Method for promoting biosynthesis of polyphenol

Abstract

To provide a method for promoting the biosynthesis of a polyphenol that can promote biosynthesis of a polyphenol in a site in a plant capable of biosynthesizing a polyphenol without supplying a plasma irradiation aqueous solution to soil in which the plant is grown.SOLUTION: A method for promoting the biosynthesis of a polyphenol comprises a step for performing such a treatment that a plasma irradiation aqueous solution obtained by irradiating an aqueous solution containing sodium L-lactate with atmospheric plasma is applied to a site in a plant having a site capable of biosynthesizing a polyphenol. The method for promoting the biosynthesis of a polyphenol can increase the amount of the polyphenol accumulated in the site. The treatment is preferably performed by injecting or applying the plasma irradiation aqueous solution into or to the site.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for promoting polyphenol biosynthesis. [Background technology]

[0002] Polyphenols, which are biosynthesized in plants, are known to be pigments and components responsible for bitterness and astringency, and have strong antioxidant properties. Anthocyanins are known as representative polyphenols.

[0003] Previously, attempts have been made to increase polyphenols in the fruits of agricultural crops. For example, Patent Document 1 discloses a method for producing agricultural crops, which includes an aqueous solution preparation step of preparing a first aqueous solution containing sodium L-lactate, a plasma irradiation step of irradiating the first aqueous solution with atmospheric pressure plasma to form a second aqueous solution, and an aqueous solution supply step of supplying the second aqueous solution to soil in which agricultural crops such as strawberries are grown. This document describes that the above agricultural crop production method was able to increase anthocyanins in strawberries. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6758681 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the technology of Patent Document 1 has a limitation in that in order to promote polyphenol biosynthesis in the parts of the plant capable of polyphenol biosynthesis, a plasma-irradiated aqueous solution must be supplied to the soil in which the plant is grown, and there is room for improvement.

[0006] The present invention has been made in view of the above-mentioned problems, and aims to provide a method for promoting polyphenol biosynthesis that can promote polyphenol biosynthesis in a part of a plant capable of polyphenol biosynthesis without supplying a plasma-irradiated aqueous solution to the soil in which the plant is grown. [Means for solving the problem]

[0007] One aspect of the present invention is The method for promoting polyphenol biosynthesis includes a step of treating a part of a plant capable of polyphenol biosynthesis with a plasma-irradiated aqueous solution obtained by irradiating an aqueous solution containing sodium L-lactate with atmospheric pressure plasma. [Effects of the Invention]

[0008] The method for promoting polyphenol biosynthesis has the above-described configuration. Therefore, the method for promoting polyphenol biosynthesis can increase the amount of polyphenols accumulated in the plant part. Therefore, the method for promoting polyphenol biosynthesis can promote polyphenol biosynthesis in the part of the plant capable of polyphenol biosynthesis without supplying a plasma-irradiated aqueous solution to the soil in which the plant is grown. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating the flow of a method for promoting polyphenol biosynthesis according to one embodiment carried out in Experimental Example 1. [Figure 2] FIG. 2 shows photographs of the appearance of immature fruit parts of strawberries treated in each manner, taken on the day of treatment and two days after treatment, obtained in Experimental Example 1. [Figure 3] FIG. 3 is a diagram showing the relationship between the type of treatment solution used in each treatment (horizontal axis) and the total anthocyanin content (vertical axis) obtained in Experimental Example 1. [Figure 4]FIG. 4 shows photographs of the appearance of immature fruits (white fruits) of Dutch strawberries that had been subjected to each treatment, taken on the day of treatment and three days after treatment, obtained in Experimental Example 2. [Figure 5] FIG. 5 shows photographs of the appearance of immature fruits (green fruits) of Dutch strawberries that had been subjected to each treatment, taken on the day of treatment and three days after treatment, obtained in Experimental Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0010] The method for promoting polyphenol biosynthesis of this embodiment will be described in detail below.

[0011] The method for promoting polyphenol biosynthesis of this embodiment (hereinafter sometimes simply referred to as the present method) includes a step of treating a part of a plant capable of polyphenol biosynthesis with a plasma-irradiated aqueous solution obtained by irradiating an aqueous solution containing sodium L-lactate with atmospheric pressure plasma.

