Edible composite preservative film and preparation method and application thereof

Abstract

The application discloses an edible composite preservative film and a preparation method and application thereof, and belongs to the technical field of food preservation materials.The edible composite preservative film provided by the application comprises the following components in percentage by mass: modified black garlic black pigment 4-10%, prickly pear residue extract 2-5%, prickly pear residue nano-cellulose 3-6%, starch 18-28%, gelatin 18-37%, D-sorbitol 18-37%, and water 9-12%.The edible composite preservative film prepared by the application has a uniform and compact structure, a smooth surface, good mechanical properties, oxygen barrier property and antioxidant property, is beneficial to the maintenance of moisture, color and oil state of nut food during storage, and contains rich bioactive substances, so that the edible composite preservative film is beneficial to human bodies.The raw materials of the application are widely sourced, cheap, easy to obtain and green and environment-friendly.

Description

Technical Field

[0001] This invention relates to the field of food preservation materials technology, specifically to an edible composite preservation film, its preparation method, and its application. Background Technology

[0002] Currently, plastic packaging is the most widely used food packaging on the market, and its raw materials mainly include polyethylene, polypropylene, and polyethylene terephthalate. Plastic packaging is causing increasingly serious "white pollution" problems. With the gradual increase in people's environmental awareness, biodegradable packaging films made from renewable resources such as natural polymers are considered a substitute for traditional plastics. Starch and gelatin have advantages such as wide availability, edibility, renewability, and low price, and also have good film-forming properties, making them a promising type of packaging film for edible foods.

[0003] Melanoids are complex polymers that naturally form during food processing and preservation, produced in the later stages of the Maillard reaction by consuming carbonyl compounds of sugars and amino compounds of amino acids. They are an important source of the black color in black garlic. Currently, melanoidins in black garlic are reported to mainly consist of amines, phenols, esters, furans, and carbonyl compounds. Due to their negative charge and the presence of phenolic and antioxidant peptide sequences, melanoidins exhibit strong antioxidant activity. However, due to their polymeric nature, the amount of antioxidant substances they contain is somewhat limited, making it difficult to achieve their optimal antioxidant effect. Therefore, finding a simple and efficient method to release the antioxidant substances in melanoidins and enhance their antioxidant activity is helpful in further maximizing their biological activity.

[0004] Prickly pear pomace, a byproduct comprising about 50% of the fresh fruit weight, is left after juicing prickly pears. It retains the characteristics of the fruit and is rich in polyphenols, flavonoids, vitamin C, and other active substances. Prickly pear extract mainly contains rutin and quercetin, whose antibacterial and antioxidant properties have been widely used in the development of active membranes. However, its extremely low water solubility leads to uneven dispersion in aqueous membranes, limiting its activity. Melanoids, as hydrophilic anionic nitrogen-containing polymers, can non-covalently bind to polyphenols through hydrogen bonding and hydrophobic interactions, possessing the potential to improve the water solubility of prickly pear polyphenols.

[0005] In summary, modifying melanoidins is a potential strategy to simultaneously improve antioxidant activity and the dispersibility of prickly pear polyphenols in aqueous solutions. However, there are currently no technical routes for modifying and improving melanoidins, nor are there any reports of their use in edible food packaging films. Summary of the Invention

[0006] Purpose of the invention: This invention aims to overcome the defects of the prior art and provide an edible composite preservation film, its preparation method and application. Based on modified black garlic melanin and prickly pear residue extract, a biodegradable composite preservation film for food is prepared with a uniform and dense film structure, smooth surface, and strong mechanical properties, barrier properties, antioxidant properties and thermal stability. This reduces plastic pollution and, when applied to food preservation, helps maintain the oil state of nuts such as walnuts during storage, thus extending the shelf life of nuts.

[0007] Technical solution: An edible composite preservation film, comprising the following components by weight percentage: 4-10% modified black garlic melanin, 2-5% prickly pear pomace extract, 3-6% prickly pear pomace nanocellulose, 18-28% starch, 18-37% gelatin, 18-37% D-sorbitol, and 9-12% water.

[0008] The present invention does not have any special limitation on the source of the above-mentioned components; products prepared by commercially available products or conventional preparation methods known to those skilled in the art are acceptable.

[0009] Prickly pear residue extract is rich in bioactive components such as polysaccharides and polyphenols, which can improve the antibacterial and antioxidant activities of composite membranes. It is also widely available, with readily available raw materials and low cost. Furthermore, prickly pear residue extract can disrupt intramolecular and intermolecular hydrogen bonds in gelatin and starch molecules, forming new hydrogen bonds, increasing the degree of cross-linking and density, thereby improving the mechanical properties of the composite membrane. This invention limits the mass content of prickly pear residue extract within the aforementioned range, which can improve the antibacterial and antioxidant properties of the composite membrane and ensure its uniform dispersion within the membrane, preventing aggregation and thus improving membrane performance.

[0010] Using cassava starch and corn starch as film-forming matrices, the raw materials are abundant and inexpensive. The resulting edible film has a tight and orderly hydrogen bond network structure, exhibiting good mechanical properties and good resistance to oils and gases. At the same time, the prepared edible film is odorless, tasteless, non-toxic, and has low oxygen permeability.

[0011] Gelatin is used as a film-forming matrix because it has functional properties such as water binding ability, gel forming ability, water vapor barrier, film forming, foam forming ability and emulsification tendency, as well as good film-forming properties, which makes it possible to make natural edible films.

[0012] Furthermore, the modified black garlic melanin is prepared using an ultrasound-assisted enzymatic hydrolysis method. This method includes the following steps: mixing black garlic with water, grinding, and extracting in an ultrasonic water bath; filtering, adding dichloromethane to the supernatant for defatting, then dialyzing and freeze-drying to obtain black garlic melanin; dissolving the obtained black garlic melanin in water, adding a complex protease for enzymatic hydrolysis in an ultrasonic water bath, filtering, boiling to inactivate the enzyme, and freeze-drying to obtain the modified black garlic melanin. The modified melanin exhibits significantly enhanced bioactivity, improving the antibacterial and antioxidant activity of the edible composite membrane, helping to better maintain the oil content within nuts and extend shelf life.

