Preparation method of activated pectin-agar composite film loaded with ginger essential oil nanoemulsion and Pickering emulsion

Abstract

The invention discloses a preparation method of an activated pectin-agar composite film loaded with ginger essential oil nanoemulsion and Pickering emulsion. The preparation method comprises the following steps: (1) preparing the ginger essential oil loaded nanoemulsion; (2) preparing a Pickering emulsion loaded with ginger essential oil; and (3) adding the two emulsions into the pectin-agar mixed solution, stirring to form a film-forming solution, casting the film-forming solution into a plastic culture dish, and drying to obtain the pectin-agar composite film. According to the pectin-agar composite film disclosed by the invention, by adding the ginger essential oil, the barrier property of ultraviolet light / visible light is remarkably improved, so that the pectin-agar composite film can be used for packaging easily-oxidized food, has a filtering effect on ultraviolet light, and is beneficial to reducing oxidative deterioration of the food due to ultraviolet irradiation when the film is used for preserving the food; meanwhile, the pectin-agar composite film has excellent antioxidant activity, and in addition, the pectin-agar composite film has a relatively good antibacterial effect on staphylococcus aureus and is suitable for packaging meat, eggs, fishes and other products.

Description

Technical Field

[0001] The invention relates to the technical field of food fresh-keeping packaging, and in particular to a method for preparing a pectin-agar composite film loaded with a ginger essential oil nanoemulsion and activated by a Pickering emulsion. Background Art

[0002] In recent years, microbial contamination has been a serious food safety issue and may lead to various foodborne diseases. Food packaging is an important barrier to prevent microbial contamination of food. During food processing and packaging, a small amount of planktonic bacteria will inevitably be introduced. These bacteria will grow rapidly into biofilms under nutrient-rich conditions and are difficult to eliminate. Therefore, developing an antibacterial food packaging film material that can prevent the attachment of planktonic bacteria is an effective means to avoid the formation of biofilms.

[0003] Common antibacterial packaging materials are mainly divided into polymers with antibacterial properties, functionalized antibacterial polymers and antibacterial polymer composite materials. For the first two types of antibacterial food packaging materials, the antibacterial time is short because the antibacterial materials are in direct contact with food to sterilize. The third type of antibacterial packaging material can be developed by doping nanomaterials to achieve sustainable release antibacterial composite packaging materials. However, as the importance of food packaging material safety continues to rise, the market demand for food packaging continues to increase, and the antibacterial function alone is no longer sufficient. It is hoped that the packaging material can have antioxidant activity, etc. to ensure the quality of food during the shelf life. Therefore, it is necessary to modify the existing technology.

[0004] Existing studies have shown that the main chemical components of ginger essential oil in plant essential oils are sesquiterpenes, mainly α-zingiberene, α-curcumene, γ-ylang-ylangene, β-bisabolene, γ-bisabolene, and β-sesquiterpenes, which have antioxidant, antibacterial, anti-inflammatory, and analgesic effects. However, there are currently no reports on food packaging films activated by ginger essential oil that have both anti-ultraviolet properties, antioxidant activity, and antibacterial effects. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and provide a method for preparing a pectin-agar composite film loaded with a ginger essential oil nanoemulsion and activated by a Pickering emulsion.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is:

[0007] A method for preparing a pectin-agar composite film loaded with a ginger essential oil nanoemulsion and activated by a Pickering emulsion comprises the following steps:

[0008] (1) preparing ginger essential oil loaded nanoemulsion (NE);

[0009] (2) preparing Pickering emulsion (PE) loaded with ginger essential oil;

[0010] (3) adding the ginger essential oil loaded nanoemulsion (NE) and the ginger essential oil loaded Pickering emulsion (PE) to a pectin-agar mixed solution and stirring to form a mixed nanocarrier, adding glycerol to the obtained mixed nanocarrier and continuing to stir and mix to form a film-forming solution, casting the film-forming solution on a plastic culture dish and drying to obtain a pectin-agar composite film activated by the ginger essential oil loaded nanoemulsion and the Pickering emulsion;

[0011] The specific operation method for preparing the ginger essential oil-loaded nanoemulsion described in step (1) is as follows: ginger essential oil (GEO) and Tween-80 (Tween 80) are gradually added to distilled water under high-speed stirring to prepare a crude emulsion; the obtained crude emulsion is subjected to ultrasonic emulsification treatment to convert it into a ginger essential oil-loaded nanoemulsion (NE);

[0012] The specific operation method for preparing the Pickering emulsion loaded with ginger essential oil described in step (2) is as follows: whey protein (WPI) and inulin are added to distilled water to prepare a biopolymer suspension; the obtained biopolymer suspension is dispersed at high speed to obtain a biopolymer dispersion; ginger essential oil (GEO) is slowly added to the obtained biopolymer dispersion under high-speed stirring to obtain a pre-emulsion; the obtained pre-emulsion is ultrasonically emulsified to be converted into a Pickering emulsion (PE) loaded with ginger essential oil.

