Gel of polymerized whey protein and dendrobium officinale polysaccharide and application of gel in preparation of yoghourt or gel base membrane

Abstract

The invention relates to the field of gel, in particular to gel of polymerized whey protein and dendrobium officinale polysaccharide and application of the gel in preparation of yoghourt or a gel base membrane. Comprising the following steps: (1) dissolving whey protein and dendrobium officinale polysaccharide powder in deionized water, and uniformly mixing; adding an inducer, adjusting the pH value, heating and cooling to prepare polymerized whey protein and dendrobium officinale polysaccharide hydrogel; (2) dissolving goat milk powder with deionized water, adding sugar, sterilizing, cooling, adding polymerized whey protein and dendrobium officinale polysaccharide gel, inoculating a leavening agent, and fermenting to obtain yoghourt; (3) adding glycerol into the polymerized whey protein and dendrobium officinale polysaccharide gel, and stirring to obtain a film forming solution; and uniformly spreading the film forming liquid, and drying to obtain the gel base film. According to the invention, the texture of the goat milk yoghourt is improved, and the application of polymerized whey protein and dendrobium officinale polysaccharide in dairy products is widened; the quality of the fruits is improved, and the application of the protein and the dendrobium officinale polysaccharide gel base membrane is widened.

Description

Technical Field

[0001] The invention relates to the field of gel, in particular to a gel of polymerized whey protein and dendrobium officinale polysaccharide and application of the gel in preparing yogurt or a gel-based film. Background Art

[0002] Whey protein isolate contains more than 90% protein, including α-lactalbumin, β-lactoglobulin, bovine serum albumin, etc. It is widely used in dairy products, desserts and beverages in the food industry because of its excellent physical and chemical properties, such as foaming, emulsification and gelation. Polymerized whey protein is a protein polymer that is polymerized by physical, chemical or enzymatic methods using whey protein isolate or whey protein concentrate as the main raw material. The structural matrix of polymerized whey protein can be used to embed water, flavor substances and probiotics. However, the brittleness and environmental sensitivity of polymerized whey protein gel limit its application potential in the food industry.

[0003] Goat milk yogurt is rich in nutrition, contains a variety of vitamins, minerals and high-quality proteins, is easy to digest and absorb, can effectively supplement the nutrients needed by the human body, and promote physical health. Its fat globule particles are small and easier to be absorbed by the human body, which helps to beautify the skin, enhance immunity, etc. However, the texture of goat milk yogurt is often thin and the taste is poor. The main reason is that the casein content in goat milk is relatively low, and the whey protein content is high, resulting in the gel structure formed during the fermentation process is not tight enough, and the lactose content in goat milk is low, and lactic acid is produced less, which further affects the formation and stability of the gel structure. Traditional thickeners such as pectin are expensive and easily denatured under high temperature or acidic conditions, which limits its application. Therefore, it is of great significance to apply polymerized whey protein-polysaccharide gel to the preparation of goat milk yogurt and improve its texture.

[0004] Apples are crispy, sweet, and juicy. They contain a variety of nutrients such as vitamins, minerals, and dietary fiber, which are beneficial to human health. However, there are many challenges in preserving apples after harvest. On the one hand, apples have strong respiration after harvest, and their peels are thin and easily damaged. They are very likely to spoil due to mechanical damage and microbial infection during logistics, transportation, and storage. In addition, apples are also prone to water loss at room temperature, which causes the fruit to shrink and taste worse, seriously affecting its quality and shelf life. On the other hand, the current methods for preserving fruits after harvest mainly include chemical methods and physical methods, but both have certain limitations. Although chemical preservation methods can inhibit the growth of microorganisms to a certain extent, they are not in line with the trend of green development because traditional chemical preservatives have problems such as chemical residues, environmental pollution, and bacterial resistance; and physical preservation methods such as low-temperature refrigeration and controlled atmosphere preservation require specific equipment and places, are cumbersome to operate, take a long time, and are difficult to achieve preservation and transportation at the same time, which is not conducive to the commercial promotion and application of fruit preservation. Therefore, it is of great practical significance to develop a new, efficient and environmentally friendly plastic wrap material for use in the preservation of apples and to improve the preservation effect of apples.

[0005] Polymerized whey protein is a protein polymer made of whey protein isolate or whey protein concentrate through physical, chemical or enzymatic polymerization. Its structural matrix can be used to embed water, nutrients, etc., and has good film-forming properties and certain mechanical strength. However, polymerized whey protein gel is brittle and environmentally sensitive, which limits its potential application in fruit preservation.

[0006] Dendrobium officinale polysaccharide has strong pharmacological activities such as anti-aging, anti-oxidation, anti-tumor and enhancing body immunity. There is no report on the technology of forming polymers between Dendrobium officinale polysaccharide and whey protein. Summary of the invention

[0007] In view of the deficiencies of the prior art, the object of the present invention is to provide a polymerized whey protein-Dendrobium officinale polysaccharide gel and its application in the preparation of yogurt or gel-based film.

[0008] By adding polymerized whey protein and Dendrobium officinale polysaccharide gel (which is a hydrogel), the prepared goat milk yogurt not only has excellent texture, delicate taste and unique flavor, but also has high bioavailability, thereby better meeting consumers' demand for high-quality dairy products.

[0009] By using polymerized whey protein and Dendrobium officinale polysaccharide gel as gel-based film materials, the preserved apples can not only effectively reduce the respiration intensity and ethylene release, but also delay the aging process. The film formed by polymerized whey protein and Dendrobium officinale polysaccharide gel can effectively block oxygen and moisture, reduce the activity of pectinase, thereby slowing down the decomposition of pectin, slowing down the degradation and destruction of cell walls, maintaining the hardness and structural integrity of fruits, and preventing fruits from softening. Dendrobium officinale polysaccharide has antibacterial and antioxidant properties, which can reduce the damage of microorganisms and oxidation reactions to fruits, and further delay the degradation of cell walls. The gel film can form a physical barrier, reduce the impact of external factors on fruits, and maintain their freshness. In summary, this gel film can effectively slow down the degradation of cell walls and extend the shelf life of fruits by inhibiting the activity of pectinase and providing physical protection.

