Method for improving stability of fermented milk by ultrasonic and polysaccharide in cooperation and fermented milk

Abstract

The application provides a method for improving the stability of fermented milk by ultrasonic and polysaccharide and fermented milk, and relates to the technical field of dairy products.The method comprises the following steps: ultrasonic treatment is conducted on a mixture of homogenized and sterilized raw milk and sodium alginate to obtain a fermentation base, wherein the ultrasonic treatment conditions are as follows: the ultrasonic treatment power is 144-240 W, the frequency is 20-40 kHz, and the treatment time is 4-10 min.In the application, sodium alginate is added to the raw milk, and the stability of the fermented milk is improved by ultrasonic and polysaccharide;ultrasonic treatment breaks long chains of sodium alginate, specifically activates casein binding sites, efficiently induces the formation of an 'egg box structure', and further constructs a more compact and stable three-dimensional network gel structure, so that the product quality and storage stability of the fermented milk are improved.

Description

Technical Field

[0001] This invention relates to the field of dairy technology, and in particular to a method for improving the stability of fermented milk through ultrasound-polysaccharide synergy, and the fermented milk itself. Background Technology

[0002] Yogurt is a widely consumed dairy product, not only an excellent source of protein, minerals, and vitamins, but also offering multiple functions such as alleviating lactose intolerance, regulating immunity, and lowering cholesterol and blood sugar levels. Room-temperature fermented milk, without relying on traditional cold chain storage and transportation methods, has a shelf life of 3-6 months, providing similar nutritional value to refrigerated fermented milk. This meets diverse market demands for portability and nutrition, and broadens the leisure attributes and consumption scenarios of dairy products. Although room-temperature fermented milk has experienced explosive market growth in the past decade, it faces significant challenges in maintaining storage stability due to the need for a second pasteurization process after fermentation to extend shelf life at room temperature. Thickeners, emulsifiers, and stabilizers are typically added to room-temperature fermented milk to improve sensory defects and maintain shelf-life stability. However, the additional use of various additives not only increases production costs and contradicts clean labeling but also places an additional burden on consumer health. Sodium alginate is a naturally derived, bioactive anionic polysaccharide from algae. It is one of the stabilizers approved for use in dairy processing in my country's food additive standard GB2760-2014, and it also possesses bioactivities such as lowering cholesterol and promoting intestinal health. However, due to the limited thermodynamic compatibility between protein and polysaccharide macromolecular polymers, the effect of seaweed in enhancing the gel stability of yogurt still needs improvement, and it is urgent to combine it with other methods to synergistically enhance the gel stability of fermented milk with sodium alginate. Currently, various physical processing technologies, such as ultra-high pressure and ultrasound, have been proven to enhance the stability of composite gels. However, when the same method is applied to different food composite systems, the gel enhancement effect varies greatly, and different processing conditions also have different effects on the gel system. For example, CN102150794A discloses the use of ultrasound treatment to enhance the stability of konjac polysaccharide composite gels, which requires a power density of 0.4~0.6W / cm³. 2The treatment time is 30-36 seconds. However, CN116210905A targets the soybean protein-polysaccharide complex system, using the same method, but it does not significantly improve emulsification stability. The required treatment process is an ultrasonic power of 300W and a time of 15 minutes, showing a significant difference in treatment power and time. Those skilled in the art, when improving the stability of different systems, cannot directly adjust the relevant ultrasonic process parameters due to the system characteristics (including molecular structure, charge properties, etc.) and sensitivity, making it difficult to determine the process conditions to achieve the corresponding improvement effect. Therefore, the currently disclosed methods for enhancing the stability of composite gels cannot be simply applied to the room-temperature fermented milk-sodium alginate complex system to improve the storage stability of room-temperature fermented milk.

[0003] Existing technology CN119498404A discloses a method for preparing room-temperature yogurt, which employs ultrasonic treatment combined with a stabilizer to improve the shelf-life stability of the yogurt. However, this method involves ultrasonic treatment after fermentation and demulsification. A more advanced method combines dual-frequency ultrasonic treatment with ultra-high pressure treatment, and applies ultrasonic treatment during the second fermentation stage between the first and third stages of fermentation. This would significantly improve the stringiness of the yogurt while maintaining a low bacterial count or even sterility, allowing for room-temperature storage and good stringiness. However, this ultrasonic treatment, occurring after fermentation, cannot address the structural stability and dispersibility issues of current stabilizers, especially sodium alginate, during fermentation. Summary of the Invention

[0004] This invention addresses the deficiency and inadequacy of current food compound systems, which lack an effective method to improve the gel stability and dispersibility of sodium alginate compound systems during room temperature fermentation. It provides a method for synergistically improving the stability of fermented milk using ultrasound and polysaccharides. Through a specific fermented milk preparation process, a mixture of raw milk and sodium alginate is ultrasonically treated before fermentation to obtain a fermentation base. This significantly improves the water-holding capacity and viscosity of the fermented milk, while maintaining a small and uniform protein particle size, thus endowing the fermented milk with excellent room temperature storage stability.

[0005] Another object of the present invention is to provide a fermented milk.

[0006] In a first aspect, the present invention provides a method for synergistically improving the stability of fermented milk using ultrasound and polysaccharides, comprising the following steps:

[0007] The mixture of homogenized and sterilized raw milk and sodium alginate is ultrasonically treated to obtain the fermentation substrate. The ultrasonic treatment conditions are: ultrasonic power of 144~240W, frequency of 20~40kHz, and treatment time of 4~10min.

