Method for improving quality of marinated bean curd through WOW emulsion type controlled-release coagulator

Abstract

The invention discloses a method for improving the quality of marinated bean curd through a WOW emulsion type controlled-release coagulator, and aims to overcome the defects of rough bean curd gel network and poor water binding capacity caused by too fast release of marinating liquid in the prior art. The method comprises the following steps: respectively preparing a composite inner water phase containing bittern tablets and gluconic acid-lactone, an oil phase containing a hydrophobic emulsifier and a structured outer water phase containing water-soluble polysaccharide; shearing and mixing the inner water phase and the oil phase to prepare a primary W / O emulsion, and homogenizing the primary W / O emulsion and the outer water phase to prepare the W / O / W multiple controlled-release coagulator; and finally, adding into hot soybean milk, standing, incubating, squeezing and forming. According to the preparation method disclosed by the invention, physical isolation of the multiphase emulsion and chemical phase change synergy of the double coagulators are utilized, so that the release rate of magnesium ions is effectively delayed, polysaccharide macromolecules directly participate in gel skeleton construction, a compact and uniform three-dimensional interpenetrating network is formed, the water binding capacity of the bean curd is remarkably improved, the dehydration rate is reduced, and the product is endowed with an excellent texture.

Description

Technical Field

[0001] This invention relates to the field of food processing technology, specifically to a method for improving the quality of brine tofu using WOW emulsion-type controlled-release coagulant. Background Technology

[0002] Tofu, as a plant-based protein product, holds an important position in the food industry due to its nutritional value and processing characteristics. Brine tofu is a conventional soy product made by using magnesium chloride-rich brine as a coagulant to denature and cross-link the soybean proteins in soy milk, thereby forming a gel network structure. In the construction of the soybean protein gel, the mixing method between the coagulant and the soy milk system directly determines the physical aggregation behavior of the protein molecules, thus affecting the microstructure of the final product.

[0003] In existing industrial production of tofu using brine, a direct coagulation process is typically employed. This involves adding prepared liquid brine directly to hot soy milk and stirring. Once the liquid coagulant enters the soy milk, its metal cations rapidly diffuse throughout the system. Through electrostatic shielding and ion bridging, these cations neutralize the negative charges on the surface of the soybean proteins, causing the protein molecules to overcome electrostatic repulsion and quickly bind and precipitate. After coagulation, the system is allowed to stand and gel, then mechanically pressed to remove free water, ultimately solidifying into the tofu product.

[0004] However, in existing direct brine coagulation processes, the instantaneous release of metal ions leads to disordered and uncontrollable rapid cross-linking of soybean proteins. This instantaneous, high-intensity ionic cross-linking rate far exceeds the rate of ordered unfolding and recombination of protein molecules, causing localized excessive aggregation of protein molecules before they fully unfold. This results in a coarse gel aggregate network structure with extremely uneven internal pore distribution. Because this gel network structure is loose, it cannot effectively physically retain and spatially confine water within the system, causing the finished tofu to exhibit poor water retention and high dehydration rate, severely restricting the stability and improvement of the macroscopic quality of brine-cured tofu. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for improving the quality of brine tofu using WOW emulsion-type controlled-release coagulant, which solves the problem in existing technologies where the rapid release of magnesium ions during brine tofu production leads to a coarse gel network and poor water retention.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for improving the quality of brine tofu using a W / O / W emulsion-type controlled-release coagulant, comprising the following steps: S1, Preparation of a multiphase system solution: A composite internal aqueous phase, an oil phase, and a structured external aqueous phase are prepared; the composite internal aqueous phase includes deionized water, halogen flakes as the primary coagulant, and gluconic acid as a secondary slow-release coagulant. - Lactone; the oil phase comprises a vegetable oil matrix and a hydrophobic emulsifier combination, wherein the hydrophobic emulsifier combination is selected from one or more of lecithin, mono- and diglycerides, and Span 60; the structured external aqueous phase comprises deionized water, a hydrophilic emulsifier combination, and water-soluble polysaccharides, wherein the hydrophilic emulsifier combination is selected from a combination of mono- and diglycerides and Tween 80. S2, Preparation of primary W / O emulsion: The composite aqueous phase and oil phase are mixed in a set mass ratio, and shear force is applied in a constant temperature water bath environment to disperse the composite aqueous phase in the oil phase. S3, Preparation of W / O / W multi-stage controlled-release coagulant: The primary W / O emulsion and the structured external aqueous phase are mixed in a set volume ratio and homogenized. S4, Preparation of soybean protein base: Select soybeans and distilled water, soak, grind and filter to obtain soy milk, and heat the soy milk to boil to achieve thermal denaturation of soybean protein; S5, Co-gel Assembly: Boiled soy milk is cooled to the set incubation temperature, and a W / O / W multi-stage controlled-release coagulant is added and stirred. The mixture is then kept still for incubation. During incubation, water-soluble polysaccharides interact with soy proteins to establish a network backbone, and gluconic acid-... - The lactone decomposes upon heating to generate protons, which initiates isoelectric point pregelation. This is accompanied by the release of magnesium ions from the demulsification of the multiple emulsion structures, which undergo metal ion crosslinking on the pregelation backbone. S6, Pressing and Molding: The gel network formed by static incubation is broken down and pressed and shaped to obtain brine tofu.

