Maturation inhibitor, and method for inhibiting maturation using the same

Abstract

We provide an inexpensive maturation inhibitor that is less prone to precipitation and gelation. [Solution] The present invention is a ripening inhibitor that coats fruits and the like to suppress their deterioration. The ripening inhibitor of the present invention consists of an aqueous solution of silk fibroin with a weight-average molecular weight of less than 10 kDa, as measured by gel filtration chromatography of silk fibroin.

Description

Technical Field

[0001] This invention relates to a technique for suppressing the ripening of plant fruits and the like using silk fibroin.

Background Art

[0002] Silk fibroin is a natural fibrous protein obtained from silkworm cocoons. Silkworm cocoons are mainly composed of two types of proteins, silk fibroin and sericin, and silk fibroin can be obtained by separating sericin.

[0003] Techniques for applying silk fibroin to plant fruits and the like to suppress their ripening are conventionally known (see, for example, Non-Patent Document 1 and Patent Document 1).

[0004] In Non-Patent Document 1, a technique is disclosed in which silk fibroin applied by immersing strawberries or bananas in an aqueous silk fibroin solution is subjected to steam treatment in a vacuum to increase the proportion of the β-sheet structure of silk fibroin and effectively suppress the ripening of plants.

[0005] Also, in Patent Document 1, a method for suppressing the deterioration of freshness of food during transportation by coating the food during transportation with an aqueous silk fibroin solution is disclosed. In Patent Document 1, examples of spraying an aqueous silk fibroin solution on leaves such as spinach are reported.

[0006] Thus, coating with silk fibroin is performed by immersion or spraying. However, since the aqueous silk fibroin solution causes silk fibroin to precipitate and gel, there is a problem that the concentration of silk fibroin decreases and silk fibroin cannot be sufficiently coated.

[0007] Therefore, Patent Document 2 discloses a method for producing an aqueous solution of silk fibroin that does not precipitate or gel even when left standing for a long period of time. The production method in Patent Document 2 describes that an aqueous solution of silk fibroin with a weight-average molecular weight of 10 kDa to 50 kDa, obtained by gel filtration chromatography, can be obtained that does not precipitate or gel over a long period of time. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Special Publication No. 2023-532989 [Patent Document 2] Patent No. 6019506 [Non-patent literature]

[0009] [Non-Patent Document 1] Silk Fibroin as Edible Coating for Perishable Food Preservation;B. Marelli, MA Brenckle, DL Kaplan, FG Omenetto;Scientific Reports;06 May 2016 [Non-Patent Document 2] Chung, DE; Um, IC "Effect of molecular weight and concentration on crystallinity and post drawing of wet spun silk fibroin fiber", Fibers and Polymers, Vol. 15, pp. 153-160 (2014). [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] However, the manufacturing method described in Patent Document 2 has the problem that the resulting silk fibroin aqueous solution is expensive because it includes a dissolution step with a neutral salt, which is generally performed in the silk fibroin manufacturing process, followed by a desalting step using a dialysis membrane, and then further heating / cooling and microfiltration steps. [Means for solving the problem]

[0011] This invention has been made in view of the above problems, and aims to provide an inexpensive aqueous solution of silk fibroin for inhibiting plant maturation that does not precipitate or gel over a long period of time.

[0012] The invention made to solve the above problem involves coating a part of a plant, which consists of at least a portion of the plant, with a coating to suppress the maturation of the part to be treated. to It is a maturation inhibitor, The part to be processed is the fruit of a banana, strawberry, bell pepper, green plum, grape, mango, or avocado, or the edible part of broccoli. The weight-average molecular weight of silk fibroin, as measured by gel filtration chromatography, is 1kDa or more It is characterized by consisting of an aqueous solution of silk fibroin with a density of less than 10 kDa. Here, "maturity" is not limited to the ripening of fruits, etc., but also includes plant growth, overripening, decay, and mold. This includes all changes that impair the quality of the plant, such as the occurrence of [unspecified disease / malfunction].

[0013] In this way, by setting the weight-average molecular weight of silk fibroin to less than 10 kDa, the silk fibroin does not precipitate or gel, even without the heating, cooling, and microfiltration steps after the desalting step, as described in Patent Document 2. In other words, the number of steps can be reduced compared to the silk fibroin manufacturing method of Patent Document 2, so an aqueous solution of silk fibroin can be provided at a low cost. Furthermore, because the silk fibroin does not precipitate or gel, an aqueous solution of silk fibroin with sufficient concentration can be used to immerse plants or spray plants.

[0014] Furthermore, the β-sheet structure in the membrane structure formed by silk fibroin contributes significantly to the inhibition of plant maturation by silk fibroin (see Non-Patent Literature 1, p4 "Gas diffusivity through silk membranes."), and it is conventionally known that this β-sheet structure is difficult to form when silk fibroin has a low molecular weight (see Non-Patent Literature 2). Therefore, there was a concern that if the weight-average molecular weight of silk fibroin was 10 kDa or less, the formation of the β-sheet would be suppressed, and thus the plant maturation inhibition effect would not be obtained. However, it is thought that by using silk fibroin with a low average molecular weight, the amount of silk fibroin with a small molecular weight that can penetrate into the interior of the plant may increase, and this may suppress plant maturation. It is also possible that the higher molecular weight silk fibroin in the molecular weight distribution may form the β-sheet structure. The inventors have confirmed that there are plants in which maturation can actually be inhibited by coating many plants with silk fibroin with a weight-average molecular weight of less than 10 kDa. In other words, this invention has discovered a new application for silk fibroin with a weight-average molecular weight of less than 10 kDa: the suppression of plant maturation.

