Modified koji with low methanol production and method for producing fermented foods using the same

Abstract

To provide a koji modified to produce little methanol and a method for producing the same, and a method for producing brewed food by using the modified koji.SOLUTION: The present invention discloses a method for producing a modified koji, including the step of heating a solid koji having absorbed water at 60°C or higher. The production method gives a modified koji in solid form that produces little methanol.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a modified koji with low methanol production and a method for producing the same. The present invention also relates to a method for producing a fermented food using the modified koji. [Background technology]

[0002] Shochu, sake, miso, soy sauce, and amazake are traditional Japanese fermented foods made with koji. Koji is used to produce these. During the fermentation process, enzymes derived from koji produce sugars and amino acids, which are known to play an important role in developing the taste, color, and aroma of fermented foods.

[0003] Although superior koji mold strains have been developed and provided for some time, the action of koji-derived enzymes (pectin methylesterase) in fermentation ingredients containing pectin can produce toxic methanol from the pectin, which remains in fermented foods. For this reason, Japan limits the amount of methanol contained in alcoholic beverages, stipulating it at less than 1,000 mg / L under the Food Sanitation Act. Other countries also have regulated levels, particularly in China, which are stricter than Japan's, creating a barrier to exporting alcoholic beverages from Japan. For this reason, there is a demand for safer koji with low methanol production. Furthermore, as consumer preferences diversify, there is a demand for a wider variety of flavors in fermented foods.

[0004] Examples of prior art documents relating to methods for modifying koji include Patent Document 1 and Non-Patent Documents 1 and 2 below. Patent Document 1 describes heat-treating koji at a temperature in the range of 100 to 350°C for 0.1 to several hours, and describes that by using the koji thus treated as part of the raw materials for distilled spirits or sake, the amount of HDMF (4-hydroxy-2,5-dimethyl-3(2H)-furanone) is increased, resulting in an alcoholic beverage with a good aroma and excellent flavor. Non-Patent Document 1 describes that rice koji is dried at 40°C for 2 hours and then heat-treated at 80, 90, or 100°C for 1 to 3 hours, and that this treatment produces koji with a significantly reduced general viable cell count without significantly reducing the enzymatic activity per unit weight of acid carboxypeptidase, a proteolytic enzyme produced by koji mold. Non-Patent Document 2 describes a heat treatment of koji in the primary fermentation step of sweet potato shochu, in which koji and water are mixed and then heat-treated at 30 to 60°C for 10 minutes, and describes that by using the primary mash obtained by this heat treatment in the fermentation of sweet potato shochu, it is possible to reduce the production of methanol without affecting the amount of ethanol or aroma components produced. However, this method has problems in shochu production, such as the time and energy required for heating and cooling, difficulty in temperature control, and difficulty in handling the heat-treated koji because it is in a gruel-like state and does not retain its original solid form, and poor storage stability, and has not yet been put to practical use. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2017-221111 [Non-patent literature]

[0006] [Non-Patent Document 1] "Development of soybean fermented foods using koji mold," Yamagata Prefectural Industrial Technology Center Report No. 49 (2017) [Non-patent document 2] "Study on Improving the Quality of Shochu", Masami Mizutani, Research Report No. 52, Miyazaki Prefectural Industrial Technology Center and Miyazaki Prefectural Food Development Center (2007) Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a modified koji with low methanol production and a method for producing the same. Another object of the present invention is to provide a method for producing a fermented food using the modified koji. [Means for solving the problem]

[0008] The inventors conducted extensive research to solve these problems and found that by incorporating water into koji while it maintains its original form, i.e., in a solid state, and then heat-treating it at a temperature of 60°C or higher, modified koji with a low ability to produce methanol from fermentation raw materials containing pectin (modified koji with low methanol production) can be obtained. It was also confirmed that this modified koji maintains the ethanol-producing ability it had before modification. Furthermore, it was found that the heat treatment can change the proportion of aroma components produced by the koji, imparting a favorable flavor to brewed products. Furthermore, it was confirmed that the modified koji obtained by this method maintains its original solid form and, even after subsequent drying, maintains the above-mentioned properties, making it easy to handle.

