JP7697806B2 - Method for enriching gamma-aminobutyric acid - Google Patents

Description

The present invention relates to a method for enriching wheat flour with γ-aminobutyric acid.

Gamma amino butyric acid (GABA) is an amino acid that acts as a neurotransmitter, and is biosynthesized from glutamic acid by glutamic acid decarboxylase (GABA synthetase) in vivo. GABA has been reported to have physiological effects such as lowering blood pressure and stabilizing the mind (anti-stress effect) (Non-Patent Document 1). Currently, many GABA-related foods are commercially available, but the raw materials are very expensive.
One example of a conventional method for producing GABA is a method in which the germ is separated from rice with germ and then soaked in water at about 20 to 40° C. for 2 to 12 hours (Patent Document 1). Another example of a production method is a method in which polished rice is steamed, red koji spores are attached to the surface of the rice, and the rice is cultured at about 30° C. for 7 days (Patent Document 2).
Since the purification of GABA is time-consuming and expensive, there is a problem in that products enriched with GABA are expensive.
Conventionally, methods have been proposed for efficiently using the GABA that is naturally contained in food, or for efficiently enriching food with GABA by producing GABA during the food manufacturing process.
For example, Patent Document 3 proposes a method of adding glutamic acid and the like to whole grain powder containing the germ and husk, then adding water and kneading to prepare dough, thereby producing 10 mg or more of γ-aminobutyric acid per 100 g of dough. However, this method produces a GABA-enriched substance as dough, which cannot be used for tempura flour or fried chicken, and its secondary processing applications are limited. In addition, the germ and husk contain a large amount of ash, which can cause a bitter taste.
Patent Document 4 proposes a method for producing a product with high nutritional value and GABA enrichment by separating wheat with a high magnesium content and using that wheat flour to produce a secondary processed product. Since there is a correlation between the amount of magnesium and ash in wheat, the ash content tends to be high when the magnesium content is high, and the bitterness also increases.

JP 2004-147560 A JP 2006-117551 A JP 2004-298138 A JP 2005-287496 A

Yasuhiro Sasaki and Motonobu Kono: A literature review on the efficacy and effective intake of GABA, Journal of the Society of Tasty Technology Research No. 15: 32-37, 2010

An object of the present invention is to provide a method for efficiently enriching wheat flour having a relatively low ash content with GABA.
Another object of the present invention is to provide wheat flour having a relatively low ash content and a high GABA content per gram of ash.

The inventors have found that by mixing two or more types of wheat flour with different ash contents to produce wheat flour with an adjusted ash content of a fixed ash content, and then adding water to the wheat flour and stirring it, the increase rate of GABA per ash content is higher than the sum of the increase rates of GABA in each of the wheat flours before mixing, and that the increase rate of GABA per ash content is particularly high in wheat flour with a relatively low ash content, thereby completing the present invention.
The present invention includes the following inventions.
[1] A method for efficiently producing wheat flour enriched with GABA from low-ash wheat flour having an ash content of X% by mass (X≦0.65), comprising the steps of: adding high-ash wheat flour having an ash content of Y% by mass (Y≧0.65 and Y≧X+0.20) to the low-ash wheat flour to produce ash-adjusted wheat flour having an ash content of Z% by mass (Z≦1.20); adding water to the wheat flour and stirring to produce GABA.
[2] The method according to [1], wherein the amount of low-ash wheat flour is in the range of 20 to 90% by mass relative to the mass of the ash-adjusted wheat flour.
[3] The method according to [1] or [2] above, which produces wheat flour containing 18 mg or more of GABA per gram of ash.
[4] The method according to any one of [1] to [3] above, wherein the increase in GABA per gram of ash (the amount of GABA in the wheat flour after the GABA production reaction minus the amount of GABA in the raw wheat flour) is 12 mg or more.
[5] The method according to any one of [1] to [4] above, wherein the GABA content of the low-ash wheat flour having an ash content of X% by mass (X≦0.65) is 4.0 mg/100 g or less, and the GABA content of the high-ash wheat flour having an ash content of Y% by mass (Y≧0.65 and Y≧X+0.20) is 4.0 mg/100 g or more.
[6] The method according to any one of [1] to [5] above, wherein the step of adding water to the ash-adjusted wheat flour and stirring is a step of adding 33 parts by mass or less of water per 100 parts by mass of the ash-adjusted wheat flour and stirring.
[7] GABA-enriched wheat flour having an ash content of Z1% by mass (0.40≦Z1≦1.00) and containing 20 mg or more of GABA per gram of ash.

