Method for inhibiting softening of persimmon fruit

Abstract

To provide methods and agents for inhibiting softening of persimmon fruits.SOLUTION: Methods for inhibiting softening of persimmon fruits include the step of exposing persimmon fruits to citric acid or salts thereof.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for inhibiting softening of persimmon fruits and an agent for inhibiting softening. [Background technology]

[0002] Persimmons are fruits of the genus Diospyros in the family Ebenaceae, and are cultivated all over Japan. In recent years, in order to develop new sales channels, there have been efforts to export persimmons overseas via sea transport, which is inexpensive and allows for large-scale transportation. Persimmon fruits soften early after harvest. It has been revealed that one of the causes of early softening is the activation of cell wall modifying enzymes by ethylene produced from the calyx of the fruit (Non-Patent Document 1). Techniques for preventing softening after harvest include preventing drying by using freshness-preserving films or low-moisture-permeable cardboard. It is also known that treatment with 1-methylcyclopropene (1-MCP), an ethylene inhibitor, can maintain freshness and inhibit softening.

[0003] Low temperature management is the most effective method for preserving the quality of fruits and vegetables, and nowadays, a low temperature distribution technology system (cold chain) has been developed, and long-term and long-distance transportation to overseas countries is also carried out using the cold chain. However, softening due to low temperature damage during and after long-term low temperature storage is a problem. Low temperature damage is said to occur due to changes in membrane structure associated with the phase transition of biomembrane fatty acids, increased permeability, changes in membrane enzymes, abnormalities in respiratory metabolism, and abnormalities in biomembranes and enzyme proteins due to active oxygen species generated by low temperature stress, and the mechanism of fruit softening due to low temperature damage is different from that of softening at room temperature. For example, it has been reported that the above-mentioned 1-MCP treatment reduces low temperature damage, but does not sufficiently suppress the occurrence of fruit softening. On the other hand, it has been reported that a combination of 1-MCP treatment and oxalic acid treatment of persimmon fruits delays the decrease in fruit firmness after low-temperature storage (Non-Patent Document 2). However, although oxalic acid is used as a food additive in Japan, it is a highly toxic compound that is not permitted to remain in food, making it difficult to directly apply the softening inhibition technology described in Non-Patent Document 2. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Bull. Natl. Inst. Fruit Tree Sci. 2007, 6, 11-22 [Non-Patent Document 2] Postharvest Biology and Technology, 2018, 137, 134 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention relates to providing a method for inhibiting softening of persimmon fruits and an agent for inhibiting softening. [Means for solving the problem]

[0006] The present inventors have conducted various investigations into techniques for preventing softening of persimmon fruit caused by low-temperature injury and have found that softening after low-temperature storage can be prevented by contacting the fruit with citric acid.

[0007] That is, the present invention relates to the following 1) and 2). 1) A method for inhibiting softening of persimmon fruit, comprising a step of contacting persimmon fruit with citric acid or a salt thereof. 2) An agent for inhibiting the softening of persimmon fruit, the active ingredient of which is citric acid or its salt. Effect of the Invention

[0008] According to the present invention, softening of persimmon fruits after low-temperature storage can be suppressed, and the quality of persimmon fruits can be maintained even after long-term and long-distance transportation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The method for inhibiting softening of persimmon fruit of the present invention includes a step of contacting persimmon fruit with citric acid or a salt thereof. In the present invention, the persimmon (Diospyros kaki Thunb.) is a fruit tree of the genus Diospyros in the family Ebenaceae. Persimmon varieties include astringent persimmons such as Hiratanenashi, Tonewase, Nakataniwase, Taten, Koshu Hyakume, Hachiya, Fuji, Atago, and Yamato; incompletely sweet persimmons such as Nishimurawase and Fude; and sweet persimmons such as Jiro, Fuyu, Taiaki, and Soaki. Any variety can be used in the present invention, but it is preferable to use Tonewase and Hiratanenashi.

[0010] It is preferable to use persimmon fruits that have been treated with 1-methylcyclopropene (1-MCP) after harvesting in order to suppress the ripening of the harvested fruits. For example, 1-MCP treatment can be performed by exposing persimmon fruits to a maximum concentration of 1 ppm of 1-MCP for 12 to 24 hours under sealed conditions. In addition, 1-MCP treatment is generally performed using the commercially available Smart Fresh fumigant (available from Agrofresh Japan LLC). In addition, if the persimmon is an astringent persimmon, a process for removing astringency may be carried out. Examples of the process for removing astringency include known methods such as carbonic acid removal and alcohol removal. The 1-MCP treatment and the process for removing astringency may be carried out simultaneously.