[0012] This method can increase the amount of polyphenols accumulated in the aforementioned areas, and therefore can promote polyphenol biosynthesis in the areas of plants capable of polyphenol biosynthesis without supplying a plasma-irradiated aqueous solution to the soil in which the plants are grown. This is explained in detail below.

[0013] In this method, the plant having a site capable of polyphenol biosynthesis may be a herbaceous plant or a woody plant. Furthermore, the plant having a site capable of polyphenol biosynthesis may be a vegetable (vegetable) or a fruit tree. Strawberries and the like are not fruit trees but are vegetables (fruit-like vegetables). Furthermore, the plant having a site capable of polyphenol biosynthesis may be an edible plant consumed by humans, or a non-edible plant not consumed by humans.

[0014] Examples of parts of plants capable of polyphenol biosynthesis include fruits, leaves, roots, etc. Fruits may be either simple fruits (including simple fruits and aggregate fruits) or compound fruits, and may be either true fruits or false fruits. Leaves may include not only leaf blades but also petioles, leaf sheaths, etc.

[0015] In addition, if any doubts arise regarding the classification of plants or the definitions of plant parts that are not stated in the detailed description of the invention, the definitions used by the Ministry of Agriculture, Forestry and Fisheries of Japan and the definitions in horticulture shall be followed.

[0016] Specific examples of plant parts capable of biosynthesizing polyphenols include fruit parts of strawberries (such as strawberries), blueberries, apples, cherries, peaches, grapes, prunes, mandarin oranges, tomatoes, and eggplants, leaves of red onions and purple cabbages, and root parts of purple sweet potatoes, red radishes, and red turnips. In this method, the plant part capable of biosynthesizing polyphenols is preferably the fruit part, from the viewpoints of marketability and the effect of adding high value through treatment.

[0017] Specific examples of the polyphenols include anthocyanins, isoflavones, saponins, catechins, etc. When the polyphenol is anthocyanin, the amount of anthocyanin accumulated in the area subjected to the treatment increases, thereby increasing the amount of coloring, such as reddish coloring, in the area, and promoting maturation of the area.

[0018] The part to be treated is preferably in an immature state. The term "the part is in an immature state" refers to a state in which maturity has not yet been reached. Specifically, "the part is in an immature state" includes parts where polyphenol biosynthesis is advanced and parts where polyphenol biosynthesis is not advanced, and includes cases where there is room for the amount of polyphenol accumulated to increase through subsequent polyphenol biosynthesis. More specifically, for example, when the polyphenol is an anthocyanin, "the part is in an immature state" includes parts where anthocyanin-derived coloring (e.g., reddish, which varies depending on the type of plant) is observed and parts where anthocyanin-derived coloring is not observed, and includes cases where there is room for the degree of anthocyanin-derived coloring to increase through subsequent anthocyanin biosynthesis.

[0019] If the part to be treated is immature, for example, by counting backward from the desired date by which the plant part should be at a predetermined maturity, such as the date on which the plant part will be displayed in stores or delivered to consumers, the immature part of the plant can be harvested in advance and treated with a plasma-irradiated aqueous solution, thereby maturing the immature part by the desired date. Furthermore, for example, if there is variation in the degree of maturity of the plant parts after harvest, treating the immature part with a plasma-irradiated aqueous solution can make the maturity level uniform for all parts to be shipped. Therefore, when the part to be treated is immature, the effects of this method can be fully enjoyed.

[0020] The part to be treated is preferably an immature fruit part, as this treatment has a significant effect on adding value to the fruit and is therefore more suitable from the viewpoint of marketability.

[0021] More specifically, in this method, the plant may be a strawberry, and the part to be treated may be an immature fruit of the strawberry. According to this configuration, the reddish coloration is activated in the immature fruit of the strawberry due to an increase in the accumulation of anthocyanin, a type of polyphenol. Therefore, according to this configuration, the maturation of the immature fruit of the strawberry can be promoted.

[0022] In this case, it is preferable to carry out the above treatment at any stage before the immature fruit of the Dutch strawberry changes from a completely white state to a completely red state. With this configuration, the above effects can be obtained more reliably.

