A gel of polymerized whey protein and dendrobium officinale polysaccharide and application in preparing yogurt or gel-based film

Abstract

The present application relates to the field of gel, in particular to a kind of polymeric whey protein and dendrobium officinale polysaccharide gel and application in preparing yoghurt or gel base film.The present application includes: (1) whey protein, dendrobium officinale polysaccharide powder is dissolved in deionized water, and mixed uniformly;Inducer is added, pH is adjusted, heated, and cooled to obtain polymeric whey protein and dendrobium officinale polysaccharide hydrogel;(2) goat milk powder is dissolved with deionized water, sugar is added, sterilized, cooled, polymeric whey protein and dendrobium officinale polysaccharide gel are added, inoculated with starter, and fermented to obtain yoghurt;(3) glycerol is added to polymeric whey protein and dendrobium officinale polysaccharide gel and stirred to obtain film forming liquid;Film forming liquid is uniformly laid, dried to obtain gel base film.The present application improves the texture of goat yoghurt, widens the application of polymeric whey protein and dendrobium officinale polysaccharide in dairy products;Improve the quality of fruits, widen the application of protein and dendrobium officinale polysaccharide gel base film.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of gels, in particular to a polymeric whey protein and dendrobium officinale polysaccharide gel and its application in preparing yogurt or gel-based films. BACKGROUND

[0002] Whey protein isolate contains more than 90% of protein, including α-lactalbumin, β-lactoglobulin, bovine serum albumin, etc. It is widely used in the food industry for dairy products, desserts and beverages, etc. due to its excellent physicochemical properties, such as foaming, emulsifying and gelling. Polymeric whey protein is a protein polymer synthesized by physical and chemical or enzymatic polymerization of whey protein isolate or whey protein concentrate. The structural matrix of polymeric whey protein can be used to embed water, flavor substances and probiotics. However, the polymeric whey protein gel has brittleness and environmental sensitivity, which limits its application potential in the food industry.

[0003] Goat milk yogurt is rich in nutrients, containing various vitamins, minerals and high-quality proteins, and is easy to digest and absorb, which can effectively supplement the nutrients needed by the human body and promote physical health. Its fat globules are smaller and more easily absorbed by the human body, which helps to beautify and nourish the skin, enhance immunity, etc. However, the texture of goat milk yogurt is often thin and the taste is not good enough. The main reason is that the content of casein in goat milk is relatively low and the content of whey protein is high, which leads to the formation of a less tight gel structure during fermentation. In addition, the content of lactose in goat milk is low, and the production of lactic acid is less, which further affects the formation and stability of the gel structure. Traditional thickeners have high cost and are prone to denaturation under high temperature or acidic conditions, which limits their application. Therefore, it is of great significance to apply polymeric whey protein-polysaccharide gel to the preparation of goat milk yogurt and improve its texture.

[0004] Apples are crisp, sweet, and juicy, containing various vitamins, minerals, and dietary fiber, offering numerous health benefits. However, post-harvest preservation of apples faces many challenges. Firstly, apples experience rapid respiration after harvest, and their thin, easily damaged skin makes them highly susceptible to spoilage during transportation and storage due to mechanical damage and microbial contamination. Furthermore, apples easily lose water at room temperature, leading to shriveling, a deterioration in taste, and severely impacting their quality and shelf life. Secondly, current post-harvest preservation methods primarily consist of chemical and physical methods, both of which have limitations. While chemical preservation methods can inhibit microbial growth to some extent, traditional chemical preservatives pose problems such as chemical residues, environmental pollution, and bacterial resistance, contradicting the trend of green development. Physical preservation methods, such as low-temperature refrigeration and modified atmosphere storage, require specific equipment and facilities, are cumbersome and time-consuming, and simultaneously achieving preservation and transportation is difficult, hindering their commercial application in the fruit preservation field. Therefore, developing a new, efficient, and environmentally friendly preservation film material for apple preservation to improve the preservation effect of apples is of great practical significance.

[0005] Polymeric whey protein is a protein polymer synthesized from whey protein isolates or whey protein concentrates through physicochemical or enzymatic polymerization. Its structural matrix can be used to encapsulate water, nutrients, etc., and it exhibits good film-forming properties and a certain degree of mechanical strength. However, polymeric whey protein gels are brittle and environmentally sensitive, limiting their potential application in fruit preservation.

[0006] Dendrobium officinale polysaccharides possess strong pharmacological activities, including anti-aging, antioxidant, anti-tumor, and immune-enhancing effects. However, no reports have been found regarding the technology for forming polymers from Dendrobium officinale polysaccharides with whey protein. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a polymerized whey protein-Dendrobium officinale polysaccharide gel and its application in the preparation of yogurt or gel base films.

[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, thus better meeting consumers' demand for high-quality dairy products.