[0011] Examples of the salt of citric acid include alkali metal salts such as monosodium citrate, trisodium citrate, and tripotassium citrate. Citric acid or a salt thereof may be a solvate (e.g., a hydrate) or a non-solvate, and both are included. In the present invention, citric acid or a sodium salt thereof is preferred.

[0012] The contact between the persimmon fruit and citric acid or a salt thereof can be carried out by any means as long as citric acid can be supplied to the persimmon fruit, and examples of such means include immersing the persimmon fruit in an aqueous solution of citric acid or a salt thereof, spraying the persimmon fruit with an aqueous solution of citric acid or a salt thereof, applying the aqueous solution of citric acid or a salt thereof to the persimmon fruit using a brush, etc. The contact may be carried out under normal pressure, reduced pressure, or increased pressure, but is preferably carried out under normal pressure from the viewpoint of operability. The concentration of the aqueous solution of citric acid or a salt thereof is preferably 0.1 to 59 w / v%, more preferably 0.5 to 5 w / v%, and even more preferably 1.5 to 5 w / v%, from the viewpoints of the amount required to exert the effect and ease of treatment. The amount of the aqueous solution of citric acid or a salt thereof used is preferably 1 to 20 times (by mass, the same applies below) the amount of the persimmon fruit, more preferably 2 to 5 times. For example, when the persimmon fruit is immersed in the aqueous solution of citric acid or a salt thereof, the aqueous solution used once for immersion can be reused continuously for the next persimmon fruit, etc.

[0013] The temperature at which persimmon fruit is contacted with citric acid or a salt thereof is preferably 5 to 70°C, more preferably 10 to 50°C, and most preferably 20 to 50°C, from the viewpoints of effect expression and ease of treatment.

[0014] The contact time between the persimmon fruit and citric acid or a salt thereof is preferably 5 to 120 minutes, more preferably 5 to 60 minutes, and most preferably 15 to 45 minutes, from the viewpoints of effect expression and ease of treatment.

[0015] This process preferably further includes a step of contacting the persimmon fruit with at least one selected from chitosan and a surfactant. By contacting the persimmon fruit with at least one selected from chitosan and a surfactant in addition to citric acid, softening after low-temperature storage can be further suppressed. The order of contacting persimmon fruit with citric acid or its salt, chitosan, and surfactant is not particularly limited, and they can be contacted in any order. From the viewpoint of efficiency, it is preferable to premix citric acid or its salt with at least one selected from chitosan and surfactant, and then contact the mixture with persimmon fruit. In this embodiment of the invention, the contact method, temperature, time, etc. are the same as those described above.

[0016] Chitosan (β-1,4-poly-D-glucosamine) is a deacetylated product of chitin (β-1,4-poly-N-acetyl-D-glucosamine), and can be produced, for example, by treating chitin with alkali at high temperature. Chitosan may be a low molecular weight chitosan further hydrolyzed with an acid or enzyme, chitosan oligosaccharide, etc. The origin of chitosan is not particularly limited, and any of chitosan derived from animals (shrimp, crab, insects, etc.) and plants can be used. The degree of deacetylation of chitosan is preferably 80 mol % or more. The degree of deacetylation of chitosan can be measured by colloid titration.

[0017] The concentration of the aqueous chitosan solution used for contact with persimmon fruit is preferably 0.1 to 10 w / v %, more preferably 0.5 to 2 w / v %. The amount of the aqueous chitosan solution used is preferably 1 to 20 times, and more preferably 2 to 5 times, the amount of the persimmon fruit.

[0018] Examples of the surfactant include ionic surfactants (anionic surfactants, cationic surfactants, amphoteric surfactants), nonionic surfactants, polymeric surfactants, biosurfactants, etc. The surfactant may be one type or a mixture of two or more types. From the viewpoint of applicability to foods, the surfactant is preferably at least one selected from anionic surfactants and nonionic surfactants.

