Plant source apple polysaccharide, stabilizer, preparation method and application of plant source apple polysaccharide in dairy products

Abstract

The invention provides a plant-source apple polysaccharide, a stabilizer, a preparation method and application of the plant-source apple polysaccharide in dairy products, the weight-average molecular weight of the apple polysaccharide is 361.7 kDa, and the apple polysaccharide is composed of 60%-62% of glucose, 19%-20% of mannose, 17%-18% of galactose, 1.0%-1.5% of rhamnose and 1.5%-2.0% of glucuronic acid. The botanical apple polysaccharide is similar to pectin, has unique physicochemical properties and biological activity as a natural polysaccharide extracted from plants, and can effectively improve the stability of goat milk casein under different environmental conditions, prevent protein aggregation and precipitation, improve the quality of goat milk products and prolong the shelf life of the goat milk products as a stabilizer.

Description

Technical Field

[0001] The invention belongs to the technical field of food additives, and in particular to a plant-derived apple polysaccharide, a stabilizer, a preparation method and application thereof in dairy products. Background Art

[0002] Milk is rich in various proteins, which contributes to the protein intake of people in their daily lives. In recent years, goat milk has become increasingly popular in the market due to its higher nutritional value than cow milk. A typical advantage of consuming goat milk is its good digestibility, which is attributed to its relatively low lactose content and smaller fat globules compared to cow milk. Casein is a complete protein found in cow and goat milk, accounting for 78-80% of the total protein in milk. Casein is composed of four subunits: αs1-CN, αs2-CN, β~CN and k-CN. These four monomers form the three-dimensional structure of casein through structural elements such as α-helix, β-fold, and β-rotation. Casein often shows a strong tendency to self-associate into spherical colloidal particles in milk, known as "casein micelles", with diameters ranging from 50 to 500 nanometers. Due to its amphoteric nature, casein is insoluble at pH 4.5-5.0, but soluble at pH >5.5 and <3.5, with an isoelectric point of about 4.6. Goat casein has a different composition and structure from cow casein. Feta casein generally contains a higher ratio of αs2-CN and β-CN, which makes it more digestible. In addition, the flavor and texture of feta casein are also different from cow casein.

[0003] In acidic milk-based products such as yogurt, the effect of pH on system stability is important. Usually, the pH value of yogurt is between 4.0 and 4.6, which is close to the isoelectric point of casein (4.6). In this environment, the solubility of casein is reduced, which easily leads to casein coagulation, further affecting the texture and stability of yogurt products. To overcome this problem, gelatin is often used as an additive to stabilize yogurt. Gelatin and casein form complexes through hydrogen bonds and hydrophobic interactions, thereby increasing the structural stability of dairy products and preventing protein aggregation. However, in recent years, people tend to avoid eating foods with added gelatin, which has increased the urgency of seeking polysaccharide-based stabilizers for yogurt. In the mixed system of polysaccharides and milk, interactions and phase behavior are crucial to regulating the structure and rheological behavior of the system. Generally, in aqueous solutions of polysaccharides and proteins, if there is obvious intermolecular attraction (usually electrostatic attraction), polysaccharides and proteins will combine into soluble or insoluble complexes; on the contrary, the lack of intermolecular attraction will lead to the repulsion of one polymer from the other, which will result in a uniform aqueous solution at low polymer concentrations and obvious phase separation at high polymer concentrations. The phase behavior of polysaccharide and protein mixtures is highly dependent on the molecular structures of the polysaccharides and proteins, which are believed to determine the interactions between them. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the present invention provides a plant-based apple polysaccharide, a stabilizer, a preparation method and the application of the plant-based apple polysaccharide in dairy products. The plant-based apple polysaccharide is similar to pectin. As a natural polysaccharide extracted from plants, it has unique physical and chemical properties and biological activities. As a stabilizer, it can effectively improve the stability of goat milk casein under different environmental conditions, prevent protein aggregation and precipitation, and improve the quality and shelf life of goat milk products.