[0015] The maturation inhibitor according to the present invention At Weight-average molecular weight of silk fibroin of 1 kDa or more, less than 10 kDa The reason for this is, If silk fibroin is broken down to a weight-average molecular weight of less than 1 kDa, the properties of silk fibroin may be impaired, potentially preventing it from adequately suppressing plant maturation. That is the reason.

[0016] In the maturation inhibitor according to the present invention, the concentration of silk fibroin is preferably 2 wt% to 12 wt%. This allows for more effective suppression of plant maturation.

[0017] The ripening inhibitor according to the present invention preferably has a temperature of 2°C or higher and 6°C or lower. By doing so, precipitation and gelation of silk fibroin can be more effectively suppressed. Also, ripening can be effectively suppressed when applied to plants.

[0018] The treatment target part of, Banana, strawberry, bell pepper, green plum, grape, mango, or avocado The fruit of persimmon, or the edible part of broccoli The reason for this is, By doing so, ripening of the treatment target part can be more effectively suppressed. Therefore 。

[0019] The ripening inhibitor according to the present invention may contain a neutral salt and / or alcohol. In the desalting process, it is difficult to completely remove the neutral salt and alcohol in terms of economy. By allowing the remaining neutral salt and alcohol in the ripening inhibitor to an extent that does not damage the value of fruits and the like, the ripening inhibitor can be obtained economically.

[0020] The present invention is a ripening inhibition method capable of inhibiting the ripening of a treatment target part composed of at least a part of a plant, and as a ripening inhibitor, a silk fibroin aqueous solution having a weight average molecular weight measured by gel filtration chromatography of less than 1kDa or more 10 kDa is coated, and includes a ripening inhibition method characterized by this.

[0021] In the ripening inhibition method of the present invention, it is preferable to store the coated treatment target part at a temperature of 2°C or higher and 25°C or lower.

[0022] In the maturation suppression method of the present invention, The treatment target part is the fruit of banana, strawberry, bell pepper, green plum, grape, mango, or avocado, or the edible part of broccoli 。

Effects of the invention

[0023] As described above, the ripening inhibitor and ripening inhibition method of the present invention make it possible to economically suppress the ripening of plant fruits and the like. [Brief explanation of the drawing]

[0024] [Figure 1] This table shows the results of the gelation test of the silk fibroin aqueous solution. [Figure 2] This table shows the results of a plant maturation inhibition test using silk fibroin. [Figure 3] This table shows the results of a maturation inhibition test using silk fibroin on a different plant. [Modes for carrying out the invention]

[0025] One embodiment of the present invention will be described in detail below. However, the present invention is not limited to the following embodiment, and appropriate modifications can be made without departing from the spirit of the invention.

[0026] The invention according to this embodiment is a maturation inhibitor comprising an aqueous solution of silk fibroin, which is applied to a target area to inhibit its maturation.

[0027] (Ingredients of silk fibroin) Silk fibroin is derived from silkworm cocoons. Silkworm cocoons mainly consist of two proteins, silk fibroin and sericin. In this embodiment, the raw material for silk fibroin is not particularly limited as long as it is a material derived from silkworm cocoons that has been scouring to sufficiently separate the sericin (hereinafter referred to as "scouring-processed silk fibroin raw material"). Scouring cocoons, scoured raw silk, silk thread, and their fragments and waste threads can be used as appropriate. Materials from which impurities such as oil and pigments have been removed by scouring are preferably used. The scouring rate of the scouring-processed silk fibroin raw material is preferably 65% ​​to 75%.

[0028] (Method of manufacturing silk fibroin) The method for producing silk fibroin is not particularly limited, and known production methods can be used as appropriate. Specifically, in this embodiment, the method for producing an aqueous solution of silk fibroin involves scouring the silk fibroin raw material according to a conventional method to remove sericin, then adding it to an aqueous neutral salt solution and heating and dissolving it (heating and dissolution step) to obtain an aqueous solution of silk fibroin neutral salt. Next, the obtained aqueous solution of silk fibroin neutral salt is desalted (desalting step) to obtain an aqueous solution of silk fibroin. Furthermore, filtration is performed as needed to finally obtain a clear aqueous solution of silk fibroin.

[0029] (Neutral salt) The neutral salt used in the heating and dissolution process is not particularly limited as long as it can effectively dissolve the refined silk fibroin raw material, and any known neutral salt used for this purpose can be used as appropriate. However, calcium chloride (CaCl2) and magnesium chloride (MgCl2) are preferably used, and calcium chloride is particularly preferred.

[0030] (alcohol) In the heating and dissolution step, an alcohol may be mixed with the neutral salt aqueous solution. This can improve the dispersibility and solubility of silk fibroin. Ethanol is preferably used as the alcohol, but isopropanol, butanol, and mixtures thereof can also be used.

[0031] (Temperature and time of neutral salt solution) The temperature of the neutral salt aqueous solution in the heating and dissolution step is not particularly limited, and any known temperature used in this step can be used as appropriate. However, when calcium chloride is used as the neutral salt, 70°C to 135°C is preferred, and when magnesium chloride is used as the salt, 70°C to 125°C is preferred. The processing time depends greatly on the temperature, neutral salt concentration, and the molecular weight of the desired silk fibroin aqueous solution, but at least 30 minutes are required, and under certain conditions it may exceed 24 hours. The optimal conditions should be selected as appropriate from the viewpoint of quality and economy.

