WO2006109991A1

WO2006109991A1 - A manufacturing method of whole soybean milk and soybean curd

Info

Publication number: WO2006109991A1
Application number: PCT/KR2006/001344
Authority: WO
Inventors: Byung-Serk Heo; Ho-Ryoung Kwon; Min-Choul Shin; Yu-Jin Kim; Won Shim; Ui-Chan Koh; Jong-Heon Shin; Young-Gon Lee; Gyeong-Ho Han
Original assignee: Daesang Fnf Corporation
Priority date: 2005-04-12
Filing date: 2006-04-12
Publication date: 2006-10-19
Also published as: JP2008535515A

Abstract

The present invention relates to methods for preparing whole soybean milk and soybean curd. More particularly, it relates to a method for preparing whole soybean milk using whole soybean without separating soybean pulps, and to a method for preparing soybean curd by heating and co¬ agulating the prepared whole soybean milk in a stepwise manner. According to the inventive method the inventive method can effectively prepare high-quality of whole soybean milk using whole soybean without separating the soybean pulps, which contains the nutritional components of soybean pulps intact and has a very narrow and uniform particle diameter distribution so that the precipitation of soybean particles does not occur. Also, according to the method for preparing soybean curd using the whole soybean milk, soybean curd having improved sensory charac¬ teristics and cooking suitability can be prepared by heating the whole soybean milk in a stepwise manner so as to uniformly coagulate the soybean milk.

Description

A MANUFACTURING METHOD OF WHOLE SOYBEAN MILK

AND SOYBEAN CURD

Technical Field

[1] The present invention relates to methods for preparing whole soybean milk and soybean curd. More particularly, it relates to a method for preparing whole soybean milk using whole soybean without separating soybean pulps(Okara), and to a method for preparing soybean curd by heating and coagulating the prepared whole soybean milk in a stepwise manner. Background Art

[2] Soybean-based food such as soybean milk or soybean curd is receiving attention, because it is a high-protein source that can solve a problem caused by the intake of meats. Generally, soybean milk and soybean curd are prepared using a method comprising the steps of grinding, steaming and filtering soybean. Meanwhile, the cell wall of soybean contains large amounts of cellulose, hemicellulose, pectin and water- insoluble substances, and thus has a highly complex and hard structure. Thus, it is impossible to prepare whole soybean into soybean milk in a soft and homogeneous form by a general grinding and heating method. For this reason, in a general process for the preparation of soybean milk and soybean curd, soybean pulps are removed. If the soybean pulps are not removed, there will be a problem such as the occurrence of precipitates in soybean milk due to the very wide particle diameter distribution and the non-uniform particle diameter of soybean milk. If such soybean milk is used to prepare soybean curd, particles of soybean pulps will interfere with the coagulation of the soybean milk. However, the soybean pulps contain large amounts of nutritional components, such as celluloses, lipids and inorganic substances. Thus, if soybean milk or soybean curd is prepared using a conventional method, the nutritional components contained in soybean pulps will be lost. Accordingly, there is a need for a method capable of preparing soybean milk or soybean curd in a homogeneous form without separating soybean pulps for preventing nutrient loss.

[3] Meanwhile, methods which are generally used to coagulate soybean milk include a method wherein cooled soybean milk is mixed with a coagulant and curdled at high temperature, and a method wherein heated soybean milk is mixed with a coagulant and the mixture is curded by reaction for a given time. The soybean curd which is prepared in this manner has a shortcoming of reduced texture and taste, because coagulated particles of protein in soybean milk are large due to a rapid coagulation reaction occurring at high temperature, and soybean milk is not uniformly coagulated into soybean curd due to a great difference in temperature between the surface and inside of soybean curd.

[4] Also, as another known method for preparing soybean curd, a method is used wherein high-temperature soybean milk is coagulated by the addition of a coagulant, and then crushed and pressed. The soybean curd prepared using this pressure-type method has shortcoming in that it is coarse and non-homogeneous and has nonuniform quality. Moreover, soybean curd prepared using a non-pressure type method is shortcomings in that it is difficult to handle due to a very low degree of coagulation and has significantly reduced taste. Disclosure of Invention Technical Problem

[5] The present inventors have conducted studies on methods for preparing whole soybean milk and soybean curd in order to settle the above-described problems, and as a result, have prepared whole soybean milk in a homogeneous form, which contains various nutritional components of soybean intact, through a process comprising the steps of coarse grinding, heating, cooling, fine grinding and high-pressure homog- enization of skin-peeled soybean, and have prepared soybean curd having improved sensory characteristics, such as texture and taste, and improved suitability for cooking, by heating and coagulating the prepared whole soybean milk in a stepwise manner.

[6] Accordingly, it is an object of the present invention to provide a method for preparing whole soybean milk, comprising the steps of coarse grinding, heating, cooling, fine grinding and high-pressure homogenization of soybean whose skin was peeled.

[7] It is another object of the present invention to provide a method for preparing soybean curd, comprising the steps of cooling said whole soybean milk, adding a coagulant and a protein-binding enzyme to the cooled soybean milk, and heating and coagulating the mixture in a stepwise manner. Technical Solution

[8] To achieve the above objects, the present invention provides a method for preparing whole soybean milk, comprising the steps of: (a) peeling the skin of soybean, immersing the skin-peeled soybean in water and coarse grinding the soybean; (b) heating and cooling the coarsely ground soybean from the step (a); (c) finely grinding the coarsely ground soybean from the step (b); and (d) homogenizing the finely ground soybean from the step (c) under high pressure.