[0005] To achieve the above-mentioned purpose, the present invention provides the following technical scheme: a plant-based apple polysaccharide, wherein the weight average molecular weight of the apple polysaccharide is 361.7 kDa, and the sugar composition of the apple polysaccharide is 60% to 62% glucose, 19% to 20% mannose, 17% to 18% galactose, 1.0% to 1.5% rhamnose and 1.5% to 2.0% glucuronic acid.

[0006] Furthermore, the sugar composition of apple polysaccharide is 60.38% glucose, 19.41% mannose, 17.60% galactose, 1.00% rhamnose and 1.61% glucuronic acid.

[0007] The present invention also provides the use of the plant-derived apple polysaccharide in improving the stability of goat milk casein. An apple polysaccharide solution with a concentration of 1.0% to 1.5% is added to goat milk, and the ratio of the apple polysaccharide to the goat milk casein content is 1:16.

[0008] The present invention also provides a stabilizer, which is plant-derived apple polysaccharide, the weight average molecular weight of the apple polysaccharide is 361.7 kDa, and the sugar composition of the apple polysaccharide is 60% to 62% glucose, 19% to 20% mannose, 17% to 18% galactose, 1.0% to 1.5% rhamnose and 1.5% to 2.0% glucuronic acid.

[0009] Furthermore, the sugar composition of the apple polysaccharide is 60.38% glucose, 19.41% mannose, 17.60% galactose, 1.00% rhamnose and 1.61% glucuronic acid.

[0010] The present invention also provides a method for improving the stability of goat milk casein, wherein a plant-derived apple polysaccharide solution with a concentration of 1.0% to 1.5% is added to goat milk, and the ratio of the apple polysaccharide content to the goat milk casein content is 1:16, wherein the weight-average molecular weight of the apple polysaccharide is 361.7 kDa, and the sugar composition of the apple polysaccharide is 60% to 62% glucose, 19% to 20% mannose, 17% to 18% galactose, 1.0% to 1.5% rhamnose and 1.5% to 2.0% glucuronic acid.

[0011] Furthermore, the sugar composition of the apple polysaccharide is 60.38% glucose, 19.41% mannose, 17.60% galactose, 1.00% rhamnose and 1.61% glucuronic acid.

[0012] The present invention also provides a method for preparing plant-derived apple polysaccharide, and the specific steps are as follows: Extraction of crude apple polysaccharide from apple pomace; preparing an aqueous solution of crude apple polysaccharide, heating the aqueous solution of crude apple polysaccharide to perform ethanol precipitation to obtain a precipitate; A precipitate aqueous solution is prepared, the precipitate aqueous solution is dialyzed, and freeze-dried to obtain plant-derived apple polysaccharide with metal ions removed.

[0013] Further, a 1.0% concentration aqueous solution of crude apple polysaccharide was heated to 60° C. for 2 h, and then three times the volume of 95% ethanol was added for precipitation to obtain a precipitate.

[0014] Furthermore, the dialysis is performed using a 3 kDa cut-off dialysis membrane.

[0015] Compared with the prior art, the present invention has at least the following beneficial effects: The present invention provides a plant-derived apple polysaccharide, which has a specific weight-average molecular weight (361.7 kDa) and precise sugar composition (glucose 60%-62%, mannose 19%-20%, galactose 17%-18%, rhamnose 1.0%-1.5%, glucuronic acid 1.5%-2.0%). This unique chemical structure can effectively improve the stability of goat milk casein under different environmental conditions and prevent protein aggregation and precipitation. The apple polysaccharide of the present invention is a natural polysaccharide extracted from apple pomace, which has a wide source and is safe, and meets the urgent needs of modern consumers for healthy and natural food additives.

