CN112998063A

CN112998063A - Fresh-keeping method for papaya

Info

Publication number: CN112998063A
Application number: CN202110369455.0A
Authority: CN
Inventors: 朱孝扬; 李雪萍; 范思临; 陈维信
Original assignee: South China Agricultural University
Current assignee: South China Agricultural University
Priority date: 2021-04-06
Filing date: 2021-04-06
Publication date: 2021-06-22

Abstract

The invention discloses a fresh-keeping method of papaya. According to the method, the picked papaya fruits are treated by the exogenous melatonin, so that the hardness reduction of the papaya fruits can be remarkably delayed, the respiration rate and the ethylene release peak of the fruits are remarkably reduced, and the postharvest diseases of the fruits are effectively reduced. The fresh-keeping method has the characteristics of good fresh-keeping effect, safety, environmental protection, simple and convenient operation, low cost and the like, and can be widely applied to the storage and transportation of the papaya under the normal temperature condition.

Description

Fresh-keeping method for papaya

Technical Field

The invention belongs to the technical field of fruit preservation, and particularly relates to a papaya preservation method.

Background

Papaya (Caricapapaya L.) belongs to the genus Caricaceae, papaya, also known as papaya, milk melon and papaw, and is widely planted in tropical and subtropical areas, and is mainly distributed in Thailand, Philippine, Burma, India and the like, and China is mainly distributed in Guangdong, Guangxi, Hainan, Fujian, Taiwan and the like. The papaya fruits are fragrant and sweet in taste, and also have rich nutritional value and medicinal value, so the papaya fruits are deeply loved by consumers. However, papaya is taken as a typical climacteric fruit, obvious respiration and ethylene peaks appear after the fruit is picked, the fruit is easy to turn yellow and soften, the hardness of the fruit is in a sharp decline trend in the later storage period of the papaya fruit, the pulp is quickly softened, and then the edible value and the commodity value are gradually lost. Research shows that the hardness of the papaya fruits of the 'Dabai' variety is 257N immediately after picking when the papaya fruits are yellow in three lines, the hardness of the papaya fruits is not greatly reduced in a few days before storage, the hardness of the papaya fruits is rapidly reduced 7-8d after picking, and the papaya fruits are seriously softened and only have the hardness of 14.2N at 12d after storage. Therefore, certain measures need to be taken to maintain the hardness of the fruits and delay the softening of the fruits in the production of the fruits, so that the aim of prolonging the preservation period can be fulfilled. Because the papaya grows under the conditions of high temperature and high humidity, the surface of the fruit is easy to be infected by fungi, anthracnose is one of the most important diseases causing the picked papaya fruit, the main symptoms are that the disease generally starts from two ends of the fruit, the disease spot is light brown and round at the beginning, dark brown to black at the later stage, the fruit peel is wrinkled, finally the whole fruit becomes black and dry, small black grains are distributed on the disease spot, the diseased fruit is cut open, and the fruit pulp is brown to black. Anthracnose is also the most common and serious infectious disease of papaya fruits, can be harmful to papaya fruits all year round, and is generally most serious in autumn. Pathogenic bacteria can directly invade fruits from the surfaces of wounds and peels and mainly damage young fruits and mature fruits. White or brown water-stain-like spots appear on the initially infected damaged fruits, the spots gradually expand along with the prolonging of the storage time, and the brown spots are sunken to form concentric rings, so that the whole fruit rot can be caused in severe cases (Yuan Liang you, 2004). Causing infection of diseases during storage of the fruits, leading the fruits to lose the commodity value in a short time and causing serious loss on production.

In order to prolong shelf life, fruits and vegetables are generally subjected to fresh-keeping treatment in time after being harvested, and the papayas are concentrated on the market and are harvested in high-temperature and high-humidity seasons, belong to climacteric fruits and are easy to soften and cause diseases after being harvested until the papayas are rotten and deteriorated. Therefore, the postharvest preservation technology is particularly important. For the problems that the picked papaya is easy to soften and has pathological changes, the prior production uses wider chemical agent treatment to achieve good fresh-keeping effect, but the papaya has certain toxicity and may cause adverse effects on human health, so that the need of a safe and nontoxic fresh-keeping agent is necessary.

