阅读说明：本技术 一种以豆清发酵液为凝固剂制备包浆豆腐的方法 (Method for preparing slurry-coated bean curd by taking bean curd clear fermentation liquor as coagulant ) 是由 张胤 李肯 江振桂 于 2021-02-06 设计创作，主要内容包括：本发明提供了一种以豆清发酵液为凝固剂制备包浆豆腐的方法,具体包括如下步骤：制备豆清发酵液、浸泡、去皮、磨浆、煮浆、过滤、豆清发酵液点浆、蹲脑、压榨、冷藏、浸泡、清洗、装盒、速冻。其中豆清发酵液是以豆制品生产过程中产生的副产物——豆清液(俗称黄浆水,醋水)为原料,采用多菌株益生菌周期变温分段协同发酵技术制备而成。该技术制备的豆清发酵液富含有机酸、胞外多糖、γ-氨基丁酸、游离型大豆异黄酮、B族维生素和多肽等营养物质,以其为凝固剂制备的包浆豆腐,外部色泽光亮、棱角分明、内部浆汁爽滑细嫩、呈流动状态、风味独特、营养物质丰富。(The invention provides a method for preparing slurry-coated bean curd by taking a bean curd clear fermentation liquid as a coagulant, which comprises the following steps: preparing a bean curd clear fermentation liquid, soaking, peeling, grinding into thick liquid, boiling the thick liquid, filtering, curdling the bean curd clear fermentation liquid, squatting, squeezing, refrigerating, soaking, cleaning, boxing and quick-freezing. The bean clear fermentation liquid is prepared by taking bean clear liquid (commonly called yellow serofluid and vinegar) which is a byproduct generated in the production process of bean products as a raw material and adopting a multi-strain probiotic periodic temperature-changing and segmented synergistic fermentation technology. The tofu whey fermentation liquor prepared by the technology is rich in nutrients such as organic acid, extracellular polysaccharide, gamma-aminobutyric acid, free soybean isoflavone, B vitamins, polypeptide and the like, and the slurry-coated tofu prepared by using the fermentation liquor as a coagulant has bright external color, clear edges and corners, smooth and tender internal slurry, flowing state, unique flavor and rich nutrients.)

1. A method for preparing slurry-covered bean curd by taking a bean curd clear fermentation liquid as a coagulant is characterized by comprising the following steps:

(1) preparing a bean whey fermentation liquid: firstly, collecting bean clear liquid, filtering the bean clear liquid by a sieve of 100-150 meshes, then respectively adding 3-7% of lactose, 1-3% of cane sugar, 1-3% of functional oligosaccharide and 2% of peptone by volume fraction of the bean clear liquid, sterilizing the bean clear liquid for 10-30 min at 100-121 ℃, then cooling the bean clear liquid to 42 ℃, inoculating 1-5% of mixed strains by volume fraction, periodically carrying out temperature-changing and sectional fermentation, carrying out aeration culture for 10-36 h until the total acid of the bean clear fermentation liquid is 3-5.5 g/L, stopping fermentation for later use, wherein the proportion of the mixed strains is lactobacillus casei: lactobacillus plantarum: lactobacillus rhamnosus: streptococcus thermophilus ═ 1: 1: 1: 1;

(2) soaking: according to the dry bean: soaking bean water in a ratio of 1:3 at room temperature for 4-12 h;

(3) peeling: peeling the soaked soybeans by using a peeling machine, and cleaning the soybeans for later use;

(4) grinding: according to the dry bean: grinding the bean milk in a water-to-bean milk ratio of 1: 3-7;

(5) boiling the soybean milk: boiling the pulp at 100-108 ℃, and keeping the temperature for 3-10 min;

(6) and (3) filtering: filtering with 150 meshes to obtain soybean milk for later use;

(7) curdling a soy bean whey fermentation liquid: the curdling temperature is 55-95 ℃, 15-50% of soy bean serum fermentation liquor is added according to the volume fraction of the soy bean milk, stirring is carried out while adding until a large amount of brain flowers are generated, and stirring can be stopped when light yellow supernatant is separated out;

(8) squatting: preserving the temperature for 3-20 min, sucking out supernatant and breaking the brain;

(9) squeezing: putting the encephalopathy into a box, and squeezing for 5-30 min;

(10) and (3) refrigerating: cutting the squeezed bean curd into blocks, and refrigerating at 4 ℃ for 8-20 h;

(11) soaking: soaking the refrigerated bean curd in a mixed solution of 0.1-0.5% of sodium bicarbonate and 0.1-0.3% of edible salt for 3-20 h;

(12) cleaning: washing the soaked slurry-coated bean curd with deionized water, and draining off the surface water;

(13) boxing and quick freezing: and (4) boxing the slurry-coated bean curd, quickly freezing by adopting liquid nitrogen, and preserving for half a year under a freezing condition after the quick freezing is finished.

2. The method according to claim 1, wherein the clear bean liquid in step (1) is required to have a solid content of 0.5% or more, a total acid content of 2.5g/L or less, and a pH value of 5.5 or more.

3. The method according to claim 1, wherein the functional oligosaccharide in step (1) is one or more of stachyose, raffinose, isomaltooligosaccharide, fructooligosaccharide, xylooligosaccharide, galactooligosaccharide, soybean oligosaccharide, gentiooligosaccharide and chitosan oligosaccharide.