[0016] The present invention uses apple polysaccharide to improve the stability of goat milk casein. Apple polysaccharide is added to goat milk as a stabilizer, which can effectively improve the stability of goat milk casein under different environmental conditions, prevent protein aggregation and precipitation, and thus improve the quality and shelf life of goat milk products. By preventing protein precipitation and aggregation, apple polysaccharide can maintain the uniformity and delicate taste of goat milk products, and enhance the eating experience of consumers. The method of the present invention is applicable to the processing and storage process of various goat milk products, and has broad application prospects.

[0017] The stabilizer of the present invention has plant-derived apple polysaccharide as a main component, which can replace traditional animal-derived or chemically synthesized stabilizers to meet consumers' demand for natural and healthy food additives. As a natural stabilizer, the use process of apple polysaccharide is pollution-free to the environment and conforms to the green and environmentally friendly production concept.

[0018] When the above stabilizer is used to improve the stability of goat milk casein, the operation is simple. It only needs to set the ratio of the specific concentration of apple polysaccharide to the content of goat milk casein to 1:16. No complicated process and equipment are required. It can effectively improve the stability of goat milk casein under different pH conditions, prevent protein precipitation and aggregation, significantly improve the stability and shelf life of goat milk products, maintain the uniformity and taste of the product, and have little effect on the flavor and nutritional value of goat milk products. It can retain the original nutritional components and flavor characteristics of goat milk to the greatest extent while improving the stability. Apple polysaccharide as a stabilizer has a relatively low cost, which helps to reduce the production cost of goat milk products. The preparation method of apple polysaccharide is simple and easy, including extraction, precipitation, dialysis and freeze-drying steps, which is suitable for large-scale industrial production. The method is low-cost and can efficiently prepare high-purity apple polysaccharide to meet market demand. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the appearance picture of apple polysaccharide, goat casein, and apple polysaccharide-casein complex.

[0020] Figure 2 This is the curve of the apparent viscosity of apple polysaccharide, goat casein, and apple polysaccharide-casein mixture changing with shear rate at different pH values.

[0021] Figure 3 This is the SAXS measurement of 0.5% apple polysaccharide solution at different pH values.

[0022] Figure 4 SAXS measurements of 0.1% goat milk casein solution at different pH values.

[0023] Figure 5 The effect of 0.1% apple polysaccharide on the SAXS spectrum of 0.1% goat milk casein at different pH values.

[0024] Figure 6 The following are AFM images of apple polysaccharide, goat casein, and apple polysaccharide-casein complex molecules at different pH values. The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0025] The present invention provides a stabilizer, specifically plant-derived apple polysaccharide. The apple polysaccharide is similar to pectin. As a natural polysaccharide extracted from plants, it has unique physical and chemical properties and biological activity, and has potential application value in improving the stability of goat milk casein. The specific preparation steps are as follows: 1. Preparation of Apple Polysaccharide Step 1: Purchase commercially available crude apple polysaccharide (raw material is apple pomace). Crude polysaccharide contains residual metal ions, which will affect the experimental results. Dissolve the crude polysaccharide powder in deionized water and heat at 60°C for 2 h to reach a concentration of 1.0% ( w / v ), and then add three times the volume of 95% ethanol ( v / v ) to precipitate AP molecules. The precipitate was redissolved in water, dialyzed against deionized water (room temperature, 48 h) using a 3 kDa cut-off dialysis membrane (MD 45 mm), and then freeze-dried to obtain AP of higher purity. After purification, Na + , K + and Ca 2+ The contents of were reduced to 0.07%, 0.05% and 0.97% respectively to reduce the influence of residual metal ions on the results.

[0026] The average molecular weight (Mw) of the obtained apple polysaccharide is 361.7 kDa, and the sugar composition includes 60%~62% glucose, 19%~20% mannose, 17%~18% galactose, 1.0%~1.5% rhamnose and 1.5%~2.0% glucuronic acid.

[0027] Preferably, the sugar composition of the apple polysaccharide is 60.38% glucose, 19.41% mannose, 17.60% galactose, 1.00% rhamnose and 1.61% glucuronic acid.

