Preparation technology of fruit and vegetable extract compound fermented bean curd

Abstract

The invention relates to the technical field of food processing, and discloses a preparation process of fruit and vegetable extract compound fermented bean curd, which comprises the following steps: preparing a white blank inoculated with mucor sufu spores, and fermenting to obtain a blank; placing the blank in a vacuum environment, and dipping the blank in an enzymolysis modified fruit and vegetable penetrating fluid containing low-methoxyl pectin and phytase; the penetrating blank is subjected to sectional type vacuum breaking and re-pressing operation, the environment pressure is recovered to normal pressure in stages, penetrating fluid entering pores is subjected to in-situ gelation curing, and a cured blank is obtained; and salting the cured blank, bottling and carrying out later fermentation. The phytase and the low-methoxyl pectin are introduced into the penetrating fluid, the endogenous phytate of the blank is hydrolyzed by the phytase to release calcium ions, and the pectin is induced to be gelatinized and solidified in situ in the pores of the blank, so that liquid seepage caused by osmotic pressure difference in the subsequent processing process is blocked, and the retention rate of fruit and vegetable components in the finished product is increased.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of food processing, in particular to a preparation process of fruit and vegetable extract compounded fermented bean curd. BACKGROUND

[0002] Fermented bean curd is a traditional condiment made of soybeans as the main raw material through microbial fermentation. It is widely loved by consumers because of its unique fermentation flavor and delicate taste. With the development of food processing technology and the diversification of consumer dietary needs, the development of fruit and vegetable compounded fermented bean curd rich in vitamins and dietary fiber has become a research direction to enrich the flavor and nutritional value of traditional fermented bean curd. At present, the industry mainly adds fruit and vegetable juice to the grinding process, mixes it into the later fermentation soup or directly soaks the blank, etc. to try to introduce the flavor substances of fruits and vegetables into the fermented bean curd matrix to prepare new fermented bean curd products with complex taste.

[0003] However, the existing preparation process has certain technical limitations in actual application. Because the fermented bean curd blank has a complex micro-pore structure, and the fruit and vegetable slurry without enzyme treatment usually has high viscosity, it is difficult for fruit and vegetable ingredients to overcome the capillary resistance and penetrate deeply into the interior of the blank, resulting in uneven distribution of flavor in the finished product. At the same time, the fruit and vegetable juice that enters the pores of the blank by physical soaking lacks an effective fixation mechanism, and in the subsequent high-salt pickling and long-period later fermentation process, it is easily affected by the external high-osmotic-pressure environment and diffuses reversely and seeps out into the soup, resulting in the loss of fruit and vegetable flavor and nutritional ingredients in the finished product. In addition, if the introduction of exogenous liquid is not properly handled, it can easily damage the original protein network structure of the blank, causing the finished product to be soft and deformed, affecting the forming degree and texture of the product.

[0004] Therefore, how to improve the penetration efficiency of fruit and vegetable ingredients in the fermented bean curd blank and enhance their retention rate and structural stability in the subsequent processing process is a technical problem to be solved in the field. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a preparation process of fruit and vegetable extract compounded fermented bean curd, which solves the problems that fruit and vegetable ingredients are difficult to penetrate deeply into the internal pores of the fermented bean curd blank and are easily lost by seepage due to osmotic pressure difference in the subsequent processing process.

[0006] To solve the above problems, the present application provides the following technical solutions: The present application provides a preparation process of fruit and vegetable extract compounded fermented bean curd, which adopts the following technical solutions: A preparation process of fruit and vegetable extract compounded fermented bean curd, comprising the following steps: S10, preparing a white blank inoculated with fermented bean curd mold spores, and obtaining a blank after fermentation; S20, placing the blank in a vacuum environment, and immersing the blank in an enzymatically modified fruit and vegetable permeate solution to allow the enzymatically modified fruit and vegetable permeate solution to enter the pores of the blank, thereby obtaining a permeated blank; the enzymatically modified fruit and vegetable permeate solution contains low-methoxyl pectin and phytase; S30, performing a segmented vacuum breaking and pressure recovery operation on the permeated blank to recover the ambient pressure to normal pressure in stages, so that the enzymatically modified fruit and vegetable permeate solution that has entered the interior of the pores of the permeated blank is in-situ gelled and solidified, thereby obtaining a solidified blank. S40, performing salting, bottling and post-fermentation on the solidified blank to obtain a finished product of compound fermented bean curd.

[0007] By using the above technical solution, the fluid dynamics mechanism in the vacuum environment is used to remove the gas in the porous medium of the blank, so that the enzymatically modified fruit and vegetable permeate solution can overcome the capillary resistance and fill into the micro-pores of the blank.

[0008] The application constructs an in-situ gelling reaction system of phytase, phytic acid, calcium ions and low-methoxyl pectin. The phytic acid contained in the soybean raw material is easy to combine with calcium ions to form calcium phytate precipitate, which limits the free calcium ions. By introducing phytase into the enzymatically modified fruit and vegetable permeate solution, when the enzymatically modified fruit and vegetable permeate solution enters the pores of the blank, the phytase specifically hydrolyzes the phytate in the soybean protein network to release free calcium ions in the micro-pores. The released calcium ions and the low-methoxyl pectin in the enzymatically modified fruit and vegetable permeate solution undergo ion crosslinking reaction to form a thermally irreversible gel network in-situ in the pores of the blank. The gel network locks the fruit and vegetable flavor substances and nutritional ingredients in the fermented bean curd matrix, blocks the leakage of fruit and vegetable ingredients in the subsequent salting and fermentation process, and improves the flavor retention rate and the tightness of the finished product.