4. The method according to claim 1, wherein the periodic temperature-variable staged fermentation in the step (1) is a stepwise temperature-regulated fermentation, namely the fermentation time is 0-4 h, and the fermentation temperature is 42 ℃; the fermentation time is 4-10 or 4-36 h, and the fermentation temperature is 36 ℃.

5. The method according to claim 1, wherein in the step (1), the aeration culture is performed for 0-6 h by introducing sterile oxygen, the dissolved oxygen is ensured to be 1-5 mg/L, and the anaerobic fermentation of the strain is promoted by introducing sterile nitrogen for 6-10/36 h.

6. The method according to claim 1, wherein in the step (2), the soaking time of the soybeans in summer is 4-6 h, the soaking time of the soybeans in winter is 8-12 h, the soaking time of the soybeans in spring and autumn is 6-10 h, the soaked soybeans are full, the section of the soybeans does not have obvious hard center, and the weight of wet soybeans is about 2-3 times of that of dry soybeans.

7. The method according to claim 1, wherein before the whey fermentation liquid is coagulated in the step (7), the whey fermentation liquid is heated to 35-70 ℃, and the total acid of the whey fermentation liquid is sampled and measured, so that the total acid of the whey fermentation liquid is 3-5.5 g/L.

8. The method according to claim 1, wherein before the soaking in the step (11), the temperature of the deionized water is adjusted to 10-30 ℃, and then 0.1-0.5% of sodium bicarbonate and 0.1-0.3% of edible salt are added into the deionized water in volume fraction, and mixed and dissolved, so as to ensure that the temperature of the soaking water is 10-30 ℃.

9. The method according to claim 1, wherein liquid nitrogen is adopted for quick freezing in the step (13), the method further comprises a tunnel storehouse body besides the liquid nitrogen deep-freezing equipment, liquid nitrogen spray pipes are sequentially arranged from a discharge port to a feed port of the tunnel storehouse body, the rotating speed of a nozzle is 100-600 r/min, and 5 bean curd runs for 3-10 min in an environment of-50 to-40 ℃. The finished product can be preserved for 6 months under the condition that the freezing preservation temperature is-18 to-20 ℃.

Technical Field

The invention relates to the field of bean product processing, in particular to a method for preparing slurry-coated bean curd by taking a bean curd clear fermentation liquid as a coagulant.

Background

The slurry-coated bean curd is rich in vitamins, plant proteins, trace elements, mineral substances and the like, has the effects of enriching blood and supplementing calcium, and tonifying spleen and nourishing stomach, is particularly suitable for old people, women, children and people with high blood pressure, high blood sugar and high blood sugar, has the digestibility of more than 95 percent, is fresh, tender and delicious in taste, and is deeply loved by people.

The existing slurry-coated bean curd is mainly prepared by taking bean clear fermentation liquor (commonly called sour pulp and vinegar) prepared by naturally fermenting bean clear liquid (commonly called yellow serofluid and vinegar) in the production process of bean curd as a coagulant for coagulating slurry. The natural fermentation process is uncontrollable, the fermentation period is long and unstable, the technology is low and the skill is strong, the production efficiency is low, the product quality is unstable, the quality guarantee period is short, the standardized, mechanized and large-scale production is difficult to realize, pathogenic bacteria are easily infected, and the potential safety hazard exists.

Chinese patent Drinking a Dendrobium covered slurry Bean curd and its preparation method (patent application No. 202010496839.4) discloses a Dendrobium covered slurry Bean curd and its preparation method. The dendrobium juice is added in the process of preparing the slurry-coated bean curd, so that the product is light green, the appearance is more attractive, the nutritive value can be improved, citric acid water is adopted to be matched with informing water for solidification and forming, a chemical additive is additionally added, the flavor of the product is easily influenced, the taste is poor, the informing water is naturally fermented, the fermentation process is uncontrollable, the quality is unstable, and the potential safety hazard exists due to the pollution.

Chinese patent 'A coated bean curd and its preparation method' (patent application No. 201910971360.9) discloses a coated bean curd and its preparation method. The curdling temperature (80-90 ℃) and the pH value (7-8) of the acid water tofu are strictly controlled in the curdling part, so that the product quality is ensured, but the coagulator and other key steps are not explained.

Chinese patent 'A coated bean curd and its preparation method' (patent application No. 201810987166.5) discloses a coated bean curd and its preparation method. The method adopts citric acid, underground well water and notice water to carry out curdling to prepare the slurry-coated bean curd, fully utilizes original components in local water, but also brings chemical additives additionally, so that the flavor of the product is easily influenced, the taste is poor, the notice water is naturally fermented, the fermentation process is uncontrollable, the quality is unstable, and potential safety hazards exist due to the pollution.

Chinese patent 'a paste-coated bean curd and its preparation method' (patent application No. 200810144539.9) discloses a paste-coated bean curd and its preparation method, which is prepared by using bean curd, water, sodium bicarbonate and selenium iodine salt as raw materials according to a certain weight ratio, cutting the bean curd into blocks, drying in the air, soaking and fermenting for 1.5-4h with sodium bicarbonate and selenium iodine salt aqueous solution, draining the water, bagging and sealing, adding external chemical reagents such as selenium iodine salt and the like, which is easy to influence the flavor of the product, resulting in poor taste, and informing that water is natural fermentation, the fermentation process is uncontrollable, the quality is unstable, and the pollution has potential safety hazard.

