JP3368733B2 - Method for producing modified soy protein - Google Patents

Description

Description [0001] The present invention relates to a method for producing a modified soybean protein. 2. Description of the Related Art Soy protein contains a large amount of amide-type amino acids such as glutamine and asparagine, and 18% of all amino acids in glycinin are these amide-type amino acids. From these characteristics, the deamidation of soy protein increases the negative charge of glutamic acid and aspartic acid, lowering the stability of the higher-order structure, resulting in solubility,
It has been predicted that important functional properties such as emulsifying properties and foaming properties as food materials will be altered, and research has been conducted. [0003] However, the dilute acid treatment used so far (Matsudomi, N., Sasaki, T., Kato, A. an
d Kobayashi, K. (1985) "Conformational changes and
functional properties of acid-modified soy protei
n. "Agric. Biol. Chem., Vol. 49, p1251-1256.) and protease treatment (Kato, A., Tanaka, A., Matsudomi,
N. and Kobayashi, K. (1987) "Deamidation of food pr
oteins by protease inalkaline pH .: J. Agric. Food
Chem., 35, 224-227.), It was difficult to accurately examine the effect of deamidation alone because the deamidation of the protein was accompanied by cleavage of the peptide. [0004] Patent publications relating to deamidation include the following. JP-A-59-210097 (Japanese Patent Publication No. 5-37635) The "production method of modified protein" is obtained by reacting an amino group of a protein with maleic anhydride and / or a maleic anhydride derivative. A method for producing a modified protein in which a transglutaminase is allowed to act on an acylated protein to deamid and then deacylate the acylated protein is disclosed. [0005] Japanese Patent Application Laid-Open No. 3-91445, entitled "Method for Producing Enzymatically Modified Protein", discloses that an aqueous slurry of protein is subjected to hydrolysis and deamidation to increase the solubility of the protein without causing bitter components in the protein. Methods for treating proteins that are effective in increasing the functionality of the proteins are disclosed. Japanese Patent Application Laid-Open No. 3-53850 discloses a method for producing a hydrolyzed plant protein, etc., which comprises adding a plant protein to an aqueous solution having at least one protease, hydrolyzing the protein, and decomposing an insoluble mass from the soluble protein. And adding an acid to the hydrolyzed soluble protein, heating the mixture and substantially deamidating the hydrolyzate. [0007] JP-A-63-36797, "Protein modification method" includes:
It is disclosed that a protein is deamidated using a protease in a deamidation pH region and a deamidation temperature region. However, a method for modifying soybean protein by deamidation as in the present invention is not known. SUMMARY OF THE INVENTION An object of the present invention is to modify functional properties (emulsifying properties, foaming properties, etc.) without relatively reducing the solubility of soybean proteins. Means for Solving the Problems The present inventors have studied deamidation of various proteins by heating. However, while egg white can be deamidated only by heating, soybean protein is insolubilized when deamidated only by heating. Therefore, as a result of intensive research, it was found that by storing dried soybean protein at normal temperature or high temperature in nitrogen gas, deamidation could be performed without relatively lowering the solubility, and the functional characteristics of soybean protein could be modified. Thus, the present invention has been completed. That is, the present invention relates to a method for producing a modified soybean protein, characterized by storing the dried soybean protein in a non-oxygen gas. The dried soybean protein used in the present invention comprises:
Dry soy protein is suitable. It is not preferable that the soybean protein is moist because the solubility of the soybean protein decreases during storage even in non-oxygen gas. Usually, it can be water (for example, not more than 15% by weight, preferably not more than 12% by weight, more preferably not more than 10% by weight) in which microorganisms hardly grow. As the non-oxygen gas, any known gas other than oxygen, in other words, any gas having no oxidizing action can be used. Nitrogen gas is easily available and practical. The relative humidity of the atmosphere during storage of non-oxygen gas of soybean protein is suitably about 75% or less, preferably 60% or less. If the relative humidity of the atmosphere during storage of the soybean protein is high, the solubility of the soybean protein tends to decrease, which is not preferable. The deamidation rate can be changed by the pH of the soybean protein.