[9] Also, the present invention provides a method for preparing soybean curd, comprising the steps of cooling the whole soybean milk prepared in said method; adding a coagulant and a protein-binding enzyme to the cooled milk; and heating and coagulating the mixture in a stepwise manner.

[10] As used herein, the term "whole soybean milk" refers to soybean milk prepared using whole soybean without removing soybean pulps. The whole soybean milk has characteristics in that it contains nutritional components of soybean pulps intact.

[11] As used herein, the term "soybean curd" refers to processed food prepared by coagulating soybean milk.

[12]

[13] Hereinafter, the present invention will be described in detail.

[14]

[15] The inventive method for preparing whole soybean milk is characterized in that whole soybean milk in a homogeneous form, which contains various nutritional components of soybean pulps, can be prepared using whole soybean without separating soybean pulps. More specifically, the inventive method for preparing whole soybean milk comprises the steps of: coarsely grinding skin-peeled whole soybean without separating soybean pulps; heating the coarsely ground soybean to soften the cell wall of soybean; finely grinding the coarsely ground soybean using an ultrafine grinder; and homogenizing the resulting soybean milk using a high-pressure homogenizer.

[16]

[17] Hereinafter, each of the steps of the inventive method for preparing whole soybean milk will be described.

[18]

[19] Step 1 : Skin peeling, w ater immersion and coarse grinding of soybean

[20] The skin peeling of soybean is preferably performed by removing the skin portion of soybean in an amount of about 5-20% based on the whole soybean using a skin peeler. More preferably, the skin peeling of soybean is performed in the range where the embryo of soybean is conserved. If whole soybean milk is prepared without peeling the skin of soybean, there will be problems of an increase in the viscosity of soybean milk, generating odd taste, grinding failure, etc. As the skin peeler, a peeler known in the art can be used, and preferably a peeler consisting of a skin peeling unit, a skin collecting unit and a colorimeter can be used. More specifically, in the skin peeler, upper and lower rotating plates rotate in a direction opposite to each other, and the upper and lower surfaces thereof, which are brought into contact with soybean, are embossed to promote friction, so that a skin and a grain are separated from soybean. Herein, the degree of peeling may be controlled with the colorimeter, so that only the skin may be selectively removed while embryos containing large amounts of nutrients may remain intact.

[21] The water immersion of soybean is preferably performed by immersing the skin- peeled soybean in 2-10 times of water the weight of the soybean for 2-12 hours. [22] For the coarse grinding of soybean, the soybean immersed in water is taken up and water is added to the soybean in an amount of 4-5 times the weight of the soybean. The coarse grinding can be performed using a soybean grinder (e.g., chopper mill) known in the art. The particle diameter of the coarsely ground soybean is preferably 100-3000 D.

[23] The coarse grinding of soybean may further comprise the step of adding an anti- foaming agent. As the antifoaming agent may be used without any particular limitation as long as it is an edible antifoaming agent known in the art. Examples of the antifoaming agent, which can be used in the present invention, include a fatty acid-based antifoaming agent, a silicone-based antifoaming agent, and a highly oxidized oil (palm oil)-based antifoaming agent. More preferably, the fatty acid-based antifoaming agent may be used. The antifoaming agent may be added in an amount of about 0.002-2 wt% based on the total weight of soybean and water.

[24]

[25] Step 2: Heating and cooling of coarsely ground soybean

[26] The coarsely ground soybean obtained in said step 1 is heated to soften the cell wall of the soybean.

[27] The heating of the soybean is preferably carried out in a condition where the cell wall of the soybean is softened while the denaturation of protein is inhibited. More preferably, the heating of the soybean is carried out at 95-100 ⁰C for 5-20 minutes. If the soybean is heated below 95 ⁰C, the cell wall of the soybean will not be softened, and thermally instable anti-nutritive factors, such as trypsin inhibitors, hemagglutin, and lipoxygenase will not be inactivated. On the other hand, if the heating is carried out at a temperature exceeding 100 ⁰C, the soybean protein will be denatured. The denaturation of the soybean protein deteriorates the quality of soybean milk, and if such soybean milk is used to prepare soybean curd, there will be a problem in that the coagulation of the soybean milk does not occur. Also, if the heating time is shorter than 5 minutes, the cell wall of the soybean will not be completely softened, and if it exceeds 20 minutes, the denaturation of the soybean protein will occur. The present inventors examined the correlation between the inactivation of anti-nutritive factors of soybean and the utilization of protein and, as a result, could fount that if soybean was thermally treated at 100 ⁰C for 10 minutes, the inactivation of anti-nutritive factors would be maximized, and if soybean was thermally treated at 100 ⁰C for 20 minutes, the problem of the denaturation of protein would arise (see FIG. 1).

[28] The heated coarsely ground soybean is preferably cooled to 0-20 ⁰C, more preferably 0-10 ⁰C, and most preferably 0-5 ⁰C. The cooling step may be performed using a cooling device known in the art, such as a heat exchange-type cooler.

[29] [30] Step 3: Fine grinding of coarsely ground soybean

[31] The coarsely ground soybean heated in said step 2 is finely ground with an ultrafine grinder. As an ultrafine grinder, a friction-type ultrafine grinder may preferably be used. For example, a millstone-type non-porous ultrafine mill consisting of two upper and lower grinders can be used, which can make soybean ultrafine and in which the interval between the two grinders can be freely controlled. The mesh size of the non-porous grinders is preferably 46-210 meshes. Examples of the non-porous grinders, which can be used in the present invention, include Supermasscolloider series, such as Model MKG-A, MKG-C, MKB-A, MKB-C and MKFC, which are commercially available from Masuko, Japan.