The method of the present invention, which uses two or more types of low-ash and high-ash wheat flour in combination, can produce wheat flour with a higher GABA content (per ash content) than a method using wheat flour (fraction) with the same ash content alone. This is believed to be due to the increased concentration of GABA synthase. Since the product of the present invention has a low ash content relative to the GABA content, it is possible to provide a wheat flour product that is enriched in GABA while suppressing bitterness.
Furthermore, the method of the present invention, which uses a combination of two or more types of low-ash and high-ash wheat flour, can increase the amount of GABA increase per ash amount (the amount of GABA after reaction minus the amount of GABA before reaction) compared to when the low-ash and high-ash wheat flours (fractions) are reacted alone before being combined, and can efficiently produce wheat flour enriched with GABA.
Furthermore, the present invention can provide wheat flour with a high GABA content, rather than a dough-like product, and therefore can be applied to various products enriched with GABA.

A first aspect of the present invention is a method comprising the steps of:
A method for efficiently producing wheat flour enriched with GABA from low-ash wheat flour having an ash content of X% by mass (X≦0.65), comprising the steps of: adding high-ash wheat flour having an ash content of Y% by mass (Y≧0.65 and Y≧X+0.20) to the low-ash wheat flour to produce ash-adjusted wheat flour having an ash content of Z% by mass (0.4≦Z≦1.2); adding water to the wheat flour and stirring to produce GABA.
Hereinafter, this will also be referred to as the "GABA enrichment method."

By combining two or more types of low-ash and high-ash wheat flour, wheat flour with a higher GABA content and GABA synthesis enzyme concentration is produced compared to wheat flour with the same ash content. Furthermore, by mixing with water, drying, and producing wheat flour again, wheat flour with a higher GABA content can be produced. As the product of the present invention has a low ash content relative to its GABA content, it is a wheat flour that is enriched in GABA while suppressing bitterness.

The wheat flour used in the GABA enrichment method of the present invention is not particularly limited and may be any of strong flour, medium flour, weak flour, whole wheat flour, durum wheat flour, etc.
In the present invention, the "low-ash wheat flour having an ash content of X% by mass (X≦0.65)" may be any wheat flour having an ash content of 0.65% by mass or less as measured by the ash content measurement method described below. For example, 40 to 50 types of flour obtained by the step-type milling method have an ash content of 0.30 to 4.00% by mass, and one type may be selected from the flour as a fraction having an ash content of 0.65% by mass or less, or two or more types may be mixed to prepare wheat flour with any ash content. In addition, wheat flour having an ash content of 0.30 to 2.00% by mass may be classified by particle size to obtain a fraction having an ash content of 0.65% by mass or less.
X is preferably 0.60 or less, more preferably 0.50 or less, and even more preferably 0.40 or less. The lower limit of X is preferably 0.20 or more, and even more preferably 0.30 or more.
The "low-ash wheat flour having an ash content of X% by mass (X≦0.65)" used as the raw material in the GABA enrichment method of the present invention is more preferably a fraction having an ash content of 0.65% by mass or less obtained by the above-mentioned known method, and preferably has a GABA content of 4.0 mg/100 g or less, more preferably 3.5 mg/100 g or less, even more preferably 2.0 mg/100 g or less, and even more preferably 1.0 mg/100 g or less.

In the present invention, "high-ash wheat flour having an ash content of Y% by mass (Y≧0.65 and Y≧X+0.20)" may be any wheat flour having an ash content Y of 0.65% by mass or more as measured by the ash content measurement method described below, and satisfying Y≧X+0.20 with respect to the ash content X of low-ash wheat flour. For example, it may be a fraction obtained from the flour with an ash content of 0.65% by mass or more. It may also be a fraction obtained by classifying ordinary wheat flour with an ash content of 0.30 to 2.00% by mass into particle sizes and then classifying the fraction with an ash content of 0.65% by mass or more.
Y is preferably 0.80 or more, more preferably 0.90 or more, even more preferably 1.00 or more, and even more preferably 1.10 or more (for example, 1.20 or more). The upper limit of Y is preferably 2.80 or less, more preferably 2.00 or less, and even more preferably 1.50 or less.
The "high-ash wheat flour having an ash content of Y mass % (Y≧0.65 and Y≧X+0.20)" used as the raw material in the GABA enrichment method of the present invention is more preferably a fraction having an ash content of 0.65 mass % or more obtained by the above-mentioned known method, and preferably has a GABA content of 4.0 mg/100 g or more, more preferably 5.0 mg/100 g or more, even more preferably 9.0 mg/100 g or more, and even more preferably 15 mg/100 g or less.

