A method for producing edible steamed indigo that does not contain indigo components.

Abstract

Dried indigo leaves, which are blue due to the formation of indigo within the leaves, are used as food. These dried leaves, in which indigo is formed due to the activity of indican-degrading enzymes, also contain several fermentation products produced during the indigo formation process, which are thought to be responsible for a unique bitter taste. The safety of some indigo and the substances produced during its formation process has not been confirmed. The blue color is considered an appetite-suppressing color, making it visually unsuitable for consumption. [Solution] Immediately after harvesting, the indigo plants are steamed to inactivate the indican-degrading enzyme, retaining indican in the leaves and preventing the formation of fermentation products and indigo during the indigo formation process. By incorporating a steaming process, a sun-drying process, and a roasting process to adjust the flavor after harvesting, steam-dried indigo with a good balance of taste, flavor, and aroma, and free of indigo components, is produced. Indigo-free dried indigo leaves can be used as a delicious and safe food ingredient.

Description

Technical Field

[0001] The present invention relates to a manufacturing technique of steamed and exposed Polygonum tinctorium leaves without indigo components, in which β-glucosidase, an indican degrading enzyme in Polygonum tinctorium, is inactivated immediately after harvesting and within the temperature range of about 45°C to 200°C.

Background Art

[0002] Research using Polygonum tinctorium has long been industrially noted. In modern times, research on Polygonum tinctorium has focused on industrial research on how to efficiently increase the yield of indigo contained in the leaves as a raw material for dyes. Therefore, there has been almost no research on its edibility, and there is no production or edible use of Polygonum tinctorium dried leaves without indigo components. In Japan, in recent years, there have been attempts to use Polygonum tinctorium for edible purposes, but leaves of Polygonum tinctorium that have been dried in the same process as for making dyes, using organically grown Polygonum tinctorium, are being used. In Patent Document 1, Polygonum tinctorium is a dried product that is dried as it is after harvesting, and it is blue dried leaves in which indigo is formed in the leaves, just like the leaf indigo used as a raw material for dyes. Prior to the present invention, there was no technical example of using indigo-free Polygonum tinctorium dried leaves as food ingredients.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Non-Patent Documents

[0004]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

[0005] In recent years, research has begun on the edible potential of Polygonum tinctorium, but the dried leaves used are those that have been dried untreated after harvesting. These dried leaves, which are dried as is after harvesting and have indigo formed within them, are blue in color and do not taste good.

[0006] Dried leaves of Polygonum tinctorium, containing indigo and fermentation and oxidation products produced during the indigo formation process, have a distinctive astringent, bitter, and tatami-like taste, likely due to these products, making them unpalatable as food. Furthermore, various impurities produced during the indigo formation process include substances whose safety has not been confirmed.

[0007] Dried leaves of the Japanese indigo plant, which have been treated with indigo dye, exhibit a blue color. Generally, the blue color in natural foods is said to be an appetite-suppressing color and is visually unappealing. [Means for solving the problem]

[0008] In a method for producing steamed and dried indigo leaves, which are edible dried indigo leaves that do not contain indigo, the method includes: a steaming process in which the indigo leaves are steamed with steam at a temperature between approximately 45°C and 200°C after harvesting to produce steamed and matured indigo; a drying process in which the steamed and matured indigo obtained in the steaming process is dried in the sun or in a dryer to produce dried indigo; and a roasting process in which the dried indigo obtained in the drying process is roasted to produce steamed and dried indigo leaves, which are edible dried indigo leaves that do not contain indigo.

