Application of Astragalus polysaccharides in promoting metabolism of lactic acid bacteria and improving quality and stability of fermented products

Abstract

The application discloses an application of astragalus polysaccharide in promoting lactic acid bacteria metabolism and improving quality and stability of fermented products, and belongs to the technical field of fermented dairy product processing. The application adds 2 ‰ to 10 ‰ of astragalus polysaccharide and sucrose in skimmed milk with respect to the mass of the skimmed milk, inoculates lactic acid bacteria starter after pasteurization, and constant-temperature fermentation is carried out until the end point to prepare fermented products. The application utilizes the dual functions of astragalus polysaccharide in promoting lactic acid bacteria metabolism and strengthening milk protein gel network to realize the synergistic improvement of quality and stability of fermented products. Experiments show that when the addition amount of astragalus polysaccharide is 4 ‰, the sensory score of the fermented product reaches 87.3, and the water holding capacity is increased by 11.95 % compared with the control group; scanning electron microscopy shows that the gel network is dense and has few pores; when the addition amount is 6 ‰, the viable cell count reaches 1.23 x 10 8 CFU / ml; and when the addition amount is 8 ‰, the texture characteristics are optimal. The application is simple in operation, suitable for industrial production, and provides a new way for the development of functional fermented dairy products.

Description

Technical Field

[0001] This application relates to the field of fermented dairy product processing technology, specifically to the application of astragalus polysaccharide in promoting lactic acid bacteria metabolism and improving the quality and stability of fermented products. Background Technology

[0002] Fermented milk is a product with a distinctive flavor made from cow's milk through fermentation under specific conditions. Due to its high digestibility and bioavailability of protein, potassium, calcium, and B vitamins, it has gained widespread scientific recognition and has become a highly valuable nutritional supplement in the daily diet. The quality and stability of fermented milk are core indicators for evaluating its product quality. Among these, the textural properties (such as hardness and viscosity), water-holding capacity, and whey separation rate during storage directly affect the product's taste, sensory appeal, and shelf-life stability.

[0003] Astragalus, a traditional Chinese medicine with a long history, was included in the list of food and medicine homologous ingredients in 2023. Its main active ingredient, astragalus polysaccharide, is a water-soluble heteropolysaccharide, mainly composed of hexuronic acid, glucose, fructose, rhamnose, arabinose, galacturonic acid, and glucuronic acid, possessing multiple functional effects such as antiviral, antitumor, and antioxidant properties. In the food processing field, reports have shown that adding 5 g of astragalus polysaccharide to 145 g of dough can significantly delay dough digestion and inhibit glucose release, thereby regulating blood sugar levels. The addition of astragalus polysaccharide can promote the growth of *Lactobacillus plantarum* ATCC11974 and *Lactobacillus rhamnosus*. Furthermore, the addition of astragalus polysaccharide can improve the physicochemical properties of protein gels, shortening the gelation time from 1128 s to 871.8 s and making the structure of heat-treated protein gels more compact. Adding astragalus extract to millet and glutinous rice for fermenting rice wine can impart a unique astragalus flavor to the product.

[0004] Although Astragalus polysaccharides have shown unique potential in promoting the proliferation of probiotics and strengthening gel networks, there are few reports, both domestically and internationally, on their direct application in fermented milk fermentation systems and their comprehensive effects on fermentation characteristics, textural properties and long-term storage stability of fermented milk, especially whether they can achieve synergistic improvement in quality and stability.

[0005] In summary, existing technologies lack a solution that leverages the unique functional properties of Astragalus polysaccharides to significantly enhance the sensory quality and storage stability of fermented milk. Therefore, developing a novel strategy for preparing fermented milk based on Astragalus polysaccharides to simultaneously address the dual technical challenges of improving fermented milk quality and ensuring long-term stability is a pressing issue in this field. Summary of the Invention

[0006] In view of this, the purpose of this application is to provide an application of astragalus polysaccharide in promoting lactic acid bacteria metabolism and improving the quality and stability of fermented products. This application involves adding 2‰ to 10‰ of the mass of skim milk astragalus polysaccharide and sucrose to skim milk, followed by pasteurization and inoculation with a starter culture, and then fermenting at a constant temperature until the endpoint, thus obtaining an astragalus polysaccharide fermented product. In this astragalus polysaccharide fermented product, astragalus polysaccharide acts as a prebiotic, promoting lactic acid bacteria metabolism, shortening fermentation time, and increasing the number of viable bacteria; simultaneously, it interacts with milk proteins to form a dense gel network, significantly improving the water-holding capacity and textural properties of the fermented product, and continuously inhibiting whey separation during storage, achieving a synergistic improvement in quality and stability.