[0013] Furthermore, in the step 1, the mass fraction of ginger essential oil (GEO) is 4%, and Tween 80 (Tween 80) and ginger essential oil (GEO) are mixed in a mass ratio of 10:3.

[0014] Furthermore, the speed of the high-speed stirring in step 1 is 3000 rpm, and the speed of the high-speed stirring in step 2 is 5000 rpm.

[0015] Furthermore, the ultrasonic emulsification treatment is specifically performed by immersing an instrument probe of an ultrasonic cell disruptor with a diameter of 15 mm into the treated emulsion for ultrasonic treatment, and the operating conditions of the ultrasonic cell disruptor are a frequency of 20 kHz and a power of 200 W.

[0016] Furthermore, the ultrasonic emulsification time in step 1 is 15 minutes, and the ultrasonic emulsification time in step 2 is 20 minutes.

[0017] Furthermore, in step 2, the mass fraction of whey protein (WPI) is 2%, the mass fraction of inulin is 2%, the mass fraction of ginger essential oil (GEO) is 4%, and the core-coating ratio of the pre-emulsion is 1:4.

[0018] Furthermore, the instrument used for the high-speed dispersion treatment in step 2 is an IKA T18 basic high-speed homogenizer, the speed of the high-speed homogenizer is 10000 rpm, and the high-speed dispersion treatment time is 5-10 min.

[0019] Furthermore, in step 3, the mass ratio of pectin to agar is 9:1, and the mass ratio of glycerol to the pectin-agar mixed solution is 1:5.

[0020] Furthermore, the preparation method of agar in step 3 is as follows: fresh agaraman is dried, ground into powder, passed through an 80-100 mesh sieve, and added with anhydrous ethanol at a ratio of 1g:10-20mL for soaking for 28-36h; the agaraman soaked in anhydrous ethanol is naturally air-dried after removing the ethanol, and extracted by hot water reflux method (the material-liquid ratio is 1:60-1:70, the reflux temperature is 95-100°C, and the extraction time is 150-180min); the extract obtained by hot water reflux extraction is cooled to room temperature, the pH is adjusted to 4.4-5.4, and acid hydrolyzed at 50°C for 1-1.5h, so that the molecular weight of agaraman is controlled at 1.2×10 6 ~1.8×10 6 g / mol; the temperature of the solution after acid hydrolysis is reduced to -18--20°C within 240-300 minutes and maintained for more than 24 hours; the solution after low-temperature treatment is re-dissolved at room temperature, centrifuged, and the lower layer of jelly is taken out; the jelly is quickly frozen with liquid nitrogen, and vacuum freeze-dried to obtain agar.

[0021] Furthermore, in step 3, the stirring time of the NE, PE and pectin-agar mixed solution is 15 minutes, the drying temperature of the film-forming solution is 35-45° C., and the drying time is 48 hours.

[0022] Compared with the prior art, the present invention adds ginger essential oil-loaded nanoemulsion (NE) and ginger essential oil-loaded Pickering emulsion (PE) to a pectin-agar mixed solution to prepare a pectin-agar composite film activated by ginger essential oil (GEO) stabilized by the nanoemulsion (NE) and the Pickering emulsion (PE). Compared with the pectin-agar composite film without a nanocarrier loaded with GEO, the present invention has the following specific advantages:

[0023] (1) The pectin-agar composite film of the present invention significantly improves the UV / visible light barrier performance by adding GEO, so that it can be used as a packaging for easily oxidized foods, such as fresh meat products, etc., and has a filtering effect on ultraviolet rays, which helps the film to reduce the exposure of foods to ultraviolet light and thus oxidation and deterioration when preserving foods.

[0024] (2) The pectin-agar composite film of the present invention has good oxygen permeability, and the effect is obvious at a specific NE or PE concentration, which helps the film to reduce oxygen oxidation of food when preserving food, improve food quality and extend its shelf life. The overall transparency is low, and it is suitable for food packaging where the contents of the package do not need to be visible.

[0025] (3) The pectin-agar composite film of the present invention has the same excellent antioxidant activity as the pectin-agar composite film without the nanocarrier loaded with GEO. As the content of the nanoemulsion loaded with ginger essential oil or the Pickering emulsion loaded with ginger essential oil increases, the antioxidant activity of the film gradually increases and then decreases. This is attributed to the presence of sesquiterpenes in ginger essential oil, including α-gingerene, α-curcumene, γ-ylang-ylang, β-bisabolene, γ-bisabolene, β-sesquiphellandrene, etc., which have good free radical scavenging ability.

[0026] (4) The pectin-agar composite film of the nanoemulsion loaded with ginger essential oil or the Pickering emulsion loaded with ginger essential oil of the present invention has a good antibacterial effect on Staphylococcus aureus and is suitable for packaging of meat, eggs, fish and other products. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The ultraviolet light blocking properties of the film samples with different ginger essential oil contents prepared by the present invention within 280nm ultraviolet light.

[0028] Figure 2 The transmittance of the film samples with different ginger essential oil contents prepared in the present invention within the visible light of 660nm.

