Preparation method of high-dietary-fiber bean curd based on high-temperature pressure treatment

Abstract

The invention discloses a preparation method of high-dietary-fiber bean curd based on high-temperature pressure treatment. The preparation method comprises the following steps: performing superfine grinding on peeled soybeans to obtain peeled soybean powder; adding the peeled soybean powder into water, and heating to complete soybean milk boiling; adding a compound coagulator into the soybean milk, uniformly stirring, and then putting the soybean milk into a high-temperature pressurized digester for secondary heating to obtain a bean curd blank; placing the bean curd blank in cold water for standing, cooling and shaping to obtain the high-dietary-fiber bean curd; the compound coagulator is prepared from glucolactone and glutamine transaminase. According to the method, the peeled soybeans are subjected to superfine grinding and then boiled, the soybean milk is solidified by adopting the compound coagulant, and secondary high-temperature pressurizing treatment is performed after the compound coagulant is added, so that the hardness of the bean curd is improved, the content of insoluble dietary fibers in the bean curd is remarkably reduced, and the content of soluble dietary fibers in the bean curd is remarkably increased; the conversion from insoluble dietary fibers to soluble dietary fibers is promoted.

Description

Technical Field

[0001] The invention relates to the technical field of bean product food processing, and in particular to a preparation method of high-dietary fiber tofu based on high-temperature pressure treatment. Background Art

[0002] Soybeans are rich in protein, fat, dietary fiber and bioactive substances, and are loved by people for their excellent nutritional value. Soybeans are mainly used as soy products such as tofu, soy milk and bean curd skin, but a large amount of dregs will be produced during the production process. Bean dregs have a high water content and are difficult to handle. They are often discarded as feed or waste and cannot be used at a high value, resulting in a waste of resources. In the process of making tofu, if the dregs can be preserved, the material utilization rate and nutritional value of soybeans can be greatly improved. Wang Chenzhi et al. used three pulping techniques to prepare whole soybean tofu and found that tofu prepared by ultrafine grinding of soybean powder had a sensory score comparable to that of traditional tofu. Fine grinding of soybeans or soy milk can significantly reduce particles and help improve the quality of tofu.

[0003] The tofu preparation methods in the prior art mostly include the steps of pulping, boiling and coagulation.

[0004] For example, document 1: CN 112641049 A A soy product soybean peanut tough lactone tofu processing technology document 1 discloses the following preparation method:

[0005] S1. Cleaning: Take soybeans and peanuts, remove the shells and sieve them. The weight of soybeans is 3 to 5 times the weight of peanuts. Clean the dust on the surface of soybeans and remove the red skin on the surface of peanuts.

[0006] S2. Soaking, soaking soybeans and peanuts separately in water, wherein the amount of water used for soaking soybeans is generally 1:2.5-3.5 by weight of soybeans to water, and the amount of water used for soaking peanuts is generally 1:3-5 by weight of soybeans to water;

[0007] S3, grinding, taking out the soaked soybeans and peanuts, grinding them in a soybean to water weight ratio of 1:6-7 to form soybean slurry, and grinding them in a peanut to water weight ratio of 1:5-6.5 to form peanut slurry;

[0008] S4, boiling the slurry, pouring the filtered soybean slurry and peanut slurry into the pot in turn, with the ratio of soybean slurry to peanut slurry being 5-7:1, skimming the foam on the surface of the slurry during the boiling process, and stirring and mixing the slurry clockwise by a stirring rod, heating the slurry to 100° during the boiling process to make the slurry boil, and cooling the boiled slurry to 35°;

[0009] S5, adding brine, adding 400g warm water to gluconolactone and mixing evenly, the weight ratio of gluconolactone to the mixed slurry is 0.03-0.06:1, adding the mixed brine to the cooled slurry, slowly stirring the slurry with a stirring rod, and letting it stand for 15 minutes to form tofu pudding;

[0010] S6, extrusion molding, put the tofu pudding into the mold and squeeze and dehydrate it with heavy objects to form it.

[0011] Document 2: CN114794387A A method for making special tofu and its formula

[0012] The preparation method disclosed in document 2 comprises the following steps:

[0013] S1. Prepare the raw materials: soybeans, sesame, wolfberry, red dates, clean water, glucose lactone and coagulant; soak the soybeans in water for 6 to 24 hours until they are 2 to 3 times of their original volume, and wash the soaked soybeans in clean water;

[0014] S2. Use a blender to blend sesame, wolfberry, red dates, water and soybeans in proportion until they become a paste, use a centrifuge or filter with gauze to filter out the dregs, and mix well to form soy milk;

[0015] S3. Put the soy milk into a cooking container and heat it over medium heat. Bring the soy milk to a boil and cook for 2-3 minutes. Stir the soy milk with a spoon while heating.

[0016] S4. Take gluconolactone, dissolve it in an appropriate amount of water, quickly add it to the soy milk, and stir it evenly with a spoon, then pour the semi-solidified soy milk into an aluminum container, heat it with steam for 20-25 minutes, the steam heating temperature is 80-90° C., and then cool it again to form tofu pudding;

[0017] S5. Pour the tofu pudding into the tofu mold and press it into shape. Take it out after 10-35 minutes and the tofu will be formed.

[0018] Documents 1 and 2 disclose the most traditional method for preparing tofu, which mainly involves washing and soaking soybeans, grinding them into a slurry, boiling them to form soy milk, and then adding gluconolactone to the soy milk after it is cooled to coagulate it. After coagulation, the milk is allowed to stand to form tofu brain, which is then dehydrated to form tofu.

