Preparation method of mulberry leaf extract and application of mulberry leaf extract in papaya preservative

Abstract

The invention discloses an application of a mulberry leaf extract in preparation of a papaya preservative capable of resisting diseases and delaying maturity. The papaya preservative is a mulberry leaf extract aqueous solution with the mass percentage concentration of 15-25%. The papaya preservative disclosed by the invention is wide in raw material source, natural, safe and low in cost, has a relatively good preservation effect on papayas, can delay decay and softening of the papayas, reduces the weight loss ratio of the papayas in a storage process, and can also reduce damage of cell membranes, so that fruit aging is delayed, good texture of the papayas is kept, and the papaya preservative is suitable for being used in papayas. The mulberry leaf extract-containing papaya preservative can maintain the flavor and nutritional value of papaya, is simple and easy to use, is suitable for large-scale application, and saves time and labor since the mulberry leaf extract-containing aqueous solution is directly sprayed or coated on the surface of the picked papaya.

Description

Technical Field

[0001] The invention belongs to the technical field of fruit storage and preservation, and particularly relates to a preparation method of a mulberry leaf extract and application of the extract in a papaya preservative. Background Art

[0002] Red papaya is a representative tropical fruit in Hainan. The main production areas are located in Sanya, Baoting and other places in Hainan. It has a soft and sweet taste and contains a variety of vitamins and minerals. It is rich in nutrition and is loved by consumers. Papaya is a respiratory climacteric fruit. It matures quickly after harvesting, the fruit softens, and is susceptible to pathogens. As a tropical fruit, it is prone to chilling damage when transported in a cold chain at a lower temperature, resulting in a shorter shelf life. Therefore, it is necessary to preserve the papaya after picking during storage or transportation to extend its shelf life.

[0003] At present, there are two common preservation methods for papaya: one is chemical means, which has a high antibacterial effect, but it is easy to produce drug residues, destroy the nutritional components of the fruit, which does not meet people's current demand for healthy and safe food and causes food safety problems; the other is physical means, such as controlled atmosphere preservation, which has a good preservation effect, but has high equipment requirements and difficult operation methods. It is not easy to achieve large-scale industrial applications and has a small scope of use. Therefore, it is worth further developing a simple, safe, natural and effective papaya preservation technology. Summary of the invention

[0004] Therefore, the purpose of the present invention is to develop a new type of safe and efficient preservative, which can be used in the post-harvest storage and transportation of red papaya to extend its shelf life, reduce the economic losses caused by rot and deterioration, and improve the economic benefits of the industry.

[0005] The first aspect of the present invention provides an application of mulberry leaf extract in preparing a papaya preservative having the functions of resisting diseases and delaying ripening.

[0006] Preferably, the papaya preservative is an aqueous solution of mulberry leaf extract with a mass percentage concentration of 15% to 25%.

[0007] Preferably, the papaya preservative is an aqueous solution of mulberry leaf extract with a mass percentage concentration of 20%.

[0008] Preferably, the mulberry leaf extract is prepared by first soaking mulberry leaf powder in an ethanol aqueous solution with a volume percentage concentration of 65% to 75% at a material-liquid mass ratio of 1:(10 to 20) for 2 to 4 hours and then ultrasonically extracting the powder, performing ultrasonic extraction 2 to 4 times, each time for 1 hour, combining the extracts, and drying them with a rotary evaporator to obtain mulberry leaf ethanol extract, which is then freeze-dried with a freeze dryer to obtain the extract.

[0009] Preferably, the mulberry leaf powder is obtained by crushing spring mulberry leaves or frosted mulberry leaves into powder using a high-speed grinder and then passing through a 300-mesh sieve.

[0010] Preferably, the papaya preservative is applied to the surface of the harvested papaya in the form of a spray or a coating.