[0007] Furthermore, in the composite aqueous phase, halogenated tablets and gluconic acid- - The mass ratio of lactone is set to 5:1 to 10:1; in the structured aqueous phase, the water-soluble polysaccharide is a soybean complex polysaccharide or a soluble alginate.

[0008] Furthermore, the total hydrophilic-lipophilic balance (LPB) of the hydrophobic emulsifier combination is in the range of 3 to 5; the total LPB of the hydrophilic emulsifier combination is set in the range of 8 to 10. The total LPB of the combination of multiple single emulsifiers follows a weighted average calculation principle, and is the sum of the products of the theoretical LPB of each single emulsifier in the combination system and its mass fraction in the total mass of the combined emulsifier combination.

[0009] Furthermore, when the total hydrophilic-lipophilic balance value of the hydrophobic emulsifier combination is set to 4, the mass ratio of lecithin, mono- and diglycerides to Span 60 is set to 2:1:1; when the total hydrophilic-lipophilic balance value of the hydrophilic emulsifier combination is set to 8, the mass ratio of mono- and diglycerides to Tween 80 is set to 1.95:1.05.

[0010] Furthermore, when preparing the oil phase, the heating temperature must reach above the melting temperature of the hydrophobic emulsifier combination; when preparing the structured external aqueous phase, the heating temperature is set within the range of 90°C to 100°C.

[0011] Furthermore, the mass ratio of the composite internal aqueous phase to the oil phase is set in the range of 1:2 to 2:1, the emulsification temperature is set in the range of 50°C to 70°C, and the rotation speed for applying shear force is set in the range of 1000 rpm to 1200 rpm; the volume ratio of the primary W / O emulsion to the structured external aqueous phase is set in the range of 1.5:1 to 2.5:1, and the homogenization rotation speed is set in the range of 3000 rpm to 3500 rpm.

[0012] Furthermore, the total solids content of the filtered soy milk is set to be in the range of 10% to 14%; the duration of the simmering state during heating is set to be 3 to 8 minutes.

[0013] Furthermore, the static incubation adopts a stepped temperature control mechanism, and the specific steps include: the mixed system is initially placed in a temperature range of 85°C to 90°C for a short incubation of 3 to 5 minutes; then the temperature is lowered to a temperature range of 70°C to 75°C and maintained for 15 to 30 minutes, so that magnesium ions are continuously released into the system for cross-linking and recombination.

[0014] Furthermore, the static incubation adopts a constant temperature control mechanism, and the specific steps are as follows: the mixed system is statically incubated at a constant temperature of 85°C for 15 to 25 minutes.

[0015] Furthermore, the amount of W / O / W multi-controlled release coagulant added is set to 8 mL to 12 mL per 500 mL of soy milk; the pressing time with mechanical pressure is maintained for 1.5 to 2.5 hours.

[0016] This invention provides a method for improving the quality of brine tofu using a WOW emulsion-type controlled-release coagulant. It has the following beneficial effects: 1. This invention overcomes the shortcomings of single emulsion encapsulation by providing a physical barrier space for magnesium ions through a W / O / W multi-emulsion structure, while utilizing gluconic acid in the inner aqueous phase. - The lactone undergoes a chemical phase transition that produces acid upon heating. During the gel assembly stage, the early penetration of hydrogen ions promotes slight isoelectric point pregelation of the system. Subsequently, magnesium ions released during demulsification undergo dense cross-linking on the pregelated backbone. This mechanism provides a sufficient time window for the unfolding and orderly recombination of soybean proteins, effectively avoiding disordered protein cross-linking caused by the instantaneous release of metal ions. As a result, the final product has a uniformly distributed and dense aggregate network, which significantly improves the water retention of brine tofu and reduces the dehydration rate.

[0017] 2. This invention introduces water-soluble polysaccharides into a structured external aqueous phase, allowing the emulsion to directly participate in the construction of the gel backbone while performing its ion-carrying function. The polysaccharide macromolecules preferentially mix with the soybean milk along with the external aqueous phase, and spatially overlap and interpenetrate with the soybean protein matrix beforehand. The released magnesium ions not only promote the cross-linking of protein molecules, but also serve as a connecting medium to consolidate the three-dimensional interpenetrating network of polysaccharides and proteins. The formation of this structure significantly reduces the rigid friction between protein backbones, increases the content of weakly bound water in the system, and gives the tofu product a soft and elastic texture, significantly reducing hardness and adhesiveness.

