High-dietary-fiber dried bean curd and preparation method thereof

Abstract

The invention relates to high-dietary-fiber dried bean curds and a preparation method thereof, and belongs to the technical field of food processing. The dried bean curd is prepared by mixing the raw soybean milk and the soybean dreg powder which is subjected to superfine grinding to be in the micron order, and compared with the dried bean curd prepared by mixing the cured soybean milk and the soybean dregs, the prepared dried bean curd can better maintain the hardness of the dried bean curd and the resilience characteristic of dried bean curd gel; the bean dreg particles and the protein matrix form closer internal connection, and the formed gel network structure is more compact and reasonable, so that a more suitable moisture distribution state can be realized while good water holding performance is maintained, the chewiness is better, and the overall taste is better. Moderate heating treatment, ultrasonic treatment and compound treatment are further combined, so that the damage effect of addition of the bean dregs on a gel network of the dried bean curd can be more effectively repaired, and the hardness, cohesiveness, chewiness and other quality indexes of the bean dreg reinforced dried bean curd are close to or even reach the level of a control group without addition of the bean dregs; the high-value utilization of the bean dreg byproducts is realized.

Description

Technical Field

[0001] This invention relates to the field of food processing technology, and in particular to a high-dietary-fiber dried bean curd and its preparation method. Background Technology

[0002] Dried tofu, a significant representative of traditional Chinese soy products, is a typical salt-coated protein gel food with a wide consumer base and market recognition. However, a large amount of soybean residue generated during soy product processing suffers from defects such as large particle size, coarse texture, and low sensory appeal, leading to its mostly being used as animal feed or disposed of as waste, resulting in serious resource waste. Soybean residue is rich in dietary fiber (40-50%), protein (25-30%), and bioactive substances such as isoflavones, and its high-value utilization has become an important research direction in the field of food science.

[0003] With the increasing public awareness of nutrition and health and the development of functional food science, the market demand for fiber-rich foods has shown a significant growth trend. Dietary fiber has multiple physiological regulatory functions, including regulating blood lipid metabolism, improving blood glucose homeostasis, and promoting intestinal microecological balance. At present, high-fiber tofu products on the market mainly rely on exogenous dietary fiber (such as konjac flour and oat fiber) for nutritional fortification. However, exogenous fiber raw materials are expensive and have limited compatibility with the soy protein system, which restricts their large-scale application in soy products. In contrast, soybean residue, as an endogenous by-product of soy product processing, is not only cost-effective but also has natural molecular compatibility with soy protein, showing significant application potential in the development of fiber-rich tofu. However, how to overcome the negative effects of soybean residue addition on product quality and realize the functional application of soybean residue in soy products remains a key technical bottleneck that urgently needs to be overcome.

[0004] Physical processing techniques have shown promising application prospects and theoretical value in improving the gel properties of proteins. For example, moderate heat treatment is beneficial for the construction of a three-dimensional gel network of soybean protein molecules; ultrasonic treatment significantly enhances the emulsifying and foaming properties of soybean protein, and so on. However, research on applying physical processing techniques to soybean residue-fortified soy products is still relatively limited, which to some extent restricts the industrial application of soybean residue in high-quality soy products. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a high-dietary-fiber dried bean curd and its preparation method.

[0006] To address the negative effects of soybean residue addition on the gel properties of dried bean curd, this invention employs ultrafine grinding technology to refine soybean residue particles to the micron level (average particle size 56 μm), and further combines this with appropriate heat treatment, ultrasonic treatment, and their combined treatment to regulate the quality of soybean residue-enhanced dried bean curd. It was found that ultrafine grinding combined with appropriate heat treatment and / or ultrasonic technology can effectively repair the destructive effect of soybean residue addition on the gel network of dried bean curd, making the quality indicators of soybean residue-enhanced dried bean curd, such as hardness, cohesion, and chewiness, approach or even reach the levels of the control group without soybean residue. This realizes the nutritional fortification function of soybean residue in soy products, providing a theoretical basis and technical support for the high-value utilization of soybean residue by-products and the development of dietary fiber-rich dried bean curd products.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a method for preparing high-dietary-fiber dried bean curd, comprising the following steps: S1. Soak soybeans in water until softened, drain the water, and mix the softened soybeans with water. Grind them into a paste and separate the raw soybean milk and soybean residue. The soybean residue is then ultra-finely pulverized, sieved, and made into soybean residue powder with a particle size of microns. S2. Mix the soybean residue powder obtained in step S1 with raw soybean milk, heat the mixture to cook it, and then coagulate the cooked mixture to obtain tofu pudding. Press the mixture to remove water and obtain high dietary fiber tofu.