[0009] By using polylactalbumin and Dendrobium officinale polysaccharide gel as the gel base membrane material, the preserved apples not only effectively reduce respiration intensity and ethylene release, thus slowing down the aging process, but the membrane formed by the polylactalbumin and Dendrobium officinale polysaccharide gel also effectively blocks oxygen and moisture, reduces pectinase activity, thereby slowing down pectin decomposition, cell wall degradation and damage, maintaining the firmness and structural integrity of the fruit, and preventing softening. Dendrobium officinale polysaccharide has antibacterial and antioxidant properties, which can reduce the damage to the fruit caused by microorganisms and oxidative reactions, further delaying cell wall degradation. The gel membrane forms a physical barrier, reducing the impact of external factors on the fruit and maintaining its freshness. In summary, this gel membrane, by inhibiting pectinase activity and providing physical protection, can effectively slow down cell wall degradation and extend the shelf life of the fruit.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A gel of polymerized whey protein and Dendrobium officinale polysaccharide is prepared as follows: whey protein powder and Dendrobium officinale polysaccharide powder are dissolved in deionized water and mixed evenly to achieve a whey protein mass concentration of 8-12% and a Dendrobium officinale polysaccharide mass concentration of 0.5-2.5%. Then, 0.1-0.3% sodium carbonate is added as an inducer to obtain a mixed solution containing whey protein, Dendrobium officinale polysaccharide, and the inducer. The solution is stirred at 20-30°C for 15-30 minutes. The pH of the mixed solution is adjusted to 6.5-7.5 (this pH facilitates gel formation), and the solution is heated at 80-90°C for 15-30 minutes. After cooling, the gel of polymerized whey protein and Dendrobium officinale polysaccharide is obtained. The whey protein powder is either isolated whey protein powder or concentrated whey protein powder.

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

[0013] Another objective of this invention is to disclose the application of a gel of polymeric whey protein and Dendrobium officinale polysaccharide in the preparation of yogurt. The yogurt preparation process is as follows: 6-8% sucrose is added to goat milk, and the mixture is pasteurized, sterilized at high temperature, or sterilized at low temperature by induction electric field, and then cooled. Then, 0.5-1.5% w / v gel of polymeric whey protein and Dendrobium officinale polysaccharide is added and a starter culture is inoculated to obtain yogurt through fermentation.

[0014] In a preferred embodiment, goat milk powder is dissolved in deionized water to a final concentration of 10-15% w / v; 6-8% sucrose is added to the goat milk; the mixture is heated at 80-90°C for 5-15 minutes; after cooling to 41-45°C, a gel of 0.5-1.5% w / v polymerized whey protein and Dendrobium officinale polysaccharide is added; 0.02-0.05% w / v ABY-8 starter culture is inoculated; fermentation continues at 41-45°C until the final pH value is 4.35±0.10. In this invention, the amount of polymerized whey protein and Dendrobium officinale polysaccharide gel added during yogurt preparation is relatively small, only 0.5-1.5% w / v is required, and the resulting yogurt exhibits significantly improved textural properties, particle size reduction due to dehydration shrinkage, and microstructure.

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

[0016] The present invention also provides an application of a gel of polymeric whey protein and Dendrobium officinale polysaccharide in the preparation of a gel-based membrane. Glycerol is added to the gel of polymeric whey protein and Dendrobium officinale polysaccharide and stirred evenly to obtain a film-forming solution. The film-forming solution is poured into a petri dish with a thickness controlled at 0.5-1.0 mm, sealed, and dried to obtain a gel-based membrane.

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

[0018] Preferably, the drying temperature is 45℃-65℃ and the drying time is 10-20h.

[0019] The present invention also discloses a gel-based membrane, wherein 2-4% glycerol is added to a gel of polymerized whey protein and Dendrobium officinale polysaccharide, and stirred evenly to obtain a film-forming solution; the film-forming solution is poured into a petri dish, the thickness is controlled at 0.5-1.0 mm, sealed, and dried to obtain a gel-based membrane.

[0020] The final objective of this invention is to disclose the application of the aforementioned polymeric whey protein and Dendrobium officinale polysaccharide gel or gel-based film in fruit preservation. In use, the fruit surface is wrapped with the gel-based film, and the fruit storage temperature is controlled at 0-4℃.

[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 in this invention forms a gel with excellent viscosity and stability by combining isolated whey protein with Dendrobium officinale polysaccharide. The combination of the emulsifying and gelling properties of isolated whey protein with the thickening and bioactivity of Dendrobium officinale polysaccharide can significantly improve the quality of goat milk yogurt, making it thicker and smoother, and improving its taste and appearance. At the same time, this composite gel can also enhance the nutritional value and health functions of goat milk yogurt, thereby improving the overall quality of goat milk yogurt.

[0023] (2) The gel-based film (a gel-based preservation film) prepared by this invention, composed of polymeric whey protein and Dendrobium officinale polysaccharide, utilizes the excellent film-forming properties of polymeric whey protein, the thickening properties of Dendrobium officinale polysaccharide, and the moisturizing properties of glycerin. 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 preservation film, improving its overall performance. Glycerin effectively maintains the moisture content of apples, significantly extending their shelf life. In addition, this preservation film also provides apples with antioxidant and other health benefits, enhancing the quality and added value of apples.

[0024] (3) The preparation method of this invention is simple. Both the polymerized whey protein and Dendrobium officinale polysaccharide are natural ingredients, widely available and inexpensive, thus reducing production costs. The preparation process is environmentally friendly, producing no harmful substances, with a short production cycle and high economic value. Compared with traditional thickeners, the thickener of this invention is not only superior in function but also has significant advantages in cost and environmental protection, making it suitable for large-scale industrial production. Compared with traditional preservation methods, the gel-based film material of this invention has significant advantages in preservation effect, cost, and environmental protection, making it suitable for large-scale industrial production and widespread application.

