CN115606749B

CN115606749B - Preparation method of bean curd products

Info

Publication number: CN115606749B
Application number: CN202210731374.5A
Authority: CN
Inventors: 林茂; 汤鹏宇; 孟繁博; 黄道梅
Original assignee: Guizhou Characteristic Food Industry Technology Co ltd
Current assignee: Guizhou Characteristic Food Industry Technology Co ltd
Priority date: 2022-06-24
Filing date: 2022-06-24
Publication date: 2024-01-30
Anticipated expiration: 2042-06-24
Also published as: CN115606749A

Abstract

The invention provides a preparation method of bean curd products, the invention prepares white bean curd by the technologies of sectional pulp-adding, sectional frying and the like, has smooth surface, no granular matters, white and bright color, no air holes, good elasticity and special bean flavor; the surface of the fermented bean curd is smooth and swelled, is not easy to absorb oil, has no air holes, has bright yellow surface color, white and tender internal color, is not rotten after being boiled in water, and has soft and soft mouthfeel and toughness; the popped bean curd is white and has good luster, smooth surface, no air holes, tough surface, and is fluffy when being boiled or fried with water, no obvious alkali smell and good in inlet elasticity. The process of the Tianzhu white bean curd, the fermented bean curd and the fermented bean curd manufactured by the method is stable, the storage time can be as long as 1 year at the temperature of minus 18 ℃, the modified shape is avoided, the honeycomb shape is not generated inside, the manufacturing process is simple and easy to operate, and the method is suitable for large-scale industrial production.

Description

Preparation method of bean curd products

Technical Field

The invention relates to a food preparation technology, in particular to a preparation method of a bean curd product.

Background

The bean curd is a food material with rich nutrition and long history, and the popular favor of the bean curd promotes the progress and development of the bean curd making process. The main production process of the bean curd is pulping, namely, soybean is prepared into soybean milk; and secondly, coagulating and forming, namely, the soybean milk is coagulated into gel containing a large amount of water under the combined action of heat and a coagulating agent, namely, bean curd. The bean curd contains multiple microelements necessary for human body, and also contains abundant high-quality protein, called vegetable meat. The digestion and absorption rate of the bean curd is over 95 percent, and the health food is deeply favored by people all the time, but the nutrition value of the bean curd is better exerted, and the matching is needed.

In 2014, the 'traditional bean curd making technology' is selected from the fourth group of national non-matter cultural heritage representative project directory of China, and the wonderful Chinese delicacies are endowed with more cultural connotation and inheritance significance outside the commodity value. The method for producing bean curd is described in some ancient books after the open time. In the literary composition of the present invention, the rapid preparation method of bean curd and the use of coagulant are described in detail: "Bean curd method", such as He Soy bean and Bai Dou Lv bean, can be used. And (3) manufacturing: soaking in water, crushing, removing residues, steaming, and precipitating with bittern juice, alumen juice or vinegar. And gypsum powder is collected in the cylinder. It is mainly salty and bitter with pungent taste, so it can astringe the ear. The coagulants on the surface are removed and dried, the bean curd skin is named, and the bean curd skin is processed into a food with good smell and sweet, salty and cold. The bittern juice is concentrated solution of magnesium chloride, magnesium sulfate, sodium chloride, etc.; the Alumen juice is mineral containing heavy water salts such as potassium alum; gypsum is aqueous calcium sulfate; the vinegar is edible vinegar. Most of these coagulants are still in use today. The Ming Dynasty Wu's Mo Eshan record includes: when the bean curd is made, one liter of bean is added into the bean, and the bean curd is mixed with brine, the bean curd is very strong and tough when being boiled, and the bean curd is secret and secret. Meaning: when making bean curd, one tenth of mung bean is added into soybean, and the made bean curd has special toughness. This is also what we are now worthy of reference and research. The "bean curd poem" written by the Ming dynasty poem Su Bingheng is: the traditional Chinese medicine is optimal in Huainan operation, and skin is faded to the best. And (3) grinding the upflowing agar liquid, and rolling snowflakes in the boiling soup. The tile is soaked in toad with shadow, and the golden knife breaks the jade without flaw. The taste of the Chinese herbal medicine is known to be the best of the monk's home and the morgans. The invention, the preparation method, the characteristics and the food of the bean curd are concisely, flexibly and vividly depicted in poems, and people are resistant to smell on the praise paper.

The invention uses the technology of sectional pulp-adding and sectional frying, etc., the bean curd has unique taste, bright appearance and color, stable process, long storage time of 1 year at-18 ℃ without deterioration and deformation, no honeycomb shape in the interior, simple and easy operation of the manufacturing process, and suitability for large-scale industrialized production and market investment.

Disclosure of Invention

The invention aims to provide a preparation method of a bean curd product. The technical scheme of the invention is as follows:

a preparation method of bean curd products comprises soaking dry soybean, pulping, boiling, performing sectional type pulp curdling and solidification with coagulant, molding, and squeezing to obtain white bean curd; and then the white bean curd is processed by high-temperature frying processing or alkaline water processing to prepare the fermented bean curd or the pulp-explosion bean curd.

The preparation method of the bean curd products comprises the following steps of:

(1) Preparing a coagulant: adding gypsum powder into water, and stirring to obtain a coagulant A; adding magnesium chloride into water, and stirring to obtain coagulant B;

(2) Soaking soybean, namely soaking dry soybean in water, wherein the water adding amount is 5-10 times of that of the dry soybean by weight, the specific standard is that the soybean swells to no white soybean core when absorbing water in spring and summer for 5-8 hours and in autumn and winter for 8-12 hours, the soybean is stopped in a seamless state, the water for soaking the soybean is removed, the soybean is washed by adding water, and the wet soybean is obtained by filtering water;

(3) Preparing cooked pulp: grinding the wet soybeans in the step (2) by adding water, removing upper foam from the ground soybean to obtain soybean milk containing bean dregs, heating and boiling the soybean milk, and filtering the bean dregs while the soybean milk is hot to obtain cooked soybean milk;

(4) Preparing raw slurry: taking the wet soybeans in the step (2), adding water for pulping, separating bean dregs and soybean milk to obtain soybean milk without the bean dregs, and heating and boiling the soybean milk to obtain raw soybean milk;

(5) And (3) curdling: taking the prepared cooked or raw slurry, heating to 85-100deg.C, adding coagulator A and B for sectional curdling, and squatting for 5-10 min to obtain soft jellied bean curd;

(6) Squeezing and molding white bean curd: taking the soft jellied bean curd in the step (5), slightly taking out, placing into a squeezing frame paved with water filtering gauze, pulling out four corners of the water filtering gauze, covering the soft jellied bean curd, covering a cover plate, pressing for 20-40 minutes by a conventional air pressure method, opening the water filtering gauze after the jellied bean curd is squeezed and molded, rapidly overturning the water filtering gauze on a flat plate by 180 degrees, uncovering the water filtering gauze, and cutting into blocks to obtain the white bean curd.

