Method for producing starch-containing foods

Abstract

The present invention provides a method for producing a starch-containing food, which comprises allowing amylomaltase derived from actinomycetes to act on starch in a raw material.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a starch-containing food, and more particularly to a method for producing a starch-containing food, which comprises the action of amylomaltase derived from the genus Corynebacterium or Streptomyces. [Background technology]

[0002] The food industry faces a variety of challenges. For example, consumer preferences are becoming increasingly diverse and sophisticated, creating a demand for the development of foods with new textures and flavors that have never existed before. Furthermore, because the quality of many foods deteriorates over time, developing methods to reduce this deterioration is also a major challenge. Furthermore, because food ingredients are limited, establishing manufacturing methods that minimize waste during the manufacturing process is also recognized as an important issue.

[0003] As one option for solving the problems in the food industry described above, methods characterized by modifying the physical properties of food using enzymes have been reported. For example, Patent Document 1 discloses a method for modifying food using β-amylase. Patent Document 2 discloses a method for producing cooked rice foods or processed wheat foods using transglucosidase. Furthermore, Patent Document 3 discloses a method for producing enzyme-treated starch granules that are resistant to retrogradation using 4-α-glucanotransferase.

[0004] Amylomaltase is known to be one of the enzymes that can be used in food production. Amylomaltase (hereinafter sometimes referred to as "AM" in this specification) is an enzyme that catalyzes the degradation of amylose in starch and the elongation of amylopectin sugar chains, and is known to exist widely in nature. Microorganisms that produce amylomaltase include Escherichia coli and other microorganisms. However, thermostable amylomaltases derived from Thermus bacteria, such as Thermus flavus, Thermus aquaticus, or Thermus thermophilus (hereinafter sometimes referred to as "Tt" in this specification), are commonly used in food processing (Patent Document 3, Patent Document 4, Non-Patent Document 1).

[0005] Corynebacterium glutamicum (hereinafter referred to as "Cg" or "Coryne bacteria"), a member of the Corynebacterium genus, is also known to produce amylomaltase. Corynebacterium glutamicum was isolated in Japan in 1957 as a microorganism that excretes L-glutamic acid into the culture medium. It is a non-spore-forming, non-motile, aerobic, Gram-positive bacterium belonging to the mycolic acid-containing actinomycete group. Currently, more than 2 million tons of monosodium L-glutamate (a savory taste component) are produced worldwide by fermentation using this bacterium. Corynebacterium glutamicum is also used to produce many useful substances, including amino acids such as lysine, nucleic acids, and organic acids, in addition to glutamic acid. However, the effects of amylomaltase derived from Corynebacterium glutamicum on edible starch or starch in foods remain unknown. It is also known that amylomaltase derived from Streptomyces bacteria (e.g., Streptomyces avermitilis, Streptomyces cinnamoneus, Streptomyces griseus, Streptomyces thermoviolaceus, or Streptomyces violaceoruber) can be used as a food additive. Amylomaltase derived from Streptomyces and Corynebacterium glutamicum is known to share a relatively high amino acid identity (approximately 40%) and is thought to have similar enzymatic properties to amylomaltase derived from Corynebacterium glutamicum. However, there is no information on the effect of amylomaltase derived from the genus Streptomyces when it is allowed to act on edible starch or starch in foods. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5715346 [Patent Document 2] Patent No. 4475276 [Patent Document 3] Patent No. 5944839 [Patent Document 4] Patent No. 4187305 [Non-patent literature]

[0007] [Non-Patent Document 1] Nguyen DH. et al.,(2014) Modification of rice grain starch for lump-free cooked rice using thermostable disproportionating enzymes. Food Research International 63: 55-61. Summary of the Invention [Problem to be solved by the invention]

[0008] When using thermostable enzymes in food manufacturing processes to modify their quality, the enzymes' temperature characteristics can pose challenges. For example, because thermostable enzymes retain their activity even after the starch in a food is gelatinized, they can also modify the gelatinized starch, resulting in problems such as burning (it is difficult to direct the enzymes only to ungelatinized starch). Furthermore, many thermostable enzymes have low activity in the temperature ranges commonly used in food manufacturing processes for storage, mixing, and molding (refrigerated to room temperature). Therefore, when enzymes are used in these processes, their effectiveness is reduced, resulting in the need for large amounts of enzyme. Furthermore, if an enzyme has high heat resistance, it requires high-temperature, long-term processing during the food manufacturing process to deactivate it, which can have a significant impact on food ingredients. Furthermore, depending on the type of food, the heat intensity may be insufficient to completely inactivate the enzyme. [Means for solving the problem]

[0009] As a result of extensive research into the above-mentioned problems, the inventors discovered that CgAM (1) acts only on ungelatinized starch in foods because it is inactivated before the starch in foods is gelatinized by heat, (2) has higher activity than TtAM in the temperature range (refrigerated to room temperature) commonly used in food manufacturing processes, and (3) is easily inactivated by heat. In addition to these findings, the researchers surprisingly discovered that (4) CgAM can inhibit hardening due to aging while maintaining the original physical properties of starch, (5) cooked rice to which CgAM has been added has improved stickiness and can inhibit deterioration of texture over time while maintaining that stickiness, (6) cooked rice to which CgAM has been added significantly reduces the occurrence of burnt rice during cooking, and (7) the Δblood glucose AUC values ​​2 hours after ingestion in rats that ate sucrose or starch modified with CgAM were lower than the Δblood glucose AUC 2 hours after ingestion in rats that ate sucrose or starch modified with TtAM. Based on these findings, the researchers conducted further research and completed the present invention. That is, the present invention is as follows.

[0010] [1] A method for producing a starch-containing food, which comprises treating starch in a raw material with amylomaltase derived from actinomycetes. [2] The method of [1], wherein the actinomycete is of the genus Corynebacterium or Streptomyces. [3] The method according to [1] or [2], wherein the actinomycete is selected from the group consisting of Corynebacterium glutamicum, Streptomyces avermitilis, Streptomyces cinnamoneus, Streptomyces griseus, Streptomyces thermoviolaceus, and Streptomyces violaceoruber. [4] A manufacturing method according to any one of [1] to [3], wherein the starch-containing food is selected from the group consisting of processed rice foods, processed wheat foods, processed potato foods, processed corn foods, processed tapioca foods, and processed foods containing one or more types of starch extracted from rice, wheat, potato, corn, or tapioca. [5] The method according to any one of [1] to [4], wherein the starch-containing food contains sucrose. [6] A method for producing a starch-containing food, which comprises acting amylomaltase derived from actinomycetes on starch in a raw material, wherein the amylomaltase is an aminomaltase having an amino acid sequence shown in SEQ ID NO: 1, 3, 4, 5, or 6, or an amino acid sequence that is 90% or more identical to the amino acid sequence. [7] A method for modifying the physical properties of starch-containing foods, comprising reacting starch in the raw material with amylomaltase derived from actinomycetes. [8] The method described in [7], wherein the actinomycete is of the genus Corynebacterium or Streptomyces. [9] The method according to [7] or [8], wherein the actinomycete is selected from the group consisting of Corynebacterium glutamicum, Streptomyces avermitilis, Streptomyces cinnamoneus, Streptomyces griseus, Streptomyces thermoviolaceus, and Streptomyces violaceoruber.