[0010] In order to achieve the above object, the present invention adopts the following technical scheme:

[0011] A gel of polymerized whey protein and dendrobium officinale polysaccharide. The preparation process of the gel is as follows: dissolving whey protein powder and dendrobium officinale polysaccharide powder in deionized water, mixing them evenly to make the mass concentration of whey protein 8-12% and the mass concentration of dendrobium officinale polysaccharide 0.5-2.5%, adding 0.1-0.3% sodium carbonate as an inducer to obtain a mixed solution containing whey protein, dendrobium officinale polysaccharide and the inducer, stirring at 20-30 DEG C for 15-30 minutes; adjusting the pH of the mixed solution to 6.5-7.5 (the pH is conducive to forming a gel), heating at 80-90 DEG C for 15-30 minutes, cooling, and obtaining the gel of polymerized whey protein and dendrobium officinale polysaccharide; the whey protein powder is isolated whey protein powder or concentrated whey protein powder.

[0012] Furthermore, the concentration of Dendrobium officinale polysaccharide is 0.5-2.5%, preferably 0.5-1.5%, and more preferably 1.0-1.5%.

[0013] Another object of the present invention is to disclose an application of a gel of polymerized whey protein and dendrobium officinale polysaccharide in preparing yogurt. The preparation process of the yogurt is as follows: 6-8% sucrose is added to goat milk, and the milk is cooled after pasteurization or high-temperature sterilization or low-temperature sterilization by induction electric field, and then 0.5-1.5% w / v of the gel of polymerized whey protein and dendrobium officinale polysaccharide is added and a starter is inoculated to obtain yogurt by fermentation.

[0014] In a preferred embodiment, goat milk powder is dissolved in deionized water, and the final concentration of goat milk is 10-15% w / v; 6-8% sucrose is added to the goat milk; 80-90°C is heated for 5-15 minutes; after cooling to 41-45°C, 0.5-1.5% w / v of polymerized whey protein and gel of Dendrobium officinale polysaccharide are added; 0.02-0.05% w / v of ABY-8 starter is inoculated; fermentation is continued at 41-45°C to a final pH value of 4.35±0.10. In the yogurt preparation process of the present invention, the amount of polymerized whey protein and gel of Dendrobium officinale polysaccharide added is small, reaching 0.5-1.5% w / v, and the texture characteristics, particle size dehydration shrinkage, and microstructure of the formed yogurt are significantly improved.

[0015] Another object of the present invention is to provide a goat milk yogurt thickener, comprising the aforementioned polymerized whey protein and the gel of Dendrobium officinale polysaccharide.

[0016] The present invention also provides an application of a gel of polymerized whey protein and dendrobium officinale polysaccharide in preparing a gel-based membrane. Glycerol is added to the gel of polymerized whey protein and dendrobium officinale polysaccharide, and the mixture is stirred evenly to obtain a membrane-forming liquid. The membrane-forming liquid is poured into a flat dish, the thickness of which is controlled to be 0.5-1.0 mm, and the dish is sealed and dried to obtain the gel-based membrane.

[0017] Furthermore, the added amount of glycerol is 2-4%.

[0018] Preferably, the drying temperature is 45°C-65°C, and the drying time is 10-20 hours.

[0019] The invention also discloses a gel base film, which comprises adding 2-4% glycerol to a gel of polymerized whey protein and dendrobium officinale polysaccharide, stirring evenly to obtain a film-forming liquid; pouring the film-forming liquid into a flat dish, controlling the thickness to be 0.5-1.0 mm, sealing, and drying to obtain the gel base film.

[0020] The last object of the present invention is to disclose the application of the aforementioned polymerized whey protein and Dendrobium officinale polysaccharide gel or gel-based film in fruit preservation. When used, the fruit surface is wrapped with the gel-based film and the fruit storage temperature is controlled at 0-4°C.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The gel thickener of polymerized whey protein and Dendrobium officinale polysaccharide prepared by the present invention forms a gel with excellent viscosity and stability by compounding isolated whey protein with Dendrobium officinale polysaccharide. The emulsifying and gelling properties of isolated whey protein combined with the thickening and biological activity of Dendrobium officinale polysaccharide can significantly improve the quality of goat milk yogurt, making it thicker and more delicate, and improving the taste and appearance. At the same time, the composite gel can also enhance the nutritional value and health function of goat milk yogurt, thereby improving the overall quality of goat milk yogurt.

[0023] (2) The gel-based film of polymerized whey protein and Dendrobium officinale polysaccharide prepared by the present invention (which is a gel-based cling film) utilizes the excellent film-forming property of polymerized whey protein, the thickening property of Dendrobium officinale polysaccharide, and the moisturizing property of glycerol. Whey protein imparts good mechanical properties and stability to the gel-based film, while Dendrobium officinale polysaccharide further enhances the texture and stability of the cling film and improves its overall performance. Glycerol can effectively maintain the moisture content of apple fruit and significantly extend the shelf life. In addition, the cling film also provides apples with health functions such as anti-oxidation, thereby improving the quality and added value of apples.

[0024] (3) The preparation method of the present invention is simple, and both polymerized whey protein and Dendrobium officinale polysaccharide are natural ingredients with a wide range of sources and low cost, which reduces production costs. The preparation process is environmentally friendly, no harmful substances are produced, the production cycle is short, and the economic value is high. Compared with traditional thickeners, the thickener of the present invention is not only more superior in function, but also has significant advantages in cost and environmental protection, and is suitable for large-scale industrial production. Compared with traditional preservation methods, the gel-based film material of the present invention has significant advantages in preservation effect, cost and environmental protection, and is suitable for large-scale industrial production and promotion and application.

[0025] (4) The gel-based film material prepared by the present invention has simple use conditions and is easy to operate. The addition of whey protein and Dendrobium officinale polysaccharide gel not only improves the fresh-keeping quality of apples, but also adds health functions such as antioxidants, which helps consumers obtain healthier and safer fruit products and better meets the market demand for high-quality fresh-keeping apples. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0027] Figure 1 Schematic diagram of particle size and potential of gel of polymerized whey protein and Dendrobium officinale polysaccharide;

[0028] Figure 2 Schematic diagram of the hydrophobicity of the gel of polymerized whey protein and Dendrobium officinale polysaccharide;

[0029] Figure 3 The three-dimensional fluorescence images of the gel of polymerized whey protein and Dendrobium officinale polysaccharide, A, PWP three-dimensional fluorescence image, B, PWPD1 three-dimensional fluorescence image;

[0030] Figure 4 A is a three-dimensional fluorescence image of the gel of polymerized whey protein and Dendrobium officinale polysaccharide, C, a three-dimensional fluorescence image of PWPD2, and D, a three-dimensional fluorescence image of PWPD3;

[0031] Figure 5 A is a three-dimensional fluorescence image of the gel of polymerized whey protein and Dendrobium officinale polysaccharide, E, a three-dimensional fluorescence image of PWPD4, B, a three-dimensional fluorescence image of PWPD5;