[32] The use of such non-porous grinders for ultrafine grinding provides advantages in that contamination or deterioration caused by heat generation and friction does not occur. The millstone-type ultrafine mill and an ultrafine step utilizing the same will now be described in further detail. In the millstone-type ultrafine mill, the upper grinder is fixed and the lower grinder rotates at high speed, so that the coarsely ground soybean introduced into a hopper moves into the gap (interval) between the upper and lower grinders by the centrifugal force. The coarsely ground soybean is gradually made fine due to a strong pressure and shear stress occurring in the gap between the upper and lower grinders and friction occurring upon the rolling of objects, etc. For this reason, the millstone-type ultrafine mill enables the preparation of whole soybean milk having particles which are closer to a spherical shape and more fine, compared to other milling means. Meanwhile, the control of the interval between the upper and lower grinders of the ultrafine mill is an important factor in determining the particle diameter of soybean milk which becomes ultrafine. The control of the interval between the upper and lower grinders is performed by changing numerical value on a dashboard at the side of the mill using a control handle, in which "0" on the dashboard represents a state where the upper and lower grinders come in contact with each other, and if one click on the dashboard moves, the interval will widen 20 D. In the present invention, the fine grinding of the coarsely ground soybean is performed such that the particle diameter of the soybean milk reaches about 0.04-200 D, and preferably less than about 45 D.

[33] The fine grinding of the coarsely ground soybean using the ultrafine mill is prefe rably repeated 2-3 times. This can be easily performed by connecting the ultrafine mills with each other in series on a manufacturing process line.

[34] Also, the step of finely grinding the coarsely ground soybean may further comprise the step of adding an antifoaming agent. The kind and amount of the antifoaming agent added are as disclosed above for the step of coarsely grinding the soybean. [36] Step 4: High-pressure homogenization

[37] The soybean finely ground in said step 3 is homogenized under high pressure to prepare high-quality homogenized whole soybean milk having a very narrow particle diameter distribution. The high-pressure homogenization step may be carried out under a pressure of 150-400 bar using a high-pressure homogenizer known in the art.

[38] The whole soybean milk prepared according to the inventive method may have a mean particle diameter of less than 45 D and sugar contents (brix) of 6-16%, and preferably 12-14%.

[39] The whole soybean milk prepared according to the inventive method can be used to prepare soybean curd. Accordingly, the present invention provides a method for preparing soybean curd, comprising the steps of cooling the whole soybean milk prepared according to the inventive method, and then adding a coagulant and a protein- binding enzyme to the cooled soybean milk and heating and coagulating the mixture in a stepwise manner.

[40] In this method, the cooling of the whole soybean milk is performed to 0-10 ⁰C and preferably 5 ⁰C. The coagulant may be used without any particular limitation as long as it is generally used in a process of coagulating soybean milk. Examples of the coagulant include, but are not limited to, magnesium chloride, GDL (gluconodelta lactone), salt and calcium sulfate. The coagulant may be used in an amount of 0.05-2.0 wt% based on the total weight of the whole soybean milk. More preferably, a mixture with 0.2-0.5 wt% magnesium chloride and 0.05-0.4 wt% GDL may be used as the coagulant.

[41] The protein-binding enzyme can be used without any particular limitation as long as it is generally used in the preparation of soybean curd. Preferably, transglutaminase can be used. The protein-binding enzyme can be used in an amount of 0.1-0.8 wt% based on the total weight of the whole soybean milk.

[42] Also, in the mixing of the whole soybean milk, the coagulant and the protein- binding enzyme, 0.05-0.20 wt% salt may additionally be added.

[43] Also, the whole soybean milk, the coagulant and the protein-binding enzyme can be filled into a tray-type container, a filling container such as pack, or a closed mold.

[44] The stepwise heating and coagulation of the soybean milk according to the present invention is characterized by stepwise increasing the temperature of the soybean milk from low temperature.

[45] Preferably, the inventive method for preparing soybean curd comprises the steps of: (a) heating the cooled whole soybean milk, the coagulant curdling milk and the protein-binding enzyme at 30-70 ⁰C for 20-180 minutes; and (b) heating the mixture from said step (a) at 75-100 ⁰C for 30-90 minutes.

[46] More preferably, the inventive method may comprise the two steps of: (a) heating at 45-65 ⁰C for 30-70 minutes, more preferably at 55 ⁰C for 45-70 minutes; and (b) heating the mixture from the step (a) at 75-100 ⁰C for 30-90 minutes, and preferably at 85 ⁰C for 30-60 minutes.

[47] Also, the method for preparing soybean curd according to the present invention may further comprise the step of heating the whole soybean milk, the coagulant and the protein-binding enzyme at 10-20 ⁰C for 60-120 minutes before conducting the step (a).

[48] Accordingly, the inventive method for preparing soybean curd may consist of three steps of: (1) heating the whole soybean milk, the coagulant and the protein-binding agent at 10-20 ⁰C for 60-120 minutes; (2) heating the mixture from the step (1) at 45-65 ⁰C for 30-60 minutes; and (3) heating the mixture from the step (2) at 75-100 ⁰C for 30-90 minutes.