[0019] In the traditional preparation process of tofu, a long soaking process is often required, resulting in a long soaking time. In order to shorten the process time, there is a method in the prior art of preparing soy milk by crushing soybeans and using soybean powder.

[0020] Document 3: CN115669862A A method for preparing tofu gel rich in soybean isoflavones

[0021] The preparation method disclosed in document 3 comprises the following steps:

[0022] Crushing and leaching: crushing soybeans to obtain soybean powder, and then adding the soybean powder into ethanol leaching solution to obtain a leaching mixture;

[0023] Enzymatic hydrolysis: add β-glucosidase to the leaching mixture for 3-4 hours to obtain an enzymatic hydrolyzate;

[0024] Pulping: Add water to the enzymatic hydrolysate, then adjust the Ph of the enzymatic hydrolysate to 5.5-6 with organic acid, and mix and stir at 40-55°C until homogeneous; then heat to 80-100°C, boil for 10-120 minutes, and obtain soy milk;

[0025] Cooling and solidifying: Add a coagulant to the soy milk, stir evenly, heat at 80-100°C for 10-120 minutes, cool and solidify to obtain tofu gel.

[0026] Document 4: CN1202739C Whole bean residue-free tofu production process

[0027] Document 4 discloses the following method:

[0028] (1) Grinding: Grinding the whole soybean into soybean powder with a particle size of more than 100 mesh;

[0029] (2) Pulping: Pulping is to mix soybean powder with water and stir until homogeneous, with the stirring time ranging from 5 to 40 minutes;

[0030] (3) Heating and boiling the pulp: heating temperature is 80-100°C;

[0031] (4) Stirring: Add the composite coagulant and stir to make the coagulant evenly dispersed in the slurry;

[0032] (5) Heating and standing: heating time 5 to 35 minutes, heating temperature 80 to 100°C.

[0033] Both Document 3 and Document 4 disclose a process of pulping and boiling soybean flour, adding a coagulant gluconolactone, heating the flour to 80°C to 100°C for a second time, and then cooling and coagulating the flour to obtain tofu.

[0034] Document 5: CN116869123A A method for making high-hardness whole bean-filled tofu

[0035] Document 5 discloses the following method:

[0036] (1) Primary slurrying: controlling the temperature of whole soybean milk at 50-55° C., adding magnesium chloride and glutamine transaminase thereto under stirring, and mixing well to obtain primary slurrying soy milk;

[0037] (2) Secondary soy milk: heating the primary soy milk to 63-68°C, then adding gypsum liquid and mixing to obtain secondary soy milk;

[0038] (3) Filling and standing: After the secondary soy milk is filled, control the temperature at 63-68°C and let it stand for 20-30 minutes.

[0039] It can be seen from the specification of Document 5 that the hardness of the tofu in Examples 1 to 3 is between 359 and 372, while the hardness of the tofu in the comparative example is between 10 and 150. This shows that the hardness of tofu can be adjusted according to the process.

[0040] Document 6: CN112772847A A kind of nutritious tofu and its preparation method

[0041] Document 6 discloses the following method:

[0042] S1. Soak the soybeans overnight, add them to a colloid mill, grind them, filter them, remove the dregs, and obtain soy milk;

[0043] S2. After slowly heating the soy milk to 70°C while stirring, add nutrients, keep for 3-4 minutes, continue to heat to 90°C, add stevioside, continue to heat to boiling, and keep for 5-10 minutes;

[0044] S3. Adding yeast to tofu brine, fermenting in a biochemical incubator for 48-74 hours, sterilizing, cooling to room temperature, and obtaining fermented brine;

[0045] S4. The fermented brine is added to the soy milk obtained in step S2, stirred evenly, and the soy milk is coagulated for 20-30min;

[0046] S5. Press the shaped tofu into nutritious tofu, put it into bags, evacuate the bags, and seal them with plastic to obtain nutritious tofu.

[0047] Literature 6 describes a method for cooking soy milk by first boiling the prepared soy milk at 70°C and maintaining the constant temperature for 3-4 minutes to denature part of the protein. Then, when the temperature is heated to 90°C, stevioside (60% by mass of the soy milk) is added and boiled for 5-10 minutes to cause glycosylation, cross-linking and polymerization to occur, thereby forming a soy protein glycosylation complex, which can greatly improve the hardness, elasticity and adhesion of tofu. Compared with traditional tofu, the hardness value is increased from 192.21g to 602.23g.

[0048] In document 6, stevioside is added before adding brine to carry out glycosylation cross-linking polymerization to form a soybean protein glycosylation complex, which greatly improves the hardness of tofu.

[0049] Document 7: CN116349835A Low temperature ripening technology for improving tofu quality

[0050] Document 7 discloses the following method:

[0051] When making packaged tofu, after the cold water cooling process, it is sent to a separate low-temperature aging room and aged at a low temperature (2 to 5°C) for 3 to 168 hours, and the product temperature of the tofu is stabilized below 5°C.

[0052] Document 7 uses a low-temperature ripening method to reduce the hardness deviation of tofu, so as to obtain standardized products with smaller hardness differences; however, low-temperature ripening can only achieve the difference in hardness between tofu products, and cannot improve the hardness of the tofu products when they are prepared.

[0053] Reference 8: Zhang Zhiheng - Research on the effects of different coagulants on the coagulation process of soy milk and the gel properties of tofu - Shanxi Agricultural University.