[0007] To achieve the above objectives, this application provides the following technical solution:

[0008] Firstly, this application provides the application of Astragalus polysaccharide in promoting lactic acid bacteria metabolism and improving the quality and stability of fermented products.

[0009] In some embodiments, the amount of Astragalus polysaccharide added to skim milk is 2‰ to 10‰ of the mass of skim milk.

[0010] In some preferred embodiments, the amount of Astragalus polysaccharide added is 4‰ to 8‰ of the mass of skim milk.

[0011] Secondly, this application provides a fermented product of astragalus polysaccharide, which is prepared from the following raw materials: skim milk, sucrose, astragalus polysaccharide and fermentation agent; the amount of sucrose added is 7% of the mass of skim milk; the amount of astragalus polysaccharide added is 2‰ to 10‰ of the mass of skim milk.

[0012] In some embodiments, the amount of Astragalus polysaccharide added is 4‰ to 8‰ of the mass of skim milk.

[0013] In some preferred embodiments, the amount of astragalus polysaccharide added is 4‰, 6‰ or 8‰ of the mass of skim milk.

[0014] Thirdly, this application provides a method for preparing the Astragalus polysaccharide fermentation product described in the second aspect, comprising the following steps:

[0015] (1) Add sucrose and 2‰ to 10‰ of the weight of skim milk to skim milk and stir thoroughly.

[0016] (2) Pasteurize the mixture obtained in step (1);

[0017] (3) After cooling, inoculate with a starter containing Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus;

[0018] (4) Fermentation is carried out under constant temperature conditions until the end point, and the fermented product of Astragalus polysaccharide is obtained.

[0019] In some preferred embodiments, in step (1), the amount of sucrose added is 7% of the mass of skim milk, and the amount of astragalus polysaccharide added is 4‰ to 8‰.

[0020] In some preferred embodiments, in step (2), the pasteurization conditions are 90 °C for 20 min.

[0021] In some preferred embodiments, in step (3), the inoculum amount of the fermenting agent is 1% (v / v); in step (4), the temperature of the isothermal fermentation is 42 ℃, and the fermentation time is 5 to 10 hours.

[0022] Compared with the prior art, this application has at least the following advantages and beneficial effects:

[0023] 1. This application achieves, for the first time, a synergistic improvement in quality (sensory properties, texture, viable cell count) and stability (water-holding capacity, gel structure, and resistance to whey precipitation) in a fermentation product system by adding an appropriate amount of Astragalus polysaccharide (APS) to the fermentation product and utilizing its dual functions of promoting lactic acid bacteria metabolism and strengthening the gel network.

[0024] 2. This application determined the optimal sucrose addition amount to be 7% through single-factor experiments, at which point the fermented product had a pleasantly sweet and sour taste. Based on this, APS was added. When the APS addition amount was 4‰, the sensory score of the fermented product was further improved to 87.3 points (out of 100), with a delicate texture and harmonious flavor; water-holding capacity was increased by 11.95% compared to the control group (P<0.05), whey precipitation was significantly reduced, and storage stability was enhanced.

[0025] 3. The Astragalus polysaccharide fermented product prepared in this application, when the amount of Astragalus polysaccharide added is 6‰, can achieve a viable lactic acid bacteria count of 1.23 × 10⁻⁶ at the fermentation endpoint. 8 The CFU / ml concentration was increased by 11.5% compared to the control group, and the pH reached 4.35 after 5 hours of fermentation, significantly shortening the fermentation time. When the astragalus polysaccharide addition was 8‰, the hardness, consistency, cohesion, and viscosity of the fermented product were optimal, with the highest gel strength. Scanning electron microscopy showed that when the astragalus polysaccharide addition reached 4‰, the gel network exhibited a dense, low-porous structure, significantly improving stability compared to the loose, porous structure of the control group.