[0009] The present invention was completed based on these findings and has the following embodiments. (I) Method for producing modified koji (I-1) A method for producing modified koji, comprising a step of heat-treating hydrated solid koji at a temperature of 60°C or higher. (I-2) The production method according to (I-1), wherein the water content of the koji is 35 to 50% by mass, preferably 40 to 45% by mass; and the heat treatment temperature is 60 to 80°C, preferably 65 to 70°C. (I-3) The production method according to (I-1) or (I-2), which comprises a drying treatment step after the heat treatment step. (I-4) The production method according to any one of (I-1) to (I-3), wherein the koji is at least one selected from the group consisting of white koji, black koji, and yellow koji.

[0010] (II) Modified koji (II-1) A modified koji having a solid form and low methanol productivity, obtained by the production method according to any one of (I-1) to (I-4) above. (II-2) The modified koji described in (II-1), which is koji for producing fermented foods. (II-3) The modified koji according to (II-1) or (II-2), wherein the fermented food is a food produced using raw materials containing pectin. (II-4) The modified koji according to (II-1) or (II-2), wherein the raw material is at least one selected from the group consisting of pectin-containing potatoes, vegetables, fruits, and seeds.

[0011] (III) Methods of producing fermented foods (III-1) A method for producing a fermented food product, using the modified koji described in any one of (II-1) to (II-4). (III-2) The method according to (III-1), wherein the fermented food is a food produced using ingredients containing pectin. (III-3) A production method according to (III-1) or (III-2), wherein the raw material is at least one selected from the group consisting of potatoes, vegetables, fruits, and nuts containing pectin. [Effects of the Invention]

[0012] The method of the present invention makes it possible to produce and provide modified koji that has a low ability to produce methanol from pectin-containing raw materials without impairing ethanol production (modified koji with low methanol production). Furthermore, the method of the present invention makes it possible to prepare modified koji that changes the proportion of aroma components produced during the fermentation process, thereby imparting a favorable flavor to the brewed product. Furthermore, the modified koji obtained by the method of the present invention maintains its original solid form and, even after subsequent drying, retains the above-mentioned properties, making it easy to handle. Thus, the modified koji provided by the present invention maintains the shape of the koji and can be handled in the same way as conventional koji, and it is possible to reduce methanol production and diversify aroma components. [Brief explanation of the drawings]

[0013] [Figure 1] Sweet potato shochu was produced using modified koji (white koji, yellow koji) and unmodified koji (white koji, yellow koji) from sweet potatoes (Koganesengan), and the methanol content (mg / L) in the fermented and matured mash was measured (Experimental Example 5). [Figure 2] The above results are shown using Akemurasaki as the sweet potato (Experimental Example 5). [Figure 3] The above results are shown using Tamaakane as the sweet potato (Experimental Example 5). BEST MODE FOR CARRYING OUT THE INVENTION

[0014] The method for producing modified koji of the present invention is characterized by comprising a step of heat-treating water-containing solid koji at a temperature of 60°C or higher. The solid koji targeted by the present invention is koji used in the production of brewed foods, and is obtained by inoculating a solid protein and / or carbohydrate raw material with starter koji prepared from an koji mold normally used in the production of brewed foods, and producing koji by a conventional method.

[0015] As mentioned above, the koji mold may be any fungus commonly used in the production of fermented foods, including, for example, fungi of the genus Aspergillus, such as Aspergillus luchensis, Aspergillus oryzae, Aspergillus sojae, Aspergillus kawachii, and Aspergillus awamori; Monascus, such as Monascus purpureus; and Rhizopus. Among these, koji molds of the genus Aspergillus are preferred, and koji molds of the genus Aspergillus include black koji mold, white koji mold, and yellow koji mold. More preferred are, but not limited to, Aspergillus luchensis (white koji mold) and Aspergillus oryzae (yellow koji mold).

[0016] Examples of solid protein and / or carbohydrate raw materials used in koji production include grains such as rice, wheat, barley, and corn; pulses such as soybeans, peas, and broad beans; and various seafood, and these can be selected and used according to standard methods depending on the type of fermented food to be produced. For example, but not limited to, rice steamed according to standard methods is used as the protein and / or carbohydrate raw material in the production of shochu. Koji production can also be carried out according to standard methods depending on the type of fermented food to be produced.