[0013] Further, the mass-to-volume ratio of black garlic to water is 1:7-9; the amount of dichloromethane added is 40-60% of the supernatant volume; the molecular weight of the ultrafiltration membrane used for dialysis is 3kDa; the complex protease is a combination of trypsin, alkaline protease, and papain, with an enzyme activity ratio of 3:6:1; the amount of the complex protease added is 3000U / g; the enzymatic hydrolysis time is 1-3 hours; and the power of the ultrasound is 100-200W.

[0014] Furthermore, the prickly pear pomace extract is prepared using an ultrasound-assisted solvent extraction method; the ultrasound-assisted solvent extraction method includes the following steps: pulverizing and sieving dried prickly pear pomace, adding ethanol solution for extraction in an ultrasonic water bath, filtering to obtain the extract, and freeze-drying to obtain the prickly pear pomace extract.

[0015] Further, the sieving is performed through a 40-60 mesh sieve; the concentration of the ethanol solution is 0-40% (excluding zero values); the mass-to-volume ratio of the prickly pear pomace to the ethanol solution is 1:30-50; the power of the ultrasonic wave is 100-500W; the extraction temperature is 40-60℃; and the extraction time is 10-30 minutes.

[0016] Furthermore, the prickly pear residue nanocellulose is prepared using one of the following methods: acid hydrolysis, oxidation, and enzymatic hydrolysis.

[0017] Furthermore, the prickly pear pomace nanocellulose is prepared by acid hydrolysis. This invention does not specifically limit the steps for preparing prickly pear pomace nanocellulose by acid hydrolysis; conventional acid hydrolysis methods in the art can be used. Prickly pear pomace nanocellulose prepared by different methods may have the same crystal form, but may differ in morphology.

[0018] Preferably, the acid hydrolysis method includes the following steps: extracting prickly pear pomace → acid treatment → alkali treatment → bleaching → prickly pear pomace cellulose → sulfuric acid hydrolysis → shaking → centrifugation → washing to neutral → drying → pulverizing → sieving → prickly pear pomace nanocellulose.

[0019] In the above steps, acid treatment is used to remove non-cellulose components such as pectin from the prickly pear residue. The acid solution is preferably 0.5-1M HCl, more preferably 0.8M HCl. The volume-to-mass ratio of the acid solution to the prickly pear residue is preferably 15-25 mL:1 g, more preferably 20 mL:1 g. Preferably, after mixing the acid solution and the prickly pear residue, occasional stirring is required, with the stirring time preferably 1-2 hours, more preferably 1.5 hours. Alkali treatment is used to remove non-cellulose components such as lignin and hemicellulose from the prickly pear residue. The alkali solution is preferably 1M NaOH. The volume-to-mass ratio of the alkali solution to the prickly pear residue is preferably 15-25 mL:1 g, more preferably 20 mL:1 g. Preferably, after mixing the alkali solution and the prickly pear residue, heating and occasional stirring are required, with the heating temperature preferably 50-70℃, more preferably 60℃, and the heating time preferably 1-2 hours, more preferably 1.5 hours.

[0020] In the above steps, the filter residue obtained after removing non-cellulose components is decolorized and dried to obtain prickly pear residue cellulose powder. The preferred method for obtaining the filter residue is vacuum filtration. Preferably, sodium hypochlorite is used for decolorization. Specifically, the obtained filter residue is washed until neutral, sodium hypochlorite is added, the pH is adjusted to 3-4, and the mixture is heated in a water bath with shaking to perform decolorization. The washing is preferably done with distilled water; the sodium hypochlorite is preferably 0.5-3% v / v sodium hypochlorite, more preferably 1% v / v sodium hypochlorite; the volume-to-mass ratio of sodium hypochlorite to filter residue is preferably 3-5 mL:1 g, more preferably 4 mL:1 g. After decolorization, the mixture is filtered, the white filter residue is washed until neutral, and dried to obtain cellulose powder. The filtration method is preferably vacuum filtration; the washing method is preferably done with distilled water; the present invention does not have a specific limitation on the drying method, but oven drying is preferred.

[0021] In the above steps, prickly pear residue cellulose powder is hydrolyzed with sulfuric acid to prepare prickly pear residue nanocellulose. The acid used for sulfuric acid hydrolysis is preferably 40-60% sulfuric acid, more preferably 50% sulfuric acid; the volume-to-mass ratio of sulfuric acid to cellulose powder is preferably 10-15 mL:1 g, more preferably 12 mL:1 g. The acid hydrolysis is preferably performed by heating, the heating temperature is preferably 30-50℃, more preferably 40℃; the hydrolysis time is preferably 3-5 h, more preferably 4 h. After acid hydrolysis, preferably, centrifugation is used to condense the crystals and remove excess sulfuric acid, wherein the centrifugation speed is preferably 8000-1200 rpm, more preferably 10000 rpm; the centrifugation time is preferably 5-15 min, more preferably 10 min. After centrifugation, washing is performed. The number of washing cycles is not particularly limited in this invention; the supernatant is removed after washing until the supernatant is turbid and appears as a pale blue colloid. Drying is performed after washing. Preferably, freeze-drying is used; the specific freeze-drying method is not particularly limited in this invention, and any conventional freeze-drying method in the art can be used.

[0022] The preparation method of the above-mentioned edible composite preservation film includes the following steps: adding the modified black garlic melanin, prickly pear residue extract, prickly pear residue nanocellulose and starch to water for the first step of dissolution, then adding gelatin for the second step of dissolution, then adding D-sorbitol for the third step of dissolution, cooling, filtering to obtain composite film liquid, forming the composite film liquid into a film, and drying to obtain composite preservation film.

[0023] Furthermore, the first step of dissolution is carried out at 70-80℃ for 10-15 minutes; the second step of dissolution is carried out at 70-80℃ for 20-25 minutes; and the third step of dissolution is carried out at 75-85℃ for 30-40 minutes.