[0009] Preferably, the preparation method of the enzymatically modified fruit and vegetable permeate solution in the S20 step comprises the following steps: crushing and pulping fresh fruit and vegetable raw materials, adding enzyme preparation for primary enzymolysis, and filtering to obtain a fruit and vegetable base solution; adding low-methoxyl pectin to the fruit and vegetable base solution, heating and dissolving, and then cooling; adjusting the pH value of the solution to the acidic range, adding phytase, and stirring uniformly to obtain the enzymatically modified fruit and vegetable permeate solution.

[0010] By using the above technical solution, the primary enzymolysis can reduce the viscosity of the fruit and vegetable slurry, reduce the steric hindrance of pectin and cellulose macromolecules, and improve the diffusion rate of the enzymatically modified fruit and vegetable permeate solution in the pores of the blank. The low-methoxyl pectin is dissolved in advance and the pH value is adjusted, which provides a material basis and an acidic environment for the subsequent crosslinking reaction with calcium ions, ensures that the gelling reaction starts after permeating into the blank, and avoids gelling in the external solution.

[0011] Preferably, in the process of preparing the fruit and vegetable base liquid, the fresh fruit and vegetable raw materials are selected from one or more of carrots, tomatoes, pumpkins and red dates; the enzyme preparation is a pectinase or a compound enzyme preparation of cellulase and pectinase, and the amount of the enzyme preparation added is 0.05% to 0.10% of the total weight of the slurry; in the process of adjusting the pH value of the solution and adding the phytase, the pH value is adjusted to a range of 4.2 to 5.5; and the amount of phytase added is 150 U / kg to 400 U / kg.

[0012] By adopting the above technical solution, the compound enzyme preparation improves the cell wall disruption rate and functional component extraction rate of fruits and vegetables; the pH value of 4.2 to 5.5 is within the activity range of the phytase, which meets the acidity conditions for the formation of gel by low methoxyl pectin, and this pH range is compatible with the fermentation environment of fermented bean curd and will not inhibit the subsequent action of mucormycin; by controlling the amount of phytase added, the release rate of calcium ions is regulated, thereby achieving control over the gel formation rate in the pores.

[0013] Preferably, during the process of adding the low-methoxyl pectin and heating to dissolve it, the heating temperature is 60°C to 70°C and the holding time is 10 min to 20 min; during the process of adjusting the pH value of the solution and adding the phytase, the temperature of the solution is controlled at 40°C to 50°C.

[0014] By adopting the above technical solution, the dissolution temperature of 60°C to 70°C ensures the extension and hydration of the low-methoxyl pectin molecules, avoiding the destruction of fruit and vegetable nutrients caused by high temperature; the system temperature is adjusted back to 40°C to 50°C, which is consistent with the enzyme activity temperature of the phytase and matches the temperature of subsequent vacuum impregnation, avoiding the thermal shock of temperature fluctuations to the texture of the blank and the activity of the Rhizopus mycelium.

[0015] Preferably, during the addition of the low-methoxyl pectin, the amount of low-methoxyl pectin added is 8 g / L to 16 g / L, and the degree of esterification of the low-methoxyl pectin is 30% to 40%.

[0016] By adopting the above technical solution, the degree of esterification of the low-methoxyl pectin is limited to 30% to 40% because pectin within this esterification range is sensitive to calcium ions and can form a gel at a lower calcium ion concentration. The concentration is controlled at 8 g / L to 16 g / L, which balances the viscosity and gel strength of the enzymatically modified fruit and vegetable permeate. If the concentration is too high, it will lead to increased viscosity and hinder permeation; if the concentration is too low, it will not be able to form a gel network with sufficient strength.

[0017] Preferably, in step S10, the preparation process of the raw material includes: adjusting the concentration of soybean slurry to 10°Bx to 12°Bx, adding a coagulant to form a white raw material, cutting it into pieces, and inoculating it with *Rhizopus cuspidatum* spores, with an inoculation amount of 1×10⁻⁶ spores per piece.3 One to 1×10 4 The spores are fermented for 40 to 60 hours at a temperature of 20°C to 28°C and a relative humidity of 90% to 95%.

[0018] By adopting the above technical solution, the initial moisture content and micro-network structure of the raw material are controlled; the pre-fermentation process promotes the growth of Mucor mycelium, and the enzyme system secreted by the mycelium partially decomposes soybean protein, so that a suitable porosity is formed inside the raw material, providing a physical space channel for the subsequent entry of the enzymatically modified fruit and vegetable permeate.

[0019] Preferably, in step S20, the impregnation conditions under vacuum are as follows: the ratio of blank mass to liquid volume is 1:2 to 1:4 g / mL; the liquid temperature is 40°C to 50°C; the vacuum degree is -0.08MPa to -0.09MPa; and the vacuum maintenance time is 15 min to 25 min.

[0020] By adopting the above technical solution, a vacuum of -0.08MPa to -0.09MPa can remove air from the pores of the blank, generating an internal and external pressure difference; a temperature of 40℃ to 50℃ maintains the fluidity of the enzymatically modified fruit and vegetable permeate, promoting the catalytic reaction of the phytase; controlling the material-to-liquid ratio ensures that the blank is completely submerged and has sufficient permeate medium, guaranteeing the uniformity of the mass transfer process.