[0008] According to the method for improving the stability of fermented milk by ultrasound-polysaccharide synergy provided by the present invention, preferably, the ultrasound treatment conditions are: ultrasound treatment power of 168~216W, frequency of 25~35kHz, and treatment time of 6~8min.

[0009] According to the method for improving the stability of fermented milk by ultrasound-polysaccharide synergy provided by the present invention, preferably, the total protein content in the mixture of raw milk and sodium alginate is 2.8~3.5g / 100g, wherein the mass ratio of whey protein to casein is 0.25~0.4:1; and the mass ratio of total fat content to total protein content is 1.2~1.8:1.

[0010] According to the method for improving the stability of fermented milk by ultrasound-polysaccharide synergy provided by the present invention, preferably, the sodium alginate content in the mixture of raw milk and sodium alginate is 0.15~0.25wt%.

[0011] In the method for improving the stability of fermented milk by ultrasound-polysaccharide synergy provided by the present invention, preferably, the homogenization pressure is 13~22 MPa.

[0012] The method for improving the stability of fermented milk by ultrasound-polysaccharide synergy according to the present invention preferably further includes the following steps: inoculating the fermentation base with a fermentation agent for fermentation, demulsification, and sterilization to obtain fermented milk, wherein the fermentation agent is a compound agent containing fermentation bacteria and slime-producing bacteria.

[0013] According to the method for synergistic improvement of fermented milk stability by ultrasound and polysaccharides provided by the present invention, preferably, the concentration of the compound microbial agent is 10. 6 ~10 9 CFU / g, inoculum amount is 0.1~0.5g / L fermentation substrate.

[0014] According to the method for improving the stability of fermented milk by ultrasound-polysaccharide synergy provided by the present invention, preferably, the fermentation bacteria are selected from one or more of Lactobacillus bulgaricus, Streptococcus thermophilus, Lactobacillus acidophilus, Bifidobacterium lactis, and Bifidobacterium longum; the slime-producing bacteria are selected from two or more of Lactobacillus bulgaricus 5L6, Lactobacillus bulgaricus OLL1073R-1, Lactobacillus reuteri CCFM1175, Lactobacillus paracasei F-19, Lactococcus lactis LL O224, Lactobacillus helveticus BCRC14030, and Lactobacillus casei O1.

[0015] According to the method for improving the stability of fermented milk by ultrasound-polysaccharide synergy provided by the present invention, preferably, the fermentation temperature is 37~43℃; and the fermentation endpoint pH is 4.3~4.6.

[0016] Secondly, the present invention also provides a method for preparing fermented milk by synergistic improvement of the stability of fermented milk using ultrasound and polysaccharides.

[0017] According to the present invention, the fermented milk preferably has a water-holding capacity of 64-67%, a viscosity of 460-530 mPa·s, and an average protein particle size of 1700-2000 nm.

[0018] Beneficial effects:

[0019] This invention provides a method for improving the stability of fermented milk through ultrasound-polysaccharide synergy. Sodium alginate is added to the raw milk, and the stability of fermented milk is improved through ultrasound-polysaccharide synergy. While breaking the long chains of sodium alginate, ultrasound specifically activates casein binding sites, efficiently inducing the formation of "egg carton structure", thereby constructing a denser and more stable three-dimensional network gel structure, improving the product quality and storage stability of fermented milk. Attached Figure Description

[0020] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0021] Figure 1 Laser confocal micrographs of fermented milk from Example 1 and Comparative Examples 1-3.

[0022] Figure 2 Scanning electron microscope images of the fermented milk from Example 1 and Comparative Examples 1-3. Detailed Implementation

[0023] The following examples are for illustrative purposes only and are not intended to limit the scope of the invention. Where specific techniques or conditions are not specified in the examples, they should be performed according to the techniques or conditions described in the literature in this field, or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased from legitimate channels.

[0024] In the embodiments and comparative examples of this invention, the fermentation agent used is a compound agent, comprising fermenting bacteria and slime-producing bacteria, wherein the fermenting bacteria are Lactobacillus bulgaricus and Streptococcus thermophilus (1:1), and the slime-producing bacteria is Lactococcus lactis LLO224. The compound strain is derived from Chr. Hansen.

[0025] The fermentation bacteria (Lactobacillus bulgaricus and Streptococcus thermophilus 1:1) were derived from Chr. Hansen.

[0026] The fermented milk mentioned in this invention is room temperature fermented milk.

[0027] In a specific embodiment, the present invention provides a method for synergistically improving the stability of fermented milk using ultrasound and polysaccharides, comprising the following steps:

[0028] The mixture of homogenized and sterilized raw milk and sodium alginate is ultrasonically treated to obtain the fermentation substrate. The ultrasonic treatment conditions are: ultrasonic power of 144~240W, frequency of 20~40kHz, and treatment time of 4~10min.

[0029] It should be noted that:

[0030] Adding polysaccharides (sodium alginate) to fermented milk can improve its stability. This invention further enhances the stability of fermented milk by using specific ultrasonic treatment to synergistically enhance the stability of fermented milk by forming an ultrasonic-polysaccharide treatment system.

[0031] The method for synergistically improving the stability of fermented milk using ultrasound and polysaccharides provided in this invention targets the synergistic improvement of a specific food composite system, namely, the storage stability of a mixture of raw milk and sodium alginate. Because this composite system differs from existing food composite systems, its ultrasound synergistic treatment process is also completely different and cannot be simply adjusted by referring to existing food composite systems. In the composite system of this invention, appropriate ultrasound treatment before fermentation synchronously regulates the structure and interaction between milk proteins and sodium alginate through cavitation effects. On the one hand, it promotes the depolymerization of casein micelles and the unfolding of whey protein structures, exposing more active groups; on the other hand, it degrades the sodium alginate molecular chains, increasing its G-block ratio and interaction with Ca... 2+ The ability to combine.

