Preparation method of pomegranate peel ellagic acid-protein complex emulsion fresh-keeping film

Abstract

The application discloses a preparation method of a Punica granatum L. tannic acid-protein compound emulsion preservative film, and particularly relates to the technical field of preservative films, and the method comprises the following steps: preparing a whey protein-tannic acid nanocomposite through reverse solvent precipitation combined with ultrasonic, and using the whey protein-tannic acid nanocomposite as an emulsifier to prepare a Pickering emulsion coated with oregano essential oil. The Pickering emulsion is introduced into a konjac glucomannan-chitosan quaternary ammonium salt matrix film, so that the mechanical strength and water resistance of the konjac glucomannan-chitosan quaternary ammonium salt matrix film are significantly improved, and the konjac glucomannan-chitosan quaternary ammonium salt matrix film has good ultraviolet light defense performance; the sustained release of the oregano essential oil is realized, the antioxidant and antibacterial performances are significantly improved in cooperation with the tannic acid, the konjac glucomannan-chitosan quaternary ammonium salt matrix film has excellent biodegradability and biosafety; when the addition amount of the emulsion is 6%, the shelf life of strawberries can be prolonged, and excellent effects of maintaining the appearance, hardness and endogenous phenol content of the fruits are achieved.

Description

Technical Field

[0001] This invention relates to the field of food preservation film technology, and in particular to a method for preparing a pomegranate peel ellagic acid-protein complex emulsion food preservation film. Background Technology

[0002] With the rapid development of the food industry, the demand for food preservation packaging materials is increasing daily. Plastic wrap, as a commonly used food preservation material, can effectively block oxygen and moisture, delay food spoilage, and extend shelf life. Currently, most mainstream food preservation films on the market are made of petroleum-based polymers such as polyethylene (PE) and polypropylene (PP). While these materials possess good mechanical and barrier properties, they are difficult to biodegrade, and long-term use will cause serious environmental pollution, which is inconsistent with the trend of green and environmentally friendly development.

[0003] To address the environmental concerns of petroleum-based food preservation films, bio-based food preservation films have become a research hotspot. Natural polysaccharides such as konjac glucomannan and chitosan are widely used in the preparation of bio-based food preservation films due to their wide availability, biodegradability, and good biocompatibility. However, food preservation films prepared from single polysaccharides suffer from poor mechanical properties, insufficient flexibility, and susceptibility to breakage. Furthermore, they lack antibacterial and antioxidant functions, making it difficult to meet the long-term preservation requirements of fresh foods (such as strawberries and other berries). Summary of the Invention

[0004] The main objective of this invention is to provide a method for preparing a pomegranate peel ellagic acid-protein complex emulsion preservation film, which can effectively solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] The preparation method of pomegranate peel ellagic acid-protein complex emulsion preservation film includes the following steps:

[0007] S1: Preparation of ellagic acid-whey protein isolate nanocomposite: Whey protein isolate was dissolved in deionized water, and ellagic acid was dissolved in ethanol solution and stirred until completely dissolved; while magnetically stirring the whey protein isolate solution, the ellagic acid solution was added dropwise and stirring continued. The mixture was subjected to ice bath sonication and then rotary evaporation to remove ethanol. The mixture was then purified by ultrafiltration to obtain ellagic acid-whey protein isolate nanocomposite solution.

[0008] S2: Preparation of Pickering emulsion: Oregano essential oil is mixed with the ellagic acid-whey protein isolate nanocomposite solution obtained in step S1, premixed and homogenized at high speed to obtain oregano essential oil Pickering emulsion;

[0009] S3: Preparation of the filling plastic wrap: Konjac glucomannan and chitosan quaternary ammonium salt are dissolved in deionized water, and the Pickering emulsion and glycerin prepared in step S2 are added. After stirring evenly, the film-forming liquid is dried and peeled off to obtain the Pickering emulsion filling plastic wrap.

[0010] Preferably, in step S1, the mass ratio of whey protein isolate to ellagic acid is (1-10):(0-2), and more preferably 4:1.