In view of the above, the invention adopts modern biological fermentation technology, uses the technology of periodically, temperature-variable and sectionally cooperated fermentation of the bean clear liquid by a plurality of strains of probiotic bacteria to prepare the bean clear liquid fermentation liquid which is safer, more standard and controllable, and then uses the bean clear liquid fermentation liquid as a coagulant to prepare the slurry-coated bean curd which has no additive, has nutrition and health care functions and has good flavor and taste, so as to improve the core competitiveness of enterprises and promote the transformation and upgrade of industries.

Disclosure of Invention

The invention aims to provide a method for preparing slurry-covered bean curd by taking a bean curd fermentation liquid as a coagulant. The method adopts a technology of periodically, temperature-variable and sectionally cooperatively fermenting the bean clear liquid by using multiple strains of probiotic bacteria to prepare the bean clear liquid fermentation liquid. The tofu whey fermentation liquor prepared by the technology is rich in nutrients such as organic acid, extracellular polysaccharide, gamma-aminobutyric acid, free soybean isoflavone, B vitamins, polypeptide and the like, and the slurry-coated tofu prepared by taking the tofu as a coagulant has better flavor, longer shelf life, higher nutritional value, stronger health-care function and safer, more standard and controllable production process compared with the traditional natural fermentation. The method can reduce the discharge of the soybean clear liquid, relieve the environmental protection pressure of enterprises, reduce environmental pollution and protect the environment, can realize the comprehensive utilization of the soybean clear liquid, change waste into valuable, improve the quality of the slurry-coated bean curd products and the core competitiveness of the enterprises, promote the transformation and upgrading of the industry and realize mechanization, scale and standardization.

In order to achieve the above purpose of the present invention, the following technical solutions are adopted:

the invention provides a method for preparing slurry-coated bean curd by taking a bean curd clear fermentation liquid as a coagulant, which comprises the following steps:

(1) preparing a bean whey fermentation liquid: firstly, collecting bean clear liquid (commonly called yellow serofluid and vinegar), filtering by 100-150 meshes, then respectively adding 3-7% of lactose, 1-3% of cane sugar, 1-3% of functional oligosaccharide and 2% of peptone by volume fraction of the bean clear liquid, sterilizing for 10-30 min at 100-121 ℃, then cooling to 42 ℃, inoculating 1-5% of mixed strain (lactobacillus casei: lactobacillus rhamnosus: streptococcus thermophilus: 1: 1: 1), periodically carrying out variable-temperature sectional fermentation, carrying out aeration culture for 10-36 h until the total acid of the bean clear fermentation liquid is 3-5.5 g/L, and stopping fermentation for later use;

(2) soaking: according to the dry bean: soaking bean water in a ratio of 1:3 at room temperature for 4-12 h;

(3) peeling: peeling the soaked soybeans by using a peeling machine, and cleaning the soybeans for later use;

(4) grinding: according to the dry bean: grinding the bean milk in a water-to-bean milk ratio of 1: 3-7;

(5) boiling the soybean milk: boiling the pulp at 100-108 ℃, and keeping the temperature for 3-10 min;

(6) and (3) filtering: filtering with 150 meshes to obtain soybean milk for later use;

(7) curdling a soy bean whey fermentation liquid: the curdling temperature is 55-95 ℃, 15-50% of soy bean serum fermentation liquor is added according to the volume fraction of the soy bean milk, stirring is carried out while adding until a large amount of brain flowers are generated, and stirring can be stopped when light yellow supernatant is separated out;

(8) squatting: preserving the temperature for 3-20 min, sucking out supernatant and breaking the brain;

(9) squeezing: putting the encephalopathy into a box, and squeezing for 5-30 min;

(10) and (3) refrigerating: cutting the squeezed bean curd into blocks, and refrigerating at 4 ℃ for 8-20 h;

(11) soaking: soaking the refrigerated bean curd in a mixed solution of 0.1-0.5% of sodium bicarbonate and 0.1-0.3% of edible salt for 3-20 h;

(12) cleaning: washing the soaked slurry-coated bean curd with deionized water, and draining off the surface water;

(13) boxing and quick freezing: and (4) packing the slurry-coated bean curd into boxes, quickly freezing by adopting liquid nitrogen, and preserving under a freezing condition for half a year after the quick freezing is finished.

Further, the requirements of the bean clear liquid in the step (1) are as follows: the solid content is more than or equal to 0.5 percent, the total acid is less than or equal to 2.5g/L, and the pH value is more than or equal to 5.5.

Further, in the step (1), the functional oligosaccharide is one or more of stachyose, raffinose, isomaltooligosaccharide, fructo-oligosaccharide, xylo-oligosaccharide, galacto-oligosaccharide, soybean oligosaccharide, gentiooligosaccharide and chitosan oligosaccharide.

Further, the probiotics in the step (1) such as lactobacillus casei, lactobacillus plantarum, lactobacillus rhamnosus and streptococcus thermophilus can be used for food addition, are directly purchased from markets or professional organizations, need to be activated and expanded for 1-3 times, and then have viable count of 1.0 multiplied by 10⁸CFU/mL was measured at 1: 1: 1: 1, and then culturing the mixture for 1-3 generations.