[0018] 3. The step-temperature control mechanism of this invention matches the demulsification rate of multiple emulsions with the unfolding law of protein molecules. High temperature triggers the instability of the outer layer of the emulsion and the initial unfolding of proteins. In the subsequent medium temperature period, the semi-dense state of the inner oil film is used to achieve the continuous and limited release of magnesium ions. This temperature control process promotes the full exposure of free sulfhydryl groups and hydrophobic sites of heat-denatured soybean protein, increases the proportion of disulfide bonds and hydrophobic interactions inside the gel system, and promotes the conformational transformation of soybean protein to a tightly folded β-sheet structure, ensuring the high strength and high stability of the gel network at the microscopic molecular level. Attached Figure Description

[0019] Figure 1 This is a process flow diagram of the method of the present invention; Figure 2 This is a diagram showing the microstructure and material distribution of the present invention. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Please see the appendix Figure 1-2 This invention provides a method for improving the quality of brine tofu using WOW emulsion-type controlled-release coagulant, comprising the following steps: S1. A multiphase system solution was prepared by separately preparing a composite internal aqueous phase, an oil phase, and a structured external aqueous phase. When preparing the composite internal aqueous phase, the primary coagulant and the secondary slow-release coagulant were added together to deionized water and stirred until the solids dissolved to obtain a mixed solution. The primary coagulant was an inorganic salt that provides metal ions, specifically a magnesium chloride-based flake coagulant. The secondary slow-release coagulant was gluconate- - Lactones or organic acid salts. When preparing the oil phase, add the hydrophobic emulsifier combination to the vegetable oil and stir under heating conditions. The heating temperature must reach above the melting temperature of the aforementioned hydrophobic emulsifier to ensure its dissolution and dispersion in the vegetable oil. Rapeseed oil, soybean oil, or corn oil can be selected. The hydrophobic emulsifier combination is selected from one or more of lecithin, mono- and diglycerides, and Span 60. When preparing the structured external aqueous phase, add the hydrophilic emulsifier combination and water-soluble polysaccharide to deionized water, heat to a set temperature, and stir to fully hydrate and dissolve the water-soluble polysaccharide. The hydrophilic emulsifier combination is selected from a mixture of mono- and diglycerides and Tween 80. The water-soluble polysaccharide is a soybean complex polysaccharide or soluble alginate.

[0022] S2, Preparation of the primary W / O emulsion. The aqueous and oil phases within the composite are mixed at a predetermined mass ratio. Shear force is applied in a constant-temperature water bath to uniformly disperse the aqueous phase within the oil phase, forming a primary W / O emulsion with a water-in-oil structure. The shear force is applied using a magnetic stirrer or a mechanical homogenizer. The droplet size and distribution of the primary W / O emulsion are controlled by adjusting the shear speed and processing time.

[0023] S3, Preparation of a W / O / W multi-layer controlled-release coagulant. The primary W / O emulsion and a structured external aqueous phase are mixed at a predetermined volume ratio and then subjected to high-speed dispersion homogenization. During this process, the hydrophilic emulsifier in the structured external aqueous phase forms a secondary hydration layer on the outside of the primary W / O emulsion droplets, resulting in a homogeneous water-in-oil-in-water multi-layer emulsion system. Homogenization is performed using a high-speed shear disperser or a high-pressure homogenizer.

[0024] S4, Preparation of soybean protein base. Soybeans are soaked in distilled water, and the soaked soybeans are ground into a slurry and filtered. The resulting soy milk is then heated to boiling to achieve thermal denaturation of the soybean protein. For the soaking, grinding, filtering, and thermal denaturation of the soy milk, those skilled in the art can select conventional equipment and process parameters according to actual production needs. The dissolution and denaturation principles of soybean protein are well-known in the field and will not be elaborated here.

[0025] S5, Co-gel Assembly. Boiled soy milk was cooled to a set incubation temperature. A W / O / W multi-stage controlled-release coagulant was added to the hot soy milk and stirred. The mixture was then kept incubated at the aforementioned set temperature. During incubation, water-soluble polysaccharide molecules carried in the structured outer aqueous phase interacted with soybean proteins in the hot soy milk, establishing the initial network backbone; the gluconic acid in the complex inner aqueous phase... - When lactones are heated, they decompose to produce protons. These protons penetrate the oil film layer and enter the hot soy milk, causing local isoelectric point pregelation of soybean proteins. Accompanied by the demulsification of the multiple emulsion structures under heat-induced conditions, magnesium ions dissociated from magnesium chloride are released into the hot soy milk system. Metal ion crosslinking occurs on the pregelated backbone, which promotes the unfolding of soybean protein molecules and the formation of a dense three-dimensional network.

[0026] S6, Pressing and Quality Evaluation. The gel network formed during static incubation is broken down, and the gel fragments are transferred to a mold with drainage holes. Mechanical pressure is applied to remove free yellow whey, completing the pressing and molding of the brine tofu. The demolded brine tofu is stored at low temperature for subsequent physical property determination.