Specifically, the white bean curd is prepared according to the following method:

(1) Preparing a coagulant: adding gypsum powder into water, wherein the weight of gypsum is 0.1-5% of that of water, and stirring for 15-25 minutes to obtain a coagulant A; adding magnesium chloride into water, wherein the weight of the magnesium chloride is 1-5% of that of the water, and stirring for 10-15 minutes to obtain a coagulant B;

(2) Soaking soybean, namely soaking dry soybean in water for 5-8 hours in spring and summer and 8-12 hours in autumn and winter, wherein the specific standard is that the soybean is swelled by absorbing water until no white soybean core exists, the soybean is in a seamless state, the soaking is stopped in time, the water for soaking the soybean is removed, the water is added for cleaning, and the water is filtered to obtain wet soybean;

(3) Preparing cooked pulp: taking wet soybeans in the step (2), adding water with the weight being 4-8 times that of the wet soybeans for pulping, removing upper foam from the ground soybean to obtain soybean milk containing bean dregs, heating and boiling the soybean milk, and filtering the bean dregs while the soybean milk is hot when the temperature of the soybean milk is raised to 85-105 ℃ to obtain cooked soybean milk;

(4) Preparing raw slurry: taking wet soybeans in the step (2), adding water with the weight being 4-8 times that of the wet soybeans for grinding, separating bean dregs and soybean milk to obtain soybean milk without the bean dregs, heating and boiling the soybean milk, and obtaining raw soybean milk when the temperature of the soybean milk is increased to 85-105 ℃;

(5) And (3) curdling: taking the prepared cooked or raw pulp, heating to 85-100 ℃, adding coagulants A and B for secondary pulp-dropping, adopting the coagulants A for pulp-dropping in the first stage, adding 30-50% of the coagulant in the amount of soybean milk by weight, and keeping the temperature at more than 70 ℃; the second stage adopts coagulant B to carry out curdling, the coagulant is added to account for 50-70% of the soybean milk by weight, and the temperature is maintained to be more than 50 ℃; squatting the jellied bean curd for 5-10 minutes after the completion of the curdling to obtain the tender jellied bean curd;

More specifically, the white tofu is prepared according to the following method:

(5) And (3) curdling: taking the prepared cooked or raw pulp, heating to 85-100 ℃, adding coagulants A and B for four-stage pulp-dropping, adopting the coagulants A for pulp-dropping in the first stage, adding the coagulants which are 20-30% of the soybean milk by weight, and keeping the temperature at more than 80 ℃; the second stage adopts coagulant A to carry out curdling, the coagulant is added into the soybean milk, the amount of the coagulant is 20-30% of the amount of the soybean milk by weight, and the temperature is maintained to be more than 70 ℃; the third section adopts coagulant B to carry out curdling, the coagulant is added to 30-40% of the soybean milk by weight, and the temperature is maintained to be more than 60 ℃; the fourth stage adopts coagulant B to carry out curdling, the coagulant is added to 30-40% of the soybean milk by weight, and the temperature is maintained to be more than 50 ℃; squatting the jellied bean curd for 5-10 minutes after the completion of the curdling to obtain the tender jellied bean curd;

The preparation method of the bean curd products comprises the following steps: cutting white bean curd into white bean curd with thickness of 6-10mm, length of 6-10cm and width of 4-6cm, frying in heated mixed vegetable oil, taking out fried fermented bean curd, placing on a plate capable of filtering oil, cooling to room temperature, quick freezing with liquid nitrogen, boxing, and storing in a freezer at-18deg.C to obtain fermented bean curd.

Specifically, the preparation method of the hair bean curd comprises the following steps: cutting white bean curd into white bean curd with thickness of 6-10mm, length of 6-10cm and width of 4-6cm, and frying in heated mixed vegetable oil for 3 min at 110-120deg.C; the oil temperature of the second stage is 120-130 ℃, and the frying time is 3 minutes; the third stage oil temperature is 130-140 ℃, and the frying time is 2 minutes; taking out the fried beancurd, placing on a flat plate capable of filtering oil, cooling to normal temperature, quickly freezing with liquid nitrogen, boxing, and storing in a freezer at-18 ℃ to obtain the beancurd.

Specifically, the preparation method of the bean curd product comprises the step of mixing, by weight, camellia oil, soybean oil and rapeseed oil, wherein the ratio of the camellia oil to the rapeseed oil is 0.5-3:2-7:1-5.

More specifically, the mixed vegetable oil is prepared from camellia oil, soybean oil and rapeseed oil=1-2:3- 5:2-3.

The preparation method of the bean curd products comprises the following steps: soaking white bean curd with thickness of 4-6mm and length of 4-6cm and width of 4-6cm in alkaline water for 8-12 hr, taking out, cooling to room temperature, quick-freezing with liquid nitrogen, cooling, and storing in refrigerator to obtain the final product.

Specifically, the preparation method of the bean curd product comprises the steps of burning wormwood, straw and mugwort into powdery mildew, putting the powdery mildew into sterile water, stirring for 15-20 minutes, filtering the powdery mildew to remove the powdery mildew by 1-5% of the sterile water by weight, and preparing the alkaline water.

Benefits of the present invention over the prior art:

1. the invention adopts the sectional curdling means, the surface of the prepared white bean curd is smooth, no granular matters exist, the color is white and bright, and the white bean curd is accompanied with special bean flavor.

2. The fermented bean curd has smooth and expanded oil surface, is not easy to absorb oil, has no pores, has bright yellow surface color, white and tender internal color, is not rotten after being boiled in water, and has soft and flexible mouthfeel.

3. The popped bean curd is white and has good luster, smooth surface, no air holes, tough surface, and is fluffy when being boiled or fried with water, no obvious alkali smell and good in inlet elasticity. .

4. The white bean curd, the fermented bean curd and the pulp-explosion bean curd prepared by the method have stable processes, can be stored for up to 1 year at the temperature of minus 18 ℃ without deterioration and deformation, cannot generate honeycomb shapes inside, have simple and easy-to-operate preparation processes, and are suitable for large-scale industrial production and market investment.

Detailed Description

The invention is further illustrated by the following examples, which are not intended to be limiting.

Example 1.