[0025] (4) The gel-based membrane material prepared by this invention has simple usage conditions and is easy to operate. The addition of whey protein and Dendrobium officinale polysaccharide gel not only improves the preservation quality of apples, but also adds antioxidant and other health functions to them, which helps consumers obtain healthier and safer fruit products and better meet the market demand for high-quality preserved apples. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0027] Figure 1 A schematic diagram showing the particle size and potential of a gel composed of polymerized whey protein and Dendrobium officinale polysaccharide;

[0028] Figure 2 A schematic diagram illustrating the hydrophobicity of a gel composed of polymerized whey protein and Dendrobium officinale polysaccharide;

[0029] Figure 3 Three-dimensional fluorescence images of gels containing polywhey protein and Dendrobium officinale polysaccharide: A, PWP three-dimensional fluorescence image; B, PWPD1 three-dimensional fluorescence image.

[0030] Figure 4 Three-dimensional fluorescence images of gels containing polywhey protein and Dendrobium officinale polysaccharide, C, PWPD2, and D, PWPD3;

[0031] Figure 5 Three-dimensional fluorescence images of gels containing polywhey protein and Dendrobium officinale polysaccharide; three-dimensional fluorescence images of E and PWPD4; three-dimensional fluorescence images of B and PWPD5.

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

[0033] Figure 7 The image shows the SR-IR analysis of gels containing polywhey protein and Dendrobium officinale polysaccharide. A1-F1 are two-dimensional images of PWP, PWPD1, PWPD2, PWPD3, PWPD4, and PWPD5, respectively.

[0034] Figure 8 Two-dimensional correlation spectra (2D-COS) of gels containing polywhey protein and Dendrobium officinale polysaccharide, with AC corresponding to PWP, PWPD1, and PWPD2, respectively.

[0035] Figure 9 Two-dimensional correlation spectra (2D-COS) of gels containing polywhey protein and Dendrobium officinale polysaccharide, with DF corresponding to PWPD3, PWPD4, and PWPD5, respectively.

[0036] Figure 10 The image shows the microstructure of gels containing polymerized whey protein and Dendrobium officinale polysaccharide, with AF corresponding to PWP, PWPD1, PWPD2, PWPD3, PWPD4, and PWPD5, respectively.

[0037] Figure 11 The microstructure of various yogurt samples;

[0038] Figure 12 A schematic diagram showing the particle size dehydration and shrinkage of goat milk yogurt;

[0039] Figure 13 DSC curves of polymerized whey protein and its gel-based membranes (PWP-D1, PWP-D2, PWP-D3) composed of different concentrations of Dendrobium officinale polysaccharide;

[0040] Figure 14 Stress-strain curves of polymeric whey protein and its gel-based membranes (PWP-D1, PWP-D2, PWP-D3) composed of different concentrations of Dendrobium officinale polysaccharide;

[0041] Figure 15 This diagram illustrates the effect of polymerized whey protein and its gel-based membranes (PWP-D1, PWP-D2, PWP-D3) composed of different concentrations of Dendrobium officinale polysaccharides on the firmness of fresh-cut apples. Detailed Implementation

[0042] The present invention will be 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, all chemical reagents involved in this 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 starter culture was purchased from Dennis Sterling Ltd. Goat milk powder was purchased from Anmu (Jiangsu) Co., Ltd. Other commercially available fermentation agents can also be used in this invention.

[0045] Example 1

[0046] Preparation of hydrogels containing polymerized whey protein and Dendrobium officinale polysaccharides:

[0047] Whey protein isolate and Dendrobium officinale polysaccharide powder were dissolved separately in deionized water to obtain a 20% (w / v, g / mL) whey protein isolate stock solution and a 10% (w / v, g / mL) Dendrobium officinale polysaccharide stock solution. Both stock solutions were stirred at room temperature for 30 min at 300 rpm. A mixture of whey protein isolate and Dendrobium officinale polysaccharide was prepared (the whey protein isolate and Dendrobium officinale polysaccharide stock solutions were mixed evenly at room temperature in a certain proportion), resulting in a whey protein isolate concentration of 10% and Dendrobium officinale polysaccharide concentrations of 0.5%, 1.0%, 1.5%, 2%, and 2.5%, respectively. 0.2% sodium carbonate (0.2% of the total mass of the mixture) was added as an inducing agent, and the mixture was stirred at 25°C for 30 min to obtain the final mixture. The pH was adjusted to 7, and the mixture was heated at 85°C for 30 minutes. Subsequently, it was cooled to room temperature to obtain a hydrogel of polymerized whey protein and Dendrobium officinale polysaccharide.

[0048] Example 2

[0049] Group C:

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

[0051] (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);

[0052] (2) The above-mentioned whey protein stock solution was stirred at room temperature for 30 minutes, with the speed controlled at 300 rpm;

[0053] (3) Dissolve 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) The above Dendrobium officinale polysaccharide stock solution was stirred at room temperature for 30 minutes, with the speed controlled at 300 rpm;

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

[0056] Goat milk yogurt was then prepared by using a gel of polymerized whey protein and Dendrobium officinale polysaccharide as a thickener:

[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. Sterilize at 95°C for 10 min. After cooling to 43°C, add the gel of polywhey protein and Dendrobium officinale polysaccharide at a dosage of 1% (w / v, g / mL) to the goat milk, and inoculate with ABY-8 starter culture (0.03%, w / v, g / mL).

