serious the protein decomposition and the more serious the damage to the meat product. Therefore, the content of volatile nitrogen is also an important indicator for detecting the spoilage of meat products. Therefore, by establishing a relationship between the content of volatile nitrogen and the color change of the sensor, consumers can judge the degree of spoilage of meat products based on the color of the sensor, which can well realize the visualization of the degree of spoilage of meat products.

[0022] Beneficial effects of the present invention:

[0023] (1) The present invention utilizes a solid particle emulsifier to prepare an "oil-in-water" type Pickering nanoemulsion structure, and utilizes the amphiphilic characteristics of the polysaccharide complex emulsified particles to encapsulate pH-sensitive natural pigments in the oil phase, thereby reducing direct exposure of the pigment to the air, thereby improving the stability of the pigment and making visual detection more accurate.

[0024] (2) The present invention relates to a green nanoemulsion with an indicating function. Based on the principle that pH-sensitive natural pigments have different colors under different pH values, the nanoemulsion is used to detect the spoilage of food in real time and visualize the spoilage process of food. Consumers can judge the degree of spoilage of food by observing the color change of the indicator label with the naked eye, thereby realizing the visualization of food packaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The color development of curcumin in different pH buffer solutions.

[0026] Figure 2 It is a graph showing the changes in the storage content of curcumin in the embodiment and the control example.

[0027] Figure 3 It is the relationship between the chromaticity difference (△E) and the volatile nitrogen (TVB-N).

[0028] Figure 4 This is the color change diagram of curcumin nanoemulsion in meat product freshness monitoring. DETAILED DESCRIPTION

[0029] 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 embodiments.

[0030] Example:

[0031] This embodiment takes curcumin Pickering nanoemulsion as an example to illustrate the implementation process of the present invention, which specifically includes the following steps:

[0032] S1. Color characterization of curcumin: A buffer solution with a pH of 2-12 was prepared using 0.1 mol / L citric acid solution, 0.2 mol / L sodium dihydrogen phosphate solution, and 0.2 mol / L sodium dihydrogen phosphate solution. 0.01 g of curcumin was dissolved in a 75% ethanol aqueous solution, and then 10 μL of the solution was placed in buffer solutions of different pH values. The color of curcumin at different pH values ​​was recorded using a camera, and the colorimetric condition of curcumin was recorded using a colorimeter.

[0033] like Figure 1As shown, the color development of curcumin at different pH values ​​is shown. When the pH value is less than 7, the curcumin solution is bright yellow. As the pH value increases, the curcumin gradually turns into orange-yellow, until it becomes brown-red when the pH value is 11.

[0034] S2. Preparation of emulsifier solution: Using a complex of citrus pectin and β-cyclodextrin (β-CD) as a solid particle emulsifier, an emulsifier aqueous solution with a mass concentration of 2% (w / w) was prepared. The mass ratio of citrus pectin and β-CD was 1:3, that is, 0.05g of commercial citrus pectin and 0.15g of β-CD were respectively taken in 10g of ultrapure water, stirred in a 55°C water bath for 2h, and the magnetic stirring speed was 120r / min to obtain an emulsifier aqueous phase.

[0035] S3, preparation of curcumin oil solution: prepare a curcumin oil phase solution with a mass concentration of 0.5% (w / w); that is, take 0.05g of curcumin powder in 10g of coconut oil, disperse it in a magnetic stirring at room temperature, the stirring speed is 90r / min, and stir for 2h to obtain a curcumin oil phase solution.

[0036] S4, preparation of nanoemulsion: prepare an oil-in-water emulsion with an oil-water mass ratio of 8.5:1.5, that is, take 8.5g of emulsifier water phase and 1.5g of curcumin oil phase solution in a 25mL beaker, use a homogenizer to continuously homogenize for 1.5min at room temperature, and the homogenization speed is 11000rpm / min to obtain a crude emulsion; then put the prepared crude emulsion into a 50mL centrifuge tube, put it into a high-pressure homogenizer for homogenization, the high-pressure homogenization pressure is 30MPa, and homogenize 3 times to finally obtain a nanoemulsion containing curcumin.

[0037] Taking the curcumin aqueous solution as a control example, its initial curcumin content is the same as that of the nanoemulsion prepared in the embodiment; after storage for 30 days, compared with the curcumin aqueous solution, the nanoemulsion has better protection ability, such as Figure 2 As shown, the curcumin aqueous solution has no protective measures, and the curcumin content in it decreases at a significantly higher rate than that in the nanoemulsion. However, the curcumin nanoemulsion with an "oil-in-water" protective shell has a slower loss, indicating that the emulsion can improve the stability of curcumin.

[0038] Application of nanoemulsion: Add 1 mL of nanoemulsion with a curcumin mass concentration of 0.5% to 10 mL of chitosan film solution with a mass concentration of 5%, mix, and then pour into a culture dish with an inner diameter of 5 cm. The solution thickness is 1 mm, and blow dry in a blower at 37°C to obtain a white film as a freshness indicator sensor. The obtained sensor is stored together with the meat products for spoilage detection. During storage, a camera is used to record the color change of the sensor, and a colorimeter is used to extract the colorimetric value of the sensor, and the chromaticity difference (△E) is calculated. At the same time intervals, the volatile nitrogen in the meat product is measured, and the following is established: Figure 3 The relationship between the color difference (△E) and the volatile nitrogen (TVB-N) is shown, so that the freshness change of the meat product is indicated according to the color change of the sensor.