[10] The method according to any one of [7] to [9], wherein the starch-containing food is selected from the group consisting of processed rice foods, processed wheat foods, processed potato foods, processed corn foods, processed tapioca foods, and processed foods containing one or more types of starch extracted from rice, wheat, potato, corn, or tapioca.

[11] The method according to any one of [7] to

[10] , wherein the starch-containing food contains sucrose.

[12] A method for modifying the physical properties of starch-containing foods, which comprises acting on starch in the raw material with amylomaltase derived from actinomycetes, wherein the amylomaltase is an aminomaltase having an amino acid sequence shown in SEQ ID NO: 1, 3, 4, 5, or 6, or an amino acid sequence that is 90% or more identical to said amino acid sequence.

[13] A property modifier for starch-containing foods, comprising amylomaltase derived from actinomycetes.

[14] The agent according to

[13] , wherein the actinomycete is of the genus Corynebacterium or Streptomyces.

[15] The agent according to

[13] or

[14] , wherein the actinomycete is selected from the group consisting of Corynebacterium glutamicum, Streptomyces avermitilis, Streptomyces cinnamoneus, Streptomyces griseus, Streptomyces thermoviolaceus, and Streptomyces violaceoruber.

[16] The agent according to any one of

[13] to

[15] , wherein the starch-containing food is selected from the group consisting of processed rice foods, processed wheat foods, processed potato foods, processed corn foods, processed tapioca foods, and processed foods containing one or more types of starch extracted from rice, wheat, potato, corn, or tapioca.

[17] The agent according to any one of

[13] to

[16] , wherein the starch-containing food contains sucrose.

[18] A physical property modifier for starch-containing foods, comprising aminomaltase having an amino acid sequence shown in SEQ ID NO: 1, 3, 4, 5, or 6, or an amino acid sequence that is 90% or more identical to said amino acid sequence.

[0011] In addition, one aspect of the present invention is as follows. [1A] A method for producing a starch-containing food, comprising reacting starch in a raw material with amylomaltase derived from the genus Corynebacterium or Streptomyces. [2A] The manufacturing method described in [1A], wherein the starch-containing food is selected from the group consisting of processed rice foods, processed wheat foods, processed potato foods, processed corn foods, processed tapioca foods, and processed foods containing one or more types of refined starch extracted from rice, wheat, potato, corn, or tapioca. [3A] A production method described in [1A] or [2A], wherein the amylomaltase is an aminomaltase having an amino acid sequence shown in SEQ ID NO: 1, 3, 4, 5, or 6, or an amino acid sequence that is 90% or more identical to the amino acid sequence. [4A] A method for modifying the physical properties of starch-containing foods, comprising reacting amylomaltase derived from the genus Corynebacterium or Streptomyces on starch in the raw material. [5A] The method described in [4A], wherein the starch-containing food is selected from the group consisting of processed rice foods, processed wheat foods, processed potato foods, processed corn foods, processed tapioca foods, and processed foods containing one or more of refined starches extracted from rice, wheat, potato, corn, or tapioca. [6A] A method described in [4A] or [5A], wherein the amylomaltase is an aminomaltase having an amino acid sequence shown in SEQ ID NO: 1, 3, 4, 5, or 6, or an amino acid sequence that is 90% or more identical to the amino acid sequence. [7A] A physical property improver for starch-containing foods, comprising amylomaltase derived from the genus Corynebacterium or Streptomyces. [8A] The agent according to [7A], wherein the starch-containing food is selected from the group consisting of processed rice foods, processed wheat foods, processed potato foods, processed corn foods, processed tapioca foods, and processed foods containing one or more types of refined starch extracted from rice, wheat, potato, corn, or tapioca. [9A] The agent described in [7A] or [8A], wherein the amylomaltase is an aminomaltase having the amino acid sequence shown in SEQ ID NO: 1, 3, 4, 5, or 6, or an amino acid sequence that is 90% or more identical to the amino acid sequence. [Effects of the Invention]

[0012] According to the present invention, it is possible to produce starch-containing foods that have a pleasant texture different in quality from existing sugar-modifying enzymes, are less likely to deteriorate over time, and are less likely to increase blood sugar levels after consumption.In some cooking methods, it is possible to produce starch-containing foods with the above properties without encountering the problems specific to existing heat-resistant amylomaltases (e.g., burning on cooking utensils). [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 shows the change over time in gel strength of 10% starch gel when amylomaltase derived from each microorganism was added. [Figure 2] FIG. 2 shows the amount of burnt rice produced when amylomaltase derived from each microorganism was added. [Figure 3] Figure 3 is a graph showing that amylomaltase derived from Corynebacterium glutamicum and amylomaltase derived from Streptomyces have similar effects in modifying the physical properties of starch gel. [Figure 4] Figure 4 is a graph showing that amylomaltase derived from Corynebacterium glutamicum and amylomaltase derived from Streptomyces have similar activity in amylose degradation. [Figure 5] FIG. 5 shows the difference in the transglycosylation activity between amylomaltase derived from Thermus thermophilus and amylomaltase derived from Corynebacterium glutamicum. [Figure 6] FIG. 6 shows the schedule of a blood glucose measurement test using rats. [Figure 7] Figure 7 shows that modifying dextrin and sucrose using amylomaltase derived from Corynebacterium glutamicum suppresses the rise in blood glucose levels in rats after they ingest the ingredients (top: △Blood glucose rise curve, bottom: △Blood glucose AUC). [Figure 8]Figure 8 shows that modifying α-non-glutinous rice starch using amylomaltase derived from Corynebacterium glutamicum suppresses the rise in blood glucose levels in rats after eating the ingredient (top graph: △Blood glucose rise curve, bottom graph: △Blood glucose AUC). [Figure 9] Figure 9 shows that modifying alpha-glutinous rice starch using amylomaltase derived from Thermus thermophilus does not suppress the rise in blood glucose levels in rats after eating the ingredient (top graph: △Blood glucose rise curve, bottom graph: △Blood glucose AUC). [Figure 10] Figure 10 shows that cooking cooked rice with the addition of amylomaltase derived from Corynebacterium glutamicum suppresses the rise in blood glucose levels in rats after eating the cooked rice (top graph: △Blood glucose rise curve, bottom graph: △Blood glucose AUC). DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail below.

[0015] 1. Manufacturing method of starch-containing foods The present invention provides a method for producing a starch-containing food (hereinafter sometimes referred to as "the production method of the present invention"), which comprises allowing actinomycete-derived amylomaltase to act on starch in a raw material.

