Method for producing Japanese pears with suppressed vascular browning of fruit

Abstract

To provide means for suppressing browning of the vascular bundle of a Japanese pear fruit caused by cold storage.SOLUTION: A method for making a Japanese pear with suppressed browning of the vascular bundle of a fruit, includes the step of putting a Japanese pear fruit under high temperature conditions.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing Japanese pears in which vascular browning of the fruit is suppressed, and a method for long-term storage of Japanese pears. [Background technology]

[0002] The Japanese pear cultivar "Rinka" is expected to become popular in warmer regions as a cultivar that can cope with global warming, as it has large fruit with good fruit quality, and flower buds are stable even in warm regions. However, if this cultivar is stored at low temperatures after harvest, the vascular bundles in the flesh will brown within a few days. To mitigate this problem, the fruit should be stored at room temperature (25°C) (Kagoshima Prefectural Agricultural Development Center Research Results for 2017 (http: / / www.pref.kagoshima.jp / ag11 / pop-tech / zenbu / documents / 67478_20180815083434-1.pdf)). However, there are concerns that consumers may store the fruit in a refrigerator after purchase, which could cause the problem. In addition, the quality retention period is limited at room temperature. For these reasons, it is necessary to develop technology that can suppress the problem even when the fruit is stored at low temperatures.

[0003] It has long been known that damage caused by low-temperature storage can be suppressed by placing harvested fruits under high temperatures for a certain period of time. For example, Non-Patent Document 1 describes that low-temperature damage was suppressed by placing tomatoes under 40°C conditions for 24 hours. However, the low-temperature damage described in this document is called pitting, which is the formation of small dents on the fruit surface. There are no known reports that low-temperature damage such as browning of vascular bundles can be suppressed by placing them under high-temperature conditions. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Morimoto 2008, Plant Environmental Engineering vol.20(4), 219-227 Summary of the Invention [Problem to be solved by the invention]

[0005] "Rinka" is often harvested during the hot season of August, and consumers may store it in a refrigerator at home. Furthermore, when stored at room temperature, the quality retention period is short, and the distribution and sales period is limited. The present invention was made against this background, and aims to provide a means for suppressing low-temperature damage that occurs in "Rinka". [Means for solving the problem]

[0006] As a result of extensive research to solve the above problems, the inventors discovered that by placing Rinka fruit under high temperature conditions, the browning of vascular bundles that occurs during refrigeration can be suppressed, and thus completed the present invention.

[0007] That is, the present invention provides the following (1) to (7). (1) A method for producing Japanese pears in which vascular browning of the fruit is suppressed, the method comprising the step of placing Japanese pear fruits under high temperature conditions.

[0008] (2) The method according to (1), wherein the Japanese pear is a Japanese pear whose vascular bundles turn brown when stored in a refrigerator.

[0009] (3) The method according to (2), wherein the Japanese pear whose vascular bundles turn brown upon refrigeration is the Japanese pear cultivar "Rinka" or a Japanese pear derived from the Japanese pear cultivar "Rinka."

[0010] (4) The method according to any one of (1) to (3), wherein the high temperature conditions are temperature conditions that cause heat stress to Japanese pear.

[0011] (5) The method according to any one of (1) to (3), wherein the high temperature condition is a temperature condition of 35 to 65°C.

[0012] (6) A method according to any one of (1) to (5), comprising a step of placing Japanese pear fruit under low-temperature conditions, characterized in that this step is carried out before a step of placing Japanese pear fruit under high-temperature conditions.

[0013] (7) A method for long-term storage of Japanese pears, comprising storing Japanese pears produced by the method according to any one of (1) to (6) under low-temperature conditions. Effect of the Invention

[0014] The present invention provides a method for producing Japanese pears in which browning of the vascular bundles of the fruit is suppressed. The Japanese pear cultivar "Rinka" suffers from chilling injury, in which the vascular bundles of the fruit brown when refrigerated. The method of the present invention can solve this problem of chilling injury. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram showing the method for evaluating vascular bundle browning. The degree of vascular bundle browning on the fruit equator was evaluated on a 6-point scale from 0 (none) to 5 (severe). [Diagram 2] FIG. 13 is a graph showing changes in fruit pulp temperature. [Diagram 3] This is a diagram showing the occurrence of vascular browning in fruits harvested on August 18, 2020. [Figure 4] This is a diagram showing the occurrence of vascular browning in fruits harvested on August 25, 2020. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The present invention will be described in detail below. The present invention relates to a method for producing Japanese pears in which vascular browning of the fruit is suppressed, which is characterized by comprising a step of subjecting Japanese pear fruits to high temperature conditions.