Further, the periodic temperature-changing and segmented fermentation in the step (1) is to adopt step-type temperature-adjusting fermentation, namely the fermentation time is 0-4 h, and the fermentation temperature is 42 ℃; the fermentation time is 4-10 or 4-36 h, and the fermentation temperature is 36 ℃.

Further, in the step (1), the aeration culture is performed for 0-6 h by introducing sterile oxygen, the dissolved oxygen is ensured to be 1-5 mg/L, and the anaerobic fermentation of the strain is promoted by introducing sterile nitrogen for 6-10/36 h.

Further, the crude protein content of the soybean material is not less than 40.0%.

Further, in the step (2), the soaking time of the soybeans in summer is 4-6 h, the soaking time of the soybeans in winter is 8-12 h, the soaking time of the soybeans in spring and autumn is 6-10 h, the soaked soybeans are full, the section of the soybeans does not have obvious hard center, and the weight of wet soybeans is 2-3 times of that of dry soybeans.

Further, before the whey fermentation liquor is coagulated in the step (7), the whey fermentation liquor needs to be heated to 35-70 ℃, and the total acid of the whey fermentation liquor is sampled and measured, so that the total acid of the whey fermentation liquor is ensured to be 3-5.5 g/L.

Further, before the soaking in the step (11), the temperature of the deionized water is adjusted to 10-30 ℃, then 0.1-0.5% of sodium bicarbonate and 0.1-0.3% of edible salt are added into the deionized water according to volume fraction, and the mixture is mixed and dissolved, so that the soaking water temperature is 10-30 ℃.

Further, in the step (13), liquid nitrogen is adopted for quick freezing, besides liquid nitrogen deep-freezing equipment, the bean curd further comprises a tunnel storehouse body, liquid nitrogen spray pipes are sequentially arranged from a discharge port to a feed port of the tunnel storehouse body, the rotating speed of a nozzle is 100-600 r/min, and 5 bean curd runs for 3-10 min under the environment of-50 to-40 ℃. The finished product can be preserved for 6 months under the condition that the freezing preservation temperature is-18 to-20 ℃.

Technical effects

1. The clear bean liquid is fermented by the cooperation of multiple strains of probiotics and periodic temperature change and segmentation to obtain clear bean liquid fermentation liquid, so that the clear bean liquid fermentation liquid is rich in organic acid, extracellular polysaccharide, gamma-aminobutyric acid, free soybean isoflavone, B vitamins, polypeptide and other nutrient substances.

2. The tofu whey fermentation broth is used as a coagulant, the prepared slurry-coated tofu has unique flavor, better quality, longer shelf life, higher nutritional value and stronger health-care function, and compared with the conventional natural fermentation mode, the slurry-coated tofu produced by the method is safer, more standard and more controllable, and is beneficial to realizing mechanization, scale and standardization.

3. The method not only can reduce the discharge of the soybean clear liquid, relieve the environmental protection pressure of enterprises, reduce the environmental pollution and protect the environment, but also can realize the comprehensive utilization of the soybean clear liquid, change waste into valuable, improve the quality of the slurry-coated bean curd products and the core competitiveness of the enterprises and promote the transformation and upgrading of the industry.

Detailed Description

The present invention will be described in further detail with reference to specific embodiments.

Evaluation index and method thereof:

soybean isoflavone content: the content of the soybean isoflavone in the slurry-wrapped bean curd is measured by referring to the high performance liquid chromatography for measuring the soybean isoflavone in GB/T23788-2009 health food.

② fuzzy sensory evaluation

The same in-situ frying/roasting of the slurry-coated tofu prepared in the following examples 1 to 3, control groups 1 to 4 was performed while randomly inviting 1000 sensory evaluators. Wherein the 8-18 year old people are 200 people, the 19-30 year old people are 400 people, the 33-50 year old people are 300 people, and the 50 year old people are 100 people. Before sensory evaluation, samples are numbered, and sensory evaluation is respectively carried out on the color, smell, taste and texture of the bean curd by adopting a double-blind method, each index is divided into 3 grades of superior, good and poor, and the sensory evaluation table is shown in table 1.

TABLE 1 sensory evaluation chart

The color (U) of the bean curd was used for this comparison₁) And fragrance (U)₂) And taste (U)₃) And juice (U)₄) The fuzzy sensory analysis factor set of the obtained bean curd is U ═ U as sensory evaluation index₁,U₂,U₃,U₄}. The evaluation set is a set of ratings to which the evaluated index belongs. The bean curd is determined to have excellent evaluation grade (V) through the discussion of an evaluation group₁) Good (V)₂) A, a (V)₃) Obtaining the comment set V ═ V of the bean curd₁,V₂,V₃{90,70,50 }; determining the weight set of the sensory index of the bean curd as R ═ { R₁,R₂,R₃,R₄0.15,0.25,0.3 and 0.3, namely, the color and luster accounts for 0.15, the fragrance accounts for 0.25, the mouthfeel accounts for 0.30 and the juice accounts for 0.3. And the fuzzy mathematics comprehensive evaluation is that Y is Ry, wherein R is a weight set, Y is a fuzzy mathematics matrix, and Y is obtained by dividing the number of persons corresponding to each evaluation standard and each evaluation result by the total number of appraisers.