[0021] Preferably, in step S30, the segmented depressurization operation specifically includes: controlling the intake rate to raise the pressure to -0.055MPa to -0.045MPa and maintaining it at that pressure for 3 to 6 minutes; continuing to intake air to raise the pressure to -0.025MPa to -0.015MPa and maintaining it at that pressure for 3 to 5 minutes; and fully opening the intake valve to restore the pressure to normal atmospheric pressure.

[0022] By adopting the above technical solution, during the repressurization process, if the pressure is instantly restored to normal, the pressure shock will cause the soft tissue of the blank to deform and collapse, and the infiltrated liquid will be squeezed out. By adopting segmented step repressurization and utilizing the pressure relaxation mechanism, the pore structure of the blank is given time to buffer and adapt. During the pressure holding stage, the phytase continues to release calcium ions, which promotes the gradual gelation of the low methoxyl pectin in the pores. When the pressure is completely restored to normal, a strong semi-solid gel network has been formed inside the pores, which resists changes in external pressure, and the in-situ solidification of the enzymatically modified fruit and vegetable permeate is achieved.

[0023] Preferably, in step S40, the salt water concentration used in the salting process is 12% to 16%, and the salting time is 2 to 4 days.

[0024] By adopting the above technical solution, the raw material's resistance to salt dehydration is enhanced due to the formation of pectin gel filling in the pores. Controlling the salt concentration and time imparts a salty and umami flavor and preservative properties to the product, without damaging the formed gel structure, thus ensuring the flavor and texture of the final product.

[0025] Preferably, in step S40, the broth used in the later fermentation process comprises: 8% to 12% edible alcohol by volume, 6% to 8% salt by mass, and 2% to 5% sugar by mass; the fermentation temperature is 20°C to 30°C, and the fermentation time is 45 to 90 days.

[0026] By adopting the above technical solutions, the soup base formula is combined with the previous process. The alcohol and high-salt environment promotes the hydrolysis of enzymes and the synthesis of flavor esters. The addition of sugar works synergistically with the fruit and vegetable ingredients, resulting in a final product with a mellow taste, bright color, and stable shelf life.

[0027] This invention provides a preparation process for fermented bean curd made from a compound of fruit and vegetable extracts. It has the following beneficial effects: 1. This invention involves impregnating the pores of a raw material with an enzymatically modified fruit and vegetable permeate containing phytase and low-methoxyl pectin. Phytase hydrolyzes the endogenous phytate in the raw material in situ, releasing free calcium ions, which induces the low-methoxyl pectin to undergo an ionic cross-linking reaction, resulting in in-situ gelation and solidification. This constructs a physical barrier inside the pores of the raw material, thereby blocking the leakage of liquid caused by osmotic pressure differences during subsequent salting and fermentation, effectively improving the retention rate of fruit and vegetable components in the finished product.

[0028] 2. This invention employs a segmented cavitation and repressurization operation on the permeation blank, gradually restoring the environmental pressure to normal pressure in stages. This utilizes a pressure relaxation mechanism to mitigate the impact of instantaneous pressure difference changes on the soft tissue of the blank, preventing liquid backflow caused by pore rebound. Simultaneously, this operation prolongs the reaction time of low-methoxyl pectin within the blank pores, ensuring that a gel structure with a certain strength is formed before the pressure is fully restored to normal, thus achieving stable filling of the enzymatically modified fruit and vegetable permeate inside the blank.

[0029] 3. This invention involves adding an enzyme preparation during the preparation of the enzymatically modified fruit and vegetable permeate to perform initial enzymatic hydrolysis, thereby decomposing the large-molecule polysaccharides in the fruit and vegetable raw materials to reduce the viscosity of the liquid. Combined with impregnation conditions under vacuum, the negative pressure suction removes the gas from the pores of the blank, allowing the low-viscosity enzymatically modified fruit and vegetable permeate to overcome capillary resistance and deeply fill the micropores of the blank, thus improving the uniformity of the distribution and the tightness of the binding of fruit and vegetable components in the compound fermented bean curd product. Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the preparation examples, examples, comparative examples, and test examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Preparation Examples 1-3: Preparation Example 1: This preparation example provides an enzymatically modified fruit and vegetable permeate for use in a low-methoxyl pectin gelation system, comprising the following steps: Fresh carrots and tomatoes were selected, mixed and washed in a 1:1 mass ratio, then crushed and pulped. Pectinase (0.05% by weight of the total pulp) was added to the resulting pulp, and the pulp temperature was controlled at 45℃ for 30 minutes to reduce the pulp viscosity and increase the juice yield. After enzymatic hydrolysis, the pulp was filtered through a 100-mesh filter, and the filtrate was collected as the fruit and vegetable base liquid.

[0032] Slowly add low-methoxyl pectin with a degree of esterification of 30% at a concentration of 8 g / L to the above-mentioned fruit and vegetable base solution. While stirring, heat the solution to 60°C and maintain this temperature for 10 minutes to ensure complete dissolution and uniform distribution of the pectin. After the solution cools naturally to 40°C, adjust the pH of the system to 4.2 using citric acid solution, at which point the solution remains a highly fluid liquid. Finally, add phytase derived from food-grade Aspergillus niger to the system at a concentration of 150 U per kilogram of permeate, stir thoroughly, and maintain the solution temperature at 40°C to obtain the enzymatically modified fruit and vegetable permeate solution.

