CN112646219B - Preparation method of chondroitin sulfate-anthocyanin sensitization type food freshness indicator film - Google Patents

Abstract

The invention relates to a preparation method of a chondroitin sulfate-anthocyanin sensitized food freshness indicator film, belonging to the technical field of food packaging, storage and detection. A preparation method of chondroitin sulfate-anthocyanin sensitization type food freshness indicator film comprises mixing blueberry anthocyanin extract solution and chondroitin sulfate water solution uniformly to obtain chondroitin sulfate-anthocyanin mixed solution; adding the gelatinized starch into the chondroitin sulfate-anthocyanin mixed solution, and magnetically stirring to obtain a chondroitin sulfate-anthocyanin-starch mixed solution; adding a certain amount of glycerol into the obtained mixed solution, adjusting the pH value of the solution to 3-4, and then continuing magnetic stirring for a period of time to obtain a film forming solution; drying and forming a film by using a film forming liquid to obtain the film. The prepared indicating film can be used as a food-grade biological material in food packaging by combining co-coloring and physical embedding technologies, and consumer food spoilage is monitored and early warned in real time by pH response color change of the indicating film.

Description

Preparation of a chondroitin sulfate-anthocyanin-sensitized food freshness indication film method

Technical field

The invention relates to a method for preparing a chondroitin sulfate-anthocyanin-sensitized food freshness indicating film, and belongs to the technical field of food packaging, storage and detection.

Background technique

In recent years, as consumers' awareness of food nutrition and food safety continues to increase, the difficulty in identifying the freshness of high-protein and high-fat foods during the storage and preservation process has become the focus of public attention, prompting the rise of research on smart food packaging. Freshness indication packaging is an intelligent packaging form that indicates the freshness of food based on changes in pH of the food packaging environment. Most seafood and meat products are prone to quality deterioration due to high moisture content, free amino acids, soluble non-nitrogen-containing compounds and other ingredients. Among them, microorganisms are the main cause of spoilage of most animal products. The mechanism for monitoring the deterioration of indicator films is that microbial spoilage of proteins produces a large amount of volatile alkaline nitrogen and biogenic amines such as ammonia, methylamine, and dimethylamine, which gradually increases the pH value in the packaging headspace through the pH-sensitive membrane fixed in the polymer film. The color change of the dye reflects the freshness/spoilage of the product.

Although synthetic pH dyes have the characteristics of obvious color and rapid response, they are difficult to be accepted by consumers because of the toxicity and non-degradability of synthetic dyes themselves, which can cause potential harm to the human body. Natural dyes extracted from plants are non-toxic, renewable, pollution-free, and easy to prepare, and are more in line with consumers' expectations for food safety. Anthocyanins are plant-derived pigments widely found in nature and have sensitive pH-responsive color-changing properties, making them an ideal choice for natural indicator materials. However, existing anthocyanin freshness/spoilage indicator films have problems such as poor color sensitivity and insufficiently obvious color indications. Therefore, it is necessary to develop a highly sensitive pH-responsive food freshness indicating film.

Contents of the invention

The object of the present invention is to provide a method for preparing a chondroitin sulfate-anthocyanin-sensitized smart food freshness indication film. The color of the indication film obtained by this method changes with the freshness of the food, and can quickly indicate the products in the package. degree of freshness.

A method for preparing a chondroitin sulfate-anthocyanin-sensitized food freshness indication film. The blueberry anthocyanin extract solution and the chondroitin sulfate aqueous solution are evenly mixed to obtain a chondroitin sulfate-anthocyanin mixed solution; the gelatinized The starch is added to the above-mentioned chondroitin sulfate-anthocyanin mixed solution and magnetically stirred to obtain a chondroitin sulfate-anthocyanin-starch mixed solution; a certain amount of glycerin is added to the obtained mixed solution, and the pH of the solution is adjusted to 3 to 4 and then the magnetic stirring is continued. After a period of time, the film-forming liquid is obtained; the film-forming liquid is dried to form a film, and the film is obtained.

In the above technical solution, it is preferred that the blueberry anthocyanin extract solution is an acidic ethanol solution of blueberry anthocyanin extract, and the anthocyanin extract concentration is 1 to 4 mg/mL.

