Composite preservation method of pineapples

Abstract

The invention discloses a composite preservation method of pineapples. According to the invention, it is found that the preservation effect of film coating treatment of the fruit wax and melatonin mixed solution on pineapples is better than that of single fruit wax film coating or melatonin solution soaking, and maturation and aging of the pineapple fruits are effectively delayed, specifically, color change and hardness reduction of the pineapple fruits are delayed, the water loss rate of the pineapple fruits is reduced, and the respiration of the pineapple fruits is inhibited; the accumulation of MDA, superoxide and active oxygen in the fruits is reduced, the membrane damage of the fruits is reduced, and technical support and theoretical basis are provided for the improvement of post-harvest treatment and storage and transportation technologies of the pineapples.

Description

Technical Field

[0001] The invention belongs to the technical field of post-harvest fresh-keeping, and in particular relates to a composite fresh-keeping method for pineapples. Background Art

[0002] Pineapple (Ananas comosus), also known as pineapple, is native to South America and has now become the world's third largest tropical fruit (Gong Deqiang et al., 2010). As one of China's important tropical and subtropical economic fruits, pineapple is loved by consumers in my country because of its sweet and sour taste and unique aroma. China's pineapple producing areas are mainly distributed in Guangdong, Hainan, Fujian, Guangxi and Yunnan. (Liu Haiqing et al., 2016). In recent years, China has introduced new pineapple varieties such as "Golden Diamond" and promoted their planting in Hainan and other regions to increase production. The pineapple industry has become an important pillar of agricultural economic development in China's tropical and subtropical regions, and plays a vital role in promoting agricultural economic growth.

[0003] However, under modern industrialization, fresh pineapples still face a series of problems after harvesting. Freshly harvested pineapple fruits contain a lot of water and sugar, and are very easy to rot and deteriorate during storage and transportation. Among them, pineapple blackheart disease (BH) is particularly prominent in the storage and transportation links. Pineapple blackheart disease is a post-harvest physiological disease that is prone to almost all promoted varieties. The symptoms of blackheart disease are difficult to distinguish from the outside of the fruit. The initial browning of the fruit heart (vascular bundle close to the core) first appears, and eventually spreads to the pineapple pith and even the flesh, turning dark brown, causing the fruit to deteriorate and rot, and lose its economic value (Gu Hui et al., 2020). Therefore, it is particularly important to conduct green and efficient research on the prevention and control of pineapple blackheart disease and the post-harvest quality maintenance technology of pineapples for the sustainable development of pineapple modernization and industrialization.

[0004] Film coating is a preservation method that uses materials such as fruit wax to form a thin film on the surface of the fruit. This method has been applied and promoted in a variety of horticultural crops such as apples. Fruit wax regulates the gas environment of fruit storage by inhibiting ethylene and other substances, which can significantly reduce the respiration intensity of the fruit and is of great significance for the preservation of fruit quality. Fruit wax can also be used as a slow-release carrier for other fruit and vegetable preservatives. Fruit wax film coating is already an ideal method for commercial processing in the storage and preservation of fruits and vegetables (Zhu Zhenjia et al., 2013). Studies have shown that post-harvest pineapple can be treated with fruit wax to delay fruit discoloration, reduce organic acid content, effectively improve fruit quality, and inhibit fruit ripening (Li, 2018). Removing fruit wax from the surface of post-harvest blueberry fruit will accelerate water loss and fruit decay, shortening the fruit storage period (Chu, 2018). The key gene CER1-1 that synthesizes fruit wax in tomato fruit catalyzes the biosynthesis of waxy alkanes, which can improve the shelf life and drought resistance of the fruit (Wu, 2022). Fruit wax coating treatment of Xinjiang small white apricot can maintain a high hardness and ascorbic acid content (Cheng Linlin et al., 2012).