[0024] In the above steps, modified black garlic melanin, prickly pear pomace extract, prickly pear pomace nanocellulose, starch, and water are mixed and dissolved to obtain solution 1. This invention does not have specific limitations on the mixing operation of the modified black garlic melanin, prickly pear pomace extract, prickly pear pomace nanocellulose, starch, and water; any mixing method well-known to those skilled in the art can be used. Preferably, mixing is carried out under stirring conditions. The stirring is preferably mechanical stirring; the stirring speed is preferably 200-300 r / min, more preferably 250 r / min; the stirring time is preferably 13 min; and the stirring temperature is preferably 75℃.

[0025] Gelatin is added to solution 1 and dissolved to obtain solution 2. This invention does not impose any special limitations on the mixing operation of solution 1 and gelatin; any mixing technique well-known to those skilled in the art can be used. Preferably, solution 1 and gelatin are mixed under stirring conditions; the stirring is preferably mechanical stirring; the stirring speed is preferably 200-300 r / min, more preferably 250 r / min; the stirring time is preferably 23 min; and the stirring temperature is preferably 75℃.

[0026] D-sorbitol is added to solution 2, dissolved, cooled, and filtered to obtain the composite membrane solution. This invention does not impose any special limitations on the mixing operation of solution 2 and D-sorbitol; any mixing technique well-known to those skilled in the art can be used. Preferably, solution 2 and D-sorbitol are mixed under stirring conditions; the stirring time is preferably 35 minutes; and the stirring temperature is preferably 80°C.

[0027] Furthermore, the filtration uses a 60-80 mesh filter; the drying temperature is 25-28℃, preferably 26.5℃; the relative humidity is 50-55%, preferably 53%; and the drying time is 24-30 hours, preferably 27 hours. This invention limits the drying temperature and humidity within the above ranges, enabling a moderate rate of moisture evaporation and allowing starch and gelatin molecules to arrange themselves in an orderly manner during membrane matrix formation, resulting in high density and thus producing a membrane with good performance and appearance.

[0028] The application of the aforementioned edible composite preservative film in walnut preservation. This invention does not impose any specific limitations on the application of the edible composite preservative film in walnut preservation; any food preservation film familiar to those skilled in the art can be used.

[0029] Beneficial effects:

[0030] 1) This invention uses an ultrasound-assisted enzymatic hydrolysis method to enzymatically hydrolyze the macromolecular melanoidins in black garlic into smaller molecular weight components. The bioactivity of the modified melanoidins is significantly improved, which can effectively enhance the antibacterial and antioxidant activity of the composite preservation film, help to better maintain the oil state in the nuts, and extend the shelf life.

[0031] 2) Prickly pear residue extract contains abundant polysaccharides and polyphenols, which can synergistically improve the bioactivity of the composite film. Prickly pear residue extract can break the intramolecular and intermolecular hydrogen bonds of gelatin and starch molecules and form new hydrogen bonds, thereby improving the degree of cross-linking and density, thus improving the mechanical properties of the composite film. Moreover, prickly pear residue is widely available, the raw materials are easy to obtain, and the cost is low.

[0032] 3) By rationally proportioning the components in the membrane, especially the ratio of modified black garlic melanin and prickly pear residue extract, the present invention enables the modified black garlic melanin and prickly pear residue extract to form a non-covalent bond, thereby improving the dispersibility of prickly pear residue extract in the membrane and thus enhancing the antioxidant efficiency and free radical scavenging ability of prickly pear residue extract in the membrane.

[0033] 4) The prickly pear residue nanocellulose in this invention has a high extraction rate, high crystallinity, and good enhancement effect. The composite preservation film with added nanocellulose has a uniform and dense structure, a smooth surface, and strong mechanical properties, barrier properties, antioxidant properties, and thermal stability. It can effectively prevent nuts from getting damp and oxidized during storage, maintain the stability of nut oils, and is beneficial to the preservation of nuts.

[0034] 5) The edible composite preservation film prepared by this invention, when applied to walnut preservation, exhibits excellent preservation effects while reducing plastic pollution. Compared with aluminum foil packaging, which is widely used in the market and has good preservation effects, the moisture content of walnuts packaged with composite preservation film decreases less during storage, and the yellow-blue value of walnuts can be better maintained. Thus, the composite preservation film can effectively maintain the moisture content of walnuts and keep the color of walnuts from changing significantly during storage. During storage, the free fatty acids and antioxidant values ​​of walnuts packaged with composite preservation film are maintained at a low level, significantly lower than those of walnuts packaged with aluminum foil. Thus, the composite preservation film can inhibit the oxidation of walnuts and effectively extend their shelf life. Attached Figure Description

[0035] Figure 1 This is a comparison chart showing the results of determining the total phenolic and total flavonoid content of the composite preservative film under different amounts of modified black garlic melanin and prickly pear residue extract added in Examples 1-9 and Comparative Examples 1-2.

[0036] Figure 2 This is a comparison chart showing the antioxidant performance test results of the composite preservation film under different amounts of modified black garlic melanin and prickly pear residue extract added in Examples 1-9 and Comparative Examples 1-2.

[0037] Figure 3 A comparative graph showing the moisture content measurement results of walnut samples packaged with different materials under different storage days and temperatures;

[0038] Figure 4 A comparative graph showing the water activity measurement results of walnut samples packaged with different materials under different storage days and temperatures;

[0039] Figure 5 A comparative graph showing the L* values ​​of walnut samples packaged with different materials under different storage days and temperatures;

[0040] Figure 6A comparative graph showing the colorimetric a* values ​​of walnut samples packaged with different materials under different storage days and temperatures;

[0041] Figure 7 A comparative graph showing the colorimetric b* values ​​of walnut samples packaged with different materials under different storage days and temperatures;

[0042] Figure 8 A comparative graph showing the measurement results of free fatty acid content in walnut oil prepared from walnut samples packaged with different materials after different storage days;

[0043] Figure 9 A comparative graph showing the measurement results of peroxide value of walnut oil made from walnut samples packaged with different materials under different storage days. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0045] It should be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and / or processing steps closely related to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0046] In the following embodiments, unless otherwise specified, the raw materials or processing techniques used are conventional commercially available raw materials or conventional processing techniques in the art.