[0028] Characteristic analysis: The low acidic sugar content of apple polysaccharide makes it have the characteristics of low charge density and low sensitivity to pH changes. In the pH range of 3.0~7.0, its charge density changes little, the zeta potential is about -25 mV and does not change much with the pH value, which shows that it is an anionic polysaccharide.

[0029] 2. Formulation and preparation of stabilizer Formula composition: The stabilizer is mainly composed of apple polysaccharide.

[0030] Preparation method: Dissolve the extracted and purified apple polysaccharide powder in deionized water at room temperature, let it stand for 12 hours, then stir it at 80℃ for 2 hours to prepare 1.0~1.5% ( w / v ) of apple polysaccharide solution as stabilizer mother solution for later use. 3. Mechanism of action of stabilizers in goat milk casein system pH response mechanism: In the sheep milk casein system, there is an electrostatic interaction between apple polysaccharide and casein. When the pH value is <4.0, the electrostatic attraction between apple polysaccharide and positively charged casein is strong, which can interfere with the self-aggregation of casein when it is close to its isoelectric point (pI is about 4.0), thereby reducing the viscosity of the system and preventing protein precipitation; when the pH value is equal to 4.0, the presence of apple polysaccharide increases the solubility of casein and maintains the stability of the system; when the pH value is >4.0, the electrostatic attraction is weakened, but it can still promote the combination of apple polysaccharide and casein to form a complex, reduce the number of large casein particles, and further stabilize the system.

[0031] Microstructure influence: Small angle X-ray scattering (SAXS) and atomic force microscopy (AFM) analysis showed that the addition of apple polysaccharide changed the aggregation state and microstructure of casein. In the pH range of 3.0-7.0, apple polysaccharide and casein formed complexes to varying degrees, affecting the size, distribution and aggregation state of casein particles, making them form more stable complex particles, thereby improving the stability of the system. For example, at pH 3.0, apple polysaccharide and casein formed larger aggregated particles; as the pH value increased to 5.0-7.0, the degree of aggregation weakened, but there was still a certain degree of complex formation.

[0032] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention described and shown in the drawings here can usually be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0033] Example 1: Preparation of stabilizer 1. Purchase crude apple polysaccharide (raw material is apple pomace) from the market. Crude polysaccharide contains residual metal ions, which will affect the experimental results. Dissolve the crude polysaccharide powder in deionized water and heat at 60°C for 2 h to reach a concentration of 1.0% ( w / v ), and then add three times the volume of 95% ethanol ( v / v ) to precipitate AP molecules. The precipitate was redissolved in water, dialyzed against deionized water (room temperature, 48 h) using a 3 kDa cut-off dialysis membrane (MD 45 mm), and then freeze-dried to obtain AP with higher purity.

[0034] 2. Dissolve the purified apple polysaccharide powder in deionized water to prepare 1.0% ( w / v ) of apple polysaccharide solution as a stabilizer.

[0035] Example 2: Application of stabilizer in goat milk casein solution 1. Collect fresh goat milk, skim it and extract goat milk casein by isoelectric precipitation method at pH 4.1. After determining the casein content, prepare 16.0% ( w / v ) of casein solution.

[0036] 2. Take a certain amount of 1.0% ( w / v ) Apple polysaccharide solution was added to 16.0% ( w / v ) in the casein solution to make the final concentration of apple polysaccharide 0.5% ( w / v ), the final casein concentration was 8.0% ( w / v ), mixed well, as the experimental group. At the same time, set 8.0% ( w / v ) casein solution and 0.5% ( w / v ) Apple polysaccharide solution was used as the control group.