[0054] Document 8 discloses the following:

[0055] (1) There are three main types of coagulants: salt coagulants, acids

[0056] Coagulants and enzyme coagulants. Different coagulants have different coagulant mechanisms, so the sensory quality of tofu prepared is very different. Salt coagulants are a traditional coagulant. The common salt coagulants on the market are mainly divided into two types: magnesium salts and calcium salts. Commonly used ones are brine (the main component is MgCl2) and gypsum (the main component is Ca2SO4). Tofu made with salt coagulants has a delicious flavor, a high yield but a short storage period; common acid coagulants mainly include gluconolactone acid, and lactone tofu has a delicate structure, a tender taste, and a white color; acid-made tofu has a delicate taste and good water retention; enzyme coagulants commonly used in production include transglutaminase, papain, etc.

[0057] (2) There are different views on the coagulation mechanism of salt coagulants. The first is the ion bridge theory, the second is the salting out theory, and the third is the isoelectric point theory.

[0058] (3) Commonly used acid coagulants include gluconolactone and whey fermentation broth (Physalis). Gluconolactone dissolves in soy milk and releases gluconic acid. Since the H+ release rate is relatively slow, the weakening of the electrostatic repulsion on the protein surface is delayed, and the formation of the protein network structure is relatively slow, which is conducive to the formation of a uniform and delicate structure. Therefore, the lactone tofu produced has the advantages of being refreshing, smooth and delicate in texture, but also has the disadvantages of poor hardness and unsuitability for frying. Compared with gluconolactone, the H+ in whey fermentation broth Physalis exists in the form of organic acids such as lactic acid. The H+ release rate in soy milk is faster, causing the protein to aggregate rapidly. The sensory properties of Physalis tofu and lactone tofu are very different. Physalis tofu has a delicate taste, good water retention, and sweet taste. The yellow pulp wastewater produced can continue to be fermented and used as a new coagulant. Compared with salt coagulants, it avoids the risk of introducing heavy metal ions. Enzyme coagulants are a type of enzyme that can promote the coagulation of soy protein. They can be divided into three categories according to their properties: acidic, alkaline, and neutral. The most commonly used enzyme coagulant is transglutaminase (TG enzyme). Enzyme-catalyzed tofu is similar to renone tofu in processing and appearance, but it is more elastic and less likely to loosen than renone tofu. Compared with salt coagulants and other acid coagulants, the enzyme has a longer action time and relatively mild conditions. The resulting tofu has a more delicate taste, better viscoelasticity, and the aroma of soy milk, without sourness, astringency, or other odors. No heavy metal ions are introduced in the production process. Its disadvantages are high production costs and long coagulation time.

[0059] (4) Reference 8 believes that: the texture of lactone tofu is soft and elastic, and increasing the amount of lactone added during the preparation of lactone tofu can significantly improve the hardness, elasticity and chewiness of tofu. However, from Table 3 of Reference 8 on the effect of lactone addition on the texture of tofu, it can be seen that when the amount of lactone added increases, the degree of improvement in its hardness has gradually decreased. This shows that when the amount of lactone added reaches a certain level, increasing the lactone content will not significantly increase the hardness of tofu.

[0060] Document 9: CN201711040005.7 A method for preparing whole cotyledon tofu by enzymatic hydrolysis

[0061] Document 9 discloses the following preparation method:

[0062] (1) Raw material selection: Select soybeans that are plump, free of insect bites and mildew, and remove impurities;

[0063] (2) Peeling: Dry and peel the soybeans, and soak them in water at 12 to 16°C for 9 to 11 hours, with the amount of water being 3 to 5 times the volume of the soybeans;

[0064] (3) Grinding: Grinding and beating the soaked soybeans to obtain coarse soy milk;

[0065] (4) Enzymatic hydrolysis: adding water to the crude soy milk to boil the soy milk, stopping boiling the soy milk when the concentration is 8% to 12%, cooling the soy milk to a temperature of 40 to 55° C., adding a mixed enzyme to hydrolyze for 30 to 55 minutes, and controlling the degree of hydrolysis to 5%;

[0066] (5) Adding tofu brain: Adding foliate vine fruit juice to the enzymatically hydrolyzed soy milk to obtain tofu brain;

[0067] (6) Let the tofu pudding stand for 9 to 11 minutes;

[0068] (7) Pressing and molding: Pressing and molding the cloth containing tofu pudding in the mold, the pressing time is 14 to 16 minutes, and the pressure is 0.9 to 1.1 MPa;

[0069] (8) Cooling: After the tofu is formed, the wrapping is removed and it is cut into pieces according to the required size. The pieces are quickly immersed in cold water to cool and become finished tofu.

[0070] In summary, several different types of coagulants are disclosed in the prior art, and the gelation mechanism of different coagulants and the characteristics of the finished tofu are somewhat different. For the preparation method using gluconolactone as a coagulant, the tofu produced has a delicate taste, but poor hardness. In the preparation process of tofu, most of them use a temperature of less than 100°C for slurry cooking, and then use a coagulant to treat the slurry. After the treatment, some documents directly cool and use a mold to shape, and some documents continue to heat to 80°C to 100°C, and then cool again to shape. During the continued heating, there is no process of using high temperature and pressure for treatment. At the same time, due to the influence of the gelation mechanism, in the preparation method using salt coagulants and enzyme coagulants, after the addition of the coagulant, it is often not necessary or possible to perform a secondary high-temperature heating treatment. First, high temperature is not conducive to the accumulation and molding of the already formed tofu pudding, and second, high temperature easily inactivates the enzyme. However, when gluconolactone is used as a coagulant, it needs to be at high temperature to release hydrogen ions. Therefore, in the tofu preparation method using gluconolactone as a coagulant, there is often a process step of secondary high-temperature heating. Summary of the invention

[0071] The purpose of the invention is to provide a method for preparing high-dietary fiber tofu based on high-temperature pressure treatment.