[0005] Melatonin (MLT) is a multifunctional hormone widely present in plants and is involved in many aspects of plant growth and development. Melatonin is widely used in various research fields. In response to the needs of increasing crop yields and extending the storage period of fruits, researchers have conducted in-depth research on melatonin in the preservation of postharvest fruits in recent years. Experiments have shown that melatonin can effectively delay fruit aging and has the potential to be promoted and applied as a new generation of preservatives. Melatonin treatment can delay fruit softening, the decline in titratable acidity and soluble solids content, reduce respiration intensity and fruit corruption, and maintain good fruit quality (JAKARIA, 2019). Melatonin coating treatment can delay the quality attenuation of blueberry fruits during cold storage and improve the antioxidant system (Petriccione, 2022). Melatonin treatment can reduce ethylene production and maintain the fruit quality of apples during postharvest storage (Onik, 2021). Chitosan and melatonin composite coating treatment can reduce the weight loss rate and respiration intensity of fresh-cut broccoli, and effectively delay the yellowing of broccoli to maintain its quality (Tan Yunxiu et al., 2023). During the storage and transportation of horticultural crops, black spots of varying degrees may appear on the surface of apples, lychees, etc. Qiao Pei et al. (2022) studied the effect of melatonin on the preservation of lychees and tested different concentrations of melatonin treatment. The results showed that melatonin treatment can significantly reduce the degree of browning of lychees.

[0006] The mechanism of melatonin in delaying fruit aging is mainly regulated through four aspects, namely, scavenging oxygen active free radicals, inhibiting ethylene synthesis, preventing antioxidant enzyme passivation and reducing the browning index (Gao Zhiping et al., 2022). Reactive oxygen free radicals (ROS) are harmful compounds produced by oxidation in the body. Excessive accumulation of ROS is one of the causes of browning of fruits. In order to slow down the browning and deterioration of fruits, antioxidant enzymes that can scavenge ROS in plant cells are very important. Melatonin in the fruit itself can increase the activity of antioxidant enzymes (Guo Xingke et al., 2020). On the contrary, while ethylene promotes fruit ripening, it also accelerates fruit aging. Melatonin can delay fruit aging by inhibiting ethylene synthesis (JAKARIA, 2019). Peroxides in plants can be converted into non-toxic substances under the action of antioxidant enzymes.

[0007] In order to achieve better preservation of fruits and vegetables, combining multiple preservation methods has become a research hotspot in the storage and transportation of fruits and vegetables in recent years. However, there is no literature on the effect of fruit wax coating combined with melatonin treatment on the preservation of post-harvest pineapples, so it has research value potential. Summary of the invention

[0008] The present invention utilizes fruit wax coating and melatonin to compositely treat pineapples, and utilizes fruit wax to adjust the storage gas environment of the fruit and the antiseptic and fresh-keeping effect of melatonin, thereby reducing the respiratory intensity and enzymatic browning of the pineapple fruit, reducing nutritional loss, delaying fruit deterioration, and ultimately achieving the purpose of extending the storage period of the pineapple. The present invention performs composite coating and melatonin treatment under normal temperature conditions to achieve the purpose of preserving the post-harvest pineapples, and provides a theoretical basis for improving the storage and transportation technology of pineapples.

[0009] The first object of the present invention is to provide a preservative, wherein the active ingredients of the preservative include fruit wax and melatonin.

[0010] Preferably, the concentration of the fruit wax is 65g·L -1 The concentration of melatonin is 600 μmol·L -1 .

[0011] A second object of the present invention is to provide a composite fresh-keeping method for pineapples, comprising the following steps:

[0012] S1. Wash the harvested pineapple with water to remove surface dirt, sterilize it, and dry it;

[0013] S2. soaking the pineapple with the preservative and drying it.

[0014] Preferably, the sterilization is carried out using 50 mg·L -1 Soak in chlorine dioxide for 10 min and then dry it. -1 of prochloraz and 500mg·L -1 Soak in the solution of cyprodinil for 1 min.

[0015] Preferably, soaking the pineapple in the preservative is soaking the pineapple in the preservative for 30 minutes.

[0016] Beneficial effects of the present invention:

[0017] The melatonin and fruit wax mixed coating treatment provided by the present invention has the best preservation effect, which is better than the fruit wax or melatonin treatment alone, delays the color change and hardness reduction of pineapple fruit, reduces the water loss rate of pineapple fruit, inhibits the respiration of pineapple fruit, reduces the accumulation of MDA, superoxide and active oxygen in the fruit, reduces the membrane damage of the fruit, is conducive to effectively extending the shelf life of pineapple, and better guarantees the storage and transportation value of pineapple. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The phenotypes of pineapple fruits after different treatments and storage for different days; CK water is CK1 (control group 1): pineapple fruits are washed with water and then dried; CK sterilization is CK2 (control group 2): pineapple fruits are washed with water and then sterilized and dried; fruit wax is fruit wax coating treatment: pineapple fruits are treated with 65g·L-1 After being treated with fruit wax solution, the fruit was dried. Melatonin was treated with melatonin: pineapple fruit was treated with 600 μmol·L -1 Melatonin solution was soaked for 30 minutes and then dried, and mixed to form a mixed coating: 65g·L -1 Fruit wax + 600μmol·L -1 Apply the melatonin mixed solution to a film and let it dry.