[0026] 4. This application specifies the following process parameters: 7% sucrose addition, 2‰ to 10‰ APS addition (preferably 4‰ to 8‰), sterilization at 90 ℃ for 20 min, and fermentation at 42 ℃ for 5 to 10 h. The process is simple to operate and suitable for large-scale production. Attached Figure Description

[0027] Figure 1The effect of different sucrose addition amounts on the sensory scores of fermented products.

[0028] Figure 2 Sensory evaluation of fermented products with different amounts of Astragalus polysaccharide added.

[0029] Figure 3 The color differences of fermented products with different amounts of Astragalus polysaccharide added.

[0030] Figure 4 The pH changes during fermentation of fermented products with different amounts of Astragalus polysaccharide were studied.

[0031] Figure 5 The effects of different amounts of Astragalus polysaccharide added on pH and titratable acidity of fermented products after 10 hours of fermentation were investigated; where A represents the effect on pH and B represents the effect on titratable acidity.

[0032] Figure 6 The changes in viable cell count at the fermentation endpoint of fermented products with different amounts of Astragalus polysaccharide were investigated.

[0033] Figure 7 The effect of different amounts of Astragalus polysaccharide added on the water-holding capacity of fermented products.

[0034] Figure 8 The effect of different amounts of Astragalus polysaccharide added on the rheological properties of fermented products is shown; where A is the storage modulus of fermented products with different amounts of Astragalus polysaccharide added; and B is the loss modulus of fermented products with different amounts of Astragalus polysaccharide added.

[0035] Figure 9 The effects of different amounts of Astragalus polysaccharide added on the microstructure of fermented products were shown. Image A is the SEM image of the fermented product without Astragalus polysaccharide; image B is the SEM image of the fermented product with 2‰ Astragalus polysaccharide added; image C is the SEM image of the fermented product with 4‰ Astragalus polysaccharide added; image D is the SEM image of the fermented product with 6‰ Astragalus polysaccharide added; image E is the SEM image of the fermented product with 8‰ Astragalus polysaccharide added; and image F is the SEM image of the fermented product with 10‰ Astragalus polysaccharide added. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0037] The materials used in the following embodiments are not limited to those listed below, and other similar materials may be used instead. Unless otherwise specified, the instruments shall be used under conventional conditions or as recommended by the manufacturer. Those skilled in the art should have relevant knowledge of the use of conventional materials and instruments.

[0038] In this application, unless the context clearly indicates otherwise, the terms “including,” “comprising,” “containing,” “having,” etc., shall be understood as open-ended and mean “including but not limited to.”

[0039] To better understand this teaching and without limiting its scope, all figures and other numerical values ​​used in the specification and claims to express quantities, percentages, or proportions should, in all cases, be understood to be modified by the term "about." Therefore, unless otherwise stated, the numerical parameters set forth in the following specification and appended claims are approximate values ​​that may be adjusted according to the desired performance. At a minimum, each numerical parameter should be interpreted based on the reported significant figures and by applying common rounding techniques.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the subject matter of this application pertains. Before a detailed description of this application, the following explanations of terminology are provided to better understand this application.

[0041] 1. Astragalus Polysaccharide (APS): The Astragalus polysaccharide used in this application is a water-soluble heteropolysaccharide extracted from Astragalus root, with a purity ≥90%. Its main components include hexuronic acid, glucose, fructose, rhamnose, arabinose, galacturonic acid, and glucuronic acid. In this application, it functions as both a prebiotic (promoting the growth and metabolism of lactic acid bacteria) and a gel fortifier (interacting with milk proteins to improve the gel network structure).

[0042] 2. Synergistic improvement of quality and stability: This refers to the fact that while the sensory quality (such as color, odor, taste, and texture), textural properties (such as hardness, consistency, cohesion, and viscosity), and fermentation properties (such as viable cell count and fermentation time) of fermented products are improved, their storage stability (such as water holding capacity, whey precipitation inhibition, and gel network structure stability) is also enhanced accordingly. The two show a mutually promoting and synergistic effect, rather than a separate improvement or a trade-off between individual indicators.