[0008] This invention utilizes raw soy milk mixed with soy pulp with micron-sized particles to prepare dried tofu. Compared to mixing cooked soy milk with soy pulp, the dried tofu prepared by this invention can better maintain the hardness and elasticity of the soy pulp gel. The soy pulp particles form a tighter internal connection with the protein matrix, resulting in a more compact and reasonable gel network structure. This allows for better water retention while achieving a more suitable moisture distribution, resulting in better chewiness and an overall better taste.

[0009] In a preferred embodiment of the preparation method described in this invention, in step S1, the raw soy milk has a protein content of 7.76~8.24 g / 100 g and a pH value of 6.4~6.8. This protein content is sufficient to form higher quality dried soy.

[0010] In a preferred embodiment of the preparation method of the present invention, in step S1, the mass ratio of the softened soybeans to water is 1:4.5~5.5.

[0011] In a preferred embodiment of the preparation method described in this invention, the mass ratio of softened soybeans to water is 1:5.

[0012] In a preferred embodiment of the preparation method of the present invention, in step S1, the average particle size of the soybean residue powder is 50~60μm, preferably 56μm.

[0013] In a preferred embodiment of the preparation method described in this invention, in step S2, the ratio of soybean residue powder to raw soybean milk is 8-12 g:1 L. Preferably, it is 10 g:1 L.

[0014] In a preferred embodiment of the preparation method of the present invention, in step S2, the ripening conditions are 95~100℃ for 30 min.

[0015] As a preferred embodiment of the preparation method of the present invention, in step S2, the "making brain" involves cooling the cooked mixture to 80-85°C, adding MgCl2 (0.4g / 100mL based on the volume of raw soy milk), and keeping it warm for 30 minutes.

[0016] As a preferred embodiment of the preparation method of the present invention, in step S2, the conditions for pressing and dehydration are pressing for 120 min at a pressure of 0.5 MPa.

[0017] In a preferred embodiment of the preparation method of the present invention, in step S2, the mixture is subjected to moderate heating and / or ultrasonic treatment before heating and maturation; the temperature of the moderate heating treatment is 30~50℃; and the ultrasonic power of the ultrasonic treatment is 200~400W.

[0018] In a preferred embodiment of the preparation method described in this invention, in step S2, the temperature of the moderate heating treatment is 40~45℃; and the ultrasonic power of the ultrasonic treatment is 300~350W.

[0019] In a preferred embodiment of the preparation method of the present invention, in step S2, the temperature of the moderate heating treatment is 45°C; and the ultrasonic power of the ultrasonic treatment is 350W.

[0020] In a preferred embodiment of the preparation method of the present invention, in step S2, the time for the appropriate heating treatment is 25~35 min.

[0021] In a preferred embodiment of the preparation method of the present invention, in step S2, the temperature of the ultrasonic treatment is 10~20℃; the time of the ultrasonic treatment is 25~35min; and the pulse mode of the ultrasonic treatment is 2 seconds on and 2 seconds off.

[0022] Secondly, the present invention provides high-dietary-fiber dried bean curd prepared using the above-described preparation method.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention utilizes a mixture of raw soy milk and ultra-finely pulverized soybean residue powder (down to the micron level) to prepare dried tofu. Compared to using cooked soy milk and soybean residue, the dried tofu produced by this invention better maintains its firmness and the elasticity of its gel. The soybean residue particles form a tighter internal connection with the protein matrix, resulting in a more compact and rational gel network structure. This allows for better water retention while achieving a more suitable moisture distribution, resulting in superior chewiness and an overall better taste. Furthermore, by combining appropriate heat treatment, ultrasonic treatment, and their combined treatments, the destructive effect of soybean residue addition on the dried tofu's gel network can be effectively repaired. This allows the quality indicators of soybean residue-fortified dried tofu, such as firmness, cohesion, and chewiness, to approach or even reach the levels of the control group without soybean residue. This invention realizes the nutritional fortification function of soybean residue in soy products, providing a theoretical basis and technical support for the high-value utilization of soybean residue by-products and the development of dietary fiber-rich dried tofu products. Attached Figure Description