[0009] A method for producing steamed and dried indigo leaves, which are edible dried leaves of Polygonum tinctorium that do not contain indigo, wherein the steaming process includes: a steaming process in which the Polygonum tinctorium is steamed with steam within 120 minutes after harvesting to produce steamed and dried indigo; a drying process in which the steamed and dried indigo obtained in the steaming process is dried in the sun or in a dryer until it weighs 20% or less of the weight of the harvested Polygonum tinctorium to produce dried indigo; and a roasting process in which the dried indigo obtained in the drying process is roasted at a temperature of 150°C or higher to produce steamed and dried indigo. [Effects of the Invention]

[0010] We believe that the factors hindering the use of indigo in food are its unique astringency, tatami-like odor, bitterness, appetite-suppressing effect due to the blue color of the dried leaves, and concerns about the safety of indigo as well as the fermentation and oxidation products produced during the indigo formation process. These are caused by the decomposition of indican by indican-degrading enzymes. This invention blocks the indigo formation process by inactivating the indican-degrading enzymes immediately after harvesting, thereby retaining indican in the indigo leaves and solving the problems of its unique astringency, the blue coloration of dried indigo leaves, and concerns about safety.

[0011] When the cells of Polygonum tinctorium are destroyed, the enzymatic degradation reaction between indican-degrading enzyme and indican begins, and the indigo formation process proceeds spontaneously and sequentially, with each reaction proceeding at a fairly rapid rate (Figure 4). When the leaves become dried, indigo has formed in the leaves and the dried leaves are blue in color. By quickly deactivating the indican-degrading enzyme after harvesting, before the leaves become blue and dried, it was possible to produce delicious, non-blue, steam-blown indigo that does not contain unconfirmed impurities.

[0012] Although blue is considered an appetite-suppressing color in food, steamed and dried indigo does not contain blue pigment after drying because indigo is not formed in the leaves. The appearance of steamed and dried indigo is yellow or reddish-brown. Furthermore, the color of tea brewed with steamed and dried indigo is a translucent amber or a yellowish scarlet. The manufacturing method of this invention eliminates any elements that suppress appetite when eating or drinking. [Brief explanation of the drawing]

[0013] [Figure 1] Comparison of the steam-bleached indigo processing process and the conventional dried indigo leaf processing process. [Figure 2] Changes in the composition of indigo during its formation process [Figure 3] The beginning of the enzymatic reaction of indican [Figure 4] Reaction rate of indican-degrading enzyme [Figure 5] Taste Test Questionnaire [Modes for carrying out the invention]

[0014] In this invention, as shown in Figure 2, the indican degradation reaction is blocked by inactivating β-glucosidase, an indican-degrading enzyme, during the indigo formation process. This prevents the indigo formation process from starting, thus stopping the production of products and halting indigo production. As a result, dried indigo leaves, which retain indican and lack indigo, can be used as a delicious food ingredient in many dishes and as a raw material for tea. Furthermore, by adding a roasting process, steamed and dried indigo leaves with a balanced taste, flavor, and aroma are produced. This makes it easier for the body to absorb the beneficial components of indigo. In this invention, dried leaves of Polygonum tinctorium, obtained by steaming and roasting them, were used as steamed and roasted indigo.

[0015] Polygonum tinctorium of the Polygonaceae family accumulates a large amount of the colorless glycoside indican (indican / indoxyβ-D-glucoside), which is a precursor of indigo formation, inside cells. The amount reaches several percent of the fresh leaf weight at the peak period. When these glycosides are extracted from cells due to cell disruption and encounter indican-degrading enzymes, they are enzymatically decomposed to produce indoxyl as an intermediate. This is the process at the beginning of the indican enzyme reaction (Figure 3). Since this indoxyl is very unstable, it is immediately oxidized when exposed to air and spontaneously non-enzymatically polymerizes to become stable indigo.

[0016] Research using Polygonum tinctorium has been industrially developed since ancient times for the purpose of using indigo contained in leaves as a dye. However, due to the chemical synthesis and industrialization of indigo, even basic research has been left behind in the general public's concerns. In recent years, research on Polygonum tinctorium has progressed from industrial research on indigo dyes contained in leaves to research on using it for food. However, research on Polygonum tinctorium only focuses on how to cook leaf blue. There is a record that Polygonum tinctorium was used as a crude drug for traditional Chinese medicine in ancient China, but the manufacturing method and specific usage form have not been left.