[0011] Preferably, in step S1, the ultrasonic treatment power is 400-550W and the treatment time is 8-15min; the ultrafiltration purification uses an ultrafiltration tube with a molecular weight cutoff of 8-12kDa, the centrifugation speed is 3500-4500rpm, the centrifugation time is 12-18min, and the purification process is repeated 2-4 times.

[0012] Preferably, in step S2, the mass ratio of oregano essential oil to ellagic acid-whey protein isolate nanocomposite solution is (0.4-0.8):(8.5-10.5); the premixing time is 8-15 min, the high-speed homogenization speed is 12000-16000 rpm, and the homogenization time is 2-5 min.

[0013] Preferably, in step S3, the mass of both konjac glucomannan and chitosan quaternary ammonium salt is 0.3-0.7g, the volume of deionized water is 80-120mL, and the total volume of film-forming solution is 15-25mL.

[0014] Preferably, in step S3, the amount of Pickering emulsion added is 0%-10% (v / v), preferably 6% (v / v).

[0015] Preferably, in step S3, the amount of glycerol added is 25%-35% (w / w) of the total mass of konjac glucomannan-chitosan quaternary ammonium salt; the stirring time is 1.5-3h, the drying temperature is 35-45℃, and the drying time is 10-15h.

[0016] Preferably, in step S1, ellagic acid is derived from pomegranate peel; the concentration of the whey protein isolate solution is 25-35 g / L; and the ellagic acid ethanol solution is completely dissolved after stirring for 10-18 hours.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The Pickering emulsion-filled food preservation film prepared by this invention combines excellent environmental friendliness and functionality, exhibiting high biodegradability and no cytotoxicity, effectively reducing environmental burden. Its Pickering emulsion is stabilized by an ellagic acid-whey protein isolate complex, significantly improving the film's mechanical strength, flexibility, and water-blocking properties, while also imparting good UV shielding capabilities. The synergistic effect of ellagic acid and oregano essential oil enhances the antibacterial and antioxidant effects, and the emulsion structure enables the continuous release of essential oils, extending the functional shelf life. This food preservation film effectively delays moisture loss, softening, and spoilage of fresh foods (such as strawberries), significantly extending shelf life. With a wide range of controllable process parameters, it is suitable for large-scale production and has significant practical value in the field of food preservation packaging. Detailed Implementation

[0019] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0020] Example 1: A method for preparing a pomegranate peel ellagic acid-protein complex emulsion preservation film, comprising the following steps:

[0021] S1. Preparation of ellagic acid-whey protein isolate nanocomposite: 0.6 g whey protein isolate was dissolved in 20 mL deionized water (concentration 30 g / L), and 0.15 g ellagic acid was dissolved in ethanol solution and magnetically stirred for 12-16 h until completely dissolved; while magnetically stirring the whey protein isolate solution, the ellagic acid solution was added dropwise and stirring was continued for 30 min; the mixture was ultrasonicated in an ice bath at 480 W for 10 min, and the ethanol was removed by rotary evaporation; the composite dispersion was transferred to a 10 kDa ultrafiltration tube, centrifuged at 4000 rpm for 15 min, the filtrate was discarded, and the mixture was resuspended in an equal volume of deionized water. This process was repeated 3 times to obtain an ellagic acid-whey protein isolate nanocomposite solution with a mass ratio of 4:1.

[0022] S2. Preparation of Pickering emulsion: 0.6g of oregano essential oil was mixed with 9.4g of the complex solution obtained in step S1 (mass ratio 0.6:9.4), premixed with magnetic stirring for 10min, and homogenized at high speed of 14000rpm for 3min to obtain oregano essential oil Pickering emulsion.

[0023] S3. Preparation of the filling plastic wrap: Dissolve 0.5g of konjac glucomannan and 0.5g of chitosan quaternary ammonium salt in 100mL of deionized water and stir at room temperature until dissolved; add 3% (v / v) Pickering emulsion and 30% (w / w) glycerol (based on the total mass of polysaccharides) to 20mL of the film-forming solution and stir at room temperature for 2h; take 20g of the film-forming solution and pour it into a 90mm×90mm plastic petri dish, dry at 40℃ for 12h, and peel off to obtain the filling plastic wrap.