In the present invention, the ash content X% by mass and Y% by mass of "low ash wheat flour" and "high ash wheat flour" are preferably Y≧X+0.30, more preferably Y≧X+0.40, even more preferably Y≧X+0.50, and even more preferably Y≧X+0.60, from the viewpoint of effectiveness.

The GABA enrichment method of the present invention comprises adding high-ash wheat flour to the low-ash wheat flour to produce ash-adjusted wheat flour having an ash content of Z mass % (Z≦1.20), adding water to the wheat flour and stirring to produce GABA.
By adjusting the ash content Z of the ash-adjusted wheat flour to 1.20% by mass or less, the low-ash wheat flour and the high-ash wheat flour are mixed in an appropriate range, and the amount of GABA produced per gram of ash can be efficiently increased. Z is preferably 0.40≦Z≦1.00, more preferably 0.50≦Z≦0.90, even more preferably 0.50≦Z≦0.80, and even more preferably 0.50≦Z≦0.65.

The mixing ratio (mass ratio) of low ash wheat flour to high ash wheat flour is preferably high ash wheat flour: low ash wheat flour = 5:95 to 95:5, more preferably 20:80 to 90:10, and even more preferably 30:70 to 80:20.
In the GABA enrichment method of the present invention, the amount of low-ash wheat flour is preferably in the range of 20 to 90% by mass, more preferably in the range of 30 to 80% by mass, and may be in the range of 40 to 80% by mass, or may be in the range of 50 to 80% by mass, based on the mass of the ash-adjusted wheat flour.

By the GABA enrichment method of the present invention, it is possible to produce wheat flour containing, for example, 18 mg or more of GABA per 1 g of ash. In the experiments of the present inventors, when GABA was produced using only low-ash wheat flour with an ash content of 0.65 mass% or less, the maximum GABA content was about 17 mg per 1 g of ash.
In the GABA enrichment method of the present invention, the amount of GABA per gram of ash in the produced wheat flour is preferably 19 mg or more, more preferably 20 mg or more, even more preferably 23 mg or more, and even more preferably 25 mg or more.

By the GABA enrichment method of the present invention, the increase in GABA per gram of ash (the amount of GABA in the wheat flour after the GABA production reaction minus the amount of GABA in the raw wheat flour) is preferably 12 mg or more, more preferably 13 mg or more, even more preferably 15 mg or more, and even more preferably 16 mg or more.
In the experiments conducted by the present inventors, when GABA was produced using the low ash wheat flour or high ash wheat flour of the present invention alone, the maximum increase in GABA was 11.4 mg per 1 g of ash.

In the GABA enrichment method of the present invention, GABA is produced by adding water to ash-adjusted wheat flour and stirring. GABA synthase is activated by water to produce GABA. The amount of water is not particularly limited, but it is preferable to add 33 parts by mass or less of water to 100 parts by mass of ash-adjusted wheat flour and stir the mixture. It is believed that the more water there is to 100 parts by mass of ash-adjusted wheat flour, the greater the amount of GABA produced, but if the amount of water exceeds 33 parts by mass, it becomes doughy and cannot maintain a powdery state that can be called wheat flour, which is not preferable. More preferably, 5 parts by mass to 25 parts by mass of water is added.

When adding water, it is preferable to mix so that the moisture is uniform. The mixing method can be selected arbitrarily as long as the moisture is distributed throughout the mixture. The temperature during mixing is not critical as long as the enzyme is not inactivated at the temperature, and may be 10°C to 65°C, preferably 20°C to 60°C, but is more preferably 35°C to 45°C, which is the optimal temperature for the enzyme.
After adding water, it is preferable to keep the mixture at a constant temperature (10° C. or higher and 65° C. or lower, preferably 20° C. or higher and 60° C. or lower, and more preferably 35° C. or higher and 45° C. or lower) for about 5 to 300 minutes (preferably about 30 to 240 minutes).