[0032] In this process, the refined casein can assemble into a denser gel network framework; low molecular weight sodium alginate, through its carboxyl group (-COO) - ) and the amino group (-NH3) of casein + Electrostatic bridging occurs, filling the pores of the gel network framework; and the sodium alginate G block and Ca... 2+ The formed ionic cross-linked network, together with the covalent network constructed by unfolded whey protein and κ-casein through disulfide bonds, spatially interpenetrates within the casein micelles, jointly enhancing the compactness and mechanical properties of the gel structure, thereby improving the stability of fermented milk. It is important to note that excessively low or high ultrasonic intensity will prevent the achievement of the aforementioned multi-dimensional synergistic effect; therefore, precise control of processing parameters is necessary to achieve the optimal stability enhancement. Considering the specific characteristics of the composite system and the particularity of the stability effect, this application ultimately determined the ultrasonic processing power to be 144–240 W, the frequency range to be 20–40 kHz, and the processing time to be 4–10 min.

[0033] Under the specific ultrasonic treatment conditions of this invention, ultrasonic treatment can break the sodium alginate molecular chains and refine casein, promoting the formation of a denser and more uniform gel network during subsequent fermentation, thereby significantly improving the water-holding capacity and viscosity of the fermented milk. Simultaneously, ultrasonic treatment promotes uniform dispersion of sodium alginate by breaking its molecular chains and forms a dense protective layer on the protein surface during fermentation, inhibiting particle aggregation and achieving the smallest and most uniform protein particle size, further significantly improving the storage stability of low-temperature fermented milk.

[0034] The ultrasound-polysaccharide synergistic gel strengthening mechanism of this invention differs from existing methods that add composite stabilizers. It combines the ultrasonic cavitation effect with sodium alginate stabilizer. While breaking the long chains of sodium alginate, ultrasound specifically activates casein binding sites, efficiently inducing the formation of an "egg carton structure," thereby constructing a denser and more stable three-dimensional network gel structure and improving the product quality and storage stability of fermented milk.

[0035] “Egg box structure”: A porous three-dimensional structure with regular holes or concave and convex units, similar to an egg box.

[0036] Furthermore, this invention uses ultrasonic processing technology, employing ultrasonic equipment to process fermented milk, resulting in a simple, efficient, and easily controllable process.

[0037] In some specific embodiments, for example, the ultrasonic processing power mentioned in this invention can be a point value or any range of values, such as 144W, 148W, 150W, 152W, 155W, 158W, 160W, 162W, 165W, 168W, 170W, 175W, 178W, 180W, 182W, 185W, 190W, 192W, 195W, 198W, 200W, 205W, 208W, 210W, 212W, 216W, 220W, 225W, 228W, 230W, 232W, 235W, 238W, 240W. For example, the lower limit of the ultrasonic processing frequency range mentioned in this invention can be a value such as 20kHz, 21kHz, 22kHz, 23kHz, 24kHz, 25kHz, etc., and the upper limit of the ultrasonic processing frequency range can be a value such as 33kHz, 34kHz, 35kHz, 36kHz, 37kHz, 38kHz, 39kHz, 40kHz, etc. For example, the ultrasonic processing time mentioned in this invention can be a value such as 4min, 5min, 6min, 7min, 8min, 9min, 10min, etc., or any range of values.

[0038] In some specific implementations, in order to achieve better stability control, the preferred control conditions for ultrasonic processing are: ultrasonic processing power of 168~216W, frequency of 25~35kHz, and processing time of 6~8min.

[0039] In the method for synergistic improvement of fermented milk stability by ultrasound-polysaccharide mentioned in this invention, the synergistic gel strengthening effect of ultrasound-polysaccharide varies significantly for different mixtures (composite systems) of raw milk and sodium alginate. Adjustment of other components in the system can further optimize the overall stability effect. In some specific embodiments, it is preferable to control the total protein content in the mixture of raw milk and sodium alginate to 2.8~3.5g / 100g through raw milk standardization treatment, wherein the mass ratio of whey protein to casein is 0.25~0.4:1; and the mass ratio of total fat content to total protein content is 1.2~1.8:1.

[0040] In some specific embodiments, for example, the total protein content in the mixture of raw milk and sodium alginate can be controlled to be a point value or any range of 2.8g / 100g, 2.9g / 100g, 3.0g / 100g, 3.1g / 100g, 3.2g / 100g, 3.3g / 100g, 3.4g / 100g, or 3.5g / 100g; wherein the mass ratio of whey protein to casein can be a point value or any range of 0.25:1, 0.30:1, 0.35:1, or 0.40:1; and the mass ratio of total fat content to total protein content can be a point value or any range of 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, or 1.8:1.

[0041] In some specific embodiments, the total fat content can be further selected as 3.7g and the total protein content as 3.0g.

[0042] The mass ratio of whey protein to casein in the milk base affects the texture of fermented yogurt. When the mass ratio is below 0.25:1, the resulting gel structure is relatively hard and dense, making whey precipitation more likely. Appropriately increasing the whey protein ratio can improve the yogurt texture, making the gel network finer and softer, and enhancing water retention. When the ratio exceeds 0.4:1, excessive whey protein hinders casein cross-linking, leading to a fragile gel structure and reduced stability. Therefore, this invention preferably controls the mass ratio of whey protein to casein to be 0.25~0.4:1.