[0024] Example 2 differs from Example 1 in that the amount of Pickering emulsion added in step S3 is 6% (v / v), while the remaining steps and parameters are the same as in Example 1.

[0025] Example 3 differs from Example 1 in that the amount of Pickering emulsion added in step S3 is 9% (v / v), while the remaining steps and parameters are the same as in Example 1.

[0026] Example 4 differs from Example 2 in that the amount of ellagic acid added in step S1 is 0.075g, the mass ratio of whey protein isolate to ellagic acid is 8:1, and the remaining steps and parameters are the same as in Example 2.

[0027] The difference between Example 5 and Example 2 is that the amount of ellagic acid added in step S1 is 0.3g, the mass ratio of whey protein isolate to ellagic acid is 2:1, and the remaining steps and parameters are the same as in Example 2.

[0028] Example 6 differs from Example 2 in that the amount of ellagic acid added in step S1 is 0.6g, the mass ratio of whey protein isolate to ellagic acid is 1:1, and the remaining steps and parameters are the same as in Example 2.

[0029] Example 7 differs from Example 2 in that ellagic acid was not added in step S1, and the mass ratio of whey protein isolate to ellagic acid was 8:0. The remaining steps and parameters are the same as in Example 2.

[0030] Comparative Example 1 differs from Example 1 in that Pickering emulsion was not added in step S3, while the remaining steps and parameters are the same as in Example 1.

[0031] Comparative Example 2 differs from Example 3 in that, in step S3, free oregano essential oil of equivalent mass to that in the emulsion of Example 3 was directly added, and the Pickering emulsion was not prepared by coating with ellagic acid-whey protein isolate nanocomposite. The remaining steps and parameters were the same as in Example 3.

[0032] The plastic wraps prepared in Examples 1-7 and Comparative Examples 1-2 were subjected to performance tests.

[0033] Test methods for the performance data of the complex and emulsion: The microstructure was observed by transmission electron microscopy (JEM-2100UHR) and cryo-scanning electron microscopy (SU8010); the average particle size, polydispersity index (PDI) and zeta potential were measured by dynamic light scattering instrument.

[0034] Table 1: Comparison of Performance Data of Complex and Emulsion

[0035]

[0036] As shown in the table above, when the mass ratio of whey protein isolate to ellagic acid is in the range of (1-10):(0-2), the complex of Example 2 (4:1) has the smallest average particle size, the lowest PDI, and the most uniform structure. Although the performance of Examples 4 (8:1) and 5 (2:1) is slightly inferior, they are all better than Examples 7 (8:0) and 6 (1:1), which confirms that the complexes in this ratio range have good emulsification potential, and the core ratio (4:1) has the best effect.

[0037] Test method for mechanical properties of thin films: Tensile strength and elongation at break were determined using a texture analyzer (TA-XTplus). The sample size was 12-18 mm × 25-35 mm, the initial clamping distance was 12-18 mm, and the transverse speed was 25-35 mm / min.

[0038] The folding resistance was assessed by repeatedly folding the film and recording the maximum number of folds without cracks; the surface hardness was measured using a Shore hardness tester.

[0039] Table 2: Comparison of Mechanical Properties of Thin Films

[0040]

[0041] Data shows that, within the range of ultrasonic power 400-550W and homogenization rotation speed 12000-16000rpm, the mechanical properties of all embodiments are significantly better than those of Comparative Example 1 and Comparative Example 2.

[0042] Example 2 (6% emulsion addition, 4:1 mass ratio) showed the best tensile strength and elongation at break. Example 3's performance declined because the emulsion addition was close to the upper limit of the range (10%). Comparative Example 2 had the worst mechanical properties because it did not use the Pickering emulsion stabilization system. This proves that the parameter range can effectively ensure the film structure enhancement effect, and the core parameter combination (6% emulsion + 4:1 mass ratio) performed best.

[0043] Test methods for water resistance and optical properties of thin films: The contact angle of the thin film surface is measured by an optical contact angle meter; the initial weight of the thin film is recorded, and after drying at 110℃ for 24 hours, it is weighed and the moisture content is calculated.