[0027] The core of constructing a water-in-oil-in-water multiphase controlled-release coagulant lies in the selection of raw materials and the proportioning of components in the multiphase system. To support the stable existence of the multiphase emulsion system and the assembly of the gel network, the controlled-release coagulant raw material system involved in step S1 is divided into three basic component modules, specifically including: The first component module is a composite internal aqueous phase. This phase includes deionized water, a primary coagulant, and a secondary slow-release coagulant. The primary coagulant provides metal cations that promote protein cross-linking; the primary coagulant is a magnesium chloride flake. The mass ratio of the flake to deionized water is set at 7:13. The secondary slow-release coagulant is gluconate- - Lactone, halogenated tablets and gluconic acid - - The mass ratio of lactone to gluconate is set at 5:1 to 10:1. - Lactones remain stable at room temperature, but undergo hydrolysis upon heating to produce gluconic acid and release protons, causing the pH of the system to decrease.

[0028] The second component module is the oil phase. The oil phase comprises a vegetable oil matrix and a hydrophobic emulsifier combination. The vegetable oil matrix serves as the continuous phase matrix encapsulating the aqueous phase; the vegetable oil matrix may be rapeseed oil, soybean oil, or corn oil. For the pressing, extraction, and refining processes of vegetable oils, those skilled in the art can consult food engineering manuals according to industry standards. Vegetable oil processing is a well-known technology in this field and will not be elaborated upon here. The hydrophobic emulsifier combination is distributed at the interface between the aqueous phase and the vegetable oil matrix. The hydrophobic emulsifier combination is selected from lecithin, mono- and diglycerides, and Span 60. As a concrete implementation of the lower-level concept, the chemical name of Span 60 is sorbitan monostearate.

[0029] To form a stable oil-in-water physical interface, the total hydrophilic-lipophilic balance (TLP) of the hydrophobic emulsifier combination must be within the range of 3 to 5. In specific embodiments, the TLP is set to 4 or 4.3. When the TLP is set to 4, the mass ratio of lecithin, mono- and diglycerides, and Span 60 is set to 2:1:1; when the TLP is set to 4.3, the mass ratio of lecithin, mono- and diglycerides, and Span 60 is set to 1:1:2. The TLP of the combination of multiple single emulsifiers follows a weighted average calculation model, as follows: in: Limited to the total hydrophilic-lipophilic balance value of the compound emulsifier combination; Limited to the number of different types of single emulsifiers contained in the compound system, and the value is a positive integer; Limited to the first in the compound system The theoretical hydrophilic-lipophilic balance value of a single emulsifier; Limited to the first in the compound system The mass fraction of a single emulsifier in the total mass of a compound emulsifier combination.

[0030] The third component module is the structured external aqueous phase. This phase includes deionized water, a hydrophilic emulsifier combination, and water-soluble polysaccharides. The hydrophilic emulsifier combination is distributed at the interface between the vegetable oil matrix and the external aqueous phase, and is selected from mono- and diglycerides and Tween 80. As a specific implementation of the lower-level concept, the chemical name of Tween 80 is polyoxyethylene sorbitan monooleate. Based on the aforementioned weighted average calculation model, the total hydrophilic-lipophilic balance value of the hydrophilic emulsifier combination is set within the range of 8 to 10. When the total hydrophilic-lipophilic balance value is set to 8, the mass ratio of mono- and diglycerides to Tween 80 is set to 1.95:1.05; when the total hydrophilic-lipophilic balance value is set to 10, the mass ratio of mono- and diglycerides to Tween 80 is set to 1.4:1.6.

[0031] The water-soluble polysaccharide is either a soybean complex polysaccharide or a soluble alginate. After dissolving in deionized water, the water-soluble polysaccharide forms a high-molecular-weight solution with steric hindrance. During the mixing stage of the controlled-release coagulant and soy milk, the macromolecular segments of the water-soluble polysaccharide act as physical cross-linking points, participating in the network connection process of soybean protein macromolecules.

[0032] The microstructural stability of water-in-oil-in-water multiple emulsion systems and the final formation quality of soybean protein gel networks depend on the setting of core process steps and parameters. The specific implementation process involves the control of the following technical parameters: When preparing the oil phase and the structured aqueous phase, the heating temperature is set within the range of 90°C to 100°C. Too low a temperature will prevent the hydrophobic emulsifier or water-soluble polysaccharide from completely hydrating and dissolving, while too high a temperature may cause oxidative denaturation of the vegetable oil matrix or thermal degradation of macromolecules. In one specific embodiment, the container holding the oil phase matrix or the structured aqueous phase matrix is ​​placed in a constant temperature water bath at 95°C for heating. The heating process is accompanied by continuous stirring, with the stirring duration set between 20 and 30 minutes, and in a specific embodiment, 25 minutes, until the corresponding emulsifier and macromolecules are completely dissolved in their respective phase systems to form a clear solution.