Disclosure of Invention

The invention aims to solve the problems that the picked papaya fruits are easy to soften and attack diseases at present, and provides a method for prolonging the fruit fresh-keeping period in a normal-temperature storage environment so as to more effectively inhibit the picked papaya from rotting and deteriorating, prolong the shelf life of the fruits and meet the requirements of green, health and non-toxicity.

The invention relates to a fresh-keeping method of papaya, which is to soak papaya fruits with aqueous solution of melatonin and then store the papaya fruits at normal temperature.

Preferably, the fresh-keeping method of the papaya comprises the following steps:

s1, collecting healthy papaya fruits with a mature degree of 'three-line yellow';

s2, cutting a papaya stalk into a short section, and keeping the length of the papaya stalk to be more than 1 cm;

s3, performing surface disinfection treatment on the papaya, then soaking the papaya in 800 mu mol/L melatonin aqueous solution with the concentration of 100-.

Preferably, the surface sterilization treatment in step S2 is to soak the fruits in 0.2% by weight aqueous solution of cifluanid for 1min, and then air-dry the fruits. This step is advantageous for converging the wound at the carpopodium.

Preferably, the melatonin is soaked in an aqueous solution of melatonin with the concentration of 100-.

Preferably, the melatonin aqueous solution is 400 mu mol/L melatonin aqueous solution.

Preferably, the single fruit package is carried out by using a PE bag with the thickness of 0.02 mm.

Preferably, the normal-temperature storage is carried out under the conditions of 25 +/-1 ℃ and 60-80% of relative humidity.

Compared with the prior art, the invention has the beneficial effects that:

aiming at the characteristics that the papaya is easy to soften quickly after being harvested, the quality is easy to deteriorate, diseases are easy to generate, the influence of a chemical bactericide on human health and the like, the invention screens out a proper exogenous melatonin concentration treatment through experiments, and can obviously reduce the softening speed of papaya fruits, reduce the fruit morbidity and delay the deterioration of the fruit quality. The concentration of 400 mu mol/L melatonin aqueous solution is screened out, so that the hardness reduction of the papaya fruits can be remarkably delayed, the preservation time is prolonged, the respiration rate of the fruits is inhibited, the ethylene release peak of the fruits is delayed, and the storage life of the papaya fruits is prolonged.

The fresh-keeping method has the characteristics of good fresh-keeping effect, safety, environmental protection, simple and convenient operation, low cost and the like, and can be widely applied to the storage and transportation of the papaya under the normal temperature condition.

Drawings

FIG. 1 is a graph of the effect of different treatments on papaya fruit firmness (25. + -. 1) C; wherein CK represents a control group, 100 represents a melatonin concentration treatment group of 100 mu mol/L, 400 represents a melatonin concentration treatment group of 400 mu mol/L, and 800 represents a melatonin concentration treatment group of 800 mu mol/L; different letters represent significant differences in t-test (P.ltoreq.0.05).

FIG. 2 is a graph of the effect of different treatments on papaya fruit color (25. + -. 1 ℃ C.); FIG. 2a shows papaya fruit L treated by different treatments^*Influence of value (color brightness) (25 ± 1) ° c; FIG. 2b shows papaya fruit C treated with different treatments^*Influence of value (color saturation) (25 ± 1) ° c; FIG. 2c is the effect of different treatments on papaya fruit h (hue angle) (25. + -.1) deg.C; wherein CK represents a control group, 100 represents a melatonin concentration treatment group of 100 mu mol/L, 400 represents a melatonin concentration treatment group of 400 mu mol/L, and 800 represents a melatonin concentration treatment group of 800 mu mol/L; different letters represent significant differences in t-test (P.ltoreq.0.05).

FIG. 3 is a graph of the effect of different treatments on the ethylene release rate of papaya fruits (25. + -. 1 ℃ C.); wherein CK represents a control group, 100 represents a melatonin concentration treatment group of 100 mu mol/L, 400 represents a melatonin concentration treatment group of 400 mu mol/L, and 800 represents a melatonin concentration treatment group of 800 mu mol/L; LSD represents the minimum difference at a level of P.ltoreq.0.05.

FIG. 4 is a graph of the effect of different treatments on the respiration rate of papaya fruits (25. + -. 1 ℃ C.); wherein CK represents a control group, 100 represents a melatonin concentration treatment group of 100 mu mol/L, 400 represents a melatonin concentration treatment group of 400 mu mol/L, and 800 represents a melatonin concentration treatment group of 800 mu mol/L; LSD represents the minimum difference at a level of P.ltoreq.0.05.