[0032] Figure 6 Schematic diagram of thermal stability and apparent viscosity of gel of polymerized whey protein and Dendrobium officinale polysaccharide;

[0033] Figure 7 It is the SR-IR analysis diagram of the gel of polymerized whey protein and Dendrobium officinale polysaccharide, A1-F1 are the two-dimensional images of PWP, PWPD1, PWPD2, PWPD3, PWPD4, and PWPD5 respectively;

[0034] Figure 8 Two-dimensional correlation spectra (2D-COS) of the gel of polymerized whey protein and Dendrobium officinale polysaccharide, AC corresponds to PWP, PWPD1, and PWPD2, respectively;

[0035] Fig. 9 Two-dimensional correlation spectra (2D-COS) of the gel of polymerized whey protein and Dendrobium officinale polysaccharide, DF corresponds to PWPD3, PWPD4, and PWPD5, respectively;

[0036] Fig.10 The microstructure of the gel of polymerized whey protein and Dendrobium officinale polysaccharide. AF corresponds to PWP, PWPD1, PWPD2, PWPD3, PWPD4, and PWPD5, respectively;

[0037] Fig.11 The microstructure of various yogurt samples;

[0038] Fig.12 This is a schematic diagram of the particle size syneresis shrinkage of goat milk yogurt;

[0039] Fig.13 The DSC curves of polymerized whey protein and its gel-based films (PWP-D1, PWP-D2, PWP-D3) composited with different concentrations of Dendrobium officinale polysaccharide;

[0040] Fig.14 The stress-strain curves of polymerized whey protein and its gel-based films (PWP-D1, PWP-D2, PWP-D3) composited with different concentrations of Dendrobium officinale polysaccharide;

[0041] Fig.15 Schematic diagram of the effect of polymerized whey protein and its gel-based films (PWP-D1, PWP-D2, PWP-D3) composited with different concentrations of Dendrobium officinale polysaccharides on the hardness of fresh-cut apples. DETAILED DESCRIPTION

[0042] The present invention is further described in detail below through specific preferred embodiments, but the present invention is not limited to the following embodiments.

[0043] It should be noted that, unless otherwise specified, the chemical reagents involved in the present invention were purchased through commercial channels.

[0044] Whey protein isolate was purchased from Fonterra (Auckland, New Zealand) with a protein content of 93.14%. Dendrobium officinale polysaccharide was purchased from Baichuan Kangze Biotechnology Co., Ltd. with a purity of 98%. ABY-8 fermentation agent was purchased from Dennisit Co., Ltd. Goat milk powder was purchased from Anmu (Jiangsu) Co., Ltd. In the present invention, other commercially available fermentation agents can also be used.

[0045] Example 1

[0046] Preparation of hydrogel of polymerized whey protein and Dendrobium officinale polysaccharide:

[0047] Dissolve whey protein isolate and Dendrobium officinale polysaccharide powder in deionized water to obtain whey protein isolate stock solution with a mass concentration of 20% (w / v, g / mL) and Dendrobium officinale polysaccharide stock solution with a mass concentration of 10% (w / v, g / mL), respectively. Stir the whey protein isolate stock solution and the Dendrobium officinale polysaccharide stock solution at room temperature for 30 minutes, respectively, and control the rotation speed at 300rpm. Prepare a mixed solution of whey protein isolate and Dendrobium officinale polysaccharide (the whey protein isolate stock solution and the Dendrobium officinale polysaccharide stock solution are mixed uniformly at room temperature in a certain proportion), so that the mass concentration of whey protein isolate in the mixed solution is 10%, and the mass concentration of Dendrobium officinale polysaccharide is 0.5%, 1.0%, 1.5%, 2% and 2.5%, respectively. Add 0.2% sodium carbonate (referring to the mass of sodium carbonate being 0.2% of the total mass of the mixed solution) as an inducing agent, stir for 30 minutes at 25°C to obtain a mixture. The pH was adjusted to 7, and the mixture was heated at 85° C. for 30 minutes and then cooled to room temperature to obtain a hydrogel of polymerized whey protein and Dendrobium officinale polysaccharide.

[0048] Example 2

[0049] Group C:

[0050] The preparation method of the gel of polymerized whey protein and Dendrobium officinale polysaccharide as a goat milk yogurt thickener is prepared according to the following process:

[0051] (1) dissolving whey protein isolate in water to prepare a whey protein isolate stock solution with a mass concentration of 20% (w / v, g / mL);

[0052] (2) stirring the whey protein isolate stock solution at room temperature for 30 min at a speed of 300 rpm;

[0053] (3) dissolving the Dendrobium officinale polysaccharide in water to prepare a Dendrobium officinale polysaccharide stock solution with a mass concentration of 10% (w / v, g / mL);

[0054] (4) stirring the above-mentioned Dendrobium officinale polysaccharide stock solution at room temperature for 30 minutes, and the rotation speed was controlled at 300 rpm;

[0055] (6) The separated whey protein stock solution and the Dendrobium officinale polysaccharide stock solution obtained in steps (2) and (4) are mixed with deionized water to obtain a mixed solution of whey protein with a final concentration of 10% (w / v, g / mL) and 0.5% (w / v, g / mL) of Dendrobium officinale polysaccharide, 0.2% sodium carbonate is added as an inducer, the mixture is stirred at 25° C. for 30 minutes, the pH is adjusted to 7, the mixture is heated to 85° C. and heated at a constant temperature for 30 minutes, with continuous stirring during the heating process, and then cooled to room temperature to obtain a gel of polymerized whey protein and Dendrobium officinale polysaccharide.

[0056] Then, the gel of polymerized whey protein and Dendrobium officinale polysaccharide is used as a goat milk yogurt thickener to prepare goat milk yogurt:

[0057] (7) Dissolve goat milk powder in deionized water at 40°C. The final concentration of goat milk is 12.5% ​​(w / v, g / mL, referring to the concentration of milk powder in goat milk). Then, add 7% (w / v, g / mL) sucrose to the goat milk. Heat at 95°C for 10 min for high temperature sterilization. After cooling to 43°C, add the gel of polymerized whey protein and Dendrobium officinale polysaccharide to the goat milk at an addition amount of 1% (w / v, g / mL), and inoculate ABY-8 starter (0.03%, w / v, g / mL).

[0058] (8) Ferment at 43°C for 8 hours until the final pH value is 4.35±0.10. Cool to room temperature and refrigerate at 4°C to obtain the finished yogurt.

[0059] Group D:

[0060] A mixed solution of whey protein with a final concentration of 10% (w / v) and 1% (w / v) Dendrobium officinale polysaccharide was obtained, and the remaining steps were the same as those of Group C.