[0072] To achieve the above object, one embodiment of the present invention provides a method for preparing high dietary fiber tofu based on high temperature pressure treatment, comprising the following steps:

[0073] Step (1) ultrafinely grinding dehulled soybeans to obtain dehulled soybean powder, wherein the particle size of the dehulled soybean powder is 80 meshes to 150 meshes;

[0074] Step (2) adding dehulled soybean powder into water, stirring and mixing, and then heating to 90° C. to 100° C. to complete boiling to obtain soybean milk;

[0075] Step (3) adding a composite coagulant to the soy milk, stirring evenly, and placing the soy milk in a high-temperature pressurized cooking pot for secondary heating to obtain tofu blanks; placing the tofu blanks in cold water for cooling and shaping to obtain high dietary fiber tofu;

[0076] Among them, the compound coagulant is gluconolactone and glutamine transaminase, the amount of gluconolactone is 0.3% to 0.7% of the mass of soy milk, and the amount of glutamine transaminase is 0.01% to 0.03% of the mass of soy milk; the heating temperature of the secondary heating is 115°C to 125°C, the heating pressure is 0.17MPa to 0.25MPa, and the heating time is 15min to 25min.

[0077] Preferably, the specific processing process of step (1) of the present invention is: the dehulled soybeans are coarsely crushed by a grinder, and the coarse crushing is passed through a 40-mesh sieve to obtain soybean coarse powder, the soybean coarse powder is then ultrafinely crushed by an ultrafine grinder, and the ultrafinely crushed whole soybean powder is sieved through a sieve of 80-150 meshes to obtain dehulled soybean powder.

[0078] Preferably, in step (2), the ratio of dehulled soybean powder to water is 1:5-8; and the heating is followed by keeping warm for 8-15 minutes.

[0079] Preferably, in step (3), the soy milk is first cooled to room temperature before adding the compound coagulant, the amount of gluconolactone used is 0.5% of the mass of the soy milk, and the amount of glutamine transaminase used is 0.02% of the mass of the soy milk.

[0080] Preferably, in step (3), the secondary heating temperature is 120° C., the heating pressure is 0.22 MPa, and the heating time is 20 min; and the tofu blank is placed in cold water and allowed to stand for 30 min to cool and set to obtain high dietary fiber tofu.

[0081] In summary, the present invention has the following advantages:

[0082] The method comprises the following steps: superfinely grinding the dehulled soybeans and then boiling the dehulled soybeans, coagulating the dehulled soybeans with a compound coagulant, and performing a secondary high-temperature pressure treatment after adding the compound coagulant. After the treatment, the texture and microstructure of the tofu are significantly different from those of conventional tofu, and the hardness of the tofu is improved. Meanwhile, the content of insoluble dietary fiber in the tofu after the high-temperature pressure treatment is significantly reduced, and the content of soluble dietary fiber is significantly increased, thereby promoting the conversion of the insoluble dietary fiber into the soluble dietary fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0083] Figure 1The surface hydrophobicity test results of soymilk prepared from soy flours with different mesh sizes in one embodiment of the present invention;

[0084] Figure 2 This is a SEM image of tofu prepared from soybean flour of different mesh sizes in one embodiment of the present invention. DETAILED DESCRIPTION

[0085] The present invention provides a method for preparing high-dietary fiber tofu based on high-temperature pressure treatment, comprising the following steps:

[0086] Step (1) ultrafinely grinding dehulled soybeans to obtain dehulled soybean powder, wherein the particle size of the dehulled soybean powder is 80 meshes to 150 meshes;

[0087] Step (2) adding dehulled soybean powder into water, stirring and mixing, and then heating to 90° C. to 100° C. to complete boiling to obtain soybean milk;

[0088] Step (3) adding a composite coagulant to the soy milk, stirring evenly, and placing the soy milk in a high-temperature pressurized cooking pot for secondary heating to obtain tofu blanks; placing the tofu blanks in cold water for cooling and shaping to obtain high dietary fiber tofu;

[0089] Among them, the compound coagulant is gluconolactone and glutamine transaminase, the amount of gluconolactone is 0.3% to 0.7% of the mass of soy milk, and the amount of glutamine transaminase is 0.01% to 0.03% of the mass of soy milk; the heating temperature of the secondary heating is 115°C to 125°C, the heating pressure is 0.17MPa to 0.25MPa, and the heating time is 15min to 25min.

[0090] The specific processing process of step (1) is as follows: the dehulled soybeans are coarsely crushed by a grinder, and the coarse crushing is passed through a 40-mesh sieve to obtain soybean coarse powder, the soybean coarse powder is then ultrafinely crushed by an ultrafine grinder, and the ultrafinely crushed whole soybean powder is sieved through a sieve of 80-150 meshes to obtain dehulled soybean powder.

[0091] In step (2), the ratio of dehulled soybean powder to water is 1:5-8; and the heating is followed by heat preservation for 8-15 minutes.

[0092] In step (3), the soy milk is first cooled to room temperature and then the composite coagulant is added. The amount of gluconolactone is 0.5% of the mass of the soy milk, and the amount of glutamine transaminase is 0.02% of the mass of the soy milk.