FIG. 5 is the effect of different treatments on the index of the disease of papaya fruits (25. + -. 1 ℃ C.); wherein CK represents a control group, 100 represents a melatonin concentration treatment group of 100 mu mol/L, 400 represents a melatonin concentration treatment group of 400 mu mol/L, and 800 represents a melatonin concentration treatment group of 800 mu mol/L; different letters represent significant differences in t-test (P.ltoreq.0.05).

FIG. 6 is the effect of different treatments on the incidence of papaya fruit (25. + -. 1 ℃ C.); wherein CK represents a control group, 100 represents a melatonin concentration treatment group of 100 mu mol/L, 400 represents a melatonin concentration treatment group of 400 mu mol/L, and 800 represents a melatonin concentration treatment group of 800 mu mol/L; different letters represent significant differences in t-test (P.ltoreq.0.05).

FIG. 7 is a graph of the effect of different treatments on the commercial rate of papaya fruits (25. + -. 1 ℃ C.); wherein CK represents a control group, 100 represents a melatonin concentration treatment group of 100 mu mol/L, 400 represents a melatonin concentration treatment group of 400 mu mol/L, and 800 represents a melatonin concentration treatment group of 800 mu mol/L; different letters represent significant differences in t-test (P.ltoreq.0.05).

FIG. 8 is the effect of different treatments on papaya fruit MDA (25. + -. 1) deg.C; wherein CK represents a control group, and 400 represents a melatonin concentration treatment group with 400 mu mol/L; LSD represents the minimum difference at a level of P.ltoreq.0.05.

FIG. 9 shows the effect of different treatments on the APX of papaya fruits (25. + -. 1 ℃ C.); wherein CK represents a control group, and 400 represents a melatonin concentration treatment group with 400 mu mol/L; LSD represents the minimum difference at a level of P.ltoreq.0.05.

FIG. 10 is the effect of different treatments on the PPO of the papaya fruits (25. + -. 1). degree.C.; wherein CK represents a control group, and 400 represents a melatonin concentration treatment group with 400 mu mol/L; LSD represents the minimum difference at a level of P.ltoreq.0.05.

FIG. 11 shows the effect of different treatments on the papaya fruits CHI (25. + -. 1 ℃ C.); wherein CK represents a control group, and 400 represents a melatonin concentration treatment group with 400 mu mol/L; LSD represents the minimum difference at a level of P.ltoreq.0.05.

FIG. 12 is a graph of the effect of different treatments on the beta-1, 3-GA of papaya fruits (25. + -. 1) deg.C; wherein CK represents a control group, and 400 represents a melatonin concentration treatment group with 400 mu mol/L; LSD represents the minimum difference at a level of P.ltoreq.0.05.

Detailed Description

The following examples are further illustrative of the present invention and are not intended to be limiting thereof.

Example 1

1. Fresh-keeping method for papaya fruits

(1) Pretreatment:

after the papaya test material is cleaned and aired, fruits with consistent maturity, similar sizes, no plant diseases and insect pests, no mechanical damage and maturity of 'three-line yellow' are selected for subsequent tests. Firstly, the fruit stalks are cut short, the wound harvested in the field (because the wound may be infected by pathogenic bacteria) is removed, a new wound is exposed, the length of the fruit stalks is kept to be 1cm, the fruits are soaked in an aqueous solution of 0.2 mass percent of strong disinfectant (Dingli strong disinfectant, manufacturer: veterinary research institute pharmaceutical factory in China academy of agricultural science) for 10min, the fruits are taken out and slightly dried, and the fruits are further treated by melatonin.

(2) After being cleaned, the pretreated papaya fruits are respectively soaked in melatonin aqueous solution with the concentration of 0 mu mol/L, 100 mu mol/L, 400 mu mol/L and 800 mu mol/L for 2 hours and then are aired. Each of the above treatments was repeated 3 times, each for 15 fruits. And finally, packing the treated and control fruits in a PE bag with the thickness of 0.02mm singly and storing the packed and control fruits at room temperature, wherein the indoor temperature is 25 +/-1 ℃ and the relative humidity is 60-80%. Regularly observing and recording the hardness, color and fruit disease rate of each treated fruit, and sampling to determine various quality and physiological indexes.

Among them, melatonin was purchased from Biotechnology engineering (Shanghai) Co., Ltd.