[0047] Example 1

[0048] (1) Preparation of modified black garlic melanin: Black garlic and water were mixed at a mass-volume ratio of 1:8, ground, and extracted in an ultrasonic water bath. After filtration, dichloromethane was added to the supernatant for defatting (the amount of dichloromethane added was 50% of the volume of the supernatant). Then, the mixture was dialyzed with a 3 kDa ultrafiltration membrane and freeze-dried to obtain black garlic melanin. The prepared black garlic melanin was dissolved in water, and a complex protease (according to the enzyme activity ratio, trypsin: alkaline protease: papain = 3:6:1) was added for enzymatic hydrolysis in an ultrasonic water bath. The ultrasonic power was 150 W and the ultrasonic temperature was 37 °C. After enzymatic hydrolysis for 2 h, the mixture was filtered, and the enzyme was inactivated by boiling to obtain the enzymatic hydrolysate. The modified black garlic melanin was obtained by freeze-drying.

[0049] (2) Preparation of prickly pear residue extract: The dried prickly pear residue was crushed and passed through a 50-mesh sieve. 40% ethanol solution with a weight-volume ratio of 40% was added and extracted in a 300W ultrasonic water bath at a temperature of 50℃. After 20 minutes, the extract was filtered and freeze-dried to obtain the prickly pear residue extract.

[0050] (3) Preparation of prickly pear pomace nanocellulose: Approximately 200g of pomace was placed in 1.2L of hot water and boiled for 30min. The mixture was then filtered to remove sugars and phenolic substances. The resulting residue was added to 1.2L of 1M HCl solution and heated at 85℃ for 30min with continuous stirring. The residue was then collected by vacuum filtration. This step was repeated with 0.5M HCl solution. Then, 1.2L of 1M NaOH was added to the residue and stirred at 85℃ for 30min. This step was repeated three times. After alkali treatment, the residue was bleached twice with NaClO to remove lignin. The resulting precipitate was washed with distilled water until the pH of the eluent reached neutral to obtain bleached fiber. 10g of bleached fiber was hydrolyzed with 90mL of sulfuric acid (50% vol / vol) at 40℃ for 4h with continuous stirring using a magnetic stirrer. Then, twice the volume of cold distilled water was added to stop the hydrolysis. The mixture was centrifuged at 10,000 rpm for 10 min to remove excess sulfuric acid. The precipitate was washed several times until the supernatant became turbid, yielding a pale blue colloidal suspension. The suspension was dialyzed to neutral using a dialysis bag with a molecular weight of 12 kDa. The resulting suspension was then sonicated at 300 W for 10 min and freeze-dried to obtain prickly pear residue nanocellulose.

[0051] (4) Preparation of composite preservation film: Raw materials were prepared according to the following mass content: 0.5% modified black garlic melanin, 0.3% prickly pear pomace extract, 0.5% prickly pear pomace nanocellulose, 2.5% starch, 3% gelatin, 3% D-sorbitol, and water was added to 100%. First, the modified black garlic melanin, prickly pear pomace extract, prickly pear pomace nanocellulose and starch were dissolved in water and stirred at 75℃ and 250r / min for 13min to obtain solution 1; gelatin was added to solution 1 and stirred at 75℃ and 250r / min for 23min to dissolve and obtain solution 2; then D-sorbitol was added to solution 2 and stirred at 80℃ and 250r / min for 35min to dissolve and filter to obtain composite film liquid. The composite film liquid was dried at 26.5℃ and 53% relative humidity for 27h to form a film and obtain composite preservation film.

[0052] Example 2

[0053] The difference from Example 1 is that in step (4), the amount of prickly pear residue extract added is 0.4%.

[0054] Example 3

[0055] The difference from Example 1 is that in step (4), the amount of prickly pear residue extract added is 0.5%.

[0056] Example 4

[0057] Compared with Example 1, the difference is that in step (4), the amount of modified black garlic black essence added is 0.75%.

[0058] Example 5

[0059] The difference from Example 4 is that in step (4), the amount of prickly pear residue extract added is 0.4%.

[0060] Example 6

[0061] The difference from Example 4 is that in step (4), the amount of prickly pear residue extract added is 0.5%.

[0062] Example 7

[0063] The difference from Example 1 is that in step (4), the amount of modified black garlic black essence added is 1%.

[0064] Example 8

[0065] The difference from Example 7 is that in step (4), the amount of prickly pear residue extract added is 0.4%.

[0066] Example 9

[0067] The difference from Example 7 is that in step (4), the amount of prickly pear residue extract added is 0.5%.

[0068] Comparative Example 1

[0069] Compared with Example 3, the difference is that in step (4), the amount of modified black garlic black essence added is 0%.

[0070] Comparative Example 2

[0071] The difference from Example 7 is that in step (4), the amount of prickly pear residue extract added is 0%.

[0072] Performance testing of the composite preservation film prepared by this invention

[0073] Moisture content test: The film sample (2cm×2cm) was first weighed (W0) and dried in an oven at 105±2℃ for 2 hours. Then, the dry weight of the film (W1) was measured, and the moisture content was calculated: MC(%)=((W0-W1) / W0)*100

[0074] Water solubility test: Cut the membrane into 3cm x 3cm sheets, dry them in a forced-air drying oven to constant weight, and record the weight as W0. Then immerse each membrane separately in a sealed glass bottle containing 100mL of deionized water. After 48 hours, remove them, dry them to constant weight, and record the weight as W1. The water solubility of each membrane can be expressed as the percentage of membrane dissolution: WS(%) = (W0 - W1 / W0) × 100%

[0075] Oxygen permeability test: Add 10 mL of 30% hydrogen peroxide to a test tube, then add 0.1 mol / L FeCl3 solution. Seal the tube opening with composite membranes of different concentrations, shake well, and react for 10 h. Measure the residual oxygen concentration inside the membrane using an oxygen analyzer. The residual oxygen concentration is inversely proportional to the membrane's oxygen permeability; therefore, the membrane's oxygen permeability is expressed by the residual oxygen concentration inside the membrane.

[0076] The test results are shown in Table 1.