[0011] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0012] The papaya preservative of the invention is prepared by dissolving mulberry leaf extract in water. The raw material source is extensive, natural and safe, and the cost is low. The preservative has a good preservative effect on papaya, can delay the decay and softening of papaya, reduce the weight loss rate of papaya during storage, and can also reduce the damage of cell membrane, thereby delaying the aging of fruit, so that the fruit can maintain good texture, and can also maintain the flavor and nutritional value of papaya. The preservative is relatively simple and easy to use, and the aqueous solution of mulberry leaf extract can be directly sprayed or coated on the surface of papaya after harvesting. The preservative is suitable for large-scale application and saves time and labor. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The papaya phenotype and rot index of Example 1 and Example 4 are shown.

[0014] Figure 2 It is the papaya hardness of Example 2 and Example 4.

[0015] Figure 3 It is the weight loss rate of papaya in Example 3 and Example 4.

[0016] Figure 4 The soluble solids and vitamin C contents in the papaya of Example 1 and Example 4.

[0017] Figure 5 The activities of POD, CAT and SOD in the papaya of Example 1 and Example 4.

[0018] Figure 6 The activities of GR and APX in the papaya of Example 1 and Example 4 are shown.

[0019] Figure 7 The activity of PAL in papaya of Example 1 and Example 4.

[0020] Figure 8 The activities of PG, PL and cellulase in the papaya of Example 1 and Example 4 are shown.

[0021] Fig. 9 The activity of cellulase in papaya of Example 1 and Example 4.

[0022] Fig.10This is the phenotype diagram of the mulberry leaf extracts of Example 1 and Example 4 when used as mango preservatives.

[0023] Fig.11 This is the phenotype diagram of the mulberry leaf extracts of Example 1 and Example 4 when used as banana preservatives. DETAILED DESCRIPTION

[0024] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0025] Example 1

[0026] (1) Preparation of Spring Mulberry Leaf Extract

[0027] 500g of spring mulberry leaves were crushed into powder by a high-speed pulverizer, passed through a 300-mesh sieve, and placed in a 4°C refrigerator for later use. Then, they were soaked in 70% ethanol solution at a solid-liquid ratio of 1:15 for 2 hours, ultrasonically extracted twice for 1 hour each time, and the extracts were combined and dried by rotary evaporation to obtain mulberry leaf ethanol extract. After freeze drying by a freeze dryer, mulberry leaf extract freeze-dried powder was obtained and placed in a 4°C refrigerator for later use. The components and contents of the extracts were determined, and the results are shown in Table 1.

[0028] Table 1 Analysis of main chemical components of spring mulberry leaf ethanol extract

[0029]

[0030] (2) Application of mulberry leaf extract as papaya preservative

[0031] Seven-ripe red papayas from a plantation in Sanya, Hainan were selected and delivered to the laboratory within 24 hours after picking, rinsed with tap water, soaked in 0.05% sodium hypochlorite solution, and dried. The freeze-dried powder of spring mulberry leaf extract was dissolved in water to prepare an aqueous solution with a concentration of 20 mg / mL, and the aqueous solution was evenly sprayed on the surface of the red papaya, avoiding the fruit stalk, and after drying, it was placed in a perforated fresh-keeping box and stored at room temperature.

[0032] Example 2

[0033] The preparation process and application of spring mulberry leaf extract in this embodiment are the same as those in Example 1, except for the concentration of the spring mulberry leaf extract aqueous solution sprayed on the surface of the papaya. In this embodiment, a mulberry leaf extract aqueous solution with a concentration of 15 mg / mL is sprayed on the surface of the papaya.

[0034] Example 3

[0035] The preparation process and application of spring mulberry leaf extract in this example are the same as those in Example 1, except for the concentration of the spring mulberry leaf extract aqueous solution sprayed on the papaya surface. In this example, a 25 mg / mL spring mulberry leaf extract aqueous solution is sprayed on the papaya surface.