2. Method for measuring physiological indexes of papaya fruits

(1) Determination of papaya fruit hardness

Referring to the Nudo (2009) method, the hardness of the fruit was measured using a fruit and vegetable material hardness tester model 5542 from Instron, USA, with a probe diameter of 2mm and a probe moving speed of 2mm/s, and the maximum stress value during the pressing down process was taken as the hardness value of the fruit in newtons (N). Randomly 3 fruits were taken from each treatment, and about 0.1mm peel of papaya was removed by a knife, and the peel and flesh hardness of 5 portions on the equatorial plane of each fruit was measured to have a maximum value of the whole fruit hardness value. And (6) taking an average value.

(2) Determination of papaya fruit color

Fruit color is one of important indexes for evaluating fruit appearance quality, 3 fruits are taken for each treatment, and L of 5 parts on the central equatorial plane of each fruit is measured by a Minolta type color difference meter manufactured by Konika-Menten Kogyo Co., Ltd^*Value (color brightness), C^*The values (color saturation) and h ° (hue angle) are averaged, respectively.

(3) Determination of papaya fruit ethylene release rate

The ethylene release rate is an important index for identifying the ripening quality of fruits, and the ethylene release rate is measured by using a gas chromatography instrument GC6820 of Shimadzu Japan. And (3) respectively putting 3 fruits into a sealed tank for each treatment, placing the sealed tank at normal temperature, sealing for 2 hours, slightly shaking the sealed tank (paying attention to not hurt the fruits), uniformly mixing ethylene gas in the tank, extracting 1mL of gas by using a 1mL syringe, inserting the gas into a rubber stopper to be tested, and measuring the volume and the weight of the fruits.

The working conditions of the gas chromatograph are as follows: the chromatographic column alumina packing column has the column temperature of 80 deg.c, the sample inlet temperature of 140 deg.c, the carrier gas He in the flow rate of 30mL/min and the FID temperature of 150 deg.c. Each treatment was repeated 3 times, with 3 pins each. The calculation formula is as follows:

(4) determination of papaya fruit respiration rate

Referring to an ethylene release rate can sealing method, 3 fruits are respectively taken in each treatment and are placed in a sealed can, the sealed can is placed at normal temperature and sealed for 2 hours, the sealed can is slightly shaken, after gas in the can is uniformly mixed, 1mL of gas is extracted by a 1mL injector and inserted into a rubber stopper to be detected, and the volume and the weight of the fruits are detected.

Each treatment was repeated 3 times, 3 needles each, and the measuring apparatus used a gas chromatograph model G3900 from Hitachi. The new fruit is changed every 2-3 times. The calculation formula is as follows:

(5) determination of papaya fruit disease index

30 fruits are reserved for each treatment, three times of treatment are carried out, 10 fruits are repeated for each treatment, the morbidity of the stored fruits is observed every day, the statistics and the record are carried out, and the disease index of the papaya is calculated according to a formula. The degree of fruit development was classified into 8 grades with reference to the Lay-Yee (1998) method.

Level 0: the fruit is disease-free;

level 1: no more than 20 scattered sporadic small disease spots with the diameter of less than 0.5 cm;

and 2, stage: the number of scattered small scabs with the diameter of less than 0.5cm is more than 20, or one scab with the diameter of 1-1.5 cm;

and 3, level: the diameter of the largest lesion or the connected lesion is 1.5-3cm, and the total area of the lesion does not exceed 1/16 fruit areas;

4, level: the diameter of the maximum lesion spot is more than 3cm, and the area of the whole fruit lesion spot is not more than 1/8 fruit surface area;

and 5, stage: 1/8-1/4 rot of fruit surface;

and 6, level: 1/4-1/2 rot of fruit surface;

and 7, stage: 1/2-2/3 rot of fruit surface;

and 8, stage: the whole fruit is rotten.

Disease index (%). sigma (number of diseased fruit at each stage x the disease stage)/(total number of investigated fruits x highest disease index) × 100%.

(6) Determination of papaya fruit morbidity

The incidence of papaya fruits was determined by counting, the incidence of disease was expressed as number of fruits affected/total number of fruits examined x 100%.

(7) Determination of commodity rate of papaya fruits

The papaya is classified into the commodity value and the commodity value when the disease condition grade is less than 2.

The commercial fruit ratio (%) × 100% (number of fruits having commercial value/number of inspected fruits).