[0029] Figure 3 The antioxidant activity of the film samples with different ginger essential oil contents prepared in the present invention.

[0030] Figure 4 The transmittance variation results of the film samples with different ginger essential oil contents prepared by the present invention within the visible-ultraviolet wavelength range of 200-800nm.

[0031] Figure 5 The film discs are film discs showing the experimental results after the antibacterial activity of the film samples with different ginger essential oil contents prepared by the present invention is measured. DETAILED DESCRIPTION

[0032] In order to further understand the present invention, the present invention is described below in conjunction with embodiments. These descriptions are only to further explain the features and advantages of the present invention and are not intended to limit the claims of the present invention.

[0033] The present invention discloses a method for preparing a pectin-agar composite film loaded with a ginger essential oil nanoemulsion and activated by a Pickering emulsion, comprising the following steps:

[0034] (1) GEO (mass fraction 4%) and Tween 80 were gradually added to distilled water at a mass ratio of 10:3 under high-speed stirring at 3000 rpm to obtain a crude emulsion; an ultrasonic cell disruptor probe was immersed into the crude emulsion at a depth of 25 mm and ultrasonicated for 15 min under the conditions of 20 kHz and 200 W to convert the crude emulsion into a ginger essential oil-loaded nanoemulsion (NE);

[0035] (2) whey protein (mass fraction 2%) and inulin (mass fraction 2%) were added to distilled water in a mass ratio of 1:1 to prepare a biopolymer suspension, and the biopolymer suspension was dispersed at 10000 rpm for 5-10 min using an IKA T18 basic high-speed homogenizer to ensure that a fully saturated biopolymer dispersion was obtained; GEO (mass fraction 4%) was slowly added to the biopolymer dispersion under high-speed stirring at 5000 rpm to obtain a pre-emulsion with a core-coating ratio of 1:4; an ultrasonic cell disruptor probe was immersed in the pre-emulsion and ultrasonicated for 20 min at 20 kHz and 200 W to convert the pre-emulsion into a Pickering emulsion (PE) loaded with ginger essential oil;

[0036] (3) A mixture of pectin and agar (wherein the mass ratio is 9:1) is dispersed in 100 mL of distilled water and completely hydrated by magnetic stirring at room temperature. After the pectin and agar are completely dissolved, the above-mentioned ginger essential oil-loaded nanoemulsion (NE) and ginger essential oil-loaded Pickering emulsion (PE) are added to the pectin-agar mixed solution and stirred to form a mixed nanocarrier. The amount of addition should keep the concentration of GEO constant. After the nanocarrier is completely mixed by stirring for 15 minutes, glycerol (the mass ratio of glycerol to pectin is 1:5) is added as a plasticizer and mixed with a magnetic stirrer. The film-forming solution is cast on a plastic culture dish (side length 10 cm) and dried at 40±5°C for 48 hours to obtain a pectin-agar composite film activated by the ginger essential oil-loaded nanoemulsion and the Pickering emulsion.

[0037] The preparation method of agar is as follows: fresh agar is dried and ground into powder, passed through an 80-100 mesh sieve, and anhydrous ethanol is added in a ratio of 1 g: 10-20 mL to soak for 28-36 hours; the agar soaked in anhydrous ethanol is naturally air-dried after removing the ethanol, and extracted by hot water reflux method (the material-liquid ratio is 1:60-1:70, the reflux temperature is 95-100° C., and the extraction time is 150-180 minutes); the extract obtained by hot water reflux extraction is cooled to room temperature, the pH is adjusted to 4.4-5.4, and acid hydrolyzed at 50° C. for 1-1.5 hours, so that the molecular weight of agar is controlled at 1.2×10 6 ~1.8×10 6 g / mol; the temperature of the solution after acid hydrolysis is reduced to -18--20°C within 240-300 minutes and maintained for more than 24 hours; the solution after low-temperature treatment is re-dissolved at room temperature, centrifuged, and the lower layer of jelly is taken out; the jelly is quickly frozen with liquid nitrogen, and vacuum freeze-dried to obtain agar.

[0038] The main chemical components of ginger essential oil are sesquiterpenes, mainly α-Zingiberene (37.49%), α-Curcumene (9.57%), γ-Muurolene (9.79%), β-Bisabolene (8.34%), γ-bisabolene (1.05%), and β-sesquiphellandrene (14.56%). The remaining components are mainly some oxidized sesquiterpenes, monoterpenes, and oxidized monoterpenes. GEO is rich in sesquiterpenes, such as the more typical α-Zingiberene, β-sesquiphellandrene, and camphene. In addition, some monoterpenes are the main aroma substances of ginger, including geraniol and cynamol. GEO has antioxidant, antibacterial, anti-inflammatory, and analgesic effects.