[0036] Example 4

[0037] (1) Preparation of frost mulberry leaf extract

[0038] 500g of dried frost mulberry leaves were crushed into powder by a high-speed pulverizer, passed through a 300-mesh sieve, and placed in a 4°C refrigerator for standby use. Then, they were soaked in 70% ethanol solution at a solid-liquid ratio of 1:15 for 2 hours, ultrasonically extracted twice for 1 hour each time, and the extracts were combined and dried by rotary evaporation to obtain mulberry leaf ethanol extract. After freeze drying by a freeze dryer, mulberry leaf extract freeze-dried powder was obtained and placed in a 4°C refrigerator for standby use. The components and contents of the extracts were determined, and the results are shown in Table 2.

[0039] Table 2 Analysis of the main chemical components of frost mulberry leaf alcohol extract

[0040]

[0041]

[0042] (2) Application of mulberry leaf extract as a papaya preservative

[0043] Seven-ripe red papayas from a plantation in Sanya, Hainan were selected and delivered to the laboratory within 24 hours after picking, rinsed with tap water, soaked in 0.05% sodium hypochlorite solution, and dried. The above-mentioned frost mulberry leaf extract freeze-dried powder was dissolved in water to prepare a mulberry leaf extract aqueous solution with a concentration of 20 mg / mL, and the mulberry leaf extract aqueous solution was evenly sprayed on the surface of the red papaya, paying attention to avoiding the fruit stalk, and after drying, it was placed in a perforated fresh-keeping box for storage at room temperature.

[0044] Comparative Example 1

[0045] In this comparative example, clean water was sprayed on the surface of the red-heart papaya and then the papaya was placed in a perforated fresh-keeping box for storage.

[0046] Comparative Example 2

[0047] The difference between this comparative example and Example 1 lies in the concentration of the mulberry leaf extract aqueous solution sprayed on the surface of the red-heart papaya. The concentration of the mulberry leaf extract aqueous solution used in this comparative example is 10 mg / mL, and the rest is the same as Example 1.

[0048] Comparative Example 3

[0049] The difference between this comparative example and Example 1 lies in the concentration of the mulberry leaf extract aqueous solution sprayed on the surface of the red-heart papaya. The concentration of the mulberry leaf extract solution used in this comparative example is 30 mg / mL, and the rest is the same as Example 1.

[0050] Comparative Example 4

[0051] The difference between this comparative example and Example 1 is that the spring mulberry leaf extract in this comparative example is extracted by water extraction, and the rest of the preparation process and spraying method are the same as those in Example 1.

[0052] Comparative Example 5

[0053] The difference between this comparative example and Example 1 is that the spring mulberry leaf extract in this comparative example is extracted by methanol, and the rest of the preparation process and spraying method are the same as those in Example 1.

[0054] Experimental Example 1

[0055] The phenotypes of the red papayas treated in Examples 1-4 and Comparative Examples 1-5 were observed at room temperature on the 3rd, 6th, 9th and 12th days of storage and the changes in the color of the peel surface were recorded. The results are as follows

[0056] As shown in Table 3.

[0057]

[0058] From the above results, it can be seen that: after 12 days of storage, the papayas of Examples 1-4 had not yet developed spots, indicating that the use of spring mulberry leaf and frost mulberry leaf extracts as papaya preservatives can delay the decay of papayas, thereby extending the shelf life. When the spring mulberry leaf extract exceeding the concentration range (less than 15%, greater than 25%) was used as a papaya preservative, black spots appeared on the papaya on the 12th day. Although it has a certain extension effect compared with the blank control group (Comparative Example 1), the extension time is relatively short. When the spring mulberry leaves were extracted by water extraction and methanol extraction, black spots appeared on the 9th and 12th days respectively, indicating that the active ingredients in the mulberry leaves that play a key preservation role can be extracted through ethanol extraction.

[0059] Experimental Example 2

[0060] The various indicators of the red-heart papayas treated with Examples 1-3 (spring mulberry leaf treatment group), Example 4 (frost mulberry leaf treatment group) and Comparative Example 1 (control group) were observed after storage at room temperature for 12 days. The weight loss rate, hardness, rot rate, etc. were measured on the 3rd, 6th, 9th and 12th days of storage, and the pulp was sampled and the enzyme activity was measured after being frozen in a -40°C ultra-low temperature refrigerator.