[0044] The dried film was soaked in 20 mL of deionized water for 24 h. The residue was separated, dried, and weighed. The water solubility was calculated.

[0045] According to the formula WVP(10) -11 g·m -1 ·Pa -1 ·s -1The water vapor transmission rate is calculated as (Δm×d) / (A×t×ΔP) (Δm is the increase in mass of the weighing bottle, d is the film thickness, A is the exposed area, t is the measurement time, and ΔP=3169Pa).

[0046] The 200-800 nm range was scanned using a UV-Vis spectrophotometer, and the transmittance at 550 nm and the UV shielding rate at 280 nm were recorded.

[0047] Table 3: Comparison of Water Resistance and Optical Performance Data of Thin Films

[0048]

[0049] Based on the water-blocking data, within the parameter range of drying temperature 35-45℃ and stirring time 1.5-3h, as the emulsion addition amount increased within the range of 0%-10% (v / v), the film contact angle gradually increased, while the moisture content, water solubility, and water vapor transmission rate gradually decreased. Examples 2 and 3 exhibited the best water-blocking performance. Regarding optical performance, the UV shielding rates of all examples were significantly higher than those of the comparative examples. Example 3, with the highest emulsion addition, achieved a UV shielding rate of 86.7%, confirming that this parameter range can effectively control the water-blocking and optical properties of the film, meeting the light-proof and moisture-proof requirements of food packaging.

[0050] Test methods for membrane functional properties: The membrane was immersed in a 10% ethanol solution, and the absorbance at 275 nm was measured periodically at 25°C. The cumulative release rate of oregano essential oil over 7 days was calculated using a standard curve. The free radical scavenging rate was determined using the DPPH method (absorbance at 517 nm) and the ABTS method (absorbance at 734 nm). The diameter of the inhibition zone against Escherichia coli and Staphylococcus aureus was determined by the agar diffusion method, and the inhibition rate was calculated using the bacterial growth curve method.

[0051] Table 4: Comparison of Thin Film Functional Properties Data

[0052]

[0053] Antioxidant tests showed that Example 3 exhibited the highest free radical scavenging rate, which was related to the increased content of ellagic acid and oregano essential oil due to the increased emulsion addition. Although the scavenging rate of Example 2 was slightly lower than that of Example 3, the cumulative release rate of essential oil over 7 days was moderate (52.3%), ensuring a continuous supply of active ingredients during preservation while preventing rapid loss. Regarding antibacterial properties, all examples showed better inhibitory effects against Staphylococcus aureus than against Escherichia coli, and significantly better than Comparative Example 2, confirming that the coating of active ingredients by Pickering emulsion enhances their persistence of action.

[0054] Preservation effect data testing method: Fresh strawberries were sealed with different films, with the unsealed group and the PE film group as controls. After 7 days of storage, the appearance was recorded with a digital camera and the decay rate was calculated; the color difference ΔE was measured using a colorimeter; the initial weight and the weight after storage were weighed and the weight loss rate was calculated; the fruit firmness was measured using a texture analyzer; and the total phenol content (expressed as gallic acid equivalent GEA) was determined by the Folin-Ciocalteu method.

[0055] Table 5: Comparison of Film Preservation Effect Data

[0056]

[0057] The strawberry quality data after 7 days of storage showed that Example 2 (6% emulsion + 4:1 mass ratio) had the lowest weight loss (13.2%), the highest firmness (1.39N), and the best retention of total phenolic content (52.8mgGEA / 100g), with a rot rate of only 8%, significantly better than other groups. All examples effectively delayed strawberry spoilage, with Examples 1-4 showing superior preservation effects, proving that the preservation films prepared within this parameter range all have good preservation performance, and the core parameter combination (6% emulsion + 4:1 mass ratio) has the best effect.

[0058] Biodegradability and safety testing methods: The film was buried in outdoor soil (10 cm deep), with PE film as a control. The degradation was recorded over 15 days, and the degradation rate was calculated. The MTT assay was used to co-incubate IEC-6 intestinal epithelial cells and RAW264.7 macrophages with 10 μg / mL film samples for 24 h. The absorbance at 570 nm was measured, cell viability was calculated, and biosafety was assessed.