[0061] Group E:

[0062] A mixed solution of whey protein with a final concentration of 10% (w / v) and 1.5% (w / v) of Dendrobium officinale polysaccharide was obtained, and the remaining steps were the same as those of Group C.

[0063] Group F:

[0064] A mixed solution of whey protein with a final concentration of 10% (w / v) and 2% (w / v) polysaccharide from Dendrobium officinale was obtained, and the remaining steps were the same as those of Group C.

[0065] Group G:

[0066] A mixed solution of whey protein with a final concentration of 10% (w / v) and 2.5% (w / v) of Dendrobium officinale polysaccharide was obtained, and the remaining steps were the same as those of Group C.

[0067] Comparative Example 1

[0068] Group A (pure goat yogurt): Dissolve goat milk powder with deionized water at 40°C. The final concentration of goat milk is 12.5% ​​(w / v, g / mL, referring to the concentration of milk powder in goat milk). Then, add 7% (w / v, g / mL) sucrose to the goat milk. Sterilize at high temperature at 95°C for 10 minutes. After cooling to 43°C, inoculate ABY-8 starter (0.03%, w / v, g / mL). Ferment at 43°C for 8 hours to a final pH of 4.35±0.10. Cool to room temperature and refrigerate at 4°C to obtain the finished yogurt.

[0069] Group B (goat yogurt + whey protein isolate, without Dendrobium officinale polysaccharide):

[0070] (1) dissolving whey protein isolate in water to prepare a whey protein isolate stock solution with a mass concentration of 20% (w / v, g / mL);

[0071] (2) stirring the whey protein isolate stock solution at room temperature for 30 min at a speed of 300 rpm;

[0072] (3) The isolated whey protein stock solution obtained in step (2) is mixed with deionized water to obtain a whey protein solution with a final concentration of 10% (w / v), 0.2% sodium carbonate is added as an inducer, and the mixture is stirred at 25° C. for 30 minutes, the pH is adjusted to 7, the mixture is heated to 85° C. and heated at a constant temperature for 30 minutes with continuous stirring, and the mixture is cooled to room temperature to obtain a polymerized whey protein gel.

[0073] (4) Dissolve goat milk powder in deionized water at 40°C. The final concentration of goat milk is 12.5% ​​(w / v, g / mL, referring to the concentration of milk powder in goat milk). Then, add 7% (w / v, g / mL) sucrose to the goat milk. Heat for 10 min at 95°C for high temperature sterilization. After cooling to 43°C, add polymerized whey protein gel at an addition amount of 1% (w / v, g / mL) to the goat milk and inoculate ABY-8 starter (0.03%, w / v, g / mL).

[0074] (5) Ferment at 43°C for 8 hours until the final pH value is 4.35±0.10. Cool to room temperature and refrigerate at 4°C to obtain the finished yogurt.

[0075] Example 3

[0076] PWP-D1 Group:

[0077] The preparation method of the gel of polymerized whey protein and Dendrobium officinale polysaccharide is prepared according to the following process:

[0078] (1) Dissolve whey protein isolate in water to prepare a whey protein isolate stock solution with a mass concentration of 20% (w / v, g / mL).

[0079] (2) The above whey protein isolate stock solution was stirred at room temperature for 30 min with the rotation speed controlled at 300 rpm.

[0080] (3) Dissolving the Dendrobium officinale polysaccharide in water to prepare a Dendrobium officinale polysaccharide stock solution with a mass concentration of 10% (w / v, g / mL).

[0081] (4) The Dendrobium officinale polysaccharide stock solution was stirred at room temperature for 30 min, with the rotation speed controlled at 300 rpm.

[0082] (5) adding deionized water to the separated whey protein stock solution and the Dendrobium officinale polysaccharide stock solution obtained in steps (2) and (4) to obtain a mixed solution of whey protein with a final concentration of 10% (w / v) and 0.5% (w / v) of Dendrobium officinale polysaccharide, adding 0.2% sodium carbonate as an inducer, stirring at 25° C. for 30 minutes; adjusting the pH to 7, heating at a constant temperature of 85° C. for 30 minutes, stirring continuously during the heating process, and then cooling to room temperature to obtain a polymerized whey protein and Dendrobium officinale polysaccharide gel.

[0083] Then, the polymerized whey protein and the Dendrobium officinale polysaccharide gel are used to prepare a gel-based film material for fruit preservation, and the specific steps are as follows:

[0084] (6) After the polymerized whey protein and Dendrobium officinale polysaccharide gel is cooled to room temperature, 3% (w / w, meaning that the mass of glycerol accounts for 3% of the total mass of the polymerized whey protein and Dendrobium officinale polysaccharide gel and glycerol) of glycerol is added and stirred evenly to obtain a film-forming solution.

[0085] (7) Pour the film-forming liquid into a flat dish with a thickness of 0.8 mm, seal it with a conventional commercially available plastic wrap, and dry it in an oven at 45°C for 16 hours.

[0086] (8) After the drying is completed, the plate is taken out, the conventional commercially available cling film is removed, the gel base film is peeled off from the plate, and the plate is placed in a desiccator and cooled to room temperature, thereby obtaining a polymerized whey protein and Dendrobium officinale polysaccharide gel base film material.

[0087] (9) After the apples are cleaned and cut into pieces, the surface of the apple pieces is wrapped with the prepared gel-based membrane material.

[0088] (10) The apple pieces wrapped with the gelatin base film are stored in an environment of 0-4°C.

[0089] PWP-D2 Group:

[0090] A mixed solution of whey protein with a final concentration of 10% (w / v) and 1% (w / v) polysaccharide from Dendrobium officinale was obtained, and the remaining steps were the same as those of the PWP-D1 group.

[0091] PWP-D3 Group:

[0092] A mixed solution of whey protein with a final concentration of 10% (w / v) and 1.5% (w / v) of Dendrobium officinale polysaccharide was obtained, and the remaining steps were the same as those of the PWP-D1 group.

[0093] Comparative Example 2 (without Dendrobium officinale polysaccharide)

[0094] (1) Dissolve whey protein isolate in water to prepare a whey protein isolate stock solution with a mass concentration of 20% (w / v, g / mL).

[0095] (2) The above whey protein isolate stock solution was stirred at room temperature for 30 min with the rotation speed controlled at 300 rpm.

[0096] (3) adding deionized water to the isolated whey protein stock solution obtained in step (2) to obtain a whey protein solution with a final concentration of 10% (w / v), adding 0.2% sodium carbonate as an inducer, and stirring at 25° C. for 30 minutes; adjusting the pH to 7, heating at a constant temperature of 85° C. for 30 minutes, and stirring continuously during the heating process, and then cooling to room temperature to obtain a polymerized whey protein gel.