[0024] Figure 1 The images shown are actual pictures of dried tofu from Embodiments 1, 2, 7, 12 and Comparative Examples 1 and 3 of the present invention. a represents Comparative Example 1, b represents Comparative Example 3, c represents Embodiment 1, d represents Embodiment 7, e represents Embodiment 2, and f represents Embodiment 12. Figure 2 SEM images of dried tofu from Examples 1, 2, 7, 12 and Comparative Examples 1 and 3 of the present invention are shown. a represents Comparative Example 1, b represents Comparative Example 3, c represents Example 1, d represents Example 7, e represents Example 2, and f represents Example 12. Figure 3 The bar chart shows the hardness and chewiness of the dried tofu in Examples 1, 2, 7, 12 and Comparative Examples 1-2 of the present invention. Figure 4 This is a bar chart showing the moisture content of dried tofu in Examples 1, 2, 7, 12 and Comparative Examples 1-2 of the present invention. Detailed Implementation

[0025] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0026] Unless otherwise specified, all other materials and reagents used in the examples are commercially available.

[0027] Example 1 An embodiment of the present invention provides a high-dietary-fiber dried bean curd. The preparation method of this high-dietary-fiber dried bean curd includes the following steps: S1. Soak soybeans in water (soybean to water mass ratio of 1:3) for 12 hours to soften them. Drain the softened soybeans and mix them with water (softened soybean to water mass ratio of 1:5), then grind them into a paste. Separate the paste (filter through 80-mesh gauze) to obtain raw soy milk and soy pulp. Grind the obtained soy pulp into ultrafine powder, sieve it, and obtain soy pulp powder with an average particle size of 56μm. The raw soy milk has a protein content of 8.0±0.24 g / 100 g and a pH of 6.6±0.2. S2. Mix the soybean residue powder obtained in step S1 with raw soybean milk at a ratio of 10g:1L. Heat the mixture to 95℃ and keep it for 30 minutes to mature. After the matured mixture is cooled to 85℃, slowly add MgCl2 (0.4g / 100mL based on the volume of raw soybean milk). Keep it at 80℃ for 30 minutes to coagulate. Place the resulting tofu curd in a tofu mold and press it under 0.5MPa pressure for 120 minutes to remove water, thus obtaining high dietary fiber tofu curd.

[0028] Example 2 This invention provides an embodiment of a high-fiber tofu product. The difference between this embodiment and Embodiment 1 lies only in step S2 of the preparation method. In this embodiment, step S2 includes ultrasonic treatment. The preparation method of this high-fiber tofu product includes the following steps: S1, same as step S1 in Example 1; S2. Mix the soybean residue powder obtained in step S1 with raw soybean milk at a ratio of 10g:1L. Sonicate the mixture under the following conditions: 10~20℃, 350W for 1800 s, pulse mode: 2 s on, 2 s off. Heat the ultrasonically treated mixture to 95℃ and keep it for 30 min to mature. After the matured mixture is cooled to 85℃, slowly add MgCl2 (0.4g / 100mL based on the volume of raw soybean milk) and keep it at 80℃ for 30 min to coagulate. Place the resulting tofu curd in a tofu mold and press it under 0.5 MPa pressure for 120 min to obtain high dietary fiber tofu curd.

[0029] Examples 3-6 This invention provides four embodiments of a high-fiber dried bean curd. The difference between Embodiments 3-6 and Embodiment 2 lies only in the ultrasonic power used in step S2 of the preparation method; specifically, Example 3: Compared with Example 2, the ultrasonic power in step S2 of the preparation method in Example 2 was adjusted from 350W to 200W to prepare high dietary fiber dried bean curd; Example 4: Compared with Example 2, the ultrasonic power in step S2 of the preparation method in Example 2 was adjusted from 350W to 250W to prepare high dietary fiber dried bean curd; Example 5: Compared with Example 2, the ultrasonic power in step S2 of the preparation method in Example 2 was adjusted from 350W to 300W to prepare high dietary fiber dried bean curd; Example 6: Compared with Example 2, the ultrasonic power in step S2 of the preparation method in Example 2 was adjusted from 350W to 400W to prepare high dietary fiber dried bean curd.

[0030] Example 7 This invention provides an embodiment of a high-fiber tofu product. The difference between this embodiment and Embodiment 1 lies only in step S2 of the preparation method. In this embodiment, step S2 includes an additional moderate heating treatment. The preparation method of this high-fiber tofu product includes the following steps: S1, same as step S1 in Example 1; S2. Mix the soybean residue powder obtained in step S1 with raw soybean milk at a ratio of 10g:1L. Heat the mixture in a water bath at 45℃ for 30 minutes for moderate heating treatment. After moderate heating treatment, heat the mixture to 95℃ and keep it at 30 minutes for maturation. After maturation, cool the mixture to 85℃ and slowly add MgCl2 (0.4g / 100mL based on the volume of raw soybean milk). Keep it at 80℃ for 30 minutes for coagulation. Place the resulting tofu curd in a tofu mold and press it under a pressure of 0.5 MPa for 120 minutes to obtain high dietary fiber tofu curd.