[0023] Immature Dutch strawberry fruits can generally be broadly classified into green fruits, which are entirely green; white fruits, which are more mature than green fruits and are entirely white; and colored fruits, which are more mature than white fruits and are a mixture of white and red. Green fruits can be broadly classified into small green (SG) fruits, which are relatively small, and big green (BG) fruits, which are relatively large. White fruits are also sometimes called white (Wt). Immature Dutch strawberry fruits are typically classified after the white (Wt) stage based on the degree of red coloration. They progress through the initial red (IR) stage, which is beginning to turn red but not yet completely red, the full red (FR) stage, which is completely red, and finally reach full maturity. The initial red (IR) stage can also be further subdivided into start red (SR), which is beginning to turn red, and half red (HR), which is about half red. Therefore, any stage in which the immature fruit of the Dutch strawberry described above reaches the stage before it turns from the completely white state to the full red state, in which it turns completely red, includes any stage from the white state to the initial red (IR) state.

[0024] In this method, the plasma-irradiated aqueous solution used in the treatment is prepared by irradiating an aqueous solution containing sodium L-lactate with atmospheric pressure plasma. Note that the aqueous solution containing sodium L-lactate is the one before being irradiated with atmospheric pressure plasma.

[0025] The concentration of sodium L-lactate in the aqueous solution containing sodium L-lactate can be, for example, 0.5 g / L or more and 5 g / L or less. The aqueous solution containing sodium L-lactate is preferably an aqueous solution containing sodium L-lactate that does not contain inorganic salts such as sodium chloride and potassium chloride. In this method, the plasma-irradiated aqueous solution is directly applied to a plant site capable of polyphenol biosynthesis, which makes it easier to eliminate effects other than an increase in the amount of polyphenols accumulated in the treated site.

[0026] Specific examples of aqueous solutions containing sodium L-lactate include sodium lactate Ringer's solution (manufactured by Otsuka Pharmaceutical Factory, Inc., "Lactec (registered trademark)"), sodium lactate Ringer's solution (manufactured by Otsuka Pharmaceutical Factory, Inc., "Lactec (registered trademark)") from which inorganic salts other than sodium L-lactate have been removed, and solutions obtained by diluting these with distilled water.

[0027] The atmospheric pressure plasma irradiated onto the aqueous solution containing sodium L-lactate can be specifically non-equilibrium atmospheric pressure plasma (low-temperature atmospheric pressure plasma). Note that atmospheric pressure plasma as used in this disclosure refers not only to plasma generated under atmospheric pressure, but also to plasma generated under pressures ranging from 0.5 to 2.0 atmospheres. Examples of gases used to generate plasma include rare gases such as Ar, He, and Ne.

[0028] The plasma density is, for example, 1×10 14 cm -3 More than 1×10 17 cm -3The plasma irradiation time can be, for example, 30 seconds or more and 30 minutes or less. The number of plasma irradiations can be one or more. The plasma temperature can be, for example, 1000 K or more and 2500 K or less. The plasma irradiation distance can be, for example, more than 0 mm and 30 mm or less.

[0029] The plasma irradiation apparatus for irradiating an aqueous solution containing sodium L-lactate with atmospheric pressure plasma and other plasma irradiation conditions will be exemplified in the experimental examples described below, but known techniques described in Japanese Patent Nos. 6758681 and 7097543 may also be used as appropriate. The techniques described in these publications may be incorporated into the present disclosure as necessary.

[0030] In this method, the treatment of applying the plasma-irradiated aqueous solution to the plant part can be carried out by injecting or applying the plasma-irradiated aqueous solution to the plant part. In this case, it is possible to ensure an increase in the amount of polyphenols accumulated in the plant part. Note that the treatment of applying the plasma-irradiated aqueous solution to the plant part is a treatment in which the plasma-irradiated aqueous solution is directly applied to the plant part, and therefore cases in which the plasma-irradiated aqueous solution is indirectly supplied to the plant part from the soil via the plant roots are excluded from the start.

[0031] Specifically, the injection treatment of the plasma irradiated aqueous solution into the above-mentioned plant parts can be carried out using a known syringe, injection device, etc. Injection treatment has the advantage of making it easy to accurately adjust the amount of plasma irradiated aqueous solution to be placed inside the above-mentioned plant parts. Furthermore, application of the plasma irradiated aqueous solution to the above-mentioned plant parts can be carried out by various application methods, specifically, spray application, brush application, dipping, etc. Application treatment makes it relatively easy to impregnate the above-mentioned plant parts from the surface to the inside with the plasma irradiated aqueous solution. Furthermore, application treatment makes it easy to treat a large number of parts at once.