[0033] Preparation Example 2: This preparation example provides an enzymatically modified fruit and vegetable permeate for use in a low-methoxyl pectin gelation system, comprising the following steps: Select fresh pumpkin, peel and deseed it, cut it into chunks, and blend it with water. Add 0.08% (by weight) of a cellulase and pectinase complex enzyme preparation to the resulting pulp, control the pulp temperature at 48℃, and perform enzymatic hydrolysis for 45 minutes. After enzymatic hydrolysis, filter the pulp through a 150-mesh filter to remove large fiber particles, and collect the filtrate as a fruit and vegetable base liquid.

[0034] Low-methoxylated pectin with a degree of esterification of 35% was added to the fruit and vegetable base solution at a concentration of 12 g / L. The stirring device was turned on, and the solution was heated to 65°C and maintained for 15 minutes to allow the pectin molecules to fully expand and dissolve. The solution was then cooled to 45°C, and the pH of the system was adjusted to 4.8 using sodium carbonate solution to create a suitable acid-base environment for subsequent reactions. At this temperature, food-grade phytase was added to the system at a concentration of 280 U per kilogram of permeate. The mixture was thoroughly stirred and mixed, and the temperature of the solution was strictly controlled at 45°C to obtain the enzymatically modified fruit and vegetable permeate.

[0035] Preparation Example 3: This preparation example provides an enzymatically modified fruit and vegetable permeate for use in a low-methoxyl pectin gelation system, comprising the following steps: Select fresh red dates, remove the pits, boil them in water to soften them, and then blend them into a pulp. Add 0.10% pectinase by weight of the pulp to the resulting pulp, control the pulp temperature at 50℃, and perform deep enzymatic hydrolysis for 60 minutes to fully release the polysaccharide components in the red dates and reduce viscosity. After enzymatic hydrolysis, filter the pulp through a 200-mesh filter and collect the filtrate as a fruit and vegetable base liquid.

[0036] Low-methoxylated pectin with a degree of esterification of 40% was added to the fruit and vegetable base solution at a concentration of 16 g / L. The solution was heated to 70°C and maintained at this temperature for 20 minutes under high-speed stirring to ensure complete dissolution of the high-concentration pectin. When the solution temperature dropped to 50°C, the pH of the system was adjusted to 5.5 using citric acid solution. Finally, high-activity food-grade phytase was added to the system at a concentration of 400 U per kilogram of permeate, and the mixture was stirred evenly while maintaining the solution temperature at 50°C to obtain the enzymatically modified fruit and vegetable permeate solution.

[0037] Examples 1-3: Example 1

[0038] This embodiment provides a preparation process for fermented bean curd made from fruit and vegetable extracts, including the following steps: S10. Grind the soybeans into a slurry and adjust the soy milk concentration to 10°Bx. After boiling, cool to 80°C and add 2.5% calcium sulfate coagulant (by weight of dry soybeans) for coagulation. Press under 0.2 MPa pressure for 20 minutes to make white curd. Cut into pieces and inoculate with *Mucor* spores at a rate of 1×10⁻⁶ spores per piece. 3 One spore is fermented at 20℃ and 90% relative humidity for 40 hours to obtain a raw material; S20. Place the above blank in a vacuum impregnation tank and inject the enzymatically modified fruit and vegetable permeate of Preparation Example 1. The material-to-liquid ratio is 1:2 (g / mL) of blank mass to liquid volume. Maintain the material temperature at 40°C. Start the vacuum pump and evacuate the vacuum in the tank to -0.08 MPa. Maintain this vacuum for 15 minutes to allow the gas in the blank pores to be discharged and the permeate to initially enter the surface of the blank. S30. After infiltration, perform a segmented pressure-re-pressurization operation: First, control the air intake rate to raise the pressure inside the tank to -0.055MPa and maintain this pressure for 3 minutes; then continue to intake air to raise the pressure inside the tank to -0.025MPa and maintain this pressure for 3 minutes; finally, fully open the air intake valve to restore the pressure to normal, let it stand for 2 minutes, and then drain the excess liquid to complete the in-situ gelation and curing. S40. Take out the processed blanks and drain them. Soak them in a 12% salt solution for 2 days. Then bottle them and add broth containing 8% edible alcohol, 6% salt and 2% sugar. Seal them and ferment them at 20℃ for 45 days to obtain the finished product. Example 2

[0039] This embodiment provides a preparation process for fermented bean curd made from fruit and vegetable extracts, including the following steps: S10. Grind soybeans into a slurry and adjust the slurry concentration to 11°Bx. After boiling, cool to 82°C and add a compound coagulant at 3.2% of the dry soybean weight for coagulation. Press under 0.3MPa pressure for 25 minutes to make white curd. Cut into pieces and inoculate with *Mucor* spores at a rate of 5 × 10 spores per piece. 3 One spore is fermented at 25°C and 92% relative humidity for 50 hours to obtain a raw material; S20. Place the above blank in a vacuum impregnation tank and inject the enzymatically modified fruit and vegetable permeate of Preparation Example 2. The material-to-liquid ratio is 1:3 (g / mL) of blank mass to liquid volume. Maintain the material temperature at 45°C. Start the vacuum pump and evacuate the vacuum in the tank to -0.085MPa. Maintain this vacuum for 20 minutes to allow the gas in the blank pores to be discharged and the permeate to initially enter the surface of the blank. S30. After infiltration, perform a segmented pressure-re-pressurization operation: First, control the air intake rate to raise the pressure inside the tank to -0.050MPa and maintain this pressure for 4 minutes; then continue to intake air to raise the pressure inside the tank to -0.020MPa and maintain this pressure for 4 minutes; finally, fully open the air intake valve to restore the pressure to normal, let it stand for 3 minutes, and then drain the excess liquid to complete the in-situ gelation and curing. S40. Remove the processed blanks and drain them. Soak them in a 14% salt solution for 3 days. Then bottle them and add broth containing 10% edible alcohol, 7% salt, and 3.5% sugar. Seal them and ferment them at 25°C for 60 days to obtain the finished product. Example 3