[0019] Figure 2 It is the result diagram of the influence of each treatment on the chromaticity of pineapple peel; among them, A is the influence of each treatment on the chromaticity L* of pineapple peel, B is the influence of each treatment on the saturation C* of pineapple peel, and C is the influence of each treatment on the hue h° of pineapple peel; CK2 means the pineapple fruit is washed with clean water and then sterilized and dried, fruit wax means fruit wax coating treatment, melatonin means melatonin solution immersion treatment, and mixed means fruit wax and melatonin mixed solution coating treatment.

[0020] Figure 3 It is a graph showing the effects of various treatments on the hardness of pineapples; wherein, CK2 indicates that the pineapple fruit is washed with clean water, sterilized and dried, fruit wax indicates fruit wax coating treatment, melatonin indicates melatonin solution immersion treatment, and mixed indicates fruit wax and melatonin mixed solution coating treatment.

[0021] Figure 4 It is a graph showing the effect of various treatments on the weight loss rate of pineapple; among them, CK2 means the pineapple fruit is washed with clean water and then sterilized and dried, fruit wax means the fruit wax coating treatment, melatonin means the melatonin solution immersion treatment, and mixed means the fruit wax and melatonin mixed solution coating treatment.

[0022] Figure 5 It is a result diagram of the effect of each treatment on the ethylene release of pineapple; among them, CK2 means the pineapple fruit is washed with clean water and then sterilized and dried, fruit wax means the fruit wax coating treatment, melatonin means the melatonin solution immersion treatment, and mixed means the fruit wax and melatonin mixed solution coating treatment.

[0023] Figure 6 It is a graph showing the effects of various treatments on the respiration rate of pineapples; wherein, CK2 indicates that the pineapple fruit is washed with clean water and then sterilized and dried, fruit wax indicates the fruit wax coating treatment, melatonin indicates the melatonin solution immersion treatment, and mixed indicates the fruit wax and melatonin mixed solution coating treatment.

[0024] Figure 7 This is a graph showing the effects of various treatments on the malondialdehyde (MDA) content in pineapple fruit; CK2 indicates that the pineapple fruit is washed with clean water and then sterilized and dried; fruit wax indicates the fruit wax coating treatment; melatonin indicates the melatonin solution immersion treatment; and mixed indicates the fruit wax and melatonin mixed solution coating treatment.

[0025] Figure 8It is a graph showing the effects of various treatments on the activity of catalase (POD) in pineapple peel; wherein, CK2 indicates that the pineapple fruit is washed with clean water and then sterilized and dried, fruit wax indicates fruit wax coating treatment, melatonin indicates melatonin solution immersion treatment, and mixed indicates fruit wax and melatonin mixed solution coating treatment.

[0026] Fig. 9 It is a graph showing the effects of various treatments on the activity of catalase (CAT) in pineapple fruit; wherein, CK2 indicates that the pineapple fruit is washed with clean water and then sterilized and dried, fruit wax indicates fruit wax coating treatment, melatonin indicates melatonin solution immersion treatment, and mixed indicates fruit wax and melatonin mixed solution coating treatment. DETAILED DESCRIPTION

[0027] The following examples are provided to further illustrate the present invention, rather than to limit the present invention.

[0028] The following examples use pineapple fruit as experimental material, mainly exploring the effects of fruit wax and melatonin on the preservation of pineapple fruit under room temperature storage, and the effects of appropriate concentrations of fruit wax and melatonin on the enzyme activity of pineapple resistance. The main contents are as follows:

[0029] 1. The effects of fruit wax and melatonin treatment on the phenotypic indicators of pineapple fruit, including color, firmness, yellowing index, weight loss rate, ethylene release, and respiratory rate.

[0030] 2. The effects of appropriate concentrations of fruit wax and melatonin on the activities of malondialdehyde (MDA), catalase (CAT), and peroxidase (POD) related resistance enzymes in pineapple fruit.