H4.5) can be excluded, but the deamidation rate can be increased as the soybean protein is more alkaline. However, if the pH is too alkaline, lysinoalanine or the like may be formed. Therefore, the pH is practically about 5 to 11, preferably 7 to 10, and more preferably 8 to 10. In the present invention, the higher the temperature at which the dried soybean protein is stored, the faster the rate of deamidation can be increased.
It can be stored at room temperature for a long period of time, or it can be stored at a high temperature for a short period of time to deamid and then refrigerated. For example, if the dry soybean protein is 65% relative humidity and the storage temperature is 60 ° C., it is stored for 7 days and the deamidation rate is 8.2 at pH 5.5.
%, 12.2% at pH 8.0, and 14.3% at pH 10.0. According to the method of the present invention, deamidation can be performed without relatively lowering the solubility of soybean protein. For example, deamidation at a deamidation rate of 8 to 15% can be performed. By this deamidation, functional characteristics such as emulsifying property and foaming property of soybean protein can be modified. The higher the deamidation rate, the better the emulsifying and foaming properties. At the same time, emulsion stability and bubble stability are improved. For example, the emulsifiability is 1.2 to 1.
It can increase the emulsification stability by 2.5 times, the foaming power by 1.5 times, and the foam stability by more than 2 times. The embodiments of the present invention will be described below with reference to examples. Example 1 (Preparation of acid-precipitated soybean protein) 20-fold (weight ratio) water was added to cold-extracted defatted soybean (manufactured by Fuji Oil Co., Ltd.), stirred for 1 hour to form a slurry, centrifuged, and insoluble Fractions (so-called okara) are removed, and the obtained solution fraction (so-called soy milk)
PH was adjusted to 4.5 by adding hydrochloric acid to the mixture, and the resulting precipitate fraction (so-called curd) was collected by centrifugation, and about 19 times the amount of water (weight ratio to low-temperature extracted defatted soybean) was added to form a dispersion. , Adjusted to pH 7 with sodium hydroxide,
Lyophilized to acid precipitated protein (APP), which was used as soy protein. (Deamidation of soybean protein) Acid precipitation Soybean protein was dissolved in water, adjusted to pH 5.5, 8.0, 10.0 and freeze-dried. These powders (about 5% by weight of water) were heated at 60 ° C. in a desiccator controlled to various relative humidity in nitrogen gas.
Deamidation was performed by storing for 1-2 weeks. (Measurement of Deamidation Rate) A sample deamidated under the above conditions for 7 days is dialyzed against distilled water for 48 hours to remove free amide groups. After dialysis, each sample was freeze-dried, and the obtained dry powder sample (50 mg) was dissolved in 1 ml of 2N hydrochloric acid, hydrolyzed in a sealed tube at 110 ° C for 2 hours, and the remaining amide was captured in hydrochloric acid as ammonia gas. And 10% of the equivalent
A TCA solution was added, protein was removed, and insoluble matter was removed by centrifugation to prepare a clear supernatant. Ammonia in the hydrochloric acid solution thus obtained was quantified using an ammonia ion electrode.
