Fresh tofu capable of being frozen and stored and preparation method thereof

Abstract

The invention discloses a fresh tofu that can be frozen and stored and a preparation method thereof. The preparation method of the fresh tofu that can be frozen and stored provided by the invention comprises the following steps: soaking and beating soybeans, removing slag, and obtaining soy milk; boiling the soy milk to obtain soy milk; cooling the soy milk to room temperature, adding curdlan, mixing, and then adding a compound coagulant for reaction and coagulation to obtain a primary tofu product; cutting the primary tofu product and then quick-freezing it to obtain fresh tofu that can be frozen and stored. The fresh tofu that can be frozen and stored provided by the invention has a smooth cross-section after thawing, and does not have the "honeycomb" phenomenon of ordinary tofu after thawing. The texture and taste after thawing are almost the same as those of fresh tofu, and the preparation process is simple, which is more suitable for industrial production.

Description

Technical Field

[0001] The invention belongs to the field of food, and relates to fresh tofu capable of being frozen and stored and a preparation method thereof. Background Art

[0002] Fresh tofu contains a lot of water, is easily corrupted, has a short shelf life, and is difficult to store and sell over long distances. Although freezing can solve the corruption problem, the structure of fresh tofu undergoes significant changes due to the freezing of water in the fresh tofu to form ice crystals, resulting in large pores, sponge-like texture, and rough taste. The soft, tender and smooth quality inherent in fresh tofu is lost, and the texture deteriorates.

[0003] Some patents have proposed solutions to the problem of deterioration of texture and taste of tofu after freezing. CN1617677A proposed a production method for preparing tofu with freeze-resistance by adding raw materials such as gellan gum and modified starch to soy milk; similarly, CN1323168A proposed adding sugar and transglutaminase to unripened soy milk while adding starch. Although the hydrophilicity of tofu will increase after adding modified starch, it will also increase viscosity, making it difficult for tofu to maintain its original delicate texture, resulting in a poor taste; and it is not conducive to pipeline transportation in industrial production. CN103027128A and CN103027131A use soy protein isolate and curdlan as raw materials, add protein cross-linking agents and other seasoning accessories, and the freeze-resistance and boiling resistance are improved. However, this tofu made with soy protein isolate as raw material belongs to thousand-layer tofu, which is significantly different from the production process and taste of fresh tofu made by soaking and beating soybeans with water extract in traditional production.

[0004] It can be seen that there is currently no industrial production method that has a simple process, a small number of additives, and allows fresh tofu to maintain its original fresh and tender quality after frozen storage. Summary of the invention

[0005] The invention aims to provide fresh tofu which can be frozen and stored and a preparation method thereof. The obtained fresh tofu has small pore size and fine texture after thawing, and maintains the soft, tender and smooth taste of the fresh tofu. The preparation process is simple, the types of additives are few, and the tofu is suitable for industrial production.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing fresh tofu that can be frozen and stored, comprising the following steps:

[0008] S1, soaking and beating soybeans, removing slag, and obtaining soy milk;

[0009] S2, boiling the soymilk to obtain soy milk;

[0010] S3, cooling the soy milk to room temperature, adding curdlan, mixing, and then adding a composite coagulant to react and coagulate to obtain a primary tofu product;

[0011] S4, cutting the primary tofu and then quick-freezing it to obtain fresh tofu that can be frozen and stored.

[0012] In step S1, the soaking conditions are: the temperature is 3-5°C, preferably 4°C, and the time is 11-13h, preferably 12h. Generally speaking, the soaking standard is: the surface of the soaked soybeans is smooth, without wrinkles, the bean skin does not fall off easily, and it feels strong; the soaked soybeans are twisted into two pieces, and the inner surface of the bean is basically flat, with a slight collapse, and it is easy to break when pinched by fingers, and the cross section is soaked without a hard core.

[0013] In step S1, the mass ratio of water used in the soaking and pulping to the soybeans is (5-9):1, preferably 7:1.

[0014] In step S1, the beating conditions are: temperature of 15-30°C, preferably 20-25°C; time of 2-3 min, preferably 2.5 min.

[0015] In step S1, the slag removal is performed by filtering with a 100-mesh screen.

[0016] In step S1, the solid content of the soymilk is 6-11°Brix, preferably 9°Brix.