[0016] Amylomaltase (EC number: 2.4.1.25) is an enzyme that catalyzes the chemical reaction of transferring a portion of a 1,4-α-glucan chain to the 4-OH group of glucose or another α-glucan. When the substrate is sufficiently large, amylomaltase causes an intramolecular transfer, resulting in a cyclic product.

[0017] As used herein, "α-glucan" refers to α-1,4-glucan (a polysaccharide with a chain structure consisting of maltose as a disaccharide unit) or α-1,4-glucan with an α-1,6-branched structure. "α-glucan" includes, but is not limited to, amylose, amylopectin, starch, and glycogen, as well as waxy starch, high-amylose starch, soluble starch, dextrin, starch hydrolysates, and enzymatically synthesized amylopectin using phosphorylase.

[0018] As used herein, "cyclic glucan" includes cyclic α-1,4-glucans having only α-1,4-glucosidic bonds, as well as branched cyclic glucans having both α-1,4-glucosidic bonds and α-1,6-glucosidic bonds. "Branched" refers to having at least one glucosidic bond other than α-1,4-bond. Examples of branched cyclic glucans include internally branched cyclic glucans containing a branched structure with α-1,6-bonds within the cyclic structure, and externally branched cyclic glucans having a non-cyclic structural portion in addition to the cyclic structure.

[0019] The amylomaltase used in the present invention may be an amylomaltase derived from the genus Corynebacterium or Streptomyces, or a mutant thereof. As used herein, "amylomaltase derived from the genus Corynebacterium or Streptomyces" refers to an amylomaltase produced by bacteria (whether wild-type or mutant) classified in the genus Corynebacterium or Streptomyces, or an amylomaltase obtained by genetic engineering techniques using the amylomaltase gene of bacteria (whether wild-type or mutant) classified in the genus Corynebacterium or Streptomyces. Therefore, a recombinant amylomaltase protein expressed by a host transformed or transduced with an amylomaltase gene (whether wild-type or mutant) obtained from bacteria classified in the genus Corynebacterium or Streptomyces also falls under the category of "amylomaltase derived from the genus Corynebacterium or Streptomyces."

[0020] Examples of amylomaltases suitable for use in the production method of the present invention include, but are not limited to, Corynebacterium glutamicum, Streptomyces avermitilis, Streptomyces cinnamoneus, Streptomyces griseus, Streptomyces thermoviolaceus, and Streptomyces violaceolvera. Examples of amylomaltases derived from Corynebacterium glutamicum include those having the amino acid sequence set forth in SEQ ID NO: 1. Examples of amylomaltases derived from Streptomyces avermitilis include those having the amino acid sequence set forth in SEQ ID NO: 3. Examples of amylomaltases derived from Streptomyces cinnamoneus include those having the amino acid sequence set forth in SEQ ID NO: 4. Examples of amylomaltases derived from Streptomyces griseus include those having the amino acid sequence set forth in SEQ ID NO: 5. An example of amylomaltase derived from Streptomyces violaceolva is amylomaltase having the amino acid sequence set forth in SEQ ID NO: 6. Variants thereof also include amylomaltases having amino acid sequences in which one or more amino acids have been added, deleted, inserted, or substituted relative to the amino acid sequence set forth in SEQ ID NO: 1, 3, 4, 5, or 6. Amylomaltases having one or more mutations may contain any mutations or modifications as long as they have enzymatic properties equivalent to (or superior to) those of wild-type amylomaltase derived from Corynebacterium glutamicum, Streptomyces avermitilis, Streptomyces cinnamoneus, Streptomyces griseus, Streptomyces thermoviolaceus, or Streptomyces violaceolva.Amylomaltases having one or more mutations relative to the amino acid sequence shown in SEQ ID NO: 1, 3, 4, 5, or 6 typically have an amino acid sequence that is 70% or more, preferably 80% or more, more preferably 90% or more, even more preferably 95% or more, even more preferably 98% or more, and particularly preferably 99% or more identical to the amino acid sequence of SEQ ID NO: 1, 3, 4, 5, or 6, and have amylomaltase activity equivalent to (or greater than) that of the corresponding wild-type amylomaltase. In this specification, "identity" of an amino acid sequence or a nucleotide sequence refers to the degree to which identical amino acids (or nucleotides, when comparing nucleotide sequences) appear between two sequences. The "identity" of a sequence can be easily determined by a person skilled in the art using methods known per se.

[0021] Amylomaltase having the amino acid sequence shown in SEQ ID NO: 1, 3, 4, 5, or 6, or mutant amylomaltase having one or more mutations in the amino acid sequence shown in SEQ ID NO: 1, 3, 4, 5, or 6, can be produced by methods known per se. As an example, amylomaltase can be prepared by inserting the nucleotide sequence (SEQ ID NO: 2) encoding amylomaltase having the amino acid sequence shown in SEQ ID NO: 1 into an appropriate gene expression vector, expressing it in a known protein mass expression system such as Escherichia coli, and purifying it using an appropriate means. Alternatively, mutant amylomaltase can be prepared by first modifying a portion of the nucleotide sequence shown in SEQ ID NO: 2 using genetic engineering techniques such as site-directed mutagenesis, inserting it into a gene expression vector, expressing it in a known protein mass expression system such as Escherichia coli, and purifying it.

[0022] In this specification, amylomaltase activity is measured and defined as follows: Amylomaltase solution is added to 30 mM Tris-HCl buffer (pH 7.5) containing 0.05% potato starch and 0.05% maltose, and the mixture is incubated in a water bath at 30-70°C (varies depending on the type of amylomaltase) for a set period of time. The reaction is then stopped by heating to 96°C for 5 minutes. 0.1 ml of this reaction mixture is mixed with 1 ml of iodine solution (0.02% iodine, 0.2% potassium iodide), and the absorbance at 600 nm is measured. The activity value is calculated by subtracting the absorbance at the time of enzyme addition from the absorbance of a blank sample containing Milli-Q water instead of the enzyme solution. The amount of enzyme required to reduce the absorbance at 600 nm by 1 per minute is defined as 1 unit (U).

[0023] The optimum temperature of the amylomaltase derived from Corynebacterium glutamicum used in the production method of the present invention is 30°C to 38°C. The optimum temperature of the amylomaltase derived from Streptomyces used in the production method of the present invention is 45°C to 55°C (e.g., 50°C). As used herein, "optimum temperature" refers to the temperature at which amylomaltase exhibits the highest activity when allowed to act for 10 minutes at each temperature in 30 mM Tris-HCl buffer (pH 7.5) in the presence of 0.05% potato starch and 0.05% maltose. The optimum temperature of amylomaltase derived from Thermus thermophilus is approximately 70°C.

[0024] The optimum pH of the amylomaltase derived from Corynebacterium glutamicum used in the production method of the present invention is 6 to 7. The optimum pH of the amylomaltase derived from Streptomyces used in the production method of the present invention is 4 to 9 (e.g., 7). As used herein, "optimum pH" refers to the pH at which amylomaltase is most active when allowed to act in 30 mM acetate buffer (pH 3 to 5.5), 30 mM phosphate buffer (pH 6 to 7), or 30 mM Tris-HCl buffer (pH 7.5 to 10) in the presence of 0.1% potato starch and 0.05% maltose at each pH at 37°C for 10 minutes.