[0033] In the preparation stage of the primary water-in-oil emulsion, the ratio of the composite aqueous phase to the oil phase and the setting of shear conditions determine the embedding efficiency of the inner oil film. The mass ratio of the composite aqueous phase to the oil phase is set in the range of 1:2 to 2:1. In a specific embodiment, the composite aqueous phase and the oil phase are mixed at a mass ratio of 2:2. The mixture is placed in a constant temperature water bath to maintain the set emulsification temperature, which is set in the range of 50°C to 70°C to prevent water evaporation and emulsifier deactivation during the emulsification process. Continuous stirring is performed using a magnetic stirrer. The speed of the magnetic stirrer is set between 1000 rpm and 1200 rpm. Too low a speed will not form uniform primary droplets, while too high a speed may cause localized excessive shearing, leading to leakage of the inner aqueous phase. In a specific embodiment, the speed of the magnetic stirrer is 1100 rpm, and the continuous shearing stirring time is set to 30 minutes.

[0034] The preparation of the multiple controlled-release coagulant relies on a two-stage homogenization process. The primary oil-in-water emulsion and the structured external aqueous phase are mixed at a volume ratio of 1.5:1 to 2.5:1; in a specific embodiment, the volume ratio is 2:1. The mixed solution is processed using a high-speed dispersion homogenizer. The homogenization speed is set between 3000 rpm and 3500 rpm; in a specific embodiment, the homogenization speed is set to 3200 rpm. The homogenization time is set between 5 minutes and 10 minutes; in a specific embodiment, the processing time is 6 minutes. These homogenization parameters enable the primary emulsion to be dispersed into smaller water-in-oil-in-water droplets without damaging the inner oil film, ensuring that the hydrophilic emulsifier in the structured external aqueous phase constructs a stable secondary interface layer on the droplet surface.

[0035] In preparing soy milk, soybeans and distilled water are mixed and soaked at a mass ratio of 1:2 to 1:4, with a specific ratio of 1:3 in this embodiment. The soaking temperature is set to 20°C to 30°C, and the soaking time is 10 to 14 hours, with a specific embodiment soaking at 25°C for 12 hours. After soaking, the soybeans and distilled water are ground at a weight-to-volume ratio of 1:5 to 1:8, with a specific embodiment grinding weight-to-volume ratio of 1:6. The ground slurry is filtered through a sieve with a mesh size of 80 to 120 mesh, with a specific embodiment using a 100 mesh sieve, to obtain soy milk with a total solids content set between 10% and 14%, with a specific embodiment having a total solids content of 12%. The filtered soy milk is heated to 100°C and maintained at a gentle boil for 3 to 8 minutes, with a specific embodiment maintaining this gentle boil for 5 minutes, to ensure sufficient thermal denaturation of the soybean protein.

[0036] In the co-gel assembly process, the addition ratio of the controlled-release coagulant and the incubation temperature need to be controlled. The boiled soy milk is cooled to the set incubation temperature. The amount of controlled-release coagulant added is set to 8 mL to 12 mL per 500 mL of soy milk; in a specific embodiment, 10 mL of controlled-release coagulant is added per 500 mL of soy milk. To achieve gluconate- The rates of lactone hydrolysis, polysaccharide molecule intercalation, and magnesium ion release are matched, and the incubation process employs a stepped temperature control mechanism or a constant temperature control mechanism. In the examples using the constant temperature control mechanism, the mixture is incubated at a constant temperature of 85°C for 15 to 25 minutes; in a specific example, it is incubated at a constant temperature for 20 minutes to complete the gelation process. In the examples using the stepped temperature control mechanism, the mixture is initially placed in a higher temperature range of 85°C to 90°C for a short incubation of 3 to 5 minutes, triggering multiple emulsion outer layer instability and gluconic acid- - Initial decomposition of lactones; then rapid cooling to a moderate temperature range of 70°C to 75°C and maintaining it for 15 to 30 minutes. Within the moderate temperature range, with the inner oil film in a semi-dense state, magnesium ions are continuously released into the soy milk system, causing the soybean protein molecular chains to undergo dense cross-linking and recombination.

[0037] The gel network is solidified and formed through a pressing process. The incubated, intact gel network is broken up, and the material containing gel fragments is transferred into a mold. The mold size is set according to actual needs; in a specific embodiment, the mold size is 13cm × 13cm × 9.5cm. A pressure plate is placed on top of the mold, and uniform mechanical pressure is applied for pressing for 1.5 to 2.5 hours; in a specific embodiment, pressing is performed for 2 hours to remove the yellowish liquid that the gel network could not bind. The resulting brine tofu is wrapped in plastic wrap and stored in a refrigerator at 0°C to 4°C; in a specific embodiment, the storage temperature is 4°C, thereby slowing down the passive diffusion of moisture from the soybean protein gel during storage.