[0039] from Figure 3 It can be seen that the linear equation of chromaticity difference (△E) and volatile nitrogen (TVB-N) is y=1.04725x-4.27681, R 2 It is 0.98779, indicating that the color difference (△E) is linearly correlated with the volatile nitrogen (TVB-N), so the freshness of meat products can be judged according to the color change of the sensor.

[0040]

[0041] L* value is brightness, a* value is red to green, b* value is yellow to blue, △L*=L*-L*0, △a*=a*-a*0, △b*=b*-b*0, L*0, a*0, b*0 are the initial chromaticity values ​​of the sensor, L*, a*, b* are the chromaticity values ​​during the storage process.

[0042] like Figure 4 As shown in the figure, it respectively represents the situation that the indicator film and the meat product are stored at 4°C for 0 day and 4 days. On the 0th day, the meat product is fresh, so the film is white and no color change occurs. Until the 3rd day, the film begins to change color and the color is light pink. On the 4th day of storage, it turns red. At this time, the corresponding △E is 15.6, and the chromaticity changes. According to the linear relationship between the chromaticity difference (△E) and volatile nitrogen (TVB-N), it can be calculated that the TVB-N content of the meat product at this time is 18.98 mg / 100g. The "National Food Safety Standard for Fresh (Frozen) Livestock and Poultry Products" (GB2707-2016) stipulates that the maximum limit of volatile basic nitrogen in fresh (frozen) livestock and poultry products is 15 mg / 100g. It is inferred that the TVB-N of the meat product under the indicator film has exceeded the national standard, indicating that the meat product has been corrupted and the degree of corruption is unacceptable to the human body.

[0043] Note: The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention; therefore, although this specification has described the present invention in detail with reference to the above embodiments, a person skilled in the art should understand that the present invention can still be modified or replaced by equivalents; and all technical solutions and improvements thereof that do not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a nanoemulsion having the function of indicating the freshness of food, characterized in that: The following steps are involved: S1. Screening pH-sensitive natural pigments; preparing a buffer solution with a pH of 2-12, adding a natural pigment to the buffer solution, recording the colorimetric conditions of the pH-sensitive natural pigments at different pH values, and screening to obtain pH-sensitive natural pigments; S2. Preparation of emulsifier aqueous phase: dissolving a solid particle emulsifier in ultrapure water, and dissolving by magnetic stirring in a hot water bath to form an emulsifier aqueous phase; the solid particle emulsifier includes clay, silicon dioxide, titanium dioxide, starch, cellulose, citrus pectin or β-cyclodextrin; S3. Preparation of pH-sensitive natural pigment oil phase: using vegetable oil as a carrier, adding the pH-sensitive natural pigment selected in S1 into the vegetable oil, and dispersing it evenly by magnetic stirring to obtain a pH-sensitive natural pigment oil phase; S4, preparation of nanoemulsion: the pH-sensitive natural pigment oil phase obtained in S3 is mixed with the emulsifier water phase prepared in S2, and firstly homogenized at room temperature to form a crude emulsion; then the crude emulsion is subjected to a secondary treatment using a high-pressure homogenizer to obtain a nanoemulsion.

2. The method for preparing a nanoemulsion having the function of indicating food freshness according to claim 1, characterized in that: The buffer solution in S1 with a pH of 2-12 is composed of citric acid solution, disodium hydrogen phosphate solution and sodium dihydrogen phosphate solution; the molar concentration range of the citric acid solution is 0.01mol / L to 0.1mol / L, the molar concentration range of the disodium hydrogen phosphate solution is 0.02mol / L to 0.2mol / L, and the molar concentration range of the sodium dihydrogen phosphate solution is 0.02mol / L to 0.2mol / L; the colorimetric conditions of the pH-sensitive natural pigment at different pH values ​​are recorded, and the chromaticity value is an RGB system or a LAB system.

3. The method for preparing a nanoemulsion having the function of indicating food freshness according to claim 1, characterized in that: The pH-sensitive natural pigments in S1 include curcumin, alizarin, and cochineal red.

4. The method for preparing a nanoemulsion having the function of indicating food freshness according to claim 1, characterized in that: The mass concentration of the solid particle emulsifier in the S2 in the water phase is 1% to 2%; the heating temperature of the water bath is 45° C. to 60° C., and the stirring speed is 100 r / min to 150 r / min.

5. The method for preparing a nanoemulsion having the function of indicating food freshness according to claim 1, characterized in that: The mass concentration of the pH-sensitive natural pigment in the vegetable oil in S3 is 0.1% to 1%; the magnetic stirring speed is 80 r / min to 100 r / min.

6. The method for preparing a nanoemulsion capable of indicating food freshness according to claim 1, characterized in that: The mass ratio of the pH-sensitive natural pigment oil phase to the emulsifier water phase in S4 is 1-2:8-9.

7. The method for preparing a nanoemulsion capable of indicating food freshness according to claim 1, characterized in that: The conditions for the first homogenization in S4 are: a rotation speed of 10000 rpm / min to 12000 rpm / min, and a time of 1 to 2 minutes.

8. The method for preparing a nanoemulsion capable of indicating food freshness according to claim 1, characterized in that: The processing condition of the high pressure homogenizer in S4 is 25-35 MPa, and the homogenization is performed 2-4 times.

9. Use of the nanoemulsion having the function of indicating food freshness prepared according to any one of claims 1 to 8 in indicating food freshness.

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