[0043] 3. Water-holding capacity: This refers to the ability of a fermented product to retain moisture under centrifugation conditions. It is used to evaluate the ability of the gel network of a fermented product to retain water and inhibit whey separation. Specific measurement methods and formulas are described in this application.

[0044] 4. Storage modulus (G′) and loss modulus (G″): In this application, the storage modulus (G′) reflects the elastic behavior of the fermentation product gel, representing the ability of the sample's internal structure to store deformation energy; a larger value indicates a more stable gel network structure. The loss modulus (G″) reflects the viscous behavior of the fermentation product gel, representing the sample's ability to dissipate deformation energy. When G′>G″, the fermentation product exhibits a weakly gel-like structure dominated by elasticity, which is a rheological characteristic that gives the fermentation product good quality and stability.

[0045] 5. Dense gel network structure: In this application, this refers to the microstructural characteristics of the fermentation product under a scanning electron microscope (SEM), specifically characterized by: tight protein cross-linking, small mesh pore size, uniform pore distribution, and good network continuity. In contrast, a "loose porous structure" is characterized by large mesh pore size, weak protein connections, and uneven pore distribution. The dense gel network structure is the microscopic basis for the high water-holding capacity and excellent textural properties of the fermentation product.

[0046] This application proposes to apply Astragalus polysaccharide (APS) to fermentation systems to achieve synergistic improvement in the quality (sensory characteristics, texture, viable cell count) and stability (water-holding capacity, gel structure, and resistance to whey precipitation) of fermented products, based on the dual characteristics of APS: prebiotic activity (promoting lactic acid bacteria growth and metabolism, accelerating acid production) and gel-strengthening function (interacting with milk proteins to form a dense network structure). To verify the above-mentioned inventive concept and determine the optimal process parameters, this application designed a systematic research scheme: First, single-factor experiments were conducted to investigate the effects of sucrose addition (5%–9%) and Astragalus polysaccharide addition (0‰–10‰) on the sensory scores of fermented products, determining the appropriate addition range; then, the physicochemical properties (pH, titratable acidity), fermentation characteristics (viable cell count, OD value), stability indicators (water-holding capacity, texture properties, rheological properties), and microstructure (scanning electron microscopy) of fermented products under different APS addition amounts were measured, systematically revealing the influence and mechanism of APS on the quality and stability of fermented products. Specific experimental materials, methods, and results are detailed below.

[0047] 1. Materials and Reagents

[0048] Skim milk: 0% fat, 5% protein, purchased from Yili Group;

[0049] Astragalus polysaccharide: purity ≥90%, purchased from Shanghai Zhanming Biotechnology Co., Ltd.;

[0050] Sucrose: food grade, purchased from Guangdong Huasheng Food Biotechnology Co., Ltd.;

[0051] Distilled water and sodium hydroxide: purchased from Sinopharm Chemical Reagent Co., Ltd.

[0052] Phenolphthalein: Purchased from Fuchen Chemical Reagent Co., Ltd.;

[0053] MRS solid culture medium: purchased from Guangdong Huankai Microbial Technology Co., Ltd.;

[0054] Sodium chloride: purchased from Tianjin Ke Mao Chemical Reagent Co., Ltd.;

[0055] Commercial compound fermentation product starter: contains Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus, purchased from Microcare Probiotics (Suzhou) Co., Ltd.

[0056] 2. Preparation method of fermented products

[0057] Take a clean fermentation flask, fill it with skim milk, and add sucrose and astragalus polysaccharide (APS) according to the formula. Stir thoroughly to ensure even mixing. Pasteurize the mixture at 90 °C for 20 min, then cool to room temperature. Add 1% (v / v) of the activated commercial compound fermentation starter (i.e., 1 mL of starter per 100 mL fermentation system), mix well, and place in a 42 °C constant temperature incubator for static fermentation for 6 hours, until the pH reaches approximately 4.3 (fermentation endpoint). Remove and quickly cool to 4 °C to obtain the astragalus polysaccharide fermented product.