[0077] Table 1. Changes in water solubility, moisture content, and oxygen permeability of composite plastic wrap under different amounts of modified black garlic melanin and prickly pear pomace extract.

[0078]

[0079] Table 1 shows that there is no significant correlation between water content and the amount of melanoidin and extract added. The water content is highest when the added amounts are 0.75% melanoidin and 0.4% prickly pear pomace extract. Water solubility gradually decreases with increasing melanoidin addition, while the prickly pear pomace extract additive shows no significant difference in water solubility. Oxygen permeability is represented by the oxygen concentration remaining in the membrane; a higher oxygen concentration indicates lower membrane oxygen permeability. It can be seen that with the addition of melanoidin and prickly pear pomace extract, oxygen permeability first deteriorates and then improves, indicating that the composite preservation film has the worst oxygen permeability when the added amounts of the two substances are 0.75% and 0.4%, respectively, which is beneficial for nut storage.

[0080] Thickness measurement: The thickness of each film was measured using a micrometer, with 10 points measured for each film, and the average value was taken.

[0081] Mechanical property testing: The tensile strength and elongation at break of each membrane were tested using a texture analyzer. Before testing, the membrane was cut into rectangular strips of 4.0 cm × 1.2 cm and placed in a constant temperature and humidity chamber for at least 48 hours. The tests were conducted in a constant temperature and humidity chamber at 20°C and 50% RH, under the following conditions: probe speed of 1 mm / s. Each sample was measured 6 times, and the average value was taken.

[0082] The test results are shown in Table 2.

[0083] Table 2. Changes in the thickness, mechanical properties, and light transmittance of the composite preservation film under different amounts of modified black garlic melanin and prickly pear pomace extract.

[0084]

[0085] As shown in Table 2, the thickness of the composite plastic wrap gradually increases with the increase of the amount of melanoidin and prickly pear pomace extract. The tensile strength and elongation at break are the highest when the amount of melanoidin is 0.75% and the amount of prickly pear pomace is 0.4%, reaching 35.32±1.28MPa and 29.58±2.95%, respectively.

[0086] Antioxidant performance test of the composite preservation film prepared by this invention

[0087] Sample extraction: Weigh 1g of the ground sample and place it in a 100mL beaker. Add 10mL of 70% ethanol and perform ultrasonic-assisted extraction for 0.5h at room temperature in the dark. After 0.5h, centrifuge the extract at 4000rpm for 15min and collect the supernatant. Continue extraction of the residue twice more, each time with 5mL of 70% ethanol. Collect the supernatants from the three extractions, store them in a 4℃ refrigerator, and analyze them within 24h.

[0088] Total phenol content determination: The total phenol content of the sample was determined using the Folin-Ciocalteu colorimetric method. 0.2 mL of the extract was placed in a 10 mL volumetric flask, 1.0 mL of Folin-Ciocalteu reagent was added, followed by 3 mL of 10% sodium carbonate solution. The mixture was stirred, diluted to volume with water, and shaken thoroughly. The mixture was then allowed to react at room temperature in the dark for 2 hours. The absorbance was measured at 765 nm, and the result was used to calculate the phenol concentration (μg / mL) using the standard curve.

[0089] Establishment of the standard curve: Accurately pipette 0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 mL of 70 μg / mL gallic acid standard dilution into 10 mL volumetric flasks. Add 1.0 mL of Folin-Ciocaileu reagent, followed by 3 mL of 10% sodium carbonate solution (the time interval between these additions should not exceed 8 min). Mix well, dilute to volume with water, and mix again. Incubate at room temperature in the dark for 2 hours, and measure the absorbance at 765 nm. Plot the standard curve with absorbance on the ordinate and standard solution concentration on the abscissa. The polyphenol content in the sample is calculated using gallic acid standard.

[0090] Total flavonoids determination: The total flavonoid content of the sample was determined using a spectrophotometer. Experimental procedure: 10 mL of the extract was taken, and 0.75 mL of 5% sodium nitrite (w / v) was added. The reaction was allowed to proceed for 5 minutes. Subsequently, 1.5 mL of 10% AlCl3 (w / v) was added and allowed to proceed for 6 minutes. Then, 5 mL of 1M NaOH and 5 mL of deionized water were added sequentially. After centrifugation at 10000 rpm for 2 minutes, the absorbance of the solution against the blank reagent at 510 nm was measured. Quantification was performed according to the rutin standard curve, and the data were expressed as rutin equivalents per g of sample (mg·RE / g·DW).

[0091] Establishment of the standard curve: Prepare a 500 μg / mL rutin standard solution. Take 1, 2, 3, and 4 mL of the standard solution respectively, and bring the volume to 10 mL. Add 0.75 mL of 5% sodium nitrite (w / v) and react for 5 minutes. Then, add 1.5 mL of 10% AlCl3 (w / v) and maintain for 6 minutes. Add 5 mL of 1M NaOH and 5 mL of deionized water sequentially. After centrifuging at 10000 rpm for 2 minutes, measure the absorbance of the solution against the blank reagent at 510 nm. Plot the standard curve with absorbance on the ordinate and standard solution concentration on the abscissa.

[0092] See the attached document for test results. Figure 1 .

[0093] Antioxidant Properties Measurement: This experiment explored the antioxidant properties of an edible composite food preservation film based on modified black garlic melanin and prickly pear pomace extract. The DPPH and ABTS free radical scavenging abilities of the composite food preservation film prepared in this invention were measured. The experimental results are attached. Figure 2 .

[0094] DPPH radical scavenging ability: Add 10 μL of sample to 200 μL of 0.15 mM DPPH in 50% ethanol. Shake the mixture and then let it stand in the dark at room temperature for 30 minutes, measuring its absorbance at 517 nm. Simultaneously, replace the sample solution with ethanol to measure the absorbance Ac of the blank control. DPPH radical scavenging ability is expressed as inhibition percentage (I%) and calculated according to the following formula:

[0095] I% = [(A control -A sample ) / A control ]×100%

[0096] In the formula: A sample Indicates the absorbance value of the sample; A control This indicates the absorbance value of the blank control.

[0097] A standard curve was plotted using Trolox solution. The results are expressed as trolox equivalents per gram of sample (μmol TE / g).