[0031] Examples 8-11 This invention provides four embodiments of a high-fiber tofu product. Embodiments 8-11 differ from Embodiment 7 only in the temperature of the moderate heating treatment in step S2 of the preparation method; specifically, Example 8: Compared with Example 7, the heating temperature of moderate heating treatment in step S2 of the preparation method in Example 7 was adjusted from 45°C to 30°C to prepare high dietary fiber dried bean curd; Example 9: Compared with Example 7, the heating temperature of moderate heating treatment in step S2 of the preparation method in Example 7 was adjusted from 45°C to 35°C to prepare high dietary fiber dried bean curd; Example 10: Compared with Example 7, the heating temperature of moderate heating treatment in step S2 of the preparation method in Example 7 was adjusted from 45°C to 40°C to prepare high dietary fiber dried bean curd; Example 11: Compared with Example 7, the heating temperature of moderate heating treatment in step S2 of the preparation method in Example 7 was adjusted from 45°C to 50°C to prepare high dietary fiber dried bean curd.

[0032] Example 12 This invention provides an embodiment of a high-fiber tofu product. The difference between this embodiment and Embodiment 7 lies only in step S2 of the preparation method. In this embodiment, step S2 includes ultrasonic treatment. The preparation method of this high-fiber tofu product includes the following steps: S1, same as step S1 in Example 1; S2. Mix the soybean residue powder obtained in step S1 with raw soybean milk at a ratio of 10g:1L. Heat the resulting mixture in a water bath at 45℃ for 30 minutes for moderate heating treatment. After moderate heating treatment, the mixture is then ultrasonically treated under the following conditions: 10~20℃, 350 W for 1800 s, pulse mode: 2 s on, 2 s off. The ultrasonically treated mixture is then heated to 95℃ and kept at 30 minutes for maturation. After maturation, the mixture is cooled to 85℃ and MgCl2 is slowly added (0.4g / 100mL based on the volume of raw soybean milk). The mixture is then kept at 80℃ for 30 minutes for curdling. The resulting curd is placed in a tofu mold and pressed under 0.5 MPa pressure for 120 minutes to obtain high dietary fiber tofu.

[0033] Examples 13-16 This invention provides four embodiments of a high-fiber tofu product. Embodiments 13-16 differ from Embodiment 12 only in the ultrasonic power used in step S2 of the preparation method; specifically, Example 13: Compared with Example 12, the ultrasonic power in step S2 of the preparation method in Example 12 was adjusted from 350W to 200W to prepare high dietary fiber dried bean curd; Example 14: Compared with Example 12, the ultrasonic power in step S2 of the preparation method in Example 12 was adjusted from 350W to 250W to prepare high dietary fiber dried bean curd; Example 15: Compared with Example 12, the ultrasonic power in step S2 of the preparation method in Example 12 was adjusted from 350W to 300W to prepare high dietary fiber dried bean curd; Example 16: Compared with Example 12, the ultrasonic power in step S2 of the preparation method in Example 12 was adjusted from 350W to 400W to prepare high dietary fiber dried bean curd.

[0034] Examples 17-20 This invention provides four embodiments of a high-fiber tofu product. Embodiments 13-16 differ from Embodiment 12 only in the temperature of the moderate heating treatment in step S2 of the preparation method; specifically, Example 17: Compared with Example 12, the heating temperature of moderate heating treatment in step S2 of the preparation method in Example 12 was adjusted from 45°C to 30°C to prepare high dietary fiber dried bean curd; Example 18: Compared with Example 12, the heating temperature of moderate heating treatment in step S2 of the preparation method of Example 12 was adjusted from 45°C to 35°C to prepare high dietary fiber dried bean curd; Example 19: Compared with Example 12, the heating temperature of moderate heating treatment in step S2 of the preparation method of Example 12 was adjusted from 45°C to 40°C to prepare high dietary fiber dried bean curd; Example 20: Compared with Example 12, the heating temperature of moderate heating treatment in step S2 of the preparation method in Example 12 was adjusted from 45°C to 50°C to prepare high dietary fiber dried bean curd.