[0017] In step S2, the cooking is achieved by heating in a boiling water bath; the cooking conditions are: temperature of 95-100°C, preferably 95°C, time of 3-5min, preferably 5min.

[0018] In step S3, based on 100 ml of soy milk, the amount of the curdlan is 2-2.5 g / 100 ml of the mass of the soy milk.

[0019] In step S3, the curdlan has a purity of greater than 90% and a Mw of 74,000 Da. The curdlan is added in the form of an aqueous solution.

[0020] In step S3, the compound coagulant is one or more of magnesium chloride, gluconolactone, calcium sulfate, transglutaminase, malic acid and citric acid, preferably a combination of magnesium chloride, gluconolactone and transglutaminase.

[0021] In step S3, based on 100 ml of soy milk, the dosage of the composite coagulant is 0.5-1 g / 100 ml of the mass of the soy milk.

[0022] According to an embodiment of the present invention, the composite coagulant is composed of magnesium chloride, gluconolactone and transglutaminase; wherein based on 100ml of soy milk, the amount of magnesium chloride is 0.4-1.0g / 100ml of the mass of the soy milk, preferably 0.4-0.8g / 100ml; the amount of gluconolactone is 0.1%-0.3g / 100ml of the mass of the soy milk, preferably 0.15-0.3g / 100ml; the amount of transglutaminase is 0.02%-0.2g / 100ml of the mass of the soy milk, preferably 0.02-0.15g / 100ml, such as 0.02g / 100ml, 0.04g / 100ml.

[0023] In step S3, the compound coagulant is used in the form of an aqueous solution.

[0024] In step S3, the reaction solidification conditions are: temperature of 80-95°C, preferably 90-95°C, time of 20-40 min, preferably 25-35 min.

[0025] In step S4, the cutting size requirements are: length 15-25 mm, width 15-25 mm, height 15-25 mm, preferably 20 mm×20 mm×20 mm.

[0026] In step S4, the quick freezing conditions are: temperature of -40--30°C, preferably -40°C, and time of 1-3 min, preferably 1 min.

[0027] In a second aspect, the present invention also provides fresh tofu that can be frozen and stored and is obtained by the preparation method.

[0028] The beneficial effects achieved by the present invention are as follows:

[0029] 1. In the process of preparing fresh tofu using soybean as raw material, the present invention adds curdlan to soybean milk to form a thermally irreversible gel, thereby improving the mechanical strength of the fresh tofu and reducing its thawing dehydration rate after freezing, thereby greatly improving the antifreeze performance of the fresh tofu.

[0030] 2. The present invention further selects a compound coagulant for use in combination with curdlan to make the gel network cross-linking more dense, and the texture and taste of the tofu after thawing during frozen storage are still close to those of traditional fresh tofu, thus solving the problem of honeycomb and rough taste of fresh tofu after freezing. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 These are comparison photos of the cross-sections of the tofu products obtained in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 before and after freezing. DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments.

[0033] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0034] Unless otherwise specified, the reagents, biological materials, instruments, etc. used in the following examples can be obtained from commercial sources.

[0035] Example 1

[0036] (1) Soaking the soybeans completely, beating the soybeans at a soybean-water ratio of 1:7, removing the dregs with a 100-mesh nylon net, and obtaining soymilk with a solid content of 9° Brix;

[0037] (2) heating the obtained soymilk in a boiling water bath and maintaining the temperature at the center at 95° C. for 5 minutes to obtain soymilk;

[0038] (3) cooling the soy milk naturally to room temperature, adding the curdlan aqueous solution, and mixing evenly; continuing to add the magnesium chloride aqueous solution, the gluconolactone aqueous solution, and the glutamine transaminase aqueous solution, and then placing in a 90° C. water bath for 25 minutes, cooling to room temperature after heating, and coagulating to obtain the first tofu product;

[0039] Among them, based on 100ml of soy milk, the added amount of curdlan is 2g / 100ml, the added amount of magnesium chloride is 0.5g / 100ml, the added amount of gluconolactone is 0.3g / 100ml, and the added amount of glutamine transaminase is 0.04g / 100ml.