[0032] In this method, the amount of the aqueous solution to be applied to the area to be treated can be preferably 0.75% or more of the volume of the area to ensure an increase in the amount of accumulated polyphenols, etc. The amount of the aqueous solution to be applied to the area to be treated can be preferably 10% or less of the volume of the area to prevent moisture damage due to an increase in the moisture content of the area to be treated.

[0033] In this method, the portion to be treated may or may not be detached from the plant, i.e., the portion to be treated may or may not have been harvested from the plant.

[0034] The part to be treated is preferably separated from the plant, and in this case, the treatment can be carried out not only in the plant production field but also, for example, during the distribution process of the plant part, thereby increasing the amount of polyphenols accumulated in the plant part and promoting the maturation of the plant part.

[0035] In this method, after the treatment, the portion is preferably kept at a temperature of 25°C or less for 6 to 72 hours. In this case, the amount of polyphenols accumulated in the portion can be increased while maintaining the freshness of the portion after the treatment. The keeping temperature can be preferably 25°C or less, more preferably 23°C or less, and even more preferably 20°C or less, from the viewpoint of maintaining the freshness of the portion. The keeping temperature can be preferably 4°C or more, more preferably 10°C or more, and even more preferably 15°C or more, from the viewpoints of promoting polyphenol biosynthesis and maintaining the physiological activity of the portion after the treatment. The keeping time can be preferably 6 hours or more, more preferably 12 hours or more, and even more preferably 24 hours or more, from the viewpoints of promoting polyphenol biosynthesis and promoting ripening of the portion after the treatment. The keeping time can be preferably 72 hours or less, more preferably 60 hours or less, and even more preferably 48 hours or less, from the viewpoints of maintaining the freshness of the portion and reducing storage costs.

[0036] The method for promoting polyphenol biosynthesis of this embodiment will be described in more detail below using experimental examples.

[0037] (Experimental Example 1) In Experimental Example 1, as shown in Figure 1, strawberry, a plant with fruits capable of biosynthesizing anthocyanins, was used, and after applying a plasma-irradiated aqueous solution to immature strawberry fruits (hereinafter simply referred to as immature fruits), the coloring of the fruits was confirmed and the anthocyanin content was measured. Details are explained below.

[0038] 1.1 Preparing unripe strawberries Immature strawberries were harvested from cultivated strawberries (variety: Tochiotome, producer: King Farm). Specifically, harvesting was performed by separating the stem (peduncle) from the immature strawberry at the calyx. As strawberries mature, the amount of anthocyanin accumulated in the flesh tissue increases, and the color (redness) derived from anthocyanins increases. Here, immature strawberries in a white state (Wt (white) state) were harvested and used in the experiment, as shown in Figure 1.

[0039] In addition, the small bumps on the surface of strawberries are not seeds; each one is a fruit, and each one contains a seed. Therefore, a single strawberry is an aggregate fruit made up of hundreds of fruits, and the edible reddish part is a false fruit, which is a swollen flower receptacle at the tip of the stem.

[0040] 1.2 Preparation of processing solution An aqueous solution containing sodium L-lactate was prepared by removing inorganic salts other than sodium L-lactate from commercially available sodium lactate Ringer's solution (Otsuka Pharmaceutical Factory, "Lactec (registered trademark)"). The prepared aqueous solution containing sodium L-lactate was irradiated with non-equilibrium atmospheric pressure plasma using Ar gas using a plasma irradiation device described in Japanese Patent No. 6758681 to prepare a plasma-irradiated aqueous solution. The plasma irradiation width was 0.3 mm × 20 mm. The Ar gas flow rate was 2 slm. The applied voltage was 9 kV. The frequency was 60 Hz. The solution volume was 8 mL. The plasma irradiation distance, which is the distance from the plasma irradiation port to the liquid surface, was 3 mm. The plasma irradiation time was 5 minutes. The obtained plasma-irradiated aqueous solution was diluted 25 times with distilled water.

[0041] In addition, as a comparative treatment solution to the above plasma-irradiated aqueous solution, an aqueous solution containing sodium L-lactate before plasma irradiation (hereinafter, this may be abbreviated as "non-plasma-irradiated aqueous solution") and distilled water were prepared. The non-plasma-irradiated aqueous solution was diluted 25 times with distilled water.