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

[0059] Group D:

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

[0061] Group E:

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

[0063] Group F:

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

[0065] Group G:

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

[0067] Comparative Example 1

[0068] Group A (Pure Goat Yogurt): 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. Sterilize at 95°C for 10 minutes. After cooling to 43°C, inoculate with ABY-8 starter culture (0.03%, w / v, g / mL). 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.

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

[0070] (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);

[0071] (2) The above-mentioned whey protein stock solution was stirred at room temperature for 30 minutes, with the speed controlled at 300 rpm;

[0072] (3) The 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, and the temperature is raised to 85°C and kept constant for 30 minutes with continuous stirring. The mixture is then cooled to room temperature to obtain 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) of sucrose to the goat milk. Sterilize at 95°C for 10 minutes. After cooling to 43°C, add polymerized whey protein gel at 1% (w / v, g / mL) to the goat milk, and inoculate with ABY-8 starter culture (0.03%, w / v, g / mL).

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

[0075] Example 3

[0076] PWP-D1 Group:

[0077] 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-mentioned whey protein stock solution was stirred at room temperature for 30 minutes, with the speed controlled at 300 rpm.

[0080] (3) Dissolve 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) Stir the Dendrobium officinale polysaccharide stock solution at room temperature for 30 minutes, with the speed controlled at 300 rpm.

[0082] (5) The whey protein stock solution and Dendrobium officinale polysaccharide stock solution obtained in steps (2) and (4) are mixed with deionized water to obtain a final concentration of 10% (w / v) whey protein and 0.5% (w / v) Dendrobium officinale polysaccharide mixed solution. 0.2% sodium carbonate is added as an inducer and stirred at 25°C for 30 minutes. The pH is adjusted to 7 and heated at 85°C for 30 minutes with constant stirring during the heating process. Then it is cooled to room temperature to obtain polymerized whey protein and Dendrobium officinale polysaccharide gel.

[0083] Then, a gel-based film material for fruit preservation was prepared using polymerized whey protein and Dendrobium officinale polysaccharide gel. The specific steps are as follows:

[0084] (6) After cooling to room temperature, add 3% (w / w, which means 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, stir evenly, and obtain the film-forming solution.

[0085] (7) Pour the film-forming solution into a petri dish, control the thickness to 0.8 mm, seal it with commercially available plastic wrap, and dry it in a 45°C oven for 16 hours.

[0086] (8) After drying, remove the petri dish, remove the conventional commercial plastic wrap, peel the gel base film off the petri dish, and put it in a desiccator to cool to room temperature to obtain the polymerized whey protein and Dendrobium officinale polysaccharide gel base film material.

[0087] (9) After cleaning and cutting the apple into pieces, wrap the apple pieces with the prepared gel-based film material.

[0088] (10) Store the apple pieces wrapped in the gel base film in an environment of 0-4℃.

[0089] PWP-D2 group:

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

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

[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-mentioned whey protein stock solution was stirred at room temperature for 30 minutes, with the speed controlled at 300 rpm.

[0096] (3) The 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 inducing agent and stirred at 25°C for 30 minutes. The pH is adjusted to 7 and heated at 85°C for 30 minutes with constant stirring during the heating process. Then it is cooled to room temperature to obtain polymerized whey protein gel.

[0097] (4) After the polymerized whey protein gel is cooled to room temperature, add 3% (w / w, which means that the mass of glycerol accounts for 3% of the total mass of whey protein gel and glycerol) of glycerol, stir evenly, and obtain film-forming solution.

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

[0099] (6) After drying, remove the petri dish, peel off the commercially available plastic wrap from the petri dish, and place it in a desiccator to cool to room temperature to obtain whey protein gel base film material.

[0100] (7) After cleaning and cutting the apple into pieces, wrap the apple pieces with the prepared gel-based film material.

[0101] (8) Store the apple pieces wrapped in gel base film in an environment of 0-4℃.

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

[0103] I. Characterization of the Polymeric Whey Protein (PWP)-Dendrobium officinale Polysaccharide (DOP) Hydrogel Prepared in Example 1

[0104] 1. Particle size

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

[0106] 2. Potential

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

[0108] 3. Hydrophobicity

[0109] Compared to PWP, the addition of 0.5% DOP significantly improved the hydrophobicity of PWP. This is attributed to the acetylation of acetyl groups in DOP. As the DOP concentration increased from 1.0% to 2.5%, the hydrophobicity of the PWP-DOP complex decreased with increasing concentration. Specifically, the abundant hydrophilic hydroxyl groups in DOP enhance the polarity of the surrounding environment, promoting the aggregation of nonpolar molecules within the protein through non-covalent interactions, thus reducing hydrophobicity. Figure 2 As shown.