[0032] (Desalination method) In the desalination process, any known method used for desalination of the fibroin neutral salt aqueous solution can be used as appropriate, but dialysis or ultrafiltration is preferred. For the dialysis membrane, filters made of cellulose or cellulose ester are preferred, and for the ultrafiltration membrane, polysulfone or polyethersulfone is preferred.

[0033] (Degree of desalination) In the desalting process, desalting removes neutral salts and alcohol to a degree that does not impair the value of the fruit, etc. Complete removal of either is economically impractical; therefore, it is acceptable for neutral salts and alcohol to remain in the fibroin aqueous solution at a certain concentration, which is called substantial desalting. In other words, the "silk fibroin aqueous solution" as defined in the patent claims may contain neutral salts and alcohol. Specifically, if the neutral salt is calcium chloride, a concentration of 1 wt% or less is preferred, and if the alcohol is ethanol, a concentration of 1 wt% or less is preferred.

[0034] (Powdered silk fibroin) A silk fibroin aqueous solution may be formed by dissolving powdered silk fibroin in water. The silk fibroin powder can be obtained by drying the silk fibroin aqueous solution obtained by the above method using known methods such as freeze-drying or spray-drying. Powdering reduces the transportation costs of the silk fibroin.

[0035] (Weight-average molecular weight of silk fibroin) It is important that the weight-average molecular weight (hereinafter referred to as "Mw") of silk fibroin in an aqueous solution of silk fibroin is less than 10 kDa. By keeping the weight-average molecular weight within this range, precipitation and gelation of silk fibroin can be prevented over a long period of time.

[0036] Furthermore, the Mw of silk fibroin in the silk fibroin aqueous solution is preferably 1 kDa or greater. If the Mw of silk fibroin is less than 1 kDa, the molecules become too small to fully obtain the desired properties for plants, which may result in insufficient inhibition of plant maturation, and in addition, the manufacturing costs will be very high, making it uneconomical.

[0037] (Concentration of silk fibroin aqueous solution) The concentration of silk fibroin in the aqueous solution of silk fibroin is preferably 2 wt% to 12 wt%, more preferably 3 wt% to 11 wt%, and even more preferably 4 wt% to 10 wt%. This allows for efficient suppression of the maturation of the treated part.

[0038] (Temperature of silk fibroin aqueous solution) It is preferable to store the silk fibroin aqueous solution at a temperature of 2°C to 6°C. This suppresses the precipitation and gelation of silk fibroin over a longer period compared to storage at room temperature.

[0039] (Processing target section) The part to be treated refers to the part whose maturation is inhibited by coating it with silk fibroin. It is not particularly limited to any part of the plant, and may be a fruit, root, stem, leaf, flower, or any other part.

[0040] (Coating on the part to be treated) In this embodiment, the silk fibroin aqueous solution is applied to the surface of the part to be treated. This coats the surface of the part to be treated with silk fibroin from the silk fibroin aqueous solution. The silk fibroin aqueous solution may be applied to the surface of the part to be treated by brushing or spraying, or the part to be treated may be immersed in the silk fibroin aqueous solution. In this embodiment, since the weight-average molecular weight of the silk fibroin is less than 10 kDa, it does not precipitate or gel and is sufficiently dispersed in the aqueous solution. Furthermore, because it has low viscosity, the silk fibroin can be sufficiently distributed to the surface of the plant even when applied to the part to be treated by brushing, spraying, or immersion. Moreover, because the weight-average molecular weight is low, it is presumed that the proportion of low-molecular-weight silk fibroin within the molecular weight distribution range of the silk fibroin is high, and it is thought that these penetrate into the interior of the part to be treated, thereby effectively suppressing the maturation of the part to be treated.

[0041] (Storage temperature of the part to be processed) The preferred storage temperature for the treated area coated with the silk fibroin aqueous solution is between 2°C and 6°C. Storing at 2°C to 6°C allows for the maturation inhibition effect to be obtained even in plants where the maturation inhibition effect from the silk fibroin aqueous solution is not achieved when stored at higher temperatures.

[0042] <Exam> The gelation test and maturation inhibition test conducted using the silk fibroin aqueous solution according to the examples and comparative examples of the present invention will be described in detail below. However, the present invention is not limited to the following examples.

[0043] <Gellation Test> (Example 1) Raw silk was used as the raw material for silk fibroin, and it was alkali-scouring according to a conventional method. The resulting scoured raw silk was heated, dissolved, and desalted to obtain an aqueous solution of silk fibroin, based on Japanese Patent No. 1118278. The concentration of silk fibroin in the thus obtained aqueous solution was calculated from the weight obtained after evaporation to dryness, and the weight-average molecular weight (Mw) was determined using gel filtration chromatography (Shimadzu LC10 high-performance liquid chromatograph, PROTEIN KW-804 column (Shodex). Mobile phase: 1 / 15M phosphate buffer + 2M urea + 0.1M sodium sulfate. Flow rate: 0.5 mL / min. Column temperature: 40°C. Calibration: standard pullulan). The obtained aqueous solution of silk fibroin had a concentration of 3.1% and an Mw of 9 kDa. When this was left to stand at room temperature and its changes over time were observed, it did not gel even after more than 500 days.

