Preparation method of water-in-water (W / W) emulsion sustained-release coagulation system for making old tofu

Abstract

The present invention relates to a preparation method of a water-in-water (W / W) emulsion sustained-release coagulation system for making old tofu, belonging to the technical field of food processing. First, soybean lipophilic protein (SLP) and cellulose nanocrystals (CNC) form soybean lipophilic protein-cellulose nanocrystal composite particles (SLP-CNC) through electrostatic interaction under the condition of pH = 3.0. Using guar gum solution as the internal aqueous phase and the gelatinized lotus seed resistant starch solution as the external aqueous phase, the bittern is encapsulated in the internal aqueous phase, and the SLP-CNC solid particles are adsorbed at the interface to form a protective layer, constructing a water-in-water (W / W) type emulsion sustained-release system. The specific application method is as follows: at the point of making old tofu and adding the bittern, an appropriate amount of the water-in-water (W / W) emulsion sustained-release coagulation system encapsulating the bittern is added to the cooked soy milk. The sustained-release system slowly releases Ca and Mg ions in the bittern, promoting the protein to form a uniform three-dimensional gel network structure, and finally producing old tofu with delicate texture and relatively soft and tender taste. The emulsion sustained-release coagulation system prepared by the present invention has good biocompatibility, edibility and nutritional functional characteristics. The application of this new sustained-release system in the field of soy product processing realizes the controllable release of the coagulant.

Description

Technical Field

[0001] The present invention relates to a preparation method of a water-in-water (W / W) emulsion-type sustained-release coagulation system for making old tofu, and the sustained-release system is applied to the processing field of soy products such as old tofu. Background Art

[0002] Old tofu, namely bittern tofu, is made by the cations of CaCl2 and MgCl2 in bittern combining with the negatively charged amino acid residues on the surface of heat-denatured soy protein, shielding the surface charge of the protein, and reducing the repulsion between protein molecules to aggregate and form a gel. Pointing the slurry is the most critical step in the process of making tofu, which has a decisive impact on the product quality. Among them, the type and addition method of the coagulant are important factors affecting the gel structure and quality difference of tofu protein. In the traditional method of making old tofu, when pointing the slurry, the bittern contacts the soy protein quickly, instantly causing the protein in the soy milk to aggregate and solidify. The interaction is fast and intense, resulting in an uneven structure and rough texture of the tofu product. Moreover, the network structure of the tofu protein is prone to shrinkage, the yield is low, and the product cannot be stored for a long time. The above problems have always troubled the development of the tofu processing industry and are key problems that need to be solved urgently. The traditional method of addition requires manual control of the addition speed by experience, thus hindering the intelligent processing of tofu. In addition, the poor gelation of the protein in the tofu will lead to poor water retention of the tofu, resulting in more loss of active nutritional components with the yellow slurry water during the pressing process of the tofu. At present, with the acceleration of the intelligent and large-scale development of the food industry, it is necessary to construct an appropriate sustained-release system to solve the problems of fast, insufficient and severe water loss in the gelation of tofu protein. Previously, Li Jinlong and Guangdong Lingnan Thanksgiving Biotechnology Co., Ltd. developed W / O and W / O / W emulsion-type coagulants to achieve the slow release of bittern during the process of pointing the slurry, improve the gel structure of tofu protein, reduce the gel hardness, increase the elasticity, and reduce the loss of tofu nutrients. However, the presence of oil in the oil-water sustained-release emulsion will also affect the aggregation process of soy milk protein to a certain extent, and then affect the gel quality of tofu protein.