[0110] 4.3D intrinsic fluorescence

[0111] like Figures 3-5 As shown, the fluorescence intensity of the PWP-DOP gel decreased as the DOP concentration increased from 0% to 2.5%. This indicates that tryptophan was 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 hydrophilic hydroxyl groups in 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 (DSC) can be used to determine the thermal stability of protein-polysaccharide complexes during heating and cooling. PWPD1 corresponds to group C, PWPD2 to group D, PWPD3 to group E, PWPD4 to group F, and PWPD5 to group G. Figure 6 The thermal transition peak temperature of the PWP DSC curve in Figure A is 81.03℃. The peak temperature of the endothermic transition increases from 81.69℃ to 95.89℃ from PWPD1 to PWPD3. Higher saturation temperatures correlate with better thermal stability. The results indicate that the addition of DOP significantly improves the thermal stability of the PWP-DOP gel. This can be attributed to the fact that the addition of DOP enhances the hydrogen bond network structure, promoting a more stable conformation. The midpoint temperatures of the thermal transition for PWPD4 and PWPD5 are 93.07℃ and 85.13℃, respectively. This is because excess DOP molecules disrupt the original gel structure, reducing its thermal stability; therefore, PWPD3 exhibits 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 investigate their rheological behavior. All solution samples exhibited shear thinning characteristics, meaning that viscosity decreased with increasing shear rate. The increased shear rate may have disrupted the aggregated protein network, thereby reducing flow resistance and apparent viscosity. With increasing DOP concentration, the apparent viscosity of the PWP-DOP gel increased compared to PWP. The consistency coefficient and apparent viscosity increased with increasing polysaccharide concentration, indicating stronger cross-linking between the polysaccharide and protein. Furthermore, heat treatment enhanced interactions such as hydrophobic interactions, hydrogen bonds, and disulfide bonds, which facilitated the adhesion and binding of DOP molecules to the PWP surface, resulting in higher shear viscosity, such as... Figure 6 As shown in B in the diagram.

[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 hydrogen bond density. Furthermore, amide I (1700–1600 cm⁻¹) -1 ) and amide II (1600~1500cm) -1 The bands are attached to the peptide backbone via hydrogen bonds. The two-dimensional structure of SR-IR is shown below. Figure 7 As shown. 3450–3200 cm⁻¹ was observed in all samples. -1 The broad peaks between NH and OH correspond to the stretching vibrations of NH and OH, indicating the presence of hydrogen bonds in the system. The PWP gel shows a peak at 1630.49 cm⁻¹. -1 A sharp peak appears at this point, and... Figure 7 The C=O stretching in A1 corresponds to this. The PWPD1 spectrum is obtained from PWP (1630.49 cm⁻¹). -1 ) transformed into PWPD1 (1629.33cm) -1 ), PWPD2 (1635.96cm) -1 PWPD3 (1636.22cm) -1 ), PWPD4 (1635.93cm) -1 ) and PWPD5 (1635.89cm) -1 This is because the formation of hydrogen bonds during heating alters the frequency of the C=O stretching vibration. The PWP gel measured 3270.21 cm⁻¹. -1 The absorption peak at 3270.21 cm⁻¹ exhibits a blue shift. -1 The peak values ​​at these locations are PWPD1 (3264.49 cm⁻¹). -1 ), PWPD2 (3258.38cm) -1 ), PWPD3 (3252.52cm) -1), PWPD4 (3254.52cm) -1 ) and PWPD5 (3252.05cm) -1 This is because hydrogen bonds exist during the formation of the PWP-DOP gel. When the DOP concentration is 1.5%, at 1559.11 cm⁻¹... -1 1443.85cm -1 1401.33cm -1 1380.25cm -1 1242.64cm -1 and 1155.10cm -1 A new peak appeared at this point, indicating that the presence of DOP has a significant impact on the structure of PWP. (1559.11cm) -1 The bands are formed by the stretching of NH and the bonding of amide II. 1443.85 and 1401.33 cm -1 The peak at 1380.25 cm⁻¹ is caused by the vibrations of NH₃ and CN₂. -1 and 1242.64cm -1 The nearby peaks are caused by the symmetric bending vibrations of the methyl CH and o-acetyl groups, matching the characteristic peaks of DOP. Furthermore, at 1155.10 cm⁻¹... -1 The peaks at the [specific locations] are also related to COC, COH, and OH in the pyranose ring, indicating that the pyranose groups of DOP are retained in the gel. These changes suggest that the formation of the PWP-DOP complex gel involves hydrogen bonding and affects its secondary structure.

[0118] 8. Two-dimensional correlation spectrum

[0119] Compared to FT-IR, two-dimensional correlation spectroscopy (2D-COS) is an effective tool for describing functional group transformations and reaction sequences in fingerprint regions. Synchronous and asynchronous correlation infrared spectra of 2D-COS are shown below. Figure 8 and Figure 9 As shown. Compared to PWP, the addition of DOP increases the autocorrelation peaks and cross-peaks in the synchronous correlation spectrum. It is mainly concentrated in the 1628-1656 cm⁻¹ range. -1 and 1681-1700cm -1 The phase difference between these phases typically belongs to an intramolecular β-sheet structure. This may be attributed to the increase in intramolecular hydrogen bonds. Asynchronous correlation spectroscopy describes the phase difference between the changes in different vibrational modes. Cross peaks mainly appear between 1652 and 1697 cm⁻¹. -1The regions correspond to the stretching vibrations of C=O and C=C. The number of cross-peaks in the PWP-DOP gel is in the order of PWPD3 > PWPD2 > PWP > PWPD5 > PWPD4 > PWPD1. This indicates that changes in DOP concentration significantly alter the conformation of PWP. PWPD3 exhibits more cross-peaks and autocorrelation peaks in both synchronous and asynchronous correlated spectra. This is due to a higher degree of group transformation and synergistic effect among the vibrational modes of the PWPD3 molecule.