[0035] Comparative Example 1 This invention provides a comparative example of high-dietary-fiber dried tofu. The difference between this comparative example and Example 1 is that no soybean residue powder is added. The preparation method of this comparative example of dried tofu includes the following steps: S1. Soak soybeans in water (the mass ratio of soybeans to water is 1:3) for 12 hours to soften them. After draining the water, mix the softened soybeans with water (the mass ratio of softened soybeans to water is 1:5) and grind them into a paste. Separate the paste (filter through 80-mesh gauze) to obtain raw soy milk and soy pulp. S2. Heat the raw soy milk obtained in step S1 to 95℃ and keep it for 30 min to mature. After the matured soy milk is cooled to 85℃, slowly add MgCl2 (0.4g / 100mL based on the volume of raw soy milk), keep it at 80℃ for 30 min to coagulate. Place the resulting tofu curd in a tofu mold and press it under 0.5 MPa pressure for 120 min to remove water, thus obtaining tofu curd.

[0036] Comparative Example 2 This invention provides a comparative example of high-fiber tofu. The only difference between this comparative example and Example 1 is the cooking step. The preparation method of this comparative example of high-fiber tofu includes the following steps: S1, same as step S1 in Example 1; S2. Heat the raw soy milk obtained in step S1 to 95℃ and keep it for 30 minutes to cook it, so as to obtain cooked soy milk. Mix the soybean residue powder obtained in step S1 with the cooked soy milk in a ratio of 10g:1L. After the mixture is cooled to 85℃, slowly add MgCl2 (0.4g / 100mL based on the volume of raw soy milk). Keep it at 80℃ for 30 minutes to coagulate. Place the resulting tofu curd in a tofu mold and press it under 0.5 MPa pressure for 120 minutes to remove water, so as to obtain high dietary fiber tofu.

[0037] Comparative Example 3 This invention provides a comparative example of high dietary fiber dried bean curd. The only difference between this comparative example and Example 1 is the particle size of the bean curd residue powder. The bean curd residue powder in this comparative example is not ultra-finely ground and is directly obtained from the separation of bean curd residue.

[0038] Test Example 1 Actual images of the dried tofu from Examples 1, 2, 7, 12 and Comparative Examples 1 and 3 are shown below. Figure 1 As shown, a represents Comparative Example 1, b represents Comparative Example 3, c represents Example 1, d represents Example 7, e represents Example 2, and f represents Example 12.

[0039] The microstructure of the dried tofu from Examples 1, 2, 7, 12 and Comparative Examples 1, 3 was observed using scanning electron microscopy, and tests were performed accordingly. SEM images of the dried tofu from Examples 1, 2, 7, 12 and Comparative Examples 1, 3 are shown below. Figure 2 As shown, a represents Comparative Example 1, b represents Comparative Example 3, c represents Example 1, d represents Example 7, e represents Example 2, and f represents Example 12. The results show that all samples exhibit a typical "porous network structure," but with significantly different pore distribution characteristics and network density. The bean curd in Comparative Example 1 exhibits a relatively uniform and dense protein network structure with regular pore distribution and moderate size. Comparative Example 3, with the addition of un-ultra-finely ground soybean residue, exhibits an extremely uneven and loose network structure, characterized mainly by large pores and structural defects. In Example 1, with the addition of ultra-finely ground soybean residue, the network pores of the bean curd are smaller and more uniformly distributed than those in Comparative Example 3, indicating that ultra-fine grinding effectively improves structural integrity. The bean curd in Examples 2 and 7 further exhibit a denser network architecture with significantly reduced pore size. The bean curd in Example 12 has the most dense and uniform network structure, with a highly regular pore distribution, almost identical to the structural characteristics of Comparative Example 1.

[0040] Test Example 2 Using the dried tofu samples from Examples 1-20 and Comparative Examples 1-2 as samples, the texture, water holding capacity (WHC), and moisture content of the samples were tested.

[0041] 1. Texture includes hardness, elasticity, cohesiveness, and chewiness. Texture profile analysis (TPA) of dried bean curd was performed using a texture analyzer (TA-XT plus, Stable MicroSystems, UK).

[0042] The samples were cut into 2.5 cm × 2.5 cm × 1.0 cm cubes and measured using a P36R cylindrical probe at room temperature (25 ℃). Test parameters: initial velocity 2 mm / s, test velocity 1 mm / s, post-test velocity 2 mm / s, compression degree 40%, trigger force 5 g. Five test points were randomly selected for each sample, and the average value was taken. Hardness, elasticity, cohesion, and chewiness were measured, where hardness was the maximum force value during the first compression process. Elasticity refers to the sample's ability to recover its initial shape and size after the first compression deformation, expressed as the ratio of the recovered height to the deformed height, with a value of 0~1 and no unit. Cohesion is the ratio of the area of ​​the second compression peak to the area of ​​the first compression peak, and chewiness is the product of hardness, elasticity, and cohesion.