Further, the acidic ethanol solution is composed of 1 mol/L acetic acid and absolute ethanol in a volume ratio of 3:17.

Further, the blueberry anthocyanin extract solution and the chondroitin sulfate aqueous solution are mixed and magnetically stirred, the stirring rate is 250-300r/min, and the stirring time is 10-30min.

In the above technical solution, it is preferred that the mass ratio of the blueberry anthocyanin extract and chondroitin sulfate is 1:20-60.

In the above technical solution, it is preferred that the concentration of the chondroitin sulfate aqueous solution is 2 to 6 mg/mL.

In the above technical solution, it is preferred that the starch is potato starch.

Further, the gelatinized starch is prepared by the following method: gradually heating the starch solution with a concentration of 50 to 70 mg/mL under magnetic stirring until the starch is not completely gelatinized, and the magnetic stirring rate is 500 to 800r /min, the stirring time is 20~40min.

Furthermore, the starch solution with a concentration of 50 to 70 mg/mL is gradually heated to 58 to 62°C under magnetic stirring to allow the starch to reach an incomplete gelatinized state.

In the above technical solution, it is preferred that the mass ratio of starch to chondroitin sulfate is 10 to 30:1.

Further, the magnetic stirring rate is 500-800r/min, and the stirring time is 20-40min.

In the above technical solution, it is preferable to add a certain amount of glycerin to the obtained chondroitin sulfate-anthocyanin-starch solution, adjust the pH of the solution to 3-4, and then continue magnetic stirring for 20-40 minutes at a stirring rate of 500-800 r/min.

Further, the added amount of glycerol is 1% to 3% of the total volume of the film-forming liquid.

Further, the pH of chondroitin sulfate-anthocyanin-starch is adjusted to 3-4 using 0.1 mol/L HCl solution or 0.1 mol/L NaOH solution.

In the above technical solution, it is preferable to cast the obtained film-forming liquid into a film-forming plate, place it in a blast drying oven, and dry it to form a film. The drying temperature is 40°C to 45°C, and the drying time is 12 to 24 hours.

The chondroitin sulfate used in the present invention, as a negatively charged acidic mucopolysaccharide, can be combined with anthocyanins to produce a co-coloring effect to form a stable nanocomposite, making the color development effect more significant. Potato starch is cheap, biodegradable and has good film-forming properties. Improving the stability of anthocyanins in the indicator film through encapsulation and embedding technology is beneficial to maintaining the sensitivity of pH-responsive color-sensitive indicators. The present invention combines co-coloring and physical embedding technology to prepare a chondroitin sulfate-anthocyanin-sensitized intelligent food freshness indicating film. The prepared indicating film can be used as a food-grade biological material and applied in food packaging. The discoloration of the membrane in response to pH can provide real-time visual monitoring and early warning of food spoilage to consumers.

A preferred technical solution of the present invention is as follows:

A method for preparing a chondroitin sulfate-anthocyanin-sensitized food freshness intelligent indication film, including the following steps:

(1) Dissolve the blueberry anthocyanin extract in the acidic ethanol solution and prepare an anthocyanin extract solution of a certain concentration;

(2) Add the anthocyanin extract solution obtained in step (1) to a certain concentration of chondroitin sulfate solution, and stir magnetically for 10 to 30 minutes;

(3) Slowly add the gelatinized starch solution to the anthocyanin-chondroitin sulfate mixed solution obtained in step (2), and stir magnetically for 10 to 30 minutes;

(4) Add a certain volume fraction of glycerol dropwise to the anthocyanin-chondroitin sulfate-starch solution obtained in step (3), adjust the final pH to 3-4, and continue magnetic stirring for 20-40 minutes;

(5) Cast the solution obtained in step (4) into a film-forming plate, place it in a blast drying oven, and dry it to form a film. After the film is formed, balance it in the dryer for a period of time and then peel it off.

Preferably, in the step (1), the anthocyanin extract concentration is 1 to 4 mg/mL, and the acidic ethanol solution is prepared by mixing 1 mol/L acetic acid and absolute ethanol in a ratio of 3:17.

Preferably, in the step (2), the chondroitin sulfate solution has a concentration of 2 to 6 mg/mL, is dissolved in distilled water, and the stirring rate is 250 to 300 r/min.