[0017] The present invention is a method for modifying the solid koji obtained by such koji production so that it has a low methanol-producing ability while maintaining its solid form, and the method includes a step of heat-treating the solid koji in a hydrated state at a temperature of 60°C or higher. Hereinafter, for convenience, modifying koji so that it has a low methanol-producing ability will be abbreviated as "MeOH reduction." The koji can be modified by adjusting the koji to a water content of 30 to 50% by mass and heating it in this state at a temperature of 60°C or higher, preferably 60 to 80°C.

[0018] If the moisture content is significantly lower than 30% by mass, a sufficient MeOH reduction effect cannot be obtained. On the other hand, if the moisture content is significantly higher than 50% by mass, although the MeOH reduction effect can be obtained, gelatinization progresses, and the solid koji becomes semi-liquid to liquid, making it difficult to handle. The moisture content is preferably 35 to 50% by mass, more preferably 40 to 48% by mass, and particularly preferably 40 to 45% by mass. The moisture content of solid koji can be measured using the loss on drying method. Specifically, 5 g of solid koji is placed in a thermostatic chamber at 104°C (at normal pressure) and heated and dried for 2 hours. The moisture content of the solid koji before drying can be calculated from the loss in weight (dry mass) measured after 2 hours.

[0019] If the heating temperature is significantly lower than 60°C, the MeOH reduction effect will not be sufficient or the heat treatment will take a long time. On the other hand, if the heating temperature is significantly higher than 80°C, the MeOH reduction effect will be achieved, but the enzymes contained in the koji will be inactivated and the koji will lose its function. As a result, the ethanol production ability will decrease. The heating temperature is preferably 65 to 80°C, more preferably 65 to 75°C, and particularly preferably 65 to 70°C.

[0020] The treatment time for the solid koji may be any time long as it maintains its solid form, does not significantly adversely affect the ethanol production ability, and modifies the koji to have low methanol production ability. While not limited, examples of the treatment time under the above conditions include 0.5 hours or more, preferably 0.5 to 4 hours. For example, when a heating temperature of 75°C or less is used, heating is preferably performed for 1 to 4 hours, and when a heating temperature higher than 75°C is used, heating is preferably performed for 0.5 hours or less.

[0021] By heat-treating the solid koji with the moisture content adjusted in this way, it is possible to modify the solid koji so that it has low methanol-producing ability (low MeOH content) while maintaining its original solid form. Here, "methanol-producing ability" refers to the ability or characteristic to produce methanol from pectin as a raw material, and "low methanol-producing ability" (low methanol-producing property) means that this ability or characteristic is low. The modified koji produced by the method of the present invention is characterized by having low methanol-producing ability compared to the koji before modification. The methanol-producing ability of the modified koji can be evaluated by fermenting a pectin-containing raw material and comparing the methanol content produced with that of the koji before modification. For example, an example using sweet potato as a pectin-containing raw material is described in the experimental examples below.

[0022] The pectin-containing raw material is not limited to sweet potatoes, and may be any edible material containing pectin, such as potatoes (e.g., potatoes, sweet potatoes), vegetables (e.g., pumpkin, carrot, paprika, eggplant, radish, cabbage, etc.), fruits (e.g., apples, citrus fruits, avocados, figs, quince, bananas, persimmons, strawberries, kiwi, mangoes, papayas, plums, pears, plums, peaches, grapes, watermelons, etc.), and nuts and seeds (e.g., walnuts, peanuts, chestnuts).

[0023] Furthermore, the modified koji produced by the method of the present invention maintains its ethanol production ability, which is approximately equivalent to that of the koji before modification. The methanol production ability of the modified koji can be evaluated by fermenting a pectin-containing raw material and comparing the ethanol content produced with that of the koji before modification. For example, an example using sweet potato as a pectin-containing raw material is described in the experimental examples below.