The preparation method of the white bean curd comprises the following steps:

preparing a coagulant: adding gypsum powder into water, wherein the weight of gypsum is 1.0% of that of the water, and stirring for 20 minutes to obtain a coagulant A; adding magnesium chloride into water, wherein the weight of the magnesium chloride is 2.5% of that of the water, and stirring for 12 minutes to obtain a coagulant B;

soaking soybean in water, which is to soak dried soybean in an amount which is 8 times of the weight of the dried soybean for 6 hours, removing the water for soaking the soybean, adding water for cleaning, and filtering out water to obtain wet soybean;

preparing cooked pulp: taking wet soybeans, adding water with the weight of 6 times of that of the wet soybeans for pulping, removing upper foam from the ground soybean to obtain soybean milk containing bean dregs, heating and boiling the soybean milk, and filtering the bean dregs while the soybean milk is hot when the temperature of the soybean milk is raised to 85-105 ℃ to obtain cooked soybean milk;

And (3) curdling: taking the prepared cooked pulp, heating to 85-100 ℃, adding coagulators A and B for two-stage pulp-dropping, adopting coagulators A for pulp-dropping in the first stage, adding 40% of coagulators in the amount of soybean milk by weight, and keeping the temperature at more than 70 ℃; the second stage adopts coagulant B to carry out curdling, the coagulant is added into the soybean milk according to the weight of 60 percent, and the temperature is maintained to be more than 50 ℃; squatting the jellied bean curd for 8 minutes after the completion of the curdling to obtain tender jellied bean curd;

squeezing and molding white bean curd: taking out soft jellied bean curd, slightly taking out, placing into a squeezing frame paved with water filtering gauze, pulling out four corners of the water filtering gauze, covering onto the soft jellied bean curd, covering a cover plate, pressing for 30 minutes by a conventional air pressure method, opening the water filtering gauze after the jellied bean curd is squeezed and molded, rapidly overturning the water filtering gauze on a flat plate by 180 degrees, uncovering the water filtering gauze, and cutting into blocks to obtain the white bean curd.

Example 2.

The preparation method of the fermented bean curd comprises the following steps:

and (3) preparing mixed vegetable oil: 1kg of camellia oil, 3kg of soybean oil and 2kg of rapeseed oil are taken according to weight.

Cutting the white bean curd of example 1 into white bean curd with thickness of 6-10mm, length of 6-10cm and width of 4-6cm, and frying in heated mixed vegetable oil for 3 min at 110deg.C; the oil temperature of the second stage is 120 ℃, and the frying time is 3 minutes; the third section of oil temperature is 130 ℃, and frying time is 2 minutes; taking out the fried beancurd, placing on a flat plate capable of filtering oil, cooling to normal temperature, quickly freezing with liquid nitrogen, boxing, and storing in a-18 ℃ ice warehouse to obtain the beancurd.

Example 3.

The preparation method of the white bean curd comprises the following steps:

preparing a coagulant: adding gypsum powder into water, wherein the weight of gypsum is 0.1% of that of the water, and stirring for 15 minutes to obtain a coagulant A; adding magnesium chloride into water, wherein the weight of the magnesium chloride is 1% of that of the water, and stirring for 10 minutes to obtain a coagulant B;

soaking soybean in water, which is to soak dry soybean in an amount 5 times of the dry soybean by weight for 8 hours, removing water for soaking soybean, cleaning with water, and filtering out water to obtain wet soybean;

preparing raw slurry: taking wet soybeans, adding water with the weight being 4 times that of the wet soybeans for pulping, separating bean dregs and soybean milk to obtain soybean milk without the bean dregs, heating and boiling the soybean milk, and obtaining raw soybean milk when the temperature of the soybean milk is increased to 85-105 ℃;

and (3) curdling: taking the prepared raw slurry, heating to 85-100 ℃, adding coagulants A and B for four-section slurry-dropping, adopting the coagulants A for slurry-dropping in the first section, adding a coagulant dosage which is 20% of the soybean milk by weight, and keeping the temperature at more than 80 ℃; the second stage adopts coagulant A to carry out curdling, the coagulant is added to be 20 percent of the soybean milk by weight, and the temperature is maintained to be more than 70 ℃; the third section adopts coagulant B to carry out curdling, the coagulant is added to 30 percent of the soybean milk by weight, and the temperature is maintained to be more than 60 ℃; the fourth section adopts coagulant B to carry out curdling, the coagulant is added to 30 percent of the soybean milk by weight, and the temperature is maintained to be more than 50 ℃; squatting the jellied bean curd for 5 minutes after the completion of the curdling to obtain tender jellied bean curd;

Squeezing and molding white bean curd: taking out soft jellied bean curd, slightly taking out, placing into a squeezing frame paved with water filtering gauze, pulling out four corners of the water filtering gauze, covering onto the soft jellied bean curd, covering a cover plate, pressing for 25 minutes by a conventional air pressure method, opening the water filtering gauze after the jellied bean curd is squeezed and molded, rapidly overturning the water filtering gauze on a flat plate by 180 degrees, uncovering the water filtering gauze, and cutting into blocks to obtain the white bean curd.

Example 4.

and (3) preparing mixed vegetable oil: 2kg of camellia oil, 5kg of soybean oil and 3kg of rapeseed oil are taken according to weight.

Cutting the white bean curd of example 3 into white bean curd with thickness of 6-10mm, length of 6-10cm and width of 4-6cm, and frying in heated mixed vegetable oil for 3 min at 120deg.C; the second stage of oil temperature 130, frying time is 3 minutes; the third stage of oil temperature 140, and frying time is 2 minutes; taking out the fried beancurd, placing on a flat plate capable of filtering oil, cooling to normal temperature, quickly freezing with liquid nitrogen, boxing, and storing in a-18 ℃ ice warehouse to obtain the beancurd.

Example 5.

The preparation method of the white bean curd comprises the following steps:

preparing a coagulant: adding gypsum powder into water, wherein the gypsum accounts for 5% of the weight of the water, and stirring for 25 minutes to obtain a coagulant A; adding magnesium chloride into water, wherein the weight of the magnesium chloride is 5% of that of the water, and stirring for 15 minutes to obtain a coagulant B;

Soaking soybean in water 10 times of the dry soybean for 10 hr until the soybean swells to no white soybean core, removing water, cleaning with water, and filtering to remove water to obtain wet soybean;

preparing cooked pulp: taking wet soybeans, adding water with the weight being 7 times that of the wet soybeans for pulping, removing upper foam from the ground soybean to obtain soybean milk containing bean dregs, heating and boiling the soybean milk, and filtering the bean dregs while the soybean milk is hot when the temperature of the soybean milk is raised to 85-105 ℃ to obtain cooked soybean milk;

and (3) curdling: taking the prepared cooked pulp, heating to 85-100 ℃, adding coagulators A and B for two-stage pulp-dropping, adopting coagulators A for pulp-dropping in the first stage, adding coagulators which account for 50% of the soybean milk by weight, and keeping the temperature at more than 70 ℃; the second stage adopts coagulant B to carry out curdling, the coagulant is added to account for 55% of the soybean milk by weight, and the temperature is maintained to be more than 50 ℃; squatting the jellied bean curd for 10 minutes after the completion of the curdling to obtain tender jellied bean curd;

Example 6.

The preparation method of the pop bean curd comprises the following steps:

alkaline water preparation: burning Artemisia princeps, straw and mugwort to obtain powdery mildew, stirring in sterile water for 18 min, filtering to remove powdery mildew 3 wt% of the sterile water, and preparing alkali water.

Soaking white bean curd with thickness of 4-6mm in alkaline water for 10 hr, taking out, cooling to room temperature, quick freezing with liquid nitrogen, cooling, and storing in refrigerator to obtain the final product.

Example 7.