[0040] This embodiment provides a preparation process for fermented bean curd made from fruit and vegetable extracts, including the following steps: S10. Grind soybeans into a slurry and adjust the slurry concentration to 12°Bx. After boiling, cool to 85°C and add 4.0% magnesium chloride coagulant (by weight of dry soybeans) for coagulation. Press under 0.4 MPa pressure for 30 minutes to form white curds. Cut into pieces and inoculate with *Mucor* spores at a rate of 1×10⁻⁶ spores per piece. 4 One spore is fermented at 28°C and 95% relative humidity for 60 hours to obtain a raw material; S20. Place the above blank in a vacuum impregnation tank and inject the enzymatically modified fruit and vegetable permeate of Preparation Example 3. The material-to-liquid ratio is 1:4 (g / mL) of blank mass to liquid volume. Maintain the material temperature at 50°C. Start the vacuum pump and evacuate the vacuum in the tank to -0.09 MPa. Maintain this vacuum for 25 minutes to allow the gas in the blank pores to be discharged and the permeate to initially enter the surface of the blank. S30. After infiltration, perform a segmented pressure-re-pressurization operation: First, control the air intake rate to raise the pressure inside the tank to -0.045MPa and maintain this pressure for 6 minutes; then continue to intake air to raise the pressure inside the tank to -0.015MPa and maintain this pressure for 5 minutes; finally, fully open the air intake valve to restore the pressure to normal, let it stand for 5 minutes, and then drain the excess liquid to complete the in-situ gelation and curing. S40. Take out the processed blanks and drain them. Soak them in a 16% salt solution for 4 days. Then bottle them and add broth containing 12% edible alcohol, 8% salt and 5% sugar. Seal them and ferment them at 30℃ for 90 days to obtain the finished product.

[0041] Comparative Examples 1-4: Comparative Example 1: Compared with Example 2, the difference is that no phytase was added during the preparation of the enzymatically modified fruit and vegetable permeate, while the other parameters and steps were the same.

[0042] Comparative Example 2: Compared with Example 2, the difference is that in step S30, after the permeation is completed, the segmented venting and repressurization operation is not performed. Instead, the air intake valve is directly opened to restore the pressure to normal. All other parameters and steps are the same.

[0043] Comparative Example 3: Compared with Example 2, the difference is that phytase was not added during the preparation of the enzymatically modified fruit and vegetable permeate, but calcium chloride at a concentration of 0.5% (w / v) was added. All other parameters and steps are the same.

[0044] Comparative Example 4: Compared with Example 2, the difference is that steps S20 and S30 are replaced with atmospheric pressure soaking treatment. Specifically, the blank is completely immersed in the enzymatically modified fruit and vegetable permeate solution of Preparation Example 2, and soaked for 48 hours at room temperature and pressure. Then it is taken out and drained for subsequent operations. All other parameters and steps are the same.

[0045] Test Examples 1-5: Test Example 1: Determination of Changes in Free Calcium Content Inside the Blank Experimental instructions and procedures: This experiment aimed to investigate the changes in the concentration of free calcium ions in the central region of fermented bean curd blanks under different processing conditions, in order to verify the technical mechanism of enzymatic release of endogenous calcium. Ten blanks each prepared after permeation in Examples 1-3, Comparative Examples 1 and 3 were randomly selected as test samples.

[0046] To eliminate interference from calcium ions in the surface-adhered liquid and accurately reflect the biochemical reactions inside the blank, a stainless steel scalpel was used to remove approximately 5 mm of the surface layer of all samples, and only a cube of approximately 1 cubic centimeter at the geometric center of the blank was selected for testing.

[0047] Accurately weigh the intercepted center sample, add deionized water for homogenization, and then centrifuge at 4000 rpm for 15 minutes. Collect the supernatant. Determine the calcium ion content in the supernatant using flame atomic absorption spectrometry as specified in the National Food Safety Standard GB5009.92, and calculate the content of water-soluble free calcium per unit mass of sample.

[0048] Experimental data: Table 1. Results of free calcium content determination in the central region of blanks from different treatment groups

[0049] Experimental conclusion: Analysis of the test results shown in Table 1 shows that the free calcium content in the center of the blanks in Examples 1 to 3 showed a significant increasing trend, and the values ​​were all significantly higher than those in Comparative Example 1 and Comparative Example 3.

[0050] The main difference between Examples 1, 2, and 3 lies in the increasing amount of phytase added to the enzymatically modified fruit and vegetable permeate. Data shows that as the phytase concentration increases, the concentration of free calcium detected inside the raw material also increases. This phenomenon indicates that the phytase in the permeate successfully penetrated deep into the porous medium inside the raw material via vacuum permeation and underwent enzymatic hydrolysis with the calcium phytate present in the soybean protein network, releasing the previously bound calcium, which was not easily reacted, into water-soluble free calcium ions.

[0051] In contrast, Comparative Example 1 did not add phytase during the preparation process, and its detected calcium content was only 124.33 mg / 100g. This mainly came from a small amount of background free calcium remaining during tofu making and some background values ​​from fruit and vegetable liquids that diffused in physically. The value was at a low level, indicating that in the absence of enzymatic hydrolysis, the bound calcium in the soybean matrix could not be automatically converted into an active calcium source.