[0039] Preparation process of pectin-agar composite film without GEO loading: disperse the mixture of pectin and agar (mass ratio of 9:1) in 100 mL of distilled water and completely hydrate by magnetic stirring at room temperature. After the pectin and agar are completely dissolved, the nanocarriers are completely mixed by stirring for 15 minutes, and glycerol (the mass ratio of glycerol to pectin-agar mixture is 1:5) is added as a plasticizer and mixed with a magnetic stirrer. The film-forming solution is cast on a plastic culture dish (side length of 10 cm) and dried at 40±5°C for 48 hours to obtain a pectin-agar composite film without GEO loading.

[0040] Example 1

[0041] 0.75 g GEO and 0.225 g Tween 80 were gradually added to 17.775 g distilled water under high-speed stirring at 3000 rpm to obtain a crude emulsion. The ultrasonic cell disruptor probe was immersed into the crude emulsion at a depth of 25 mm and ultrasonicated for 15 min under the conditions of 20 kHz and 200 W to convert the crude emulsion into 18.75 g ginger essential oil-loaded nanoemulsion.

[0042] A mixture of 3 g of pectin and agar (with a mass ratio of 9:1) was dispersed in 100 g of distilled water and completely hydrated by magnetic stirring at room temperature. After the pectin and agar were completely dissolved, the above-mentioned 18.75 g of the nanoemulsion loaded with ginger essential oil was added to the pectin-agar mixed solution and stirred to form a mixed nanocarrier. The amount added should keep the concentration of GEO constant (25% of pectin and agar). After the nanocarrier was completely mixed by stirring for 15 minutes, 0.6 g of glycerol was added as a plasticizer and mixed with a magnetic stirrer. 50 ml of the film-forming solution was cast on a plastic culture dish (side length 10 cm) and dried at 35°C for 48 hours to obtain a 25NE film sample.

[0043] Embodiment 2:

[0044] 1.5 g GEO and 0.45 g Tween 80 were gradually added to 35.55 g distilled water under high-speed stirring at 3000 rpm to obtain a crude emulsion. The ultrasonic cell disruptor probe was immersed into the crude emulsion at a depth of 25 mm and ultrasonicated for 15 min under the conditions of 20 kHz and 200 W to convert the crude emulsion into 37.5 g ginger essential oil-loaded nanoemulsion.

[0045] A mixture of 3 g of pectin and agar (with a mass ratio of 9:1) was dispersed in 100 g of distilled water and completely hydrated by magnetic stirring at room temperature. After the pectin and agar were completely dissolved, the above 37.5 g of the nanoemulsion loaded with ginger essential oil was added to the pectin-agar mixed solution and stirred to form a mixed nanocarrier. The amount added should keep the concentration of GEO constant (50% of pectin and agar). After the nanocarrier was completely mixed by stirring for 15 minutes, 0.6 g of glycerol was added as a plasticizer and mixed with a magnetic stirrer. 50 ml of the film-forming solution was cast on a plastic culture dish (side length 10 cm) and dried at 40°C for 48 hours to obtain a 50NE film sample.

[0046] Example 3

[0047] 2.25 g GEO and 0.675 g Tween 80 were gradually added to 53.325 g distilled water under high-speed stirring at 3000 rpm to obtain a crude emulsion. The ultrasonic cell disruptor probe was immersed into the crude emulsion at a depth of 25 mm and ultrasonicated for 15 min under the conditions of 20 kHz and 200 W to convert the crude emulsion into 56.25 g ginger essential oil-loaded nanoemulsion.

[0048] A mixture of 3 g of pectin and agar (with a mass ratio of 9:1) was dispersed in 100 g of distilled water and completely hydrated by magnetic stirring at room temperature. After the pectin and agar were completely dissolved, the above-mentioned 56.25 g of the ginger essential oil-loaded nanoemulsion was added to the pectin-agar mixed solution and stirred to form a mixed nanocarrier. The amount added should keep the concentration of GEO constant (75% of pectin and agar). After the nanocarrier was completely mixed by stirring for 15 minutes, 0.6 g of glycerol was added as a plasticizer and mixed with a magnetic stirrer. 50 ml of the film-forming solution was cast on a plastic culture dish (side length 10 cm) and dried at 45°C for 48 hours to obtain a 75NE film sample.

[0049] Example 4

[0050] 0.375 g of whey protein and 0.375 g of inulin were added to 17.25 distilled water to prepare 18 g of biopolymer suspension, and the 18 g of biopolymer suspension was dispersed at 10000 rpm with an IKA T18 basic high-speed homogenizer for 5-10 min to ensure that a fully saturated 18 g of biopolymer dispersion was obtained; 0.75 g of GEO was slowly added to the 18 g of biopolymer dispersion under high-speed stirring at 5000 rpm to obtain 18.75 g of pre-emulsion with a core-coating ratio of 1:4; an ultrasonic cell disruptor probe was immersed in the pre-emulsion and ultrasonicated for 20 min under 20 kHz and 200 W conditions to convert the pre-emulsion into 18.75 g of Pickering emulsion loaded with ginger essential oil;

[0051] A mixture of 3 g of pectin and agar (with a mass ratio of 9:1) was dispersed in 100 g of distilled water and completely hydrated by magnetic stirring at room temperature. After the pectin and agar were completely dissolved, the above-mentioned 18.75 g of Pickering emulsion loaded with ginger essential oil was added to the pectin-agar mixed solution and stirred to form a mixed nanocarrier. The added amount should keep the concentration of GEO constant (25% of pectin and agar). After the nanocarrier was completely mixed by stirring for 15 minutes, 0.6 g of glycerol was added as a plasticizer and mixed with a magnetic stirrer. 50 ml of the film-forming solution was cast on a plastic culture dish (side length 10 cm) and dried at 35°C for 48 hours to obtain a 25PE film sample.