It is preferable to dry the flour after keeping it warm, or to dry it while keeping it warm at a constant temperature. Drying is preferable because it produces flour in powder form rather than dough form. It is believed that leaving it for a given period of time at the optimum temperature for glutamic acid decarboxylase will increase the amount of GABA produced.

In this specification, the amount of "ash" in wheat flour may be measured by any conventionally known method, but for example, a weighed sample can be incinerated in a crucible using a combustion improver or the like, cooled to room temperature in a desiccator, and then weighed to measure the amount of ash per unit mass of wheat flour.

In this specification, the amount of "GABA" in wheat flour may be measured by any conventional method known in the art. For example, GABA can be extracted from wheat flour using a solvent such as an aqueous ethanol solution, the extract is dried, and then the volume is adjusted with distilled water, and the resultant can be analyzed, for example, by HPLC using a calibration curve quantification method using amino acid standards.

A second aspect of the present invention is GABA-enriched wheat flour having an ash content of Z1% by weight (0.40≦Z1≦1.00) and containing at least 20 mg of GABA per gram of ash.
In the second embodiment, Z1 is more preferably 0.50≦Z1≦0.90, even more preferably 0.50≦Z1≦0.80, and even more preferably 0.50≦Z1≦0.65.
The amount of GABA per gram of ash is more preferably 22 mg or more, even more preferably 23 mg or more, and even more preferably 25 mg or more.
Such GABA-enriched wheat flour can be produced by the GABA-enrichment method described above.

The relatively low-ash wheat flour enriched with GABA produced by the method of the present invention has a high concentration of GABA synthase, so by adding it to foods containing glutamic acid, such as tomatoes and cheese, it is possible to produce products with a high GABA content.

<Method for measuring ash content in wheat flour>
The ash content (g/100 g) of each wheat flour sample was analyzed as follows:
40g of magnesium acetate tetrahydrate (special grade) was mixed with 300ml of distilled water and 6ml of acetic acid (special grade), stirred thoroughly, and then methanol (special grade) was added to make 3L to prepare a combustion improver. 5g of wheat flour sample was weighed into a crucible. 5ml of the combustion improver was added, ignited, pre-fired for 90 minutes, and then incinerated at 800°C for 90 minutes. After cooling to room temperature in a desiccator, it was weighed and the ash content per 100g of wheat flour was calculated.

<Method for measuring GABA content in wheat flour>
The amount of GABA (mg/100 g) in each wheat flour sample was analyzed as follows.
90 ml of 75% (v/v) ethanol aqueous solution was added to 3 g of wheat flour sample, stirred and extracted, and filtered using filter paper to obtain an extract. The extract was dried using an evaporator and the volume was adjusted to 15 ml with distilled water. The adjusted volume of the extract was filtered using a 0.45 μm membrane filter, and the filtrate was centrifuged at 5000 rpm for 10 minutes to obtain a supernatant, which was ultrafiltered using AmiconUltra (molecular weight 3000), and the filtrate was used as a test liquid for HPLC analysis. The analysis was performed using an amino acid analyzer L-8900 manufactured by Hitachi High-Tech Co., Ltd. as an HPLC analyzer. The eluent was a buffer solution for biological fluid analysis manufactured by Kanto Chemical Co., Ltd., and the post-column reaction solution was an amino acid kit ninhydrin reagent Wako amino acid automatic analyzer kit manufactured by Fujifilm Wako Pure Chemical Co., Ltd. The amount of GABA was analyzed by a calibration curve method using a mixed amino acid standard solution, L-asparagine, L(+)-glutamine and L-tryptophan, all of which are available from Fujifilm Wako Pure Chemical Industries, Ltd.

[Test Example 1]
Using the wheat flour of Test Example 1 shown in Table 1 below as a raw material, the amount of water added was varied within the range of 5 parts by mass to 25 parts by mass as shown in Table 2 (the amount of wheat flour was adjusted so that the total amount of wheat flour and water was 100 parts by mass), and the mixture was stirred in a food processor at room temperature for 10 minutes to conduct a GABA production test. In this test, the amount of GABA was measured immediately after stirring for 10 minutes. The amount of GABA increased approximately in proportion to the amount of water added.
The more water added, the higher the GABA, but even when the water content was 5 parts by mass, the GABA content increased. On the other hand, when no water was added (water content 0 parts by mass), the GABA content did not change (Table 2). As the water content was increased, the flour was granulated (some parts became dough-like), and the flour became less uniform and fine dough-like granules were mixed in. The flour:water ratio was approximately uniform from 95:5 to 75:25, but became non-uniform at 70:30, and extraction did not go well when measuring GABA. In the following examples, the ratio of 80:20, which has a high GABA content and high uniformity, was used as the standard.