[0052] Although calcium chloride was added exogenously to the permeate in Comparative Example 3, the free calcium content in its central region was 167.56 mg / 100g, significantly lower than the 268.92 mg / 100g in Example 2. This confirms that directly added exogenous calcium ions readily undergo a rapid gelation reaction with low-methoxyl pectin on the surface of the blank, forming a dense barrier layer that hinders the further diffusion of calcium ions and fruit and vegetable components into the depth of the blank.

[0053] Test Example 2: Verification of Internal Gel Formation Experimental description: This experiment indirectly characterizes the physical state and gelation degree of the fruit and vegetable permeate inside the fermented bean curd blank by measuring the liquid separation rate under mechanical centrifugal force. If a high-strength calcium pectate gel network has formed inside the blank, its binding ability for water and fruit and vegetable components will be enhanced, resulting in a lower centrifugal separation rate; conversely, if the interior is still mainly a free-flowing liquid or has a weak gel structure, the liquid will easily migrate and be ejected from the pores under centrifugal force. The blanks processed according to Examples 1 to 3 and Comparative Examples 1 to 3, but not yet salted, were selected as test samples.

[0054] Experimental steps: Five blank samples were randomly selected from each group. To eliminate the effect of the dense surface structure on the migration of internal liquid, each blank was cut into small cubic blocks with a side length of about 1.0 cm to expose the internal cross-section. Accurately weigh the initial mass of the diced sample, then place it in a centrifuge tube lined with filter paper. Set the centrifuge speed to 1000 rpm and the centrifugation time to 5 min. After centrifugation, remove the sample and gently blot away any adhering liquid with absorbent paper. Weigh the sample again accurately. Calculate the percentage of liquid separation based on the mass difference before and after centrifugation, and use this value to quantitatively evaluate the water-holding capacity of the internal gel.

[0055] Experimental data: Table 2. Data on the centrifugation liquid separation rate of raw samples in each group

[0056] Experimental conclusion: The experimental data in Table 2 reveal the profound impact of different process conditions on the physical state of the matrix inside the blank. The liquid exudation rate of the sample groups in the example groups remained at a low level, with Example 3 at only 2.65% and Example 2 at 3.01%. This indicates that after being treated by the process of the present invention, the fruit and vegetable permeate inside the blank no longer exists in a free-flowing liquid form, but is transformed into a solid gel with a three-dimensional spatial network structure.

[0057] Based on the technical mechanism analysis of this invention, the phytase added in Examples 1-3 penetrates deep into the substrate during the vacuum permeation stage, releasing free calcium ions in situ. These calcium ions act as cross-linking agents, inducing the formation of a stable egg-box model structure between the infiltrated low-methoxyl pectin molecular chains. This polysaccharide gel system, interpenetrating within the soybean protein network, generates strong capillary forces and chemisorption forces, thereby effectively resisting the effects of external mechanical centrifugal forces and firmly locking water and fruit and vegetable nutrients within the matrix.

[0058] Test Example 3: Permeation Weight Gain Rate Test Experimental description: This experiment aimed to quantitatively evaluate the actual loading capacity of fruit and vegetable extracts in fermented bean curd blanks under different processing conditions. Penetration gain rate is a key macroscopic indicator for measuring vacuum impregnation efficiency and the solid-liquid retention capacity within the matrix. This indicator directly reflects whether fruit and vegetable components effectively enter and remain in the pores inside the blank, rather than merely adhering to the surface. A higher gain rate means that more flavor substances and nutrients are introduced into the fermented bean curd matrix, and no significant loss occurs during the pressure recovery process and subsequent operations.

[0059] Experimental steps: Seventy samples were randomly selected from the fermented raw materials and divided into seven groups, corresponding to Examples 1 to 3 and Comparative Examples 1 to 4. Before vacuum permeation or soaking treatment, the initial total mass of each group of samples was accurately weighed using an electronic balance and denoted as M0.

[0060] Perform fruit and vegetable liquid permeation treatment according to the corresponding process parameters for each group. After treatment and sample removal, immediately place the sample on an inclined draining rack and let it stand for 5 minutes. Gently wipe the sample surface with absorbent paper to remove excess liquid adhering to the surface, ensuring that the weighing result mainly reflects the internal permeation amount. Accurately weigh the total mass of the treated sample and record it as M1.

[0061] According to the formula Calculate the average permeation weight gain rate for each group.

[0062] Experimental data: Table 3. Test results of permeability gain rate of preforms in each group

[0063] Experimental conclusion: The data in Table 3 show significant differences, strongly demonstrating the advantages of the combined process proposed in this invention in improving material loading rate. Example 2 achieved the highest weight gain rate of 33.62%, while Examples 1 and 3 also maintained a high level of over 26%, indicating that the present invention can effectively introduce and lock fruit and vegetable components into the interior of the preform.

[0064] Comparing the data from Example 2 and Comparative Example 2 reveals that the segmented cavitation and repressurization process is crucial to the weight gain rate. Comparative Example 2 used the same enzymatic hydrolysate system as Example 2, but due to the rapid restoration of atmospheric pressure after infiltration, its weight gain rate was only 13.11%, even lower than Comparative Example 1. The mechanism lies in the fact that the fermented bean curd blank has a porous elastic structure similar to a sponge. Under vacuum, gas is expelled from the pores, causing the matrix to expand; if atmospheric pressure is restored instantaneously, the huge pressure difference causes the matrix skeleton to undergo violent elastic recoil, generating a mechanical squeezing effect, forcibly expelling the liquid that has just been absorbed but has not yet gelled and solidified, much like squeezing a sponge. The segmented repressurization process used in the example, utilizing a gradient pressure recovery process, not only maintains a moderate expansion state but also provides the necessary time window for enzymatic reactions and gelation. Before the pressure is fully restored, the internal liquid viscosity has significantly increased or a primary gel has formed, effectively counteracting the matrix's recoil force and achieving in-situ liquid retention.