[0017] The Japanese pear used in the present invention is preferably a Japanese pear whose fruit vascular bundles turn brown when stored in a refrigerator. An example of such a Japanese pear is the Japanese pear variety "Rinka". "Rinka" is a variety registered under the Seed and Seedlings Act (Registration Number: 23912, Variety Registered by: National Agriculture and Food Research Organization). Japanese pears produced by using "Rinka" as a breeding parent or by modifying the genes of "Rinka" by genome editing may have the same possibility of having their fruit vascular bundles turn brown when stored in a refrigerator as "Rinka". Such Japanese pears can also be used in the present invention. In this specification, Japanese pears obtained from "Rinka" by breeding or genome editing are referred to as "Japanese pears derived from Rinka".

[0018] An example of the "high temperature condition" in the present invention is a "temperature condition that causes heat stress to Japanese pears". In addition, since heat shock proteins are usually induced by heat stress, the "temperature condition that induces heat shock proteins in Japanese pears" is also an example of the "high temperature condition" in the present invention. Many literatures (e.g., Morimoto 2008, Shokubutsu Kankyo Kogaku vol.20(4), 219-227, Lurie et al. 1998, Postharvest Biology and Technology, vol.14, 257-269, etc.) describe what temperature conditions cause heat stress to plants, so those skilled in the art can appropriately set the "temperature condition that causes heat stress to Japanese pears" by referring to such literatures. The temperature in the "high temperature condition" is not particularly limited as long as it is a temperature that can cause heat stress to Japanese pears, but may be 35 to 65°C, 35 to 55°C, 35 to 50°C, 35 to 45°C, or 38 to 42°C.

[0019] The time for placing under high temperature conditions can be determined according to the temperature, and the higher the temperature, the shorter the time can be, and the lower the temperature, the longer the time can be. Specifically, the time may be 10 to 70 hours, 20 to 60 hours, 30 to 50 hours, or 35 to 45 hours.

[0020] The Japanese pear fruits to be placed under high temperature conditions may be those immediately after harvest or those that have been harvested some time ago.

[0021] Before placing Japanese pear fruits under high-temperature conditions, the fruits may be placed under low-temperature conditions so that the fruits experience greater high-temperature stress. The "low temperature" referred to here may be any temperature that is sufficiently different from the temperature under high-temperature conditions and that allows the fruits to experience high-temperature stress, and may be, for example, a temperature 10 to 30°C lower, or 15 to 25°C lower, than the temperature under high-temperature conditions. The specific temperature under low-temperature conditions depends on the temperature under high-temperature conditions as described above, and may be, for example, a temperature around room temperature (20 to 25°C) or a temperature lower than room temperature (10 to 19°C).

[0022] The time for which the fruit is placed under low-temperature conditions depends on the difference between the temperature under low-temperature conditions (set temperature) and the temperature immediately before being placed under low-temperature conditions, and the greater the temperature difference, the longer the fruit is placed under low-temperature conditions. The specific time is not particularly limited as long as it is a time that causes the fruit to feel high-temperature stress, and may be, for example, 10 to 40 hours, or 20 to 30 hours.

[0023] In Japanese pears produced by the method of the present invention, browning of the vascular bundles of the fruit is suppressed, so that refrigeration does not cause the vascular bundles of the fruit to brown and reduce the commercial value. Therefore, Japanese pears produced by the method of the present invention can be stored for long periods under low-temperature conditions. Storage under low-temperature conditions may be carried out immediately after the treatment under the above-mentioned high-temperature conditions, but they may also be placed under room temperature conditions once and then stored under low-temperature conditions. Note that "low-temperature conditions" here refers to general temperature conditions for long-term storage of Japanese pears, and specifically refers to temperature conditions for refrigerated storage (e.g., 1 to 10°C) and temperature conditions for ice-temperature storage (e.g., -2 to 0°C). EXAMPLES

[0024] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0025] Example 1 (A) Materials and Methods (1) Material The test used fruits of the Japanese pear variety "Rinka" planted at the NARO Fruit and Tea Division (Tsukuba, Ibaraki Prefecture). The fruits were harvested on August 26, 2019, the optimum harvest time, and sorted into an untreated area and a high-temperature treatment area so that the size and ripeness of the fruits in each treatment area were uniform.