Example 1

(1) Preparing a bean whey fermentation liquid: firstly, collecting bean clear liquid (commonly called yellow serofluid), filtering by 150 meshes, respectively adding 3% of lactose, 3% of cane sugar and 2% of functional oligosaccharide by volume fraction, sterilizing at 115 ℃ for 20min, cooling to 42 ℃ by volume fraction, inoculating 3% of mixed strain (lactobacillus casei: lactobacillus plantarum: lactobacillus rhamnosus: streptococcus thermophilus: 1: 1: 1), periodically carrying out temperature-changing segmented fermentation, and carrying out aeration culture for 15h until the total acid of the bean clear fermentation liquid is 5g/L, and stopping fermentation for later use;

(2) soaking: according to the dry bean: soaking bean water at a ratio of 1:3 at room temperature for 4h (summer);

(3) peeling: peeling the soaked soybeans by using a peeling machine, and cleaning the soybeans for later use;

(4) grinding: according to the dry bean: grinding the bean water ratio of 1: 4;

(5) boiling the soybean milk: boiling at 105 deg.C for 5 min;

(6) and (3) filtering: filtering with 150 meshes to obtain soybean milk for later use;

(7) curdling a soy bean whey fermentation liquid: the curdling temperature is 80 ℃, 30 percent of soy whey fermentation liquor is added according to the volume fraction of the soybean milk, the stirring is carried out while adding until a large amount of brain flowers are generated, and the stirring can be stopped when light yellow supernatant is separated out;

(8) squatting: keeping the temperature for 5min, sucking out the supernatant and breaking the brain;

(9) squeezing: putting the encephalopathy into a box, and squeezing for 20 min;

(10) and (3) refrigerating: cutting the squeezed bean curd into blocks, and refrigerating at 4 ℃ for 10 h;

(11) soaking: soaking the refrigerated bean curd in a mixed solution of 0.4% sodium bicarbonate and 0.2% edible salt for 10 h;

(12) cleaning: washing the soaked slurry-coated bean curd with deionized water, and draining off the surface water;

(13) boxing and quick freezing: and (4) packing the slurry-coated bean curd into boxes, quickly freezing by adopting liquid nitrogen, and preserving under a freezing condition for half a year after the quick freezing is finished.

Example 2

(1) Preparing a bean whey fermentation liquid: firstly, collecting bean clear liquid (commonly called yellow serofluid), filtering by 150 meshes, respectively adding 5% of lactose, 3% of cane sugar and 1% of functional oligosaccharide by volume fraction, sterilizing at 115 ℃ for 20min, cooling to 42 ℃, inoculating 2% of mixed strain (lactobacillus casei: lactobacillus plantarum: lactobacillus rhamnosus: streptococcus thermophilus: 1: 1: 1) by volume fraction), periodically carrying out temperature-changing and sectional fermentation, and carrying out aeration culture for 18h until the total acid of the bean clear fermentation liquid is 5.5g/L, and stopping fermentation for later use;

(2) soaking: according to the dry bean: soaking bean water at a ratio of 1:3 at room temperature for 4h (summer);

(3) peeling: peeling the soaked soybeans by using a peeling machine, and cleaning the soybeans for later use;

(4) grinding: according to the dry bean: grinding the bean milk with water in a ratio of 1: 5;

(5) boiling the soybean milk: boiling the pulp at 102 deg.C, and keeping the temperature for 7 min;

(6) and (3) filtering: filtering with 150 meshes to obtain soybean milk for later use;

(7) curdling a soy bean whey fermentation liquid: the curdling temperature is 90 ℃, 20 percent of the whey fermentation liquor is added according to the volume fraction of the soybean milk, the stirring is carried out while adding until a large amount of brain flowers are generated, and the stirring can be stopped when light yellow supernatant is separated out;

(8) squatting: keeping the temperature for 3min, sucking out supernatant and breaking the brain;

(9) squeezing: putting the encephalopathy into a box, and squeezing for 15 min;

(10) and (3) refrigerating: cutting the squeezed bean curd into pieces, and refrigerating at 4 ℃ for 8 h;

(11) soaking: soaking the refrigerated bean curd in a mixed solution of 0.2% sodium bicarbonate and 0.3% edible salt for 18 h;

(12) cleaning: washing the soaked slurry-coated bean curd with deionized water, and draining off the surface water;

(13) boxing and quick freezing: and (4) packing the slurry-coated bean curd into boxes, quickly freezing by adopting liquid nitrogen, and preserving under a freezing condition for half a year after the quick freezing is finished.