[0040] (4) The coagulated tofu was cut into blocks of 20 mm in length, width and height, and 20 mm in width and height, and frozen at -40°C for 1 min to obtain fresh tofu that can be frozen and stored. The fresh tofu was then frozen and stored at -18°C.

[0041] Example 2

[0042] (1) Soaking the soybeans completely, beating the soybeans at a soybean-water ratio of 1:7, removing the dregs with a 100-mesh nylon net, and obtaining soymilk with a solid content of 9° Brix;

[0043] (2) heating the obtained soymilk in a boiling water bath and maintaining the temperature at the center at 95° C. for 5 minutes to obtain soymilk;

[0044] (3) cooling the soy milk naturally to room temperature, adding 2.5% of curdlan by weight of the soy milk, and mixing evenly; continuing to add 0.4% of magnesium chloride aqueous solution by weight of the soy milk, 0.15% of gluconolactone aqueous solution, and 0.02% of glutamine transaminase aqueous solution, and then placing in a 95° C. water bath for 30 minutes, cooling to room temperature after heating, and coagulating to obtain a primary tofu product;

[0045] (4) The coagulated tofu was cut into blocks of 20 mm in length, width and height, and 20 mm in width and height, and frozen at -40°C for 1 min to obtain fresh tofu that can be frozen and stored. The fresh tofu was then frozen and stored at -18°C.

[0046] Comparative Example 1

[0047] (1) Soaking the soybeans completely, beating the soybeans at a soybean-water ratio of 1:7, removing the dregs with a 100-mesh nylon net, and obtaining soymilk with a solid content of 9° Brix;

[0048] (2) heating the obtained soymilk in a boiling water bath and maintaining the temperature at the center at 95° C. for 5 minutes to obtain soymilk;

[0049] (3) cooling the soy milk naturally to room temperature, adding a 0.3% gluconolactone aqueous solution by weight of the soy milk, and then placing it in a 90° C. water bath for 25 min. After heating, cooling it to room temperature and coagulating it to obtain a primary tofu product (i.e., gluconolactone tofu);

[0050] (4) The tofu obtained by coagulation as described above was cut into blocks of 20 mm in length × 20 mm in width × 20 mm in height, frozen at -40°C for 1 min, and then stored frozen at -18°C.

[0051] Comparative Example 2

[0052] (1) Soaking the soybeans completely, beating the soybeans at a soybean-water ratio of 1:7, removing the dregs with a 100-mesh nylon net, and obtaining soymilk with a solid content of 9° Brix;

[0053] (2) heating the obtained soymilk in a boiling water bath and maintaining the temperature at the center at 95° C. for 5 minutes to obtain soymilk;

[0054] (3) cooling the soy milk naturally to room temperature, adding 2% of curdlan by weight of the soy milk, and mixing evenly; adding 0.3% of gluconolactone aqueous solution by weight of the soy milk, and then placing in a 90° C. water bath for 25 min, cooling to room temperature after heating, and coagulating to obtain a primary tofu product;

[0055] (4) The tofu obtained by coagulation as described above was cut into blocks of 20 mm in length × 20 mm in width × 20 mm in height, frozen at -40°C for 1 min, and then stored frozen at -18°C.

[0056] Effect verification

[0057] 1. Appearance of tofu before and after freezing

[0058] like Figure 1 As shown, the tofu obtained in Example 1 and Example 2 maintained the same shape and had a smooth cross section after being frozen for one month, while the tofu obtained in Comparative Example 1 shrank in appearance and decreased in volume after being frozen for one month, and a honeycomb-like network structure appeared on the cross section; tiny protein particles existed on the surface of the tofu obtained in Comparative Example 2, indicating weak coagulation, and tiny concave holes appeared in the appearance after being frozen for one month, and the texture of the cross section was uneven.

[0059] 2. The texture (hardness, elasticity, chewiness), moisture content and water retention of the products obtained from Example 1 and Comparative Example 2 were measured after being stored at -18°C for 1 month. The average values ​​are shown in Table 1.

[0060] Determination method of hardness, elasticity and chewiness:

[0061] Two compression tests were conducted using a Brookfield texture analyzer CT-3. The tofu was cut into cubes with a length × width × height of 10 mm × 10 mm × 10 mm. The test probe was an acrylic probe with a flat surface (TA 25 / 1000 probe, diameter 50.8 cm, length 20 mm, weight 23 g). The target value was 40% of the original height, the trigger point load was 5 g, the test speed was 0.5 mm / s, the return speed was 0.5 mm / s, and the cycle was repeated twice. TexturePro CT V1.8 software was used to record the curve of the compression process and calculate the hardness, elasticity, and chewiness.

