Method for delaying pericarp browning of litchi after harvest by plant sulfokinin PSK

Abstract

The present invention discloses a method for delaying the browning of litchi pericarp after harvest by plant sulfokinin PSK. (1) Treat litchi with prochloraz, and use it after air-drying the surface moisture; (2) Immerse it in the plant sulfokinin solution, and store it after air-drying. By treating litchi fruits with the PSK solution, under normal temperature storage conditions, the present invention can effectively delay the browning process of litchi pericarp after harvest, maintain a good taste of litchi, improve the commercial fruit rate of litchi, and extend the shelf life of litchi fruits. It has important guiding significance for helping to extend the storage and transportation period of litchi and reducing the post-harvest loss of litchi.

Description

Technical Field:

[0001] The present invention relates to the field of fresh preservation, and particularly to a method for delaying the browning of litchi pericarp after harvest by phytosulfokine PSK. Background Art:

[0002] Litchi belongs to the Sapindaceae plant and is a famous and high-quality fruit native to South China. The litchi industry is a dominant and characteristic industry in South China. The litchi pericarp has bright color, the pulp is sweet, juicy and rich in nutrition. The pericarp is rich in phenolic substances such as anthocyanins and is a natural and excellent antioxidant resource. Litchi has extremely high economic value. However, the harvesting period of litchi is short, and the litchi fruits are extremely prone to browning, mildew and rot after harvest, with difficult fresh preservation, short shelf life, and being difficult to store for a long time and transport over long distances. These factors are the main reasons restricting the market development and export trade of litchi. The storage and fresh preservation of litchi is a bottleneck problem in the development of the litchi industry. At present, many researchers have conducted a large number of studies on the post-harvest physiology and fresh preservation technology of litchi, such as heat treatment, sulfur fumigation, melatonin treatment, nitric oxide treatment, etc., but there is no application of phytosulfokine (abbreviated as PSK) in the post-harvest fresh preservation of litchi fruits. PSK is a novel plant peptide growth regulatory substance discovered by Japanese scholars Matsubyashi et al. in the cell culture medium of asparagus in 1996, consisting of a pentapeptide and two sulfonic groups. In recent years, studies have found that PSK widely exists in most plants, regulates plant growth by promoting cell enlargement and division, and participates in many biological processes such as pollen germination, pollen tube guidance, plant immunity and plant resistance. There are also a few reports on the application of PSK in the post-harvest fresh preservation of fruits and vegetables. For example, PSK can delay the senescence of strawberry fruits during cold storage and reduce their rot, and help tomatoes and watermelons in disease defense by enhancing their own immunity. Therefore, inventing a method for PSK to delay the browning of litchi pericarp after harvest will help extend the storage and transportation period of litchi and reduce the post-harvest loss of litchi, which has important guiding significance. Summary of the Invention:

[0003] The object of the present invention is to provide a method for delaying the browning of litchi pericarp after harvest by phytosulfokine PSK to solve the problems existing in the above-mentioned prior art. Through PSK treatment, the purpose of post-harvest fresh preservation of litchi is achieved, the original taste of litchi is ensured, the process of browning during post-harvest storage of litchi is delayed, the commercial fruit rate of litchi during normal temperature storage is increased, and the browning rate of litchi is reduced.

[0004] To achieve the above object, the present invention provides the following solution, and the specific steps are as follows:

[0005] (1) Treat litchi with prochloraz, and wait for use after air-drying the surface moisture.

[0006] (2) Soak in the phytosulfokine solution and air-dry before storage.

[0007] Preferably, the phytosulfokine solution is a 50 - 300 nM phytosulfokine solution.

[0008] Preferably, the specific steps are as follows:

[0009] (1) Soak the litchi fruits in 0.05% v / v prochloraz for 3 minutes, then air-dry the surface moisture and set aside.

[0010] (2) Soak in a 50 - 300 nM PSK solution for 8 minutes, air-dry and store at room temperature.

[0011] Furthermore, the storage at room temperature is in a sealed environment at 22 - 25 °C with a relative humidity of 80% - 90%.

[0012] Furthermore, the storage time is 0, 2, 4, 7, 10 days.

[0013] The present invention has the following beneficial effects:

[0014] By treating litchi fruits with the PSK solution, under the condition of room temperature storage, the present invention can effectively delay the postharvest browning process of litchi pericarp, maintain a good taste of litchi, improve the commercial fruit rate of litchi and extend the shelf life of litchi fruits. It has important guiding significance for extending the storage and transportation period of litchi and reducing postharvest losses of litchi. Description of the drawings:

[0015] Figure 1 Observation of the browning process of litchi fruits stored for different days under different treatment conditions.