(8) Assay of papaya fruit Malondialdehyde (MDA)

According to the determination method, referring to a Malondialdehyde (MDA) spectrophotometry kit of Ming biology company of Suzhou, Jiangsu, the MDA in the lipid peroxide degradation product can be condensed with thiobarbituric acid (TBA) to form a red product, and the maximum absorption peak is at 532 nm. (9) Determination of ascorbic Acid Peroxidase (APX) of Carica papaya fruits

The determination method refers to ascorbic Acid Peroxidase (APX) content kit of Ming biology company of Suzhou of Jiangsu, APX catalyzes H₂O₂AsA was oxidized, and APX activity was measured by measuring the oxidation rate of AsA at 290 nm.

(10) Determination of papaya fruit Polyphenol oxidase (PPO)

Extracting the papain solution: adding liquid nitrogen into a part of frozen papaya flesh sample, grinding into powder, weighing 1.0g of sample powder, adding 4mL of 0.05mol/L pre-cooled phosphate buffer (pH7.8) containing 0.5% PVP, shaking by an oscillator to fully mix the sample, centrifuging at 18000g at 4 ℃ for 30min, and taking the supernatant for enzyme activity determination.

Preparation of PPO reagent: 0.25g of 0.1% catechol was weighed out and dissolved in 250mL of distilled water, and the solution was placed in a brown reagent bottle and stored in a refrigerator at 4 ℃ for one week.

Reference is made to the method of Tan Xingjie et al (1984). 0.1% (w/v) catechol was used as a substrate, 2.6mL of catechol was placed in a glass cuvette, 0.4mL of enzyme solution was added rapidly, and OD was recorded using 0.1(w/v) catechol solution as a reference₃₉₈Change over time. The enzyme activity is 1 enzyme activity unit (U) with OD value increased by 0.01, and the enzyme activity is U.g^-1(FW)·min^-1And (4) showing.

(11) Assay of papaya fruit Chitinase (CHI)

The determination method refers to Chitinase (CHI) content micro-assay kit of Ming biology of Suzhou, Jiangsu. Chitinase hydrolyzes chitin to generate N-acetylglucosamine, and further generates a red compound with p-dimethylaminobenzaldehyde, a characteristic absorption peak is generated at 585nm, and the activity of the chitinase is calculated according to the increase rate of the light absorption value.

(12) Determination of papaya fruit beta-1, 3-glucanase

The determination method refers to a beta-1, 3-glucanase (beta-1, 3-GA) content kit of Guire biological company of Jiangsu Suzhou, beta-1, 3-GA hydrolyzes laminarin, beta-1, 3-glucosidic bonds are cut internally, reducing ends are generated, an absorbance value is determined at 550nm, and the enzyme activity is calculated by determining the generation rate of reducing sugar.

3. Results of physiological index test

(1) As shown in figure 1, the hardness of the papaya fruits does not decrease obviously in 3d before storage, the hardness of the fruits decreases rapidly in 3-5 days, and the hardness of the 400 mu mol/L melatonin treated group fruits is obviously higher than that of the control group fruits in 5 days after storage; on day 7, the hardness of the fruits of the 100, 400 and 800 μmol/L treatment groups was significantly different from that of the control group; the papaya fruit hardness was significantly higher in the 10 th, 100, 400 and 800 μmol/L treated groups than in the control.

(2) As shown in figure 2a, the brightness of the papaya fruits treated in each step is increased and then decreased along with the prolonging of the storage time, the brightness of the endocarp of the papaya fruits stored for 3-5 days is increased most rapidly, the brightness reaches the highest level on the 7 th day of storage, and the brightness slightly decreases again from 9 to 11 days. The control group also showed the highest brightness on day 7 of storage, and the decline was more pronounced than in the other treatment groups. On the 9 th day of storage, the brightness of the 100 μmol/L melatonin concentration-treated group was significantly different from that of the control group; 100. the differences between the 400 and 800 μmol/L melatonin concentration treatment groups and the control group on day 11 of storage both reached significant levels of brightness. As can be seen from FIG. 2b, the color saturation of the pericarp gradually increased during the ripening of the papaya fruits, with the greatest magnitude of increase occurring within days 3-5 of storage. In the storage process, the color saturation of each melatonin concentration treatment group is not obviously different from that of the control group. As can be seen from fig. 2c, during ripening of the papaya fruits, h ° gradually decreases with time, and decreases most rapidly in days 3-5 of storage. 100. The h ° of 400 and 800 μmol/L melatonin concentration treatment groups were significantly different from the control group on day 7 of storage; on day 9 of storage, the difference between h ° of the 100 and 800 μmol/L melatonin concentration-treated groups and the control group reached a significant level.