[49] Furthermore, the step (a) of the inventive method for preparing soybean curd may consist of: (i) heating the whole soybean milk, the coagulant and the protein-binding enzyme at 45-55 ⁰C for 20-60 minutes; and (ii) heating the mixture from the step (i) at 60-70 ⁰C for 30-60 minutes.

[50] Accordingly, the inventive method for preparing soybean curd may consist of four steps of: (1) heating the whole soybean milk, the coagulant and the protein-binding agent at 10-20 ⁰C for 60-120 minutes; (2) heating the mixture from the step (1) at 45-55 ⁰C for 20-60 minutes; (3) heating the mixture from the step (2) at 60-70 ⁰C for 30-60 minutes; and (4) heating the mixture from the step (3) at 75-100 ⁰C for 30-90 minutes.

[51] Also, the step (a) of the inventive method for preparing soybean curd may consist of the steps of: (i) heating the whole soybean milk, the coagulant and the protein- binding enzyme at 30-45 ⁰C for 20-60 minutes; (ii) heating the mixture from the step (i) at 50-60 ⁰C for 30-60 minutes; and (iii) heating the mixture from the step (ii) at 65-70 ⁰C for 30-60 minutes.

[52] Accordingly, the inventive method for preparing soybean curd may consist of five steps of: (1) heating the whole soybean milk, the coagulant and the protein-binding enzyme at 10-20 ⁰C for 60-120 minutes; (2) heating the mixture from the step (1) at 30-45 ⁰C for 20-60 minutes; (3) heating the mixture from the step (2) at 50-60 ⁰C for 30-60 minutes; (4) heating the mixture from the step (3) at 65-70 ⁰C for 30-60 minutes; and (5) heating the mixture from the step (4) at 80-100 ⁰C for 30-70 minutes (see FIG. 5).

[53] The soybean curd prepared according to the inventive method can be made into products through packaging, sterilization and cooling steps. However, in the case of soybean curd (packed soft tofu or uncurdled tofu) prepared in a packed form, a sterilization step may be omitted because sterilization action occurs in a heating and co- agulation step.

[54] Also, in the inventive method for preparing soybean curd, preparation conditions may varying depending on the kind or type of soybean curd to be prepared, and any person skilled in the art this variation easily perform on the basis of a technology known in the art and the disclosure of the present invention. Examples of soybean curd, which can be prepared according to the inventive method, include, but are not limited to, uncurled soybean curd, packed soft tofu, filled Kinugoshi (silken tofu) and Kinugoshi (silken tofu).

[55] In the method for preparing soybean curd according to the present invention, the temperature of soybean milk is slowly increased from low temperature in a stepwise manner to coagulate the soybean milk, such that the difference in temperature between the surface and inside of the resulting soybean curd is reduced, making the coagulation reaction uniform. For this reason, the soybean curd prepared according to the inventive method has characteristics in that it is smooth and firm, has a good taste, is not easily broken upon cooking and is convenient to handle.

[56] Also, the inventive method for preparing soybean curd has an advantage in that, because a step of pressing soybean curd after coagulation into the soybean curd is not carried out, water-soluble nutrients and functional substances, which are lost upon the pressing of the soybean curd, can be contained intact in the soybean curd. Brief Description of the Drawings

[57] FIG. 1 is a graphic diagram showing the correlation of the trypsin inhibitor activity of soybean with the utilization rate of soybean protein according to heating time. .

[58] FIG. 2 shows analysis results for the particle diameter of whole soybean milk prepared in one example of the present invention.

[59] FIG. 3 shows analysis results for the particle diameter of whole soybean milk prepared in comparative examples of the present invention.

[60] FIG. 4 shows analysis results for the particle diameter at various positions (upper, intermediate and lower positions) of whole soybean milk which was prepared in one example of the present invention after leaving it for a long time.

[61] Blue colored line: lower layer portion

[62] Red colored line: intermediate portion

[63] Green colored line: upper layer portion

[64] FIG. 5 is a graphic diagram showing a heating and coagulation method consisting of five steps according to the present invention.

[65] FIG. 6 shows measurement results for the changes with time of the surface and internal temperatures of soybean curd prepared by a known method.

[66] FIG. 7 shows measurement results for the changes with time of the surface and internal temperatures of soybean curd prepared by the inventive method. Best Mode for Carrying Out the Invention

[67] Hereinafter, the present invention will be described in detail with reference to examples. It is to be understood, however, that these examples are for illustrative purposes only and are not to be construed to limit the scope of the present invention.

[68]

[69] Example 1: Preparationof whole soybean milk according to inventive method

I

[70] The skin of 100 kg soybean was removed using a skin peeler. The skin-peeled soybean was immersed in a 5-fold weight of water for 3-6 hours. The immersed soybean was taken out of water and added to a 4-5-fold weight of water and then coarsely ground with a grinder (Daeruck Machine Co. Ltd., Korea). Herein, the particle diameter of the coarsely ground soybean was about 100-3000D. The coarsely ground soybean was heated at 100 ⁰C for 10 minutes and cooled to 0-10 ⁰C with a cooler. Then, the coarsely ground soybean was finely crushed using an ultrafine mill (commercially available from Masuko, Japan). Herein, the upper grinder (MKG-A) of the ultrafine mill was fixed and the lower grinder (MKG-A) was moved upward or downward at an interval of 1/100 mm by turning the control handle right or left, and then was rotated at high speed. The particle diameter of the finely ground soybean was 0.04-200D. The finely ground soybean was homogenized with a high-pressure ho- mogenizer (Alfa Tech Co., Ltd., Korea) under a high pressure of 150-400 bar. As a result, whole soybean milk having a sugar content of 6-16% (brix) was prepared.