[0058] 3. Single-factor experimental design

[0059] To determine the appropriate amounts of Astragalus polysaccharide and sucrose, separate single-factor experiments were conducted. The sucrose single-factor experiment and the Astragalus polysaccharide single-factor experiment were not conducted in the same batch. Slight differences may have existed in the evaluation panel members involved in the sensory evaluation, the environment on the evaluation day, and the sample processing conditions, resulting in the absolute scores of the two experiments not being directly comparable. This experiment focused more on the relative trends within the same experiment, i.e., the comparison between each addition group and its corresponding control group, to determine the optimal addition amount.

[0060] 3.1 Single-factor experiment on sucrose addition amount

[0061] With a fixed addition of Astragalus polysaccharide at 4‰ of the mass of skim milk and a fermentation time of 6 h, the effects of sucrose additions of 5%, 6%, 7%, 8%, and 9% (all percentages of skim milk mass) on the sensory scores of the fermented product were investigated. Other preparation steps were the same as those in Section 2, Fermented Product Preparation Method.

[0062] 3.2 Single-factor experiment on the amount of Astragalus polysaccharide added

[0063] With a fixed sucrose addition of 5% and a fermentation time of 6 h, the effects of astragalus polysaccharide additions of 0‰, 2‰, 4‰, 6‰, 8‰, and 10‰ (all per thousand parts by weight of skim milk) on the sensory scores of the fermented product were investigated. Other preparation steps were the same as in Section 2.

[0064] 4. Measurement Method

[0065] 4.1 Sensory evaluation

[0066] Ten experts familiar with professional sensory evaluation were selected to score the fermented products in four aspects: color, aroma, taste, and texture. The final score was the average of the three experiments. The sensory evaluation criteria are shown in Table 1.

[0067] Table 1 Sensory Evaluation Table of Astragalus Polysaccharide Fermented Products

[0068]

[0069] 4.2 pH Measurement

[0070] The pH value was determined using a pH meter (FE28-Standard, Mettler Toledo Technologies Co., Ltd.) in accordance with the method in the national food safety standard "Determination of pH value in food" (GB 5009.237-2016).

[0071] 4.3 Titration Acidity Determination

[0072] Refer to the method in the National Food Safety Standard "Determination of Acidity in Food" (GB 5009.239-2016). Weigh 5 g of the fermented product, dilute it with 45 mL of distilled water, add 2-3 drops of phenolphthalein solution and mix well. Titrate with 0.1 mol / L NaOH solution until a faint pink color appears, and record the volume of sodium hydroxide consumed. Calculate the acidity (T) using the following formula:

[0073] ;

[0074] Wherein, X - the acidity of the sample, in degrees (T);

[0075] C represents the concentration of the sodium hydroxide standard solution, expressed in moles per liter (mol / L).

[0076] V1 is the volume of sodium hydroxide standard solution consumed during titration, in milliliters (mL).

[0077] V0 represents the volume of sodium hydroxide standard solution consumed in the blank test, in milliliters (mL).

[0078] 100 refers to a 100 g sample;

[0079] m is the mass of the sample, in grams (g).

[0080] 0.1 is the theoretical definition of sodium hydroxide molar concentration, expressed in moles per liter (mol / L).

[0081] 4.4 Determination of total lactic acid bacteria count

[0082] The method was followed according to the national standard GB 4789.35-2023 "National Food Safety Standard - Microbiological Examination of Food - Examination of Lactic Acid Bacteria". 1 g of fermented product sample was taken and serially diluted 10-fold with 9 mL of physiological saline. 1 mL of the diluted bacterial solution was added to a sterile Petri dish containing MRS agar medium and incubated at 42 ℃ for 48 h in a WPL-230BE electric thermostatic incubator (Tianjin Tester Instrument Co., Ltd.). The results were then counted and expressed as CFU / mL.

[0083] 4.5 Water Holding Capacity (WHC) Measurement

[0084] Take 10 mL of fermentation product sample and place it in a centrifuge tube of known weight. Record the total weight of the centrifuge tube and the sample. Centrifuge at 6000 r / min for 15 min, let stand for 10 min, discard the supernatant, and weigh the centrifuge tube and the remaining precipitate. The water-holding capacity is calculated using the following formula:

[0085] ;

[0086] Where W1 is the weight of the centrifuge tube, in grams (g);

[0087] W2 represents the weight of the centrifuge tube and sample, in grams (g).