Table 1

Table 2 Comparison by amount of water added

[Test Example 2]
Among the preparation conditions of Test Example 1, the water addition conditions were changed to 85 parts by weight of wheat flour and 15 parts by weight of water at 25°C, and the mixture was stirred in a food processor at room temperature for 10 minutes, and then further kept warm at the temperature and time shown in Table 3, after which the amount of GABA was measured. The warming temperature is the temperature of the thermostatic bath, not the product temperature of the wheat flour. Although the amount of GABA increases by adding a warming time of 40°C, the amount of GABA increases sufficiently even by stirring for 10 minutes at room temperature, so in the following examples, stirring for 10 minutes at room temperature was used as the standard method.

Table 3 Comparison of additional incubation temperatures and times

[Examples 1 to 9 and Comparative Example 1]
<Production Example 1>
Wheat flours L1, L2, H1, H2 and H3 shown in Table 4 were produced by mixing two or more types of flour obtained in the milling process.
Table 4

<Production Example 2>
Wheat flours L1, L2, H1, H2 and H3 in Table 4 were mixed in the mixing ratios shown in Tables 6-1 to 6-3 to produce wheat flours with various ash contents (Examples 1 to 9 and Comparative Example 1). The ash contents of each wheat flour were measured by the method described above (Tables 6-1 to 6-3).

<Test 1>
For each of the wheat flours in Table 4 and Tables 6-1 to 6-3, 20 parts by mass of water at 25°C was added to 80 parts by mass of the wheat flour, and the mixture was stirred in a food processor at room temperature for 10 minutes, and then dried in a thermostatic chamber at 60°C for 60 minutes.
For each treated wheat flour, the amount of GABA before the addition of water and the amount of GABA after the reaction were measured by the method described above.
The values in Table 5 and Tables 6-1 to 6-3 have the following meanings.
"Ash content (g/100g)": The amount of ash (g) per 100g of each flour.
"Amount of GABA before reaction (R1) (mg/100 g)": The amount of GABA (mg) per 100 g of flour before adding water to each flour.
"Amount of GABA after reaction (R2) (mg/100 g)": The amount of GABA (mg) per 100 g of flour after the reaction was carried out for each wheat flour under the conditions of Test 1.
"Amount of GABA after reaction (R2)/Ash content (mg/g)": This is the value obtained by dividing the "Amount of GABA after reaction (R2) (mg/100g)" by the "Ash content (g/100g)" of each flour.
"GABA increase (R2-R1) (mg/100g)": This is the value obtained by subtracting "GABA amount before reaction (R1) (mg/100g)" from "GABA amount after reaction (R2) (mg/100g)".
"GABA increase (R2-R1)/Ash content (mg/g)": This is the value obtained by dividing the "GABA increase (R2-R1) (mg/100g)" by the "Ash content (g/100g)" of each flour.
"Reference pre-reaction GABA amount (C1) (mg/100g)": This value is calculated by multiplying the "pre-reaction GABA amount (R1) (mg/100g)" of each of the flours L1, L2, H1, H2, and H3 listed in Table 5 by the mixing ratio to calculate the "pre-reaction GABA amount (R1) (mg/100g)" based on the mixing ratio of each flour used in the combination, and then adding these values together.
"Reference amount of GABA after reaction (C2) (mg/100g)": This value is calculated by multiplying the "amount of GABA after reaction (R2) (mg/100g)" of flours L1, L2, H1, H2, and H3 shown in Table 5 by the mixing ratio to calculate the "amount of GABA after reaction (R2) (mg/100g)" based on the mixing ratio of each flour used in the combination, and then adding them together.
"Reference amount of GABA after reaction (C2)/Ash content (mg/g)": This is the value obtained by dividing "Reference amount of GABA after reaction (C2) (mg/100g)" by the "Ash content (g/100g)" of each flour.
"Reference GABA increase (C2-C1) (mg/100g)": This is the value obtained by subtracting "Reference amount of GABA before reaction (C1) (mg/100g)" from "Reference amount of GABA after reaction (C2) (mg/100g)".
"Reference GABA increase (C2-C1)/Ash content (mg/g)": This is the value obtained by dividing the "Reference GABA increase (C2-C1) (mg/100g)" by the "Ash content (g/100g)" of each flour.