[0019] Anionic surfactants have negatively charged hydrophilic groups as hydrophilic sites, such as carboxylates, sulfates, sulfonates, ethoxy sulfates, ethoxy acetates, and phosphates. Specific examples include fatty acid salts (potassium oleate soap, potassium castor oil soap, etc.), alkyl ether carboxylates, polyoxyalkylene alkyl ether carboxylates, N-acyl amino acid salts, alkyl sulfates, polyoxyalkylene alkyl ether sulfates, polyoxyalkylene alkenyl ether sulfates, sulfosuccinic acid alkyl ester salts, polyoxyalkylene sulfosuccinic acid alkyl ester salts, α-olefin sulfonates, N-acyl alkyl taurine salts, etc.

[0020] Nonionic surfactants have uncharged hydrophilic groups. Examples of nonionic surfactants include those having a polyoxyethylene chain, such as polyoxyethylene alkyl ethers, polyoxyethylene alkenyl ethers, polyoxyethylene polyoxypropylene glycols, polyoxyethylene polyoxypropylene alkyl ethers, polyoxyethylene polyoxypropylene alkenyl ethers, polyoxyethylene fatty acid esters, polyoxyethylene resin acid esters, polyoxyethylene glycerin fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, polyoxyethylene castor oil, and polyoxyethylene hydrogenated castor oil; polyglycerin fatty acid esters, glycerin fatty acid esters, ethylene glycol fatty acid esters, propylene glycol fatty acid esters, butylene glycol fatty acid esters, sorbitan fatty acid esters, sucrose fatty acid esters, and alkyl glucosides. The HLB of the nonionic surfactant is preferably 1 to 17, more preferably 4 to 14. Here, HLB (hydrophile-lipophile balance) indicates the molecular weight of the hydrophilic group portion in the total molecular weight of the surfactant. HLB is calculated by the Griffin formula.

[0021] Of the anionic surfactants and nonionic surfactants, from the viewpoint of exerting the effect, it is preferable to contain at least one selected from polyoxyethylene resin acid esters, sorbitan fatty acid esters, and castor oil potassium soap, and it is more preferable to contain a sorbitan fatty acid ester. From the viewpoint of exerting the effect, the content of the sorbitan fatty acid ester in the surfactant is preferably 20 to 100% by mass, and more preferably 50 to 90% by mass.

[0022] The surfactant may be used by mixing it in advance with a solvent for dissolving or dispersing it in. Examples of the solvent include alcohol-based solvents (ethanol, 1-butanol, isobutanol, etc.) and hydrocarbon-based solvents (light liquid isoparaffin, etc.). When the surfactant is dissolved or dispersed in the solvent, the concentration of the surfactant in the mixed liquid is preferably 1 to 90 w / w %, and more preferably 4 to 71 w / w %.

[0023] The concentration of the surfactant solution used for contact with persimmon fruit is preferably 0.001 to 1 w / v %, and more preferably 0.01 to 0.1 w / v %. The amount of the surfactant solution used is preferably 1 to 20 times, and more preferably 2 to 5 times, the amount of the persimmon fruit.

[0024] After the contact step, the mixture is wiped off, washed with water, dehydrated, dried, etc. as necessary, and then stored at a low temperature. Note that since citric acid is highly safe, washing is not necessarily required. The temperature during low-temperature storage of persimmon fruits is preferably 0 to 10°C, and most preferably 0°C. The humidity during low-temperature storage of persimmon fruits is preferably 70 to 99%. The storage period is not particularly limited, but is preferably 10 to 45 days, and more preferably 14 to 30 days.

[0025] In the present invention, persimmon fruits are preferably stored at low temperatures in a freshness-preserving film or in a low-moisture-permeable cardboard box in order to prevent drying.

[0026] As shown in the examples below, persimmon fruits that have been subjected to the contact process of the present invention do not show softening during low-temperature storage, and softening is suppressed even when kept at room temperature after low-temperature storage. Therefore, citric acid or a salt thereof, and further a combination of citric acid or a salt thereof with at least one selected from chitosan and a surfactant, are useful as softening inhibitors for suppressing softening of persimmon fruits due to low-temperature damage. EXAMPLES

[0027] Examples 1 to 3 and Comparative Example 1 The following tests were conducted with reference to the method described in Horticultural Research 20(4):455-461.2021. (1) Persimmon The persimmon fruits were obtained 7 days after harvest from outdoor-grown Tono Wase persimmons from Wakayama Prefecture (harvested on October 4, 2021). The persimmon fruits were subjected to a carbon dioxide removal treatment [CO 2 The fumigants were treated with 1-methylcyclopropene (concentration 1 ppm, product name: Smart Fresh fumigant, obtained from AgroFresh Japan LLC) at the same time, and then packed in regular cardboard boxes. These were stored at room temperature until the day of purchase, which was the seventh day after harvest. On the day of purchase, the hardness was measured using a hardness meter described below, and was found to be 2.4 to 3.2 kg (kg / cm 2 These were divided into treatment groups of 4-7, and treated with the following agents.