[0065] Test Example 4: Pickling Loss Rate Test Experimental description: This experiment aims to evaluate the water retention capacity and structural stability of each group of raw bean curd sheets under subsequent high-salinity pickling conditions. The salting process in fermented bean curd production typically involves high-concentration salt solutions, which creates a significant osmotic pressure difference between the inside and outside of the raw bean curd sheet. In conventional processes, this pressure difference leads to substantial water loss from the inside of the sheet, causing shrinkage, hardening, and loss of water-soluble nutrients. This test examines whether the in-situ gel network constructed in this invention can effectively counteract the dehydration effect caused by osmotic pressure by comparing the quality changes before and after pickling.

[0066] Experimental steps: Samples from Examples 1 to 3 and Comparative Examples 1 to 4, which had undergone osmosis and re-pressure treatment but had not yet been salted, were randomly selected from each group, with 20 samples chosen at a time. Free moisture on the sample surface was blotted dry with filter paper, and the total initial mass of each group of samples was accurately determined and denoted as m. a .

[0067] Each group of samples was immersed in a 14% saline solution, with the liquid level 5 cm above the sample surface, and pickled at a constant temperature of 25°C for 72 hours. After pickling, the samples were removed, placed on a 2 mm mesh filter to drain for 10 minutes, and the surface was gently wiped to remove excess brine. The total final mass of each group of samples was accurately measured again and recorded as m. b .

[0068] According to the formula Calculate the average pickling loss rate for each group.

[0069] Experimental data: Table 4. Results of marinating loss rate of raw curds in each group

[0070] Experimental conclusion: The test results in Table 4 clearly show that the samples prepared using the technical solution of this invention have a significant advantage in dehydration resistance. The pickling loss rate of Example 2 was only 8.61%, lower than that of the comparative examples. Examples 1 and 3 also showed excellent water retention performance, with loss rates controlled within 12%.

[0071] The fundamental reason for the data discrepancy lies in the different states of water presence inside the blanks. In Comparative Example 1, since no phytase was added, the fruit and vegetable juice that entered the blanks mainly existed in the form of free water within the pores. When faced with the osmotic pressure stress of high-concentration saline solution from the outside, this free water followed the principle of osmotic diffusion, rapidly migrating outwards to balance the osmotic pressure, resulting in a significant decrease in the quality of the blanks, with a loss rate as high as 33.88%.

[0072] Conversely, the example group initiated an in-situ gelation reaction of low-methoxyl pectin by releasing calcium ions through phytase. The resulting calcium pectate gel network exhibits extremely strong hydration capacity, converting free water into bound water or gel water physically confined within a three-dimensional network. This gel structure not only increases the resistance to water molecule movement but also provides additional mechanical support to counteract volume shrinkage due to water loss.

[0073] Test Example 5: Texture Property Analysis Experimental description: This experiment aims to perform total texture analysis (TPA) on the finished fermented bean curd products prepared in each group using a texture analyzer, in order to quantitatively evaluate the physical structural characteristics of the products. As a fermented soybean product, fermented bean curd typically has a soft and mushy texture and lacks elasticity, making it fragile during transportation and prone to crumbling when picked up for consumption. This invention introduces a calcium pectate gel network into the fermented bean curd matrix, which is expected to improve the product's mechanical properties. This test will focus on three key indicators: hardness, elasticity, and chewiness, to verify the enhancing effect of the dual-network structure on the texture of the fermented bean curd.

[0074] Experimental steps: Fifteen pieces of fermented bean curd prepared and matured in Examples 1 to 3 and Comparative Examples 1 to 4 were selected. The samples were carefully removed, the liquid on the surface was drained, and all samples were trimmed into standard cubes with a side length of 2.0 cm to ensure geometric consistency of the test conditions.

[0075] The measurements were performed using a TMS-Pro texture analyzer with a 36 mm diameter cylindrical probe (P / 36R). The test parameters were set as follows: The running speed before the test was 1.0 mm / s, the running speed during the test was 1.0 mm / s, and the return speed after the test was 1.0 mm / s; the trigger force was set to 0.05 N; the deformation compression ratio was set to 40%; and the interval between the two compressions was 5 s.

[0076] Each sample was measured 10 times, and the arithmetic mean was taken after removing the maximum and minimum values.

[0077] Among them, hardness represents the maximum peak force during the first compression; elasticity represents the ratio of the deformation degree of the second compression to the deformation degree of the first compression; chewiness is calculated by multiplying hardness, cohesiveness and elasticity.

[0078] Experimental data: Table 5. Test data on the textural properties of finished fermented bean curd products in each group.

[0079] Experimental conclusion: The textural test results in Table 5 reveal the significant improvement in the physical properties of fermented bean curd achieved by the process of this invention. The sample from Example 2 achieved a hardness of 238.91 g and an elasticity ratio of 0.88, both of which are significantly better than those of the comparative examples.

[0080] From a mechanistic perspective, the microstructure of traditional fermented bean curd mainly relies on the gel network of soybean protein. After a long period of enzymatic fermentation, the protein network is partially degraded and broken, resulting in an extremely soft and mushy texture with an elasticity coefficient of only 0.58. This means that the product is difficult to recover its shape after being compressed and is extremely fragile.