Example 3

(1) Preparing a bean whey fermentation liquid: firstly, collecting bean clear liquid (commonly called yellow serofluid), filtering by 150 meshes, respectively adding 7% of lactose, 1% of cane sugar and 3% of functional oligosaccharide by volume fraction, sterilizing at 115 ℃ for 20min, cooling to 42 ℃, inoculating 1% of mixed strain (lactobacillus casei: lactobacillus plantarum: lactobacillus rhamnosus: streptococcus thermophilus: 1: 1: 1) by volume fraction), periodically carrying out temperature-changing segmented fermentation, and carrying out aeration culture for 10h until the total acid of the bean clear fermentation liquid is 3.2g/L, and stopping fermentation for later use;

(2) soaking: according to the dry bean: soaking bean water at a ratio of 1:3 at room temperature for 4h (summer);

(3) peeling: peeling the soaked soybeans by using a peeling machine, and cleaning the soybeans for later use;

(4) grinding: according to the dry bean: grinding the bean milk in a ratio of water to bean milk of 1: 6;

(5) boiling the soybean milk: boiling the pulp at 102 deg.C, and keeping the temperature for 8 min;

(6) and (3) filtering: filtering with 150 meshes to obtain soybean milk for later use;

(7) curdling a soy bean whey fermentation liquid: the curdling temperature is 95 ℃,50 percent of the whey fermentation liquor is added according to the volume fraction of the soybean milk, the stirring is carried out while adding until a large amount of brain flowers are generated, and the stirring can be stopped when light yellow supernatant is separated out;

(8) squatting: keeping the temperature for 15min, sucking out the supernatant and breaking the brain;

(9) squeezing: putting the encephalopathy into a box, and squeezing for 30 min;

(10) and (3) refrigerating: cutting the squeezed bean curd into blocks, and refrigerating at 4 ℃ for 16 h;

(11) soaking: soaking the refrigerated bean curd in a mixed solution of 0.5% sodium bicarbonate and 0.3% edible salt for 8 h;

(12) cleaning: washing the soaked slurry-coated bean curd with deionized water, and draining off the surface water;

(13) boxing and quick freezing: and (4) packing the slurry-coated bean curd into boxes, quickly freezing by adopting liquid nitrogen, and preserving under a freezing condition for half a year after the quick freezing is finished.

Comparative example 1

Preparing slurry-wrapped bean curd with naturally fermented bean curd liquid (commonly called sour pulp and vinegar) as coagulant

(1) Preparing a bean whey fermentation liquid: collecting bean clear liquid (commonly called yellow serofluid), filtering by 150 meshes, naturally fermenting for 36-72 h at room temperature until the total acid of the bean clear fermentation liquid is 3.5g/L, and stopping fermentation for later use;

(2) soaking: according to the dry bean: soaking bean water at a ratio of 1:3 at room temperature for 4h (summer);

(3) peeling: peeling the soaked soybeans by using a peeling machine, and cleaning the soybeans for later use;

(4) grinding: according to the dry bean: grinding the bean milk in a ratio of water to bean milk of 1: 6;

(5) boiling the soybean milk: boiling the pulp at 102 deg.C, and keeping the temperature for 8 min;

(6) and (3) filtering: filtering with 150 meshes to obtain soybean milk for later use;

(7) curdling a soy bean whey fermentation liquid: the curdling temperature is 85 ℃,50 percent of the whey fermentation liquor is added according to the volume fraction of the soybean milk, the stirring is carried out while adding until a large amount of brain flowers are generated, and the stirring can be stopped when light yellow supernatant is separated out;

(8) squatting: keeping the temperature for 15min, sucking out the supernatant and breaking the brain;

(9) squeezing: putting the encephalopathy into a box, and squeezing for 30 min;

(10) and (3) refrigerating: cutting the squeezed bean curd into blocks, and refrigerating at 4 ℃ for 16 h;

(11) soaking: soaking the refrigerated bean curd in a mixed solution of 0.3% sodium bicarbonate and 0.2% edible salt for 14 h;

(12) cleaning: washing the soaked slurry-coated bean curd with deionized water, and draining off the surface water;

(13) boxing and quick freezing: and (4) packing the slurry-coated bean curd into boxes, quickly freezing by adopting liquid nitrogen, and preserving under a freezing condition for half a year after the quick freezing is finished.

Comparative example 2

The slurry-coated bean curd is prepared by using citric acid, underground well water and water as coagulants.

Raw materials: selecting non-transgenic soybean, with no impurity, full grain, no mildew, no disease spot, etc., and protein content not less than 42%;

soaking: cleaning semen glycines, and soaking in water at 20 deg.C for 5.8 hr.

Grinding: adding water and grinding to obtain 365 kg of primary pulp liquid per 47kg of soybeans. The fineness of the powder is 110 meshes.

Boiling the soybean milk: the primary slurry was boiled at 110 ℃ for 6 minutes.

And (3) filtering: filtering with 110 meshes, and keeping the soybean milk for later use.

Preparing solidified water: 475 kg of underground well water was added to every 250 g of citric acid to obtain a diluted citric acid solution. Then 26 kg of water is added into each 100 kg of citric acid diluent to obtain the coagulating water. The water was allowed to stand for 20 hours in advance.

Curdling: adding underground well water into the soybean milk to reduce the temperature of the soybean milk to 76 ℃, wherein the pH value of the soybean milk is 6.5, and then mixing the soybean milk with the soybean milk according to the weight ratio of 3: 2, soybean milk: mixing the coagulating water in proportion.

Squatting: the time for squatting is 4 minutes until the tofu pudding is formed. After the tofu pudding is precipitated, the notice water above the tofu pudding is completely pumped out by gauze and a filter screen until the tofu pudding is at the height, and the tofu pudding can be stopped, wherein the shape and the color of the tofu pudding are similar to those of cotton. The water is collected for centralized treatment and is used for preparing the solidification water next time.