[0044] (Example 2) Using the same lot of refined raw silk as in Example 1, and following the same flow as in Example 1, an aqueous solution of silk fibroin was obtained by doubling the dissolution time. Physical properties were measured in the same manner as in Example 1, and the concentration was 3.6 wt% and Mw 8 kDa. When this solution was left standing at room temperature and its changes over time were observed, no gelation was observed after 430 days.

[0045] (Example 3) Using the same lot of refined raw silk as in Example 1, and following the same flow as in Example 1, an aqueous solution of silk fibroin was obtained by quadrupling the dissolution time. Physical properties were measured in the same manner as in Example 1, and the concentration was 3.1 wt% and Mw 7 kDa. When this solution was left standing at room temperature and its changes over time were observed, no gelation was observed even after 500 days.

[0046] (Example 4) In Example 1, the neutral salt aqueous solution of silk fibroin obtained by heating and dissolving was left to stand at room temperature without desalting, and the changes over time were observed. It did not gel even after 500 days.

[0047] (Example 5) In Example 3, when the neutral salt aqueous solution of silk fibroin obtained by heating and dissolving was left to stand at room temperature without desalting and its changes over time were observed, it did not gel even after 500 days.

[0048] (Comparative Example 1) Using pre-scouring raw silk with less stringent scouring conditions than in Example 1, an aqueous solution of silk fibroin was obtained under the same conditions as in Example 2. Physical properties were measured in the same manner as in Example 1, and the concentration was found to be 6.1 wt% and Mw 13 kDa. When this solution was left standing at room temperature and its changes over time were observed, gelation was confirmed after 38 days.

[0049] (Comparative Example 2) Using the same lot of refined raw silk as in Comparative Example 1, an aqueous solution of silk fibroin was obtained under the same conditions as in Example 1. Physical properties were measured in the same manner as in Example 1, and the concentration was found to be 5.9 wt% and Mw 18 kDa. When this solution was left standing at room temperature and its changes over time were observed, gelation was confirmed after 57 days.

[0050] (Comparative Example 3) Using scraps of silk fabric as the raw material for silk fibroin, an aqueous solution of silk fibroin was obtained using the same flow as in Example 1, but with significantly relaxed dissolution conditions (dissolution temperature lowered by 30°C and dissolution time shortened to 1 / 30th). Physical properties were measured in the same manner as in Example 1, and the concentration was 7.8 wt% and Mw 38 kDa. When this was left to stand under refrigeration and the changes over time were observed, gelation was confirmed after 144 days.

[0051] (Results of the gelation test) Figure 1 shows the results of the gelation tests for Examples 1 to 5 and Comparative Examples 1 to 3. SF in the figure represents silk fibroin.

[0052] (What can be learned from the gelation test results) The gelation test results showed that for the desalted silk fibroin aqueous solution to not gel, it is important that the Mw measured by gel filtration chromatography is less than 10 kDa. Furthermore, the results from Examples 4 and 5, in which no desalting was performed after the heating and dissolution step, showed that the presence of a neutral salt and / or alcohol in the silk fibroin aqueous solution is effective in suppressing gelation. In addition, the results from Comparative Examples 1, 2 and 3 showed that the period until gelation could be extended by storing the silk fibroin aqueous solution in a refrigerator (2°C to 6°C).

[0053] <Maturation Inhibition Test> Next, we will describe a maturation inhibition test of the treated parts using the silk fibroin aqueous solution according to the present invention. The fruits used in this test, with the exception of Pakistani mangoes and Okinawan mangoes, were purchased at Mekkemon Hiroba in Iwade City, Wakayama Prefecture.

[0054] (Bananas, Test Examples 1 and 2) • Test method Commercially available water-soluble silk powder (Mw8kDa) was diluted with distilled water to form a 4 wt% by weight silk fibroin aqueous solution, which was sprayed onto two bunches of bananas. After drying at room temperature (25°C), one bunch was stored at 4°C (Test Example 1) and the other at 20°C (Test Example 2) for 7 days. The maturation process was compared with that of control example 1 (MilliQ water, 4°C) and control example 2 (MilliQ water, 20°C), in which one bunch of bananas was sprayed only with MilliQ water and stored in the same manner for the same period.

[0055] • Test results In both Test Example 1 (4wt%, 4℃) and Control Example 1 (MilliQ water, 4℃), browning of the fruit peel was observed from day 4 of storage, and the browning gradually progressed until day 7 of storage. From day 5 of storage, the browning progression was suppressed in Test Example 1 compared to Control Example 1. In both Test Example 2 (4wt%, 20°C) and Control Example 2 (MilliQ water, 20°C), spots were observed after 3 days of storage, and browning of the fruit peel was confirmed after 4 days of storage. Subsequently, no significant difference was observed between the two until 7 days of storage. The test conditions and test results are summarized in Figure 2.

[0056] (Strawberries, Test Examples 3-6) • Test method In the same manner as in Test Example 1, maturation inhibition tests were conducted for Test Examples 3 to 6 and Control Examples 3 to 6 under the conditions shown in Figure 2. Test examples 5 and 6, and control examples 5 and 6, were conducted on different days using different strawberry varieties than those used in test examples 3 and 4, and control examples 3 and 4.