[0061] 1. Effect of mulberry leaf extract on phenotype and decay rate of red papaya fruit

[0062] The phenotypes of the red-heart papayas of Example 1 (spring mulberry leaf treatment group), Example 4 (frost mulberry leaf treatment group) and Comparative Example 1 (control group) were observed at the 3rd, 6th, 9th and 12th day of storage, and their decay rates were determined. The total number of papayas in each group was 30, and the 30 papayas were divided into 10 groups, with 3 papayas in each group. The fruit decay rate was determined by counting method, and the number of papaya fruits with browning on the skin or moldy fruit stalks in the 30 papaya fruits was recorded at the 3rd, 6th, 9th and 12th day, and calculated by the formula: Fruit decay rate (%) = number of papaya fruits with browning on the skin or moldy fruit stalks ÷ total number × 100%.

[0063] The results are as follows Figure 1 As shown, in Figure 1 In the figure, A is the phenotype of papaya, and B is the rot rate of papaya. Figure 1 As shown in Figure A (only one of the subgroups in each group is shown), when the red-heart papayas in the control group (Comparative Example 1) were stored for 6 days, the red-heart papayas in the control group (Comparative Example 1) began to turn yellow significantly, black spots appeared on the 9th day (the flesh began to rot), and large areas of rot occurred on the 12th day. However, the spring mulberry leaf treatment group (Example 1) only showed slight discoloration on the 12th day, without large-scale rot. The frost mulberry leaf treatment group (Example 4) had a certain degree of discoloration on the 12th day, but the degree of rot was lighter than that of the control group (Comparative Example 1).

[0064] from Figure 1 As shown in Figure B, the control group (Comparative Example 1) began to rot (internal flesh) on the 6th day, and the rot index increased rapidly. The mulberry leaf treatment group began to rot (internal flesh) on the 9th day. The rot index of the control group (Comparative Example 1) reached 60% on the 12th day, while the rot index of the spring mulberry leaf treatment group (Example 1) was lower. It was about 40% at 12 days; the frost mulberry leaf treatment group (Example 4) was between the two, about 45% at 12 days. This shows that both spring mulberry leaf and frost mulberry leaf extracts have a certain effect on papaya preservation, and can delay the rot time and maintain good texture, but the spring mulberry leaf effect is better.

[0065] 2. Effect of mulberry leaf extract on the hardness of red papaya fruit

[0066] Hardness is an important indicator of fruit maturity. During the storage period of fruit, hardness and the storage properties of the fruit often show a certain positive correlation.

[0067] The hardness of the red papayas of Example 2, Example 4 and Comparative Example 1 was measured at 3, 6, 9 and 12 days of storage. The hardness was measured by using a hardness meter, specifically, the hardness meter was placed vertically on the surface of the treated fruit, the indenter of the hardness meter was evenly pressed into the fruit, and the hardness was recorded. The results are shown in FIG. Figure 2 shown.

[0068] from Figure 2 It can be seen that as the storage time increases, the hardness of the fruit gradually decreases, which is related to the transformation of pectin substances during the ripening and aging of the fruit and the degradation of cellulose in the cell wall of the pericarp. Among them, the fruit hardness of the control group (Comparative Example 1) at 0 days was about 6 kg / cm 2 As time went by, the hardness decreased significantly and was close to 0 on the 12th day, while the hardness of the fruit treated with mulberry leaf extract was still 1kg / cm on the 12th day. 2 The above indicates that the sample will soften quickly without mulberry leaf extract treatment. The spring mulberry leaf group (Example 2) has a slower hardness decline rate than the control group, and the hardness is still about 3 kg / cm at the 9th day. 2 The hardness of the frosted mulberry leaf group (Example 4) at 0d was comparable to that of the other two groups, and the downward trend of hardness was between that of the control group and the spring mulberry leaf group.