[0052] Example 5

[0053] 0.75 g of whey protein and 0.75 g of inulin were added to 34.5 g of distilled water to prepare 36 g of biopolymer suspension, and the 36 g of biopolymer suspension was dispersed at 10000 rpm with an IKA T18 basic high-speed homogenizer for 5-10 min to ensure that a fully saturated 36 g of biopolymer dispersion was obtained; 1.5 g of GEO was slowly added to the 36 g of biopolymer dispersion under high-speed stirring at 5000 rpm to obtain 37.5 g of pre-emulsion with a core-coating ratio of 1:4; an ultrasonic cell disruptor probe was immersed in the pre-emulsion and ultrasonicated for 20 min under 20 kHz and 200 W conditions to convert the pre-emulsion into 37.5 g of Pickering emulsion loaded with ginger essential oil;

[0054] A mixture of 3 g of pectin and agar (with a mass ratio of 9:1) was dispersed in 100 g of distilled water and completely hydrated by magnetic stirring at room temperature. After the pectin and agar were completely dissolved, the above 37.5 g of Pickering emulsion loaded with ginger essential oil was added to the pectin-agar mixed solution and stirred to form a mixed nanocarrier. The added amount should keep the concentration of GEO constant (50% of pectin and agar). After the nanocarrier was completely mixed by stirring for 15 minutes, 0.6 g of glycerol was added as a plasticizer and mixed with a magnetic stirrer. 50 ml of the film-forming solution was cast on a plastic culture dish (side length 10 cm) and dried at 40°C for 48 hours to obtain a 50PE film sample.

[0055] Example 6

[0056] 1.125 g of whey protein and 1.125 g of inulin were added to 51.75 g of distilled water to prepare 54 g of biopolymer suspension, and the 54 g of biopolymer suspension was dispersed at 10000 rpm with an IKA T18 basic high-speed homogenizer for 5-10 min to ensure that a fully saturated 54 g of biopolymer dispersion was obtained; 2.25 g of GEO was slowly added to the 54 g of biopolymer dispersion under high-speed stirring at 5000 rpm to obtain 56.25 g of pre-emulsion with a core-coating ratio of 1:4; an ultrasonic cell disruptor probe was immersed in the pre-emulsion and ultrasonicated for 20 min at 20 kHz and 200 W to convert the pre-emulsion into 56.25 g of Pickering emulsion loaded with ginger essential oil;

[0057] A mixture of 3 g of pectin and agar (with a mass ratio of 9:1) was dispersed in 100 g of distilled water and completely hydrated by magnetic stirring at room temperature. After the pectin and agar were completely dissolved, 56.25 g of the Pickering emulsion loaded with ginger essential oil was added to the pectin-agar mixed solution and stirred to form a mixed nanocarrier. The amount added should keep the concentration of GEO constant (75% of pectin and agar). After the nanocarrier was completely mixed by stirring for 15 minutes, 0.6 g of glycerol was added as a plasticizer and mixed with a magnetic stirrer. 50 mL of the film-forming solution was cast on a plastic culture dish (side length 10 cm) and dried at 45°C for 48 hours to obtain a 75PE film sample.

[0058] Comparative Example 1

[0059] A mixture of 3 g of pectin and agar (with a mass ratio of 9:1) was dispersed in 100 g of distilled water and completely hydrated by magnetic stirring at room temperature. After the pectin and agar were completely dissolved, the nanocarriers were completely mixed by stirring for 15 minutes, 0.6 g of glycerol was added as a plasticizer, and mixed with a magnetic stirrer. The film-forming solution was cast on a plastic culture dish (side length of 10 cm) and dried at 40°C for 48 hours to obtain a pectin-agar composite film sample.

[0060] (1) Color measurement

[0061] The surface color of the film was measured using a JZ-350 colorimeter using light source D65 and an observation angle of 10°, with a white standard color plate (L*=95.94, a*=2.16, b*=0.17) as the standard background for color measurement. The colors of all the above film samples (film samples prepared in Examples 1 to 6 and Comparative Example 1) were evaluated as Hunter-L (brightness), a (-a / green to +a / red), and b (-b / blue to +b / yellow) values. The total color difference (ΔE) was calculated according to the following formula, where ΔL, Δa, and Δb are the differences between the color values ​​of the standard color plate and the film sample, respectively. At least 10 positions were randomly selected for each film sample to measure and record the color parameters, and each film sample was repeated 3 times, and the average value was taken to obtain the results in Table 1.