[0093] The heating temperature of the secondary heating in step (3) is 120° C., the heating pressure is 0.22 MPa, and the heating time is 20 min. The tofu blank is placed in cold water and allowed to stand for 30 min to cool and set to obtain high dietary fiber tofu.

[0094] Example 1

[0095] A method for preparing high dietary fiber tofu based on high temperature pressure treatment comprises the following steps:

[0096] Step (1) coarsely crushing the dehulled soybeans using a grinder, and passing the coarse crushing through a 40-mesh sieve to obtain soybean coarse powder, and then superfine crushing the soybean coarse powder using an ultrafine grinder, and sieving the superfinely crushed soybean whole powder through a 120-mesh sieve to obtain dehulled soybean powder;

[0097] Step (2) adding dehulled soybean powder into water and stirring to mix evenly, wherein the ratio of dehulled soybean powder to water is 1:6, and then heating to 95° C. and keeping the temperature for 10 minutes to complete boiling to obtain soybean milk;

[0098] Step (3) first cools the soy milk to room temperature and then adds a composite coagulant, the composite coagulant is gluconolactone and glutamine transaminase, the amount of gluconolactone is 0.5% of the mass of the soy milk, and the amount of glutamine transaminase is 0.02% of the mass of the soy milk. After stirring evenly, it is packaged, and after being packaged into stainless steel containers, it is placed in a high-temperature pressurized cooking pot for secondary heating to obtain tofu blanks, and the heating process generally lasts for about 30 minutes. During the heating process, the heating temperature of the secondary heating is 120°C, the heating pressure is 0.22MPa, and the heating time is 20min. The tofu blank is placed in cold water and cooled for 30min before being shaped to obtain high dietary fiber tofu.

[0099] Example 2

[0100] A method for preparing high dietary fiber tofu based on high temperature pressure treatment comprises the following steps:

[0101] Step (1) coarsely crushing the dehulled soybeans using a grinder, and passing the coarsely crushed soybeans through a 40-mesh sieve to obtain soybean coarse powder, and then superfinely crushing the soybean coarse powder using an ultrafine grinder, and sieving the superfinely crushed soybean whole powder using a 100-mesh sieve to obtain dehulled soybean powder;

[0102] Step (2) adding dehulled soybean powder into water and stirring to mix evenly, wherein the ratio of dehulled soybean powder to water is 1:7, and then heating to 92° C. and keeping the temperature for 12 minutes to complete boiling to obtain soybean milk;

[0103] Step (3) first cools the soy milk to room temperature and then adds a compound coagulant, wherein the compound coagulant is gluconolactone and glutamine transaminase, wherein the amount of gluconolactone is 0.4% of the mass of the soy milk, and the amount of glutamine transaminase is 0.015% of the mass of the soy milk. After being stirred evenly, the soy milk is placed in a high-temperature pressurized cooking pot for secondary heating to obtain a tofu blank; the heating temperature of the secondary heating is 116° C., the heating pressure is 0.19 MPa, and the heating time is 22 minutes. The tofu blank is placed in cold water and allowed to stand for cooling for 30 minutes before being shaped to obtain a high-dietary fiber tofu.

[0104] The detection methods of the relevant detection items of the present invention are as follows.

[0105] A1. Basic ingredients

[0106] The protein content of tofu is determined by the combustion method in GB 5009.5-2016, with a conversion factor of 5.71;

[0107] The dietary fiber content of tofu is determined according to GB 5009.88-2023.

[0108] A2. Particle size

[0109] The laser particle size analyzer was used for measurement. The dispersion medium was distilled water, the real part of the refractive index was 1.56, the imaginary part was 0.05, the ideal shading ratio was 1-2, the medium refractive index was 1.33, and the ultrasound was performed for 1 min.

[0110] A3. Surface hydrophobicity

[0111] The method of Achouri et al. was used for determination: the soy milk was centrifuged and the supernatant was taken to adjust the protein concentration to 10 mg / mL. 15 μL of ANS solution (8 mmol / L) was added to 3 mL of the supernatant, and ultrapure water plus ANS was used as a blank to measure the fluorescence intensity of the blank and the sample. The excitation wavelength and absorption wavelength were set to 365 nm and 400-600 nm respectively, and the maximum fluorescence intensity was used as the surface hydrophobicity index H. 0 .

[0112] A4. Tofu yield

[0113] Tofu yield is defined as the mass of tofu produced from 100 g of soybean flour.

[0114] A5. Water holding capacity

[0115] The water holding capacity WHC is determined by centrifugation. During the determination, about 1g of gel sample is evenly cut and weighed as W1, then placed in a centrifuge tube with absorbent cotton at the bottom, centrifuged at 20℃ and 7500r / min for 10min, and the gel after centrifugation is weighed as W2. After that, the gel sample is placed in a 105℃ oven and dried for 6h, and weighed and recorded as W3. The formula for calculating the gel WHC is as follows.

[0116]

[0117] A6. Hardness and texture characteristics analysis

[0118] The texture analyzer was used for measurement: the gel was cut into a cylinder with a diameter of 40 mm and a height of 10 mm using a special mold for measurement. The TPA mode was used with the following parameters: probe model P / 36R (diameter 36 mm), pre-measurement rate 5.00 mm / s, measurement rate 1.00 mm / s, measurement rate 1.00 mm / s, post-measurement rate 1.00 mm / s, interval time 5 s, and compression deformation rate 30%. All samples were measured at least 6 times.