[0098] Standard curve plotting: Prepare trolox solutions of different concentrations (100, 200, 300, 400, 500 μmol / L). Take 10 μL of trolox solution and mix it with 200 μL of DPPH·50% ethanol solution (0.15 mmol / L). After mixing, incubate in the dark for 30 min and measure the absorbance As at 517 nm.

[0099] ABTS free radical scavenging ability: Prepare an ABTS mixture by mixing equal volumes of 7.4 mM ABTS and 2.6 mM potassium persulfate solution, reacting at room temperature in the dark for 12 h, and then set aside for use. Then dilute the solution by mixing 1.2 mL of ABTS solution with 50 mL of methanol, and measure the absorbance at 734 nm to obtain 0.85 ± 0.20 to obtain the ABTS working solution.

[0100] Mix 10 μL of sample with 200 μL of LABTS working solution and incubate in the dark at room temperature for 6 minutes. Measure the absorbance of the sample at 734 nm. Calibrate as described in the DPPH assay. The final result is expressed as μmol TE / mg.

[0101] like Figure 1-2 As shown, Figure 1 The total phenolic and total flavonoid contents of the composite preservative films under different amounts of modified black garlic melanin and prickly pear residue extract added in Examples 1-9 and Comparative Examples 1-2 are shown. Figure 2 The figures show the DPPH and ABTS free radical scavenging abilities of the composite preservation films under different amounts of modified black garlic melanin and prickly pear pomace extract added in Examples 1-9 and Comparative Examples 1-2. It is evident that the amount of melanin and prickly pear pomace extract added is significantly positively correlated with the total phenolic and flavonoid content and antioxidant properties, indicating that the higher the added amount, the stronger the free radical scavenging ability. This may be because melanin is rich in polyphenols and antioxidant-active proteins and polysaccharides, while prickly pear is rich in superoxide dismutase (SOD), flavonoids, polyphenols, and other active substances, possessing strong antioxidant capabilities, thus enhancing the antioxidant capacity of the prepared film. Simultaneously, the addition of modified black garlic melanin leads to non-covalent bonding between the modified black garlic melanin and prickly pear pomace extract, improving the dispersibility of the prickly pear pomace extract in the film, thereby increasing the antioxidant efficiency and free radical scavenging ability of the prickly pear pomace extract in the film.

[0102] The composite preservation film prepared in this invention was used in the performance test of walnut preservation.

[0103] Walnut packaging: Whole walnut kernels were first used, and two methods were selected: sealed packaging with aluminum foil bags and packaging with the edible composite preservation film prepared in Example 5 of this invention. The net weight of each package was controlled to ensure that the net weight of each bag remained at 15g.

[0104] Walnut storage: After packaging the walnut samples, the packaged samples were stored at 40℃ and 60℃ respectively, while maintaining the relative humidity (RH) at 60%. During the experiment, samples were taken from the stored samples every 10 days to measure the indicators, and the selected samples were stored for a total of 40 days.

[0105] Indicator Testing:

[0106] The moisture content and water activity of walnut samples packaged with different materials under different temperatures and storage days were analyzed to compare the preservation effects of different packaging materials. The test results are attached. Figure 3-4 .

[0107] Moisture content determination: First, the moisture content of walnut samples taken under specific conditions and at specific times during storage was determined. The method for determining moisture content followed the national standard GB 5009.3-2016. Taking a specific sample as an example, 1.00 g of the walnut sample was weighed into a pre-dried aluminum dish and completely dried in a drying oven at 105℃ using a drying method. Subsequently, the dried sample was taken, and its mass was measured again. The moisture content of the walnut sample was determined by calculating the change in mass before and after drying.

[0108] Water activity determination: The water activity of walnut samples taken under specific conditions and at specific times during storage was determined. The method for determining water activity refers to standard GB 5009.238-2016, and a water activity meter was used to determine the water activity of the walnut samples. At room temperature, approximately 1.00 g of the walnut sample was weighed into a 3.5 cm diameter circular plastic dish. The dish was placed in the measuring chamber of the water activity meter, and the measuring chamber was closed before measurement began. The response value displayed after water diffusion equilibrium was obtained is the water activity of the nut sample.

[0109] like Figure 3-4 As shown, Figure 3-4The results of moisture content and water activity measurements of walnut samples packaged in aluminum foil and composite preservative film prepared in Example 5 of this invention are shown under different storage days and temperatures. It can be seen that the moisture content of the aluminum foil-packaged walnut samples decreased significantly during storage, while the moisture content of the composite preservative film-packaged walnut samples was effectively maintained without excessive decrease. Overall, the water activity of the walnut samples packaged in composite preservative film increased more significantly during storage. However, at 60℃, the water activity of the walnuts packaged in composite preservative film was not significantly different from that of aluminum foil, demonstrating an effect comparable to aluminum foil packaging.

[0110] Color difference analysis was performed on walnut samples packaged with different materials and stored for different days at different temperatures to compare the preservation effects of different packaging materials. Test results are attached. Figure 5-7 .

[0111] Colorimetric determination: The colorimetric properties of walnut samples taken under specific conditions and at specific times during storage were determined. A colorimeter was used to measure the colorimetric properties of the products. Six parallel measurements were performed on each sample, and the L*, a*, and b* values ​​of each measurement were recorded. The average of the six parallel measurements was calculated and used as the colorimetric analysis result for each sample. A larger L* value indicates a brighter sample color; a* represents redness / greenness, with a larger a* value indicating a redder sample color; and b* represents yellowness / blueness, with a larger b* value indicating a yellower sample color. The advantages of a colorimeter are that it provides traceable and accurately quantifiable data. The standards adopted in drawing qualitative conclusions from the data are also strictly defined. Furthermore, colorimeter measurements are relatively objective; the data obtained by different people using a colorimeter will show very little difference.

[0112] like Figure 5-7 As shown, Figure 5-7 The results of colorimetric measurements of walnut samples packaged in aluminum foil and composite preservation film prepared in Example 5 of this invention are shown under different storage days and temperatures. It can be seen that, overall, the walnut samples packaged in composite preservation film have a larger L* value during storage, indicating a brighter color; the overall red and green hues remain relatively stable, fluctuating slightly; overall, aluminum foil packaging increases the yellow-blue value, while the composite preservation film better maintains the yellow-blue value of the walnuts.