[0097] (4) After the polymerized whey protein gel is cooled to room temperature, 3% (w / w, meaning that the mass of glycerol accounts for 3% of the total mass of the whey protein gel and glycerol) of glycerol is added and stirred evenly to obtain a membrane-forming solution.

[0098] (5) Pour the film-forming liquid into a flat dish with a thickness of 0.8 mm, seal it with a conventional commercially available plastic wrap, and dry it in a 45°C oven for 16 hours.

[0099] (6) After drying, the plate is taken out, a conventional commercially available cling film is peeled off from the plate, and the plate is placed in a dryer and cooled to room temperature, thereby obtaining a whey protein gel-based film material.

[0100] (7) After the apples are cleaned and cut into pieces, the surface of the apple pieces is wrapped with the prepared gel-based membrane material.

[0101] (8) The apple pieces wrapped with the gelatin base film are stored in an environment of 0-4°C.

[0102] The material obtained in Comparative Example 2 is the PWP group.

[0103] 1. Characterization of the polymerized whey protein (PWP)-Dendrobium officinale polysaccharide (DOP) hydrogel prepared in Example 1

[0104] 1. Particle size

[0105] like Figure 1 In A, when the concentration of Dendrobium officinale polysaccharide increased from 0% to 1.5%, the particle size increased from 90.1±1.88nm to 119.4±1.74nm. DOP molecules filled in the gaps between the PWP surface particles, enhancing the protein-polysaccharide interaction. However, excess polysaccharide (2% and 2.5%) caused the PWP-DOP particle size to decrease to 95.1±1.70nm and 97.1±1.97nm. This is due to the steric hindrance of the acetyl group in DOP, which hindered the PWP-DOP complex.

[0106] 2. Potential

[0107] like Figure 1 In Figure B, as the DOP concentration increases from 0% to 2.5%, the zeta potential level of the PWP-DOP gel increases from -33.81±1.04mV to -39.55±0.71mV. This can be attributed to the modification of the molecular structure, which affects the orientation and conformation of the molecules at the solution interface and enhances the overall negative charge of the system. Compared with PWP, the PWP-DOP gel has more negative charge, indicating that the colloidal stability of the complex is enhanced.

[0108] 3. Hydrophobicity

[0109] Compared with PWP, the addition of 0.5% DOP significantly increased the hydrophobicity of PWP. This was attributed to the acetylation of the acetyl groups in DOP. As the DOP concentration increased from 1.0% to 2.5%, the hydrophobicity of the PWP-DOP composite system decreased with increasing concentration. Specifically, the large number of hydrophilic hydroxyl groups in DOP enhanced the polarity of the surrounding environment, promoted the aggregation of non-polar molecules inside the protein through non-covalent interactions, and reduced the hydrophobicity, such as Figure 2 shown.

[0110] 4.3D Intrinsic Fluorescence

[0111] like Figure 3-5 As shown in the figure, as the DOP concentration increases from 0% to 2.5%, the fluorescence intensity of the PWP-DOP gel decreases. This indicates that tryptophan is transferred to a more hydrophilic environment, increasing the hydrophilicity of the sample and producing a shielding effect. This is closely related to the incorporation of the hydrophilic hydroxyl groups of DOP, and the decrease in fluorescence intensity is also due to the construction of a more compact tertiary conformation.

[0112] 5. Thermal stability test

[0113] Differential scanning calorimetry can be used to determine the thermal stability of protein-polysaccharide complexes during heating and cooling. PWPD1 corresponds to group C, PWPD2 corresponds to group D, PWPD3 corresponds to group E, PWPD4 corresponds to group F, and PWPD5 corresponds to group G. Figure 6 A in the figure shows that the thermal transition peak temperature of the PWP DSC curve is 81.03℃. The peak temperature of the endothermic transition increases from PWPD1 to PWPD3, from 81.69℃ to 95.89℃. The higher the saturation temperature, the better the thermal stability. The results show that the addition of DOP significantly improves the thermal stability of PWP-DOP gel. This can be attributed to the fact that the addition of DOP enhances the hydrogen bond network structure and promotes a more stable conformation. The midpoint temperatures of the thermal transitions of PWPD4 and PWPD5 are 93.07℃ and 85.13℃, respectively. This is because the excess DOP molecules destroy the original gel structure and reduce its thermal stability, so PWPD3 has the highest thermal stability.

[0114] 6. Apparent viscosity of PWP-DOP gel

[0115] Steady-state shear measurements were performed on PWP and PWP-DOP composite solutions to study their rheological behaviors. All solution samples showed shear thinning characteristics, which means that the viscosity decreased with increasing shear rate. The increase in shear rate may have destroyed the aggregated protein network, thereby reducing the flow resistance and apparent viscosity. With the increase in DOP concentration, the apparent viscosity of PWP-DOP gel increased compared with PWP. With the increase in polysaccharide concentration, the consistency coefficient and apparent viscosity increased, indicating that stronger cross-links were formed between polysaccharides and proteins. In addition, heat treatment can also enhance interaction forces, such as hydrophobic interactions, hydrogen bonds, and disulfide bonds, which are conducive to the adhesion and binding of DOP molecules to the PWP surface, thereby obtaining higher shear viscosity, such as Figure 6 As shown in B.