The preparation method of the white bean curd comprises the following steps:

preparing a coagulant: adding gypsum powder into water, wherein the weight of gypsum is 2.0% of that of the water, and stirring for 25 minutes to obtain a coagulant A; adding magnesium chloride into water, wherein the weight of the magnesium chloride is 3.5% of that of the water, and stirring for 15 minutes to obtain a coagulant B;

soaking soybean in water, wherein the water content is 9 times of that of the dry soybean, soaking for 12 hours, removing water for soaking soybean, cleaning with water, and filtering to remove water to obtain wet soybean;

(3) Preparing raw slurry: taking wet soybeans, adding water with the weight being 7 times that of the wet soybeans for pulping, separating bean dregs and soybean milk to obtain soybean milk without the bean dregs, heating and boiling the soybean milk, and obtaining raw soybean milk when the temperature of the soybean milk is increased to 85-105 ℃;

(4) And (3) curdling: taking the prepared cooked or raw slurry, heating to 85-100 ℃, adding coagulants A and B for four-stage slurry preparation, adopting the coagulants A for slurry preparation in the first stage, adding a coagulant dosage which is 25% of the soybean milk by weight, and keeping the temperature at more than 80 ℃; the second stage adopts coagulant A to carry out curdling, the coagulant is added to 30 percent of the soybean milk by weight, and the temperature is maintained to be more than 70 ℃; the third section adopts coagulant B to carry out curdling, the coagulant is added into the soybean milk according to the weight of 35 percent, and the temperature is maintained to be more than 60 ℃; the fourth section adopts coagulant B to carry out curdling, the coagulant is added into the soybean milk, the weight of the coagulant is 40 percent of the weight of the soybean milk, and the temperature is maintained to be more than 50 ℃; squatting the jellied bean curd for 7 minutes after the completion of the curdling to obtain tender jellied bean curd;

squeezing and molding white bean curd: taking out soft jellied bean curd, slightly taking out, placing into a squeezing frame paved with water filtering gauze, pulling out four corners of the water filtering gauze, covering onto the soft jellied bean curd, covering a cover plate, pressing for 35 minutes by a conventional air pressure method, opening the water filtering gauze after the jellied bean curd is squeezed and molded, rapidly overturning on a flat plate by 180 degrees, uncovering the water filtering gauze, and cutting into blocks to obtain the white bean curd.

Example 8.

The preparation method of the pop bean curd comprises the following steps:

The preparation method of the alkaline water comprises the following steps: burning Artemisia princeps, straw and mugwort to obtain powdery mildew, stirring in sterile water for 15 min, filtering to remove powdery mildew 5 wt% of the sterile water, and preparing alkali water.

Soaking white bean curd with thickness of 4-6mm in alkaline water for 9 hr, taking out, cooling to room temperature, quick freezing with liquid nitrogen, cooling, and storing in refrigerator to obtain the final product.

To verify the effect of the present invention, the inventors conducted the following experiments:

experimental example:

1 materials and methods

1.1 materials and reagents

Soybean, anhui beans, purchased in local farmer markets; the water source is natural spring water subjected to ultra-micro filtration; plaster of paris, magnesium chloride, nisin purchased from Henan Wanbang industries, inc.; the series of synthetic media (MRS, bengalia red, nutrient agar) are all Biochemical Reagents (BR).

1.2 instruments and apparatus

SPX-150B-Z electric heating constant temperature incubator Shanghai BoXie Co., ltd; the VORTEX oscillator Shanghai damm practice limited; SJ-CJ-2FDQ ultra clean bench Sujie medical instruments (Suzhou) Co., ltd; BKQ-B50II full-automatic high-pressure steam sterilizer, shandong Boke biological industry Co., ltd; XC-30 colony counter Shanghai foreman electric instruments, inc; portable electronic nose, airsense company, germany; PEN3 texture analyzer, TMS-PRO physical property analyzer (equipped with two-way tensile probe, P/BS shearing probe) FTC company in America.

1.3 Single factor investigation

1.3.1 Bean soaking experiments

1.3.1.1 temperature and time screening

Soaking soybean in 5-10 times of water at 0-4deg.C, 10-15deg.C, 25-30deg.C, 30-35deg.C, soaking soybean in water until soybean is swelled to no white soybean core, recording soaking soybean time, removing water soaking soybean, cleaning with water, and filtering to remove water to obtain wet soybean;

foaming soybeans 2h, 4h, 6h, 8h, 10h and 12h at 5-10 ℃, foaming soybeans 2h, 4h, 6h and 8h at 10-20 ℃, foaming soybeans 2h, 4h and 6h at 20-30 ℃, foaming soybeans 2h and 4h at 30-35 ℃ and observing the soybean soaking results of each sample (the non-foaming control group and the four groups of sample soybean soaking results are shown in figures 1-5):

(1) The bean core is completely expanded after the bean is cut for 12 hours at the water temperature of 0-4 ℃, the center is free of a cavity and a white core after the bean is cut, the soaking water is clear, the expansion degree of the bean is changed after the soaking is continued for 24 hours, the bean core is slightly turbid, and the rest is free of obvious differences, so that the soaking time of the bean at the water temperature of 0-4 ℃ is preliminarily determined to be more than or equal to 12 hours.

(2) The bean cores are basically unfolded after 6 hours at the water temperature of 10-15 ℃, but the beans are basically round, but can be slightly soaked, and the beans with low water absorption degree possibly caused by stacking are placed, so that the beans are fully unfolded after the soaking time is continuously prolonged to 8 hours, and the bean cores are expanded without holes. The bean soaking time at 10-15 ℃ is preliminarily determined to be 6-8 hours.

(3) After the bean is soaked for 4 hours at the water temperature of 25-30 ℃, the surface of the bean is basically round, no skin wrinkles exist, only a small slit is visible in the bean core, the bean core is soaked for 6 hours continuously, the expansion of the bean core is good, and the bean is round and full. After the soaking is continued for 8 hours, the soaking bean water becomes turbid, few bubbles appear on the water surface (as shown in fig. 6), and a small amount of peculiar smell is generated, so that the soaking bean time under the temperature condition is not higher than 6 hours and not lower than 5 hours.

(4) After 2 infusions at the water temperature of 30-35 ℃, the surfaces of the beans are basically round, no skin wrinkles exist, only a small slit is visible in the bean cores, the beans are continuously infused for 4 hours, the expansion of the bean cores is good, and the beans are round and full. After the soaking is continued for 6 hours, the soaking bean water becomes abnormally turbid, a small amount of bubbles appear on the water surface (as shown in fig. 6), and peculiar smell is generated, so that the soaking bean time under the temperature condition is not higher than 4 hours and not lower than 3 hours.

1.3.1.2 Water content detection results

The moisture content of the unfoamed beans is 7.84% ± 0.21, and the moisture content is detected according to the observed result of the soaking beans, wherein the final moisture content of the soaking beans of the four groups of samples is basically maintained at 50-53%, and the skin of the beans is round, no skin wrinkles exist, the cut inner core is good in expansion, and the beans have brittleness (see figure 6).