[0003] Therefore, in order to achieve the slow release of brine in tofu making, it is necessary to construct a more miscible emulsion slow-release coagulation system to upgrade the traditional slow-release system's slurry-doping process, control the gelation rate of protein through the slow release of brine, delay the coagulation process, improve the gel quality, and solve the problems of soy milk protein coagulation too fast, uneven gel structure, and easy loss of nutrients. Water-in-water (W / W) emulsions are constructed by a two-phase mixed system. The oil-free all-aqueous emulsion environment is more suitable for the application of food systems and has extremely high biocompatibility and bioaccessibility. However, the interfacial tension between the water-water phases is extremely low, so the stability is not good, and a suitable stabilizer needs to be added to maintain the structure of the emulsion system. In addition, water-water emulsions have a thicker interface layer, and most small molecule surfactants cannot cross the entire phase interface due to size restrictions, and are not suitable for the construction of water / water systems. Studies have shown that solid emulsified particles have more advantages. Currently commonly used colloidal particles of different structures and properties (proteins, polysaccharides, inorganic particles, liposomes) can accumulate at the water-water interface and adsorb to form a protective layer to irreversibly stabilize the water-water emulsion and effectively avoid the coalescence of the two-phase droplets.

[0004] The present invention selects guar gum with dietary fiber function and anti-digestion ability and gelatinized lotus seed resistant starch solution as the inner water phase and the outer water phase respectively, takes brine as the encapsulation object, utilizes soybean lipophilic protein-cellulose nanocrystal composite particles (SLP-CNC) to stabilize the emulsion system, and constructs a new water-in-water (W / W) emulsion slow-release coagulant. The system has good compatibility, edible and nutritional functions, and effectively solves the problems of too fast protein gelation rate, tofu quality decline and serious nutrient loss in the slurry point process of old tofu. The slow-release system has simple production process, low energy consumption, low cost, and is suitable for industrialized and large-scale automated production of tofu, providing technical support for subsequent practical applications. Summary of the invention

[0005] In view of the problems existing in the prior art such as the rapid and intense interaction between brine and soybean protein, which leads to rough product structure, poor water holding capacity, loss of nutrients, etc., the present invention provides a method for preparing a water-in-water (W / W) emulsion type sustained-release coagulation system for making old tofu. This sustained-release system can control the slow release of brine in the slurrying process, prolong the action time of soybean protein and brine, make the protein molecules aggregate more fully, form a denser and more complete protein network structure, and reduce the loss of water and nutrients.

[0006] The present invention discloses a water-in-water (W / W) emulsion type sustained-release coagulation system method for making old tofu. The specific technical scheme is as follows:

[0007] A water-in-water (W / W) emulsion type sustained-release coagulation system for making old tofu, comprising the following components:

[0008] Guar gum solution, gelatinized lotus seed resistant starch solution, and soy lipoprotein-cellulose nanocrystal composite particles (SLP-CNC) as stabilizing particles.

[0009] Preferably, the concentration of the guar gum solution is 0.4%. After dissolving the guar gum powder in deionized water and stirring for 10 h to fully dissolve, adjust the pH to 3.0, and centrifuge at 9000×g for 15 min to remove insoluble impurities. Then add a brine tablet with a mass fraction of 15%.

[0010] Preferably, the concentration of the lotus seed resistant starch solution is 4%. Dissolve the lotus seed resistant starch in deionized water, adjust the pH to 3.0, heat and stir in a water bath at 90 °C for 30 min, and then ultrasonicate for 30 min to make the solution uniformly dispersed.

[0011] Preferably, soy lipoprotein and cellulose nanocrystals are respectively dissolved in deionized water. After adjusting the pH to 3.0, they are mixed in different mass ratios and magnetically stirred for 1 h to obtain a suspension sample through electrostatic adsorption, and then freeze-dried for 48 h to obtain composite particles;

[0012] Preferably, the composite mass ratio of soy lipoprotein to cellulose nanocrystals is 4:1.

[0013] The preparation method of the above water-in-water emulsion sustained-release coagulation system includes the following steps:

[0014] Mix the guar gum solution, gelatinized lotus seed resistant starch solution, and soy lipoprotein-cellulose nanocrystal composite particle (SLP-CNC) suspension in a certain proportion, first perform high-speed homogenization and then magnetic stirring to obtain a water-in-water emulsion sustained-release coagulation system.

[0015] Preferably, the volume ratio of the guar gum solution to the gelatinized lotus seed resistant starch solution is 1:3, and the mass fraction of the soy lipoprotein-cellulose nanocrystal composite particle (SLP-CNC) is 0% - 0.8%.