[0028] (2) Persimmon fruit treatment Comparative Example 1 The obtained persimmon fruits were stored as they were.

[0029] Example 1 As a treatment solution, 3 L of 2 w / v% citric acid solution containing 60 g of citric acid was prepared, and 4-7 persimmon fruits were immersed in this for 30 minutes at room temperature so that the fruits were completely immersed. After that, they were removed from the citric acid solution and wiped off the moisture with Kimwipes.

[0030] Example 2 The same treatment as in Example 1 was carried out except that 3 L of a 1 w / v % citric acid + chitosan aqueous solution in which 30 g of citric acid and 30 g of chitosan (product name: Chitosan 10, obtained from Fujifilm Wako Pure Chemical Industries) were dissolved was prepared as the treatment liquid.

[0031] Example 3 The same treatment as in Example 1 was carried out except that 3 L of a 1 w / v % citric acid + squash aqueous solution in which 30 g of citric acid and 3 mL of a sorbitan fatty acid ester-containing composition (product name: Squash, obtained from Maruwa Biochemical) were dissolved was prepared as the treatment liquid.

[0032] (3) Packaging and storage The treated persimmons were placed in a moisture-proof cardboard box (manufactured by Rengo) in a single layer with the stems facing downwards. The moment when the cardboard boxes were placed in a refrigerator in two rows and four layers was counted as day 0 of storage, and the fruit was kept refrigerated for up to 30 days. Temperature and humidity data inside the cardboard box during the storage period was collected using an ultra-compact temperature and humidity logger (Hygrochron, KN Laboratories). According to this, the temperature during storage was 2-3°C and the humidity was 82-85%. The boxes were then opened at room temperature and left for half a day, then sealed again and stored at 3°C ​​for five days (storage days 30-34). Finally, the boxes were opened and stored at room temperature for one week (storage days 35-42).

[0033] (4) Quality assessment after storage 4-1) Hardness measurement 1 (touch test) Hardness measurements by tactile inspection were conducted seven times in total, on days 30, 35, 36, 37, 38, 39, and 42 of storage. The softening was judged by the touch test as follows: [Tactile survey] I: Stiff enough. II: Overall it becomes quite soft but still firm. III: The fruit is likely to crumble when pressed with your fingers, or some of the flesh is waterlogged. IV: Very soft or part of the skin is broken. Among these, fruits that reached grades III and IV were judged to have softened, and the softening rate (number of softened fruits / total number of fruits x 100) (%) was calculated.

[0034] 4-2) Hardness measurement 2 (measurement of hardness using a hardness tester) Hardness measurements were performed using a fruit hardness meter after 39 days of storage. Using a fruit hardness meter (MK type, Fujiwara Seisakusho), measurements were taken at three points on the equator of one persimmon fruit with an average degree of softening from each treatment group, and the average value was used as the measured value. The results are shown in Table 1.

[0035] [Table 1]

[0036] As shown in Table 1, no softening of fruit was observed in any of the examples during low-temperature storage up to 35 days of storage, but in Comparative Example 1, the fruit began to soften from 36 days of storage when it was returned to room temperature from low temperature, and the softening rate reached 100% by 37 days of storage. In contrast, in Example 1, softening of fruit was observed on the 37th day of storage, but the softening rate was only 33% even on the 39th day of storage. In particular, in Examples 2 and 3, no softening of fruit was observed up to 39 days of storage, and it was confirmed that softening was suppressed for 5 days or more at room temperature compared to Comparative Example 1. Regarding the hardness of the persimmon fruit on the 39th day of storage, in Example 1, the hardness was the same as in Comparative Example 1, but in Examples 2 and 3, it was higher than in Comparative Example 1.