[0025] Furthermore, with regard to the heat resistance of the amylomaltase derived from Corynebacterium glutamicum used in the production method of the present invention, the enzyme is stable at temperatures below 40°C. Furthermore, the amylomaltase derived from the Streptomyces genus used in the production method of the present invention is stable at temperatures below 50°C. As used herein, "heat resistance" means that the amylomaltase does not lose its activity in 30 mM Tris-HCl buffer (pH 7.5) for 10 minutes.

[0026] Furthermore, the amylomaltase derived from Corynebacterium glutamicum used in the production method of the present invention has a pH stability of 6 to 8. The amylomaltase derived from Streptomyces used in the production method of the present invention has a pH stability of 4 to 9. As used herein, "pH stability" means that the amylomaltase does not lose its activity in a buffer solution (25°C) for approximately 18 hours.

[0027] The amount of amylomaltase derived from Corynebacterium glutamicum or amylomaltase derived from Streptomyces used in the production method of the present invention to be added is not particularly limited as long as the desired effect is obtained, but it may be typically 0.00001 to 10,000 U, preferably 0.0001 to 1,000 U, more preferably 0.001 to 100 U, even more preferably 0.01 to 10 U, and particularly preferably 0.1 to 1 U per gram of starch in the raw material. For example, when the starch-containing food produced by the production method of the present invention is cooked rice, typically 0.00001 to 10,000 U, preferably 0.0001 to 1,000 U, more preferably 0.001 to 100 U, even more preferably 0.01 to 10 U, and particularly preferably 0.1 to 1 U of amylomaltase may be added per gram of dried rice before cooking.

[0028] Furthermore, the timing of addition of amylomaltase derived from the genus Corynebacterium or Streptomyces is not particularly limited as long as the desired effect can be obtained. The timing of addition of the enzyme can be appropriately determined taking into consideration the type of food to be produced and the cooking procedure, the type of starch raw material used, consumer preferences, etc., and is not particularly limited. Therefore, the enzyme can be added to the starch-containing food before, during, or after cooking, or before consumption. However, one preferred embodiment is to add or mix amylomaltase with raw materials to produce or process the food, or to add or mix amylomaltase with food during production or processing, allowing the enzyme to act on the starch in the raw materials. As a specific example, when producing cooked rice, dried rice is washed with water, and the washed rice is mixed with water and amylomaltase derived from Corynebacterium or Streptomyces, and left to stand at room temperature (10°C to 30°C) for a certain period of time (e.g., 0.5 to 2 hours), and then cooked using a conventional method, thereby preparing cooked rice having the desired effects of the present invention.

[0029] In the production method of the present invention, the temperature or time for which amylomaltase derived from the genus Corynebacterium or Streptomyces is allowed to act on starch in the raw material is not particularly limited, as long as the desired effect is obtained. The enzyme acting temperature can be appropriately set taking into consideration the amount of enzyme used, the type of food to be produced and the cooking procedure, the type of starch raw material used, consumer preferences, etc., and is not particularly limited. However, it should be noted that amylomaltase derived from the genus Corynebacterium or Streptomyces has a lower optimum temperature than amylomaltase derived from thermotolerant bacteria. Therefore, in one embodiment, the temperature of the food when the enzyme is added can be typically 1 to 100°C, preferably 5 to 50°C, more preferably 10 to 45°C, even more preferably 20 to 40°C, and particularly preferably 30 to 37°C. The enzyme activity time is also not particularly limited, but is usually 0.1 to 48 hours, preferably 0.2 to 36 hours, more preferably 0.5 to 24 hours, even more preferably 0.8 to 20 hours, and particularly preferably 1 to 18 hours. For example, when producing cooked rice by adding 0.1 to 1 U of amylomaltase per 1 g of dried rice, water and amylomaltase derived from the genus Corynebacterium or Streptomyces are added to washed rice, and the rice is modified with the enzyme at 4 to 40°C for 0.1 to 18 hours, preferably at 10 to 38°C for 0.25 to 6 hours, and more preferably at 20 to 37°C for 0.5 to 1 hour, followed by cooking in a conventional manner, thereby producing cooked rice having the desired effects of the present invention.

[0030] In the manufacturing method of the present invention, the pH environment when amylomaltase derived from the genus Corynebacterium or Streptomyces is allowed to act on the raw material starch is adjusted in advance to, for example, pH 6 to pH 7, using a pH adjuster that can be added to food, as necessary, taking into account the optimal pH and pH stability of the enzyme, as described above.

[0031] Starch-containing foods produced by the production method of the present invention include any food containing starch. The origin of the starch contained in the starch-containing food is not particularly limited and may be one or more selected from the group consisting of rice starch, barley starch (including wheat, barley, rye, etc.), potato starch, sweet potato starch, corn starch, soybean starch, and tapioca starch. Specific examples of starch-containing foods include, but are not limited to, processed rice foods, processed wheat foods, processed potato foods, processed corn foods, processed tapioca foods, and processed foods containing one or more refined starches extracted from rice, wheat, potato, corn, or tapioca. In this specification, processed rice foods include, but are not limited to, cooked rice or processed products thereof (such as red rice, pilaf, seasoned rice, rice congee, risotto, rice balls, sushi, mochi, and mochi confectionery), rice noodles or processed products thereof, etc. Wheat processed foods include, but are not limited to, noodles such as pasta, ramen, and udon; breads, pizza, naan, and other bread doughs; and confectioneries such as cookies and cakes. Potato processed foods include, but are not limited to, potato salad, French fries, boiled potatoes, mashed potatoes, and potato snacks such as potato chips. Corn processed foods include, but are not limited to, tacos, tortillas, arepas, and their dough. Tapioca processed foods include, but are not limited to, steamed tapioca dumplings and tapioca pudding. Processed foods containing one or more refined starches extracted from rice, wheat, potato, corn, or tapioca include, but are not limited to, kamaboko, imitation crab meat, sausage, and hamburger steak.

[0032] 2. Method for improving the physical properties of starch-containing foods The present invention also provides a method for modifying the physical properties of starch-containing foods (hereinafter sometimes referred to as "the method of the present invention"), which comprises allowing amylomaltase derived from actinomycetes to act on starch in the raw material.

[0033] The actinomycete amylomaltase used in the method of the present invention, its amount added, timing of addition, reaction temperature, reaction pH, preparation method, etc., as well as the type of starch-containing food, are all the same as those described in "1. Method for producing starch-containing food."

[0034] 3. Physical property modifier for starch-containing foods The present invention also provides an agent for modifying the physical properties of starch-containing foods (hereinafter sometimes referred to as "the agent of the present invention"), which comprises amylomaltase derived from actinomycetes.