[71]

[72] Example 2: Preparation of whole soybean milk according to inventive method

II

[73] Whole soybean milk was prepared in the same manner as in Example 1, except that, upon grinding with the ultrafine mill, a fatty acid-based antifoaming agent (RikenVita) was added in an amount of 0.002-0.2 wt% based on the total weight of the coarsely ground soybean.

[74]

[75] Example 3: Preparation of whole soybean milk according to inventive method

III

[76] Whole soybean milk was prepared in the same manner as in Example 2, except that the ultrafine grinding step was performed using two untrafine mills connected with each other in series in a production process line.

[77]

[78] Comparative Example 1 [79] Coarsely ground soybean was finely ground without heating, and whole soybean milk was obtained without carrying out high-pressure homogenization.

[80] That is, the skin peeling, water immersion and coarse grinding of soybean were conducted in the same manner as in Example 1, and then the coarsely ground soybean was finely ground using an ultrafine mill (Masuko) without heating.

[81]

[82] Comparative Example 2

[83] Coarsely ground soybean was heated at 120 ⁰C for 15 minutes and finely ground with an ultrafine mill, thus preparing whole soybean milk. Then, a high-pressure homogenization step was not carried out.

[84]

[85] Comparative Example 3

[86] Whole soybean milk was prepared in the same manner as in Example 1, except that the coarsely ground soybean was not heated.

[87]

[88] Comparative Example 4

[89] Whole soybean milk was prepared in the same manner as in Example 1, except that the coarsely ground soybean was not finely ground.

[90]

[91] Test Example 1: Analysis of mean particle diameter and particle diameter dis- tribution of whole soybean milk

[92] The mean particle diameter and particle diameter distribution of each of the whole soybean milks prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were analyzed. The analysis of particle diameter was performed using Submicron Particle Size Analyzer (LS230 & N4PLUS, Coulter Corporation, USA).

[93]

[94] The analysis results showed that the whole soybean milks prepared according to the inventive methods (Examples 1 to 3) were emulsified whole soybean milks having a mean ultrafine particle diameter of less than 45 D. More specifically, the whole soybean milk according to the present invention was shown to be 45 D in mean particle diameter and less than 200 D in the maximum particle diameter 200 D. Accordingly, it can be seen that the whole soybean milk had a very narrow particle diameter distribution (see FIG.

2).

[95] On the other hand, the whole soybean milks prepared in Comparative Examples 1 to 4 were shown to be 67-110 D in mean particle diameter. Also, these milks had a very wide particle diameter distribution. Particularly in the case of Comparative Examples 1 and 3 where the coarsely ground soybean was not heated (i.e., the cell wall was not softened), whole soybean milk having a mean particle diameter of about 100 D and thus a rough taste was prepared (see FIG. 3). Also in the case of Comparative Example 4 where the high-pressure homogenization step was carried out without conducting the ultrafine grinding step, the diameter of particles resulting from the coarse grinding step was very large, and thus taking a load at the high-pressure homogenizer, the working time was extended at least four times, and soybean milk having a very rough taste was prepared.

[96] [97] Test Example 2: Analysis of particle diameter and concentration of whole soybean milk after long-term standing

[98] 30 liters of each of the whole soybean milks prepared in Examples 1 to 3 and Comparative Examples 1 to 4 was left to stand in a 40-liter cylindrical bucket for 10-24 hours. Then, 10 liters of a sample was collected from each of the upper layer portion, intermediate portion and lower layer portion of the bucket and analyzed for particle diameter and concentration. The analysis of particle diameter was carried out in the same manner as in Test Example 1, and the analysis of concentration was carried out using Refrectometer according to a method known in the art.

[99] The results of analysis of particle diameter depending of various positions of the whole soybean milks stood for a long time showed that the whole soybean milks prepared according to the inventive method did not show a change in particle diameter, even when they were left to stand for a long time. Accordingly, it could be observed that the inventive whole soybean milk was very uniform (see FIG. 4). On the other hand, it could be found that the whole soybean milk according to Comparative Examples showed a change in particle diameter depending on positions, and thus was non-uniform.

[100] Meanwhile, in the analysis results for concentrations depending on positions of the whole soybean milks stood for a long time, the whole soybean milks prepared according to the present invention showed a constant concentration depending on positions, even when there were left to stand for a long time, whereas the whole soybean milks according to Comparative Examples 1 to 4 showed precipitation upon long-term standing, so that concentrations different depending on positions were shown (see Table 1).

[101] [102] Table 1 Concentration of whole soybean milk (brix)

[103] [104] Test Example 3: Sensory evaluation for each of whole soybean milks [105] Preference for each of the whole soybean milks prepared in Examples 1 to 3 and Comparative Examples 1 to 4 was evaluated by 10 trained sensory panelists using a five-point hedonic scale. The evaluation of preferences for taste, flavor and appearance was performed on a five-point hedonic scale.

[106] The evaluation results showed that the whole soybean milks prepared according to the present invention (Examples 1 to 3) were the most excellent in taste, flavor and appearance. Particularly the case of repeating ultrafine grinding step (Example 3) had the most excellent preference for appearance. However, in the cases where the coarsely ground soybean was not heated (cell wall was not softened; Comparative Examples 1 and 3), the case where the coarsely ground soybean was heated at a higher temperature to cause the denaturation of soybean protein (Comparative Example 2), and the case where the ultrafine grinding step was not carried out (Comparative Example 4), it was shown that the whole soybean milks were relatively inferior to those of the present invention with respect to taste and flavor, and also much heterogeneous (see Table 2).