[0037] Examples 4 to 5 and Comparative Example 2 (1) Persimmon The persimmons are Tono Wase persimmons grown outdoors in Wakayama Prefecture (harvested on September 30, 2022, and will be treated to remove bitterness by carbonation [CO2] from October 1). 2The fruits (average 180g) were obtained 5 days after harvest after simultaneous treatment with [concentration of 95% or more, 25°C, 16 hours] and 1-methylcyclopropene [concentration 1 ppm, product name: Smart Fresh fumigation agent, obtained from AgroFresh Japan LLC]. On the day of purchase, one was selected and its hardness was measured using the hardness tester mentioned above. The result was 2.82 kg (kg / cm 2 The individuals for which hardness was measured were excluded, and the remaining individuals were divided into treatment groups of 5 each, and treated with the respective agents shown below.

[0038] (2) Persimmon fruit treatment Comparative Example 2 The obtained persimmon fruits were stored as they were.

[0039] Example 4 As a treatment solution, 3 L of 1 w / v% citric acid solution containing 30 g of citric acid was prepared, and the five persimmons were immersed in this for 30 minutes at room temperature so that the entire persimmon was immersed. After that, they were removed from the citric acid solution and wiped off the moisture with Kimwipes.

[0040] Example 5 The same treatment as in Example 4 was carried out, except that 3 L of a 1 w / v % aqueous solution of trisodium citrate in which 30 g of trisodium citrate dihydrate had been dissolved was prepared as the treatment liquid.

[0041] (3) Packaging and storage The treated persimmons were placed in two layers with the stems facing downwards in moisture-proof cardboard packaging (manufactured by Rengo Co., Ltd.). The moment they were placed in the refrigerator was counted as day 0, and they were kept refrigerated for up to 29 days. Temperature and humidity data inside the cardboard during the storage period was collected using an ultra-compact temperature and humidity logger (Hygrochron, KN Laboratories). According to this, the temperature during storage was -1-3°C, and the humidity was 70-90%. The boxes were then opened at room temperature and left for 6 hours, after which they were sealed again and stored at 3°C ​​for 5 days (storage days 29-33).Finally, the boxes were opened and stored at room temperature for 1 week (storage days 34-41).

[0042] (4) Quality assessment after storage 4-1) Hardness measurement 1 (touch test) Hardness measurements by tactile inspection were conducted seven times in total on days 29, 34, 35, 36, 37, 38, and 41 of storage. The softening was evaluated by touch test in the same manner as in Example 1. The softening rate was N=5 on the 29th, 34th, 35th, 36th, and 37th days, and N=4 on the 38th and 41st days after hardness measurement 2.

[0043] 4-2) Hardness measurement 2 (measurement of hardness using a hardness tester) The hardness was measured using a hardness meter after 37 days of storage. The hardness was measured in the same manner as in Example 1. The results are shown in Table 2.

[0044] [Table 2]

[0045] As shown in Table 2, no softening of the fruit was observed in any of the cases during the low-temperature storage up to 29 days of storage, but in Comparative Example 2, the softening rate reached 80% on the 36th day of storage after returning from low temperature to room temperature. In contrast, in Examples 4 and 5, the softening rate on the 36th day of storage was only 40%. Furthermore, the hardness of the persimmon fruit on the 37th day of storage was higher in Examples 4 and 5 than in Comparative Example 2.

Claims

1. A method for inhibiting the softening of persimmon fruit, comprising the step of contacting the persimmon fruit with citric acid or a salt thereof.

2. The method for suppressing the softening of persimmon fruit according to claim 1, wherein an aqueous solution of 0.1 to 59 w / v% citric acid or its salt is brought into contact with the persimmon fruit in an amount of 1 to 20 times its mass.

3. Furthermore, the method for suppressing the softening of persimmon fruit according to claim 1 or 2, further comprising the step of contacting the persimmon fruit with at least one selected from chitosan and a surfactant.

4. A method for suppressing the softening of persimmon fruit according to claim 3, comprising contacting the persimmon fruit with an aqueous solution of 0.1 to 10 w / v% chitosan in an amount of 1 to 20 times its mass, and / or contacting the persimmon fruit with a surfactant solution of 0.001 to 1 w / v% in an amount of 1 to 20 times its mass.

5. The method for suppressing the softening of persimmon fruit according to claim 3, wherein the surfactant is at least one selected from anionic surfactants and nonionic surfactants.

6. The method for suppressing the softening of persimmon fruit according to claim 3, wherein the surfactant contains a sorbitan fatty acid ester.

7. A persimmon fruit softening inhibitor containing citric acid or its salt as an active ingredient.