[0035] The amount of actinomycete-derived amylomaltase (e.g., amylomaltase derived from the genus Corynebacterium or Streptomyces) contained in the agent of the present invention is not particularly limited, but may be any amount that can be added at a rate of typically 0.00001 to 10,000 U, preferably 0.0001 to 1,000 U, more preferably 0.001 to 100 U, even more preferably 0.01 to 10 U, and particularly preferably 0.1 to 1 U per gram of starch in the raw material.

[0036] The agent of the present invention may contain components other than amylomaltase derived from the genus Corynebacterium or Streptomyces, including, but not limited to, excipients, buffers, suspending agents, stabilizers, preservatives, antiseptics, and flavorings.

[0037] The dosage form of the agent of the present invention is not particularly limited, and may be a solid form such as powder or granules, a liquid form, or a paste form.

[0038] Other conditions for using the agent of the present invention can be appropriately determined by a person skilled in the art by referring to the conditions explained in "1. Method for producing starch-containing foods."

[0039] The present invention will be explained in more detail in the following examples, but the present invention is not limited to these examples in any way. [Example]

[0040] [Example 1] Effect on the physical properties of starch gel A 10% suspension of rice starch was treated with 50 U / g starch of amylomaltase from Corynebacterium glutamicum or Thermus thermophilus (hereinafter referred to as "CgAM" or "TtAM") and incubated at 37°C for 1 hour with stirring. The mixture was then heated to 98°C for 10 minutes and cooled to 50°C. The cooled starch gel was then molded into a 5 mm diameter, 20 mm high cylinder using a plastic cylindrical tube and stored at 5°C for 1 to 7 days. The resulting starch gel was removed from the tube and molded into a 5 mm diameter, 5 mm high cylinder using a razor blade. Compression tests were performed using a texture analyzer (TA-XT Plus). The gel strength was measured on days 1, 3, and 7. The results are shown in Figure 1.

[0041] As shown in Figure 1, when amylomaltase was not added (Control), the starch gel gradually hardened during refrigerated storage due to starch retrogradation. Furthermore, when TtAM was added, the viscosity of the starch decreased significantly, and gel formation took longer. After gelation, the gel hardened rapidly. When CgAM was added, a gel with physical properties similar to those of the enzyme-free starch gel was formed. Furthermore, the gel hardly hardened even after several days.

[0042] [Example 2] Texture improvement of cooked rice 150 g of dried rice was washed, and water and amylomaltase (1.0 U / g dry rice) derived from each microorganism were added to make a 325 g volume. The rice was then left at room temperature (20°C) for 1 hour. The rice was then cooked using a Panasonic SR-13GP rice cooker. The cooked rice was removed from the rice cooker, transferred to a plastic container with a lid, and left at room temperature for 1 hour before undergoing a sensory evaluation by a panel of four experts.

[0043] Sensory evaluation was performed on three items: "softness," "graininess," and "stickiness." In this specification, "softness" refers to the small resistance felt when chewing cooked rice, "graininess" refers to the rice grains remaining strong and not breaking apart when chewed, and "stickiness" refers to the rice grains adhering to each other. The evaluation criteria are as follows: "softness," "graininess," and "stickiness" of cooked rice prepared without enzyme addition were set as the standard (0 points), and the level of each item was evaluated on a scale of -2 points to +2 points (in increments of 0.5 points). Samples other than the standard product (enzyme-free) were presented blind. The scores were calculated as the average of the scores of four expert panels. The results are shown in Table 1.

[0044] [Table 1]

[0045] As shown in Table 1, unlike cooked rice prepared with the addition of TtAM, cooked rice prepared with the addition of CgAM had a soft and sticky texture.

[0046] [Example 3] Preventing deterioration of cooked rice over time

[0047] Cooked rice was prepared under the same conditions as in Example 2. The cooked rice was left to stand in a thermostatic chamber set at 20°C for 18 hours and then subjected to sensory evaluation. The conditions and method for the sensory evaluation were the same as those used in Example 2. The results are shown in Table 2.

[0048] [Table 2]

[0049] As shown in Table 2, cooked rice without enzyme addition decreased in softness and stickiness after 18 hours of storage at 20°C. When TtAM was added, softness and stickiness decreased immediately after cooking, and the changes in physical properties after 18 hours of storage at 20°C were small. On the other hand, when CgAM was added, softness and stickiness increased immediately after cooking, and although there was a slight decrease in softness and stickiness after 18 hours of storage at 20°C, compared to TtAM, the physical properties of the cooked rice prepared without enzyme addition were generally similar to those on the day of cooking.

[0050] [Example 4] Suppression of burning Cooked rice was prepared under the same conditions as in Example 2, and the amount of scorching was examined. The amount of scorching refers to the weight of the rice remaining on the inner pot when the inner pot containing the cooked rice was removed from the rice cooker immediately after cooking was completed, and the rice was dropped upside down. The results are shown in Table 3 and Figure 2. The values ​​shown in Table 3 are averages calculated from the values ​​obtained in three tests.

[0051] [Table 3]

[0052] As shown in Table 3 and Figure 2, when TtAM was added, a scorched, candy-like deposit formed on the bottom of the pot, whereas when CgAM was added, almost no scorching occurred.

[0053] [Example 5] Prevention of deterioration of wheat starch-containing foods over time To confirm the effect of CgAM in inhibiting the deterioration of wheat starch-containing foods over time, bread containing CgAM was prepared and the degree of deterioration in texture of the bread after storage for a set period of time was examined. Specifically, water was measured into a metal container attached to a bread maker (MK Seiko, HBK-100) and the specified amount of CgAM (Test Group 1: no additive, Test Group 2: 0.01 U / g wheat flour, Test Group 3: 0.1 U / g wheat flour, Test Group 4: 1.0 U / g wheat flour) was added. A premix of bread flour, sugar, skim milk, and salt was then added to the water. Dry yeast and shortening were then added to the water, and the bread was kneaded and baked using the specified program (white bread, medium browning) to prepare the bread. The actual amounts of each ingredient are shown in Table 4 below. After baking, the cake was left to cool at room temperature for 1.5 hours, then sliced ​​into 2cm thick pieces, sealed in a plastic bag with a zipper, and stored at a temperature of 10°C and humidity of 50% for 2 days.

[0054] [Table 4]

[0055] The texture (dryness) of the bread stored under the above conditions was evaluated by a sensory test conducted by three expert panelists. The evaluation criteria used in the sensory test were as follows:

[0056] ×: Very dry △: Dry ○: A little dry ◎: Moist

[0057] The results are shown in Table 5 below.

[0058] [Table 5]

[0059] As shown in Table 5, the bread containing CgAM remained less dry even two days after baking.

[0060] [Example 6] Effect of potato starch on physical properties Potato flakes ("Potato Flakes" by Daibou Co., Ltd.) were weighed (40 g per test) and mixed with 120 g of city water. CgAM was added and stirred with a spatula until homogenous. The resulting mixture was left to stand at room temperature for 30 minutes. After 30 minutes of standing, the mixture was divided into three 50 g packs and sealed with a vacuum sealer. The sealed packs were immersed in boiling water for 30 minutes and then cooled to approximately 25°C under running water. The packs were opened and the contents were dispensed into a 24-well microplate. The packs were stored refrigerated (5°C) and subjected to compression tests using a texture analyzer on the day of dispensing, one day later, one week later, and two weeks later to measure the paste hardness.