[0069] The results showed that mulberry leaf extract can effectively maintain the structural stability of the fruit cell wall, and can delay the decrease of fruit hardness and the softening of papaya to a certain extent, but the effect of spring mulberry leaf extract is slightly better than that of frost mulberry leaf extract.

[0070] 3. Effect of mulberry leaf extract on weight loss rate of red papaya fruit

[0071] The weight loss rate of the red-heart papayas of Example 3, Example 4 and Comparative Example 1 was measured. The weight loss was measured by weighing method. The fruit was stored for 12 days, and the fruit weight was measured on the 3rd, 6th, 9th and 12th days during the storage period. There were 3 papayas in each group. The weight loss of each papaya was measured and the average value was taken as the weight loss rate of each group. The weight loss calculation formula was:

[0072] Weight loss (%) = (weight of fruit before storage - weight of fruit after n days of storage) ÷ weight of fruit before storage × 100%.

[0073] The results are as follows Figure 3 As shown, from Figure 3 It can be seen that the weight loss rate of papaya in the control group (Comparative Example 1) increases rapidly over time, exceeding 12% on the 12th day, while the weight loss rate of papaya treated with mulberry leaf extract is about 8% on the 12th day, indicating that papaya loses water faster when not treated with mulberry leaf extract. Among them, the weight loss rate of the spring mulberry leaf group (Example 3) increases relatively slowly, indicating that the spring mulberry leaf extract can reduce the water loss of papaya to a certain extent, while the weight loss rate of the frost mulberry leaf group (Example 4) is close to that of the spring mulberry leaf group, indicating that the frost mulberry leaf extract also has a certain effect on the water retention of papaya. The use of spring mulberry leaf and frost mulberry leaf extracts can reduce the weight loss rate of papaya during storage, which has a positive effect on the preservation of papaya.

[0074] 4. Effect of mulberry leaf extract on soluble solids and vitamin C content in red papaya fruit

[0075] The increase or decrease in soluble sugar content has a great relationship with the life activities of the fruit during the preservation process. The soluble sugar content of the fruit is the main reference factor for the quality of the fruit.

[0076] The soluble solids and vitamin C contents of the red papayas treated in Example 1, Example 4 and Comparative Example 1 were measured at 3, 6, 9 and 12 days of storage.

[0077] The determination process of soluble solids is as follows: peel each papaya fruit, take the middle pulp, squeeze the juice, centrifuge at 4000r for 10 minutes, take the supernatant, and set aside for testing. Open the cover of the refractometer, calibrate with distilled water, drop the extract on the surface of the prism, observe and record the data.

[0078] The vitamin C content of the fruit was determined using a kit from Suzhou Grace Biotech Co., Ltd. according to the instructions.

[0079] The results are as follows Figure 4 As shown, from Figure 4 As shown in Figure A, the soluble solid content of the fruits treated with Example 1, Example 4 and Comparative Example 1 increased significantly on the 3rd day, and then gradually decreased with the increase of time. The increase on the 3rd day is because the fruit will undergo after-ripening after picking, and the content of various organic substances in the fruit will increase during the after-ripening process. When it reaches maturity, the body will gradually age and die. During this process, the organic matter in the body will be consumed due to respiration, resulting in a slow decrease in its content.

[0080] On the 6th day, the soluble solids content of the fruits treated with Example 1 (spring mulberry leaf treatment group) and Example 4 (frost mulberry leaf treatment group) showed a smaller decreasing trend, while the soluble solids content of the fruits treated with Comparative Example 1 (control group) showed a larger decreasing trend. Moreover, after the 6th day, the soluble solids content of the fruits treated with Example 1 (spring mulberry leaf treatment group) and Example 4 (frost mulberry leaf treatment group) was greater than that of the fruits treated with Comparative Example 1 (control group), indicating that mulberry leaf extract can delay the decrease of soluble solids in papaya fruit.

[0081] from Figure 4 As shown in Figure B, the vitamin C content of the fruits of Example 1, Example 4 and Comparative Example 1 did not change much during the entire storage period, and the nutrients were well preserved during the storage process, maintaining the flavor and nutritional value of the papaya.