Casting: when the cloth is spread, attention needs to be paid, the die and the gauze need to be clean and free of impurities, and edges and corners in a spreading state are in a shape without leakage angles. The mold is filled during pouring, the pouring is uniform and consistent, and the quality of the poured state is as uniform as possible.

Squeezing: generally, the finished product is squeezed for 4 minutes with 480 kg of force, then the mold is taken down (the product is in the mold at the moment) and is separately aired to a bean curd shelf, and the bean curd can be turned when cooled to 23 ℃ to obtain a semi-finished product.

Soaking: the semi-finished product is soaked in 26 liters of soaking solution for 5 hours. The soaking solution comprises package slurry and edible salt, wherein the weight ratio of the package slurry to the edible salt is 5: 1. the pack slurry comprised 8kg of sodium carbonate and 47kg of sodium bicarbonate. 940g of the semi-finished product is added into each 28 liters of the soaking solution.

And (5) after soaking, obtaining the slurry-coated bean curd.

Comparative example 3

The slurry-wrapped bean curd is prepared by taking brine (magnesium chloride) as a coagulant.

(1) Preparing brine: according to the proportion of magnesium chloride: water 1: 7 to obtain a magnesium chloride solution;

(2) soaking: according to the dry bean: soaking bean water at a ratio of 1:3 at room temperature for 4h (summer);

(3) peeling: peeling the soaked soybeans by using a peeling machine, and cleaning the soybeans for later use;

(4) grinding: according to the dry bean: grinding the bean milk in a ratio of water to bean milk of 1: 6;

(5) boiling the soybean milk: boiling the pulp at 102 deg.C, and keeping the temperature for 8 min;

(6) and (3) filtering: filtering with 150 meshes to obtain soybean milk for later use;

(7) magnesium chloride curdling: the curdling temperature is 75 ℃,0.3 percent magnesium chloride solution is added according to the volume fraction of the soybean milk, the stirring is carried out while adding until a large amount of brain flowers are generated, and the stirring can be stopped when light yellow supernatant is separated out;

(8) squatting: keeping the temperature for 3min, sucking out supernatant and breaking the brain;

(9) squeezing: putting the encephalopathy into a box, and squeezing for 15 min;

(10) and (3) refrigerating: cutting the squeezed bean curd into blocks, and refrigerating at 4 ℃ for 16 h;

(11) soaking: soaking the refrigerated bean curd in a mixed solution of 0.3% sodium bicarbonate and 0.2% edible salt for 10 h;

(12) cleaning: washing the soaked slurry-coated bean curd with deionized water, and draining off the surface water;

(13) boxing and quick freezing: and (4) packing the slurry-coated bean curd into boxes, quickly freezing by adopting liquid nitrogen, and preserving under a freezing condition for half a year after the quick freezing is finished.

Comparative example 4

The slurry-coated bean curd is prepared by taking gypsum (calcium sulfate) as a coagulant.

(1) Soaking: according to the dry bean: soaking bean water at a ratio of 1:3 at room temperature for 4h (summer);

(2) peeling: peeling the soaked soybeans by using a peeling machine, and cleaning the soybeans for later use;

(3) grinding: according to the dry bean: grinding the bean milk in a ratio of water to bean milk of 1: 6;

(4) boiling the soybean milk: boiling the pulp at 102 deg.C, and keeping the temperature for 8 min;

(5) and (3) filtering: filtering with 150 meshes to obtain soybean milk for later use;

(6) slurry flushing: the temperature of the soybean milk is 85 ℃,0.3 percent of gypsum is weighed according to the volume fraction of the soybean milk, is placed at the bottom of a curdling barrel and is dissolved by a small amount of warm water, and finally, the soybean milk is flushed into the curdling barrel until large-area peanut shells are formed;

(7) squatting: preserving the heat for 10 min;

(8) squeezing: putting the encephalopathy into a box, and squeezing for 20 min;

(9) and (3) refrigerating: cutting the squeezed bean curd into blocks, and refrigerating at 4 ℃ for 16 h;

(10) soaking: soaking the refrigerated bean curd in a mixed solution of 0.3% sodium bicarbonate and 0.2% edible salt for 10 h;

(12) cleaning: washing the soaked slurry-coated bean curd with deionized water, and draining off the surface water;

(13) boxing and quick freezing: and (4) packing the slurry-coated bean curd into boxes, quickly freezing by adopting liquid nitrogen, and preserving under a freezing condition for half a year after the quick freezing is finished.

Comparative example 5

(1) Preparing a bean whey fermentation liquid: firstly, collecting bean clear liquid (commonly called yellow serofluid), filtering by 150 meshes, respectively adding 3% of lactose, 3% of cane sugar and 2% of functional oligosaccharide by volume fraction, sterilizing at 115 ℃ for 20min, cooling to 42 ℃ by volume fraction, inoculating 3% of mixed strain (lactobacillus casei: lactobacillus plantarum: lactobacillus rhamnosus: streptococcus thermophilus ═ 1: 1: 1: 1), keeping the temperature at 36 ℃ for fermentation, and performing aeration culture for 15h until the total acid of the bean clear fermentation liquid is 5g/L, and stopping fermentation for later use;

(2) soaking: according to the dry bean: soaking bean water at a ratio of 1:3 at room temperature for 4h (summer);