1.3.1.3 shear force detection results

When the sample is not infused, the initial shearing force is 61.6N+/-4.2, the shearing force shows a descending trend along with the time of soaking beans and the temperature increases, wherein each group has the fastest descending of the shearing force at the time of soaking beans for 0-2 hours, and then has slow descending and gradually becomes stable. The shear force at the end point of soaking beans in the four groups of samples was maintained at about 17N. It is illustrated that the difference in the end of infusion samples is not great for four different temperature samples at different infusion times (see fig. 7).

1.3.1.4 Experimental summary of soaking beans

Actual situation analysis summary: for the stability of bean soaking experiments, the laboratory limits the temperature of bean soaking water, in practical cases, because of the large difference of specific heat capacity of water, the temperature of air temperature and the temperature of domestic water are greatly different, in general, the domestic water temperature in autumn and winter is not lower than 0 ℃, and even in hot summer with the temperature of more than 35 ℃, the domestic water temperature is not higher than 28 ℃, so that the bean soaking time is shortened according to the experimental results and the practical cases, the bean soaking time in spring and summer is controlled to be 5-8 hours, and the autumn and winter are more suitable. Because the amount of beans soaked each time affects the bean soaking time, when the amount of beans soaked is small, the distance between the beans is large, and the density is low, the interior of the beans can be fully stretched to absorb water, the bean soaking time can be shortened, and vice versa, the bean soaking container is recommended to be enlarged as much as possible so as to reduce the bean soaking time. The time of soaking beans in a laboratory is only used for strip reference, and the method specifically takes complete soaking of bean cores, the white inner cores are not used as standards, and no obvious middle seam is reserved in transverse cutting to the standards, so that soaking is stopped in time, and bacteria are prevented from growing.

1.3.2 selection of raw and cooked pulps

Respectively taking wet soybeans according to weight, adding 2 times of water, 4 times of water, 8 times of water and 10 times of water into the wet soybeans for grinding, separating bean dregs and soybean milk to obtain bean dreg-free soybean milk, heating and boiling the soybean milk, and obtaining the prepared raw soybean milk when the temperature of the soybean milk is raised to 85-105 ℃.

Respectively taking wet soybeans, adding 2 times of water, 4 times of water, 8 times of water and 10 times of water according to the weight, grinding, removing upper foam from the ground soybean milk to obtain soybean milk containing bean dregs, heating and boiling the soybean milk, filtering the bean dregs while the soybean milk is hot when the temperature of the soybean milk is raised to 85-105 ℃, obtaining prepared cooked soybean milk, and curdling according to the process of the example 1. (see table 1 and fig. 8 for results):

TABLE 1 evaluation of appearance of white tofu made from different raw or cooked pulps

Results: the raw pulp or cooked pulp is used, and water with the amount of 4-8 times is added for best.

1.3.3 selection of coagulant concentration and method of size-casting

A first group: selecting gypsum, 0.05% of water by weight to obtain a coagulant A, and 0.5% of magnesium chloride by weight to obtain the coagulant A, wherein the four-stage pulp-dropping and white bean curd squeezing process is performed according to the embodiment 1;

second group: selecting gypsum, wherein the gypsum accounts for 0.1% of water by weight to obtain a coagulant A, and the magnesium chloride accounts for 1.0% of water by weight to obtain the coagulant A, and performing the two-stage pulp curdling and white bean curd squeezing process according to the embodiment 2;

Third group: selecting gypsum, 3.0% of water by weight to obtain a coagulant A, and 3.0% of magnesium chloride by weight to obtain the coagulant A, wherein the four-stage pulp-dropping and white bean curd squeezing process is performed according to the embodiment 1;

fourth group: selecting gypsum, 5.0% of water by weight to obtain a coagulant A, and 5.0% of magnesium chloride by weight to obtain the coagulant A, wherein the two-stage curdling and white bean curd squeezing process is performed according to the embodiment 2;

fifth group: selecting gypsum, 6.0% of water by weight to obtain a coagulant A, and 5.5% of magnesium chloride by weight to obtain the coagulant A, wherein the four-stage pulp-dropping and white bean curd squeezing process is performed according to the embodiment 1;

sixth group: the procedure of example 2 was followed with two-stage curdling and white tofu pressing, with gypsum 6.5% by weight of water to obtain coagulant A and magnesium chloride 6.0% by weight of water to obtain coagulant A.

See Table 2 and FIG. 9

TABLE 2 appearance description of Bean curd prepared with different coagulants at different temperatures

	Color of	Appearance of	Mouthfeel of the product
				First group of	White color	Honeycomb shape accompanied by granular material	No special bean flavor
Second group of	White color	Smooth surface and no granular matter	Has special bean flavor
				Third group of	White and bright color	Smooth surface and no granular matter	Has special bean flavor
Fourth group	White and bright color	Smooth surface and no granular matter	Has special bean flavor
				Fifth group of	White, dark	Honeycomb shape accompanied by granular material	Has special bean flavor
Sixth group of	White, dark	The honeycomb shape is not obvious, accompanied by granular materials	No special bean flavor

Results: the gypsum is used in an amount of 0.1-5% by weight, and the magnesium chloride is used in an amount of 1-5% by weight.

1.3.4 selection of different Mixed vegetable oils and frying temperatures

Different vegetable oils are selected to prepare mixed vegetable oil, and the vegetable oil is selected from tea oil, soybean oil and rapeseed oil, and the preparation is carried out according to the following proportions:

mixing vegetable oil A: according to the weight ratio: camellia oil: soybean oil: rapeseed oil = 0.5:5.0:2.0;

mixing vegetable oil B: according to the weight ratio: camellia oil: soybean oil: rapeseed oil = 1.0:3.0:3.0;

mixing vegetable oil C: according to the weight ratio: camellia oil: soybean oil: rapeseed oil = 1.0:6.0:1.0;

mixing vegetable oil D: according to the weight ratio: camellia oil: soybean oil: rapeseed oil = 1.0:5.0:2.0;

blend vegetable oil E: according to the weight ratio: camellia oil: soybean oil: rapeseed oil = 2.0:3.0:3.0;

mixing vegetable oil F: according to the weight ratio: camellia oil: soybean oil: rapeseed oil = 3.0:1.0:4.0.

A first group: placing the white bean curd of example 1 into mixed vegetable oil A, frying at 120deg.C for 5 min, heating to 140deg.C, frying for 3 min, taking out the fried bean curd, placing on a plate capable of filtering oil, cooling to room temperature, rapidly freezing with liquid nitrogen, boxing, and storing in ice warehouse at-18deg.C to obtain the bean curd.

Second group: placing the white bean curd of example 1 into mixed vegetable oil B, frying at 110deg.C for 2 min, heating to 130deg.C for 3 min, heating to 140deg.C, frying for 2 min, taking out the fried bean curd, placing on a plate with oil filtering, cooling to room temperature, quick freezing with liquid nitrogen, boxing, and storing in ice warehouse at-18deg.C.