[0082] 5. Effect of mulberry leaf extract on the activities of POD, CAT, SOD, GR and APX in red papaya fruit

[0083] Antioxidant enzymes play an important role in the growth, development, maturity and aging of fruits, and are involved in physiological processes such as anti-oxidation, disease resistance and resistance to adverse stress. The activity of these antioxidant enzymes can promptly remove the reactive oxygen produced in the fruit, reduce oxidative stress damage, enhance the antioxidant capacity of the fruit, and thus delay the aging process.

[0084] The activities of POD (peroxidase), CAT (catalase), SOD (superoxide dismutase), GR (glutathione reductase), and APX (ascorbate peroxidase) of the red papaya treated by Example 1, Example 4, and Comparative Example 1 were measured at 3, 6, 9, and 12 days of storage. The determination of these antioxidant enzymes was performed using the kits of Suzhou Grace Biotechnology Co., Ltd. according to the instructions.

[0085] The activity results of POD, CAT and SOD are as follows Figure 5 As shown. Figure 5 As shown in Figure A, the POD activity of the control group (Comparative Example 1) showed a continuous downward trend, and the spring and frost mulberry leaf treatment groups (Example 1 and Example 4) remained stable and slightly increased in the first 3 days, and slowly decreased after the 3rd day, but the activity at each time point was significantly higher than that of the control group in the same period. This shows that the mulberry leaf extract reduces the decline of POD enzyme to a certain extent and prolongs the defense time of the fruit against external stress.

[0086] from Figure 5 As shown in Figure B, the CAT activity of the control group continued to decrease, and the spring and frost mulberry leaf groups decreased overall, but the decline at each time point was small, and the activity at each time point was higher than that of the control group during the same period. Figure 5 As shown in Figure C, the SOD activity of the control group continued to decline, while that of the spring mulberry leaf group increased significantly first and then decreased, reaching a peak value at 6 days, close to 150U / g. The increase in the frost mulberry leaf treatment group was smaller than that of the spring mulberry leaf group, but compared with the control group, both groups had a significant effect on improving the SOD activity.

[0087] from Figure 5 It can be seen that over time, the activities of the three antioxidant enzymes in the control group (Comparative Example 1) continued to decline, which is due to the gradual consumption of enzymes by the metabolism of the fruit itself, and the lack of effective external stimulation to maintain or improve enzyme activity. In the spring mulberry leaf and frost mulberry leaf treatment groups, the activities of antioxidant enzymes such as POD, CAT, and SOD were maintained at a higher level in the treatment group, especially the activity of SOD, which was significantly higher than that of the control group in the same period. It shows that the extracts of these two mulberry leaves can improve the activities of these antioxidant enzymes, so that POD, CAT, and SOD are maintained at a higher level, and the active oxygen generated in the fruit can be removed in time, oxidative stress damage can be reduced, and the antioxidant capacity of the fruit can be enhanced, thereby delaying the aging process of the fruit.

[0088] The results of the activity of GR and APX are as follows Figure 6 As shown in . Figure 6 As shown in Figure A, the overall GR activity level of the control group was low and the range of change was small. The levels of the treatment group and the control group were close on the 3rd day, but after the 3rd day, the mulberry leaf treatment group was significantly greater than the control group, especially the spring mulberry leaf treatment group, which had the highest activity on the 6th day and then decreased. The activity change trend of the frost mulberry leaf treatment group was similar to that of the spring mulberry leaf treatment group, which also increased first and then decreased, but the activity values ​​at each time point were lower than those of the spring mulberry leaf treatment group.

[0089] from Figure 6 As shown in Figure B, the APX activity of the control group was relatively stable with little fluctuation. The activity of the mulberry leaf treatment group increased first and then decreased. Among them, the spring mulberry leaf treatment group reached a peak on the 6th day, which was similar to the change of GR activity. It increased significantly on the 6th day and then decreased. The activity change trend of the frost mulberry leaf group was the same as that of the spring mulberry leaf group, but the overall activity was lower than that of the spring mulberry leaf group.