[0116] 7. SR-IR Analysis of PWP-DOP Gel

[0117] SR-IR can reflect the structural changes of PWP-DOP gel during heating in real time. The presence of amide groups is significantly correlated with the hydrogen bond density. In addition, amide I (1700-1600 cm -1 ) and amide II (1600~1500cm -1 ) band is connected to the peptide backbone by hydrogen bonds. Figure 7 The wavelengths between 3450 and 3200 cm-1 were observed in all samples. -1 The broad peak between NH and OH corresponds to the stretching vibration of NH and OH, which indicates the existence of hydrogen bonding in the system. -1 There is a peak at Figure 7 The PWPD1 spectrum is from PWP (1630.49 cm -1 ) into PWPD1(1629.33cm -1 )、PWPD2(1635.96cm -1 )、PWPD3(1636.22cm -1 )、PWPD4(1635.93cm -1 ) and PWPD5(1635.89cm -1 ), which is due to the formation of hydrogen bonds during heating, which changes the frequency of C=O stretching vibration. PWP gel at 3270.21cm -1 The absorption peak at 3270.21 cm -1 The peaks at PWPD1 (3264.49 cm -1 )、PWPD2(3258.38cm -1 )、PWPD3(3252.52cm -1)、PWPD4(3254.52cm -1 ) and PWPD5(3252.05cm -1 ). This is because of the presence of hydrogen bonds during the formation of PWP-DOP gel. When the DOP concentration is 1.5%, at 1559.11 cm -1 、1443.85cm -1 、1401.33cm -1 、1380.25cm -1 、1242.64cm -1 and 1155.10cm -1 A new peak appeared at 1559.11cm, indicating that the presence of DOP has a significant effect on the structure of PWP. -1 The bands at 1443.85 and 1401.33 cm are formed by NH stretching combined with amide II. -1 The peak at 1380.25cm is caused by NH and CN vibration. -1 and 1242.64cm -1 The nearby peaks are caused by the symmetrical bending vibrations of the methyl CH and o-acetyl groups, which match the characteristic peaks of DOP. In addition, at 1155.10 cm -1 The peaks at are also related to COC, COH, and OH in the pyranose ring, indicating that the pyranose group of DOP is retained in the gel. These changes indicate that the formation of the PWP-DOP composite gel involves hydrogen bonding and affects its secondary structure.

[0118] 8. Two-dimensional correlation spectroscopy

[0119] Compared with FT-IR, two-dimensional correlation spectroscopy (2D-COS) is an effective tool for describing the transformation and reaction sequence of functional groups in the fingerprint region. Synchronous and asynchronous correlation infrared spectra of 2D-COS are shown in Figure 2. Figure 8 and Fig. 9 Compared with PWP, the addition of DOP increases the autocorrelation peak and cross peak in the synchronous correlation spectrum. It is mainly concentrated in 1628-1656cm -1 and 1681-1700cm -1 The cross peaks mainly appear at 1652-1697 cm -1region, corresponding to the stretching vibrations of C=O and C=C. The number of cross peaks of PWP-DOP gel is PWPD3>PWPD2>PWP>PWPD5>PWPD4>PWPD1. This indicates that the change of DOP concentration significantly changes the conformation of PWP. PWPD3 shows more cross peaks and autocorrelation peaks in both synchronous and asynchronous correlation spectra. This is due to the higher degree of group transformation and synergistic effect between the vibration modes of PWPD3 molecules.

[0120] 9. Molecular Docking

[0121] In order to deeply analyze the interaction between DOP and PWP, molecular docking simulations were performed. β-Lg accounts for about 70% of WPI and is therefore selected for molecular docking. Pymol and LigPlus software were used for three-dimensional and two-dimensional interaction analysis, respectively. The shape of the protein surface matches the conformation of the ligand, indicating that the binding sites of DOP and β-Lg are both on the protein surface. Lower binding energy means a stronger binding between molecules. The binding energy of β-Lg to DOP is -6.2 kcal / mol, indicating that DOP can bind tightly to β-Lg. DOP forms 12 hydrogen bonds with Pro 48, Glu 55, Glu 51, Lys 70, Asp 85, Lys 69, Lys 60, Pro 38, Ser 116, Gln 115, Ser 30 and Asp 28 residues of β-Lg, with an average bond length of There were 11 hydrophobic interactions between DOP and β-Lg at Thr 49, Pro 50, Ile 72, Ile 71, Leu 39, Asn 90, Ile 84, Met 107, Glu 112, Leu31, and Asn 109. The results showed that hydrogen bonding and hydrophobic interactions were the main binding forces between DOP and β-Lg, which supported the conclusions of surface hydrophobicity and SR-IR analysis.

[0122] 10. Microstructure

[0123] Cryo-SEM was used to obtain microstructural information about PWPI-DOP gels. Fig.10As shown in Figure A, the network structure of PWP is loose, bulky, and relatively uneven. This is due to the significant enlargement of the pore size caused by sodium ions and the weakening of the connection between adjacent structures. However, compared with PWP gel, PWP-DOP gel exhibits higher interconnectivity and a more compact network. This indicates that the complex coacervation between DOP and PWP has a synergistic effect. The compact network structure is mainly due to the hydrophobic interaction and hydrogen bonding between PWP and DOP, which is conducive to the formation of three-dimensional layer-layer stacking coacervates. Subsequently, at a DOP concentration of 2%, larger pores and looser structures were observed, which may be related to the dissociation of PWP-DOP gel. When the DOP concentration reached 2.5%, the network structure was destroyed and irregular agglomerates were formed. In this case, the excess DOP destroyed the interaction between PWP and led to changes in the microstructure.

[0124] 2. Yogurt Results Analysis

[0125] 1. Microstructure of goat milk yogurt

[0126] The microstructure of the yogurt samples was analyzed using cryogenic scanning. All samples were frozen using liquid nitrogen. The frozen samples were moved to the preparation chamber and broken using a cold scalpel blade set to -177°C. The samples were broken to expose the surface and then sublimated at -85°C for 15 minutes. The samples were sputter-plated with platinum at 10mV for 60 seconds. Finally, the samples were examined using a scanning electron microscope. The scanning electron microscope was set to -140°C and 5.0kV for observation.

[0127] Figure 8 The microstructure of various yogurt samples is shown. Fig.11 In A, pure goat milk yogurt showed irregular pore size and finer network. Fig.11 In B, the addition of whey protein enhances the network structure of yogurt. This is because the polymerized whey protein interacts with casein to form a micellar complex, resulting in a tight porous structure in the yogurt gel, thereby improving the consistency of goat milk yogurt. Fig.11 As shown in CE, compared with groups A and B, the three-dimensional protein network of yogurt was significantly improved with the increase of dendrobium polysaccharide concentration. The reason is that the composite gel of polymerized whey protein and dendrobium polysaccharide is embedded in the casein network to form a casein-gel complex, which reduces the gaps between protein clusters and makes the protein network structure more compact. However, the network structure of groups F and G is too dense or even destroyed, which affects the palatability of yogurt.

[0128] 2. Particle size syneresis of goat milk yogurt

[0129] The goat milk yogurt sample was centrifuged at 1200 rpm for 15 minutes. The syneresis was calculated by weighing the liquid emptied during the centrifugation. The calculation formula is syneresis (%) = (weight of collected liquid / weight of sample) × 100.