[0062]

[0063] Table 1 Color parameters of different pectin-agar composite films

[0064]

[0065]

[0066] From the results in Table 1, we can see that the L values ​​of all film samples are between 33.67 and 42.64, indicating that the transparency of the film is generally low, which is consistent with the measured T 660 The results are consistent, indicating that the prepared film is suitable for food packaging where the contents of the package do not need to be visible.

[0067] (2) Transmittance and opacity measurement

[0068] The transmittance of the film samples was measured using a UV-vis spectrophotometer in the wavelength range of 200-800 nm. 280 )、660nm(T 660 ) to represent the UV blocking performance and light transmittance of the film sample; at the same time, the opacity of the film sample was calculated according to the following formula. The cuvette without film was used as a blank, and each film sample was measured 3 times. 600nm is the absorbance value at 600nm, L is the film thickness (mm). All readings were repeated 3 times, and the results of the ultraviolet blocking performance and light transmittance of the film samples are as follows Figure 1 and Figure 2 ,The opacity results are shown in Table 2.

[0069]

[0070] Table 2 Opacity of films with different essential oil contents

[0071]

[0072] Depend on Figure 1 , Figure 2 From the results in Table 2, we can see that the pectin-agar film samples with NE and PE added have a filtering effect on ultraviolet rays, which helps the film to reduce the exposure of food to ultraviolet rays and visible light and thus oxidation and deterioration when preserving food.

[0073] (3) Oxygen permeability (OP) measurement

[0074] 3.0g of deoxidizer (reduced iron powder, sodium chloride, activated carbon in the ratio of 0.5g:1.5g:1.0g) was placed in an aluminum round cup, and the cup mouth was sealed with a film sample; the aluminum round cup was placed in a desiccator containing a saturated BaCl2 solution at the bottom at 25°C for 48h. The OP was calculated according to the following formula, and the transparency (OP) results are shown in Table 3.

[0075] Table 3 Oxygen permeability (OP) of different films

[0076]

[0077] From the results in Table 3, we can see that the OP values ​​of the two film samples with NE and PE added are greater than those of the pectin-agar composite film sample, and the effect is obvious at a specific concentration. This may be because the pores generated in the inner film matrix after the addition of GEO become good channels for the diffusion of oxygen molecules. And NE and PE can promote the circulation of oxygen. In comparison, the oxygen permeability of the 75NE film sample is closest to the measured value of the control pectin-agar composite film sample, while the OP values ​​of the other five GEO film samples are all greater than those of the pectin-agar composite film sample, which may be due to the higher volatility of ginger essential oil.

[0078] (4) Antioxidant activity assay

[0079] The antioxidant activity of the film was evaluated by the DPPH free radical scavenging test. First, 1000 mg of each film sample was dissolved in 20 mL of distilled water, and then 10 mL of the film extract was added to 2 mL of DPPH ethanol solution (0.04 g / L). The mixture was vortexed vigorously and kept in a dark room at room temperature for 30 minutes. The absorbance at 517 nm was measured using a UV-visible spectrophotometer with the DDPH ethanol solution as a control. Finally, the DPPH free radical scavenging ability, which is the antioxidant activity, was calculated according to the following formula. The experiment was repeated 3 times for each film sample, and the average value was taken. The results are shown in Figure 3 shown.

[0080]

[0081] Where A0 represents the absorbance value of the control group, and A1 represents the absorbance of the film sample group.

[0082] Depend on Figure 3 The results show that the control pectin-agar composite film sample also showed good antioxidant activity, and its DPPH free radical scavenging rate was 64.93%. The antioxidant activity of the pectin-agar composite film may be attributed to the free radical scavenging ability: the specific functional group components contained in pectin and agar can directly react with free radicals, thereby interrupting the free radical chain reaction and achieving the purpose of scavenging free radicals.

[0083] With the increase of the content of nanoemulsion (NE) loaded with ginger essential oil, the antioxidant activity of the film samples gradually increased and then decreased, with the lowest being 59.30% and the highest being 83.77%, while the Pickering emulsion (PE) also showed the same trend, with the lowest being 67.78% and the highest being 71.04%, both higher than that of the control film. This is attributed to the presence of sesquiterpenes in ginger essential oil, including α-gingerene, α-curcumene, γ-ylang-ylang, β-bisabolene, γ-bisabolene, β-sesquiterpenes, etc., which have good free radical scavenging ability.