[0057] • Test results In Test Example 3 (4wt%, 4℃), no discoloration was observed even after 7 days of storage. However, in Control Example 3 (MilliQ water, 4℃), black discoloration was observed from 5 days of storage, and water-soaked discoloration was observed after 7 days of storage. In Test Example 4 (4 wt%, 20°C), mold growth was observed after 4 days of storage, while in Control Example 4 (MilliQ water, 20°C), mold growth was observed after 3 days of storage. In Test Example 5 (10 wt%, 4°C), no discoloration or mold growth was observed even after 7 days of storage, but in Control Example 5 (MilliQ water, 4°C), black discoloration was observed from 3 days onwards. In both Test Example 6 (10 wt%, 20°C) and Control Example 6 (MilliQ water, 20°C), mold growth was observed after 2 days of storage.

[0058] (Cucumber, Test Examples 7-10) • Test method Cucumber storage experiments were conducted under the conditions shown in Figure 2, in the same manner as in Test Example 1, except that the cucumbers were stored in a low-density polyethylene (LDPE) bag (0.02 mm thick) at 4°C and 20°C for 9 days.

[0059] • Test results In control example 7 (MilliQ water, 4°C), stored at 4°C, pitting, a form of chilling injury, was observed from the third day of storage. However, in test examples 7 (4wt%, 4°C) and 9 (10wt%, 4°C), pitting was only observed from the fifth day of storage, indicating an effect of delaying the onset of chilling injury. However, after the ninth day of storage, the development of pitting was observed in all treatment groups. In all three cases—Test Example 8 (4 wt%, 20°C), Test Example 10 (10 wt%, 20°C), and Control Example 8 (MilliQ water, 20°C)—storage was observed during the experiment, and subsequent development of wilting was confirmed in all treatment groups.

[0060] (Bell peppers, Test Examples 11-14) • Test method A storage experiment with bell peppers was conducted under the conditions shown in Figure 2, in the same manner as in Test Example 1.

[0061] • Test results Test examples 12 (4 wt%, 20°C) and 14 (10 wt%, 20°C), stored at 20°C, showed no difference from control example 10 (MilliQ water, 20°C). On the other hand, test examples 11 (4 wt%, 4°C) and 13 (10 wt%, 4°C), stored at 4°C, showed a slight effect of delaying the occurrence of pitting compared to control example 9 (MilliQ water, 4°C). Furthermore, upon examining the internal condition, it was confirmed that browning around the seeds was suppressed in test example 13 (10 wt%, 4°C) compared to control example 9 (MilliQ water, 4°C) and test example 11 (4 wt%, 4°C).

[0062] (Lettuce, Test Examples 15, 16) • Test method One head of lettuce was cut into four quarters, and a lettuce storage experiment was conducted under the conditions shown in Figure 2, in the same manner as in Experimental Example 1.

[0063] • Test results In test example 16 (4 wt%, 20°C), the cut surface browned after one day of storage, and significant browning progressed after three days, with some spoilage also observed. However, in control example 12 (Milli-Q water, 20°C), browning was only observed after three days of storage, and spraying with silk fibroin aqueous solution accelerated the browning. In both test example 16 (4 wt%, 20°C) and control example 11 (Milli-Q water, 20°C), storage was discontinued after three days due to the progression of spoilage. In Test Example 15 (4wt%, 4℃), slight browning was observed from the third day of storage, similar to Test Example 16 (4wt%, 20℃), and by the tenth day of storage, the browning had progressed considerably. On the other hand, in Control Example 11 (4℃, MilliQ water), only slight browning was observed after ten days of storage.

[0064] (Lemon, Test Examples 17, 18) • Test method Lemon storage experiments were conducted under the conditions shown in Figure 2, in the same manner as in Test Example 1. Test Example 18 (4 wt%, 20°C) and control example 14 (Milli-Q water, 20°C) were stored for 10 days. Test Example 17 (4 wt%, 4°C) and control example 13 (Milli-Q water, 4°C) were stored for 6 months to observe changes during long-term storage at 4°C.

[0065] • Test results No changes were observed in any of the test cases or control groups.

[0066] (Green plum, test examples 19-22) • Test method Green plums were sprayed with a silk fibroin aqueous solution under the conditions shown in Figure 2, similar to Test Example 1, and stored for 16 days.

[0067] • Test results In Test Example 20 (4 wt%, 20°C), discoloration to yellow began after 3 days of storage, and by 8 days of storage, all fruits had turned yellow. In Test Example 22 (10 wt%, 20°C), suppression of discoloration to yellow was confirmed, but all fruits turned yellow by 8 days of storage. However, in control example 15 (MilliQ water, 4°C) stored at 4°C, slight browning was observed from the 5th day of storage, and browning was observed in all fruits by the 13th day of storage. In contrast, in test example 21 (10wt%, 4°C), browning was observed from the 3rd day of storage, similar to control example 15, but the degree of browning was milder than in control example 15 even after 16 days of storage. Furthermore, in test example 19 (4wt%, 4°C), no browning was observed even after 16 days of storage, and the appearance was maintained from the time of initial storage.