[107] [108] Table 2 Results of sensory evaluation for whole soybean milk

[109] [HO] Example 4: Preparation of soybean curd using inventive whole soybean milk I (two-step heating and coagulation)

[111] A coagulant and a protein-binding enzyme were mixed with each of the whole soybean milks prepared in Examples 1 to 3, and each of packed soybean curds (uncurlded tofu, packed soft tofu and filled Kinugoshi) and kinugoshi was prepared from the mixture using the two-step heating and coagulation method according to the present invention.

[112] In the case of uncurdled tofu and packed soft tofu, 0.2 wt% transglutaminase, 0.15 wt% magnesium chloride (100% pure), 0.1 wt% salt and 0.2 wt% GDL (gluconodeltalactone) were added to whole soybean milk cooled to 5 ⁰C, and in the case of filled Kinugoshi and Kinugoshi, 0.3 wt% transglutaminase, 0.33 wt% magnesium chloride (100% pure), 0.1 wt% salt and 0.1 wt% GDL (gluconodeltalactone) were added to whole soybean milk cooled to 5 ⁰C.

[113] Then, the mixture was packed in each of a packing container (tube pack for uncurdled tofu or container for packed soft tofu) and a mold and coagulated by heating at 55 ⁰C for 60 minutes and then heating at 85 ⁰C for 90 minutes. In the case of uncurdled tofu, packed soft tofu and filled Kinugoshi, the soybean curds subjected to the heating and coagulation step were prepared into final products by sterilization and cooling, and in the case of kinugoshi, the soybean curd was prepared into final products by cutting, packaging, sterilization and cooling steps.

[114]

[115] Example 5: Preparation of soybean curd using inventive whole soybean milk

II (two-step heating and coagulation)

[116] Uncurdled tofu, packed soft tofu, filled Kinugoshi and Kinugoshi were prepared in the same manner as in Example 4, except that the heating and coagulation step was performed by heating at 55 ⁰C for 60 minutes and then heating at 85 ⁰C for 60 minutes.

[117]

[118] Example 6: Preparation of soybean curd using inventive whole soybean milk

III (three-step heating and coagulation)

[119] Uncurdled tofu, packed soft tofu, filled Kinugoshi and Kinugoshi were prepared in the same manner as in Example 4, except that a mixture of cooled soybean milk, a coagulant and a protein-binding enzyme was packed in each of a tube pack for uncurdled tofu, a container for packed soft tofu and a mold and then coagulated by heating at 20 ⁰C for 120 minutes, at 55 ⁰C for 60 minutes and then at 85 ⁰C for 80 minutes. Then, in the cases of uncurdled tofu, packed soft tofu and filled Kinugoshi, the soybean curd subjected to the heating and coagulation step was prepared into final products by sterilization and cooling, and in the case of Kinugoshi, the soybean curd was prepared into final products by cutting, packaging, sterilization and cooling steps.

[120] [121] Example 7: Preparation of soybean curd using inventive whole soybean milk

IV (three-step heating and coagulation)

[122] Uncurdled tofu, packed soft tofu, filled Kinugoshi and Kinugoshi were prepared in the same manner as in Example 6, except that the heating and coagulation step was carried out at 20 ⁰C for 60 minutes, at 55 ⁰C for 40 minutes and at 85 ⁰C for 50 minutes.

[123]

[124] Example 8: Preparation of soybean curd using inventive whole soybean milk

V (four-step heating and coagulation)

[125] Uncurdled tofu, packed soft tofu, filled Kinugoshi and Kinugoshi were prepared in the same manner as in Example 4, except that a mixture of cooled soybean milk, a coagulant and a protein-binding enzyme was packed in each of a tube pack for uncurdled tofu, a container for packed soft tofu and a mold and then coagulated by heating at 20 ⁰C for 120 minutes, at 50 ⁰C for 60 minutes, at 65 ⁰C for 40 minutes and at 85 ⁰C for 90 minutes. Then, in the cases of uncurdled tofu, packed soft tofu and filled Kinugoshi, the soybean curd subjected to the heating and coagulation step was prepared into final products by sterilization and cooling, and in the case of kinugoshi, the soybean curd was prepared into final products by cutting, packaging, sterilization and cooling steps.

[126]

[127] Example 9: Preparation of soybean curd using inventive whole soybean milk

VI (four-step heating and coagulation)

[128] Uncurdled tofu, packed soft tofu, filled Kinugoshi and Kinugoshi were prepared in the same manner as in Example 8, except that the heating and coagulation step was carried out by heating at 20 ⁰C for 60 minutes, at 50 ⁰C for 40 minutes, at 65 ⁰C for 30 minutes and at 85 ⁰C for 50 minutes.