[0016] Figure 2 Detection of fruit quality indexes of litchi fruits stored for different days.

[0017] Figure 3 Browning classification of litchi fruits after 10 days of storage at room temperature.

[0018] Figure 4 Statistics of the commercial fruit rate and browning index of litchi fruits after 10 days of storage.

[0019] Figure 5 Detection of fruit physiological indexes of litchi fruits under different storage conditions. Specific embodiments:

[0020] To better illustrate the purpose, technical solution and advantages of the present invention, the present invention will be further described below with specific embodiments.

[0021] To make the objectives, technical solutions and beneficial effects of the present invention clearer, the present invention will be further described in detail in conjunction with the following embodiments. It should be understood that the embodiments described in this specification are only for explaining the present invention and not for limiting the present invention. The parameters, ratios, etc. of the embodiments can be selected according to local conditions without substantial impact on the results.

[0022] In the following embodiments, various processes and methods not described in detail are conventional methods well known in the art. The primers used are indicated when they first appear, and the same primers used later are the same as those indicated for the first time.

[0023] The following embodiments are further illustrations of the present invention rather than limitations thereof.

[0024] The materials, reagents, etc. used in the following embodiments can be obtained from commercial channels unless otherwise specified.

[0025] The instruments, equipment, etc. used in the following embodiments are conventional instruments and equipment in the art unless otherwise specified.

[0026] Example 1: Treatment of litchi fruits by soaking in PSK

[0027] (1) Randomly select litchi fruits with generally the same degree of maturity, uniform color, no mechanical damage and pests and diseases as test materials. Each group of test fruits is 120.

[0028] (2) Soak the litchi fruits in 0.05% (v / v) prochloraz for 3 minutes, and then air-dry the surface moisture for later use.

[0029] (3) Soak the litchi fruits after step (2) in PSK solutions with concentrations of 0 nM, 50 nM, 150 nM and 300 nM respectively. After soaking for 8 minutes, take them out, dry them, and then pack and store them in polyethylene fresh-keeping bags, with 30 fruits in each bag. Store them in a closed environment at a temperature of 22 - 25 °C and a relative humidity of 80% - 90%.

[0030] (4) Observe the surface browning of litchi fruits under different treatment conditions at 0, 2, 4, and 7 days of storage. The results are as Figure 1 shown. Compared with the control group (soaked in 0 nM PSK), the browning degree of litchi fruits in the treatment groups soaked in 50 - 300 nM PSK is lower. Among them, the 150 nM PSK treatment group has the best effect on delaying fruit browning.

[0031] Example 2: Detection of quality indicators of litchi stored under different treatment conditions for different times

[0032] To investigate the effects of PSK treatment on the quality of litchi fruits, the sugar-acidity, pericarp conductivity, and chromaticity of litchi fruits with different treatments were statistically analyzed at 0, 2, 4, and 7 days of storage. The taste evaluation of litchi was mainly based on the soluble solids (TSS), titratable acid (TA), and their sugar-acid ratio (TSS / TA) in the pulp. The contents of TSS and TA were detected using a handheld sugar-acidity meter (PAL-Patissier, ATAGO, Japan). The change in pericarp conductivity can reflect the change in cell membrane permeability. The pericarp conductivity of litchi was detected using a DDS-11A conductivity meter (Shanghai scientific instruments, Shanghai, China). The pericarp chromaticity was detected using a Konica Minolta color difference meter CR-400 (Konica Minolta, Minolta, Japan), and the two parameters of L value and Hue chromaticity angle (h°) were used to evaluate and analyze the fruit chromaticity. The L value represents the lightness and darkness of the color, with a range of 0 - 100, representing from black to white. The range of the h° chromaticity angle is 0 - 360°. The smaller the h° value, the closer it is to red, and the larger the chromaticity angle, the closer the hue is to blue. The results are as Figure 2 shown. Compared with the control group, the litchi fruits treated with PSK still maintained a higher soluble sugar content and a lower titratable acid content with the increase of storage time, had a higher sugar-acid ratio, and had a better taste. In addition, the treatment with 150 nM PSK could still keep the pericarp conductivity of litchi low at 7 days of storage, while there was no significant difference in the conductivity between the low-concentration (50 nM) PSK or high-concentration (300 nM) PSK treatment groups and the control group. With the increase of storage time, the pericarp color of litchi fruits gradually deepened and even turned brown, and the L value and H° value of the litchi pericarp also decreased with time. The L value of the litchi in the 150 nM PSK treatment group was higher than that of the control group at 7 days of storage, while there was no significant difference in the L value between the low-concentration (50 nM) PSK or high-concentration (300 nM) PSK treatment groups and the control group. Correspondingly, the treatment with low-concentration (50 - 150 nM) PSK could delay the browning rate of litchi. At 7 days of storage, its H° value was higher than that of the control group, while there was no significant difference in the H° value between the litchi in the high-concentration (300 nM) PSK treatment group and the control group.