[0119] A7. Microstructure Observation

[0120] The microstructure of tofu was observed and analyzed using a scanning electron microscope (SEM). The sample pretreatment was as follows: the tofu was cut into blocks of about 2 mm × 2 mm × 5 mm, fixed with 2.5% (v / v) glutaraldehyde, pH 7.2, at 4°C for 2 h, and then washed with 0.01M, pH 7.2 PBS 3 times, 10 min each time. Then, it was dehydrated with 50%, 70%, 80% and 90% ethanol by volume, 10 min each time; and then dehydrated with anhydrous ethanol 3 times, 10 min each time. After that, it was replaced with anhydrous ethanol-tert-butyl alcohol (1:1, v / v) and pure tert-butyl alcohol once, each for 15 min. After dehydration, the sample was freeze-dried, and the dried sample was fixed on the sample stage with conductive glue. After gold was sprayed on the sample by ion sputtering, the sample was transferred to the SEM table, and the morphology of the gel was observed and photographed at an accelerating voltage of 10 kV.

[0121] A8. Sensory evaluation

[0122] Invite 15 trained sensory evaluators to score the color, flavor, appearance, taste and texture of tofu. The sensory scoring criteria are shown in the table below.

[0123]

[0124] Experimental example HTPC

[0125] A method for preparing high dietary fiber tofu based on high temperature pressure treatment comprises the following steps:

[0126] Step (1) coarsely crushing the dehulled soybeans using a grinder, and passing the coarse crushing through a 40-mesh sieve to obtain soybean coarse powder, and then superfine crushing the soybean coarse powder using an ultrafine grinder, and sieving the superfinely crushed soybean whole powder through a sieve of 80-150 meshes to obtain dehulled soybean powder;

[0127] Step (2) adding dehulled soybean powder into water and stirring to mix evenly, wherein the ratio of dehulled soybean powder to water is 1:6, and then heating to 95° C. and keeping the temperature for 10 minutes to complete boiling to obtain soybean milk;

[0128] Step (3) first cools the soy milk to room temperature and then adds a composite coagulant, wherein the composite coagulant is gluconolactone and glutamine transaminase, wherein the amount of gluconolactone is 0.5% of the mass of the soy milk, and the amount of glutamine transaminase is 0.02% of the mass of the soy milk. After being stirred evenly, the soy milk is placed in a high-temperature pressurized cooking pot for secondary heating to obtain a tofu blank; the heating temperature of the secondary heating is 120° C., the heating pressure is 0.22 MPa, and the heating time is 20 min. The tofu blank is placed in cold water and allowed to stand for cooling for 30 min before being shaped to obtain a high-dietary fiber tofu.

[0129] Experimental Example TC

[0130] A method for preparing high dietary fiber tofu based on high temperature pressure treatment comprises the following steps:

[0131] Step (1) coarsely crushing the dehulled soybeans using a grinder, and passing the coarse crushing through a 40-mesh sieve to obtain soybean coarse powder, and then superfine crushing the soybean coarse powder using an ultrafine grinder, and sieving the superfinely crushed soybean whole powder through a sieve of 80-150 meshes to obtain dehulled soybean powder;

[0132] Step (2) adding dehulled soybean powder into water and stirring to mix evenly, wherein the ratio of dehulled soybean powder to water is 1:6, and then heating to 95° C. and keeping the temperature for 10 minutes to complete boiling to obtain soybean milk;

[0133] Step (3) first cools the soy milk to room temperature and then adds a compound coagulant, wherein the compound coagulant is gluconolactone and glutamine transaminase, wherein the amount of gluconolactone is 0.5% of the mass of the soy milk, and the amount of glutamine transaminase is 0.02% of the mass of the soy milk. After being stirred evenly, the soy milk is placed in a cooking pot for secondary heating to obtain a tofu blank; the heating temperature of the secondary heating is 85° C., the pressure is normal pressure, and the heating time is 40 minutes. The tofu blank is placed in cold water and allowed to stand for cooling for 30 minutes before being shaped to obtain a high dietary fiber tofu.

[0134] The method of Experimental Example HTPC is the same as that of Example 1. In Experimental Example HTPC, sieves with different meshes are used for sieving to verify the effect of different particle sizes on protein content. Compared with Example 1, Experimental Example TC selects the heating temperature in the prior art during secondary heating, and the pressure during heating is normal pressure. Experimental Example TC also uses particle sizes with different meshes, which is the same as Experimental Example HTPC; the heating temperature of the secondary heating in Example 1 is 115°C to 125°C, and the heating pressure is 0.17MPa to 0.25MPa.

[0135] Experimental Example 1. Determination of protein content in Experimental Example HTPC and Experimental Example TC

[0136] The materials related to the experimental example HTPC and the experimental example TC were tested, and the test results are as follows:

[0137]

[0138] The dehulled soybean powder in the above table is the dehulled soybean powder obtained in step (1), and the soy milk is the soy milk obtained in step (2). The above table lists the protein content of dehulled soybean powder and soy flours of different particle size ranges and their product tofu. It can be seen from the above table that the protein content of 100-mesh dehulled soybean powder is the highest, which is 36.80%, and there is no significant difference in the protein content of soy flours with different particle sizes. The soy milk prepared with 80-mesh soy flour has the lowest protein content because its particles are larger and the protein is not easily dissolved. There is no significant difference in the protein content of tofu prepared with soy flours of different mesh sizes in the experimental example HTPC, but it is slightly higher than the tofu of the corresponding experimental example TC. It may be that the tofu of the experimental example TC has less water content, which increases the protein content.