[0062] Method for determining moisture content:

[0063] Refer to the method in national standard GB / T 5009.3-2016.

[0064] Determination of water retention: Use a centrifuge tube with a cannula inside to determine the water retention of tofu. Place a filter paper of the same size at the bottom of the cannula, take a certain amount of sample and put it into the cannula to weigh it, centrifuge it at 1000g for 10 minutes, discard the centrifuge liquid and weigh it. Water retention (WHC) is calculated according to the following formula.

[0065]

[0066] Where: m0-total weight of filter paper and sleeve (g)

[0067] m1-total weight of filter paper, sleeve and sample (g)

[0068] m2-total weight of filter paper, cannula and sample after centrifugation (g)

[0069] MC-water content (g / 100g)

[0070] Table 1 Comparison of quality evaluation of the products of the embodiment and the comparative example after frozen storage for 1 month

[0071]

[0072]

[0073] As can be seen from Table 1, after the tofu obtained in Example 1 and Example 2 was frozen and stored for one month, its hardness, chewiness and water retention were significantly higher than those of Comparative Example 1 and Comparative Example 2, and its elasticity and moisture were significantly higher than those of Comparative Example 1, and were equivalent to those of Comparative Example 2. This shows that the combined use of curdlan and the compound coagulant can significantly improve the mechanical properties of fresh tofu and reduce its dehydration rate after thawing after freezing, thereby greatly improving the antifreeze performance of fresh tofu. At the same time, it also makes the tofu maintain a texture and taste close to that of traditional fresh tofu after thawing during frozen storage, solving the problem of honeycomb and rough taste of fresh tofu after freezing.

[0074] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements may be made thereto based on the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing fresh tofu that can be frozen and stored, comprising the following steps: S1, soaking and beating soybeans, removing slag, and obtaining soy milk; S2, boiling the soymilk to obtain soy milk; S3, cooling the soy milk to room temperature, adding curdlan, mixing, and then adding a composite coagulant to react and coagulate to obtain a primary tofu product; In step S3, the compound coagulant is a combination of magnesium chloride, gluconolactone and transglutaminase; Based on 100 ml of soy milk, the amount of the curdlan is 2-2.5 g / 100 ml of the mass of the soy milk; Based on 100 ml of soy milk, the amount of magnesium chloride is 0.4-1.0 g / 100 ml of the soy milk, the amount of gluconolactone is 0.1-0.3 g / 100 ml of the soy milk, and the amount of glutamine transaminase is 0.02-0.2 g / 100 ml of the soy milk; S4, cutting the primary tofu and then quick-freezing it to obtain fresh tofu that can be frozen and stored.

2. The method for preparing fresh tofu capable of being frozen and stored according to claim 1, It is characterized in that In step S1, the soaking conditions are: temperature of 3-5°C and time of 11-13h; The mass ratio of water used in the soaking and beating to the soybeans is (5-9):1; The beating conditions are: temperature of 15-30°C and time of 2-3 minutes; The slag removal is carried out by filtering with a 100-mesh screen.

3. The method for preparing fresh tofu capable of being frozen and stored according to claim 1 or 2, It is characterized in that In step S1, the solid content of the soymilk is 6-11° Brix.

4. The method for preparing fresh tofu capable of being frozen and stored according to claim 1 or 2, It is characterized in that In step S2, the cooking is achieved by heating in a boiling water bath; The cooking conditions are: temperature of 95-100° C. and time of 3-5 min.

5. The method for preparing fresh tofu capable of being frozen and stored according to claim 1 or 2, It is characterized in that In step S3, the reaction solidification conditions are: temperature of 80-95° C. and time of 20-40 min.

6. The method for preparing fresh tofu capable of being frozen and stored according to claim 1 or 2, It is characterized in that In step S4, the quick freezing conditions are: temperature of -40--30°C and time of 1-3 minutes.

7. Fresh tofu that can be frozen and stored obtained by the preparation method according to any one of claims 1 to 6.

Images