[0038] To further disclose the specific implementation details of the water-in-oil-in-water multi-controlled release coagulant and brine tofu, the following specific embodiments and comparative examples are set to support the technical features of process parameters and component ratios.

[0039] Example 1 provides a method for preparing a water-in-oil-in-water multi-stage controlled-release coagulant and brine tofu. When preparing the composite internal aqueous phase, 7g of brine flakes, whose main component is magnesium chloride, and 1g of gluconate- - Lactone, together with 13g of deionized water, was stirred with a magnetic stirrer at room temperature until the solids were completely dissolved. To prepare the oil phase, 17mL of rapeseed oil was taken, and 1g of a compound hydrophobic emulsifier containing lecithin, mono- and diglycerides, and Span 60 was added. The mass ratio of lecithin, mono- and diglycerides, and Span 60 in the aforementioned compound hydrophobic emulsifier was set to 2:1:1, with a total hydrophilic-lipophilic balance value of 4. The rapeseed oil containing the hydrophobic emulsifier was heated in a 95°C constant temperature water bath for 25 minutes, continuously stirred until the solution became clear. To prepare the structured external aqueous phase, 17mL of deionized water was taken, and 1g of a compound hydrophilic emulsifier containing mono- and diglycerides and Tween 80 was added. The mass ratio of mono- and diglycerides to Tween 80 was set to 1.95:1.05, with a total hydrophilic-lipophilic balance value of 8. Simultaneously, 0.5g of soybean complex polysaccharide was added to deionized water as a structural macromolecule, and heated and stirred in a 95℃ constant temperature water bath for 25 minutes until completely dissolved. The resulting composite inner aqueous phase and oil phase were mixed at a mass ratio of 2:2 and placed in a 60℃ constant temperature water bath. The mixture was continuously stirred at 1100 rpm for 30 minutes using a magnetic stirrer to prepare a primary oil-in-water emulsion. 40mL of the primary oil-in-water emulsion was mixed with 20mL of the structured outer aqueous phase and homogenized using a high-speed dispersion homogenizer at 3200 rpm for 6 minutes to obtain a water-in-oil-in-water multi-stage controlled-release coagulant.

[0040] The preparation method of soybean protein base and gel in Example 1 is as follows: Soybeans and distilled water were selected and soaked at 25°C for 12 hours at a mass ratio of 1:3. After soaking, the soybeans were mixed with distilled water at a weight-to-volume ratio of 1:6 and ground. The slurry was filtered through a 100-mesh sieve to obtain soy milk. 500 mL of the obtained soy milk was heated to 100°C and kept at a gentle boil for 5 minutes, and then cooled to 85°C. 10 mL of the prepared water-in-oil-in-water multi-stage controlled-release coagulant was added to the hot soy milk cooled to 85°C and stirred to mix. The mixture was incubated in an 85°C water bath for 20 minutes to complete the gelation process. The formed gel was subjected to a dehydration treatment, transferred to a 13cm×13cm×9.5cm mold, covered with a pressure plate, and pressed under uniform pressure for 2 hours to dehydrate. After demolding, brine tofu was obtained, wrapped with plastic wrap, and stored in a refrigerator at 4°C.

[0041] Example 2 provides a preparation method for altering the hydrophilic-lipophilic balance of the outer aqueous phase. The preparation steps of Example 2 are identical to those of Example 1, except for the preparation parameters of the structured outer aqueous phase. When preparing the structured outer aqueous phase, the mass ratio of mono- and diglycerides to Tween 80 is adjusted to 1.4:1.6, and the total hydrophilic-lipophilic balance is set to 10.

[0042] Example 3 provides a preparation method for altering the hydrophilic-lipophilic balance value of the oil phase. The preparation steps of Example 3 are identical to those of Example 1, except for the ratio parameters of the hydrophobic emulsifier in the oil phase. When preparing the oil phase, the mass ratio of lecithin, mono- and diglycerides, and Span 60 is adjusted to 1:1:2, and the total hydrophilic-lipophilic balance value is set to 4.3.

[0043] To verify the interaction between the dual coagulant and the structural macromolecule in a multiple controlled-release coagulant, Comparative Example 1 was established. Comparative Example 1 used a basic multiple emulsion system without the introduction of structural macromolecules and secondary slow-release coagulants. The preparation steps of Comparative Example 1 were identical to those of Example 1, except for the raw material components of the composite inner aqueous phase and the structured outer aqueous phase. Only 7g of halogen tablets were added when preparing the composite inner aqueous phase; gluconate was not added. - Lactone; When preparing the structured external aqueous phase, only 1g of mono- and diglycerides in a mass ratio of 1.95:1.05 and Tween 80 are added, without adding soybean polysaccharides.