[0043] In some specific embodiments, the sodium alginate content in the mixture of raw milk and sodium alginate mentioned in this invention is 0.15~0.25wt%, for example, it can be a point value of 0.15wt%, 0.18wt%, 0.20wt%, 0.23wt%, 0.25wt%, or any range of values.

[0044] The sodium alginate content mentioned in this invention is calculated based on the quality of the raw milk.

[0045] In some specific embodiments, in order to achieve sufficient homogenization of raw milk and sodium alginate, the homogenization and sterilization treatment pressure mentioned in this invention is 13~22MPa, for example, it can be 13MPa, 14MPa, 15MPa, 16MPa, 17MPa, 18MPa, 19MPa, 20MPa, 21MPa, 22MPa, etc. or any range of values.

[0046] In some specific implementations, the method for synergistic improvement of fermented milk stability by ultrasound and polysaccharides mentioned in this invention also includes some conventional room-temperature fermented milk preparation steps, which can be flexibly adjusted and adapted according to actual production needs. The specific processing technology of each step can also be adjusted with reference to conventional processes, for example, including the following steps:

[0047] Fermented milk is obtained by inoculating the fermentation substrate with a fermentation agent, fermenting, breaking the emulsion, and sterilizing. The fermentation agent is a compound agent, which includes a fermenting agent and slime-producing bacteria.

[0048] In some specific implementations, the concentration of the compound microbial agent mentioned in this invention is 10. 6 ~10 9 CFU / g, inoculum size is 0.1~0.5g / L fermentation substrate. For example, the concentration of compound microbial agent can be 10. 6 CFU / g, 10 7 CFU / g, 10 8 CFU / g, 10 9 CFU / g, etc., and the inoculation amount can be, for example, 0.1g / L fermentation substrate, 0.2g / L fermentation substrate, 0.3g / L fermentation substrate, 0.4g / L fermentation substrate, 0.5g / L fermentation substrate, etc.

[0049] The compound microbial agent mentioned in this invention comprises fermenting bacteria and slime-producing bacteria. The fermenting bacteria are selected from one or more of *Lactobacillus bulgaricus*, *Streptococcus thermophilus*, *Lactobacillus acidophilus*, *Bifidobacterium lactis*, and *Bifidobacterium longum*. The slime-producing bacteria are selected from two or more of *Lactobacillus bulgaricus* 5L6, *Lactobacillus bulgaricus* OLL1073R-1, *Lactobacillus reuteri* CCFM1175, *Lactobacillus paracasei* F-19, *Lactococcus lactis* LLO224, *Lactobacillus helveticus* BCRC14030, and *Lactobacillus casei* O1.

[0050] In some specific implementations, the fermentation temperature mentioned in this invention is 37~43℃, and the final fermentation pH is 4.3~4.6. The fermentation time required by this invention is 4.5~5 hours. Specific fermentation conditions, for example, can be 42℃ for 5 hours.

[0051] In some specific embodiments, the present invention may also provide an exemplary method for synergistic improvement of fermented milk stability by ultrasound and polysaccharides, which includes the following steps:

[0052] Step 1: Inspect the raw milk and cool and store the raw milk that has passed the inspection (conforming to the GB19301-2010 National Food Safety Standard for Raw Milk).

[0053] Step 2: Purify the qualified raw milk to remove impurities;

[0054] Step 3: Standardize the purified raw milk. The specific operation of the standardization process is to test and adjust the fat and non-fat solids content of the raw milk to the standard value.

[0055] Step 4: Preheat the standardized raw milk and feed it to the mixing machine, adding sodium alginate (or conventional ingredients, such as pectin, carrageenan, glyceryl monostearate, etc.).

[0056] Step 5: Homogenize the materials from Step 4;

[0057] Step Six: Sterilize the material homogenized in Step Five. This sterilization is the first sterilization. The sterilization is carried out using ultra-high temperature sterilization. The treatment conditions are: temperature 121~133℃.

[0058] Step 7: Cool the material after sterilization in Step 6;

[0059] Step 8: The material cooled in Step 7 is subjected to ultrasonic treatment to obtain the fermentation substrate;

[0060] Step 9: Inoculate the fermentation substrate after ultrasonic treatment in Step 8 with fermentation bacteria;

[0061] Step 10: Transfer the inoculated liquid from Step 9 to the fermentation tank for fermentation;

[0062] Step 11: Demulsify the fermented milk after fermentation is complete;

[0063] Step 12: Perform a second sterilization treatment on the fermented milk after demulsification in Step 11. This sterilization is a second sterilization, which is pasteurization. The treatment conditions are: temperature 70-80℃.

[0064] Step 13: Cool and bottle the fermented milk after secondary sterilization.

[0065] Furthermore, the fermentation temperature is 42–43℃, and the time is 4.5–5 hours.

[0066] In a specific implementation, the present invention also provides a method for preparing fermented milk based on the synergistic improvement of fermented milk stability by ultrasound and polysaccharides.

[0067] The fermented milk prepared by this invention has excellent storage stability. In some specific embodiments, the water holding capacity of the fermented milk is 64-67%, the viscosity is 460-530 mPa·s, and the average protein particle size is 1700-2000 nm.

[0068] Example 1

[0069] A method for synergistically improving the stability of fermented milk using ultrasound and polysaccharides includes the following steps:

[0070] (1) The standardized raw milk (total fat content of 3.7g, total protein content of 3.0g, and whey protein to casein content of 0.3:1) was preheated to 50°C, 0.2wt% sodium alginate was added, stirred and dissolved until homogeneous, homogenized at 18MPa and then sterilized for the first time at 121°C. The sterilized material was then cooled to 42°C (fermentation temperature).