[0059] Table 6: Comparison of Biodegradability and Safety Data

[0060]

[0061] Biodegradability tests showed that all examples and comparative examples exhibited a degradation rate exceeding 88% after 15 days, with Example 2 showing the highest degradation rate (95%). The PE film, however, showed almost no degradation, demonstrating good environmental friendliness. Regarding biosafety, all samples maintained the viability of both cell types above 89% at a concentration of 10 μg / mL, meeting Level 1 biosafety standards and exhibiting no cytotoxicity, thus satisfying the safety requirements for food packaging materials.

[0062] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a pomegranate peel ellagic acid-protein complex emulsion preservation film, characterized in that, Includes the following steps: S1: Preparation of ellagic acid-whey protein isolate nanocomposite: Whey protein isolate was dissolved in deionized water, and ellagic acid was dissolved in ethanol solution and stirred until completely dissolved; while magnetically stirring the whey protein isolate solution, the ellagic acid solution was added dropwise and stirring continued. The mixture was subjected to ice bath sonication and then rotary evaporation to remove ethanol. The mixture was then purified by ultrafiltration to obtain ellagic acid-whey protein isolate nanocomposite solution. S2: Preparation of Pickering emulsion: Oregano essential oil is mixed with the ellagic acid-whey protein isolate nanocomposite solution obtained in step S1, premixed and homogenized at high speed to obtain oregano essential oil Pickering emulsion; S3: Preparation of the filling plastic wrap: Konjac glucomannan and chitosan quaternary ammonium salt are dissolved in deionized water, and the Pickering emulsion and glycerin prepared in step S2 are added. After stirring evenly, the film-forming liquid is dried and peeled off to obtain the Pickering emulsion filling plastic wrap.

2. The method for preparing the pomegranate peel ellagic acid-protein complex emulsion preservation film according to claim 1, characterized in that, In step S1, the mass ratio of whey protein isolate to ellagic acid is (1-10):(0-2), preferably 4:

1.

3. The method for preparing the pomegranate peel ellagic acid-protein complex emulsion preservation film according to claim 1, characterized in that, In step S1, the ultrasonic treatment power is 400-550W and the treatment time is 8-15min; the ultrafiltration purification uses an ultrafiltration tube with a molecular weight cutoff of 8-12kDa, the centrifugation speed is 3500-4500rpm, the centrifugation time is 12-18min, and the purification process is repeated 2-4 times.

4. The method for preparing the pomegranate peel ellagic acid-protein complex emulsion preservation film according to claim 1, characterized in that, In step S2, the mass ratio of oregano essential oil to ellagic acid-whey protein isolate nanocomposite solution is (0.4-0.8):(8.5-10.5); the premixing time is 8-15 min, the high-speed homogenization speed is 12000-16000 rpm, and the homogenization time is 2-5 min.

5. The method for preparing the pomegranate peel ellagic acid-protein complex emulsion preservation film according to claim 1, characterized in that, In step S3, the mass of both konjac glucomannan and chitosan quaternary ammonium salt is 0.3-0.7g, the volume of deionized water is 80-120mL, and the total volume of film-forming solution is 15-25mL.

6. The method for preparing the pomegranate peel ellagic acid-protein complex emulsion preservation film according to claim 1, characterized in that, In step S3, the amount of Pickering emulsion added is 0%-10% (v / v), preferably 6% (v / v).

7. The method for preparing the pomegranate peel ellagic acid-protein complex emulsion preservation film according to claim 1, characterized in that, In step S3, the amount of glycerol added is 25%-35% (w / w) of the total mass of konjac glucomannan-chitosan quaternary ammonium salt; the stirring time is 1.5-3h, the drying temperature is 35-45℃, and the drying time is 10-15h.

8. The method for preparing the pomegranate peel ellagic acid-protein complex emulsion preservation film according to claim 1, characterized in that, In step S1, ellagic acid is derived from pomegranate peel; the concentration of the whey protein isolate solution is 25-35 g / L, and the ellagic acid ethanol solution is completely dissolved after stirring for 10-18 hours.

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