[0024] The modified koji of the present invention maintains its properties even after drying and can therefore be used as dried koji. The modified koji of the present invention can be used in its original or dried state to produce fermented foods (brewed foods) by adding edible raw materials. The fermented foods are not particularly limited, and examples thereof include shochu (shochu type A, shochu type B, and a mixture of shochu types A and B), spirits, amazake (sweet sake), distilled alcoholic beverages, and fruit juice-containing alcoholic beverages. Examples of shochu include sweet potato shochu, rice shochu, barley shochu, buckwheat shochu, brown sugar shochu, and awamori. Brewed foods produced using ingredients containing pectin are preferred. Examples of such fermented foods include, but are not limited to, sweet potato shochu, potato shochu, chestnut shochu, pumpkin shochu, carrot shochu, fruit spirits, fruit miso, and fruit amazake. These fermented foods can be produced according to standard methods appropriate for the type of fermented food, except that the modified koji of the present invention is used instead of conventional solid koji. [Example]

[0025] The present invention will be described below using experimental examples. However, the present invention is not limited to the following experimental examples. In the following description, "%" means % by mass unless otherwise specified. Furthermore, the experimental examples were carried out at room temperature and atmospheric pressure unless otherwise specified. Furthermore, in the following experimental examples, the moisture content (%) of the koji was calculated by measuring the mass of the koji before and after drying at 104°C for 2 hours, and assuming the reduced mass (loss on drying) to be the moisture content of the koji.

[0026] In the following experimental examples, the following white koji for shochu (Aspergillus luchuensis) and yellow koji for sake (Aspergillus oryzae) were used as seed koji. L-type white koji: Obtained from Kawachi Genichiro Shoten White koji: Obtained from Kawachi Genichiro Shoten. Hereinafter referred to as "Kawachi white koji." Yellow koji: Hikami Ginjo A. oryzae (obtained from Higuchi Matsunosuke Shoten Co., Ltd.)

[0027] Experimental Example 1: Evaluation of modified koji using L-type white koji (1) L-type white koji was used as seed koji, and this was inoculated onto steamed rice and koji was produced according to the usual method to obtain rice koji (water content 32.1%). The moisture content of the obtained rice koji was adjusted to 15% to 55% by adding water or by ventilation drying at 40°C, and the koji was placed in a sealable polyethylene bag and left to stand for 2 hours while maintaining this moisture content, after which it was heat-treated in a constant-temperature air-blowing oven at 60°C for 3 hours (modification treatment).Shochu was produced using the obtained modified koji and koji that had not been subjected to either moisture adjustment or heat treatment (control koji).

[0028] In shochu production, the primary mash was prepared by adding 5 ml of water and 0.2 ml of shochu yeast (Miyazaki yeast: Saccharomyces cerevisiae) to 10 g of modified koji or control koji, and fermenting at 28°C for 4 days. Then, 40 ml of water and 50 g of sweet potato (Koganesengan) were added, and fermented at 28°C for 7 days. The sweet potato was pre-steamed (steaming time: 50 minutes), and to eliminate variation between samples, it was sliced ​​into 1 cm wide rings, and then further cut into 8 to 12 equal fan-shaped pieces.

[0029] The resulting fermented and matured mash was filtered through filter paper (No. 2), then through a 0.45 μm membrane filter, and diluted two-fold. The methanol and ethanol in the mash were analyzed and quantified using a gas chromatograph (Agilent Technologies HP6890, column DB-WAX (φ0.53 mm × 30 m), detector (FID)).

[0030] The results are shown in Table 1. The results are the average of three samples. In Table 1, the methanol content indicates the concentration (mg / L) contained in the fermented and matured mash, and the ethanol content indicates the content ratio (V / V%) contained in the fermented and matured mash. Table 1 also shows the shape of the koji (modified koji, control koji) used in shochu production, and the properties of the resulting fermented and matured mash.

[0031] [Table 1]

[0032] As shown in Table 1, it was confirmed that the use of modified koji that had been subjected to moisture adjustment and heat treatment in shochu production significantly reduced the amount of methanol produced without affecting the amount of ethanol produced. In particular, when koji containing 30% or more moisture and heat-treated was used as the modified koji, the amount of methanol produced began to decrease significantly, peaking at a moisture content of 45% and remaining unchanged even with further increases in moisture content. However, when the moisture content exceeded 50%, the koji began to gelatinize, reducing its ease of handling. Therefore, it was confirmed that, from the viewpoints of methanol production ability and shape retention of the koji, it is preferable to adjust the moisture content of the koji during heat treatment to between 30% and 50%, preferably 45% or less.