Third group: placing the white bean curd of example 1 into mixed vegetable oil C, frying at 110deg.C for 5 min, frying at 140deg.C for 4 min, taking out the fried bean curd, placing on a plate capable of filtering oil, cooling to room temperature, rapidly freezing with liquid nitrogen, boxing, and storing in ice warehouse at-18deg.C to obtain the bean curd.

Fourth group: placing the white bean curd of example 1 into mixed vegetable oil D, heating to 115 ℃ for 3 min, heating to 130 ℃ for 2 min, heating to 135 ℃ for 1 min, taking out the fried bean curd, placing on a plate capable of filtering oil, cooling to normal temperature, quickly freezing with liquid nitrogen, boxing, and storing in a ice warehouse at-18 ℃ to obtain the bean curd.

Fifth group: placing the white bean curd of example 1 into mixed vegetable oil E, heating to 120deg.C, frying for 3 min, heating to 125deg.C, frying for 3 min, heating to 140deg.C, frying for 2 min, taking out the fried bean curd, placing on a plate with oil filtering, cooling to room temperature, quick freezing with liquid nitrogen, boxing, and storing in ice warehouse at-18deg.C.

Sixth group: placing the white bean curd of example 1 into mixed vegetable oil F, heating to 115deg.C, frying for 3 min, heating to 130deg.C, frying for 2 min, heating to 150deg.C, frying for 2 min, taking out the fried bean curd, placing on a plate with oil filtering, cooling to normal temperature, quick freezing with liquid nitrogen, boxing, and storing in ice warehouse at-18deg.C.

See Table 3 and FIG. 10

TABLE 3 appearance description of tofu made with different vegetable oils blend at different frying temperatures

Results: camellia oil, soybean oil, rapeseed oil=1-2:3-5:2-3, oil temperature of the first stage is 110-120 ℃, and frying time is 3 minutes; the oil temperature of the second stage is 120-130 ℃, and the frying time is 3 minutes; the third stage has oil temperature of 130-140 deg.C and frying time of 2 min.

1.3.5 selection of different alkaline Water concentrations

A first group: the white bean curd of the example 1 is soaked in the prepared alkaline water for 10 hours, taken out, cooled to normal temperature, quickly frozen by liquid nitrogen, cooled and put into a refrigerator for preservation, and the explosion slurry is obtained.

Second group: the white bean curd of the example 1 is soaked in the prepared alkaline water for 8 hours, taken out, cooled to normal temperature, quickly frozen by liquid nitrogen, cooled and put into a refrigerator for preservation, and the explosion slurry is obtained.

Third group: the white bean curd of the example 1 is soaked in the prepared alkaline water for 12 hours, taken out, cooled to normal temperature, quickly frozen by liquid nitrogen, cooled and put into a refrigerator for preservation, and the explosion slurry is obtained. (you)

Fourth group: the white bean curd of the example 1 is soaked in the prepared alkaline water for 10 hours, taken out, cooled to normal temperature, quickly frozen by liquid nitrogen, cooled and put into a refrigerator for preservation, and the explosion slurry is obtained. (you)

Fifth group: the white bean curd of the example 1 is soaked in the prepared alkaline water for 8 hours, taken out, cooled to normal temperature, quickly frozen by liquid nitrogen, cooled and put into a refrigerator for preservation, and the explosion slurry is obtained. (you)

Sixth group: the white bean curd of the example 1 is soaked in the prepared alkaline water for 12 hours, taken out, cooled to normal temperature, quickly frozen by liquid nitrogen, cooled and put into a refrigerator for preservation, and the explosion slurry is obtained.

TABLE 4 appearance and mouthfeel of popped tofu prepared with different alkaline water concentrations

	Color of	Appearance of	Mouthfeel of the product
				First group of	White, dark	The soybean milk has pores, poor toughness of the epidermis and soybean milk inside	Inelastic
Second group of	White, dark	The soybean milk has pores, poor toughness of the epidermis and soybean milk inside	Having elasticity
				Third group of	White and good luster	The soybean milk is smooth, has no air holes, has toughness on the surface and soybean milk inside	Having elasticity
Fourth group	White and good luster	The soybean milk is smooth, has no air holes, has toughness on the surface and soybean milk inside	Having elasticity
				Fifth group of	White, dark	The soybean milk is smooth, has no air holes, has toughness on the surface and soybean milk inside	Having elasticity
Sixth group of	Off-white color	Indicating pores, poor toughness of the surface, honeycomb shape inside	Inelastic

Results: the powdery mildew ash accounts for 1-5% of the sterile water by weight and is optimal.

1.4 analysis of microbial changes in shelf-life "tofu development

1.4.1 storage modes comparative analyses were performed in four groups:

(1) normal temperature control group;

naturally cooling bean curd after frying to normal temperature, and keeping the temperature at 25 ℃ in a constant temperature incubator

(2) Refrigeration and preservative group

Preparing GB-2760 limit natamycin preservative, soaking the finished fermented bean curd for 5min, draining, and storing in a constant temperature refrigerator at 4deg.C

(3) Quick-freezing group

Quickly storing in freezing chamber at-20 deg.C after quick freezing treatment with liquid nitrogen

(4) "high temperature + preservative" group

Soaking the finished fermented bean curd in antiseptic solution for 5min, packaging, sterilizing at 121deg.C for 10min, and naturally storing at room temperature

1.4.2 changes in colony count

As shown in FIG. 11, the total number of colonies of "beancurd forming" in each treatment group during storage was measured, and as shown by the measurement of the total number of colonies during storage, the total number of colonies of "beancurd forming" showed a general tendency to increase in the whole storage period, and the initial total number of colonies was 3.6X103 cfu/g higher, which resulted from the fact that the environment for producing "beancurd forming" was unable to meet the production requirements and was contaminated to some extent. The total number of colonies of the normal temperature control group is obviously increased on the 1 st day of storage until the total number of colonies reaches 7.5X107 cfu/g on 3 days, and the normal temperature control group is obviously rotten and deteriorated when 'beancurd' is generated. The total number of colonies started to increase sharply on day 4 of storage in the cold storage + preservative group, reaching 3.9X108 cfu/g on 16 days, at which time the product had obvious off-flavors and had a milder appearance. The total colony count of the quick-frozen group and the high-temperature and preservative group is obviously reduced at the 4 th day of storage, wherein the high-temperature and preservative group is not detected, the analysis is that the quick-frozen and killed part of microorganisms and the high-temperature treatment kill most microorganisms, and the total colony count of the quick-frozen group is 3.2 multiplied by 102cfu/g and the high-temperature and preservative group is not detected at the time of not more than 10cfu/g in a 24d storage period.