[0042] 1.3 Processing As shown in Figure 1, a syringe (TERUMO 22-G needle and TERUMO 1 mL syringe) was used to inject the plasma-irradiated aqueous solution into the stem of an unripe strawberry. In this experimental example, eight unripe strawberries were treated as described above. The amount of plasma-irradiated aqueous solution injected into each unripe strawberry was 0.3 mL. This injection amount of 0.3 mL corresponds to approximately 3.0-6.0% of the volume of the unripe strawberry.

[0043] The unripe strawberries that had undergone the above treatment were kept at a constant temperature for a certain period of time. Specifically, the unripe strawberries that had undergone the above treatment were placed in an artificial climate chamber and kept under light conditions at 15°C for 2 days (48 hours).

[0044] Further, each comparative treatment was carried out in the same manner except that instead of the treatment of injecting the plasma-irradiated aqueous solution, a treatment of injecting distilled water or a treatment of injecting an aqueous solution that had not been irradiated with plasma was carried out.

[0045] 1.4 Confirmation of fruit color and measurement of anthocyanin content The appearance of the unripe strawberries treated with each treatment was visually inspected on the day of treatment and two days after treatment. The results are shown in Figure 2. The anthocyanin content of each unripe strawberry was also measured two days after treatment. The anthocyanin content was measured using a modified version of the method described by Hossain et al. (2018). Specifically, 0.1 g of fruit was ground under liquid nitrogen, and acidic methanol (1% HCl, w / v) was added and the fruit was left to stand at room temperature in the dark for 18 hours. The collected supernatant was then measured for A530 and A657 absorbance using a spectrophotometer (Shimadzu UV-1600). The total anthocyanin content was calculated by (A530 absorbance - 0.25 × A657 absorbance) / FW (where FW is the fresh weight of the fruit) and used for relative comparison. The total anthocyanin content was calculated as the arithmetic mean of the total anthocyanin content measured for eight strawberry fruits two days after each treatment. Figure 3 shows the relationship between the type of treatment solution used for each treatment (horizontal axis) and the total anthocyanin content (vertical axis).

[0046] 1.5 Test Results and Discussion As shown in Figures 2 and 3, when immature strawberries were injected with distilled water as a control, when an unplasma-irradiated aqueous solution (i.e., an aqueous solution containing sodium L-lactate) was injected into the immature strawberries, delayed coloring (reddish coloring) of the fruit and a decrease in anthocyanin content were observed. In contrast, when an unripe strawberry was injected with a plasma-irradiated aqueous solution, accelerated coloring (reddish coloring) of the fruit and an increase in anthocyanin content were observed.

[0047] These results confirmed that it is possible to promote anthocyanin biosynthesis in the parts of plants capable of anthocyanin biosynthesis without supplying a plasma-irradiated aqueous solution to the soil in which the plants are growing.

[0048] In this experimental example, injection of a plasma-irradiated aqueous solution into immature strawberries increased anthocyanin accumulation and promoted ripening of the immature strawberries. However, the results of this experimental example indicate that application of a plasma-irradiated aqueous solution to immature strawberries can also increase anthocyanin accumulation and promote ripening. This is because both injection and application of a plasma-irradiated aqueous solution have in common the direct application of the plasma-irradiated aqueous solution to cellular tissue. Furthermore, in this experimental example, strawberries were used as plants capable of anthocyanin biosynthesis. However, the results of this experimental example indicate that similar effects can be achieved when plants other than strawberries are used. This is because the active species in the plasma-irradiated aqueous solution promote polyphenol biosynthesis. Furthermore, although anthocyanins were investigated in detail as polyphenols in this experimental example, the results of this experimental example indicate that increased accumulation of polyphenols other than anthocyanins can also be expected. Polyphenols act as antioxidants, and it is thought that the components in the plasma-irradiated aqueous solution cause oxygen stress caused by atmospheric pressure plasma in parts such as fruits, thereby promoting the biosynthesis of these antioxidants.

[0049] (Experimental Example 2) Experimental Example 2 investigated the relationship between treatment with a plasma-irradiated aqueous solution and the state of unripe strawberries to which the treatment was applied. Details of this are described below.

[0050] As immature strawberries, immature strawberries in a white state (Wt (white) state) and immature strawberries in a green state (BG (big green) state), which is the stage before the white state, were prepared as in Experimental Example 1. In addition, in both of these immature strawberries, the stem (peduncle) and the immature strawberry were separated.