[0090] GR and APX are key enzymes in the antioxidant system, and their activity changes reflect the ability of papaya to cope with oxidative stress. The activities of these two enzymes in the control group were relatively stable and low, indicating that when there was no mulberry leaf treatment, the antioxidant enzyme system of papaya itself was at a relatively basic level. After mulberry leaf treatment, the activity of its antioxidant enzymes increased, especially after spring mulberry leaf treatment, the GR and APX activities of the fruit increased significantly on the 6th day. The changes in the activity of these enzymes are conducive to maintaining the redox balance in cells and protecting cells from oxidative damage.

[0091] Combination Figure 5 and Figure 6 It can be seen that the antioxidant enzyme activity in the fruit can be increased after being treated with mulberry leaves, especially the activity of POD and SOD. With the increase of storage time, the levels of these two antioxidant enzymes are significantly increased, which are significantly higher than the control group of the same period. The activity of the two antioxidant enzymes GR and APX increased significantly on the 6th day, and then decreased, but the overall activity was still greater than that of the control group of the same period. This shows that mulberry leaf extract can improve the antioxidant properties of fruits in different ways, thereby delaying the aging process of fruits.

[0092] VI. Effect of mulberry leaf extract on PAL enzyme activity in red papaya fruit

[0093] PAL (phenylalanine ammonia lyase) is a key enzyme in the phenylpropanoid metabolic pathway and is related to the synthesis of plant secondary metabolites such as phenols, flavonoids and other antimicrobial substances. These substances not only have antioxidant effects, but may also have a positive effect on the fruit's resistance to pathogens and disease.

[0094] The PAL activity of the red papaya treated in Example 1, Example 4 and Comparative Example 1 was measured at 3, 6, 9 and 12 days of storage. The measurement was performed using a kit from Suzhou Grace Biotech Co., Ltd. according to the method in the instruction manual.

[0095] The results are as follows Figure 7 As shown, the PAL activity of the control group (Comparative Example 1) showed a trend of first rising and then maintaining stability or slightly rising, while the mulberry leaf treatment group gradually rose over time, and the activity in the later period was significantly higher than that of the control group, especially the spring mulberry leaf treatment group, whose PAL activity change trend was more significant. This shows that mulberry leaf extract can increase the activity of PAL, promote the synthesis of phenolic and flavonoid substances, and thus enhance the antioxidant effect of fruits during storage and the anti-pathogen performance of fruits.

[0096] VII. Effect of mulberry leaf extract on PG, PL and cellulase activity in red papaya fruit

[0097] PG (protein glutaminase) and PL (pectin lyase) are related to pectin degradation and can affect the softening of fruits. Cellulase is involved in the decomposition of cell walls and affects the texture and quality of fruits.

[0098] The activities of PG, PL and cellulase of the red papaya treated in Example 1, Example 4 and Comparative Example 1 were measured at 3, 6, 9 and 12 days of storage. The test kit of Suzhou Grace Biotechnology Co., Ltd. was used and the test was performed according to the instruction method.

[0099] The results are as follows Figure 8 and Fig. 9 As shown. Figure 8 As can be seen from Figures A and B in the figure, the increase in PG and PL activities in the control group (Comparative Example 1) is relatively large, while the spring mulberry leaf and frost mulberry leaf treatment groups can inhibit the increase in PG and PL activities in papaya, thereby slowing down the decomposition of pectin, reducing the degradation of pectin, and further delaying the softening and aging of the fruit, which is beneficial to maintaining the hardness and integrity of the fruit and extending the shelf life.

[0100] from Fig. 9 It can be seen that under the treatment of spring mulberry leaves and frost mulberry leaves, the activity of cellulase in the fruit did not change much in each period during the 12-day storage period, indicating that mulberry leaf extract can inhibit the activity of cellulase, thereby reducing the decomposition of cell walls, helping to maintain the structural stability of cell walls, and maintaining the texture and quality of papaya during storage.