[0088] W3 represents the weight of the centrifuge tube and sample after discarding the supernatant, in grams (g).

[0089] 4.6 Determination of textural properties

[0090] The hardness, consistency, cohesiveness, and viscosity index of the samples were determined using a texture analyzer (TA-XTplus, UK) through reverse extrusion testing. An A / BE accessory with a compression disc (Ø=35 mm) was used. The sample was placed inside a cylinder with an inner diameter of Ø=50 mm, filling the cylinder to 75% of its height. Measurement conditions: compression distance 30 mm, initial speed 1.0 mm / s, and subsequent speed 10.0 mm / s. Each sample was measured three times, and the average value was taken.

[0091] 4.7 Rheological property determination

[0092] Measurements were performed using a Haake™ MARS™ rotational rheometer (USA). First, the instrument was calibrated using a 60 mm diameter parallel plate mold, with a 0.8 mm gap between the parallel plate and the clamp, and a test temperature of 4 °C. A small amount of sample was placed on the stage, taking care to avoid excessive spillage. Strain scanning was performed first, with a fixed scanning frequency of 1 Hz and a strain range of 0.01%–100%, to determine the linear viscoelastic region of the sample. Then, frequency scanning was performed within the linear viscoelastic region, with an angular frequency range of 0.1–100 rad / s, to determine the storage modulus (G′) and loss modulus (G″).

[0093] 4.8 Microstructure determination

[0094] A 5 g sample of fermentation product with a regular shape was taken and freeze-dried for 48 h. The freeze-dried sample was cut in half and placed with the cut side facing up on a copper metal support plate coated with conductive adhesive, and then sputtered with gold. Afterwards, it was transferred to a scanning electron microscope chamber, and the microstructure of the fermentation product gel network was observed and photographed at an appropriate magnification.

[0095] 4.9 Data Analysis

[0096] All experiments were performed in triplicate. Visualization was performed using Origin 2018 software; statistical analysis was conducted using IBM SPSS Statistics 27 software. Differences between groups were analyzed using one-way ANOVA, with P < 0.05 considered statistically significant. Different lowercase letters in the figures indicate significant differences in the corresponding indicators at different APS addition levels (P < 0.05).

[0097] 5. Results and Analysis

[0098] 5.1 Determination of the amount of sucrose added

[0099] The experiment was conducted according to the method in Section 3.1. The effect of different sucrose addition amounts on the sensory scores of fermented products was as follows: Figure 1 As shown. By Figure 1 It can be seen that the sensory score first increases and then decreases with the increase of sucrose addition. The sensory score is highest at 78 points when the sucrose addition is 7%. Therefore, except for the single-factor experiment on the addition of Astragalus polysaccharide, all subsequent experiments used a sucrose addition of 7%.

[0100] 5.2 Sensory evaluation of Astragalus polysaccharide fermentation products

[0101] Fermentation products with different APS addition amounts were prepared according to the method in Section 3.2, and the sensory evaluation results are as follows: Figure 2As shown, the sensory score first increased and then decreased with increasing APS addition. The highest sensory score (87.3 points) was achieved when the APS addition was 4‰. When the APS addition exceeded 4‰, the sensory score decreased, possibly because excessive APS addition led to a stronger medicinal flavor and darker color in the fermented product. Figure 3 This reduces consumer acceptance. Therefore, the optimal addition level of APS is 4‰.

[0102] 5.3 pH value and titration acidity

[0103] 5.3.1 pH changes during fermentation

[0104] The pH changes during fermentation were determined according to the method in Section 4.2 with different APS addition levels (0‰, 5‰, 10‰). The results are as follows: Figure 4 As shown in the figure, compared with the control group without APS, the fermentation products with 5‰ and 10‰ APS showed a significantly faster pH decrease and an earlier fermentation endpoint. At 5 h of fermentation, the pH of the APS-added group reached 4.35, indicating that APS can promote acid production by lactic acid bacteria and shorten the fermentation time.