[0044] To verify the effect of the multiple emulsion physical controlled-release system, Comparative Example 2 was established. Comparative Example 2 employed a traditional direct coagulation process without emulsion encapsulation. 7g of coagulation tablets were weighed and directly dissolved in 13g of deionized water to prepare a single pure brine coagulant. 500mL of soy milk that had been gently boiled at 100℃ for 5 minutes and then cooled to 85℃ was taken. The pure brine coagulant, containing an equal amount of active ingredient as the coagulation tablets in Example 1, was added directly to the cooled soy milk. After stirring and mixing, the mixture was incubated in an 85℃ water bath for 20 minutes. The gel network breaking, pressing, dehydration, and storage conditions were exactly the same as in Example 1. The tofu prepared in Comparative Example 2 corresponds to the traditional brine tofu control group in the basic test.

[0045] The quality performance and microscopic mechanism of the brine-cured tofu products prepared in the aforementioned examples and comparative examples were evaluated to verify the technical effects of the water-in-oil-in-water multi-controlled-release coagulant and the dual coagulation synergistic system. Macroscopic quality tests were conducted on the brine-cured tofu products. Regarding moisture content and water-holding capacity, compared with the control group tofu prepared by direct coagulation with pure brine (i.e., Comparative Example 2), the tofu sample prepared using the multi-controlled-release coagulant of this invention exhibited higher water-holding capacity and lower dehydration rate. This improvement in macroscopic characteristics is attributed to the optimization of the microscopic gel network: the physically controlled release of magnesium ions and the chemical phase transition of the secondary coagulant synergistically provide a sufficient time window for the interaction and aggregation of soybean proteins. This rate matching avoids the disordered and rapid cross-linking of proteins caused by the instantaneous release of metal ions, promoting the formation of a uniformly distributed and dense aggregate network. The dense gel network can exert a stronger physical retention and spatial binding effect on the water inside the system, thereby effectively improving the product's ability to retain moisture under stress and significantly reducing its passive diffusion and loss of moisture during low-temperature storage.

[0046] Texture analysis was performed on the finished brine-cured tofu. Compared with the control group, the tofu sample prepared using multiple controlled-release coagulants exhibited significantly reduced hardness, adhesiveness, and chewiness while maintaining good elasticity and resilience. Adhesiveness and chewiness characterize the internal gel strength of the tofu, and both are generally positively correlated with hardness. The softening of the macroscopic texture also stems from changes in the internal network assembly process: the controlled cross-linking rate promotes the formation of a mature gel network from soybean proteins, a process that retains a greater proportion of water. Water acts as a good plasticizer distributed within the protein matrix, reducing rigid friction between the protein backbones, thus giving the finished tofu a soft and elastic texture.

[0047] A comprehensive analysis of the microscopic physicochemical properties of the finished brine tofu was conducted to confirm the intermolecular forces and changes in protein conformation.

[0048] Regarding the water binding state, nuclear magnetic resonance (NMR) water state analysis results indicate that in tofu prepared using multiple controlled-release coagulants, the flowability of weakly bound water (i.e., water affected by the protein matrix but not tightly bound) is more strictly limited. This reduction in the flowability of weakly bound water directly confirms the densification process of the protein network structure at the microscopic level.

[0049] Regarding protein conformation and secondary structure, spectral analysis showed that, compared to the control group, the tofu system prepared in the examples exhibited significantly enhanced internal hydrogen bonding, which helps resist water removal during pressing. Simultaneously, the relative content of β-sheet structures in soybean protein increased, while the relative content of α-helical structures decreased. The increase in β-sheet structures promoted the formation of a more compact protein conformation, confirming that the controlled-release coagulant effectively guided the orderly aggregation of soybean protein. Furthermore, the altered intrinsic fluorescence properties indicated that soybean protein unfolded during cross-linking, exposing buried amino acid residues and further changing the protein's conformational state.

[0050] Regarding intermolecular forces and the construction of a three-dimensional network, chemical extraction and microscopic morphological observation confirmed that disulfide bonds and hydrophobic interactions are the core forces supporting the tofu gel network structure of this invention. In tofu samples using multiple controlled-release coagulants, the hydrophobic interactions and disulfide bond content of the system significantly increased. The enhanced intermolecular forces indicate that during the slow release of magnesium ions, thermally denatured protein molecules fully expose free thiol groups and hydrophobic sites, promoting the physical aggregation of proteins. Furthermore, due to the introduction of water-soluble polysaccharides in the external aqueous phase, polysaccharide macromolecules and the protein matrix achieved spatial overlap and interpenetration integration. The enhanced disulfide bonds, hydrogen bonds, and hydrophobic interactions not only consolidated the simple protein matrix but also supported the final formation of the polysaccharide-protein three-dimensional interpenetrating network, thereby fundamentally improving the overall quality of brine tofu.