[0101] Experimental Example 3 Effect of mulberry leaf extract on the preservation of other fruits (mango, banana)

[0102] (1) Experimental materials: Guifei mango, banana (both picked from a plantation in Sanya, Hainan), 20 mg / mL spring mulberry leaf extract solution (Example 1), 20 mg / mL frosted mulberry leaf extract solution (Example 4), and distilled water.

[0103] (2) Experimental process: Select fruits of uniform size and shape and free of disease and deliver them to the laboratory within 24 hours after picking, rinse with tap water, soak in 0.05% sodium hypochlorite solution, and dry. The dried Guifei mangoes and bananas were grouped and treated separately, with 5 in each group. After grouping, they were sprayed with spring mulberry leaf extract solution, frost mulberry leaf extract solution, and clean water respectively. The grouping treatment is as follows:

[0104] Experimental group 1: Guifei mango / banana + 20mg / mL spring mulberry leaf extract solution;

[0105] Experimental group 2: Guifei mango / banana + 20mg / mL spring mulberry leaf extract solution;

[0106] Blank group: Guifei mango / banana + water.

[0107] After spraying, Guifei mangoes and bananas were stored at room temperature for 12 days. Their phenotypes were observed and photographed on the 3rd, 6th, 9th and 12th days of storage.

[0108] (3) Experimental results: Fig.10 and Fig.11 As shown, in Fig.10 and Fig.11 In the figure, A represents the phenotype of the fruit at 0 days; B represents the phenotype of the fruit at 3 days; C represents the phenotype of the fruit at 6 days; D represents the phenotype of the fruit at 9 days; E represents the phenotype of the fruit at 12 days; among them, Fig.10 and Fig.11 In the AE diagram, the numbers 1, 2, and 3 from top to bottom represent the treatments with spring mulberry leaf extract solution, frost mulberry leaf extract solution, and distilled water, respectively.

[0109] from Fig.10 and Fig.11 It can be seen that the changes in the fruits treated with spring mulberry leaf extract solution and frost mulberry leaf extract solution as preservatives are not much different from those treated with distilled water. On the 12th day, the Guifei mangoes in these three groups were rotten on a large scale, while the bananas matured at the same time, and the maturity of the three groups of bananas was almost the same, indicating that the spring mulberry leaf extract solution and frost mulberry leaf extract solution cannot preserve the Guifei mangoes and bananas, and cannot delay the decay time. This further shows that mulberry leaf extract does not have a preservative effect on all fruits.

[0110] Although the present invention has been described using the above preferred embodiments, it is not intended to limit the scope of protection of the present invention. Any person skilled in the art who makes various changes and modifications to the above embodiments without departing from the spirit and scope of the present invention still fall within the scope of protection of the present invention.

Claims

1. Application of mulberry leaf extract in the preparation of a papaya preservative having disease resistance and delayed ripening properties.

2. The use according to claim 1, characterized in that: The mulberry leaf extract is prepared by first soaking mulberry leaf powder in an ethanol aqueous solution with a volume percentage concentration of 65% to 75% at a material-liquid mass ratio of 1:(10 to 20) for 2 to 4 hours and then ultrasonically extracting the powder. The ultrasonic extraction is performed 2 to 4 times, each time for 1 hour, and the extracts are combined and dried by rotary evaporation to obtain mulberry leaf ethanol extract, which is then freeze-dried by a freeze dryer.

3. The use according to claim 1, characterized in that: The mulberry leaf powder is prepared by crushing spring mulberry leaves or frost mulberry leaves into powder and then passing the powder through a 300-mesh sieve.

4. The use according to claim 1, characterized in that: The papaya preservative is a mulberry leaf extract aqueous solution with a mass percentage concentration of 15% to 25%.

5. The use according to claim 4, characterized in that: The papaya preservative is a mulberry leaf extract aqueous solution with a mass percentage concentration of 20%.

6. The use according to claim 1, characterized in that: The papaya preservative is applied to the surface of the harvested papaya in the form of spraying or coating.

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