[0037] The pH values ​​of the experimental and control group solutions were adjusted to 3.0, 4.0, 5.0, 6.0 and 7.0 respectively. After standing for a period of time at 25°C, the stability of the solutions was observed (whether there was precipitation, stratification, etc.). Figure 1 As shown. At pH values ​​of 3.0 to 7.0, the visual appearance of the 0.5% apple polysaccharide solution was relatively transparent and clear. Meanwhile, the 8.0% goat casein solution was turbid at pH values ​​of 3.0, 5.0, 6.0, and 7.0, but remained uniform, and had obvious precipitation at pH 4.0, which corresponds to its reduced solubility near the isoelectric point. In the mixture of 0.5% apple polysaccharide and 8.0% goat casein, obvious phase separation was found at pH 3.0, which was due to the electrostatic attraction between goat casein and apple polysaccharide. At other pH values, the mixture of apple polysaccharide and goat casein did not produce any obvious precipitation or phase separation, indicating that the system has good stability at these pH values.

[0038] The viscosity of the solution was measured using a strain-controlled rheometer (MCR302 AntonPaar, Austria) equipped with a rough parallel plate with a diameter of 50 mm and a gap of 1 mm. Briefly, 2 ml of the experimental and control solutions were placed on the sample stage and then covered with silicone oil to prevent water evaporation. The shear rate was set at 1 s at 25 °C. -1 ~ 100s -1The apparent viscosity of the solution is measured in the range of Figure 2 It can be seen that the viscosity of 8.0% goat casein, 0.5% apple polysaccharide and their mixtures decreases with increasing shear rate, showing shear thinning behavior. When the pH value is 3.0, the viscosity of 8.0% goat casein at each shear rate is the highest, followed by the mixture, and the viscosity of 0.5% apple polysaccharide is the second. This is because at this pH value, the aggregation degree of goat casein is significant, close to the isoelectric point of casein (pH value 4.0). Due to the electrostatic attraction between the two polymers, the addition of apple polysaccharide is believed to destroy the self-aggregation of goat casein, resulting in a decrease in viscosity. At pH 4.0, the goat casein solution showed obvious phase separation due to the decrease in solubility, so we could only test the viscosity of the solution in the supernatant, and its viscosity dropped by almost two orders of magnitude. However, the mixture still showed high viscosity, indicating that the addition of apple polysaccharide increased the solubility of goat casein at its isoelectric point, probably because there is still electrostatic attraction between the two polymers. At pH 5.0, the viscosity of the mixture was the highest, followed by the goat casein and apple polysaccharide solutions. The high viscosity at pH 5.0 was attributed to the complexation between apple polysaccharide and casein due to the electrostatic attraction between apple polysaccharide and the positive patches on feta casein. At pH 6.0 and 7.0, the viscosity of the mixture dropped sharply, almost reaching the same level as the pure apple polysaccharide solution, indicating that the electrostatic interaction in the system was no longer significant.

[0039] As can be seen from the above, through visual observation and rheological measurement, it is known that in the pH range of 3.0~7.0, the stability of the experimental group solution with 0.5% apple polysaccharide added is significantly better than that of the control group. When the pH value is equal to 4.0, the control group has obvious precipitation, while the experimental group remains uniform and stable; when the pH value is equal to 3.0, although the experimental group has a certain degree of aggregation, it is more stable than the control group, and as the pH value increases to 5.0~7.0, the stability of the experimental group solution continues to remain good.