This method can measure ammonia gas generated by making the pH alkaline before quantification. (Measurement of Solubility) A certain amount of the dry storage powder obtained under each condition was taken, and the solubility was examined by measuring the absorption at 280 nm of a sample dissolved in water. (Measurement of emulsifiability) The emulsifiability of the deamidated soybean protein was measured using the method of Pearce and Kinsella5). 1 /
The sample is dissolved in a 15 M sodium phosphate buffer (pH 7.4) to a protein concentration of 0.1%. 1 ml of corn oil is added to 3 ml of this sample solution, and homogenized at 12,000 rpm for 1 minute using a polytron. Immediately after homogenizing 0.1 ml of the formed emulsion, 1, 2, 3, 5,
Ten minutes later, the sample was taken from the bottom of the test tube, suspended in 5 ml of a 0.1% SDS solution, and the turbidity was measured at an absorbance of 500 nm. The value immediately after homogenization was expressed as relative emulsification activity, and its half-life was expressed as emulsion stability. (Measurement of foaming property) 0.1 M sodium phosphate buffer
(PH 7.4), the sample was dissolved to a protein concentration of 0.2%, and the conductivity method of Kato et al. (Kato, A., Takahashi, A.,
Matsudomi, N. and Kobayashi, K. (1983) Determinat
ion of foaming properties of proteins by conductiv
Foamability and bubble stability were measured by ity measurements., J. Food Sci., 48, 62-65.). As a result, the soybean protein was extremely insoluble by drying and heating, and was mostly insolubilized after several days under drying and heating at 60 ° C. This is a characteristic peculiar to soybean protein and is due to the formation of aggregates by the SH and SS exchange reactions. In order to prevent this insolubilization, oxidation was suppressed in a desiccator filled with nitrogen gas, and drying and heating were performed under the condition of controlling humidity. FIG. 1 shows the change in solubility of soybean protein during storage at 60% in a nitrogen gas and air at a relative humidity of 65%. When stored for 7 days under nitrogen gas filling, it can be stored with almost no change in solubility, but it dropped to 50% in air. Since storage at a relative humidity of 79% further promotes insolubilization, the properties of samples stored at 65% humidity, 60 ° C. for 7 days were examined below. Table 1 shows a relative humidity of 65% in nitrogen gas, 60 ° C., 7
The deamidation rate of the soybean protein stored for a day was shown. [Table 1] The pH of the dry powder indicates the pH of the solution before drying, and the same value is obtained for the solution after storage. From this result, it can be seen that the deamidation rate increases as the pH of the dry powder becomes more alkaline. Thus, it is very interesting that deamidation occurs as much as 8-14% during storage under dry conditions. As a control, the deamidation rate by hydrolysis at 70 ° C. for 3 hours in dilute acid (0.1N hydrochloric acid solution), which has been frequently used, is 8.5%, which indicates that the deamidation occurring under drying is also observed. Is large. Heating in a dilute acid may also hydrolyze the peptide, and there is no such side reaction under drying, which is a better method. FIG. 2 shows the emulsifiability of the deamidated soybean protein thus obtained. As is clear from the figure,
The emulsifiability of the soybean protein deamidated by drying and heating was remarkably modified, and especially those stored at pH 10 showed excellent emulsifiability. Table 2 shows values of the emulsifying activity and the emulsifying stability by deamidation. [Table 2] The emulsifying activity of the sample stored for 7 days at any pH increases 1.2 to 1.3 times before storage, and the emulsification stability is 2.5
It was modified to ~ 3.0 times. Thus, it was shown that the deamidation under drying significantly increased the emulsifiability of soybean protein. This is because the deamidation increases the negative charge, makes the higher-order structure of the protein more flexible, and makes it easier to expose some of the hydrophobic groups inside the molecule at the oil-liquid interface of the emulsion to the surface, forming an amphipathic structure It is thought that it becomes easy to do. Another important foaming modification data is shown in FIG. The foaming property was modified by deamidation by drying and heating, and the foaming power increased 1.5 times and the foam stability increased more than 2 times. However, unlike the emulsifying property, those dried and stored at pH 5.5 with a deamidation rate of 8.2% show the best foaming properties, and those dried and stored at pH 10 with a high deamidation rate are foamed. Gender rise was small. This is because the intermolecular interaction of protein molecules is an important factor for bubble film formation, but if deamidation proceeds too much, the negative charge will increase too much and the intermolecular interaction will decrease. It is thought that it is. The soybean protein can be deamidated by storing it in a non-oxygen gas such as nitrogen gas without deteriorating the solubility of the soybean protein. It was able to modify various food functional characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a drawing showing changes in the solubility of soybean protein during storage at 60% in a nitrogen gas and air at a relative humidity of 65%. FIG. 2 is a drawing showing the emulsifiability of the obtained deamidated soybean protein. FIG. 3 is a drawing showing the foaming properties of the obtained deamidated soybean protein.

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Claims (1)

(57) [Claim 1] A method for producing a modified soy protein, comprising storing dried soy protein in a non-oxygen gas.