(3) peeling: peeling the soaked soybeans by using a peeling machine, and cleaning the soybeans for later use;

(4) grinding: according to the dry bean: grinding the bean water ratio of 1: 4;

(5) boiling the soybean milk: boiling at 105 deg.C for 5 min;

(6) and (3) filtering: filtering with 150 meshes to obtain soybean milk for later use;

(7) curdling a soy bean whey fermentation liquid: the curdling temperature is 80 ℃, 30 percent of soy whey fermentation liquor is added according to the volume fraction of the soybean milk, the stirring is carried out while adding until a large amount of brain flowers are generated, and the stirring can be stopped when light yellow supernatant is separated out;

(8) squatting: keeping the temperature for 5min, sucking out the supernatant and breaking the brain;

(9) squeezing: putting the encephalopathy into a box, and squeezing for 20 min;

(10) and (3) refrigerating: cutting the squeezed bean curd into blocks, and refrigerating at 4 ℃ for 10 h;

(11) soaking: soaking the refrigerated bean curd in a mixed solution of 0.4% sodium bicarbonate and 0.2% edible salt for 10 h;

(12) cleaning: washing the soaked slurry-coated bean curd with deionized water, and draining off the surface water;

(13) boxing and quick freezing: and (4) packing the slurry-coated bean curd into boxes, quickly freezing by adopting liquid nitrogen, and preserving under a freezing condition for half a year after the quick freezing is finished.

Comparative example 6

(1) Preparing a bean whey fermentation liquid: firstly, collecting bean clear liquid (commonly called yellow serofluid), filtering by 150 meshes, respectively adding 3% of lactose, 3% of cane sugar and 2% of functional oligosaccharide by volume fraction, sterilizing at 115 ℃ for 20min, cooling to 42 ℃ by volume fraction, inoculating 3% of mixed strain (lactobacillus casei: lactobacillus plantarum: lactobacillus rhamnosus: streptococcus thermophilus ═ 1: 1: 1: 1), keeping 42 ℃ for fermentation, and performing aeration culture for 15h until the total acid of the bean clear fermentation liquid is 5g/L, and stopping fermentation for later use;

(2) soaking: according to the dry bean: soaking bean water at a ratio of 1:3 at room temperature for 4h (summer);

(3) peeling: peeling the soaked soybeans by using a peeling machine, and cleaning the soybeans for later use;

(4) grinding: according to the dry bean: grinding the bean water ratio of 1: 4;

(5) boiling the soybean milk: boiling at 105 deg.C for 5 min;

(6) and (3) filtering: filtering with 150 meshes to obtain soybean milk for later use;

(7) curdling a soy bean whey fermentation liquid: the curdling temperature is 80 ℃, 30 percent of soy whey fermentation liquor is added according to the volume fraction of the soybean milk, the stirring is carried out while adding until a large amount of brain flowers are generated, and the stirring can be stopped when light yellow supernatant is separated out;

(8) squatting: keeping the temperature for 5min, sucking out the supernatant and breaking the brain;

(9) squeezing: putting the encephalopathy into a box, and squeezing for 20 min;

(10) and (3) refrigerating: cutting the squeezed bean curd into blocks, and refrigerating at 4 ℃ for 10 h;

(11) soaking: soaking the refrigerated bean curd in a mixed solution of 0.4% sodium bicarbonate and 0.2% edible salt for 10 h;

(12) cleaning: washing the soaked slurry-coated bean curd with deionized water, and draining off the surface water;

(13) boxing and quick freezing: and (4) packing the slurry-coated bean curd into boxes, quickly freezing by adopting liquid nitrogen, and preserving under a freezing condition for half a year after the quick freezing is finished.

Example 4

The comparison results of the slurry-coated tofu prepared in examples 1, 2 and 3 and comparative examples 1, 2, 3 and 4 are shown in Table 2.

TABLE 2 comparison of results table

Categories	Sensory score/score	Soy isoflavone content/(μ g/g)
			Example 1	89.24±0.08	2759.28±4.59
Example 2	90.41±0.11	2831.11±2.78
			Example 3	90.54±0.05	2889.37±5.22
Comparative example 1	80.32±0.18	2238.42±10.12
			Comparative example 2	78.18±0.11	2119.77±2.24
Comparative example 3	70.67±0.28	1739.21±9.24
			Comparative example 4	73.89±0.32	2009.96±7.31
Comparative example 5	87.84±0.38	2576.31±3.64
			Comparative example 6	85.73±0.56	2613.83±4.15

According to the results in table 2, the sensory evaluation and the isoflavone content of the slurry-coated bean curd prepared by using the whey fermentation liquid as the coagulant are obviously higher than those of the slurry-coated bean curd prepared by using other coagulants, which shows that the comprehensive quality of the slurry-coated bean curd provided by the embodiment of the invention is better and more favored by consumers. In conclusion, the soybean clear fermentation liquid prepared by the periodic temperature-variable sectional synergistic fermentation of the multiple strains of the probiotic bacteria can reduce the discharge of the soybean clear liquid and change waste into valuable, and can improve the product flavor and quality of the slurry-coated soybean curd, improve the content of nutrient substances of the slurry-coated soybean curd, improve the core competitiveness of enterprises and promote the transformation and upgrading of industries.

The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.