[0068] It was found that spraying green plums with an aqueous solution of silk fibroin at a concentration of 4 wt% to 10 wt% can suppress browning caused by low-temperature damage at around 4°C (for example, 2°C to 6°C, preferably 3°C to 5°C). Since it is unlikely that the browning suppression effect will change significantly with slight changes in the concentration of silk fibroin, it is thought that a similar browning suppression effect can be obtained even with a concentration of silk fibroin of 2 wt% to 12 wt% or 3 wt% to 11 wt%. In particular, for browning suppression, a concentration of the aqueous solution of silk fibroin of 2 wt% to 6 wt% is preferred, and 3 wt% to 5 wt% is even more preferred. Lower concentrations of silk fibroin are also more economical.

[0069] (Eggplant, Test Examples 23, 24) • Test method Eggplants were sprayed with a silk fibroin aqueous solution under the conditions shown in Figure 2, in the same manner as in Test Example 1, and stored for 8 days. • Test results In both Test Example 23 (4wt%, 4℃) and Test Example 24 (4wt%, 20℃), no difference in appearance change was observed compared to Control Example 17 and Control Example 18.

[0070] (Broccoli, Test Examples 25, 26) • Test method Broccoli was sprayed with an aqueous silk fibroin solution under the conditions shown in Figure 2, in the same manner as in Test Example 1, and stored for 8 days.

[0071] • Test results In both Test Example 26 (4 wt%, 20°C) and Control Example 20 (MilliQ water, 20°C), stored at 20°C, yellowing began from day 1 of storage, and by day 3, the flower buds in both cases had turned yellow. By day 6, mold growth was observed in both cases. In control example 19 (MilliQ water, 4°C) stored at 4°C, yellowing of the flower buds was observed after 6 days of storage, and by 8 days of storage, the yellowing of the flower buds had progressed, and browning of the cut portion was also observed. However, in test example 25 (4wt%, 4°C), neither yellowing of the flower buds nor browning of the cut portion was observed even after 8 days of storage.

[0072] (Shimeji mushroom, Test Example 27, Test Example 28) • Test method Shimeji mushrooms were sprayed with an aqueous silk fibroin solution and stored for 8 days under the conditions shown in Figure 2, in the same manner as in Test Example 1.

[0073] • Test results In storage at 4°C, neither Test Example 27 (4wt%, 4°C) nor Control Example 21 (MilliQ water, 4°C) showed any changes even after 8 days of storage, maintaining their initial state. Under 20°C storage conditions, no differences were observed during storage between Test Example 28 (4wt%, 20°C) and Control Example 22 (MilliQ water, 20°C). Mold growth was confirmed in both cases after 6 days of storage.

[0074] (Enokitake mushroom, Test Example 29, Test Example 30) • Test method Shimeji mushrooms were sprayed with an aqueous silk fibroin solution and stored for 8 days under the conditions shown in Figure 2, in the same manner as in Test Example 1.

[0075] • Test results In storage at 4°C, neither Test Example 29 (4wt%, 4°C) nor Control Example 23 (MilliQ water, 4°C) showed any changes even after 8 days of storage, maintaining their initial state. In storage at 20°C, both Test Example 30 (4wt%, 20°C) and Control Example 24 (MilliQ water, 20°C) showed browning after 3 days of storage, and no difference was observed between the two.

[0076] (Pakistani mango, Test Example 31, Test Example 32) • Test method Pakistani mangoes, which had been air-shipped from Pakistan and stored at 2°C in Japan, were purchased from a retail store and sprayed with a silk fibroin aqueous solution under the conditions shown in Figure 2. They were then dried at room temperature (25°C), placed in the air-shipped cardboard boxes, and stored at 4°C for 16 days. A control sample (25) sprayed with water (Milli-Q water) was treated similarly.

[0077] • Test results In all three tests—Test Example 31 (4 wt%, 4°C), Test Example 32 (10 wt%, 4°C), and Control Example 25 (MilliQ water, 4°C)—some fruit began to show wilting after 6 days of storage, and wilting was observed in all fruit after 16 days of storage. No differences were observed among Test Examples 31, 32, and Control Example 25. No differences were observed in the internal appearance of the fruit among them.

[0078] (Fig, Test Example 33, Test Example 34) • Test method Figs were sprayed with a silk fibroin aqueous solution under the conditions shown in Figure 2, dried at room temperature (25°C), placed in plastic trays, and stored for 6 days. Figs sprayed with water (Milli-Q water) were treated similarly as control example 26.

[0079] • Test results In all three cases—Test Example 33 (4 wt%, 4°C), Test Example 34 (20 wt%, 4°C), and Control Example 26 (MilliQ water, 4°C)—mold growth was observed after 5 days of storage, and no differences were observed between these cases.

[0080] (Plum, Test Example 35, Test Example 36) • Test method A silk fibroin aqueous solution was sprayed onto the entire surface of each plum tree under the conditions described in Figure 2. After drying at room temperature (25°C), the plums were placed in plastic trays and stored for 19 days. A sample sprayed with water (Milli-Q water) was used as control example 27 and treated similarly.

[0081] • Test results In control example 27 (MilliQ water, 4°C), the fruit became overripe after 16 days of storage, and by 19 days, the overripeness had progressed further, causing the fruit to turn dark. In test example 35 (4wt%, 4°C), some fruit became excessively overripe and rotten after 8 days of storage. After that, by 19 days of storage, rotten fruit was observed in almost all of the fruits. In test example 36 (10wt%, 4°C), no difference from control example 27 was observed until 8 days of storage, but by 16 days of storage, excessive overripeness and rot were observed in some fruits. Furthermore, by 19 days of storage, about half of the fruit had rotted.