[0139] Experimental Example 2: Surface hydrophobicity test of soybean milk in Experimental Example HTPC and Experimental Example TC

[0140] Experimental method: The dehulled soybeans are coarsely crushed using a grinder, and after coarse crushing, the soybean coarse powder is obtained by passing through a 40-mesh sieve, and the soybean coarse powder is then ultrafinely crushed using an ultrafine grinder. The ultrafinely crushed whole soybean powder is sieved using a sieve of 80-150 meshes to obtain dehulled soybean powder. The position marked as N in the accompanying drawings of the present invention represents whole soybean powder, that is, whole soybean powder that has not been sieved.

[0141] Surface hydrophobicity is the main force to maintain the higher-order structure of proteins. It can reflect the content of hydrophobic groups in proteins and is an important indicator for characterizing protein conformation and aggregation behavior. Figure 1As shown in the figure, the surface hydrophobicity of soy milk prepared from dehulled soybean powder is the highest, which is 1063.86. As the particle size decreases, the surface hydrophobicity decreases. This may be because there are more protein particles in the soybean powder with smaller particle size, the attraction between protein molecules is greater, the formed particle aggregates are more compact, and the hydrophobic groups are not easily exposed.

[0142] Experimental Example 3: Tofu Yield Detection of Experimental Example HTPC and Experimental Example TC

[0143] The tofu yields of the experimental examples HTPC and TC were calculated, and the test results are as follows:

[0144]

[0145] From the above test results, it can be seen that the tofu yield of the experimental example TC is higher than that of the experimental example HTPC tofu, and there is no significant difference in the tofu yield prepared by bean powder with different mesh sizes. Under the processing method and conditions of the experimental example HTPC, the tofu yield is relatively stable, and it is the lowest at 80 mesh bean powder, which is 5.83%. The tofu yield and water holding capacity of the experimental example HTPC are significantly lower than those of the tofu of the experimental example TC. This may be because when the heating temperature is too high, the protein is excessively denatured, the water holding capacity of the tofu is reduced, and the yield will also decrease accordingly.

[0146] Experimental Example 4: Sensory Evaluation of Experimental Example HTPC and Experimental Example TC

[0147] The tofu obtained from the experimental examples HTPC and TC were subjected to sensory evaluation. Sensory evaluation can directly reflect the degree of consumer preference for the product and is of great significance for evaluating the quality of tofu. The sensory evaluation evaluates the tofu from five aspects: color, flavor, appearance, taste and texture. The evaluation results show that the scores of the tofu from the experimental example HTPC are better than those from the tofu from the experimental example TC with the same mesh size of soybean powder. Both can form milky white, uniform color and strong bean flavor tofu. Although the tofu from the experimental example HTPC has less improvement in color and flavor than the tofu from the experimental example TC, it can significantly improve the appearance, taste and texture of the tofu. As the mesh size increases, the sensory scores of the two tofu show a trend of first increasing and then decreasing. Among them, the tofu corresponding to the dehulled soybean powder with a mesh size of 120 in the experimental example HTPC has a complete shape, a uniform cross-section without pores, moderate hardness, elasticity and toughness, and the highest total score of 73.4 points. In Experimental Example TC, the tofu prepared with 100-mesh dehulled soybean flour had the highest total score of 57.6 points, indicating that the smaller the particle size of soybean flour is, the better, and moderate particles can promote the formation of tofu gel.

[0148] Experimental Example 5: Detection of dietary fiber content in Experimental Example HTPC and Experimental Example TC

[0149] The dietary fiber content of the tofu obtained in Experimental Example HTPC and Experimental Example TC was tested, and the test results are shown in the following table:

[0150]

[0151] As shown in the above test results, the insoluble dietary fiber (IDF) in the experimental example HTPC tofu is significantly lower than that in the experimental example TC tofu at the same mesh size, while the soluble dietary fiber (SDF) is significantly increased, and the ratio of IDF / SDF of the tofu in the experimental example HTPC is lower than that of the tofu in the experimental example TC, indicating that the HTPC treatment in the experimental example can effectively promote the conversion of IDF to SDF. The present invention adopts high temperature and pressure operation during the secondary heating process, so that the high-temperature steam in the pot can increase the accessibility to the cell wall matrix while maintaining the pressure, and can promote the cleavage of certain bonds between polysaccharides; the ratio of IDF / SDF is crucial for the component used as a functional dietary fiber resource, and a smaller ratio is more suitable for human health. In the above two experimental examples, the total dietary fiber (TDF) and insoluble dietary fiber IDF in tofu produced by the two methods showed a trend of first increasing and then decreasing with the increase of mesh size, while the soluble dietary fiber SDF did not have the same trend, indicating that IDF accounts for a large proportion of TDF and the content of SDF is less affected by the content of IDF. The TDF in the experimental example HTPC tofu is also significantly lower than that in the experimental example TC tofu. It may be that part of the SDF is lost with the yellow pulp water during the formation of tofu. The tofu yield also proves that the tofu in the experimental example HTPC has more yellow pulp water lost. More than one-third of the organic components of the yellow pulp water discharged from tofu production are soybean oligosaccharides, of which stachyose and raffinose account for 83% and 94% of the raw soybeans, respectively, and are a good source of dietary fiber.

[0152] In summary, through the comparison of the two experimental examples, it can be seen that during the secondary heating process, the high temperature and pressure process is beneficial to the conversion of insoluble dietary fiber into soluble dietary fiber, thereby making the IDF / SDF ratio in the tofu product of the experimental example HTPC smaller, thereby increasing the soluble dietary fiber content in the tofu product, which is beneficial to human absorption.