[129]

[130] Example 10: Preparation of soybean curd using inventive whole soybean milk

VII (five-step heating and coagulation)

[131] Uncurdled tofu, packed soft tofu, filled Kinugoshi and Kinugoshi were prepared in the same manner as in Example 4, except that a mixture of cooled soybean milk, a coagulant and a protein-binding enzyme was packed in each of a tube pack for uncurdled tofu, a container for packed soft tofu and a mold and then coagulated by heating at 20 ⁰C for 120 minutes, at 35 ⁰C for 40 minutes, at 55 ⁰C for 60 minutes, at 70 ⁰C for 40 minutes and at 85 ⁰C for 90 minutes. Then, in the cases of uncurdled tofu, packed soft tofu and filled Kinugoshi, the soybean curd subjected to the heating and coagulation step was prepared into final products by sterilization and cooling, and in the case of kinugoshi, the soybean curd was prepared into final products by cutting, packaging, sterilization and cooling steps. [132] [133] Example 11: Preparation of soybean curd using inventive whole soybean milk

VIII (five-step heating and coagulation)

[134] Uncurdled tofu, packed soft tofu, filled Kinugoshi and Kinugoshi were prepared in the same manner as in Example 10, except that the heating and coagulation step was carried out by heating at 20 ⁰C for 60 minutes, at 35 ⁰C for 30 minutes, at 55 ⁰C for 40 minutes, at 70 ⁰C for 30 minutes and at 85 ⁰C for 50 minutes.

[135]

[136] Comparative Example 5: Preparation of soybean curd using soybean milk prepared in each of Comparative Examples

[137] Various kinds of soybean curds were prepared in the same manner as described in

Example 4 using the whole soybean milks prepared in Comparative Examples 1 to 4. As a result, it was found that the soybean curd prepared in each of Comparative Examples was easily broken, had no firmness, felt like soybean pulps, felt rough and spread in the mouth like sand chewing.

[138]

[139] Test Example 4: Changes in the temperatures of the surface and inside of soybean curd in preparation of soybean curd according to the present invention

[140] When preparing soybean curd according to the method of Example 6, the temperatures of the surface and internal of kinugoshi were measured with a thermometer (Tracksence ValPro Logger (sensor), Ellab) at a constant time interval. As a control group, soybean curd prepared according to a general heating and coagulation method was used. That is, a mixture of the whole soybean milk of Example 6, a coagulant and a protein-binding enzyme was coagulated by heating at 85 ⁰C for 40 minutes.

[141] From the test results, it could be observed that, in the case of soybean curd prepared according to the general heating and coagulation method, the difference in temperature between the surface and internal of the soybean curd increased with the passage of time (see FIG. 6). Also, in the case of the prior heating and coagulation method, coagulated particle crystals of protein in the soybean curd were large, because the mixture containing the soybean milk was allowed to react at high temperature so that crystallization for the coagulation of the protein rapidly occurred. Accordingly, it could be observed that the soybean curd prepared according to the prior heating and coagulation method was not coagulated into uniform soybean curd consisting of one mass and was incomplete, leading to a significant reduction in quality.

[142] On the other hand, it could be observed that, in the case of the soybean curd prepared according to the inventive stepwise heating and coagulation method, the temperatures of the surface and internal of the soybean curd were uniformly increased and maintained so that the difference in temperature between the surface and inside of the soybean curd was minimized (see FIG. 7). Thus, a complete coagulation reaction occurred so that the soybean curd had excellent quality.

[143] [144] Test Example 5: Sensory evaluation and cooking suitability evaluation of soybean curd prepared according to inventive method

[145] Among the soybean curds prepared in Examples 4 to 11, kinugoshi was subjected to sensory evaluation. In the sensory evaluation, the preference for the soybean curd was evaluated by 10 trained panelists using a five -point hedonic scale. As a control group, commercially available soybean curd for frying or stewing, prepared according to the general heating and coagulation method, was used. Also, the sensory panelists were asked to cook each of the soybean curds into a pot stew or fried food and to taste the cooked food and to indicate the cooking suitability of the soybean curd on a five- point hedonic scale.

[146] The test results showed that the soybean curds prepared according to the inventive method had very high scores with respect to taste, texture, appearance and general preference, compared to the general soybean curd. Particularly, the soybean curd in a more stepwise manner, i.e., the soybean curd prepared according to the five-step heating and coagulation method of Example 10 or 11, had more excellent sensory characteristics than those of the soybean curd prepared according to the two-step heating and coagulation method of Example 4 or 5. Also, the soybean curd according to the present invention showed a very high suitability for cooking in both a pot stew or fried food, compared to the general soybean curd, and was not easily broken upon cooking and was convenient to handle (see Table 3).

[147] This is believed to be because, as the number of the sub-steps of the heating and coagulation step increased, the temperature of the soybean curd was slowly elevated, so that the difference in temperature between the surface and inside of the soybean curd was decreased and the temperature was maintained uniform, and thus a uniform coagulation reaction occurred, whereby the sensory characteristics and cooking suitability of the soybean curd were improved.

[148] [149] Table 3

Evaluation results for sensory characteristics and cooking suitability of soybean curd according to the present invention

[150] [151] Test Example 6: Measurement of hardness of soybean curd prepared according to inventive method

[152] To examine the texture of kinugoshi among the soybean curds prepared in Examples 4 to 11, the hardness of each of the soybean curds was measured. The hardness measurement was performed using Texture Analyzer (TA-XT-plus, Micro Stable System) with an SMSP/25Φ as a probe in the TPA mode. As a sample, 420 g of one cake of kinugoshi was measured for hardness at five points on the surface and inside thereof along the diagonal direction, i.e., at 10 points per one cake of the soybean curd. At least five cakes of the soybean curd were measured for hardness, and the measured values were expressed as mean and standard deviation. As a control group, commercially available soybean curd for frying or stewing, prepared according to the general heating and coagulation method, was used.