Preferably, in the step (3), the starch is potato starch. The starch is dissolved in distilled water to form a starch solution with a concentration of 50-70 mg/mL. The starch solution is gradually heated under magnetic stirring until the starch is not completely gelatinized. state, the stirring rate is 500~800r/min, the stirring time is 20~40min; the mass ratio of starch to chondroitin sulfate is 10~30:1.

Preferably, in the step (4), the final volume fraction of added glycerin is 1% to 3%, the final pH is adjusted to 3 to 4, and the stirring rate is 500 to 800 r/min.

Preferably, in the step (5), the drying temperature is 40°C to 45°C, and the drying time is 12 to 24 hours.

Beneficial effects of the present invention: The present invention introduces the chondroitin sulfate polysaccharide matrix for use in the preparation of indicator films. Through its co-coloring effect with anthocyanins, potato starch is used as the film-forming substrate to provide a combined co-coloring The method of action and physical entrapment enhances the pH-responsive discoloration sensitivity of natural pigments and improves their chemical stability. As a result, an efficient and stable freshness indicator film is obtained and applied in food packaging to monitor the freshness and spoilage of packaged products and provide consumers with a reference for purchasing high-protein and high-fat packaged foods.

Description of the drawings

Figure 1 (a) and (b) are respectively pictures of the chondroitin sulfate-starch composite blueberry anthocyanin-sensitized food freshness intelligent indication film of Example 1 of the present invention and the starch composite blueberry anthocyanin indication film of Comparative Example 1; wherein the implementation Example 1 indicates that the color of the film is pink, and Comparative Example 1 indicates that the color of the film is light pink. Compared with Comparative Example 1, the color of the indicating film in Example 1 is significantly enhanced.

Figure 2(a) is the color change diagram and UV-visible spectrum of the anthocyanin solution and chondroitin sulfate-anthocyanin mixed solution used in the present invention under pH 2.0-12.0 conditions; Figure 2(b) is the flower color under the same pH conditions Color comparison chart of glycoside solution (left) and chondroitin sulfate-anthocyanin mixed solution (right); the maximum absorption peak of anthocyanin solution under acidic conditions is near the wavelength of 520nm. As the pH increases, the maximum absorption wavelength of anthocyanins increases from 520nm to 520nm. 600nm movement, when the pH is 2.0-3.0, the solution appears pink; when the pH is 4.0-6.0, the redness of the solution gradually decreases to light pink and the color intensity decreases; when the pH is 7.0-9.0, the solution appears gray powder to gray The changing trend and gray intensity increase; when the pH is 10.0, the solution appears dark blue; when the pH is 11.0, the solution appears gray blue; when the pH is 12.0, the solution appears dark gray. The maximum absorption peak of chondroitin sulfate-anthocyanin mixed solution under acidic conditions is near the wavelength of 540nm. As the pH increases, the maximum absorption wavelength of anthocyanins moves from 540nm to 600nm. When the pH is 2.0-3.0, the solution turns purple; the pH is When the pH is 4.0-5.0, the redness of the solution gradually decreases to light pink and the color intensity decreases; when the pH is 6.0-7.0, the solution shows a changing trend from gray to gray; when the pH is 8.0-9.0, the indicator film is gray-blue And the color intensity increases; when the pH is 10.0, the solution is dark blue; when the pH is 11.0, the solution is blue-gray; when the pH is 12.0, the solution is dark gray. Compared with the anthocyanin solution alone, the color of the chondroitin sulfate-anthocyanin mixed solution was significantly enhanced, and the color difference was more obvious under different pH conditions.

Figure 3 is a picture of the chondroitin sulfate-anthocyanin-sensitized food freshness indicator film in Example 1 of the present invention under pH 2-12 conditions respectively; when the pH is 2.0-3.0, the indicator film is purple; when the pH is 4.0-5.0 , the redness of the indicator film gradually decreases to light pink and the color intensity decreases; when the pH is 6.0-7.0, the indicator film shows a changing trend from gray to gray; when the pH is 8.0-9.0, the indicator film appears gray-green and the color intensity decreases Increasingly; when the pH is 10.0, the indicator film appears dark blue; when the pH is 11.0-12.0, the indicator film appears blue-green and the color intensity increases.