[0016] Preferably, the homogenization speed of the emulsion is 5000 rpm, the time is 2 min, the magnetic stirring speed is 750 r / min, and the time is 2 h.

[0017] The advantages of the present invention are as follows:

[0018] Selecting a water-in-water emulsion to encapsulate brine to construct a sustained-release coagulation system can slow down the interaction intensity and speed between brine and soy protein, delay the coagulation effect, and improve the gel quality.

[0019] The present invention uses a water-in-water emulsion sustained-release coagulation system to replace traditional brine for coagulating soybeans. The obtained tofu product has an increased static water content, increased yield, and a decrease in the loss of nutrients.

[0020] The present invention uses soy protein lipoprotein hydrophilically modified by composite cellulose nanocrystals as stable particles with a larger particle size, which can span the two-phase interface, and the contact angle at the two-phase interface is about 90°, enabling it to adsorb more firmly on the interface, acting as a barrier to make the emulsion more stable.

[0021] The present invention selects lotus seed resistant starch solution as the external aqueous phase, which is characterized by a low glycemic index and has physiological functions such as reducing blood lipid and regulating intestinal flora.

[0022] The present invention selects guar gum solution as the internal aqueous phase, which is a commonly used thickener in food and also a high-quality prebiotic. It can affect the protein gelation process in tofu making and play a role in improving the texture of tofu. Description of the Drawings

[0023] Figure 1 : Confocal laser microscopy images of water / water (W / W) emulsions stabilized by different concentrations of SLP-CNC particles

[0024] Figure 2 : Sustained-release effect of water / water (W / W) emulsions stabilized by different concentrations of SLP-CNC particles encapsulating bittern

[0025] Figure 3 : Effects of sustained-release coagulation systems of water / water (W / W) emulsions stabilized by different concentrations of SLP-CNC particles on soybean protein aggregation, macroscopic and microscopic structures of tofu Detailed Embodiments

[0026] The following further describes the present invention in conjunction with specific implementation examples to facilitate those skilled in the relevant arts to more fully and thoroughly understand the present invention.

[0027] Example 1

[0028] Preparation of soy protein lipoprotein-cellulose nanocrystal composite particles (SLP-CNC): Soy protein lipoprotein is dissolved in deionized water and stirred at 500 rpm for 10 h to fully hydrate and prepare a 5% soy protein lipoprotein stock solution; cellulose nanocrystals are dissolved in deionized water and magnetically stirred for 3 h to fully dissolve, and the pH values of the two solutions are adjusted to 3. The two solutions are mixed at a mass ratio of soy protein lipoprotein: cellulose nanocrystals = 4:1 and magnetically stirred for 1 h to obtain a suspension sample, which is freeze-dried for 48 h to obtain composite particles.

[0029] Preparation of emulsion: A certain amount of lotus seed resistant starch was dispersed in water, and the pH was adjusted to 3.0. Under continuous stirring in a 90 °C water bath for 30 min to fully gelatinize the starch, and then ultrasonic treatment for 30 min to evenly disperse the gelatinized lotus seed resistant starch solution, thus preparing a 4 wt% lotus seed resistant starch stock solution. Guar gum powder was dissolved in it and stirred at room temperature for 12 h, and then centrifuged (9000×g, 15 min, 20 °C) to remove a small amount of insoluble substances, and then 15% mass fraction of magnesium chloride flakes was added to prepare a 0.4 wt% guar gum solution. The guar gum solution, lotus seed resistant starch solution and soy lipoprotein-cellulose nanocrystal (accounting for 0.4% of the system mass) composite particle suspension were mixed, where the volume ratio of the guar gum solution to the lotus seed resistant starch solution was 1:3, and after low-speed homogenization at 5000 rpm for 2 min, magnetic stirring (750 r / min) was carried out for 2 h.

[0030] It can be seen from Figure 1 that as the concentration of SLP-CNC composite particles increases, the size of the emulsion droplets formed gradually decreases, and the emulsion dispersion becomes more uniform and stable.

[0031] Example 2

[0032] The same operation as in Example 1 was carried out, only changing the addition amount of SLP-CNC composite particles in the emulsion to 0%, 0.1%, 0.2%, 0.6%, 0.8% of the system.