[0084] (5) Determination of antibacterial activity

[0085] The growth inhibition effect of the film on Staphylococcus aureus was evaluated according to GB 4789.10-2016 National Food Safety Standard Food Microbiology Inspection Staphylococcus aureus Inspection. The specific operation is as follows:

[0086] ① Activation of bacterial strains: thaw the Staphylococcus aureus culture medium stored in BHI broth, transfer the culture medium (0.1 mL) to 10 mL BHI broth, and culture it in a shake flask incubator at 37°C for 24 h; ② Determination of bacterial liquid concentration: The bacterial liquid concentration was determined by the plate dilution method, and the above culture (0.1 mL) was transferred to 10 mL BHI broth for the second time, and cultured at 37°C for 24 h until the end of the exponential growth phase; the culture concentration at this time was about 10 6 CFU / mL; ③ Agar diffusion method to determine antibacterial activity: Use a puncher to cut the film sample into discs (d = 10mm); then use ultraviolet radiation to sterilize each formula film for 20 to 30 minutes. Take 100μL of the prepared test bacteria suspension and add it to the solid culture medium plate, and evenly spread it with a sterile coating rod; then place the above sterilized film disc on the solid culture medium plate, and then place each plate in a constant temperature incubator to culture the bacteria at 37℃ for 24h. The experimental results are shown in Figure 5 And as shown in Table 4.

[0087] Table 4 Growth inhibition effect of the film on the test bacteria

[0088]

[0089] From Table 4 and Figure 5 It can be seen that the pectin-agar film samples with the addition of NE or PE showed a strong inhibitory effect on Staphylococcus aureus. Since the foods that are easily contaminated by Staphylococcus aureus mainly include meat, eggs, fish and their products, this shows that the pectin-agar film with the addition of NE or PE has good application potential and prospects in the packaging of meat, eggs, fish and other products.

[0090] (6) Measurement of optical properties of thin films

[0091] The transmittance of film samples containing different concentrations of GEO in the wavelength range of 200-800nm ​​was measured using a UV-vis spectrophotometer. The results are as follows: Figure 4 shown.

[0092] Depend on Figure 4The results show that the transmittance of the NE film sample is lower than that of the PE film sample, which indicates that the film sample encapsulated by NE emulsion GEO has better UV blocking performance. The transmittance of the pectin-agar composite film sample (without GEO) in the wavelength range is higher than that of the film containing GEO, because its transmittance is higher (57.8%), and it does not show good barrier performance.

[0093] It can also be found that as the content of NE or PE emulsion increases, the content of GEO increases with it, resulting in a significant decrease in the transmittance of the film samples. In the visible light region (400nm to 800nm), the film samples containing GEO show high barrier properties. The transmittance of the active film gradually decreases with the addition of the emulsion, and shows a dose-dependent decrease. This may be due to the different refractive indices of the dispersed phase and the continuous phase. The dispersed droplets in the film matrix block the passage of light, resulting in an increase in the opacity of the film sample, which is affected by the number of oil droplets in the film sample and the droplet size. Low UV transmittance is a factor in food packaging that limits lipid oxidation in food. These results confirm that the addition of GEO can significantly improve the UV / visible light barrier properties, indicating that they can be used as packaging for easily oxidized foods, such as fresh meat products.

[0094] Summarizing the above test results, the pectin-agar composite film activated by ginger essential oil (GEO) stabilized by nanoemulsion (NE) and Pickering emulsion (PE) has the following advantages:

[0095] (1) The pectin-agar composite film of the present invention has a generally low transparency and is suitable for use in food packaging where the contents of the package do not need to be visible.

[0096] (2) The pectin-agar composite film of the present invention has a filtering effect on ultraviolet rays, which helps to reduce the exposure of food to ultraviolet light and thus oxidation and deterioration when the film is used to preserve food.

[0097] (3) The pectin-agar composite film of the present invention has good oxygen permeability, and the effect is obvious at a specific NE or PE concentration, which helps the film to reduce oxygen oxidation of food when preserving food, improve food quality and extend its shelf life.

[0098] (4) The pectin-agar composite film of the present invention has good antioxidant activity, just like the pectin-agar composite film without the nanocarrier loaded with GEO. As the content of the nanoemulsion loaded with ginger essential oil or the Pickering emulsion loaded with ginger essential oil increases, the antioxidant activity of the film gradually increases. This is attributed to the presence of sesquiterpenes in ginger essential oil, including α-gingerene, α-curcumene, γ-ylang-ylang, β-bisabolene, γ-bisabolene, β-sesquiphellandrene, etc., which have good free radical scavenging ability.

[0099] (5) The pectin-agar composite film of the present invention significantly improves the UV / visible light barrier performance by adding GEO, and has a good antibacterial effect on Staphylococcus aureus, so that it can be used as a packaging for easily oxidized and perishable foods, such as fresh products such as meat, eggs, and fish.

[0100] It is understandable that those skilled in the art can make equivalent substitutions or changes based on the technical solution and inventive concept of the present invention, and all these changes or substitutions should fall within the protection scope of the claims attached to the present invention.