[0120] 9. Molecular docking

[0121] To further analyze the interaction between DOP and PWP, molecular docking simulations were performed. β-Lg, accounting for approximately 70% of WPI, was chosen for molecular docking. Three-dimensional and two-dimensional interaction analyses were performed using Pymol and LigPlus software, respectively. The protein surface shape matches the ligand conformation, indicating that the binding sites of DOP and β-Lg are both on the protein surface. A lower binding energy suggests a stronger molecular bond. The binding energy between β-Lg and DOP is -6.2 kcal / mol, indicating that DOP binds tightly to β-Lg. DOP forms 12 hydrogen bonds with the 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 [missing information]. Eleven hydrophobic interactions were observed between DOP and β-Lg on Thr 49, Pro 50, Ile 72, Ile 71, Leu 39, Asn 90, Ile 84, Met 107, Glu 112, Leu 31, and Asn 109. The results indicate that hydrogen bonding and hydrophobic interactions are the dominant binding forces between DOP and β-Lg, supporting the conclusions drawn from surface hydrophobicity and SR-IR analysis.

[0122] 10. Microstructure

[0123] Cryo-scanning electron microscopy is used to obtain information about the microstructure of PWPI-DOP gels. For example... Figure 10As shown in Figure A, the PWP network structure is loose, large, and relatively non-uniform. This is due to the significant enlargement of pore size caused by sodium ions and the weakening of connections between adjacent structures. However, compared to the PWP gel, the PWP-DOP gel exhibits higher interconnectivity and a more compact network. This indicates a synergistic effect in the composite aggregation of DOP and PWP. The compact network structure is mainly due to the hydrophobic interactions and hydrogen bonds between PWP and DOP, which facilitate the formation of three-dimensional layer-by-layer aggregates. Subsequently, at a DOP concentration of 2%, larger pores and a looser structure were observed, which may be related to the dissociation of the PWP-DOP gel. When the DOP concentration reaches 2.5%, the network structure is disrupted, forming irregular clumps. In this case, excessive DOP disrupts the interactions between PWPs, leading to changes in the microstructure.

[0124] II. Yogurt Results Analysis

[0125] 1. Microstructure of goat milk yogurt

[0126] Microstructural analysis of yogurt samples was performed using cryogenic scanning. All samples were frozen using liquid nitrogen. After being transferred to a preparation chamber, the frozen samples were broken up using a cold scalpel blade set to -177°C. Once broken up and the surface exposed, the samples were sublimated at -85°C for 15 minutes. The samples were then sputter-coated with platinum at 10 mV for 60 seconds. Finally, the samples were examined using a scanning electron microscope (SEM). The SEM was set to -140°C and 5.0 kV for observation.

[0127] Figure 8 The microstructure of various yogurt samples was shown. Figure 11 In sample A, pure goat milk yogurt exhibits irregular pore sizes and a finer network. However, in... Figure 11 In ingredient B, the addition of whey protein enhances the network structure of the yogurt. This is because the interaction between polymerized whey protein and casein forms a micellar complex, resulting in a tight, porous structure within the yogurt gel, thus improving the consistency of the goat milk yogurt. Figure 11 As shown in Figure CE, compared with groups A and B, the three-dimensional protein network of yogurt was significantly improved with increasing Dendrobium polysaccharide concentration. This is because the composite gel of polymerized whey protein and Dendrobium polysaccharide is embedded in the casein network, forming a casein-gel complex, which reduces the gaps between protein clusters and makes the protein network structure more compact. However, the network structures in groups F and G were too dense or even structurally disrupted, affecting the palatability of the yogurt.

[0128] 2. Particle size dehydration and shrinkage of goat milk yogurt

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

[0130] Dehydration shrinkage is a key parameter for evaluating the quality of fermented dairy products. The dehydration shrinkage values ​​for 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 to group A, the composite gel containing polysaccharide from *Dendrobium officinale* reduced the dehydration shrinkage of the yogurt. Figure 12 (B) 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 texture characteristics of the yogurt. The less dehydration shrinkage yogurt exhibits, the better its water-holding capacity. Yogurt with high water-holding capacity loses less moisture during storage, resulting in a richer and smoother texture. Group E showed the lowest dehydration shrinkage. Yogurt with high water-holding capacity maintains freshness better during storage and consumption, reducing water leaching.