[0105] To further refine the effect of APS addition, the pH and titratable acidity of fermented products with different APS additions (0‰, 2‰, 4‰, 6‰, 8‰, 10‰) were measured after 10 h of fermentation. The results are as follows: Figure 5 As shown in the figure, the pH of the 10‰ APS addition group was significantly different from that of the other groups after 10 h of fermentation (P<0.05), indicating that high doses of APS still had a promoting effect on the later stage of fermentation.

[0106] 5.3.2 Changes in viable cell count at the fermentation endpoint

[0107] The viable count of lactic acid bacteria at the fermentation endpoint (10 h of fermentation) was determined according to the method in Section 4.4, and the results are as follows: Figure 6 As shown, the viable bacteria count of all six fermented products met the requirement of ≥10⁻⁶ in GB 19302-2025 "National Food Safety Standard for Fermented Milk". 6 The required CFU / g concentration was as follows. The highest viable bacterial count (1.23 × 10⁻⁶) was achieved when the APS addition was 6‰. 8 The CFU / mL level was increased by 11.5% compared to the control group (0‰ group) without APS. This indicates that adding an appropriate amount of APS can promote the growth and reproduction of lactic acid bacteria.

[0108] In addition, the changes in OD value during fermentation were measured in this embodiment, and the results are shown in Table 2. The trend of OD value change was consistent with the viable cell count, further confirming the promoting effect of APS on lactic acid bacteria metabolism.

[0109] Table 2. Changes in OD values ​​of fermented products with different amounts of Astragalus polysaccharide addition during fermentation.

[0110]

[0111] Note: Lowercase letters indicate that different time periods caused significant differences in the samples (P<0.05), and uppercase letters indicate that different amounts of Astragalus polysaccharide added at different times caused significant differences in the samples (P<0.05).

[0112] 5.4 Water Holding Capacity (WHC)

[0113] The water-holding capacity of fermentation products with different APS addition levels was determined according to the method in Section 4.5, and the results are as follows: Figure 7 As shown, the water-holding capacity initially increased and then decreased with increasing APS addition. The optimal water-holding capacity was observed at APS addition levels of 2‰ and 4‰, with the 4‰ APS group exhibiting an 11.95% increase in water-holding capacity compared to the control group (0‰) (P<0.05). This may be because appropriate amounts of APS interact with fermented product proteins, forming a protein network structure with smaller pores and stronger water-binding capacity. Excessive APS may inhibit casein cluster aggregation, leading to increased whey precipitation.

[0114] 5.5 Texture properties

[0115] The hardness, consistency, cohesion, and viscosity of fermented products with different APS additions were determined according to the method in Section 4.6, and the results are shown in Table 3. With increasing APS addition, the textural properties first decreased and then increased. At an APS addition of 8‰, the hardness, consistency, and cohesion all reached their highest values ​​(hardness 34.93 g, consistency 159.89 g, cohesion 22.11 kPa), and the viscosity also reached 80.85 Pa·s, significantly higher than the control group (P<0.05). At APS additions of 6‰–8‰, the gel strength was higher and the network structure more compact. This indicates that an appropriate amount of APS can enhance casein cross-linking and improve the textural properties of fermented products.

[0116] Table 3 Effects of different amounts of Astragalus polysaccharide added on the textural properties of fermented products

[0117]

[0118] Note: Values ​​in the table are mean ± standard deviation; different capital letters in the same column indicate significant differences (P<0.05).

[0119] 5.6 Rheological properties

[0120] The storage modulus (G′) and loss modulus (G″) of fermentation products with different APS addition amounts were determined according to the method in Section 4.7. The results are as follows: Figure 8As shown in the figure, within the angular frequency range of 1–60 rad / s, all fermented products exhibited linear viscoelastic behavior, and G′ > G″, indicating that the fermented products had a weak gel-like structure. When the APS addition was 2‰, the G′ value of the fermented product was significantly higher than that of the other groups, indicating that it had the strongest gel elasticity and a more stable network structure. This may be due to the interaction between polysaccharides and milk proteins forming a more stable three-dimensional network structure.