[0031] Example 1

[0032] 1. Materials and Methods

[0033] 1.1 Experimental materials and pretreatment

[0034] The pineapple variety used in the test was "Bali", and the pineapple fruits were selected and harvested without mechanical damage and with a maturity of 70% to 80%. The fruit wax was a product of FMC Corporation of the United States (item number: Sta-Fresh 2952), and melatonin (item number: A600605) was purchased from Shanghai Shenggong Biological Co., Ltd.

[0035] Pretreatment: After harvesting fresh pineapples, they were immediately transported back to the laboratory for pretreatment. After washing the surface dirt with clean water, 50 mg·L -1 The strong cleaning agent (chlorine dioxide, purchased from Beijing Huamao Chengtian Technology Development Co., Ltd.) was soaked for 10 minutes and then dried, and then 500 mg·L -1 Prochloraz (Jiangsu Huifeng Bio-Agriculture Co., Ltd.) and 500 mg·L -1The plants were immersed in a mixed solution of cyprodinil (Jiangsu Kuaida Agrochemical Co., Ltd.) for 1 min, and then dried for 2 experimental treatments.

[0036] 2. Experimental treatment

[0037] 2.1 Treatment methods: CK1 (control group 1): pineapple fruits were washed with clean water and then air-dried. CK2 (control group 2): pineapple fruits were washed with clean water, sterilized and air-dried. Fruit wax coating treatment group: pineapple fruits were treated with 65g·L -1 Melatonin treatment group: pineapple fruits were treated with 600 μmol·L- 1 After soaking in melatonin solution for 30 minutes, the mixture was dried. 1 Fruit wax + 600μmol·L- 1 Apply the melatonin mixed solution on the surface and let it dry.

[0038] 2.2 Experimental design

[0039] This experiment was conducted in two steps. First, different preservatives (65 g·L- 1 Fruit wax solution, 600μmol·L- 1 Melatonin solution, 65g·L- 1 Fruit wax + 600μmol·L- 1 Fresh pineapples were treated with a melatonin mixed solution, dried uniformly and placed in a constant temperature box at 25°C to observe changes during storage, and phenotypic observations and physiological index measurements during the shelf life were carried out; secondly, the treatment group with the best effect was screened out, and the fruits were subjected to physiological and biochemical measurements.

[0040] 2.3 Determination indicators and sampling methods

[0041] The chromaticity, firmness, yellowing index, weight loss rate, ethylene release and respiration rate of pineapples were measured at shelf life of 1d, 3d, 5d, 7d, 9d, 11d, 13d and 15d. Five fruits were randomly selected from each treatment in each replicate, and the pulp was quick-frozen in liquid nitrogen for a total of 3 replicates and stored in a -80℃ refrigerator for subsequent determination of malondialdehyde, catalase and peroxidase-related enzyme activities.

[0042] 2.3.1 Phenotypic observation and physiological index measurement methods

[0043] (1) Fruit chromaticity measurement

[0044] The reference method (Zhu, H., Li, XP, Yuan, RC, Chen, YF, Chen, WX, 2010. Changes in volatile compounds and associated relationships with other ripening events in banana fruit. J. Hortic. Sci. Biotechnol. 85, 283–288.) was used to measure the chromaticity of pineapple peel using a CM-2300d fully automatic colorimeter. The L value, a value, b value, c value and h° value of 5 parts on the central equatorial plane of the pineapple fruit were measured, and the average value was taken and repeated 3 times. Among them, the a value, b value and c value were used to calculate the C value.

[0045] (2) Fruit firmness measurement

[0046] The reference method (Qin Jiajia. Screening of MaEBF1 interacting proteins and expression analysis of key genes in the post-ripening disorder of banana caused by low temperature stress [D]. South China Agricultural University, 2018.) was used. The high-precision analyzer model TMS-Pro was used. In this experiment, the pineapple was punctured and the hardness of the pineapple pulp was measured by the analyzer. Each repetition measured 6 points, the hardness was expressed in Newton, and 3 repetitions were performed.