[0061] The amount of CgAM used in this example was 0.1 U or 1.0 U per 1 g of dried potato flakes.

[0062] The measurement conditions for the texture analyzer used to measure the physical properties are as follows: Equipment: Texture analyzer (TA-XT Plus, manufactured by Eiko Seiki Co., Ltd.) with a 5mm diameter stainless steel spherical plunger Measurement conditions: compression speed 1 mm / sec, the center of the model potato salad filled on the plate was compressed (pierced) by 50%, and the maximum stress was recorded (N=3).

[0063] The results are shown in Table 6 (Compressive Stress) below.

[0064] [Table 6]

[0065] As shown in Table 6, CgAM was shown to inhibit the hardening of the model potato salad over time.

[0066] [Example 7] Starch modification properties of amylomaltase derived from Streptomyces genus 1 It is known that amylomaltase derived from Streptomyces and amylomaltase derived from Corynebacterium glutamicum share a relatively high degree of amino acid identity, and their functions are expected to be similar. To demonstrate this, the following experiment was carried out.

[0067] Rice starch (SIGMA) was added to 10 mM phosphate buffer (pH 7) to form a 10% suspension. CgAM, TtAM, or amylomaltase derived from Streptomyces avermitilis (hereinafter sometimes referred to as "SaAM") was added at 50 U / g starch. The mixture was incubated at 37°C for 1 hour with stirring. The enzyme was then inactivated by heating at 98°C for 10 minutes. The cooled starch gel was then dispensed into 5 mm diameter cylindrical tubes and stored at 5°C for 1 to 7 days. The starch gels were removed from the refrigerator at 1, 3, and 7 days (day 0). The resulting starch gels were then molded into 5 mm diameter, 5 mm high cylinders using a razor blade. The cut surfaces were then placed on the stage of a texture analyzer (TA-XT Plus) for compression testing to measure gel strength.

[0068] The texture analyzer and measurement conditions used for measuring the physical properties are as follows: Equipment: Texture analyzer (TA-XT Plus, Eiko Seiki Co., Ltd.) with a 15 mm diameter acrylic cylindrical plunger and a stainless steel stage. Measurement conditions: compression speed 0.5 mm / sec, maximum stress (g) obtained when starch gel piece was compressed by 90% was recorded (N = 6-9).

[0069] The results are shown in Figure 3. As shown in Figure 3, the physical properties and changes over time of the starch gel treated with SaAM were almost identical to those of the starch gel treated with CgAM. This indicates that amylomaltase derived from Streptomyces and CgAM are likely to have similar effects on starch modification.

[0070] [Example 8] Starch modification properties of amylomaltase derived from Streptomyces genus 2 Amylose (BAR-5K-1, GLICO NUTRITION CO., LTD.) was added to dimethyl sulfoxide to prepare a 10% solution, which was then diluted with Milli-Q water to prepare a 1% amylose solution. Next, 50 μL of each amylomaltase solution (SaAM, CgAM, or TtAM) adjusted to 1 U / mL was added to 500 μL of the prepared 1% amylose solution. The reaction mixture was incubated at 50°C for SaAM, 37°C for CgAM, and 70°C for TtAM for 60 minutes. The enzyme was then inactivated by heating at 100°C for 10 minutes and cooled to room temperature. After cooling, each reaction mixture was diluted with Milli-Q water to a 0.1% amylose concentration. The chain length distribution of the amylose degradation products contained in the diluted reaction mixture was analyzed using ion chromatography (Dionex). The relative peak area of ​​each glycan to the total peak area was calculated. The results are shown in Figure 4.

[0071] As shown in Figure 4, the sugar chain length distribution obtained by treating amylose with CgAM was very similar to that obtained by treating amylose with SaAM. This result also demonstrated that the starch modification properties of amylomaltase derived from Streptomyces are similar to those of CgAM.

[0072] [Example 9] Examination of glycosylation properties of CgAM and TtAM A 5% starch suspension was prepared by adding 1.5 g of rice starch to 28.5 mL of 50 mM phosphate buffer (pH 6.0). The resulting starch suspension was placed in a stand-up pouch and heated at 100°C for 15 minutes to gelatinize the starch (gelatinized starch solution 1). 1.5 g of glucose (sometimes referred to as "G1") or sucrose (sometimes referred to as "suc") was added to 28.5 mL of 50 mM phosphate buffer (pH 6.0) to prepare a 5% G1 solution or sucrose solution, which was dispensed into a 1.5 mL tube. Next, 500 μL of gelatinized starch solution 1 was mixed with 500 μL of the G1 solution, the sucrose solution, or Milli-Q water to obtain a mixed solution (1 mL).

[0073] Next, 2.5 U / mL CgAM and 2.5 U / mL TtAM solutions were prepared. 100 μL of the resulting enzyme solution was added to the mixed solution (1 mL) prepared as described above (100 U enzyme per 1 g starch). After adding the enzyme solution, the reaction solution containing CgAM was heated to 30°C, and the reaction solution containing TtAM was heated to 50°C. A control solution containing Milli-Q water instead of the enzyme solution was also heated to 30°C. After 24 hours, the enzymes in the reaction solution were inactivated by heating at 100°C for 10 minutes. Each reaction solution was subsequently subjected to TLC analysis.

[0074] TLC analysis was performed as follows. 2 μL of three types of 0.5% sugar solutions were spotted as standards. The three types of sugar solutions used as standards were as follows: Sugar solution 1: A mixture of glucose (G1), maltose (G2), maltotriose (G3), maltotetraose (G4), maltopentaose (G5), maltohexaose (G6), and maltoheptaose (G7) Sugar solution 2: sucrose solution (suc) Sugar solution 3: α-cyclodextrin (αCD) and β-cyclodextrin (βCD) mixture

[0075] After enzyme inactivation, the reaction solution was diluted 5-fold with Milli-Q water to adjust the concentration of rice starch, G1, or Suc to 0.5%, and 2 μL of the solution was spotted.

[0076] A single development was performed using a solvent composition of n-butanol:pyridine:Milli-Q water (MQ) = 6:4:1. Detection was performed by spraying 20% ​​sulfuric acid / EtOH onto the carrier, followed by heating at 110°C for approximately 10 minutes to develop color. The results are shown in Figure 5. In Figure 5, "(-)" indicates the lane containing a sample prepared by mixing gelatinized starch solution 1 (500 μL) with 50 mM phosphate buffer (pH 6.0) (500 μL), adding Milli-Q water instead of the enzyme solution, and heating at 30°C for 24 hours.