Table 5 Unmixed flour

Table 6-1 Mixed flour

Table 6-2 Mixed flour

Table 6-3 Mixed flour

As can be seen from Table 6-1, when the same low-ash wheat flour was used and the final ash content was adjusted to be the same, the GABA production amount ("GABA amount after reaction (R2)" and "GABA production amount (R2-R1)") varied depending on the ash content of the high-ash wheat flour used. In addition, the GABA production amount was higher in all combinations than when L2 with the same ash content (0.60 g/100 g) (0.60% by mass) was used alone. Among Examples 1 to 3, Example 3 (L1+H3) showed the largest final GABA amount and the highest GABA increase, followed by Example 2 (L1+H2). The same tendency can be seen from Table 6-2.
Furthermore, Table 6-2 shows that when the final ash content is adjusted to be the same, the results differ depending on the ash content of the low-ash wheat flour. That is, when Example 4 (L1+H2) is compared with Example 6 (L2+H2), or Example 5 (L1+H3) with Example 7 (L2+H3), the amount of GABA produced ("amount of GABA after reaction (R2)" and "amount of GABA produced (R2-R1)") is slightly higher in Examples 4 and 5, which use L1 with a lower ash content. The same tendency can be seen in Table 6-3.
From the above, it is better to use L1 as the low ash wheat flour to be combined than L2, and as the high ash wheat flour, H3 is the best, followed by H2 and H1.

As can be seen from Tables 6-1 to 6-3, when focusing on the adjusted ash content, the higher the ash content, the higher the GABA production amount, but when comparing the GABA production amount when each raw wheat flour is reacted alone with the "reference amount of GABA after reaction (C2)" or "reference amount of GABA increase (C2-C1)" calculated based on the mixing ratio, the lower the ash content, the larger the difference and the higher the increase rate (the higher the production efficiency). For example, in Example 3 (L1+H3, adjusted ash content 0.60g/100g), the GABA increase (R2-R1)/ash content is 17.7mg/g, while the reference amount of GABA increase (C2-C1)/ash content is 10.8mg/g, so the difference is "6.9mg/g". In contrast, in Example 5 (L1+H3, adjusted ash content 0.80 g/100 g), the GABA increase (R2-R1)/ash content was 16.8 mg/g, while the reference GABA increase (C2-C1)/ash content was 13.4 mg/g, so the difference was "3.4 mg/g."
As can be seen from Table 6-3, when low-ash wheat flour having an ash content of X% by mass (X≦0.65) was not used (Comparative Example 1), the amount of GABA produced ("amount of GABA after reaction (R2)" and "amount of GABA produced (R2-R1)") was almost the same as the amount of GABA produced when each of the raw wheat flours was reacted alone, calculated based on the mixing ratio ("reference amount of GABA after reaction (C2)" and "reference amount of GABA increase (C2-C1)"), so there was little point in combining them.

Claims (6)

A method for producing wheat flour enriched with GABA from low-ash wheat flour having an ash content of X% by mass (X≦0.65), comprising adding high-ash wheat flour having an ash content of Y% by mass (Y≧0.65 and Y≧X+0.20) to the low-ash wheat flour to produce ash-adjusted wheat flour having an ash content of Z% by mass (Z≦1.20), adding water thereto and stirring to produce GABA. The method according to claim 1, in which the amount of low-ash wheat flour is in the range of 20 to 90% by mass relative to the mass of the ash-adjusted wheat flour. The method according to claim 1 or 2, which produces flour containing 18 mg or more of GABA per gram of ash. The method according to any one of claims 1 to 3, in which the amount of GABA increase per gram of ash (the amount of GABA in the wheat flour after the GABA production reaction minus the amount of GABA in the raw wheat flour) is 12 mg or more. The method according to any one of claims 1 to 4, wherein the GABA content of low-ash wheat flour having an ash content of X% by mass (X≦0.65) is 4.0 mg/100 g or less, and the GABA content of high-ash wheat flour having an ash content of Y% by mass (Y≧0.65 and Y≧X+0.20) is 4.0 mg/100 g or more. The method according to any one of claims 1 to 5, wherein the step of adding water to the ash-adjusted wheat flour and stirring is a step of adding 33 parts by mass or less of water per 100 parts by mass of the ash-adjusted wheat flour and stirring.