Continuing to perform long-term tracking detection on the quick-frozen group and the high-temperature and preservative group, wherein the speeds of colonies of the two groups of samples are extremely slow within 210d, namely 4.1 multiplied by 102cfu/g and 6.4 multiplied by 102cfu/g respectively, after 240d, the quick-frozen group still grows slowly to be 4.4 multiplied by 102cfu/g, the total number of colonies of the high-temperature and preservative group starts to be obviously improved by 2.1 multiplied by 103cfu/g, the longest detection period is cut off by 360d, the quick-frozen group reports 9.2 multiplied by 102cfu/g, and the high-temperature and preservative group has the signs of bag expansion, deterioration and mildew successively appear, and the total number of colonies reports to be 8.9 multiplied by 107 cfu/g.

1.4.3 variation of mold count

The number of mold bacteria inoculated and naturally fermented during the whole fermentation process was measured, and the measurement results are shown in Table 5.

Table 5 24d mold count during storage of "tofu

As can be seen from Table 5, the "tofu" test of different treatments showed a general trend of overall increase in mold number throughout the storage period, the mold number of the normal temperature control group increased significantly from the 2 nd day of storage, and increased sharply from the 8 th day of storage and preservative group, and the mold number was 1600cfu/g at the 16 th day of storage. The mould numbers of the two groups of products, namely quick freezing and high temperature and preservative, are not obviously increased within 24 days of storage. The mold behavior of the quick-frozen group and the high-temperature + preservative group on long-term storage was continuously followed as shown in Table 6

TABLE 6 360d mold count during storage of "tofu

As can be seen from Table 6, the mold count of the frozen group showed a very slow increase in 360d due to the low temperature inhibition, whereas after 210d the high temperature + preservative group was examined for mold, starting to increase between 210-270d but also within an acceptable range, possibly due to the inhibition by the preservative, which decreased as the mold count increased until the tofu was mildewed.

1.4.5 changes in coliform population

The number of coliforms during storage of "beancurd" was measured, and the measurement results are shown in Table 6.

Table 7 24d coliform population count during storage of "tofu development

As is clear from Table 7, the initial coliform population count of "tofu development<Detecting coliform number of 43MPN/g at 1 st day of storage of normal temperature control group at 0.3MPN/g, and detecting coliform number after 2 nd day>1100MPN/g. The detection value of the refrigeration and preservative group on the 4 th day is 9.2MPN/g, the detection value of the refrigeration and preservative group on the 8 th day is 1100MPN/g, and the detection values of the refrigeration and preservative group on the 12 th day are all>1100MPN/g. The quick-frozen and high-temperature + preservative groups did not detect coliform bacteria within 24 days of storage. The coliform group limit standard cone of the GB 2712-2014 food safety national standard bean product is 10 ³ MPN/g, it was found that day 2 of the normal temperature control group and day 8 of the chilled + preservative group were out of standard.

Follow-up the mold behavior of the quick-frozen group and the high temperature + preservative group on long-term storage is shown in Table 8

Table 8 360d coliform population count during storage of "tofu development

In the period of 360d, the coliform group of the quick-frozen group is lower than 0.3< MPN/g, and the survival condition temperature of coliform bacteria is required to be higher than 7 ℃, the quick-frozen group treated by liquid nitrogen is stored at a low temperature higher than-18 ℃, and under the condition that the package is good and no other condition pollution is received, the product coliform group index is good. The high temperature and preservative group starts to detect a small amount of coliform bacteria at 240d, and the coliform bacteria are in an ascending state but still under a standard line at 270d, which is probably due to slow ascending of trace coliform bacteria which are not thoroughly sterilized under the action of the preservative, breaks through the efficacy of the preservative after 270d, and exceeds the national limit standard at 300d of starting to ascend sharply, so that the method has no edible significance.

The small knot: by measuring microorganisms (total colony count, mold count and coliform group count) in the storage period of 'beancurd', the microorganisms in the normal temperature control group without any treatment are found to start to multiply in a large quantity on the day 2, so that the microorganisms can only be destroyed in the present market at night. The method has the advantages that after the preservative is added, the growth of microorganisms can be inhibited to a certain extent under the refrigerating condition, but the storage and preservation period is not ideal, the preservation effect is good in two ways of quick freezing treatment and high-temperature sterilization treatment basically only for a period of one week, microorganisms are not obviously increased in the storage period of one month, bacteria are not detected in a high-temperature + preservative group before 210d, a small amount of bacteria are detected before 270d, and a large amount of propagation products such as bacteria and mold spoil after 270d, mainly in consideration of the sensory quality of the beancurd, so that the beancurd is not sterilized for a longer time, and a small amount of thermophilic bacillus and other single high-temperature + preservative group possibly remains within 210d and still belongs to the safe shelf life; the total bacteria number of the liquid nitrogen quick-freezing group shows very slow growth state in the detection period of 360d, basically has no too large change, and can be safely eaten within 360 d.

1.4.7 analysis of texture changes of "tofu" during storage

Fig. 13 shows the results of shear force and tensile force during storage of the normal temperature control sample, which had been significantly deteriorated and the toughness of the bean curd tissue lost on the third day of the experiment, and the experiment could not be continued. The results showed that the shear force and the tensile force of the sample showed a greatly decreasing trend with time within 3 days, the shear force was decreased from the first 4.2.+ -. 0.3N to 1.9.+ -. 0.2N on the third day, and the tensile force was decreased from 2.1.+ -. 0.2N to 0.2N on the third day, indicating that the spoilage of the beancurd was accompanied by a significant change in texture, especially for the tensile force.

The shelf life texture results of the preservative group are shown in fig. 14, and compared with the blank group, the shelf life of the preservative group is obviously improved, and the test cannot be continued until the shelf life of the preservative group is improved from 3d to 16 d. The change of the shearing force and the stretching force still shows a decreasing trend along with the time during the storage of the preservative group, but the change of the shearing force and the stretching force is slower at the first 12 days, which is different from the blank group, so that the preservative plays a better role in inhibiting the spoilage of the sample during the period, the change of the texture of the sample is slower, obvious loosening of the texture occurs at the 16 days, and the test cannot be continued, so that the main deterioration interval of the preservative group is between 12 and 16 days.

The quick-frozen group is different from the former two groups, and is shown in fig. 15. After the bean curd sample is frozen, the shearing force and the stretching force are changed to a certain extent, the shearing force is reduced to be about 3.4N, the stretching force is reduced to be about 0.9N, and the lower stretching force is obvious. But over time the two data are substantially on the same horizontal line. This indicates that the frozen sample remained stable at the same texture level for 28d, i.e., the frozen sample had a fairly stable texture with substantially unchanged texture.

The high temperature sterilization group is similar to the freezing group, after the beancurd sample is sterilized at high temperature, the texture data such as shearing force, stretching force and the like detected for the second time are changed, wherein the shearing force is reduced to be near 3.8N, the stretching force is reduced to be near 1.6N, and the subsequent test is basically stable in the range. For the tofu samples, the sterilization mode had less effect on texture than the freezing mode, especially on tensile force (see fig. 16).