[0033] Experimental Example 2: Evaluation of modified koji using L-type white koji (2) L-type white koji was used as seed koji, and this was inoculated onto steamed rice and koji was produced according to the usual method to obtain rice koji (moisture content 32.1%). The moisture content of the obtained rice koji was adjusted to 40% and, while maintaining the moisture content, was heat-treated at 50-90°C for 0.5-4 hours (modification treatment) as shown in Table 2 using the method described in Experimental Example 1, and then used for shochu production. Shochu was produced in the same manner as in Experimental Example 1 (using Miyazaki yeast and Koganesengan [steamed]). Note that koji that had not been modified was used as a "control koji" in contrast to the "modified koji." The contents of methanol, ethanol, and low-boiling-point aroma components (isoamyl alcohol, normal propyl alcohol) in the obtained fermented and matured mash were analyzed and quantified using gas chromatography according to the method described in Experimental Example 1.

[0034] The results are shown in Table 2. In Table 2, the methanol content is the concentration (mg / L) contained in the fermented and matured moromi, and the ethanol content is a relative value, with the ethanol content in the fermented and matured moromi produced using the control koji taken as 100. "A / P" means the ratio of "isoamyl alcohol / normal propyl alcohol."

[0035] [Table 2]

[0036] As shown in Table 2, a reduction in methanol production was observed with heat treatment above 60°C. This effect was particularly pronounced with heat treatment above 65°C, particularly at 65°C for 1 hour or more and at 70°C for 0.5 hours or more. However, to avoid a loss of ethanol production, a temperature between 60°C and 80°C was preferred, and when heating at 80°C, a heating time of 0.5 hours or less was desirable. Furthermore, as shown in Table 2, the ratio of isoamyl alcohol to n-propyl alcohol (A / P), a low-boiling aroma component, tended to increase as the koji heating temperature increased above 65°C. This confirmed that the aroma (quality) of shochu can be altered by selecting the heat treatment conditions. These findings confirm the usefulness of selecting the heat treatment temperature and time, in addition to the moisture content, in modifying koji.

[0037] Experimental Example 3: Evaluation of modified koji using various types of koji (1) As seed koji, shochu koji (L-type white koji, Kawachi white koji) and sake yellow koji were used, and these were inoculated onto steamed rice and koji was produced according to the usual method to obtain various types of rice koji (L-type white koji, Kawachi white koji, yellow koji). The moisture content of the obtained rice koji was adjusted to 40%, and after heat treatment at 65°C for 2 hours (modification treatment) while maintaining the moisture content using the method described in Experimental Example 1, it was used for shochu production. Shochu was produced in the same manner as in Experimental Example 1 (using Miyazaki yeast and Koganesengan [steamed]). Note that various types of koji (moisture content: L-type white koji 31.5%, Kawachi white koji 27.7%, yellow koji 27.7%) that had not been subjected to moisture adjustment or heat treatment were used as "control koji" in comparison with the above-mentioned "modified koji." The contents of methanol and ethanol in the resulting fermented and matured mash were analyzed and quantified using gas chromatography according to the method described in Experimental Example 1.

[0038] The results are shown in Table 3. In Table 3, the methanol content is the concentration (mg / L) contained in the fermented and matured moromi, and the ethanol content is a relative value, with the ethanol content in the fermented and matured moromi produced using the control koji set at 100.

[0039] [Table 3]

[0040] As is clear from Table 3, by heat-treating koji adjusted to a moisture content of 40% at 65°C for 2 hours, the amount of methanol produced was reduced by approximately 59 to 70% without affecting the amount of ethanol produced, regardless of the type of koji. This confirms that heat-treating koji with adjusted moisture content is effective as a treatment for reducing the amount of methanol produced, regardless of the type of koji; in other words, as a treatment for modifying koji to produce less methanol.

[0041] Experimental Example 4: Evaluation of modified koji using raw sweet potatoes with different heat treatments The sweet potatoes used in shochu production were heated using steaming (steaming time 50 minutes) and microwave heating (600W, 4 minutes), and sweet potato shochu was produced in the same manner as in Experimental Example 3 to evaluate the methanol and ethanol production ability of the modified koji.