[153] In the test results, the soybean curd for stewing or frying, prepared according to the general method, showed a great difference in hardness between the surface and inside thereof and had a severe variation in hardness, and thus a very unstable quality. On the other hand, the soybean curds of Examples 4 to 11, prepared according to the inventive method, all showed significantly uniform hardness values and a small difference in hardness between the surface and inside thereof. Particularly, the soybean curds, heated and coagulated in a more stepwise manner so as to minimize the difference in temperature between the surface and inside thereof, showed the highest hardness value (see Table 4). From the above test results, it could be found that the soybean curds prepared according to the inventive method were more hard and firm than the soybean curd prepared according to the general method.

[154] [155] Table 4 Hardness of soybean curd prepared according to inventive method

[156] [157] Test Example 7: Measurement of koshi value of soybean curd prepared according to inventive method

[158] Among the soybean curds prepared in Examples 4 to 11, kinugoshi was measured for koshi value. The koshi value is a value representing the hard and soft taste of soybean curd. The measurement of the koshi value was performed using Texture Analyzer (TA-XT-plus, Micro Stable System) with a BLADE SET (HDP/BS) as a probe. The soybean curd was cut with HDP/Bs to determine surface cutting force (N), and the case showing a large slope of a decreased value after the surface cutting could be regarded as "koshi".

[159] In the test results, the soybean curd for stewing or frying, prepared according to the general method, showed a low koshi value. This means that the soybean curd is not smoothly broken and has a drooping taste. On the other hand, the soybean curd prepared according to the inventive method showed a high koshi value. This means that the soybean curd has a very smooth taste (see Table 5).

[160] [161] Table 5 Koshi value of soybean curd prepared according to inventive method

[162] [163] This application claims priorities to Korean Patent Application Nos. 2005-30230, 2005-31683 and 2005-36333, which are incorporated herein by reference. Industrial Applicability

[164] As described above, the inventive method can effectively prepare high-quality of whole soybean milk using whole soybean without separating the soybean pulps, which contains the nutritional components of soybean pulps intact and has a very narrow and uniform particle diameter distribution so that the precipitation of soybean particles does not occur. Also, according to the method for preparing soybean curd using the whole soybean milk, soybean curd having improved sensory characteristics and cooking suitability can be prepared by heating the whole soybean milk in a stepwise manner so as to uniformly coagulate the soybean milk.

Claims

[I] A method for preparing whole soybean milk, comprising the steps of:

(a) peeling the skin of soybean, immersing the skin-peeled soybean in water and coarse grinding the soybean;

(b) heating and cooling the coarsely ground soybean of the step (a);

(c) finely grinding the coarsely ground soybean of the step (b); and

(d) homogenizing the finely ground soybean of the step (c) under high pressure.

[2] The method of Claim 1, wherein the skin peeling of the soybean in the step (a) is performed by removing the skin portion of soybean in an amount of about 5-20% based on the whole soybean.

[3] The method of Claim 1, wherein the heating of the coarsely ground soybean in the step (b) is carried out at 95-100 ⁰C for 5-20 minutes.

[4] The method of Claim 1, wherein the cooling in the step (b) is carried out at 0-20

⁰C.

[5] The method of Claim 1, further comprising the step of adding an antifoaming agent in an amount of 0.002-0.2 wt% during the coarse grinding of the step (a) and the fine grinding of the step (c).

[6] The method of Claim 1, wherein the fine grinding in the step (c) is repeated 2-3 times.

[7] The method of Claim 1, wherein the fine grinding in the step (c) is carried out such that the particle diameter of the soybean milk reaches 0.04-200 D.

[8] The method of Claim 1, wherein the whole soybean milk homogenized in the step (d) has a mean particle diameter of less than 44 D.

[9] A method for preparing soybean curd, comprising the steps of:

(a) cooling whole soybean milk prepared according to the method of Claim 1, adding a coagulant and a protein-binding enzyme to the cooled whole soybean milk and heating the mixture at 30-70 ⁰C for 20-180 minutes; and

(b) heating the mixture of the step (a) at 75-100 ⁰C for 30-90 minutes.

[10] The method of Claim 9, wherein the heating in the step (a) is carried out at 45-65

⁰C for 30-70 minutes.

[I I] The method of Claim 9, wherein the step (a) consists of the sub-steps of:

(i) adding the coagulant and the protein-binding enzyme to the cooled whole soybean milk and heating the mixture at 45-55 ⁰C for 20-60 minutes; and (ii) heating the mixture of the step (i) at 60-70 ⁰C for 30-60 minutes. [12] The method of Claim 9, wherein the step (a) consists of the sub-steps of:

(i) adding the coagulant and the protein-binding enzyme to the cooled whole soybean milk and heating the mixture at 30-45 ⁰C for 20-60 minutes; (ii) heating the mixture of the step (i) at 50-60 ⁰C for 30-60 minutes; and

(iii) heating the mixture of the step (ii) at 65-70 ⁰C for 30-60 minutes. [13] The method of any one of Claims 9 to 12, further comprising the step of adding the coagulant and the protein-binding enzyme to the cooled whole soybean milk and heating the mixture at 10-20⁰C for 60-120 minutes before carrying out the step (a). [14] The method of Claim 9, wherein the cooling of the whole soybean milk is carried out at 0-10 ⁰C. [15] The method of Claim 9, wherein the coagulant is selected from the group consisting of magnesium chloride, GDL (gluconodeltalactone) and calcium sulfate. [16] The method of Claim 9, wherein the protein-binding enzyme is transglutaminase.