Claims

1. A method for preparing a pectin-agar composite film loaded with a ginger essential oil nanoemulsion and activated by a Pickering emulsion, characterized in that: The following steps are involved: (1) preparing a ginger essential oil-loaded nanoemulsion; (2) preparing a Pickering emulsion loaded with ginger essential oil; (3) adding the ginger essential oil loaded nanoemulsion and the ginger essential oil loaded Pickering emulsion to a pectin-agar mixed solution and stirring to form a mixed nanocarrier, adding glycerol to the obtained mixed nanocarrier and continuing to stir and mix to form a film-forming solution, casting the film-forming solution on a plastic culture dish and drying it to obtain a pectin-agar composite film activated by the ginger essential oil loaded nanoemulsion and the Pickering emulsion; The specific operation method for preparing the nanoemulsion loaded with ginger essential oil in step (1) is as follows: gradually adding ginger essential oil and Tween-80 into distilled water under high-speed stirring to prepare a crude emulsion; ultrasonically emulsifying the obtained crude emulsion to convert it into a nanoemulsion loaded with ginger essential oil; The specific operation method for preparing the Pickering emulsion loaded with ginger essential oil described in step (2) is as follows: whey protein and inulin are added to distilled water to prepare a biopolymer suspension; the obtained biopolymer suspension is dispersed at high speed to obtain a biopolymer dispersion; ginger essential oil is slowly added to the obtained biopolymer dispersion under high-speed stirring to obtain a pre-emulsion; the obtained pre-emulsion is ultrasonically emulsified to convert it into a Pickering emulsion loaded with ginger essential oil.

2. The method for preparing a pectin-agar composite film loaded with ginger essential oil nanoemulsion and Pickering emulsion activation according to claim 1, characterized in that: In the step 1, the mass fraction of the ginger essential oil is 4%, and Tween-80 and the ginger essential oil are mixed in a ratio of 10:

3.

3. The method for preparing a pectin-agar composite film loaded with ginger essential oil nanoemulsion and Pickering emulsion activation according to claim 1, characterized in that: The speed of high-speed stirring in step 1 is 3000 rpm, and the speed of high-speed stirring in step 2 is 5000 rpm.

4. The method for preparing a pectin-agar composite film loaded with ginger essential oil nanoemulsion and Pickering emulsion activation according to claim 1, characterized in that: The specific operation of the ultrasonic emulsification treatment is to immerse the instrument probe of the ultrasonic cell disruptor with a diameter of 15 mm into the treated emulsion, and the operating conditions of the ultrasonic cell disruptor are a frequency of 20 kHz and a power of 200 W.

5. The method for preparing a pectin-agar composite film loaded with ginger essential oil nanoemulsion and Pickering emulsion activation according to claim 1, characterized in that: The ultrasonic emulsification time in step 1 is 15 minutes, and the ultrasonic emulsification time in step 2 is 20 minutes.

6. The method for preparing a pectin-agar composite film loaded with ginger essential oil nanoemulsion and Pickering emulsion activation according to claim 1, characterized in that: In the step 2, the mass fraction of whey protein is 2%, the mass fraction of inulin is 2%, the mass fraction of ginger essential oil is 4%, and the core-coating ratio of the pre-emulsion is 1:

4.

7. The method for preparing a pectin-agar composite film loaded with ginger essential oil nanoemulsion and Pickering emulsion activation according to claim 1, characterized in that: The instrument used for the high-speed dispersion treatment in step 2 is an IKA T18basic high-speed homogenizer, the speed of the high-speed homogenizer is 10000 rpm, and the high-speed dispersion treatment time is 5-10 min.

8. The method for preparing a pectin-agar composite film loaded with ginger essential oil nanoemulsion and Pickering emulsion activation according to claim 1, characterized in that: In step 3, the mass ratio of pectin to agar is 9:1, and the mass ratio of glycerol to the pectin-agar mixed solution is 1:

5.

9. The method for preparing a pectin-agar composite film loaded with ginger essential oil nanoemulsion and Pickering emulsion activation according to claim 1, characterized in that: The preparation method of agar in step 3 is as follows: fresh agaricus is dried, ground into powder, passed through an 80-100 mesh sieve, and added with anhydrous ethanol at a ratio of 1 g: 10-20 mL to soak for 28-36 hours; the agaricus soaked in anhydrous ethanol is naturally air-dried after removing the ethanol, and extracted by hot water reflux method (the material-liquid ratio is 1:60-1:70, the reflux temperature is 95-100° C., and the extraction time is 150-180 min); the extract obtained by hot water reflux extraction is cooled to room temperature, the pH is adjusted to 4.4-5.4, and acid hydrolyzed at 50° C. for 1-1.5 hours, so that the molecular weight of agaric is controlled at 1.2×10 6 ~1.8×10 6 g / mol; the temperature of the solution after acid hydrolysis is reduced to -18--20°C within 240-300 minutes and maintained for more than 24 hours; the solution after low-temperature treatment is re-dissolved at room temperature, centrifuged, and the lower layer of jelly is taken out; the jelly is quickly frozen with liquid nitrogen, and vacuum freeze-dried to obtain agar.

10. The method for preparing a pectin-agar composite film loaded with ginger essential oil nanoemulsion and activated by Pickering emulsion according to claim 1, characterized in that: In the step 3, the stirring time of the ginger essential oil loaded nanoemulsion, the ginger essential oil loaded Pickering emulsion and the pectin-agar mixed solution is 15 minutes, the film-forming solution is dried at a temperature of 35-45° C., and the drying time is 48 hours.

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