[0043] 2. Water Holding Capacity (WHC) Weigh a certain mass of dried bean curd sample (m1) and centrifuge at 4℃ and 10000 rpm for 10 min. After removing surface moisture with filter paper, weigh the sample (m2) and then dry it in a drying oven at 105℃ for 6 h until constant weight (m3). The water holding capacity (WHC) is calculated using the formula: WHC (%) = [(m2-m3) / (m1-m3)]*100.

[0044] 3. Moisture content Place the dried bean curd sample on filter paper and record the total mass (M1) of the sample and filter paper before drying, as well as the mass of the filter paper (M3). Dry the sample in a 105℃ oven for 4 hours to constant weight, then cool it in a desiccator for 0.5 hours and weigh it (M2). The moisture content (X) is calculated using the formula: X(%) = [(M1-M2) / (M1-M3)]*100.

[0045] The test results of hardness, elasticity, cohesiveness, chewiness, water holding capacity, and moisture content of the dried bean curd in Examples 1-20 and Comparative Examples 1-2 are shown in Table 1. The bar charts for the hardness and chewiness of the dried bean curd in Examples 1, 2, 7, 12, and Comparative Examples 1-2 are shown in Table 1. Figure 3 As shown in the bar chart, the moisture content of the dried tofu in Examples 1, 2, 7, 12 and Comparative Examples 1-2 is represented as follows. Figure 4 As shown, Table 1 According to Table 1, Example 1 and Comparative Examples 1 and 2, the dried bean curd from Comparative Example 1 had the highest hardness (9310.30 g), indicating that the sample prepared using the standard process without adding soybean residue formed the densest protein gel network. The dried bean curd prepared with raw slurry and soybean residue in Example 1 had a higher hardness than the dried bean curd prepared with cooked slurry and soybean residue in Comparative Example 2, suggesting that adding raw slurry is more beneficial for maintaining product hardness. This may be because when soybean residue is added to raw slurry, the protein has not yet denatured, allowing the soybean residue particles to be gradually embedded and integrated into the gel network during subsequent heating; while in cooked slurry, the protein has already denatured to form a network structure, making it difficult for subsequently added soybean residue to effectively integrate, thus disrupting the network's continuity. The dried bean curd from Comparative Example 1 had the highest elasticity (0.956), and the elasticity of the dried bean curd from Example 1 was higher than that of Comparative Example 2, indicating that adding soybean residue to raw slurry better maintains the gel's resilience. The cohesion also showed the same trend: the cohesion of the tofu in Comparative Example 1 was 0.872, while the cohesion of the tofu in Example 1 was higher than that in Comparative Example 2, indicating that adding soybean residue to the raw slurry helps the soybean residue particles form a tighter internal connection with the protein matrix. The tofu in Comparative Example 1 had the highest chewiness (7761.36), while the tofu in Example 1 had a higher chewiness than that in Comparative Example 2, demonstrating the advantage of adding soybean residue to the raw slurry in maintaining the overall taste of the product. The water holding capacity of the tofu in Example 1 (85.76%) was comparable to that of Comparative Example 2 (86.5%), but the water content was significantly lower, indicating that the gel network structure formed by adding soybean residue to the raw slurry in Example 1 was more compact and reasonable, achieving a more suitable moisture distribution while maintaining good water holding performance. Comprehensive analysis shows that the method of adding soybean residue to the raw slurry in Example 1 has significant advantages in the preparation of soybean residue-fortified tofu; it is the preferred process route for the production of soybean residue-fortified tofu. In the process of preparing dried bean curd by adding soybean residue to raw soy milk, soybean residue particles and proteins are dynamically integrated. Undenatured proteins gradually form a gel network during heating, and soybean residue particles are effectively embedded and well combined through intermolecular forces to form a continuous and uniform composite gel structure.