Figure 4(a) and (b) are respectively the changes in L, a, and b values (left) of the chondroitin sulfate-anthocyanin-sensitized food freshness indicating film in Example 1 of the present invention under pH 2.0-12.0 conditions. Situation diagram and color difference ΔE value (right) result diagram;

Figure 5(a) and (b) are respectively graphs of the color change of the chondroitin sulfate-anthocyanin-sensitized food freshness indicating film in the application of shrimp spoilage monitoring in Example 1 of the present invention. The left picture shows the color of the indicator film (pink) during monitoring in the initial state, and the right picture shows the color of the indicator film (gray green) after 24 hours of monitoring;

Detailed ways

The following non-limiting examples can enable those of ordinary skill in the art to understand the present invention more comprehensively, but do not limit the present invention in any way.

The test methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials described can be obtained from commercial sources unless otherwise specified.

Example 1

Preparation method of a chondroitin sulfate-starch composite blueberry anthocyanin-sensitized food freshness intelligent indication film:

Dissolve 20 mg of blueberry anthocyanin extract in an acidic ethanol solution (the acidic ethanol solution is composed of 1 mol/L acetic acid and absolute ethanol in a volume ratio of 3:17) to obtain 5 mL of a solution with a concentration of 4 mg/mL. Add 1 mL of blueberry anthocyanin extract solution to 40 mL of chondroitin sulfate solution with a concentration of 4 mg/mL, and stir magnetically for 10 min at a stirring rate of 250 r/min to obtain a chondroitin sulfate-anthocyanin mixed solution. The starch aqueous solution with a concentration of 60 mg/mL was gradually heated to 60°C under magnetic stirring to make the starch reach an incomplete gelatinization state. The magnetic stirring rate was 600 r/min and the stirring time was 30 min to obtain gelatinized potato starch. Mix the chondroitin sulfate-anthocyanin mixed solution and the gelatinized potato starch at a volume ratio of 1:1 to obtain a chondroitin sulfate-anthocyanin-starch mixture. solution. Add glycerin to the above-mentioned chondroitin sulfate-anthocyanin-starch mixed solution according to the volume fraction of 2.5%, and adjust the final pH of the solution to 3.5. Stir magnetically for 30 minutes at a stirring rate of 600 r/min to obtain a film-forming liquid, which is prepared as The final volume of film-forming solution is approximately 80 mL. Pour the film-forming liquid into the film-forming plate, dry it in an oven at 45°C for 12 hours to form a film, and balance it in a desiccator for 6 hours before peeling off the film to obtain a chondroitin sulfate-anthocyanin-sensitized food freshness indicator film. , named it S-CS-BA indicator film.

Comparative example 1

A method for preparing a starch composite blueberry anthocyanin indicating film:

The chondroitin sulfate solution in Example 1 was replaced with distilled water, and the other preparation conditions remained unchanged. Name it S-BA indicator film.

The mechanical properties, water solubility, chromaticity and color difference values of the response indicating films of Example 1 and Comparative Example 1 were tested below, and the results are as follows.

Indicate the mechanical properties of the film: Refer to the method of GB/T 1040.3-2006 "Determination of Tensile Properties of Plastics" to measure the mechanical properties. Cut the film into a long strip of 100mm × 15mm, fix it on an electronic tensile testing machine, and measure the tensile strength of the film. Tensile Strength (TS) and Elongation at Break (EB). The initial clamping distance was 80mm, the stretching rate was 250mm/s, and each group of membranes was measured three times. Tensile strength and elongation at break are calculated according to formulas [1] and [2] respectively.

TS＝F/W×d[1]

Among them, TS is the tensile strength, MPa;

F is the maximum tensile force endured by the sample when it breaks, N;

W is the width of the film, mm;

d is the thickness of the film, mm.

EB＝L ₁ /L ₀ ×100[2]

Among them, EB is the elongation at break, %;

L ₁ is the tensile length when the film breaks, mm;

L ₀ is the initial clamping distance, mm.

Water solubility: Place the indicator film in a 105°C oven and bake it to a constant mass W ₁ (g), then soak it in 50mL distilled water. After 24 hours, pour out the soaking solution, place it in a 105°C oven again, bake it to a constant mass and weigh the mass. is W ₂ (g), and each group is measured three times. Calculate water solubility according to the formula: water solubility/100%=W ₁ -W ₂ /W ₁ ×100.