[0081] In contrast, the example group successfully constructed a second network, namely a calcium pectate gel network, on top of the original protein network. This interpenetrating network (IPN) structure, formed in situ by phytase induction, played a crucial skeletal support role. The pectin molecular chains have good flexibility, giving the product excellent elasticity, allowing it to rebound under external pressure and not easily collapse; at the same time, the egg-shell structure formed by calcium ion cross-linking enhances the overall stiffness of the system and improves the hardness index. This combination of stiffness and flexibility in texture allows the fermented bean curd prepared in the example group to maintain a delicate taste while possessing good morphological stability.

Claims

1. A preparation process for compound fermented bean curd made from fruit and vegetable extracts, characterized in that, Includes the following steps: S10. Prepare white blanks inoculated with Rhizopus spores, and obtain raw blanks after fermentation; S20. The blank is placed in a vacuum environment and immersed in an enzymatically modified fruit and vegetable permeate solution, so that the enzymatically modified fruit and vegetable permeate solution enters the pores of the blank to obtain a permeated blank; the enzymatically modified fruit and vegetable permeate solution contains low-methoxyl pectin and phytase. S30. The permeation blank is subjected to a segmented cavitation and repressurization operation to restore the environmental pressure to normal pressure in stages, so that the enzymatically modified fruit and vegetable permeate that has entered the pores of the permeation blank undergoes in-situ gelation and solidification to obtain a solidified blank. S40. The solidified blank is salted, bottled, and fermented to obtain the compound fermented bean curd product.

2. The preparation process of the fruit and vegetable extract compound fermented bean curd according to claim 1, characterized in that, The preparation method of the enzymatically modified fruit and vegetable permeate in step S20 includes the following steps: Fresh fruits and vegetables are selected, crushed and pulped, enzyme preparations are added for initial enzymatic hydrolysis, and filtered to obtain fruit and vegetable base liquid. Add low-methoxyl pectin to the fruit and vegetable base liquid, heat to dissolve, and then cool. Adjust the pH of the solution to the acidic range, add phytase, and stir well to obtain the enzymatically modified fruit and vegetable permeate.

3. The preparation process of the fruit and vegetable extract compound fermented bean curd according to claim 2, characterized in that, In the process of preparing the fruit and vegetable base liquid, the fresh fruit and vegetable raw materials are selected from one or more of carrots, tomatoes, pumpkins and red dates; The enzyme preparation is a pectinase or a compound enzyme preparation of cellulase and pectinase, and the amount of the enzyme preparation added is 0.05% to 0.10% of the total weight of the slurry; During the process of adjusting the pH value of the solution and adding the phytase, the pH value is adjusted to a range of 4.2 to 5.5; the amount of phytase added is 150 U / kg to 400 U / kg.

4. The preparation process of the fruit and vegetable extract compound fermented bean curd according to claim 2, characterized in that, During the process of adding the low-methoxyl pectin and heating to dissolve it, the heating temperature is 60°C to 70°C and the holding time is 10 min to 20 min. During the process of adjusting the pH value of the solution and adding the phytase, the temperature of the solution is controlled between 40°C and 50°C.

5. The preparation process of the fruit and vegetable extract compound fermented bean curd according to claim 2, characterized in that, During the addition of the low-methoxyl pectin, the amount of low-methoxyl pectin added is from 8 g / L to 16 g / L, and the degree of esterification of the low-methoxyl pectin is from 30% to 40%.

6. The preparation process of the fruit and vegetable extract compound fermented bean curd according to claim 1, characterized in that, In step S10, the preparation process of the raw material includes: adjusting the concentration of soybean slurry to 10°Bx to 12°Bx, adding a coagulant to form a white raw material, cutting it into pieces, and inoculating it with *Rhizopus cuspidatum* spores, with an inoculation amount of 1×10 per piece. 3 One to 1×10 4 The spores are fermented for 40 to 60 hours at a temperature of 20°C to 28°C and a relative humidity of 90% to 95%.

7. The preparation process of the fruit and vegetable extract compound fermented bean curd according to claim 1, characterized in that, In step S20, the impregnation conditions under vacuum are as follows: the ratio of blank mass to liquid volume is 1:2 to 1:4 (g / mL); the liquid temperature is 40℃ to 50℃; the vacuum degree is -0.08MPa to -0.09MPa; and the vacuum maintenance time is 15min to 25min.

8. The preparation process of the fruit and vegetable extract compound fermented bean curd according to claim 1, characterized in that, In step S30, the segmented air-breaking and repressurization operation specifically includes: Control the intake rate to raise the pressure to -0.055MPa to -0.045MPa, and maintain the pressure for 3 to 6 minutes. Continue to introduce air to raise the pressure back to -0.025 MPa to -0.015 MPa, and maintain this pressure for 3 to 5 minutes. Fully open the intake valve to restore normal pressure.

9. The preparation process of the fruit and vegetable extract compound fermented bean curd according to claim 1, characterized in that, In step S40, the salt water concentration used in the salting process is 12% to 16%, and the salting time is 2 to 4 days.

10. The preparation process of the fruit and vegetable extract compound fermented bean curd according to claim 1, characterized in that, In step S40, the broth used in the later fermentation process comprises: Edible alcohol with a volume fraction of 8% to 12%, table salt with a mass fraction of 6% to 8%, and sugar with a mass fraction of 2% to 5%. The fermentation temperature is 20℃ to 30℃, and the fermentation time is 45 to 90 days.

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