[0130] Syneresis is a key parameter for evaluating the quality of fermented dairy products. The syneresis values ​​of groups A, B, C, D, E, F, and G were 40.48667%, 30.08667%, 26.23667%, 23.60333%, 22.64333%, 24.80667%, and 24.24333%, respectively. Compared with group A, the addition of the composite gel of polymerized whey protein and Dendrobium officinale polysaccharide reduced the syneresis of yogurt ( Fig.12 B in the figure). This is because the network formed by the interaction between the composite gel and goat milk hinders the free flow of water, thus ensuring the taste characteristics of the yogurt. The smaller the syneresis of the yogurt, the better its water retention. Yogurt with strong water retention loses less water during storage and has a richer and smoother taste. Among them, group E has the lowest syneresis. Yogurt with strong water retention can better maintain freshness during storage and consumption and reduce water precipitation.

[0131] 3. The texture of goat milk yogurt

[0132] Texture data was recorded using a texture analysis instrument. Texture measurements were performed using a cylindrical probe at a speed of 1 mm / s for both the pre- and post-test stages. During the test, the probe penetrated 10.0 mm into the sample at a speed of 1 mm / s.

[0133] Table 1 summarizes the textural properties of the yogurt samples, including hardness, consistency, cohesion, and viscosity. Compared with group A, the addition of D. officinale polysaccharide improved the textural properties of yogurt. The hardness value of yogurt increased significantly from 98.28 g to 130.01 g from group A to group G (P < 0.05). The addition of D. officinale polysaccharide can intercept a large amount of water, promote the formation of goat milk yogurt, and improve the hardness of yogurt. The cohesion value increased significantly from 26.10 g to 45.88 g from group A to group G (P < 0.05). The addition of D. officinale polysaccharide enhanced the viscosity of yogurt, which is due to the ability of D. officinale polysaccharide to strengthen the hydrophobic interaction between amino acid side chains and change the strength of goat milk yogurt. The results of consistency and viscosity are consistent with those of hardness and cohesion. After adding the composite gel of polymerized whey protein and D. officinale polysaccharide, the consistency and viscosity of the yogurt samples were significantly improved. In conclusion, the textural properties of goat milk yogurt were improved after adding the composite gel of polymerized whey protein and Dendrobium officinale polysaccharide.

[0134] Table 1 Effects of adding polymerized whey protein and Dendrobium officinale polysaccharide gel on the texture of goat milk yogurt

[0135]

[0136]

[0137] Note: There are statistically significant differences among different groups (P<0.05)

[0138] 3. Thin film results analysis

[0139] 1. Thermal stability of the gel-based film of polymerized whey protein and Dendrobium officinale polysaccharide

[0140] The thermal transition temperature of the gel-based film of polymerized whey protein and Dendrobium officinale polysaccharide was obtained by differential scanning calorimetry. About 3-5 mg of the film (gel-based film) sample was placed in a sealed aluminum pan, heated at a rate of 10°C per minute between 25°C and 200°C, and then cooled to 25°C. An empty aluminum pan was used for control.

[0141] Fig.13 The DSC curves of polymerized whey protein and its films composited with different concentrations of Dendrobium officinale polysaccharide (PWP-D1, PWP-D2, PWP-D3) are shown in Figure 2. The peak temperatures of thermal transitions are 84.87℃ (PWP), 91.55℃ (PWP-D1), 97.88℃ (PWP-D2), and 94.71℃ (PWP-D3), respectively. With the increase of the concentration of Dendrobium officinale polysaccharide, the peak temperature of thermal transition of the film increases, indicating that the thermal stability of the film is significantly enhanced after the addition of Dendrobium officinale polysaccharide. This is attributed to the formation of more hydrogen bonds between the Dendrobium officinale polysaccharide molecules and whey protein, which enhances the molecular network structure of the film and thus improves its thermal stability. However, the thermal transition temperatures of PWP-D2 and PWP-D3 are significantly higher than those of other samples, indicating that the addition of Dendrobium officinale polysaccharide in this concentration range is most helpful in improving the thermal stability of the film. However, when the concentration of D. officinale polysaccharide reached a higher value (2%, 2.5%), the network structure was destroyed due to excessive intermolecular competition, which reduced the thermal stability. These results confirm the potential of D. officinale polysaccharide as a functional additive in improving the thermal properties of films.

[0142] 2. Mechanical properties of gel-based films of polymerized whey protein and Dendrobium officinale polysaccharide

[0143] Mechanical propertiesA TA-XT plus C texture analyzer was used to capture the stress-strain curves of the films. For testing, the nanofibrous membranes were cut into rectangular strips of 10 mm × 50 mm. The test speed was set at 0.5 mm / s. For each type of polymerized whey protein-Dendrobium officinale polysaccharide composite film, at least five samples were subjected to the testing procedure to ensure the statistical significance and reliability of the results.

[0144] according to Fig.14Analysis of the stress-strain curve shows that the mechanical properties of different film samples vary significantly. The stress and strain of the PWP sample are both low, indicating that its mechanical properties are weak. As the polysaccharide content increases, the mechanical properties of the composite film gradually increase. PWP-D1 shows a certain improvement, but its strain is low and its ductility is relatively insufficient. In contrast, PWP-D2 has the highest stress peak, reaching about 120MPa, showing excellent tensile strength. At the same time, its strain value is close to 120%, which is significantly higher than PWP-D1 and PWP-D3. It has good ductility, reflecting the balance of strength and flexibility, and is the sample with the best mechanical performance. The strain value of PWP-D3 is significantly lower than that of PWP-D2, and the stress peak is also slightly lower than that of PWP-D2, but the mechanical properties are still insufficient. Excessive polysaccharide content changes the internal structure of the film, thereby weakening its strength. Therefore, considering the comprehensive strength and toughness indicators, PWP-D2 is the best choice and is more suitable for applications requiring high mechanical strength and moderate flexibility.

[0145] 3. Effect of polymerized whey protein and Dendrobium officinale polysaccharide gel-based film on the hardness of fresh-cut apples

[0146] The firmness of apples was determined using a TA-XT plus C texture analyzer. The test speed was 2 mm / s. At least five samples were subjected to the test procedure to ensure statistical significance and reliability of the results.

[0147] Experimental Results Fig.15 The results showed that there were significant differences in the effects of different treatment groups on the maintenance of apple hardness. The hardness of the PWP group (control group) decreased the fastest, from the initial about 350g to below 200g within 4 days, indicating that its preservation performance was poor and it was difficult to effectively delay the softening process of apples. The PWP-D1, PWP-D2 and PWP-D3 groups all significantly improved the hardness maintenance effect, especially the PWP-D2 and PWP-D3 groups, whose hardness on the 4th day was maintained at about 250g and 255g respectively, showing their superior preservation performance, while the hardness of the PWP-D1 group dropped to 222g on the fourth day, which was significantly lower than that of the PWP-D2 and PWP-D3 groups. This shows that both PWP-D2 and PWP-D3 formulas have a strong protective effect on the maintenance of apple hardness, and the concentration of Dendrobium officinale polysaccharide in the polymerized whey protein-Dendrobium officinale polysaccharide composite film has a more prominent effect on the hardness of the fruit.