[0033] According to the simulation of slow release of the emulsion in distilled water, the conductivity method was used to measure the change of conductivity in the aqueous phase, and indirectly measure the release rate of brine from the emulsion, so as to characterize the slow release performance of the emulsion. It can be seen from Figure 2 that traditional brine will be released within 10 s after adding soy milk. As the concentration of SLP-CNC composite particles in the slow release system increases, the release rate of brine significantly slows down. When the mass fraction of SLP-CNC is 0.8%, the slow release process can be delayed to about 1 min. This slow release system helps to form a more dense and complete protein network structure, provides sufficient aggregation time for protein gel formation, and helps to improve the gel quality and texture structure of tofu.

[0034] It can be seen from Figure 3 that as the concentration of SLP-CNC composite particles in the slow release system increases, the scale of soy milk protein aggregates gradually decreases, and the structure of the tofu made is more dense and uniform, and the pores gradually change from larger irregular holes to smaller honeycomb-like structures.

[0035] As described above, the embodiments of the present invention have been described in detail, but the scope protected by the present invention is not limited thereto. Those skilled in the art who make equivalent substitutions or changes based on the concept and technical solution of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for preparing a water-in-water (W / W) emulsion sustained-release coagulation system for making old tofu, characterized in that: The water-in-water emulsion was selected as the sustained-release system, the gelatinized lotus seed resistant starch solution was used as the external aqueous phase, and the guar gum solution was used as the internal aqueous phase to encapsulate the brine. Soybean lipophilic protein composite particles were constructed as solid particle stabilizers for water-in-water (W / W) emulsion systems. The specific process includes the following steps: (1) Preparation of soybean lipophilic protein-cellulose nanocrystal composite particles (SLP-CNC): Soybean lipophilic protein and cellulose nanocrystals were dissolved in deionized water, adjusted to pH 3.0, mixed in different mass ratios and magnetically stirred to obtain suspension samples by electrostatic adsorption, and freeze-dried for 48 h to obtain composite particles; (2) Preparation of a water-in-water (W / W) emulsion sustained-release system: a certain amount of lotus seed resistant starch powder is dispersed in water, heated and stirred in a water bath to fully gelatinize the starch, and further ultrasonically treated to obtain a lotus seed resistant starch solution; guar gum powder is dissolved in deionized water and stirred at room temperature to fully dissolve, and then centrifuged to remove insoluble impurities; brine flakes are dissolved in the guar gum solution, thereby preparing a brine-encapsulated guar gum solution; (3) The guar gum solution, lotus seed resistant starch solution and SLP-CNC particle suspension were mixed in a certain proportion, homogenized and then magnetically stirred to obtain a water-in-water (W / W) emulsion sustained-release coagulation system.

2. The method for preparing a water-in-water (W / W) emulsion sustained-release coagulation system for making old tofu according to claim 1, characterized in that: In step (1), the mass ratio of SLP to CNC in the SLP-CNC composite particles is 4:1, and the magnetic stirring time is 1 h.

3. The method for preparing a water-in-water (W / W) emulsion sustained-release coagulation system for making old tofu according to claim 1, characterized in that: In step (2), the mass fraction of the lotus seed resistant starch solution is 4%, the gelatinization water bath heating temperature is 90° C., the time is 30 min, and after gelatinization, ultrasound is required for 30 min to make the solution evenly dispersed. The mass fraction of the guar gum solution is 0.4%, the stirring time at room temperature is 12 h, and the centrifugation conditions are 9000×g, 15 min, and 20° C.

4. The method for preparing a water-in-water (W / W) emulsion sustained-release coagulation system for making old tofu according to claim 1, characterized in that: In step (2), the mass fraction of the halogen flakes is 15% of the guar gum solution.

5. The method for preparing a water-in-water (W / W) emulsion sustained-release coagulation system for making old tofu according to claim 1, characterized in that: In step (3), the emulsion homogenization speed is 5000 rpm / min, the time is 2 min, and the magnetic stirring speed is 750 r / min, and the time is 2 h.

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