[0046] As shown in Examples 1 and 2-6, ultrasonic treatment can improve the hardness of dried bean curd. The hardness of the dried bean curd gradually increases with the increase of ultrasonic power (from 200W to 350W). When the ultrasonic power is 350W, the hardness reaches a peak of 8439.94g, which is 22.0% higher than that of Example 1 without ultrasonic treatment. Ultrasonic treatment can effectively maintain the viscoelastic properties of the product. With the increase of power, the elasticity of the dried bean curd shows a trend of first slightly increasing and then decreasing. The highest value of 0.952 is reached at the power of 350W, and the elasticity drops back to 0.947 at the power of 400W, but it is still better than that of Example 1. Ultrasonic treatment can improve the cohesiveness of dried bean curd, and the cohesiveness shows a continuous improvement trend with the increase of ultrasonic power. The cohesiveness of the tofu in Example 1 was 0.795. Cohesiveness increased with increasing ultrasonic power (200W-350W), reaching a maximum of 0.825 at 350W, a 3.8% increase compared to Example 1. This indicates that 350W ultrasonic treatment most effectively promotes the formation of intermolecular protein interactions and enhances the internal binding strength of the gel network. Ultrasound can improve the chewiness of the tofu, showing a significant dose-response relationship. The chewiness of the tofu in Example 1 was 5076.3, increasing with increasing ultrasonic power (200W-350W), reaching a maximum of 6628.73 at 350W, a 30.58% increase compared to Example 1. When the power was further increased to 400W, the chewiness decreased, but remained higher than that of Example 1. Ultrasonic treatment significantly improved the water-holding capacity of dried tofu. The WHC of the dried tofu in Example 1 was 85.76. The WHC increased with increasing ultrasonic power (200W-350W), reaching a maximum of 87.72% at 350W, an increase of 2.3% compared to Example 1. This indicates that the protein network formed at this power was the densest, most complete, and most uniform and stable, with the strongest water-binding ability. As the power continued to increase to 400W, the WHC dropped back to 86.95. The change in moisture content showed an opposite but highly correlated trend with WHC. The moisture content of the dried tofu in Example 1 was 67.85%. The moisture content showed a continuous and significant decrease with increasing ultrasonic power (200W-350W), and rebounded to 64.68% (-4.7%) at 400W. This change corresponded to the decrease in WHC. Comprehensive analysis shows that adding ultrafine pulverized soybean residue powder to raw soy milk, combined with appropriate ultrasonic treatment, can promote the moderate unfolding and rearrangement of protein molecules, forming a more stable three-dimensional gel network, thus giving the dried tofu good textural properties and structural stability. Using 350W ultrasonic treatment can better achieve dietary fiber fortification while effectively reducing the adverse effects of fiber components on the protein gel structure, achieving an organic unity of texture and nutrition.

[0047] According to Examples 1 and 7-11, compared with Example 1 (6917.97g), the hardness of the dried bean curd showed a trend of first increasing and then decreasing with increasing processing temperature. At 45℃, the hardness of the dried bean curd reached a peak of 8295.57g, an increase of 19.9% ​​compared to Example 1, indicating that the protein reached its optimal denaturation level at this temperature. The elasticity of the dried bean curd in Example 1 was 0.923, and the elasticity value fluctuated slightly with increasing temperature; the elasticity values ​​of the dried bean curd in Examples 7-11 remained at a relatively high level of 0.938-0.947, indicating that temperature treatment had a relatively small impact on the product's rebound properties; the dried bean curd in Examples 7-11 maintained good viscoelastic properties within the temperature range. The cohesiveness of the dried bean curd in Example 1 was 0.795, and with increasing temperature, the cohesiveness showed a trend of first increasing and then decreasing, reaching a maximum value of 0.818 at 45℃. This indicates that moderate heat treatment promoted the formation of non-covalent bonds such as hydrogen bonds and hydrophobic interactions between protein molecules, enhancing the internal binding force of the gel network. The trend of chewiness changes is highly consistent with the hardness. The chewiness of the tofu in Example 1 was 5076.3, which first increased and then decreased with increasing temperature, reaching a maximum value of 6398.99 at 45℃, an increase of 26.1% compared to Example 1. This indicates that the protein network structure formed at this temperature is the most complete, giving the product the best chewy texture. The WHC of the tofu in Example 1 was 85.76%, which showed a trend of first increasing and then decreasing with increasing temperature, reaching a peak of 87.24% at 45℃. The moisture content of the tofu in Example 1 was 67.85%, which showed a trend of first decreasing and then increasing with increasing temperature, reaching a minimum value of 65.89% at 45℃, corresponding to the trend of WHC. Comprehensive analysis shows that temperature treatment affects the textural properties of tofu, as well as WHC and moisture content, by regulating the degree of protein denaturation. In the range of 30-45℃, with increasing temperature, protein molecules gradually unfold, exposing more active groups, promoting the formation of intermolecular interactions, thereby constructing a stronger three-dimensional gel network. 45℃ represents the optimal processing temperature. Under this condition, proteins reach their best denaturation state, all texture parameters reach their peak values, and WHC reaches its peak while moisture content drops to its lowest level. This indicates that the protein network formed at this temperature is the most dense and complete, effectively retaining moisture while preventing excessive free water from affecting the product's texture. However, when the temperature exceeds the optimal point and rises to 50℃, excessive heat input causes excessive aggregation of protein molecules and network contraction, destroying the original ordered structure and significantly deteriorating texture properties. Although moisture increases, it cannot be effectively bound, leading to a decrease in water-holding capacity. Therefore, 45℃ is the optimal process parameter for temperature processing.