[0042] Kawachi white koji and yellow koji were used as seed koji. Steamed rice was inoculated with these seeds and koji was produced according to standard methods to obtain various types of rice koji (Kawachi white koji and yellow koji). The moisture content of 10 g of the resulting rice koji was adjusted to 40%. The moisture content was maintained at 65°C for 2 hours (modification treatment) using the method described in Experimental Example 1, and the resulting koji was then used for shochu production. Shochu production was performed in the same manner as Experimental Example 1 (using Miyazaki yeast and Koganesengan), except that the sweet potatoes used as raw materials were heated using the steaming and microwave treatment described above. The sweet potatoes were sliced ​​into 1 cm-wide rings and then shredded into 8 to 12 equal fan-shaped pieces after steaming or before microwave treatment. Various koji that had not undergone moisture adjustment or heat treatment (moisture content: Kawachi white koji 27.7%, yellow koji 27.7%) were used as "control koji" to compare with the "modified koji" described above. The contents of methanol and ethanol in the resulting fermented and matured mash were analyzed and quantified using gas chromatography according to the method described in Experimental Example 1.

[0043] The results are shown in Table 4. In Table 4, the methanol content is the concentration (mg / L) contained in the fermented and matured moromi, and the ethanol content is a relative value, with the ethanol content in the fermented and matured moromi produced using the control koji and steamed sweet potato set at 100.

[0044] [Table 4]

[0045] As is clear from Table 4, the use of modified koji significantly reduced the amount of methanol produced without affecting the amount of ethanol produced, regardless of the heat treatment method used for the sweet potatoes used as a raw material for shochu production. In particular, this effect was enhanced by heating the sweet potatoes in a microwave oven. This confirms that the modification of koji by adjusting the moisture content and heating is an effective treatment for reducing the amount of methanol produced, regardless of the heating method used for the sweet potatoes used as a raw material for shochu production.

[0046] Experimental Example 5: Evaluation of modified koji using different varieties of sweet potatoes Sweet potato shochu was produced using three different varieties of sweet potato (Koganesengan, Akemurasaki, and Tamaakane) in the same manner as in Experimental Example 1, and the methanol and ethanol contents in the fermented and matured mash were measured to evaluate the methanol and ethanol production ability of the modified koji.

[0047] Kawachi white koji and yellow koji were used as seed koji. Steamed rice was inoculated with these seeds and koji was produced according to standard methods to obtain various types of rice koji (Kawachi white koji and yellow koji). The moisture content of 10 g of the resulting rice koji was adjusted to 40%. The resulting rice koji was then heat-treated at 65°C for 2 hours (modification treatment) while maintaining the moisture content, as described in Experimental Example 1. Shochu was produced in the same manner as in Experimental Example 1 (using Miyazaki yeast and steamed sweet potato [steaming time: 50 minutes]). Note that various koji that had not undergone moisture adjustment or heat treatment (moisture content: Kawachi white koji 27.7%, yellow koji 27.7%) were used as "control koji" in comparison with the "modified koji." The methanol and ethanol contents of the resulting fermented product (secondary mash) were measured by gas chromatography.

[0048] The results are shown in Figure 1 (Koganesengan), Figure 2 (Akemurasaki), and Figure 3 (Tamaakane) for each raw sweet potato used. As is clear from Figures 1 to 3, the use of modified koji significantly reduced the amount of methanol produced without affecting the amount of ethanol produced, regardless of the variety of sweet potato used as a raw material for shochu production. This confirms that the modification of koji by adjusting the moisture content and heating is effective in reducing the amount of methanol produced, regardless of the variety of sweet potato used as a raw material for shochu production.

[0049] Experimental Example 6: Evaluation of modified koji by trial production of fruit koji using apples Kawachi white koji and yellow koji were used as seed koji, and these were inoculated onto steamed rice and koji was produced according to standard methods to obtain various types of rice koji (Kawachi white koji and yellow koji). The moisture content of 10 g of the resulting rice koji was adjusted to 40%, and while maintaining this moisture content, it was heat-treated at 65°C for 2 hours using the method described in Experimental Example 1, and then used to produce fruit koji samples.