[0051] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for improving the quality of brine tofu using WOW emulsion-type controlled-release coagulant, characterized in that, Includes the following steps: S1, Preparation of a multiphase system solution: A composite internal aqueous phase, an oil phase, and a structured external aqueous phase are prepared; the composite internal aqueous phase includes deionized water, halogen flakes as the primary coagulant, and gluconic acid as a secondary slow-release coagulant. - Lactone; the oil phase comprises a vegetable oil matrix and a hydrophobic emulsifier combination, wherein the hydrophobic emulsifier combination is selected from one or more of lecithin, mono- and diglycerides, and Span 60; the structured external aqueous phase comprises deionized water, a hydrophilic emulsifier combination, and water-soluble polysaccharides, wherein the hydrophilic emulsifier combination is selected from a combination of mono- and diglycerides and Tween 80; S2, Preparation of primary W / O emulsion: The composite aqueous phase and the oil phase are mixed in a set mass ratio, and shear force is applied in a constant temperature water bath environment to disperse the composite aqueous phase in the oil phase; S3, Preparation of W / O / W multi-stage controlled-release coagulant: The primary W / O emulsion and the structured external aqueous phase are mixed in a set volume ratio and homogenized. S4, Preparation of soybean protein base: Select soybeans and distilled water, soak, grind and filter to obtain soy milk, and heat the soy milk to boil to achieve thermal denaturation of soybean protein; S5, Co-gel Assembly: Boiled soy milk is cooled to a set incubation temperature, and the W / O / W multi-stage controlled-release coagulant is added and stirred. The mixture is then kept still for incubation. During incubation, the water-soluble polysaccharide interacts with soy protein to establish a network backbone, and the gluconate- - The lactone decomposes upon heating to generate protons, which initiates isoelectric point pregelation. This is accompanied by the release of magnesium ions from the demulsification of the multiple emulsion structures, which undergo metal ion crosslinking on the pregelation backbone. S6, Pressing and Molding: The gel network formed by static incubation is broken down and pressed and shaped to obtain brine tofu.

2. The method according to claim 1, characterized in that, In step S1, in the composite aqueous phase, the halogen tablets and the gluconic acid- - The mass ratio of lactone is set to 5:1 to 10:1; in the structured aqueous phase, the water-soluble polysaccharide is a soybean complex polysaccharide or a soluble alginate.

3. The method according to claim 1 or 2, characterized in that, In step S1, the total hydrophilic-lipophilic balance value of the hydrophobic emulsifier combination is in the range of 3 to 5; the total hydrophilic-lipophilic balance value of the hydrophilic emulsifier combination is set in the range of 8 to 10.

4. The method according to claim 3, characterized in that, When the total hydrophilic-lipophilic balance value of the hydrophobic emulsifier combination is set to 4, the mass ratio of lecithin, mono- and diglycerides to Span 60 is set to 2:1:1; when the total hydrophilic-lipophilic balance value of the hydrophilic emulsifier combination is set to 8, the mass ratio of mono- and diglycerides to Tween 80 is set to 1.95:1.

05.

5. The method according to claim 1, characterized in that, In step S1, when preparing the oil phase, the heating temperature must reach above the melting temperature of the hydrophobic emulsifier combination; when preparing the structured external aqueous phase, the heating temperature is set within the range of 90°C to 100°C.

6. The method according to claim 1, characterized in that, In step S2, the mass ratio of the composite internal aqueous phase to the oil phase is set in the range of 1:2 to 2:1, the emulsification temperature is set in the range of 50°C to 70°C, and the rotation speed for applying shear force is set in the range of 1000 rpm to 1200 rpm; in step S3, the volume ratio of the primary W / O emulsion to the structured external aqueous phase is set in the range of 1.5:1 to 2.5:1, and the homogenization rotation speed for homogenization is set in the range of 3000 rpm to 3500 rpm.

7. The method according to claim 1, characterized in that, In step S4, the total solids content of the filtered soy milk is set to be in the range of 10% to 14%; the duration of the simmering state during heating is set to be 3 to 8 minutes.

8. The method according to claim 1, characterized in that, In step S5, the static incubation adopts a stepped temperature control mechanism. The specific steps include: the mixed system is initially placed in a temperature range of 85°C to 90°C for a short incubation of 3 to 5 minutes; then the temperature is lowered to a temperature range of 70°C to 75°C and maintained for 15 to 30 minutes, so that magnesium ions are continuously released into the system for cross-linking and recombination.

9. The method according to claim 1, characterized in that, In step S5, the static incubation adopts a constant temperature control mechanism. The specific steps are: the mixed system is statically incubated at a constant temperature of 85°C for 15 to 25 minutes.

10. The method according to claim 1, characterized in that, In step S5, the amount of the W / O / W multi-controlled release coagulant added is set to 8 mL to 12 mL per 500 mL of soy milk; in step S6, the pressing time with mechanical pressure is maintained for 1.5 hours to 2.5 hours.

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