[0077] As shown in Figure 5, TtAM transferred sugar chains to glucose (G1) to produce oligosaccharides, but did not transfer sugar chains to sucrose (suc). On the other hand, CgAM transferred sugar chains to both glucose (G1) and sucrose (suc), indicating that the reaction characteristics of the two AMs toward sucrose are different.

[0078] [Example 10] Modification of the physical properties of sucrose-containing dextrin by CgAM (Preparation of test substance) Dextrin (Matsutani Chemical Industry Co., Ltd., Pinex #100) was dissolved in Milli-Q water to make a 5% solution. Sucrose (pure chemical reagent grade) was also dissolved in Milli-Q water to make a 5% solution. These were mixed in a 1:1 ratio, and CgAM solution was added to this at 100 U per gram of dextrin. The same amount of Milli-Q water was added as a control. This mixture was left to stand in a 30°C water bath for 24 hours to allow the enzyme reaction to occur. It was then heated in a 100°C water bath for 10 minutes to inactivate the enzyme. The dextrin-sucrose solution after the enzyme reaction was stored in a -80°C freezer.

[0079] (Animal testing) Using rats, blood glucose levels after starch administration were measured using the following method, and the effect of inhibiting blood glucose elevation was evaluated. The test substance was thawed under running water on the day of the blood glucose measurement test and used for the test. Blood glucose levels were measured in the fasting state and 15, 30, 60, and 120 minutes after administration according to the blood glucose measurement method below and the test schedule in Figure 6. The test substance was administered orally at a total sugar content of 1 g / 20 mL / kg. The total sugar mass analysis of the test substance was outsourced to the Japan Food Research Laboratories, Inc., and measured using the phenol-sulfuric acid method.

[0080] (Method of measuring blood glucose level) Various glucose tolerance tests have been conducted on rats, but in this test, a modified version of the glucose tolerance test disclosed in Japanese Patent Application Laid-Open No. 2005-328776 was performed.

[0081] [animal] Animal species and strain: Rat, Slc:Wistar (SPF) Producer: Japan SLC Co., Ltd. Gender: Male Age at time of arrival: 6 weeks old Quarantine and acclimation: Animals are acclimated from the time of arrival until group allocation. However, the arrival date is counted as day 0 and the animals are quarantined for up to 7 days. General condition observations are conducted daily.

[0082] [Breeding environment] Temperature: 22±3℃ Humidity: 50±20% Lighting time: 12 hours / day

[0083] [feed] Type: Labo MR Stock solid feed (Nosan Corporation) or CRF-1 (Oriental Yeast Co., Ltd.) Feeding method: Feed ad libitum except during fasting periods.

[0084] [Drinking water] Type: Tap water Water supply: Provide water ad libitum throughout the test period.

[0085] [Animal selection and grouping] During the quarantine and acclimation period, animals to be used in the test will be selected from those that show no abnormalities in their general condition. Animals will be used at 7 weeks of age. On the final day of quarantine and acclimation, their body weight will be measured, and using this weight as an index, they will be allocated to groups of 6 to 10 animals using a stratified sequential randomization method.

[0086] [Fasting treatment] An overnight fast will begin in the evening of the day before the glucose tolerance test.

[0087] [Blood glucose measurement] The vein at the tip of the tail is incised using a scalpel blade without anesthesia. The blood leaking from the incision is used to perform the test (blood glucose level). The blood glucose level is measured using a self-testing glucose meter "Accu-Check" (Roche Diagnostics) or "Glutest Neo" (Sanwa Chemical Research Institute), and the blood glucose level displayed on the meter is recorded. This is the fasting blood glucose level. The same glucose meter was used for tests on the same day.

[0088] The evaluation items were calculated as follows. Fasting blood glucose level was defined as the blood glucose level at 0 min. The blood glucose level at each measurement time was divided by the blood glucose level at 0 minutes to obtain the "Δ blood glucose level (mg / dL)." The highest value among the △blood glucose values ​​at each measurement time was defined as each individual's "△Cmax (mg / dL)." The area under the blood glucose rise curve was calculated and designated as "blood glucose AUC (mg / dL·min)." The calculation method followed the method of the Japan Glycemic Index Study Group. The effect of suppressing an increase in blood glucose level was evaluated based on the value of the AUC of the AUC of the test substance-administered group when the AUC of the AUC of the control group was set at 100.

[0089] The test results are shown in Figure 7. The test results showed that by applying CgAM to a mixture of sucrose and dextrin, the △blood glucose AUC value 2 hours after administration was kept low, and the rise in blood glucose levels was suppressed. This is thought to be due to the effect of CgAM, which adds a sugar chain to sucrose, polymerizing the sucrose and making it less digestible, as observed in Example 9.

[0090] [Example 11] Modification of starch properties by CgAM treatment (Preparation of test substance) 10 g of alpha-glutinous rice starch (My Alpha K, Joetsu Starch Co., Ltd.) was weighed and mixed with 80 g of Milli-Q water. The mixture was transferred to a standing pouch (LamiZip Stand Type, Seisan Nippon Co., Ltd.) and sealed with a heat sealer. The mixture was then heated in a thermostatic chamber at 100°C for 15 minutes to completely gelatinize the starch. The starch paste was stirred during the process to prevent clumping. The starch paste was then returned to 37°C for the control and CgAM groups, and 50°C for the TtAM group. 10 mL of CgAM or TtAM solution, each adjusted to 1 U per gram of starch, was then added. 10 mL of Milli-Q water was added to the control. The container was then immediately sealed and placed in a thermostatic chamber. The control and CgAM groups were left at 37°C, and the TtAM group was left at 50°C for 60 minutes to allow the enzyme reaction. After the enzyme reaction, the mixture was heated in a thermostatic chamber at 100°C for 15 minutes to inactivate the enzyme. The enzyme-treated starch was returned to room temperature and then frozen at -80°C.

[0091] (Animal testing) The method of Example 10 was followed.

[0092] (Method of measuring blood glucose level) The method of Example 10 was followed.

[0093] The test results are shown in Figures 8 and 9. The test results show that the group administered CgAM-treated starch had a lower Δblood glucose AUC value 2 hours after administration compared to the control group and the TtAM-treated starch group, indicating that the rise in blood glucose levels was suppressed.

[0094] [Example 12] Improvement of the physical properties of cooked rice by CgAM treatment (Preparation of test substance) The raw material used was Hitomebore rice from Miyagi Prefecture. Brown rice was harvested on the same day from a single producer, polished on the same day, and placed in a light-blocking vacuum pack containing an oxygen absorber and refrigerated at 5°C until testing.