[0148] The superior performance of PWP-D2 and PWP-D3 is attributed to the following aspects. First, these two formulas have stronger gas regulation ability, which slows down cell wall degradation by reducing fruit respiration intensity, reducing ethylene production and inhibiting pectinase activity. In addition, their film materials have better water vapor barrier properties and higher mechanical strength, which effectively reduces water evaporation during storage of apples and maintains the firmness of the fruit at a higher level.

[0149] The present invention adopts polymerized whey protein and dendrobium officinale polysaccharide gel as thickener, which can effectively improve the texture of goat milk yogurt, make it more thick and delicate, and enhance the mouthfeel and appearance. This composite gel combines the advantages of protein and dendrobium officinale polysaccharide, and has higher nutritional value and health function. Protein and polysaccharide form gel through macromolecular interaction, which can enhance the texture, stability, thermal performance and biological performance of the gel. In the food industry, the hydrogel of polymerized whey protein and dendrobium officinale polysaccharide can improve the viscosity of yogurt, enhance its water retention, prevent water loss, and extend the shelf life of goat milk yogurt. In addition, the cost of this composite gel is relatively low, has good market application prospects and economic benefits, and can provide strong support for the quality improvement and functional characteristics improvement of goat milk yogurt.

[0150] The present invention adopts the gel of polymerized whey protein and dendrobium officinale polysaccharide as the gel-based film material, which can effectively improve the fresh-keeping effect of apples. This composite gel combines the advantages of protein and polysaccharide. Protein and dendrobium officinale polysaccharide form a gel network structure through macromolecular interaction, which can enhance the texture, stability, thermal performance and biological performance of the gel. In fruit preservation, the polymerized whey protein and dendrobium officinale polysaccharide gel preservative film (i.e., gel-based film) can be closely attached to the surface of apple fruit to form a protective film with good air permeability, which can effectively reduce the respiratory intensity and ethylene release of apples, delay the aging process of fruits, and inhibit pectinase activity, thereby slowing down cell wall degradation, and inhibiting the infection of microorganisms, reducing the decay and deterioration of fruits. In addition, the preservative film can also keep the moisture of apple fruits to a certain extent, prevent the fruit from losing water and shrinking, maintain its good appearance and taste, and extend the shelf life of apples. Moreover, the material cost of this preservative film is relatively low, has good market application prospects and economic benefits, and can provide strong support for the fresh-keeping and quality maintenance of apples.

[0151] Finally, it should be noted that the above embodiments do not limit the present invention in any form. For those skilled in the art, some modifications and improvements can be made to the present invention. Therefore, any modification or improvement made without departing from the spirit of the present invention belongs to the scope of protection claimed in the present invention.

Claims

1. A gel of polymerized whey protein and Dendrobium officinale polysaccharide, characterized in that: The preparation process of the gel is as follows: dissolving whey protein powder and dendrobium officinale polysaccharide powder in deionized water, mixing evenly to make the mass concentration of whey protein 8-12% and the mass concentration of dendrobium officinale polysaccharide 0.5-2.5%, adding 0.1-0.3% sodium carbonate as an inducer to obtain a mixed solution containing whey protein, dendrobium officinale polysaccharide and the inducer, stirring at 20-30°C for 15-30 minutes; adjusting the pH of the mixed solution to 6.5-7.5, heating at 80-90°C for 15-30 minutes, cooling, and obtaining a gel of polymerized whey protein and dendrobium officinale polysaccharide; the whey protein powder is isolated whey protein powder or concentrated whey protein powder.

2. The gel of polymerized whey protein and Dendrobium officinale polysaccharide according to claim 1, characterized in that: The concentration of Dendrobium officinale polysaccharide is 0.5-2.5%.

3. Application of a gel of polymerized whey protein and Dendrobium officinale polysaccharide in the preparation of yogurt, characterized in that: The preparation process of the yogurt is as follows: 6-8% sucrose is added to goat milk, and the milk is cooled after pasteurization or high-temperature sterilization or low-temperature sterilization by induction electric field, and then 0.5-1.5% w / v of the gel of polymerized whey protein and Dendrobium officinale polysaccharide obtained in claim 1 or 2 is added, and a starter is inoculated to obtain yogurt by fermentation.

4. The use according to claim 3, characterized in that: Dissolve goat milk powder in deionized water to a final concentration of 10-15% w / v; add 6-8% sucrose to the goat milk; heat at 80-90°C for 5-15 minutes; after cooling to 41-45°C, add 0.5-1.5% w / v of a gel of polymerized whey protein and Dendrobium officinale polysaccharide; inoculate 0.02-0.05% w / v of ABY-8 starter; and continue fermenting at 41-45°C to a final pH of 4.35±0.

10.

5. A goat milk yogurt thickener, characterized in that: A gel comprising the polymerized whey protein according to claim 1 or 2 and a Dendrobium officinale polysaccharide.

6. Use of a gel of polymerized whey protein and Dendrobium officinale polysaccharide in preparing a gel-based film, characterized in that: Add glycerol to the gel of polymerized whey protein and Dendrobium officinale polysaccharide obtained according to claim 1 or 2, stir evenly to obtain a film-forming liquid; pour the film-forming liquid into a flat dish, control the thickness to 0.5-1.0 mm, seal, and dry to obtain a gel-based film.

7. The use of a gel of polymerized whey protein and Dendrobium officinale polysaccharide according to claim 6 in preparing a gel-based film, characterized in that: The amount of glycerol added is 2-4%.

8. The use of a gel of polymerized whey protein and Dendrobium officinale polysaccharide according to claim 6 in preparing a gel-based film, characterized in that: The drying temperature is 45 ℃-65 ℃, and the drying time is 10-20 h.

9. A gel-based membrane, characterized in that: Add 2-4% glycerol to the gel of polymerized whey protein and Dendrobium officinale polysaccharide obtained in claim 1 or 2, stir evenly to obtain a film-forming liquid; pour the film-forming liquid into a flat dish, control the thickness to 0.5-1.0 mm, seal, and dry to obtain a gel-based film.

10. Use of a gel of polymerized whey protein and Dendrobium officinale polysaccharide according to claim 1 or 2 or a gel-based membrane according to claim 9 in fruit preservation, characterized in that: When in use, wrap the fruit surface with the gel-based film and control the fruit storage temperature at 0-4 ℃.

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