[0131] 3. Texture of goat milk yogurt

[0132] Texture data were recorded using a texture analysis instrument. Texture measurements were performed using a cylindrical probe at a speed of 1 mm / s before and after the test. 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 Dendrobium officinale polysaccharides improved the textural properties of the yogurt. From group A to group G, the hardness value of the yogurt increased significantly from 98.28 g to 130.01 g (P<0.05). The addition of Dendrobium officinale polysaccharides can retain a large amount of water, promote the formation of goat milk yogurt, and increase the hardness of the yogurt. From group A to group G, the cohesion value increased significantly from 26.10 g to 45.88 g (P<0.05). The addition of Dendrobium officinale polysaccharides enhanced the viscosity of the yogurt, because Dendrobium officinale polysaccharides can strengthen the hydrophobic interactions between amino acid side chains and change the strength of goat milk yogurt. The results for consistency and viscosity are consistent with the results for hardness and cohesion. After adding the composite gel of polywhey protein and Dendrobium officinale polysaccharides, the consistency and viscosity of the yogurt samples were significantly improved. In summary, the textural properties of goat milk yogurt were improved after the addition of a composite gel of polywhey protein and Dendrobium officinale polysaccharide.

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

[0135]

[0136]

[0137] Note: The differences between the groups were statistically significant (P<0.05).

[0138] III. Thin Film Result Analysis

[0139] 1. Thermal stability of gel-based membranes containing polywhey protein and Dendrobium officinale polysaccharide

[0140] The thermal transition temperatures of the gel-based membranes containing polywhey protein and Dendrobium officinale polysaccharide were obtained using differential scanning calorimetry. Approximately 3–5 mg of the membrane (gel-based membrane) sample was placed in a sealed aluminum saucepan and heated at a rate of 10 °C per minute between 25 °C and 200 °C, then cooled to 25 °C. An empty aluminum saucepan was used as a control.

[0141] Figure 13 The DSC curves of polymerized whey protein and its films (PWP-D1, PWP-D2, PWP-D3) composited with different concentrations of Dendrobium officinale polysaccharide are shown in the figure. The peak thermal transition temperatures were 84.87℃ (PWP), 91.55℃ (PWP-D1), 97.88℃ (PWP-D2), and 94.71℃ (PWP-D3), respectively. The peak thermal transition temperatures of the films increased with increasing Dendrobium officinale polysaccharide concentration, indicating a significant enhancement in the thermal stability of the films 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 strengthens the molecular network structure of the films, thereby improving their thermal stability. However, the thermal transition temperatures of PWP-D2 and PWP-D3 were significantly higher than those of the other samples, indicating that the addition of Dendrobium officinale polysaccharide within this concentration range was most beneficial in improving the thermal stability of the films. However, when the concentration of Dendrobium officinale polysaccharide reached higher values ​​(2%, 2.5%), excessive intermolecular competition disrupted the network structure, thus reducing thermal stability. These results confirm the potential of Dendrobium officinale polysaccharide as a functional additive to improve the thermal properties of thin films.

[0142] 2. Mechanical properties of gel-based membranes containing polywhey protein and Dendrobium officinale polysaccharide

[0143] Mechanical properties were assessed using a TA-XT plus C texture analyzer to capture the stress-strain profiles of the membranes. For testing, the nanofiber membranes were cut into 10mm × 50mm rectangular strips. The testing speed was set to 0.5mm / s. For each type of polymeric 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 Figure 14Analysis of the stress-strain curves revealed significant differences in the mechanical properties of different film samples. The PWP sample exhibited low stress and strain, indicating weak mechanical properties. However, the mechanical properties of the composite film gradually improved with increasing polysaccharide content. PWP-D1 showed some improvement, but its strain was low, indicating relatively insufficient ductility. In contrast, PWP-D2 had the highest peak stress, reaching approximately 120 MPa, demonstrating excellent tensile strength. Its strain value was close to 120%, significantly higher than PWP-D1 and PWP-D3, indicating good ductility and a balance between strength and flexibility, making it the sample with the best mechanical properties. PWP-D3 had a significantly lower strain value and a slightly lower peak stress than PWP-D2, indicating insufficient mechanical properties. Excessive polysaccharide content altered the internal structure of the membrane, thus weakening its strength. Therefore, considering both strength and toughness, PWP-D2 was the optimal choice and is more suitable for applications requiring high mechanical strength and moderate flexibility.

[0145] 3. Effect of gel-based membranes containing polywhey protein and Dendrobium officinale polysaccharide on the firmness 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 tested to ensure the statistical significance and reliability of the results.

[0147] Experimental results Figure 15 The results indicate significant differences in the effectiveness of different treatment groups in maintaining apple firmness. The PWP group (control group) experienced the fastest decrease in firmness, dropping from approximately 350g to below 200g within 4 days, indicating poor preservation performance and an inability to effectively delay the softening process of apples. In contrast, the PWP-D1, PWP-D2, and PWP-D3 groups significantly improved firmness retention. The PWP-D2 and PWP-D3 groups, in particular, maintained firmness at approximately 250g and 255g respectively on day 4, demonstrating superior preservation performance. The PWP-D1 group, however, saw its firmness drop to 222g on day 4, significantly weaker than the PWP-D2 and PWP-D3 groups. This suggests that both the PWP-D2 and PWP-D3 formulations have a strong protective effect on maintaining apple firmness, and the concentration of Dendrobium officinale polysaccharide in the polymerized whey protein-Dendrobium officinale polysaccharide composite film has a significant impact on fruit firmness.