[0113] Walnut oil extraction: Walnut oil was extracted from walnut samples taken under specific conditions and at specific times during storage. Organic solvent extraction was used to extract walnut oil from the samples. The specific steps were as follows: 10g of nuts were mixed evenly with 30mL of petroleum ether and stirred for 1 hour. The mixture was then allowed to stand at room temperature for 12 hours. After centrifugation at 10000rpm for 10 minutes, the supernatant was retained. 30mL of petroleum ether was added to the residue, and the mixture was stirred for 1 hour. The mixture was then extracted again at room temperature for 2 hours. The mixture was centrifuged again. The supernatants from the two centrifugations were combined, and then the supernatant was evaporated using rotary evaporation equipment at 45℃ (ensuring the pressure inside the apparatus was maintained at approximately 0.08-0.10MPa during the experiment). Once the organic solvent in the flask had completely evaporated, the prepared walnut oil was obtained.

[0114] Walnut oil made from walnut samples packaged with different materials and stored at different temperatures for different days was analyzed for free fatty acids to compare the preservation effects of different packaging materials. Test results are attached. Figure 8 .

[0115] Determination of Free Fatty Acid Content: The free fatty acid content in walnut oil obtained from walnut samples taken under specific conditions and time periods during storage was determined. The free fatty acid content of walnut oil was determined by titration. First, anhydrous diethyl ether and ethanol were mixed thoroughly at a volume ratio of 1:1. Then, 20 mL of this mixture was transferred to an Erlenmeyer flask. Next, 0.5 g of walnut oil sample was added to the flask. The mixture was gently shaken for 10 seconds at room temperature to completely dissolve the walnut oil sample in the solvent. Phenolphthalein indicator was then added to the sample, and the solution was titrated to the endpoint with 0.05 mol / L potassium hydroxide standard solution. The free fatty acid content was calculated by the volume of standard titration solution consumed, using the following formula:

[0116]

[0117] In the formula:

[0118] X—Free fatty acid content of nut oil (calculated as oleic acid), g / 100g;

[0119] V—Volume of potassium hydroxide standard titration solution consumed in the sample determination, in mL;

[0120] V0—Volume of potassium hydroxide standard titration solution consumed in blank determination, in mL;

[0121] c—The actual concentration of the potassium hydroxide standard solution, in mol / L;

[0122] m—mass of nut oil, g;

[0123] 282—Molar mass of oleic acid, g / mol.

[0124] like Figure 8 As shown, Figure 8 The results of measuring the free fatty acid content of walnut oil from walnut samples packaged in aluminum foil and the composite preservation film prepared in Example 5 of this invention at different storage days are shown. It can be seen that at low temperatures, the free fatty acid content of walnuts does not increase significantly, and there is no significant difference between aluminum foil and composite preservation film packaging. This is mainly due to the short storage time. However, at 60°C, the free fatty acid content of walnuts packaged in aluminum foil increases significantly, while the composite packaging film can suppress this upward trend, reduce the free fatty acid content, and help extend the shelf life of nuts.

[0125] Walnut oil made from walnut samples packaged with different materials and stored at different temperatures for different days was tested for peroxide value to compare the preservation effects of different packaging materials. Test results are attached. Figure 9 .

[0126] Determination of Peroxide Value in Walnut Oil Samples: The peroxide value of walnut oil extracted from walnut samples taken under specific conditions and time periods during storage was determined. The method for determining the peroxide value in the experiment followed the national standard GB / T 5009.227-2016. The specific steps for determining the peroxide value of walnut oil samples were as follows: First, approximately 1.0g-2.0g of walnut oil extracted from the walnut sample was weighed and placed in an Erlenmeyer flask. Then, a mixed solution was prepared according to a volume ratio of chloroform:glacial acetic acid = 2:3 and mixed thoroughly. Subsequently, 15mL of the chloroform-glacial acetic acid mixture (volume ratio 2:3) was pipetted into the Erlenmeyer flask containing the previously weighed walnut oil sample. The mixture was shaken for 10s to ensure the walnut oil was fully dissolved in the mixture. Then, 0.5mL of saturated potassium iodide solution was added to the Erlenmeyer flask, gently shaken for 30s, and then placed at room temperature in the dark for 3 minutes. After completing the light-protection operation, remove the conical flask containing the treated sample and add 50 mL of deionized water and 0.5 mL of starch indicator. After shaking for 10 seconds, titrate the sample mixture in the conical flask with a standard sodium thiosulfate solution until the blue color disappears and does not fade for 30 seconds. Finally, record the volume of solution used for titration and calculate the peroxide value of the walnut oil extracted from the walnut sample using the following formula:

[0127]

[0128] In the formula:

[0129] X—Peroxide value of nut oil, mmol / kg;

[0130] V—Volume of sodium thiosulfate standard solution consumed by the sample, mL;

[0131] V0—Volume of sodium thiosulfate standard solution consumed in blank determination, mL;

[0132] c—The actual concentration of the sodium thiosulfate standard solution, in mol / L;

[0133] m—mass of nut oil, g;

[0134] 1000—Conversion factor.

[0135] like Figure 9 As shown, Figure 9 The peroxide value of walnut oil produced from walnut samples packaged in aluminum foil and the composite preservation film prepared in Example 5 of this invention is shown at different storage days. It can be seen that both storage temperatures exhibit the same trend: the peroxide value of the aluminum foil-packaged walnuts increases significantly, mainly due to oil oxidation. At the same temperature, the composite preservation film significantly inhibits this trend, preventing walnut oxidation. This is mainly due to the antioxidant activity of the antioxidants contained in the composite preservation film.

[0136] The results above indicate that composite preservation film can effectively maintain the moisture content of walnuts and prevent significant changes in their color during storage. Furthermore, due to its active substances and good oxygen barrier properties, the free fatty acids and antioxidant values ​​of walnuts remain at low levels during storage, significantly lower than those of walnuts packaged in aluminum foil, effectively extending the shelf life of walnuts.