[0051] These immature strawberries were treated by injecting a plasma-irradiated aqueous solution, a non-plasma-irradiated aqueous solution, or distilled water in the same manner as in Experimental Example 1. In this experiment, when white immature strawberries were used, the number of immature strawberries in each treatment was 8. When green immature strawberries were used, the number of immature strawberries in each treatment was 10.

[0052] The treated unripe strawberries were placed in an artificial climate chamber and kept under light conditions at 15°C for 3 days (72 hours). The results are shown in Figures 4 and 5.

[0053] As shown in Figures 4 and 5, when immature strawberries in a white state were used as the immature strawberries, ripening proceeded more efficiently and in a shorter time than when immature strawberries in a green state were used.

[0054] The above results confirmed that treatment with a plasma-irradiated aqueous solution after the fruit has turned white is preferable from the standpoint of efficiency in promoting ripening.

[0055] In this experimental example, no discoloration (reddish discoloration) of the fruit was observed when the immature strawberries were green. However, this result suggests that the more immature the immature strawberries, the longer the holding time after treatment is desirable to promote ripening.

[0056] The present invention is not limited to the above-described embodiments and experimental examples, and various modifications are possible without departing from the spirit and scope of the present invention. Furthermore, the configurations shown in the above-described embodiments and experimental examples can be combined in any manner.

[0057] The features of the present invention are as follows. [1] A method for promoting polyphenol biosynthesis, comprising the step of treating a part of a plant capable of polyphenol biosynthesis with a plasma-irradiated aqueous solution obtained by irradiating an aqueous solution containing sodium L-lactate with atmospheric pressure plasma. [2] The treatment is performed by injecting or applying the plasma irradiated aqueous solution to the site. The method for promoting polyphenol biosynthesis described in [1]. [3] The part to be treated is separated from the plant. The method for promoting polyphenol biosynthesis according to [1] or [2]. [4] The polyphenol is an anthocyanin. The method for promoting polyphenol biosynthesis according to any one of [1] to [3]. [5] The part to be treated is an unripe fruit part. The method for promoting polyphenol biosynthesis according to any one of [1] to [4]. [6] the plant is strawberry, The part to be treated is an immature fruit part of the Dutch strawberry. The method for promoting polyphenol biosynthesis according to any one of [1] to [5]. [7] The treatment is carried out at any stage from when the fruit is entirely white to when it is completely red and ripe. [6] The method for promoting polyphenol biosynthesis described in [6]. [8] The amount of the plasma irradiation aqueous solution applied to the area to be treated is 0.75% or more and 10% or less of the volume of the area. The method for promoting polyphenol biosynthesis according to any one of [1] to [7]. [9] After the treatment, the site is kept at a temperature of 25°C or less for 6 hours to 72 hours. The method for promoting polyphenol biosynthesis according to any one of [1] to [8].

Claims

1. A method for promoting polyphenol biosynthesis, comprising the step of treating a part of a plant capable of polyphenol biosynthesis with a plasma-irradiated aqueous solution obtained by irradiating an aqueous solution containing sodium L-lactate with atmospheric pressure plasma.

2. The treatment is performed by injecting or applying the plasma irradiated aqueous solution to the site. The method for promoting polyphenol biosynthesis according to claim 1.

3. The part to be treated is separated from the plant. The method for promoting polyphenol biosynthesis according to claim 1.

4. The polyphenol is an anthocyanin. The method for promoting polyphenol biosynthesis according to any one of claims 1 to 3.

5. The part to be treated is an unripe fruit part. The method for promoting polyphenol biosynthesis according to any one of claims 1 to 3.

6. the plant is strawberry, The part to be treated is an immature fruit part of the Dutch strawberry. The method for promoting polyphenol biosynthesis according to any one of claims 1 to 3.

7. The treatment is carried out at any stage before the fruit part changes from a white fruit state where the whole fruit is white to a full red state where the whole fruit is red. The method for promoting polyphenol biosynthesis according to claim 6.

8. the amount of the plasma irradiation aqueous solution applied to the area to be treated is 0.75% or more and 10% or less of the volume of the area; The method for promoting polyphenol biosynthesis according to any one of claims 1 to 3.

9. After the treatment, the site is maintained at a temperature of 25°C or less for 6 hours to 72 hours. The method for promoting polyphenol biosynthesis according to any one of claims 1 to 3.

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