Table 1 Mechanical properties and water solubility measurement results of Example 1 and Comparative Example 1

Note: Different letters in the same column represent significant differences, p<0.05.

It can be seen from Table 1 that the tensile strength and elongation at break of the response indicating film without adding chondroitin sulfate are 1.34MPa and 40.85% respectively. After adding chondroitin sulfate, the tensile strength and elongation at break of the response indicator membrane increased significantly, which were 2.52MPa and 68.91% respectively. The water solubility of the more preferably prepared indicator film of Example 1S-CS-BA in the present invention is lower than that of the indicator film of Comparative Example 1S-BA. This shows that the addition of chondroitin sulfate will reduce the water solubility of the indicator film to a certain extent and promote the water solubility of the composite film. In summary, compared with a single starch-based film, the addition of chondroitin sulfate improves the mechanical properties and water solubility of the film, and improves the physical properties of the indicating film.

Measurement of chromaticity value and total color difference: Compare the chromaticity value and total color difference ΔE of the composite films of Example 1 and Comparative Example 1 and record the phenomena and data. Use L, a and b values to evaluate film color. Use the standard white plate as the color difference reference and measure on the surface of the white standard plate (L ₀ =97.16, a ₀ =-0.12, b ₀ =0.79). The total color difference value ΔE is calculated according to the formula.

Table 2 Chromaticity and color difference measurement results of Example 1 and Comparative Example 1

Note: Different letters in the same column represent significant differences, p<0.05.

Table 2 shows the images of the indicator films of Example 1 and Comparative Example 1. The parameters L, a, b and ΔE were measured. It can be seen from the images and parameters that the addition of chondroitin sulfate has a strong impact on the film color. Example 1 is pink in color, Comparative Example 1 is light pink in color, and the a, b, and ΔE values show significant differences (p<0.01). After adding chondroitin sulfate, the color of the indicator film is significantly enhanced. This is due to the co-coloring effect of chondroitin sulfate and anthocyanins, which strengthens the color of anthocyanins and improves their chemical stability, making the visual presentation of the indicator film better after film formation. More intense, easy to observe its color status, providing a good foundation for subsequent color development applications.

In summary, comparing Example 1 with Comparative Example 1, Example 1 shows advantages in terms of mechanical properties, water solubility, color development of the indicator film, etc. Therefore, application research and characterization of Example 1 (S-CS-BA indicating film) was carried out.

The S-CS-BA membrane was soaked in buffer solutions with different pH values (pH 2.0-12.0) to evaluate the color responsiveness of the S-CS-BA membrane. The parameters L, a, b and ΔE and the color changes are shown in Table 3.

Table 3 Measurement results of chromaticity, color difference and color change of Example 1 (S-CS-BA indicator film)

Note: Different letters in the same column represent significant differences, p<0.05.

When the pH is 2.0-3.0, the indicating film S-CS-BA is purple-red; as the pH increases to 4.0-5.0, the redness of the indicating film S-CS-BA gradually decreases and turns to light pink and the color intensity Decreasingly; when the pH is close to neutral, that is, 6.0-7.0, the indicating film S-CS-BA shows a changing trend from gray to gray; when the pH value continues to increase to 8.0-9.0, the indicating film S-CS-BA appears gray Green and the color intensity increases; when the pH is 10.0, the indicator film S-CS-BA appears dark blue; when the pH value reaches the range of 11.0-12.0, the indicator film S-CS-BA gradually turns blue-green and the color intensity increases. The indicator film S-CS-BA showed clear changes in different colors in the pH range of 2.0-12.0. However, the pH range of product deterioration caused by microbial spoilage of most animal product proteins is roughly between 6.0 and 8.0. Within this pH range, the color of the indicator film S-CS-BA changes significantly and is easy to distinguish with the naked eye.

Application of a chondroitin sulfate-anthocyanin-sensitized food freshness indication film:

The present invention applies the prepared indicator film to monitor the freshness of packaged shrimp. The pH, volatile base nitrogen content and total bacterial colony count are measured in accordance with GB 5009.237-2016 "Determination of Food pH Value" and GB 5009.228-2016 "Food" respectively. "Determination of Medium Volatile Base Nitrogen" and GB 4789.2-2016 "Determination of the total number of bacterial colonies in food microbiology inspection" operation requirements are measured. The measurement results and the color changes and color difference values of the indicator film are shown in Table 4.