[0082] In the case of plums, the silk fibroin solution did not improve their shelf life. Plums are thought to be protected by a substance called bloom, which is produced by cells and is found on the surface of the fruit, similar to grapes and blueberries. In this study, it is believed that spraying with the silk fibroin solution removed the bloom, which allowed the plums to rot.

[0083] (Blueberries, Test Example 37, Test Example 38) • Test method Under the conditions shown in Figure 2, an aqueous solution of silk fibroin was sprayed onto the entire blueberry fruit. These were designated as Test Example 37 and Test Example 38, respectively. After drying at room temperature (25°C), they were placed in plastic trays and stored at 4°C for 19 days. A control example (28) was treated similarly with a spray of water (Milli-Q water).

[0084] • Test results In control example 28 (MilliQ water, 4°C), bloom was observed up to 13 days of storage, and the fruit stems were slightly wilted. In test examples 37 (4 wt%, 4°C) and 38 (10 wt%, 4°C), the bloom disappeared after treatment, and wilting of the fruit stems was also observed. However, no difference was observed between control example 28 and test example 37 or 38. Furthermore, no difference was observed between test example 37 and test example 38.

[0085] (Okinawan mango, Test Example 39, Test Example 40) • Test method Okinawan mango fruits were sprayed with 4 wt% and 10 wt% silk fibroin aqueous solutions, respectively, and these were designated as Test Examples 39 and 40. After drying at room temperature (25°C), they were placed in cardboard boxes and stored at 4°C for 37 days. A control sample (29) sprayed with water (Milli-Q water) was treated similarly.

[0086] • Test results In control example 29 (Milli-Q water, 4°C), small spots were observed on the surface from the beginning of storage, but these spots enlarged from day 21 of storage, and by day 30, significant browning had occurred. Subsequently, by day 37 of storage, decay had begun in that area. In test example 39 (4 wt%, 4°C), black spots were similarly observed from the beginning of storage, but these spots enlarged from day 15 of storage, and decay was observed by day 30 of storage. In test example 40 (10 wt%, 4°C), small black spots were also observed from the beginning of storage, and these spots enlarged from around day 30 of storage. However, no fruit that progressed to decay like in control example 29 or test example 39 was observed.

[0087] This revealed that by treating the mangoes with a 10 wt% silk fibroin aqueous solution and storing them at 4°C, they could be stored for 15 days. The test results differed from those of Pakistani mangoes, which is thought to be because Pakistani mangoes are coated with wax for export, while Okinawan mangoes are not.

[0088] (Grapes, Test Example 41) • Test method Grapes (Delaware variety) were sprayed with a 4 wt% silk fibroin aqueous solution (still attached to the vine) as Test Example 40. After drying at room temperature (25°C), they were stored at 4°C. Grapes sprayed with water (Milli-Q water) were used as Control Example 30 and treated similarly.

[0089] • Test results In test example 41 (4 wt%, 4°C), no particular difference was observed in the changes in the appearance of the fruit compared to control example 30 (MilliQ water, 4°C). However, in control example 30 (MilliQ water, 4°C), many fruits detached from the branches and fell off (dropped fruit), whereas in test example 39 (4 wt%, 4°C), almost no fruits dropped.

[0090] The results for Test Examples 1 through 41 are shown in Figure 2.

[0091] (Avocado, Test Examples 42-45) • Test method Test Examples 42 and 43 involved spraying a 4 wt% silk fibroin aqueous solution onto the entire avocado fruit, placing it in a plastic case, allowing it to air dry, and then storing it at 4°C or 20°C for 7 days. Control Examples 31 and 32 involved spraying the fruit with water (Milli-Q water). Later, Test Examples 44 and 45 involved spraying a 1 wt% silk fibroin aqueous solution onto the entire avocado fruit obtained separately and storing it for 7 days in the same manner. Control Examples 33 and 34 involved spraying the fruit with water (Milli-Q water).

[0092] • Test results In Test Examples 42 (4wt%, 4℃) and 43 (4wt%, 20℃), the blackening of the peel was suppressed compared to Control Examples 31 (MilliQ water, 4℃) and 32 (MilliQ water, 20℃). In particular, in Control Example 32 (MilliQ water, 20℃), blackening began on the second day and the entire peel of all fruits turned black within 7 days, whereas in Test Example 43 (4wt%, 20℃), it was only slightly blackened after 7 days. Furthermore, when the fruits were cut open after 7 days of storage, brown discoloration was observed inside in Control Example 32, whereas no discoloration was observed in Test Example 43 (4wt%, 20℃). Test examples 44 (1 wt%, 4°C) and 45 (1 wt%, 20°C) showed no significant differences in changes compared to control example 33 (MilliQ water, 4°C) and control example 34 (MilliQ water, 20°C), respectively, and similar blackening of the skin progressed.

[0093] (Oysters, Test Examples 46, 47) • Test method Using persimmon fruit, a 1 wt% aqueous solution of silk fibroin was sprayed onto the fruit, placed in a plastic case, air-dried, and then stored at 4°C or 20°C for 7 days. These were designated as Test Examples 46 and 47, as shown in Figure 3. Samples sprayed with water (Milli-Q water) were designated as Control Examples 35 and 36.

[0094] • Test results In both Test Example 46 (1 wt%, 4°C) and Test Example 43 (1 wt%, 20°C), no significant differences in appearance were observed compared to Control Example 35 (MilliQ water, 4°C) and Control Example 36 (MilliQ water, 20°C).