The long-term follow-up test results are shown in fig. 17 and 18, the shearing force and the stretching force of the beancurd sample are basically in a constant state in the 210d storage period, and basically have no obvious difference from the 24d result, the stretching force of the high-temperature and preservative group is reduced after 210d, the shearing force is reduced after 270d, the stretching force is 1.2N at 270d, the shearing force is 3.1N, and the spoilage is lost after 300 d. The 'quick freezing' in 360d is detected by thawing, and the whole state is stable.

The small knot: shear force represents the maximum force required to sever the sample, and can indirectly demonstrate the tissue tightness of the sample; the tensile force is the maximum force required to separate the sample from the tissue and may be indicative of the degree of flexibility of the sample. With the increase of the storage time, if the beancurd is stored under normal temperature conditions without additional intervention, the tissue tightness and flexibility of the sample can be basically lost only for 3 days, so that the eating value is lost. Under the double effects of cold preservation and preservative, tissue weakening gradually begins to appear after 12d, and the eating value is lost after 16 d. While the two experimental groups with freezing and sterilizing treatments still had better tissue tightness and flexibility at experimental period 28d, where the sterilizing group had better effect and maintained the result over time before 210d, but from the appearance, the frozen group remained essentially identical to the 28d product after thawing, while the sterilizing group had a darker color change and started after 240d, the "high temperature + preservative" group had a decrease in shear force and a decrease in tensile force, and lost detection after 300 d. The 'quick freezing' in 360d is detected by thawing, and the whole state is stable.

Smell change analysis of "tofu" during 1.4.8 storage period

The principal component analysis is to find out the factors with the largest contribution rate and the most main factors by adopting a dimension reduction method, the difference among samples is reflected to the greatest extent by utilizing a PCA spatial distribution diagram, and the PCA result of the bean curd flavor analysis of quick freezing, preservative, high-temperature sterilization and normal-temperature control groups is shown in figure 19. As can be seen from fig. 19, the total contribution rate of the 1 st main component and the 2 nd main component reaches 99.904%, which indicates that PC1 and PC2 extract the main characteristics of aroma compounds of the fermented bean curd, and are suitable for the flavor analysis of the fermented bean curd with different fresh-keeping treatments, and the 4 groups of treatments have no overlap, which indicates that the PCA analysis can well distinguish the fermented bean curd with different treatment groups.

Drawings

FIG. 1 is an unfoamed bean and bean core state;

FIG. 2-1 0-4deg.C soaking bean and bean core state;

FIG. 2-2 0-4deg.C soaking bean and bean core state;

FIG. 3 shows the state of soaking beans and cores at 10-15 ℃;

FIG. 4 shows the state of soaking beans and bean cores at 25-30 ℃;

FIG. 5 shows the state of soaking beans and bean cores at 25-30 ℃;

FIG. 6 is a graph showing comparison of moisture content of beans soaked under different conditions;

FIG. 7 is a graph showing the comparison of the shearing force of beans soaked under different conditions;

FIG. 8 is a diagram showing the comparison of the appearance of white tofu made from different raw or cooked pulps;

FIG. 9 is a diagram showing the comparison of the appearance of white tofu made from different coagulants at different temperatures;

FIG. 10 is a graph showing the comparison of the appearance of tofu made from different blends of vegetable oils at different frying temperatures;

FIG. 11 "beancurd" changes in colony count during short-term storage;

FIG. 12 "beancurd development" long-term tracking of changes in colony count

FIG. 13 shelf life texture results for a normal temperature control sample;

fig. 14 preservative set sample shelf life texture results;

fig. 15 shelf life texture results for quick frozen group samples;

FIG. 16 shelf life texture results for the high temperature sterilization group samples;

FIG. 17 results of long-term texture tracking of quick frozen group samples

FIG. 18 results of long-term follow-up texture for high temperature + preservative group samples

Fig. 19 is a PCA diagram of the E-nose of the bean curd produced by different fresh-keeping treatment modes.

Claims

1. A preparation method of a bean curd product is characterized by comprising the following steps: the preparation method comprises the following steps:

(1) Preparing a coagulant: adding gypsum powder into water, wherein the weight of gypsum is 3-5% of that of the water, and stirring for 15-25 minutes to obtain a coagulant A; adding magnesium chloride into water, wherein the weight of the magnesium chloride is 3-5% of that of the water, and stirring for 10-15 minutes to obtain a coagulant B;

(2) Soaking soybean, namely soaking dry soybean in water, wherein the water content is 8 times of that of the dry soybean, the spring and summer season is 5-8 hours, the autumn and winter season is 8-12 hours, the specific standard is that the soybean is swelled by water absorption until no soybean core exists, the soybean is in a seamless state, the soaking is stopped in time, the water for soaking the soybean is removed, the water is added for cleaning, and the moisture is filtered to obtain wet soybean;

(4) Preparing raw slurry: taking the wet soybeans in the step (2), adding water with the weight being 4-8 times that of the wet soybeans for grinding, separating bean dregs and soybean milk to obtain bean dreg-free soybean milk, heating and boiling the soybean milk, and obtaining raw soybean milk when the temperature of the soybean milk is increased to 85-105 ℃;

(6) Squeezing and molding white bean curd: taking the soft jellied bean curd in the step (5), slightly taking out, placing into a squeezing frame paved with water filtering gauze, pulling out four corners of the water filtering gauze, covering the soft jellied bean curd, covering a cover plate, pressing for 20-40 minutes by a conventional air pressure method, opening the water filtering gauze after the jellied bean curd is squeezed and molded, rapidly overturning the water filtering gauze on a flat plate by 180 degrees, uncovering the water filtering gauze, and cutting into blocks to obtain the white bean curd;

the preparation method of the fermented bean curd comprises the following steps: cutting white bean curd into white bean curd with thickness of 6-10mm, length of 6-10cm and width of 4-6cm, and frying in heated mixed vegetable oil for 3 min at 110-120deg.C; the oil temperature of the second stage is 120-130 ℃, and the frying time is 3 minutes; the third stage oil temperature is 130-140 ℃, and the frying time is 2 minutes; taking out the fried beancurd, placing on a flat plate capable of filtering oil, cooling to normal temperature, quickly freezing with liquid nitrogen, boxing, and storing in a freezer at-18 ℃ to obtain the beancurd;

the mixed vegetable oil consists of camellia oil, soybean oil and rapeseed oil=1-2:3-5:2-3 by weight.

2. The method for preparing a bean curd product according to claim 1, wherein: the preparation method of the pop bean curd comprises the following steps: soaking white bean curd with thickness of 4-6mm and width of 4-6cm in alkaline water for 10-12 hr, taking out, cooling to room temperature, quick-freezing with liquid nitrogen, cooling, and storing in refrigerator to obtain the final product.

3. The method for preparing a bean curd product according to claim 2, wherein: the alkaline water is prepared by burning wormwood, straw and wormwood into powdery mildew ash, putting the powdery mildew ash into sterile water, stirring for 15-20 minutes, and filtering to remove the powdery mildew ash by 1-3% of the sterile water by weight.