[0071] (2) The cooled material was subjected to ultrasonic treatment to obtain fermentation substrate. The parameters were set as follows: frequency 28kHz, power 192W, time 8min.

[0072] (3) Inoculate the fermentation substrate with 0.1 g / L of compound microbial agent (on the order of magnitude of approximately 10). 8 ~10 9 Fermentation was carried out at 42℃ (CFU / g) with the pH value dropping to 4.5 as the fermentation endpoint.

[0073] (4) The fermented milk after fermentation is broken down and then sterilized a second time. The sterilization conditions are: 75℃, 25s. The fermented milk after the second sterilization is cooled and bottled.

[0074] Example 2

[0075] A method for synergistically improving the stability of fermented milk using ultrasound and polysaccharides includes the following steps:

[0076] (1) The standardized raw milk (total fat content of 3.7g, total protein content of 3.0g, and whey protein to casein content of 0.25:1) was preheated to 50°C, 0.2wt% sodium alginate was added, stirred and dissolved until homogeneous, homogenized at 20MPa and then sterilized for the first time at 125°C. The sterilized material was then cooled to 42°C.

[0077] (2) The cooled material was subjected to ultrasonic treatment to obtain fermentation substrate. The parameters were set as follows: frequency 25kHz, power 168W, time 6min.

[0078] (3) Inoculate the fermentation substrate with 0.1 g / L of compound microbial agent (on the order of magnitude of approximately 10). 8~10 9 Fermentation was carried out at 42℃ (CFU / g) with the pH value dropping to 4.5 as the fermentation endpoint.

[0079] (4) The fermented milk after fermentation is broken and then sterilized twice. The sterilization conditions are: 75℃, 25s. After the second sterilization, the fermented milk is cooled and bottled.

[0080] Example 3

[0081] A method for synergistically improving the stability of fermented milk using ultrasound and polysaccharides includes the following steps:

[0082] (1) The standardized raw milk (total fat content of 3.7g, total protein content of 3.0g, and whey protein to casein content of 0.35:1) was preheated to 50°C, 0.2wt% sodium alginate was added, stirred and dissolved until homogeneous, homogenized at 18MPa and then sterilized for the first time at 130°C. The sterilized material was then cooled to 42°C.

[0083] (2) The cooled material was subjected to ultrasonic treatment to obtain fermentation substrate. The parameters were set as follows: frequency 35kHz, power 216W, time 8min.

[0084] (3) Inoculate the fermentation substrate with 0.1 g / L of compound microbial agent (on the order of magnitude of approximately 10). 8 ~10 9 Fermentation was carried out at 42℃ (CFU / g) with the pH value dropping to 4.5 as the fermentation endpoint.

[0085] (4) The fermented milk after fermentation is broken and then sterilized twice. The sterilization conditions are: 75℃, 25s. After the second sterilization, the fermented milk is cooled and bottled.

[0086] Example 4

[0087] A method for synergistically improving the stability of fermented milk using ultrasound and polysaccharides includes the following steps:

[0088] (1) The standardized raw milk (total fat content of 3.7g, total protein content of 3.0g, of which the mass ratio of whey protein to casein content is 0.4:1) was preheated to 50°C, 0.30wt% sodium alginate was added, stirred and dissolved until homogeneous, and then homogenized at 18MPa before the first sterilization treatment was carried out at 121°C. The sterilized material was then cooled to 50°C.

[0089] (2) The cooled material was subjected to ultrasonic treatment to obtain fermentation substrate. The parameters were set as follows: frequency 28kHz, power 192W, time 8min.

[0090] (3) Inoculate the fermentation substrate with 0.1 g / L of compound microbial agent (on the order of magnitude of approximately 10). 8 ~10 9 Fermentation was carried out at 42℃ (CFU / g) with the pH value dropping to 4.5 as the fermentation endpoint.

[0091] (4) The fermented milk after fermentation is broken down and then sterilized a second time. The sterilization conditions are: 75℃, 25s. The fermented milk after the second sterilization is cooled and bottled.

[0092] Example 5

[0093] A method for synergistically improving the stability of fermented milk using ultrasound and polysaccharides includes the following steps:

[0094] (1) The standardized raw milk (total fat content of 3.7g, total protein content of 3.0g, of which the mass ratio of whey protein to casein is 0.3:1) was preheated to 50°C, 0.2wt% sodium alginate was added, stirred and dissolved until homogeneous, and then homogenized at 18MPa before the first sterilization treatment was carried out at 121°C. The sterilized material was then cooled to 42°C.

[0095] (2) The cooled material was subjected to ultrasonic treatment to obtain fermentation substrate. The parameters were set as follows: frequency 20kHz, power 240W, time 10min.

[0096] (3) Inoculate the fermentation substrate with 0.1 g / L of compound microbial agent (on the order of magnitude of approximately 10). 8 ~10 9 Fermentation was carried out at 42℃ (CFU / g) with the pH value dropping to 4.5 as the fermentation endpoint.

[0097] (4) The fermented milk after fermentation is broken and then sterilized twice. The sterilization conditions are: 75℃, 25s. After the second sterilization, the fermented milk is cooled and bottled.