[0137] The above-described specific embodiments have the following beneficial effects compared to the prior art:

[0138] 1) This invention uses an ultrasound-assisted enzymatic hydrolysis method to enzymatically hydrolyze the macromolecular melanoidins in black garlic into smaller molecular weight components. The bioactivity of the modified melanoidins is significantly improved, which can effectively enhance the antibacterial and antioxidant activity of the composite preservation film, help to better maintain the oil state in the nuts, and extend the shelf life.

[0139] 2) Prickly pear residue extract contains abundant polysaccharides and polyphenols, which can synergistically improve the bioactivity of the composite film. Prickly pear residue extract can break the intramolecular and intermolecular hydrogen bonds of gelatin and starch molecules and form new hydrogen bonds, thereby improving the degree of cross-linking and density, thus improving the mechanical properties of the composite film. Moreover, prickly pear residue is widely available, the raw materials are easy to obtain, and the cost is low.

[0140] 3) By rationally proportioning the components in the membrane, especially the ratio of modified black garlic melanin and prickly pear residue extract, the present invention enables the modified black garlic melanin and prickly pear residue extract to form a non-covalent bond, thereby improving the dispersibility of prickly pear residue extract in the membrane and thus enhancing the antioxidant efficiency and free radical scavenging ability of prickly pear residue extract in the membrane.

[0141] 4) The prickly pear residue nanocellulose in this invention has a high extraction rate, high crystallinity, and good enhancement effect. The composite preservation film with added nanocellulose has a uniform and dense structure, a smooth surface, and strong mechanical properties, barrier properties, antioxidant properties, and thermal stability. It can effectively prevent nuts from getting damp and oxidized during storage, maintain the stability of nut oils, and is beneficial to the preservation of nuts.

[0142] 5) The edible composite preservation film prepared by this invention, when applied to walnut preservation, exhibits excellent preservation effects while reducing plastic pollution. Compared with aluminum foil packaging, which is widely used in the market and has good preservation effects, the moisture content of walnuts packaged with composite preservation film decreases less during storage, and the yellow-blue value of walnuts can be better maintained. Thus, the composite preservation film can effectively maintain the moisture content of walnuts and keep the color of walnuts from changing significantly during storage. During storage, the free fatty acids and antioxidant values ​​of walnuts packaged with composite preservation film are maintained at a low level, significantly lower than those of walnuts packaged with aluminum foil. Thus, the composite preservation film can inhibit the oxidation of walnuts and effectively extend their shelf life.

[0143] Although the present invention has been illustrated and described with reference to preferred embodiments, those skilled in the art should understand that various changes and modifications can be made to the present invention without departing from the scope defined by the claims.

Claims

1. An edible composite food preservation film, characterized in that, By weight percentage, it includes the following ingredients: 4-10% modified black garlic melanin, 2-5% prickly pear pomace extract, 3-6% prickly pear pomace nanocellulose, 18-28% starch, 18-37% gelatin, 18-37% D-sorbitol, and 9-12% water; The modified black garlic melanin was prepared by an ultrasonic-assisted enzymatic hydrolysis method. The ultrasonic-assisted enzymatic hydrolysis method includes the following steps: mixing black garlic with water, grinding and extracting in an ultrasonic water bath, filtering and adding dichloromethane to the supernatant for defatting, then dialyzing and freeze-drying to obtain black garlic melanin; dissolving the obtained black garlic melanin in water, adding a complex protease and enzymatically hydrolyzing in an ultrasonic water bath, filtering and boiling to inactivate the enzyme to obtain the enzymatic hydrolysate, and freeze-drying to obtain the modified black garlic melanin. The prickly pear residue extract was prepared by ultrasound-assisted solvent extraction. The ultrasound-assisted solvent extraction method includes the following steps: the dried prickly pear residue was crushed and sieved, ethanol solution was added and extracted in an ultrasonic water bath, the extract was obtained by filtration, and the extract was freeze-dried to obtain the prickly pear residue extract.

2. The edible composite preservation film according to claim 1, characterized in that, The mass-to-volume ratio of black garlic to water is 1:7-9; the amount of dichloromethane added is 40-60% of the supernatant volume; the molecular weight of the ultrafiltration membrane used for dialysis is 3 kDa; the complex protease is a combination of trypsin, alkaline protease, and papain, with an enzyme activity ratio of 3:6:1; the amount of the complex protease added is 3000 U / g; the enzymatic hydrolysis time is 1-3 h; and the ultrasonic power is 100-200 W.

3. The edible composite preservation film according to claim 1, characterized in that, The sieving process involves passing the material through a 40-60 mesh sieve; the concentration of the ethanol solution is 0-40%; the mass-to-volume ratio of the prickly pear pomace to the ethanol solution is 1:30-50; the ultrasonic power is 100-500 W; the extraction temperature is 40-60℃; and the extraction time is 10-30 min.

4. The edible composite preservation film according to claim 1, characterized in that, The prickly pear residue nanocellulose is prepared by one of the following methods: acid hydrolysis, oxidation, and enzymatic hydrolysis.

5. A method for preparing an edible composite preservation film as described in any one of claims 1-4, characterized in that, The process includes the following steps: first, dissolving the modified black garlic melanin, prickly pear residue extract, prickly pear residue nanocellulose and starch in water; second, dissolving the gelatin; third, dissolving the D-sorbitol; cooling and filtering to obtain a composite membrane solution; forming the composite membrane solution into a film; and finally, drying it to obtain a composite preservation film.

6. The method according to claim 5, characterized in that, The first step of dissolution is carried out at 70-80℃ for 10-15 minutes; the second step of dissolution is carried out at 70-80℃ for 20-25 minutes; and the third step of dissolution is carried out at 75-85℃ for 30-40 minutes.

7. The method according to claim 6, characterized in that, The filtration uses a 60-80 mesh filter; the drying temperature is 25-28℃, the relative humidity is 50-55%, and the drying time is 24-30 h.

8. The application of an edible composite preservation film as described in any one of claims 1-4 in the preservation of walnuts.

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