[0033] Example 3: Browning grading situation, commercial fruit rate, and browning index statistics after 10 days of storage

[0034] The degree of fruit browning and the percentage of marketable fruits are common indicators reflecting the post-harvest freshness of litchi. The evaluation of the degree of litchi pericarp browning is divided into five grades by a grading method. Specifically: Grade 0 - no browning, Grade I - browning area less than or equal to one-fourth, Grade II - browning area greater than one-fourth and less than or equal to one-half, Grade III - browning area greater than one-half and less than or equal to three-fourths, Grade IV - browning area greater than three-fourths. The specific formula is Browning index = ∑(browning grade × number of fruits in this grade) × 100 / (total number of fruits × highest grading number); The percentage of marketable fruits is also called the edible rate, and the specific formula is Percentage of marketable fruits (%) = (number of Grade 0 fruits + number of Grade I fruits) × 100 / total number of fruits. In order to further illustrate the positive effect of PSK on the post-harvest storage and freshness preservation of litchi, litchi fruits stored for 10 days were selected for observation and statistics of the effects of PSK on the degree of litchi fruit browning and marketable fruits. The results are as Figure 3 shown. After 10 days of storage (stored in the manner of Example 1), most litchi had undergone browning and mildew and were not suitable for consumption. By counting the browning index and the percentage of marketable fruits, it can be seen that ( Figure 4 ) the litchi in the 150 nM and 300 nM PSK treatment groups had a higher percentage of marketable fruits and a lower browning index compared with the control group, and the litchi in the 150 nM PSK treatment group had the best freshness preservation degree.

[0035] Example 4: Detection of litchi physiological indexes

[0036] As can be seen from the above examples, the 150 nM PSK treatment has a better effect on the post-harvest freshness preservation of litchi fruits. In order to further reveal its mechanism of action on the post-harvest freshness preservation of litchi fruits, compared with the control group soaked in clear water, the changes in the physiological and biochemical indexes of litchi pericarp under different storage time conditions were analyzed after 150 nM PSK treatment. The physiological and biochemical indexes of litchi pericarp were detected using a kit from Suzhou Keming Biotechnology Co., Ltd. The specific detection items and methods of the physiological and biochemical indexes are shown in Table 1. The detection results are as Figure 5As shown, the contents of MDA and H2O2 both showed an overall increasing trend during the storage of litchi fruits. Compared with the control group, the contents of malondialdehyde (MDA) and H2O2 in litchi treated with 150 nM PSK were lower. Detection of its antioxidant enzymes found that the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), and glutathione reductase (GR) in the pericarp of litchi treated with 150 nM PSK were higher than those of the control group; the enzyme activity of catalase (CAT) was higher than that of the control group when stored for 2 - 4 days, but when the storage time reached 7 days, its enzyme activity tended to zero and there was no significant difference compared with the control group. In addition, the pericarp of litchi treated with 150 nM PSK had lower activities of polyphenol oxidase (PPO) and peroxidase (POD), and at the same time could maintain higher contents of anthocyanins, flavonoids, and total phenols, slowing down the process of enzymatic browning of the fruits.

Claims

1. A method for delaying the browning of litchi pericarp after harvest by phytosulfokine PSK, characterized in that, Including the following steps: (1) Soak litchi in 0.05% v / v prochloraz for 3 minutes, then air-dry the surface moisture and set aside for use; (2) Soak in 50 - 300 nM PSK solution for 8 minutes, air-dry and store at room temperature.

2. The method according to claim 1, wherein The storage at room temperature is in a sealed environment at 22 - 25°C with a relative humidity of 80% - 90%.

3. The method according to claim 1, characterized in that, For the said storage, the time is 0, 2, 4, 7 days.

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