[0153] Experimental Example 6: Testing of Tofu Hardness in Experimental Example HTPC and Experimental Example TC

[0154] The tofu obtained from Experimental Example HTPC and Experimental Example TC were tested for hardness and the tofu SEM images were taken.

[0155] The hardness test results of the tofu obtained in Experimental Example HTPC and Experimental Example TC are shown in the following table.

[0156]

[0157] The SEM test results of the tofu obtained in Experimental Example HTPC and Experimental Example TC are as follows: Figure 2 As shown, T80 represents the tofu prepared with a particle size of 80 mesh in the experimental example TC, and P80 represents the tofu prepared with a particle size of 80 mesh in the experimental example HTPC.

[0158] Hardness is an indicator of tofu's resistance to destructive force during processing and application. From the analysis of the above table, it can be seen that the hardness of tofu in Experimental Example HTPC is significantly higher than that of tofu in Experimental Example TC, but the hardness of tofu prepared by the two methods increases first and then decreases with the increase of mesh size, and is the highest at 100 mesh, which is 615g and 400g respectively. The method of Experimental Example HTPC of the present invention induces a higher degree of protein aggregation than the method of Experimental Example TC, thereby increasing the content of protein particles and expanding the size of protein particles.

[0159] Figure 2 The SEM images of tofu prepared by treating soybean powder suspensions of different particle sizes with the methods described in Experimental Examples TC and HTPC are shown. According to the images, the porous structure of tofu in Experimental Example HTPC is denser and more uniform than that in Experimental Example TC, with better continuity, and P120 tofu performs best in Experimental Example HTPC. Larger aggregates and flakes appear in the gel network of tofu in Experimental Example TC, which hinders the formation of the gel network and thus has larger pores.

[0160] In summary, in the prior art, in the preparation method using salt or enzyme coagulants, it is often formed by model compression, or considering the problem of enzyme activity, it is often not heated at high temperature again after the coagulant is added. When only gluconolactone is used as a coagulant, it is necessary to heat the coagulant after it is added to release hydrogen ions to achieve protein coagulation. The present invention adds a compound coagulant, and gluconolactone plays the main coagulation role, which has a larger content and is the main coagulant. The TG enzyme has a slow action time and is also inactivated during the second high-temperature heating. The TG enzyme can play a certain auxiliary role in the early stage of adding the compound coagulant, improving the coagulation effect. The experimental example HTPC of the present invention is the same method process as Example 1 of the present invention, which is the technical solution of the present invention. Compared with the embodiment of the present invention, the experimental example TC selects a conventional heating method during the second heating process, and the heating temperature is lower than 100 degrees. The experimental example HTPC of the present invention uses a high temperature and pressurization method during the secondary heating process, so that the density of the finished tofu is better and more uniform, the continuity is good, and there are fewer large pores. The hardness of the tofu prepared by the final experimental example HTPC is significantly higher than that of the experimental example TC. It can be seen that the method of secondary heating after adding a coagulant can significantly improve the gel solidification physical structure of tofu and increase the hardness of tofu.

[0161] Although the specific implementation of the present invention is described in detail in conjunction with the drawings, it should not be understood as limiting the scope of protection of this patent. Within the scope described in the claims, various modifications and variations that can be made by those skilled in the art without creative work still fall within the scope of protection of this patent.

Claims

1. A method for preparing high dietary fiber tofu based on high temperature pressure treatment, characterized in that: The following steps are involved: Step (1) ultrafinely grinding dehulled soybeans to obtain dehulled soybean powder, wherein the particle size of the dehulled soybean powder is 80 meshes to 150 meshes; Step (2) adding dehulled soybean powder into water, stirring and mixing, and then heating to 90° C. to 100° C. to complete boiling to obtain soybean milk; Step (3) adding a composite coagulant to the soy milk, stirring evenly, and placing the soy milk in a high-temperature pressurized cooking pot for secondary heating to obtain tofu blanks; placing the tofu blanks in cold water for cooling and shaping to obtain high dietary fiber tofu; Among them, the compound coagulant is gluconolactone and glutamine transaminase, the amount of gluconolactone is 0.3% to 0.7% of the mass of soy milk, and the amount of glutamine transaminase is 0.01% to 0.03% of the mass of soy milk; the heating temperature of the secondary heating is 115°C to 125°C, the heating pressure is 0.17MPa to 0.25MPa, and the heating time is 15min to 25min.

2. The preparation method according to claim 1, characterized in that: The specific processing process of the step (1) is as follows: the dehulled soybeans are coarsely crushed by a grinder, and the coarse crushed soybean powder is passed through a 40-mesh sieve to obtain coarse soybean powder, the coarse soybean powder is then ultrafinely crushed by an ultrafine grinder, and the ultrafinely crushed whole soybean powder is sieved through a sieve of 80-150 meshes to obtain dehulled soybean powder.

3. The preparation method according to claim 1, characterized in that: In the step (2), the ratio of dehulled soybean powder to water is 1:5-8; and the heating is followed by keeping the temperature for 8-15 minutes.

4. The preparation method according to claim 1, characterized in that: In the step (3), the soy milk is first cooled to room temperature and then the compound coagulant is added. The amount of gluconolactone is 0.5% of the mass of the soy milk, and the amount of glutamine transaminase is 0.02% of the mass of the soy milk.

5. The preparation method according to claim 1, characterized in that: The heating temperature of the secondary heating in the step (3) is 120° C., the heating pressure is 0.22 MPa, and the heating time is 20 min. The tofu blank is placed in cold water and allowed to stand for 30 min to cool and set to obtain high dietary fiber tofu.

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