[0095] The polished rice was allowed to return to room temperature 30 minutes before weighing on the day of cooking. The polished rice was weighed using an electronic balance (US6002S, Mettler-Toledo). The polished rice was placed in a colander and gently stirred clockwise 10 times in a bowl of tap water. The tap water was replaced and the same process was repeated five times. After washing, the rice was removed from the colander and transferred to a rice cooker. Tap water was added to adjust the hydration level to 150% on the electronic balance, and CgAM was added at 1 U per gram of raw rice. After soaking for 1 hour at room temperature, the rice cooker was placed in a rice cooker (SR-03GP, Panasonic Corporation) and cooked. Immediately after cooking, the rice cooker was inverted onto a tray to remove the cooked rice. The rice closest to the wall of the rice cooker was removed and pushed to the edge of the tray with a spatula. The cooked rice was leveled with a spatula, wrapped with plastic wrap leaving a small gap between the layers, and then cooled at room temperature for 15 minutes. The cooked rice was placed in a Unipack (Made in Japan, Inc.), leveled to a thickness of approximately 2 cm, and frozen in a -80°C freezer. The following day, it was freeze-dried using a freeze dryer (FDU-2100: Tokyo Rikakiki Co., Ltd.). After freeze-drying was confirmed, it was pulverized using a mixer mill (MM301: Verder Scientific Co. Ltd.). The pulverized sample was dispensed into standing pouches, sealed, and stored at room temperature.

[0096] (Animal testing) The method was the same as in Example 10, except that the test substance was suspended in Milli-Q water before use.

[0097] (Method of measuring blood glucose level) The method was the same as in Example 10. The test substance was orally administered at a total sugar content of 2 g / 20 mL / kg.

[0098] The test results are shown in Figure 10. The group administered CgAM-treated cooked rice had a lower AUC value for blood glucose level 2 hours after administration compared to the control group, indicating that the rise in blood glucose level was suppressed. [Industrial Applicability]

[0099] According to the present invention, starch-containing foods that have a pleasant texture, are less likely to deteriorate over time, and are less likely to raise blood sugar levels can be produced without the problems associated with existing thermostable amylomaltases, making it extremely beneficial in the food manufacturing industry.

[0100] This application is based on patent application No. 2018-058931 filed in Japan (filing date: March 26, 2018), the contents of which are incorporated in their entirety herein.

Claims

1. A method for producing a starch-containing food, comprising allowing amylomaltase derived from actinomycetes to act on starch in a raw material, The method for producing the starch-containing food product is selected from the group consisting of the following (1) to (4): (1) Processed foods containing rice starch or potato starch that has been inhibited from hardening over time (2) Cooked rice with a soft and sticky texture (3) Cooked rice or bread with reduced deterioration over time (4) A processed food or cooked rice containing rice starch, which has the effect of suppressing blood sugar levels.

2. The method according to claim 1, wherein the actinomycete is of the genus Corynebacterium or Streptomyces.

3. 3. The method according to claim 1, wherein the actinomycete is selected from the group consisting of Corynebacterium glutamicum, Streptomyces avermitilis, Streptomyces cinnamoneus, Streptomyces griseus, Streptomyces thermoviolaceus, and Streptomyces violaceoruber.

4. The method according to any one of claims 1 to 3, wherein the starch-containing food contains sucrose.

5. A method for producing a starch-containing food, comprising allowing amylomaltase derived from actinomycetes to act on starch in a raw material, wherein the amylomaltase is an aminomaltase having the amino acid sequence shown in SEQ ID NO: 1, 3, 4, 5, or 6, or an amino acid sequence that is 90% or more identical to said amino acid sequence, wherein the starch-containing food is selected from the group consisting of (1) to (4) below: (1) Processed foods containing rice starch or potato starch that has been inhibited from hardening over time (2) Cooked rice with a soft and sticky texture (3) Cooked rice or bread with reduced deterioration over time (4) A processed food or cooked rice containing rice starch, which has the effect of suppressing blood sugar levels.

6. A method for modifying the physical properties of a starch-containing food, which comprises allowing actinomycete-derived amylomaltase to act on starch in a raw material, wherein the starch-containing food and the modified physical properties thereof are selected from the group consisting of the following (1) to (5): (1) Suppression of hardening over time in processed foods containing rice starch or potato starch (2) Providing softness and stickiness to cooked rice (3) Suppression of deterioration of cooked rice or bread over time (4) Suppression of burning of cooked rice (5) Imparting the function of suppressing blood sugar levels to processed foods containing rice starch or cooked rice.

7. 7. The method according to claim 6, wherein the actinomycete is of the genus Corynebacterium or Streptomyces.

8. 8. The method according to claim 6 or 7, wherein the actinomycete is selected from the group consisting of Corynebacterium glutamicum, Streptomyces avermitilis, Streptomyces cinnamoneus, Streptomyces griseus, Streptomyces thermoviolaceus, and Streptomyces violaceoruber.

9. 9. The method according to any one of claims 6 to 8, wherein the starch-containing food contains sucrose.

10. A method for modifying the physical properties of a starch-containing food, comprising allowing amylomaltase derived from actinomycetes to act on starch in a raw material, wherein the amylomaltase is an aminomaltase having the amino acid sequence shown in SEQ ID NO: 1, 3, 4, 5, or 6, or an amino acid sequence that is 90% or more identical to said amino acid sequence, wherein the starch-containing food and the modification of its physical properties are selected from the group consisting of (1) to (5) below: (1) Suppression of hardening over time in processed foods containing rice starch or potato starch (2) Providing softness and stickiness to cooked rice (3) Suppression of deterioration of cooked rice or bread over time (4) Suppression of burning of cooked rice (5) Imparting the function of suppressing blood sugar levels to processed foods containing rice starch or cooked rice.

11. An agent for modifying the physical properties of starch-containing foods, comprising amylomaltase derived from actinomycetes, wherein the starch-containing foods and the physical properties thereof are modified by an agent selected from the group consisting of the following (1) to (5): (1) Suppression of hardening over time in processed foods containing rice starch or potato starch (2) Providing softness and stickiness to cooked rice (3) Suppression of deterioration of cooked rice or bread over time (4) Suppression of burning of cooked rice (5) Imparting the function of suppressing blood sugar levels to processed foods containing rice starch or cooked rice.

12. The agent according to claim 11, wherein the actinomycete is of the genus Corynebacterium or Streptomyces.

13. 13. The agent according to claim 11 or 12, wherein the actinomycete is selected from the group consisting of Corynebacterium glutamicum, Streptomyces avermitilis, Streptomyces cinnamoneus, Streptomyces griseus, Streptomyces thermoviolaceus, and Streptomyces violaceoruber.

14. The agent according to any one of claims 11 to 13, wherein the starch-containing food contains sucrose.

15. An agent for modifying the physical properties of starch-containing foods, comprising aminomaltase having an amino acid sequence shown in SEQ ID NO: 1, 3, 4, 5, or 6, or an amino acid sequence that is 90% or more identical to said amino acid sequence, wherein the starch-containing food and the modification of its physical properties are selected from the group consisting of the following (1) to (5): (1) Suppression of hardening over time in processed foods containing rice starch or potato starch (2) Providing softness and stickiness to cooked rice (3) Suppression of deterioration of cooked rice or bread over time (4) Suppression of burning of cooked rice (5) Imparting the function of suppressing blood sugar levels to processed foods containing rice starch or cooked rice.

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