[0026] (2) No treatment The harvested fruits were placed in a Japanese pear shipping cardboard box (5 kg box), sealed with packing tape, and placed in a thermostatic chamber set at 4°C.

[0027] (3) High-temperature treatment The harvested fruits were placed in a Japanese pear shipping cardboard box (5 kg box), sealed with packing tape, and placed in a thermostatic chamber set at 15°C. The next day (24 hours after being placed in the 15°C thermostatic chamber), the shipping cardboard box was moved to a thermostatic chamber set at 40°C. Two days later (41 hours after being placed in the 40°C thermostatic chamber) (3 days after harvest), the shipping cardboard box was placed in a thermostatic chamber set at 4°C.

[0028] (4) Measurement of fruit flesh temperature To monitor the flesh temperature, a thermocouple was inserted into the center of the flesh and the flesh temperature was monitored using a data logger (midi Logger GL220, GRAPHTEC).

[0029] (5) Fruit quality survey Fruit quality was evaluated on the day of harvest, immediately after high-temperature treatment (before refrigeration), and 7 and 15 days after refrigeration with or without high-temperature treatment. Eight or more fruits were used for each quality evaluation.

[0030] The ground color of the fruit was evaluated using a ground color chart for Japanese pears. The flesh hardness was measured by scraping off two pieces of the peel facing each other on the equator of the fruit to the size of a 100 yen coin, and the flesh hardness was measured using a fruit hardness meter (FT011, cylindrical plunger with a diameter of 8 mm, Fujidaira Kogyo Co., Ltd.). The sugar content and pH were measured by squeezing the juice from the flesh around the part where the flesh hardness was measured, using a digital sugar content meter (PR101α, Atago) and a pH meter (Fashion C-73, AS ONE). The degree of vascular bundle browning was evaluated on a six-point scale from 0 (absent) to 5 (occurring almost entirely) based on the proportion of vascular bundle browning that appeared on the cut surface after cutting the fruit on the equator (Figure 1). A level of vascular bundle browning of 2 (occurring in about 20-30%) or higher was considered to be a problematic level for commercial products, and the proportion of fruits with vascular bundle browning of 2 or higher was indicated.

[0031] (B) Results (1) Occurrence of vascular browning The average incidence index of vascular bundle browning and the incidence rate of fruits with an incidence index of 2 or higher are shown in the table below. [Table 1]

[0032] As shown in the table, in untreated fruit, the percentage of fruits graded "2" or higher increased with the number of days of refrigeration, but in high-temperature treated fruit, no fruits graded "2" or higher developed even after 15 days of refrigeration. This result suggests that high-temperature treatment is an effective means of suppressing vascular bundle browning.

[0033] (2) Fruit quality other than vascular browning The base color, flesh hardness, sugar content, and pH are shown in the table below. [Table 2]

[0034] Some significant differences were detected in sugar content and pH, but with regard to sugar content, it is possible that the original variation in the fruit used was detected. Also, even if high temperatures had an effect, this is not considered to be a negative effect, as sugar content tends to increase (after harvest, fruit weight decreases due to evaporation from the fruit, so sugar content tends to increase). With regard to pH, when refrigerated without treatment, acid tends to be lost during the refrigeration period (one of the aging phenomena), but since no reduction in acidity was detected in fruit refrigerated after high-temperature treatment, it is possible that the reduction in acidity was suppressed due to the effects of high-temperature treatment, such as the suppression of respiration (acid is mainly consumed through respiration). It has been reported that high-temperature treatment suppresses the respiration rate of fruit. From the above, it is considered that high-temperature treatment does not have a significant effect on fruit quality other than vascular bundle browning.

[0035] (3) Changes in flesh temperature The changes in flesh temperature of four fruits (A to D) are shown in Figure 2. Although they were treated in a thermostatic chamber at 40°C, the flesh temperature only rose to about 38°C.

[0036] Example 2 (A) Materials and Methods (1) Material The test used fruits of the Japanese pear variety "Rinka" planted at the NARO Fruit and Tea Division (Tsukuba, Ibaraki Prefecture). The fruits were harvested on August 18 and 25, 2020, which is the optimum harvest time, and were sorted into an untreated area and a high-temperature treatment area so that the size and ripeness of the fruits in each treatment area were uniform.