[0048] As demonstrated in Examples 1, 7, and 12-20, compared to ultrasonic treatment or heat treatment alone, ultrasonic treatment combined with heat treatment can further improve the textural properties of dried bean curd. Appropriate ultrasonic treatment combined with heat treatment can promote the unfolding and orderly aggregation of protein molecules, thereby strengthening the gel network structure and promoting the formation of a more ideal three-dimensional gel network with a reasonable pore distribution and stronger water binding capacity. With an ultrasonic power of 350W and a heat treatment temperature of 45℃, the dried bean curd sample achieved optimal results in key textural indicators such as hardness, cohesion, and chewiness while maintaining good elasticity, highest water holding capacity, and lowest moisture content. These conditions represent the best conditions for proteins to reach their optimal denaturation state and form an ideal gel network structure.

[0049] The above results indicate that moderate heating and / or ultrasonic treatment of soybean milk with added ultrafine soybean residue powder can effectively disperse soybean residue particles in the protein matrix and enhance the network structure; the combination of moderate heating and ultrasonic treatment is better than moderate heating or ultrasonic treatment alone. This may be because the physical treatment of the soybean residue-soybean milk system improves the conformational flexibility of protein molecules, promotes the interaction between proteins and soybean residue particles, restricts the irregular migration of water molecules in the network, and enhances the network stability of the composite gel. Optimization of the soybean residue-soybean milk mixture improves the cross-linking density and spatial arrangement between protein molecules, helping to maintain a more complete microstructure, thus making the gel network structure of the dried tofu more dense and uniform.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing high-dietary-fiber dried bean curd, characterized in that, Includes the following steps: S1. Soak soybeans in water until softened, drain the water, and mix the softened soybeans with water. Grind them into a paste and separate the raw soybean milk and soybean residue. The soybean residue is then ultra-finely pulverized, sieved, and made into soybean residue powder with a particle size of microns. S2. Mix the soybean residue powder obtained in step S1 with raw soybean milk, heat the mixture to cook it, and then coagulate the cooked mixture to obtain tofu pudding. Press the mixture to remove water and obtain high dietary fiber tofu.

2. The preparation method according to claim 1, characterized in that, In step S1, the raw soy milk has a protein content of 7.76~8.24g / 100g and a pH value of 6.4~6.

8.

3. The preparation method according to claim 1, characterized in that, In step S1, the mass ratio of the softened soybeans to water is 1:4.5~5.5; And / or, in step S1, the average particle size of the soybean residue powder is 50~60μm.

4. The preparation method according to claim 1, characterized in that, In step S2, the ratio of soybean residue powder to raw soybean milk is 8~12g:1L.

5. The preparation method according to claim 1, characterized in that, In step S2, the curing conditions are 95~100℃ for 30 min; And / or, in step S2, the "point-braised" step involves cooling the cooked mixture to 80-85°C, adding MgCl2, and keeping it warm for 30 minutes.

6. The preparation method according to claim 1, characterized in that, In step S2, the mixture is first subjected to moderate heating treatment before heating and maturation; the temperature of the moderate heating treatment is 30~50℃.

7. The preparation method according to claim 1, characterized in that, In step S2, the mixture is ultrasonically treated before heating and cooking; the ultrasonic power of the ultrasonic treatment is 200~400W.

8. The preparation method according to claim 1, characterized in that, In step S2, the mixture is subjected to moderate heating and ultrasonic treatment before heating and maturation; the temperature of the moderate heating treatment is 30~50℃; the ultrasonic power of the ultrasonic treatment is 200~400W.

9. The preparation method according to any one of claims 6 to 7, characterized in that, The temperature for the appropriate heat treatment is 40~45℃; And / or, the ultrasonic power of the ultrasonic treatment is 300~350W; And / or, the duration of the appropriate heat treatment is 25-35 minutes; And / or, the temperature of the ultrasonic treatment is 10~20℃; And / or, the duration of the ultrasonic treatment is 25-35 minutes; And / or, the pulse mode of the ultrasonic treatment is 2 seconds on and 2 seconds off.

10. High-dietary-fiber dried tofu prepared by any one of claims 1 to 9.

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