[0098] Example 6

[0099] A method for synergistically improving the stability of fermented milk using ultrasound and polysaccharides includes the following steps:

[0100] (1) The standardized raw milk (total fat content of 3.7g, total protein content of 3.0g, and whey protein to casein content of 0.3:1) was preheated to 50°C, 0.2wt% sodium alginate was added, stirred and dissolved until homogeneous, homogenized at 18MPa and then sterilized for the first time at 130°C. The sterilized material was then cooled to 42°C.

[0101] (2) The cooled material was subjected to ultrasonic treatment to obtain fermentation substrate. The parameters were set as follows: frequency 40kHz, power 144W, time 4min.

[0102] (3) Inoculate the fermentation substrate with 0.1 g / L of compound microbial agent (on the order of magnitude of approximately 10). 8 ~10 9 Fermentation was carried out at 42℃ (CFU / g) with the pH value dropping to 4.5 as the fermentation endpoint.

[0103] (4) The fermented milk after fermentation is broken down and then sterilized a second time. The sterilization conditions are: 75℃, 25s. The fermented milk after the second sterilization is cooled and bottled.

[0104] Example 7

[0105] A method for synergistically improving the stability of fermented milk using ultrasound and polysaccharides includes the following steps:

[0106] (1) Preheat the raw milk (fat content of 4.0g and protein content of 3.0g) to 50°C, add 0.2wt% sodium alginate, stir to dissolve until homogeneous, perform homogenization treatment at 18MPa and then perform the first sterilization treatment at 80°C for 10min. After sterilization, cool the material to 42°C.

[0107] (2) The cooled material was subjected to ultrasonic treatment to obtain fermentation substrate. The parameters were set as follows: frequency 28kHz, power 192W, time 8min.

[0108] (3) Inoculate the fermentation substrate with 0.1 g / L of compound microbial agent (on the order of magnitude of approximately 10). 8 ~10 9 Fermentation was carried out at 42℃ (CFU / g) with the pH value dropping to 4.5 as the fermentation endpoint.

[0109] (4) The fermented milk after fermentation is broken down and then sterilized a second time. The sterilization conditions are: 75℃, 25s. The fermented milk after the second sterilization is cooled and bottled.

[0110] Example 8

[0111] A method for synergistically improving the stability of fermented milk using ultrasound and polysaccharides includes the following steps:

[0112] (1) The standardized raw milk (total fat content of 3.7g, total protein content of 3.0g, and whey protein to casein content of 0.25:1) was preheated to 50°C, 0.2wt% sodium alginate was added, stirred and dissolved until homogeneous, homogenized at 18MPa and then sterilized for the first time at 121°C. The sterilized material was then cooled to 42°C.

[0113] (2) The cooled material was subjected to ultrasonic treatment to obtain fermentation substrate. The parameters were set as follows: frequency 28kHz, power 192W, time 8min.

[0114] (3) Inoculate the fermentation substrate with 0.1 g / L of fermentation bacteria (Lactobacillus bulgaricus and Streptococcus thermophilus 1:1, on the order of magnitude of approximately 10). 8 ~10 9 Fermentation was carried out at 42℃ (CFU / g) with the pH value dropping to 4.5 as the fermentation endpoint.

[0115] (4) The fermented milk after fermentation is broken down and then sterilized a second time. The sterilization conditions are: 75℃, 25s. The fermented milk after the second sterilization is cooled and bottled.

[0116] Comparative Example 1

[0117] A method for preparing fermented milk includes the following steps:

[0118] (1) The standardized raw milk (total fat content of 3.7g, total protein content of 3.0g, and whey protein to casein content of 0.3:1) was preheated to 50°C, homogenized at 18MPa and then sterilized for the first time at 121°C. The sterilized material was then cooled to 42°C.

[0119] (2) Inoculate the cooled material with 0.1 g / L compound microbial agent (on the order of magnitude of approximately 10). 8 ~10 9 Fermentation was carried out at 42℃ (CFU / g) with the pH value dropping to 4.5 as the fermentation endpoint.

[0120] (3) The fermented milk after fermentation is broken down and then sterilized a second time. The sterilization conditions are: 75℃, 25s. The fermented milk after the second sterilization is cooled and bottled.

[0121] The difference between Comparative Example 1 and Example 1 is that sodium alginate was not added and ultrasonic treatment was not performed.

[0122] Comparative Example 2

[0123] A method for preparing fermented milk includes the following steps:

[0124] (1) The standardized raw milk (total fat content of 3.7g, total protein content of 3.0g, and whey protein to casein content of 0.3:1) was preheated to 50°C, homogenized at 18MPa and then sterilized for the first time at 121°C. The sterilized material was then cooled to 42°C.

[0125] (2) The cooled material was subjected to ultrasonic treatment to obtain fermentation substrate. The parameters were set as follows: frequency 28kHz, power 192W, time 8min.

[0126] (3) Inoculate the fermentation substrate with 0.1 g / L of compound microbial agent (on the order of magnitude of approximately 10). 8 ~10 9 Fermentation was carried out at 42℃ (CFU / g) with the pH value dropping to 4.5 as the fermentation endpoint.

[0127] (4) The fermented milk after fermentation is broken down and then sterilized a second time. The sterilization conditions are: 75℃, 25s. The fermented milk after the second sterilization is cooled and bottled.

[0128] The difference between Comparative Example 2 and Example 1 is that sodium alginate is not added.

[0129] Comparative Example 3

[0130] A method for preparing fermented milk includes the following steps:

[0131] (1) The standardized raw milk (total fat content of 3.7g, total protein content of 3.0g, and whey protein to casein content of 0.25:1) was preheated to 50°C, 0.02wt% sodium alginate was added, stirred and dissolved until homogeneous, homogenized at 18MPa and then sterilized for the first time at 121°C. The sterilized material was then cooled to 42°C.