[0095] (Kiwi, Test Examples 48, 49) • Test method Using kiwifruit, a 1 wt% silk protein solution was sprayed onto the fruit, placed in a plastic case, air-dried, and then stored at 4°C or 20°C for 7 days. These were designated as Test Examples 48 and 49, as shown in Figure 3. Samples sprayed with water (MilliQ water) were designated as Control Examples 37 and 38.

[0096] • Test results In both Test Example 48 (1 wt%, 4°C) and Test Example 49 (1 wt%, 20°C), no significant differences in appearance were observed compared to Control Example 37 (MilliQ water, 4°C) and Control Example 38 (MilliQ water, 20°C).

[0097] (What we learned from the maturation inhibition experiment) (1) As shown in Figures 2 and 3, it was found that even if the weight-average molecular weight of the silk fibroin used for coating is less than 10 kDa, maturation can be suppressed depending on the type of plant (e.g., bananas, strawberries, bell peppers, green plums, mangoes, grapes, avocados, etc.). The silk fibroin used in this maturation suppression test had a weight-average molecular weight of 8 kDa. However, it is unlikely that a slight change in the weight-average molecular weight of silk fibroin would significantly alter its effect on plant maturation suppression. Therefore, it was found that a weight-average molecular weight of 6 kDa or more and less than 10 kDa is preferable for silk fibroin, and 7 kDa or more and less than 10 kDa is more preferable. (2) The storage temperature for plants coated with silk fibroin was found to be preferably between 4°C and 20°C (for example, 2°C to 25°C, more preferably 3°C to 22°C), as it is unlikely that a small difference in temperature from the tested temperature would result in a significant difference. (3) In some cases, such as bananas, strawberries, bell peppers, green plums, and broccoli, when stored at around 4°C (for example, 2°C to 6°C, preferably 3°C to 5°C, more preferably 4°C, and so on, which is generally considered to have little effect on 4°C), it was found that coating with silk fibroin could suppress maturation more effectively than not coating with silk fibroin. (4) For some plants (e.g., strawberries, bell peppers, mangoes, etc.), it was found that a concentration of silk fibroin aqueous solution around 10 wt% (for example, 8 wt% to 12%, preferably 9 wt% to 11 wt%) was more effective in inhibiting maturation than a concentration of 4 wt%. (5) When storing green plums at around 20°C, the concentration of the silk fibroin aqueous solution It was found that a 10 wt% concentration of silk fibroin solution had a greater maturation inhibitory effect than a 4 wt% concentration, and that when stored at around 4°C, a 4 wt% concentration of silk fibroin aqueous solution had a greater maturation inhibitory effect than a 10 wt% concentration. (6) In grapes, it was found that coating them with silk fibroin and storing them at around 4°C has an effect of suppressing berry drop. (7) In the case of mangoes that were not coated with wax, it was found that coating them with a silk fibroin aqueous solution at around 10 wt% and storing them at around 4°C had an effect of inhibiting maturation.

[0098] (8) In the case of avocados, a maturation inhibition effect was obtained at both 4°C and 20°C by coating silk fibroin with a 4 wt% silk fibroin aqueous solution, while no maturation inhibition effect was obtained at either 4°C or 20°C when a 1 wt% silk fibroin aqueous solution was used. Therefore, it was found that it is preferable to use a silk fibroin aqueous solution of 2 wt% to 6 wt%, preferably 3 wt% to 5 wt%, and to store it at 2°C to 25°C, preferably 3°C to 22°C. (9) For plants with bloom (e.g., plums and blueberries), it was found that spraying with a silk fibroin aqueous solution did not inhibit maturation because the bloom washed off.

[0099] As described above, the maturation inhibitor and maturation inhibition method of the present invention are not limited to the embodiments described above, and can be implemented in various modified and improved forms without departing from the spirit of the present invention. Furthermore, forms that combine the knowledge obtained from each of the above-described test examples are also included in the scope of the present invention.

Claims

1. A maturation inhibitor for coating a target portion of a plant, which consists of at least a part of the plant, to suppress the maturation of the target portion, The part to be processed is the fruit of a banana, strawberry, bell pepper, green plum, grape, mango, or avocado, or the edible part of broccoli. A maturation inhibitor characterized by comprising an aqueous solution of silk fibroin having a weight-average molecular weight of 1 kDa or more and less than 10 kDa, as measured by gel filtration chromatography of silk fibroin.

2. The maturation inhibitor according to claim 1, wherein the concentration of silk fibroin is 2 wt% or more and 12 wt% or less.

3. The maturation inhibitor according to claim 1 or claim 2, wherein the temperature is 2°C or more and 6°C or less.

4. The maturation inhibitor according to claim 1 or claim 2, comprising a neutral salt and / or an alcohol.

5. A method for suppressing the maturation of a part of a plant that is to be treated, comprising at least a portion of the plant, The part to be processed is the fruit of a banana, strawberry, bell pepper, green plum, grape, mango, or avocado, or the edible part of broccoli. A method for inhibiting maturation, characterized by coating with an aqueous solution of silk fibroin having a weight-average molecular weight of 1 kDa or more and less than 10 kDa, as measured by gel filtration chromatography of silk fibroin, as a maturation inhibitor.

6. The maturation suppression method according to claim 5, wherein the coated part to be treated is stored at a temperature of 2°C or more and 25°C or less.

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