[0040] The structure of goat casein and its mixture was studied using the Nano-inXider device of XenocsSAS (France) and a Cu source to generate X-rays with a wavelength of 1.54 a. 0.1% goat casein and 0.5% apple polysaccharide were used as the control group, and 0.2% apple polysaccharide and 0.2% casein solution were mixed in equal volumes as the experimental group. The pH values ​​of the experimental and control group solutions were adjusted to 3.0, 4.0, 5.0, 6.0 and 7.0, respectively. Subsequently, the experimental and control group solutions were transferred to borosilicate glass capillaries with an outer diameter of 1.5 mm and a wall thickness of 0.01 mm and sealed with AB glue to prevent water evaporation during the measurement. All measurements were performed at room temperature (25°C), and the scattering results of the polymer structure were obtained by subtracting the background (water) scattering data from the total scattering intensity of the sample. Figure 3 As shown, the range of 𝑞 is 0.003 Å −1 ~ 0.1 Å −1 , corresponding to a length range of 209 nm to 6.28 nm. First, we considered the structural characteristics of the network in the apple polysaccharide solution. Figure 3 a, at q < 0.005 Å −1 When q is 0.5%, the scattering intensity I(q) is very high and decreases sharply with the increase of q, which may be due to the presence of some aggregates. Considering that 0.5% apple polysaccharide should be a semi-dilute polymer solution, we fit the middle range of the q region (0.008 Å −1 <q<0.08Å −1 , corresponding to 78.5~7.85 nm) to extract the fractal dimension of the polymer network. In this q range, it is found that 𝐼(𝑞) decays exponentially with the increase of 𝑞, and the slope of the decay is usually considered to be the fractal dimension (d) of the polymer network, where d is a parameter that describes the compactness of the network structure. Figure 3 As can be seen in b, the d values ​​of all apple polysaccharide solutions are between 1.47 and 1.64, reaching a maximum at a pH of 4, above which the d value decreases slightly. The pH value has little effect on the network structure of apple polysaccharides, as their SAXS spectra are obviously very similar.

[0041] SAXS spectra of 0.1% goat casein solution at different pH values ​​are shown in Figure 2. Figure 4 As shown. Figure 4As shown in Fig. a, the SAXS spectra of the casein solution vary significantly with increasing pH value. Among them, I(q) increases significantly with increasing pH value in the low q range (q < 0.007, corresponding to a length scale greater than 90 nm), indicating an increase in the number of large casein particles. Especially at pH = 5.0, I(q) in the low q range is the highest, reflecting the largest number of large casein particles, which may be because pH = 5.0 is closest to the isoelectric point of casein. At pH = 4.0, the solubility of goat cheese casein drops sharply, resulting in precipitation. Therefore, we could not obtain a satisfactory SAXS profile. In the casein solutions at pH = 6.0 and 7.0, a small but distinct bump in the SAXS curve was observed in the q range of 0.02 - 0.03 Å (about 20 - 30 nm), indicating the presence of many casein particles with sizes of 20 - 30 nm. These particles carry negative charges, resulting in significant electrostatic repulsion between the particles and generating a typical bump in this q range.

[0042] In addition, considering that the 0.1% casein solution is relatively dilute, we attempted to evaluate the radius of gyration (Rg) of casein particles by constructing a Guinier plot based on the I(q) data in the low q range. As Figure 4 shown in Fig. b, we obtained a good linear fit at 0.0002 Ų < q² < 0.0007 Ų, corresponding to 0.014 Å < q < 0.025 Å (45 - 25 nm). In addition, we evaluated the Rg of casein particles to be 8.3, 11.7, 10.0, and 9.2 nm at pH = 3.0, 5.0, 6.0, and 7.0, respectively.

[0043] The SAXS spectra of the mixed solution of goat cheese casein and apple polysaccharide at different pH values are also as Figure 5 shown. As Figure 5 shown in Fig. a, at pH = 3.0, I(q) increases in the low q range of the mixed solution, indicating the formation of larger aggregated particles due to the electrostatic attraction between apple polysaccharide and goat cheese casein. In addition, a slight but recognizable bump in I(q) was observed near the q range (0.01 - 0.02 Å −1 ) corresponding to a length scale of 30 - 60 nm. The SAXS curve of the mixed solution at pH = 4.0 is very similar to that at pH = 3.0. However, at pH = 5.0 - 7.0, compared with the goat cheese casein solution, the magnitude of I(q) in the low q range decreases significantly, indicating that the presence of apple polysaccharide reduces the number of large casein particles at these pH values. However, at q = 0.02 Å −1The 𝐼(𝑞) bump centered at (corresponding to 30 nm) is still visible but has become less pronounced, indicating that the number of casein particles of this size has decreased. Figure 5 The SAXS distribution diagrams of all mixed solutions are given in f. It can be seen that in the low 𝑞 range, the size of 𝐼(𝑞) of the solutions with pH values ​​of 3.0 and 4.0 is significantly higher than that of other pH values. As the pH value increases, the protrusion of 𝐼(𝑞) moves to higher 𝑞. This shows that at pH values ​​of 3.0 and 4.0, there is obvious electrostatic attraction in the mixed solution of goat casein and apple polysaccharide, forming larger aggregate particles. At pH values ​​of 5.0~7.0, the aggregation effect between apple polysaccharide and goat casein still exists, but it is significantly weakened.