[0017] In recent years, efforts have been made to find new values of Polygonum tinctorium, and as part of this, research on the edible use of Polygonum tinctorium has also begun. However, at present, only leaf blue, which is dried Polygonum tinctorium cultivated without pesticides and contains indigo, is used.

[0018] Leaf blue contains fermentation products and acid products generated during the indigo formation process, so it is not suitable for direct consumption. Also, the safety of some impurities contained in large amounts has not been confirmed. Since no edible treatment method has been developed for safe and delicious consumption, it has a strong unique eggy smell, tatami smell, bitterness, etc., which are thought to be derived from impurities, making it not delicious and hindering its edible use due to concerns about safety.

[0019] Indican is a secondary metabolite found only in leaves and is not detected in other species, cotyledons, roots, stems, flowers, or flower buds. Indican and β-glucosidase reside in separate locations within cells, and normally, spontaneous reactions between the two do not occur within cells. However, indican is released when cells die or when leaves are damaged, such as by insects or ectarians. Furthermore, if chloroplasts are also damaged, indican-degrading enzymes are released, and the indigo formation process begins (Figure 3). Once the enzymatic degradation reaction between indican-degrading enzymes and indican begins, the indigo formation process proceeds spontaneously and sequentially, and the rate is quite rapid (Figure 4). When the leaves become dry, indigo has formed within them, and the dry leaves are blue in color. After harvesting, it is desirable to quickly deactivate the indican-degrading enzymes before the leaves turn blue and dry.

[0020] In this invention, we have succeeded in stopping the enzymatic decomposition reaction of indican, which is the beginning of the indigo formation process, by inactivating the decomposing enzyme with steam, thereby eliminating the characteristic astringency, tatami-like odor, bitterness, and blue leaf color that hinder the use of indigo in food. By inactivating β-glucosidase, the indican-degrading enzyme, through a steam-based ripening process immediately after harvesting, we stop the enzymatic decomposition reaction between the indican-degrading enzyme and indican. This stops the production of fermentation products, oxidation products, and ultimately the indigo produced, eliminating the characteristic astringency, tatami-like odor, and bitterness, and resulting in a method that allows for the delicious consumption of Japanese indigo, as it does not produce impurities. [Examples]

[0021] As shown in Figure 1, several methods were tested to select a method for inactivating the indican-degrading enzyme and preventing the indigo formation process from starting. First, in the steaming process, the enzymatic degradation of indican begins when the indigo plants are harvested, and the reaction rate of the indican enzyme is fastest immediately after harvesting, halving in about 60 minutes. It has been found that after about 120 minutes, the reaction is nearing its end and the reaction rate slows down significantly. (Figure 4) The harvested indigo plants were neatly arranged in a steamer basket to improve the efficiency of steam heating. Immediately after harvesting, steam was introduced from below the arranged indigo plants to inactivate the indican-degrading enzyme. In the drying process, the steamed indigo was spread out in a sunny location to dry in the sun. It was sun-dried for a full day until its weight after harvesting was less than 20%. This dried indigo was confirmed to be brown and not blue, which contains indigo. In traditional production methods, harvested indigo plants are simply dried, and the resulting dried leaves undergo the indigo formation process, producing fermentation products, oxidation products, and a blue color containing indigo. While some regulations mandate pesticide-free cultivation during indigo production, the dried leaves used are the same indigo leaves used in the dye and pigment manufacturing process.

[0022] One well-known method of preventing plant fermentation is the steaming process used for sencha green tea. In the case of tea leaves, the degrading enzymes are inactivated above 40°C, stopping the enzymatic reaction. Therefore, the deactivation process for sencha is often carried out at around 90°C for about one minute. However, the optimal activity temperature for β-glucosidase, an indican-degrading enzyme, is around 75°C, requiring processing at a higher temperature. In the case of Polygonum tinctorium, the techniques and machinery used for sencha cannot be used to deactivate the indican-degrading enzyme, and it was necessary to find appropriate processing conditions again. The inventors of this invention have tried several methods.