[0148] The superior performance of PWP-D2 and PWP-D3 is attributed to several factors. First, these two formulations have enhanced gas regulation capabilities, reducing ethylene production and inhibiting pectinase activity by decreasing fruit respiration intensity, thereby slowing cell wall degradation. Furthermore, their membrane materials possess better water vapor barrier properties and higher mechanical strength, effectively reducing moisture evaporation from apples during storage and maintaining fruit firmness at a high level.

[0149] This invention utilizes polymerized whey protein and Dendrobium officinale polysaccharide gel as thickeners, effectively improving the texture of goat milk yogurt, making it thicker and smoother, and enhancing its taste and appearance. This composite gel combines the advantages of protein and Dendrobium officinale polysaccharide, offering higher nutritional value and health benefits. The protein and polysaccharide form a gel through macromolecular interactions, enhancing the gel's texture, stability, thermal properties, and biological properties. In the food industry, the hydrogel of polymerized whey protein and Dendrobium officinale polysaccharide can increase the viscosity of yogurt, enhance its water retention, prevent moisture loss, and extend the shelf life of goat milk yogurt. Furthermore, this composite gel has relatively low cost, promising market application prospects and economic benefits, and can provide strong support for improving the quality and functional properties of goat milk yogurt.

[0150] This invention utilizes a gel composed of polymeric whey protein and Dendrobium officinale polysaccharide as the gel base film material, effectively improving the preservation of apples. This composite gel combines the advantages of proteins and polysaccharides. The proteins and Dendrobium officinale polysaccharide form a gel network structure through macromolecular interactions, enhancing the gel's texture, stability, thermal properties, and biological properties. In fruit preservation, the polymeric whey protein and Dendrobium officinale polysaccharide gel preservation film (i.e., the gel base film) can adhere tightly to the surface of apples, forming a highly breathable protective film. This effectively reduces the respiration rate and ethylene release of apples, slowing down the senescence process and inhibiting pectinase activity, thereby slowing cell wall degradation. It also inhibits microbial infection, reducing fruit spoilage. Furthermore, this preservation film can retain moisture in apples to a certain extent, preventing water loss and shrinkage, maintaining their good appearance and taste, and extending their shelf life. Moreover, this preservation film material has relatively low cost, promising market application prospects and economic benefits, providing strong support for apple preservation and quality maintenance.

[0151] Finally, it should be noted that the above embodiments do not limit the present invention in any way. Those skilled in the art can make modifications and improvements based on the present invention. Therefore, any modifications or improvements made without departing from the spirit of the present invention are within the scope of protection claimed by the present invention.

Claims

1. A gel containing polymerized whey protein and Dendrobium officinale polysaccharide, characterized in that, The gel preparation process is as follows: whey protein powder and Dendrobium officinale polysaccharide powder are dissolved in deionized water and mixed evenly to achieve a whey protein mass concentration of 8-12% and a Dendrobium officinale polysaccharide mass concentration of 0.5-2.5%. Then, 0.1-0.3% sodium carbonate is added as an inducer to obtain a mixed solution containing whey protein, Dendrobium officinale polysaccharide, and the inducer. The solution is stirred at 20-30℃ for 15-30 minutes. The pH of the mixed solution is adjusted to 6.5-7.5, and the solution is heated at 80-90℃ for 15-30 minutes. After cooling, a gel of polymerized whey protein and Dendrobium officinale polysaccharide is obtained. The whey protein powder is either 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 mass concentration of Dendrobium officinale polysaccharide is 0.5-1.5%.

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

4. The application 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℃ for 5-15 minutes; cool to 41-45℃, then add 0.5-1.5% w / v of polymerized whey protein and Dendrobium officinale polysaccharide gel; inoculate with 0.02-0.05% w / v of ABY-8 starter culture; continue fermentation at 41-45℃ until the final pH value is 4.35±0.

10.

5. A goat milk yogurt thickener, characterized in that, A gel comprising the polymeric whey protein and Dendrobium officinale polysaccharide as described in claim 1 or 2.

6. The application of a gel of polymerized whey protein and Dendrobium officinale polysaccharide in the preparation of gel-based membranes, characterized in that, Glycerol is added to the gel of polymerized whey protein and Dendrobium officinale polysaccharide obtained according to claim 1 or 2, and the mixture is stirred evenly to obtain a film-forming solution; the film-forming solution is poured into a petri dish, the thickness is controlled at 0.5-1.0 mm, the dish is sealed, and dried to obtain a gel base film.

7. The application of the gel of polymerized whey protein and Dendrobium officinale polysaccharide according to claim 6 in the preparation of gel-based membranes, characterized in that, The amount of glycerin added is 2-4%.

8. The application of the gel of polymerized whey protein and Dendrobium officinale polysaccharide according to claim 6 in the preparation of gel-based membranes, 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 according to claim 1 or 2, stir evenly to obtain a film-forming solution; pour the film-forming solution into a petri dish, control the thickness to 0.5-1.0 mm, seal, dry, and obtain a gel base film.

10. The application of a gel of polymerized whey protein and Dendrobium officinale polysaccharide as described in claim 1 or 2, or a gel-based membrane as described in claim 9, in fruit preservation, characterized in that... When using, wrap the fruit surface with a gel-based film and control the fruit storage temperature at 0-4 ℃.

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