(3) As shown in fig. 3, the ethylene release rate during storage of papaya fruits tends to increase and then decrease, and then increase again. As can be seen from FIG. 3, the control group and the 800. mu. mol/L-treated group exhibited ethylene release peaks on day 3 of storage, and the 100. mu. mol/L-treated group and the 400. mu. mol/L-treated group reached ethylene release peaks on

days

5 and 4 of storage, respectively, which were delayed by 2 days and 1 day, respectively, compared to the control group. On the 9 th day of storage, the ethylene release rate of fruits in each treatment group showed a remarkable rising trend, and the reason is considered to be that the ethylene release rate of fruits is increased sharply due to the aggravation of fruit diseases, and the ethylene release rate of fruits in the control group is obviously higher than that of fruits in other treatment groups.

(4) As shown in fig. 4, the respiration rates of the papaya fruits in each treatment group gradually increased from the 0 th day of storage to the 5 th day of storage, wherein the increase was fastest in the 0 th to 3 th days, the respiration rates of the papaya fruits in the treatment group with the melatonin concentration of 800 μmol/L reached a peak in the 7 th day of storage, and the respiration rates of the papaya fruits in the remaining treatment groups reached a peak in the 5 th day; the respiration rate of the papaya fruits in the control group was significantly higher than that of the other treatment groups during the 5 th day of storage; the disease of the picked fruit is aggravated along with the storage time, except for the melatonin concentration treatment group with the concentration of 800 mu mol/L, the respiration rates of other treatment groups are increased in different degrees, wherein the papaya fruits of the control group are seriously affected by the disease, the respiration effect is intensified, and the respiration rate of the papaya fruits is obviously higher than that of the melatonin treatment group on the 9 th day of storage. The result shows that melatonin treatment has a certain effect on delaying the arrival of the respiration peak of the papaya fruits after picking, and because the influence of diseases after picking on the papaya fruits is reduced by the melatonin treatment, the respiration rate of each concentration of melatonin treatment groups is lower than that of a control group from the 7 th day of storage, namely the time when the diseases after picking appear to the 9 th day of storage.

(5) As shown in fig. 5, the papaya fruits of each treatment group showed postharvest diseases from day 7 of storage, and the disease index gradually increased with the lapse of storage time; on the 10 th day of storage, the disease index of papaya fruits in the 800 mu mol/L melatonin concentration treatment group is obviously different from that of a control group; on the 11 th day of storage, the disease index of the papaya fruits in the 400 mu mol/L melatonin concentration treatment group is obviously lower than that of the control group and other melatonin concentration treatment groups; on the 12 th to 13 th days of storage, the difference between the papaya fruit disease index of the control group and the treatment group with melatonin of each concentration reaches a significant level; and the indexes of the papaya fruit diseases of the 400 mu mol/L melatonin concentration treatment group are lowest in 11 th to 13 th days of storage. Therefore, the influence of the postharvest diseases on the papaya fruits can be effectively relieved by melatonin treatment, the disease index of the postharvest papaya fruits is reduced, and the effect of 400 mu mol/L melatonin concentration is most obvious.

(6) As shown in fig. 6, the papaya fruits of each of the treatment groups except the 800 μmol/L melatonin concentration treatment group began to develop postharvest diseases on day 7 of storage, and the incidence rate increased with the lapse of storage time. On the 10 th day of storage, the incidence of papaya fruits in the 800 mu mol/L melatonin concentration-treated group was significantly lower than that in the control group; storing for 11-12 days, wherein the difference between the incidence rate of the papaya fruits in the 400 mu mol/L melatonin concentration treatment group and the incidence rate of the papaya fruits in the control group reaches a significant level; the incidence of papaya fruit in 400 and 800 μmol/L melatonin concentration-treated groups was significantly different from the control group on day 13 of storage. In the 11 th to 13 th days of storage, the incidence of papaya fruits in the group treated with 400. mu. mol/L melatonin concentration was the lowest. From this, it is understood that the melatonin treatment has a certain effect of reducing the onset of post-harvest papaya fruits as compared with the control group, and the effect is most significant at a concentration of 400. mu. mol/L.