[0132] (2) Inoculate the cooled material with 0.1 g / L compound microbial agent (on the order of magnitude of approximately 10). 8 ~10 9 Fermentation was carried out at 42℃ (CFU / g) with the pH value dropping to 4.5 as the fermentation endpoint.

[0133] (3) The fermented milk after fermentation is broken down and then sterilized a second time. The sterilization conditions are: 75℃, 25s. The fermented milk after the second sterilization is cooled and bottled.

[0134] The difference between Comparative Example 3 and Example 1 is that ultrasonic treatment is not performed.

[0135] Comparative Example 4

[0136] A method for preparing fermented milk includes the following steps:

[0137] (1) The standardized raw milk (total fat content of 3.7g, total protein content of 3.0g, of which the mass ratio of whey protein to casein is 0.3:1) was preheated to 50°C, 0.02wt% sodium alginate was added, stirred and dissolved until homogeneous, and then homogenized at 18MPa before the first sterilization treatment was carried out at 121°C. The sterilized material was then cooled to 42°C.

[0138] (2) The cooled material was subjected to ultrasonic treatment to obtain fermentation substrate. The parameters were set as follows: frequency 45kHz, power 120W, time 4min.

[0139] (3) Inoculate the fermentation substrate with 0.1 g / L of compound microbial agent (on the order of magnitude of approximately 10). 8 ~10 9 Fermentation was carried out at 42℃ (CFU / g) with the pH value dropping to 4.5 as the fermentation endpoint.

[0140] (4) The fermented milk after fermentation is broken down and then sterilized a second time. The sterilization conditions are: 75℃, 25s. The fermented milk after the second sterilization is cooled and bottled.

[0141] Comparative Example 5

[0142] A method for preparing fermented milk includes the following steps:

[0143] (1) The standardized raw milk (total fat content of 3.7g, total protein content of 3.0g, of which the mass ratio of whey protein to casein content is 0.3:1) was preheated to 50°C, 0.02wt% sodium alginate was added, stirred and dissolved until homogeneous, and then homogenized at 18MPa before the first sterilization treatment was carried out at 125°C. The sterilized material was then cooled to 42°C.

[0144] (2) The cooled material was subjected to ultrasonic treatment to obtain fermentation substrate. The parameters were set as follows: frequency 15kHz, power 250W, time 10min.

[0145] (3) Inoculate the fermentation substrate with 0.1 g / L of compound microbial agent (on the order of magnitude of approximately 10). 8 ~10 9 Fermentation was carried out at 42℃ (CFU / g) with the pH value dropping to 4.5 as the fermentation endpoint.

[0146] (4) The fermented milk after fermentation is broken down and then sterilized a second time. The sterilization conditions are: 75℃, 25s. The fermented milk after the second sterilization is cooled and bottled.

[0147] Comparative Example 6

[0148] A method for synergistically improving the stability of fermented milk using ultrasound and polysaccharides includes the following steps:

[0149] (1) The standardized raw milk (total fat content of 3.7g, total protein content of 3.0g, of which the mass ratio of whey protein to casein content is 0.25:1) was preheated to 50°C, 0.02wt% sodium alginate was added, stirred and dissolved until homogeneous, and then homogenized at 18MPa before the first sterilization treatment was carried out at 125°C. The sterilized material was then cooled to 42°C.

[0150] (2) Inoculate the cooled material with 0.1 g / L compound microbial agent (on the order of magnitude of approximately 10). 8 ~10 9 The mixture (CFU / g) was fermented at 42℃ with a pH of 4.5 as the fermentation endpoint. After fermentation, it was subjected to ultrasonic treatment with the following parameters: frequency 28kHz, power 192W, and time 8min.

[0151] (3) The fermented milk after fermentation is broken down and then sterilized a second time. The sterilization conditions are: 75℃, 25s. The fermented milk after the second sterilization is cooled and bottled.

[0152] Result detection

[0153] The performance of the fermented milk in the examples and comparative examples was tested, and the testing items and methods are as follows:

[0154] Water-holding capacity test: Weigh 30g of sample into a centrifuge tube and centrifuge at 4℃ and 4000rpm for 20min. Discard the supernatant and weigh the precipitate. Water-holding capacity WHC (%) = (precipitate weight / sample weight) × 100;

[0155] Viscosity testing: A 40mm flat plate clamp was used to perform flow scanning at 25℃ within a shear rate range of 0.1~100s⁻¹, and the apparent viscosity was measured using a rotational rheometer.

[0156] Protein particle size determination: The particle size was determined using a laser particle size analyzer, and the sample was diluted 100 times with deionized water.

[0157] pH measurement: Measured using a pH meter at room temperature (25°C);

[0158] Acidity test: The acidity was determined by titration according to the method specified in the national standard GB5009.239-2016 "Determination of Acidity in Food".

[0159] The specific test results are shown in Tables 1 and 2 below.

[0160] Table 1

[0161]

[0162] Table 2

[0163]

[0164] Combining the data in Tables 1 and 2, it can be seen that the water-holding capacity of Comparative Example 1 was 52.05%, Comparative Example 2 increased to 56.20% (an increase of 4.15%), Comparative Example 3 increased to 60.72% (an increase of 8.67%), while Example 1 reached 66.83% (an increase of 14.78%). The increase in Example 1 (14.78%) significantly exceeded the sum of the increases in Comparative Examples 2 and 3 (12.82%), and the viscosity change trend was consistent with the water-holding capacity, confirming that there is a synergistic effect between ultrasound and sodium alginate, and this effect is not a simple additive one. Further protein particle size analysis showed that the particle size of Example 1 was significantly lower than that of Comparative Example 3, indicating that ultrasound treatment, by breaking the sodium alginate molecular chains and refining casein, promoted the formation of a denser and more uniform gel network during fermentation.