[0044] Atomic force microscopy (AFM CypHer VRS1250) was used to observe the molecular morphology of goat casein, apple polysaccharide and their mixtures. The previously prepared apple polysaccharide solution and casein solution were diluted to obtain 0.002% (w / v) apple polysaccharide diluted solution and 0.0015% casein diluted solution as the control group, and then the two were mixed and diluted in equal proportions to obtain a 0.0015% mixed diluted solution as the experimental group. The pH values ​​of the experimental and control group solutions were adjusted to 3.0, 4.0, 5.0, 6.0 and 7.0, respectively. Subsequently, 5 μL of the experimental and control group solutions were respectively dropped onto the surface of the freshly cut mica sheet and dried in a dust-free environment (room temperature, 12 h). Finally, AFM imaging was performed in tapping mode, and the size of the scanned topographic image was 200 nm×200 nm. As shown in Figure 6 As shown in the figure, at pH = 3.0, pure apple polysaccharide presents dense molecular clusters, and pure goat casein presents a relatively uniform distribution of small particles with a particle size of about 50 nm, close to the diameter of most casein micelles. In their mixtures, we observed the formation of important complex particles. At pH = 4.0, the clusters of pure apple polysaccharide are sparser and more extended, and the casein micelles aggregate into larger particles with a size of more than 200 nm, corresponding to the decrease in solubility at the isoelectric point. At pH = 5.0, the morphology of apple polysaccharide molecules is more expanded, and the aggregation of casein is still obvious, but the size is smaller than that at pH = 4.0. For the mixture, the molecular morphology is similar to that at pH = 4.0. With the increase of pH value, the morphology of apple polysaccharide becomes more and more rigid, which may be due to the increase of intermolecular electrostatic repulsion. At the same time, the aggregation degree and particle size of goat casein decrease significantly due to the increase of protein solubility. There were also fewer aggregated particles in the mixture, and the particle size was similar to that of pure feta casein, which indicated that these particles might be derived from casein aggregates rather than maltosan / feta casein complex particles.

[0045] SAXS results show that at pH = 3.0, larger complex particles are formed in the experimental group solution, and the scattering intensity I(q) increases in the low q range (corresponding to larger particles); as the pH value increases, the complex particles become smaller, and the intensity of I(q) in the low q range decreases, but it is still significantly different from the control group, indicating that the interaction between apple polysaccharide and casein affects the aggregation state of casein. AFM images show that at pH = 3.0, apple polysaccharide and casein in the experimental group form larger aggregates; at pH = 4.0, the aggregates become smaller and more evenly distributed; at pH = 5.0 ~ 7.0, the casein particles become smaller and more dispersed, which is consistent with the SAXS results, further proving the stabilizing effect of apple polysaccharide on the microstructure of casein.

[0046] The above results show that the present invention is a stabilizer based on plant-based apple polysaccharide for improving the stability of goat milk casein. The stabilizer can effectively improve the stability of goat milk casein under different environmental conditions, prevent protein aggregation and precipitation, and improve the quality and shelf life of goat milk products.