[0023] The aforementioned steaming process was carried out using methods other than steam. Thirty minutes after harvesting the fresh indigo leaves, 10g of the leaves were microwaved at 600W for 5 minutes, and complete deactivation of the enzyme was confirmed. However, this method was unsuitable for deactivating large quantities. Next, boiling the fresh indigo leaves in hot water was attempted, but the indigo extract leached into the boiling water, making it unsuitable as a food processing method for delicious consumption. Ultimately, it was confirmed that steaming in a steam environment of 100°C or higher for more than 2 minutes was the optimal processing method for completely deactivating the indican-degrading enzyme without causing the indigo drip to leach out, and this condition was established as an essential condition for stopping the enzymatic decomposition reaction of indican.

[0024] The purpose of this invention is not to harvest indigo components, but rather to deliciously incorporate into the body the many secondary metabolites, beneficial polyphenols, and other components contained in Japanese indigo. Therefore, all parts of the Japanese indigo plant—leaves, stems, flowers, and seeds—are utilized without exclusion to ensure that all beneficial components are absorbed. No part of the produced Japanese indigo plant is discarded.

[0025] Furthermore, by drying the leaves to less than 20% of their original weight during the drying process, bacterial growth within the dried leaves was suppressed, preventing spoilage and ensuring a long shelf life.

[0026] The steamed indigo of this invention can be used not only as tea leaves but also as a delicious food ingredient. It is possible to do so. For example, the rehydrated vegetables can be used as an ingredient, or the cooking liquid can be used as vegetable broth in cooking. Vegetable broth can be used in a wide variety of dishes, including indigo dressing, broth for ochazuke (rice with tea), and broth for hot pot.

[0027] Furthermore, Polygonum tinctorium has been used since ancient times for its medicinal properties, and steamed Polygonum tinctorium is useful for adding to bathtubs at home or in hot spring facilities to create medicinal baths.

[0028] A taste questionnaire was conducted to compare tea brewed with steamed and bleached indigo produced using the present invention with tea brewed with commercially available indigo tea produced using conventional methods. Tea was brewed using steamed and bleached indigo and commercially available indigo tea produced using conventional methods, and 10 subjects were asked to taste and compare the teas, and rate them on six questions. The ratings for each item were answered using a five-point scale, and the average values ​​were compared for verification. In all questions regarding taste characteristics, appearance characteristics, and other aspects, the steamed and dried indigo tea leaves received high marks.

[0029] Through this invention, it has been confirmed that tea leaves produced using steamed and bleached indigo can be used to brew a more delicious tea compared to indigo tea leaves produced by conventional methods.

Claims

1. In a method for producing steamed dried indigo leaves, which are edible dried leaves of Polygonum tinctorium, The steaming process involves steaming the harvested indigo plants with steam to produce steamed indigo, A drying process is performed to produce dried indigo by drying the steamed indigo obtained in the steaming process using sunlight or a dryer, A roasting step is performed in which the dried indigo obtained in the drying step is roasted to produce distilled indigo, A method for producing steamed and dried indigo, which is edible dried indigo leaves.

2. In a method for producing steamed dried indigo leaves, which are edible dried leaves of Polygonum tinctorium, according to claim 1, The aforementioned steaming process involves steaming the indigo plants with steam within 120 minutes of harvesting to produce steamed indigo. The steaming process, The steamed indigo obtained in the aforementioned steaming process is dried in the sun or in a drying machine, and then the harvested indigo is dried. The drying process produces dried indigo, which is dried until its weight is less than 20%, A roasting step is performed in which the dried indigo obtained in the above drying step is roasted at a temperature of 150°C or higher to produce steamed indigo. A method for producing steamed and dried indigo, which is edible dried indigo leaves containing [specific ingredient].

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