[0165] Figure 1 The images show the results of laser confocal microscopy observations of Examples 1 and Comparative Examples 1-3. The white areas indicate the distribution of Rhodamine B-stained proteins in the yogurt (due to patent drawing specifications, the original red fluorescence is presented in white here). All samples exhibited discontinuous protein structures. Comparative Example 2 showed significantly finer and more uniformly distributed protein particles compared to Comparative Example 1, while Comparative Example 3 showed increased particle size due to flocculation induced by the long molecular chains of sodium alginate bridging and adsorbing milk protein particles. Ultrasonic treatment broke down the sodium alginate molecular chains, promoting uniform dispersion and forming a dense protective layer on the protein surface during fermentation, inhibiting particle aggregation and resulting in the smallest and most uniform protein particle size (consistent with the particle size data). Scanning electron microscopy images (…) Figure 2 Further evidence shows that: Comparative Example 1 has a loose gel network with uneven pore size distribution; Comparative Example 2 is refined by ultrasound to form a uniform small pore network; Comparative Example 3 has a smooth network surface due to the filling effect of sodium alginate; while Example 1 forms a dense gel structure with the smallest pores and the most uniform distribution through the synergistic effect of ultrasound and sodium alginate, while giving the product the best water retention and smooth texture.

[0166] The fermented milk samples from each example and comparative example were stored at 25°C for 180 days, and their relevant properties were monitored. The specific results are shown in Table 3.

[0167] Table 3

[0168]

[0169] As shown in Table 3, the pH and titratable acidity of fermented milk did not change significantly after 180 days of storage at 25°C. This is mainly because fermented milk, unlike low-temperature live-culture yogurt, undergoes a second pasteurization process, which eliminates live lactic acid bacteria, thus maintaining relatively stable pH and acidity. However, the water-holding capacity of fermented milk showed a decreasing trend. At the storage endpoint, the water-holding capacity of Examples 1, 1, 2, and 3 decreased by 4.49%, 5.74%, 5.62%, and 5.30% respectively compared to day 0. Among them, Examples 1 and 2 showed the smallest decrease in water-holding capacity, indicating that the synergistic effect of ultrasound and sodium alginate can overcome the limitations of single treatment and further improve the storage stability of fermented milk.

[0170] The above effects demonstrate that the ultrasound-polysaccharide synergistic gel strengthening mechanism provided by this invention differs from existing methods that add composite stabilizers. While breaking the long chains of sodium alginate, ultrasound specifically activates casein binding sites, efficiently inducing the formation of an "egg carton structure," thereby constructing a denser and more stable three-dimensional network gel structure and improving the product quality and storage stability of fermented milk.

[0171] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for synergistically improving the stability of a fermented milk by ultrasound and polysaccharides, characterized in that, The method comprises the following steps: The mixture of the homogenized and sterilized raw milk and sodium alginate is subjected to ultrasonic treatment to obtain fermentation base, wherein the ultrasonic treatment conditions are as follows: the ultrasonic treatment power is 144-240 W, the frequency is 20-40 kHz, and the treatment time is 4-10 min. The content of sodium alginate in the mixture of the raw milk and sodium alginate is 0.15-0.25 wt%. The mass ratio of the content of whey protein to the content of casein in the raw milk is 0.25-0.4:

1. The fermentation base is inoculated with a fermentation agent to be fermented, demulsified and sterilized to obtain fermented milk, wherein the viscosity of the fermented milk is 460-530 mPa·s, and the average protein particle size is 1700-2000 nm.

2. The method of claim 1, wherein the ultrasonic treatment is performed at a frequency of 20 kHz to 100 kHz. The ultrasonic treatment conditions are as follows: the ultrasonic treatment power is 168-216 W, the frequency is 25-35 kHz, and the treatment time is 6-8 min.

3. The method of claim 1, wherein the ultrasonic treatment is performed at a frequency of 20 kHz to 100 kHz. The total protein content in the mixture of the raw milk and sodium alginate is 2.8-3.5 g / 100 g; and the mass ratio of the total fat content to the total protein content is 1.2-1.8:

1.

4. The method for improving the stability of fermented milk by synergistic effect of ultrasound and polysaccharide according to any one of claims 1 to 3, characterized in that, The homogenization pressure is 13-22 MPa.

5. The method of claim 1 to 3, wherein the method is characterized by, The fermentation agent is a composite microbial agent and comprises fermentation bacteria and sticky bacteria.

6. The method of claim 5, wherein the ultrasonic treatment is performed at a frequency of 20 kHz to 100 kHz. The complex bacterial agent concentration is 10 6 ~10 9 CFU / g, the inoculation amount is 0.1~0.5 g / L fermentation base material.

7. The method of claim 5, wherein the ultrasonic treatment is performed at a frequency of 20 kHz to 100 kHz. The fermentation temperature is 37-43 ℃, and the terminal pH of fermentation is 4.3-4.

6.

8. Fermented milk prepared by the method for improving the stability of fermented milk by ultrasonic treatment and polysaccharide synergistically according to any one of claims 1-7.

9. The fermented milk according to claim 8, characterized in that, The fermented milk has a water holding capacity of 64-67%, a viscosity of 460-530 mPa·s, and an average protein particle size of 1700-2000 nm.

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