(7) As shown in fig. 7, as the post-harvest disease occurs and progresses, the commodity rate of the papaya fruits also decreases with the lapse of storage time. The commodity rate of the papaya fruits in the 400 mu mol/L melatonin concentration treatment group is remarkably higher than that of the papaya fruits in the control group on days 11-13 of storage. The melatonin treatment can effectively reduce the postharvest diseases of the papaya fruits and improve the commodity rate. Among them, the melatonin treatment effect was most remarkable at a concentration of 400. mu. mol/L as compared with other treatment concentrations.

(8) As shown in fig. 8, the fruit MDA content increased dramatically during storage at 5-13d, and the control group (CK) was significantly higher than the 400 μmol/L melatonin treated group. Indicating that 400 μmol/L melatonin treatment reduced the degree of papaya fruit cell peroxidation and thus cell membrane damage.

(9) As shown in fig. 9, the APX activity of papaya fruits increased with the increase of storage time. At the early stage of storage, the APX activity between the two treatments is not significant; 5-13d, 400. mu. mol/L melatonin treatment group APX activity was significantly higher than CK. Indicating that 400 mu mol/L melatonin treatment is helpful for improving the APX activity of the papaya fruits after picking.

(10) As shown in FIG. 10, PPO activity in papaya fruits was increasing and decreasing. PPO activity of the melatonin-treated group at 0-10d, 400. mu. mol/L showed an approximately increasing trend, and 10-13dPPO activity was decreased. The PPO activity of the CK group is obviously lower than that of the melatonin treatment group at 5-10d by 400 mu mol/L. It was shown that the 400. mu. mol/L melatonin-treated group was able to induce an increase in PPO activity to some extent.

(11) As shown in figure 11, the chitinase activity of the papaya fruits is in a descending trend after rising, the CHI activity of 400 mu mol/L melatonin treatment group is higher than that of CK in 3-10 days, the CHI activity peak of the 400 mu mol/L melatonin treatment group is reached in 10 days, the CHI activity of the melatonin treatment group is 10.4438mg/h/g, and the CHI activity of the CK group is 9.6342mg/h/g, which shows that 400 mu mol/L melatonin treatment can obviously improve the chitinase activity of the papaya fruits after picking, and the effect of resisting fungal invasion is achieved.

(12) As shown in FIG. 12, the activity of β -1,3-GA after harvest tended to increase and then decrease as the storage time of the papaya fruits was prolonged. 3-13d, the beta-1, 3-GA of the CK group is obviously higher than that of the melatonin treatment group with the concentration of 400 mu mol/L, the activity of the beta-1, 3-GA of the CK group reaches the peak at the 7 th d, the content is 88.1976mg/h/g, and the activity of the melatonin treatment group with the concentration of 400 mu mol/L reaches the peak at the 10 th d, and the activity is 55.732 mg/h/g. This indicates that melatonin treatment can significantly reduce the increase in the beta-1, 3-GA activity of the harvested papaya fruits.

In conclusion, the melatonin treatment has good comprehensive effects on the hardness, the chromaticity, the ethylene release rate, the respiration rate, the disease index, the morbidity and the commodity rate of the papaya fruits, and the 400 mu mol/L concentration treatment is optimal.

Claims

1. A method for preserving papaya is characterized in that papaya fruits are soaked in melatonin aqueous solution and then stored at normal temperature.

2. The method for preserving papaya according to claim 1, characterized by comprising the steps of:

3. The papaya fresh-keeping method of claim 2, wherein the step S2 of surface sterilization is to soak the fruits in 0.2% by weight aqueous solution of super disinfectant for 1min, and then to dry the fruits.

4. The method for preserving papaya as claimed in claim 2, wherein the soaking treatment is performed with an aqueous melatonin solution with a concentration of 100-800 μmol/L for 2 hours.

5. The method for preserving papaya of claim 2, wherein the aqueous melatonin solution is 400 μmol/L.

6. The method for preserving papaya of claim 2, wherein the single fruit packaging is performed by using a PE bag of 0.02 mm.

7. The papaya freshness keeping method according to claim 1, wherein the normal temperature storage is performed under the conditions of 25 ℃ ± 1 and a relative humidity of 60% -80%.