[0121] 5.7 Microstructure

[0122] The gel network microstructure of fermentation products with different APS addition levels was observed according to the method in Section 4.8. Scanning electron microscopy images are shown below. Figure 9 As shown. (Comparison) Figure 9 -A (0‰ APS) analysis showed that the gel network of fermentation products without APS exhibited a loose, porous structure with weaker protein-protein connections and larger pore sizes. As the amount of APS added increased, the gel network gradually became denser. Figure 9 -B (2‰) begins to show a more compact structure; Figure 9 -C (4‰) exhibits a dense and low-porosity structure, with the best compactness; Figure 9 -D (6‰) and 9-E (8‰) are still relatively dense, but slightly less dense than 4‰; Figure 9 -F (10‰) again resulted in a looser structure. This indicates that an appropriate amount of APS (especially 4‰) can promote cross-linking between casein molecules, forming a more compact and uniform gel network structure, thereby improving the stability and quality of fermented products.

[0123] 6. Conclusion

[0124] Based on the above results, this embodiment confirms that:

[0125] (1) The optimal amount of sucrose added is 7% (relative to the mass of skim milk), at which point the sweet and sour taste is just right.

[0126] (2) The optimal addition amount of Astragalus polysaccharide is 4‰ to 8‰ (relative to the mass of skim milk); among them: when the optimal addition amount of Astragalus polysaccharide is 4‰, the sensory score is the highest, the water-holding capacity is significantly improved (11.95% higher than the control group), and the micro-gel network is the densest; when the optimal addition amount of Astragalus polysaccharide is 6‰, the number of viable lactic acid bacteria is the highest (1.23×10⁻⁶). 8 (CFU / mL); when the optimal addition amount of Astragalus polysaccharide is 8‰, the textural properties (hardness, consistency, cohesion) are optimal; when it is 2‰, the storage modulus G′ is the highest and the rheological properties are optimal.

[0127] (3) Astragalus polysaccharides can achieve synergistic improvement in the quality and stability of fermented products through the dual effects of promoting lactic acid bacteria metabolism and strengthening gel network.

[0128] The present application has been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present application. The descriptions of the embodiments above are only for the purpose of helping to understand the present application and its core ideas. It should be noted that those skilled in the art can make several improvements and modifications to the present application without departing from the principles of the present application, and these improvements and modifications also fall within the protection scope of the claims of the present application.

Claims

1. Application of Astragalus polysaccharides in promoting lactic acid bacteria metabolism and improving the quality and stability of fermented products.

2. The application according to claim 1, wherein the amount of Astragalus polysaccharide added to skim milk is 2‰ to 10‰ of the mass of skim milk.

3. The application according to claim 1, wherein the amount of Astragalus polysaccharide added is 4‰ to 8‰ of the mass of skim milk.

4. A fermented product of astragalus polysaccharide, which is prepared from the following raw materials: skim milk, sucrose, astragalus polysaccharide and fermentation agent; wherein the amount of sucrose added is 7% of the mass of skim milk; and the amount of astragalus polysaccharide added is 2‰ to 10‰ of the mass of skim milk.

5. The fermented product of Astragalus polysaccharide according to claim 4, wherein the amount of Astragalus polysaccharide added is 4‰ to 8‰ of the mass of skim milk.

6. The fermented product of Astragalus polysaccharide according to claim 4, wherein the amount of Astragalus polysaccharide added is 4‰, 6‰ or 8‰ of the mass of skim milk.

7. The method for preparing the Astragalus polysaccharide fermentation product according to claim 4, comprising the following steps: (1) Add sucrose and 2‰ to 10‰ of the weight of skim milk to skim milk and stir thoroughly. (2) Pasteurize the mixture obtained in step (1); (3) After cooling, inoculate with a starter containing Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus; (4) Fermentation is carried out under constant temperature conditions until the end point, and the fermented product of Astragalus polysaccharide is obtained.

8. According to the preparation method of claim 7, in step (1), the amount of sucrose added is 7% of the mass of skim milk, and the amount of astragalus polysaccharide added is 4‰ to 8‰.

9. According to the preparation method of claim 7, in step (2), the pasteurization conditions are 90 °C for 20 min.

10. According to the preparation method of claim 7, in step (3), the inoculum amount of the fermenting agent is 1% (v / v); in step (4), the temperature of the constant temperature fermentation is 42 ℃, and the fermentation time is 5 to 10 hours.

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