[0050] Fruit koji was made by mixing 10 g of the water-adjusted and heat-treated koji (modified koji), 20 g of apples, and 30 ml of water, and heating the mixture at 60°C for 3 hours. Both heat-treated and non-heat-treated apples were used, and the heat treatment was carried out in a microwave oven (600 W) for 2 minutes. The fruit koji thus prepared was thoroughly stirred, filtered through filter paper (No. 2), and then through a 0.45 μm membrane filter. The methanol content of the resulting solution, which was then diluted two-fold, was measured by gas chromatography. Fruit koji prepared using koji that had not undergone moisture adjustment or heat treatment (water content: Kawachi white koji 27.7%, yellow koji 27.7%) was used as a "control koji" in contrast to the aforementioned "modified koji." The results are shown in Table 5.

[0051] [Table 5]

[0052] As shown in Table 5, the use of modified koji reduced the amount of methanol produced, regardless of whether the raw apples were heat-treated. This confirms that modifying koji by adjusting the moisture content and heating is also effective in suppressing methanol production in fruit koji made from fruits such as apples. In other words, it is also effective as a process for modifying fruit koji to produce less methanol.

[0053] Experimental Example 7 Evaluation of dried modified koji Rice koji (Kawachi white koji, yellow koji) made using Kawachi white koji and yellow koji as seed koji was adjusted to a moisture content of 40% and modified by heat treatment at 65°C for 2 hours. The resulting modified koji was spread on a petri dish and air-dried at 40°C for 4 hours to obtain dried modified koji (Kawachi white koji, yellow koji). These dried modified koji were used in shochu production (using Miyazaki yeast and Koganesengan [steamed]) as described in Experimental Example 3. Dried koji (unmodified koji) that had not been subjected to moisture adjustment or heat treatment was used as a "control koji" for the "dried modified koji." The contents of methanol and ethanol, as well as the contents of low-boiling-point aroma components (isoamyl alcohol, normal propyl alcohol) in the resulting fermented and matured mash were analyzed and quantified using gas chromatography according to the method described in Experimental Example 1.

[0054] The results are shown in Table 6. In Table 6, the methanol content (mg / L) indicates the concentration contained in the fermented and matured mash, and the ethanol content indicates a relative value, with the ethanol content in the fermented and matured mash produced using the control koji set at 100. "A / P" indicates the ratio of "isoamyl alcohol / normal propyl alcohol."

[0055] [Table 6]

[0056] As shown in Table 6, the koji modified by moisture adjustment and heat treatment maintained its low methanol production capacity without any reduction in ethanol production capacity even after subsequent drying. The modified koji also maintained its low-boiling-point aroma component production capacity (the tendency for isoamyl alcohol production to increase relative to normal propyl alcohol). These results suggest that the modified koji of the present invention can be used as dried koji. [Industrial Applicability]

[0057] Using the modified koji of the present invention with brewing ingredients containing pectin makes it possible to reduce the harmful methanol content in the brewed product without adversely affecting the amount of ethanol produced. The average methanol content of 25% Koganesengan sweet potato shochu, submitted to the Kumamoto Regional Taxation Bureau's 2018 Liquor Appraisal, was reported to be 266 mg / L at normal pressure and 281 mg / L at reduced pressure (2018 Brewing Year Shochu Survey (Kumamoto Regional Taxation Bureau), 41 (2020)). Using the modified koji of the present invention may enable the production of sweet potato shochu with a lower methanol content than the above. Furthermore, the modified koji of the present invention enables the stable production of brewed products with good taste and aroma. In other words, brewing with this modified koji reduces the amount of methanol, leading to improved safety, expanded exports, and improved quality.

Claims

1. A method for producing modified koji, comprising a step of subjecting the water-containing solid koji to one of the following heat treatments at a temperature of 60°C to 80°C in a state where the water content is 30% by mass or more but less than 50% by mass: (1) Heat treatment at a temperature of 60°C to 75°C for 1 to 4 hours (2) Heat treatment at a temperature of 65°C or higher and 75°C or lower for 0.5 to 4 hours, or (3) Heat treatment for 0.5 hours at a temperature of more than 75°C and not more than 80°C.

2. The method according to claim 1 , further comprising a drying step after the heating step.

3. 3. The method according to claim 1, wherein the koji is at least one selected from the group consisting of white koji, black koji, and yellow koji.

4. A modified koji having a solid form and low methanol productivity, obtained by the production method according to any one of claims 1 to 3.

5. The modified koji according to claim 4, which is koji for producing fermented foods.

6. A method for producing a fermented food product, which uses the modified koji according to claim 4 or 5.

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