[0047] In summary, the present invention has found a pectin-like apple polysaccharide. As a natural polysaccharide extracted from plants, apple polysaccharide has unique physicochemical properties and biological activity, and has potential application value in improving the stability of goat milk casein. As a nutritious dairy product, goat milk is prone to aggregation and precipitation during processing and storage, affecting the stability and quality of the product. Traditional stabilizers such as gelatin, although they can improve stability to a certain extent, have problems such as gradually reduced consumer acceptance and limited sources. Adding apple polysaccharide as a stabilizer in goat milk can effectively improve the stability of goat milk casein under different environmental conditions, prevent protein aggregation and precipitation, and improve the quality and shelf life of goat milk products. The research will have broad market prospects in the development of goat milk products with better rheological or physical stability.

Claims

1. A plant-derived apple polysaccharide, characterized in that: The weight average molecular weight of the apple polysaccharide is 361.7 kDa, and the sugar composition of the apple polysaccharide is 60% to 62% glucose, 19% to 20% mannose, 17% to 18% galactose, 1.0% to 1.5% rhamnose and 1.5% to 2.0% glucuronic acid.

2. The plant-derived apple polysaccharide according to claim 1, characterized in that: The sugar composition of the apple polysaccharide is 60.38% glucose, 19.41% mannose, 17.60% galactose, 1.00% rhamnose and 1.61% glucuronic acid.

3. The use of a plant-derived apple polysaccharide according to claim 1 or 2 in improving the stability of goat milk casein, characterized in that: When a 1.0% to 1.5% apple polysaccharide solution is added to goat milk, the ratio of apple polysaccharide to goat milk casein content is 1:

16.

4. A stabilizer, characterized in that The stabilizer is plant-derived apple polysaccharide, the weight average molecular weight of the apple polysaccharide is 361.7 kDa, and the sugar composition of the apple polysaccharide is 60% to 62% glucose, 19% to 20% mannose, 17% to 18% galactose, 1.0% to 1.5% rhamnose and 1.5% to 2.0% glucuronic acid.

5. A stabilizer according to claim 4, characterized in that: The sugar composition of the apple polysaccharide is 60.38% glucose, 19.41% mannose, 17.60% galactose, 1.00% rhamnose and 1.61% glucuronic acid.

6. A method for improving the stability of goat milk casein, characterized in that: A plant-derived apple polysaccharide solution with a concentration of 1.0% to 1.5% is added to goat milk, and the ratio of apple polysaccharide to goat milk casein content is 1:16, wherein the weight average molecular weight of the apple polysaccharide is 361.7 kDa, and the sugar composition of the apple polysaccharide is 60% to 62% glucose, 19% to 20% mannose, 17% to 18% galactose, 1.0% to 1.5% rhamnose and 1.5% to 2.0% glucuronic acid.

7. A method for improving the stability of goat milk casein according to claim 6, characterized in that: The sugar composition of the apple polysaccharide is 60.38% glucose, 19.41% mannose, 17.60% galactose, 1.00% rhamnose and 1.61% glucuronic acid.

8. The method for preparing plant-derived apple polysaccharide according to claim 1 or 2, characterized in that: The specific steps are as follows: Extraction of crude apple polysaccharide from apple pomace; preparing an aqueous solution of crude apple polysaccharide, heating the aqueous solution of crude apple polysaccharide to perform ethanol precipitation to obtain a precipitate; A precipitate aqueous solution is prepared, the precipitate aqueous solution is dialyzed, and freeze-dried to obtain plant-derived apple polysaccharide with metal ions removed.

9. The method for preparing plant-derived apple polysaccharide according to claim 8, characterized in that: A 1.0% concentration aqueous solution of crude apple polysaccharide was heated to 60°C for 2 h, and then three times the volume of 95% ethanol was added for precipitation to obtain a precipitate.

10. The method for preparing plant-derived apple polysaccharide according to claim 8, characterized in that: The dialysis was performed using a 3 kDa cut-off dialysis membrane.

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