[0037] (2) No treatment As in Example 1, the harvested fruits were placed in a cardboard box (5 kg box) for shipping Japanese pears, sealed with packing tape, and placed in a thermostatic chamber set at 4°C.

[0038] (3) High-temperature treatment The high temperature treatment was carried out in three ways: (3-1) With pretreatment As in Example 1, the harvested fruits were placed in a Japanese pear shipping cardboard box (5 kg box), sealed with packing tape, and placed in a thermostatic chamber set at 16° C. The next day (24 hours after being placed in the 16° C. thermostatic chamber), the shipping cardboard box was moved to a thermostatic chamber set at 30° C. or 40° C. Two days later, the shipping cardboard box was placed in a thermostatic chamber set at 4° C.

[0039] (3-2) No pretreatment The harvested fruits were placed in Japanese pear shipping cardboard boxes (5 kg boxes), sealed with packing tape, and moved to a thermostatic chamber set at 30°C, 35°C, or 40°C. After one or two days, the shipping cardboard boxes were placed in a thermostatic chamber set at 4°C.

[0040] (3-3) High temperature treatment followed by room temperature treatment The harvested fruits were placed in a Japanese pear shipping cardboard box (5 kg box), sealed with packing tape, and moved to a thermostatic chamber set at 40°C. After one or two days, the shipping cardboard box was placed in a thermostatic chamber set at 25°C. After five or six days, the shipping cardboard box was placed in a thermostatic chamber set at 4°C.

[0041] (4) Fruit quality survey Fruit quality was evaluated on the day of harvest, immediately after high-temperature treatment (before refrigeration), and 15 days after refrigeration with or without high-temperature treatment. Eight or more fruits were used for each quality evaluation. The ground color, flesh firmness, sugar content, and pH were measured in the same manner as in Example 1. The evaluation of vascular bundle browning was also performed in the same manner as in Example 1.

[0042] (B) Results (1) Test 1 (fruit harvested on August 18, 2020) (1-1) Occurrence of vascular browning The average incidence index of vascular bundle browning and the incidence rate of fruits with an incidence index of 2 or more are shown in Table 3 and Figure 3. [Table 3]

[0043] As shown in Table 3 and Figure 3, 40°C treatment had an inhibitory effect on vascular bundle browning even after one day. On the other hand, 30°C treatment did not have a sufficient effect. The 16°C treatment performed before the 40°C treatment was not necessarily required.

[0044] (1-2) Fruit quality other than vascular browning The base color, flesh hardness, sugar content, and pH are shown in the table below. [Table 4]

[0045] (2) Test 2 (fruit harvested on August 25, 2020) (2-1) Occurrence of vascular browning The average incidence index of vascular bundle browning and the incidence rate of fruits with an incidence index of 2 or more are shown in Table 5 and Figure 4. [Table 5]

[0046] As shown in Table 5 and Figure 4, a certain degree of effect was observed with 35°C treatment, although the effect was less than that with 40°C treatment. The effect was observed even if the product was not refrigerated immediately after high-temperature treatment (even if it was left at room temperature for about a week).

[0047] (2-2) Fruit quality other than vascular browning The base color, flesh hardness, sugar content, and pH are shown in the table below. [Table 6] [Industrial Applicability]

[0048] INDUSTRIAL APPLICABILITY The present invention relates to a method for producing Japanese pears in which vascular browning of the fruit is suppressed, and thus can be used in industrial fields that handle fruits such as Japanese pears.

Claims

1. A method for producing Japanese pears in which vascular browning of the fruit is suppressed, the method being characterized in that: 1) it comprises a step of placing Japanese pear fruits under high temperature conditions, the temperature in said high temperature conditions being 35 to 65°C, and the time for placing the fruits under said high temperature conditions being 10 to 70 hours; and 2) the Japanese pears are the Japanese pear cultivar "Rinka" or Japanese pears derived from the Japanese pear cultivar "Rinka".

2. The method according to claim 1, comprising the step of placing Japanese pear fruits under low-temperature conditions, said step being carried out before the step of placing Japanese pear fruits under high-temperature conditions, wherein the temperature under said low-temperature conditions is 10 to 30°C lower than the temperature under said high-temperature conditions, and wherein the time for placing the fruits under said low-temperature conditions is 10 to 40 hours.

3. A method for long-term storage of Japanese pears, comprising storing Japanese pears produced by the method according to claim 1 or 2 under low-temperature conditions, wherein the temperature under said low-temperature conditions is 1 to 10°C or -2 to 0°C.

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