Table 4 Deterioration monitoring indicators and indicator film color change measurement results of shrimp

Note: Different letters in the same column represent significant differences, p<0.05.

The results showed that the initial color of the indicator film was pink. After 24 hours of storage at 4°C, the color of the indicator film changed from pink to gray-green. At the same time, the pH, volatile base nitrogen and total bacterial colony count of the shrimp were monitored. The initial volatile base nitrogen content of shrimp is 10.97mg/100g. According to GB 2733-2015 "Fresh and Frozen Animal Aquatic Products", the volatile base nitrogen value in fresh fish and shrimp should be less than 20mg/100g before it is edible. The indicator film appears pink. When the storage time reaches 24 hours, the volatile base nitrogen content of the shrimp reaches 23.10 mg/100g, the pH value of the shrimp is 7.42, and the total number of bacterial colonies is 4.08 (lg (CFU/g)), indicating that the shrimp is no longer edible, and the indicator film displays The color is gray-green, and the ΔE value is 12.14. The color of the indicator film changes significantly compared with that of the shrimp when it is fresh. The change in color of the indicator film can be directly observed with the naked eye.

The deterioration pH range of most high-protein and high-fat products is concentrated in 6.0-8.0. Comparison between Example 1 and Comparative Example 1 in the present invention shows that after the addition of chondroitin sulfate, the preferred S-CS-BA indicator membrane has The color is obvious within the range and is easy to distinguish with the naked eye. Therefore, the color change of the indicator film can be used to visually monitor and warn manufacturers and consumers of the occurrence of food spoilage in real time, in order to provide a reference for the application of natural anthocyanin indicator films in food shelf life monitoring.

Claims (7)

1. A preparation method of a chondroitin sulfate-anthocyanin sensitized food freshness indicator film is characterized by comprising the following steps of: uniformly mixing the blueberry anthocyanin extract solution with the chondroitin sulfate aqueous solution to obtain a chondroitin sulfate-anthocyanin mixed solution; adding the gelatinized starch into the chondroitin sulfate-anthocyanin mixed solution, and magnetically stirring to obtain a chondroitin sulfate-anthocyanin-starch mixed solution; adding a certain amount of glycerol into the obtained mixed solution, adjusting the pH value of the solution to 3.5, and then continuing magnetic stirring for a period of time to obtain a film forming solution; drying and forming a film by using a film forming liquid to obtain the film;

the blueberry anthocyanin extract solution is an acidic ethanol solution of blueberry anthocyanin extract, and the concentration of the anthocyanin extract solution is 1-4 mg/mL; the acidic ethanol solution consists of acetic acid with the volume ratio of 1mol/L and absolute ethanol of 3:17;

the concentration of the chondroitin sulfate aqueous solution is 2-6 mg/mL, and the mass ratio of the blueberry anthocyanin extract to the chondroitin sulfate is 1:20 to 60.

2. The method according to claim 1, characterized in that: the starch is potato starch, and the gelatinized starch is prepared by the following steps: gradually heating up the starch solution with the concentration of 50-70 mg/mL to a state that the starch is not completely gelatinized under magnetic stirring, wherein the magnetic stirring speed is 500-800 r/min, and the stirring time is 20-40 min.

3. The method according to claim 1, characterized in that: the mass ratio of the starch to the chondroitin sulfate is 10-30:1.

4. The method according to claim 1, characterized in that: the magnetic stirring speed is 500-800 r/min, and the stirring time is 20-40 min.

5. The method according to claim 1, characterized in that: casting the obtained film into a film forming plate, and placing the film forming plate in a blast drying box for drying to form a film, wherein the drying temperature is 40-45 ℃ and the drying time is 12-24 h.

6. The method according to claim 1, characterized in that: the pH of the chondroitin sulfate-anthocyanin-starch mixed solution was adjusted to 3.5 using either 0.1mol/L HCl solution or 0.1mol/LNaOH solution.

7. The method according to claim 1, characterized in that: the addition amount of the glycerol is 1% -3% of the total volume of the film forming liquid.