[0047] (3) Determination of fruit weight loss rate

[0048] Weigh the pineapple sample before storage 0 , take samples and weigh them every 1 day 1 Repeat the experiment three times and calculate the weight loss rate according to the following formula:

[0049] Weight loss rate (%) = (m 0 -m 1 ) / m 0 ×100

[0050] (4) Determination of fruit ethylene release rate

[0051] The reference method (Ding Xiaochun. Study on the mechanism of CpEBF1 and its interacting proteins regulating papaya fruit ripening disorders under 1-MCP and low temperature stress [D]. South China Agricultural University.) was used to determine the ethylene release rate of pineapple. Three pineapple samples were taken from each treatment group and placed in a sealed can. After two hours, the sealed can was shaken and the gas in the can was waited for to mix evenly. The gas in the can was extracted to determine the ethylene concentration and calculate the ethylene release amount. Each treatment was repeated 3 times, and 3 injections (1 mL each) were extracted each time. The working conditions of gas chromatography were as follows: the chromatographic column was an activated alumina packed column, the column temperature was 80°C, the injection port temperature was 140°C, the carrier gas was He, and the flow rate was 30 mL.min- 1, FID temperature 150℃. The formula for calculating ethylene release is as follows:

[0052]

[0053] (5) Determination of respiratory rate

[0054] Reference method (Ding Xiaochun. Study on the mechanism of CpEBF1 and its interacting proteins regulating papaya fruit ripening disorder under 1-MCP and low temperature stress [D]. South China Agricultural University.), using the canning method, 3 pineapples were taken for each treatment, placed in a sealed can at a fixed time every day for 2 hours, and then the gas was extracted. Each treatment was repeated three times, and each repetition was 2 injections (each injection was 1 mL). GC700 gas chromatograph was used for determination.

[0055]

[0056] (6) Determination of malondialdehyde (MDA)

[0057] The malondialdehyde (MDA) content of pineapple was determined using a spectrophotometric analysis kit for malondialdehyde (MDA) (MDA-1-Y, Suzhou Keming Biotechnology Co., Ltd.). Weigh 0.1 g of pineapple pulp, add the extract, ice bath, homogenize, centrifuge, add the reaction solution, and then place 200 μL of the supernatant on a micro quartz colorimetric disk or a 96-well plate, and measure the absorbance at 532 nm and 600 nm, respectively, expressed as A532 and A600, ΔA = A532-A600, V is the total volume of the reaction system, ε is the molar absorption coefficient of malondialdehyde (155×103L / mol / cm), d is the optical path of the 96-well plate (0.5 cm), V is the volume of the added extract, and W is the sample mass. The MDA calculation formula is as follows:

[0058] MDA (nmol / g FW) = [ΔA × V total ÷ (ε × d) × 109] ÷ (W × V sample ÷ V total) = 51.6 × ΔA ÷ W

[0059] (7) Determination of peroxidase (POD)

[0060] Determination of pineapple peroxidase (POD) activity, the determination method refers to the POD activity spectrophotometric kit (POD-1-Y, Suzhou Keming Biotechnology Co., Ltd.). Weigh 0.1g of pineapple sample, draw 1mL of extract solution and add it to the kit, and perform ice bath homogenization. Centrifuge to take the supernatant, place it on ice for testing, and add the reaction solution according to the steps. Finally, measure the absorbance at 470nm. Unit definition: One enzyme activity unit is one gram of tissue per milliliter of reaction system per minute A470 change of 0.005. ΔA is the change in absorbance value during the reaction time, Vtotal is the total volume of the reaction system, W is the fresh weight of the sample, Vsample is the volume of the enzyme solution used for the determination, Vtotal is the total volume of the extracted enzyme solution, and T is the reaction time. The POD calculation formula is as follows:

[0061] POD (U / g FW) = ΔA × V total ÷ (W × V sample ÷ V total) ÷ ​​0.005 ÷ T = 4000 × ΔA ÷ W

[0062] (8) Determination of catalase (CAT)

[0063] The activity of pineapple catalase (CAT) was determined by referring to the instructions of the CAT activity spectrophotometric kit (Cat. No. CAT-2-Y, Suzhou Keming Biotechnology Co., Ltd.) Weigh about 0.1 g of pineapple pulp sample, add 1 mL of extract, and homogenize in an ice bath.

[0064] Remove the supernatant by centrifugation, place on ice, and then add the reaction solutions in sequence. Measure the absorbance at 240 nm. Unit definition: 1 nmol H catalyzed per gram of tissue per minute 2 O 2 Degradation is defined as one unit of enzyme activity. ΔA is the change in absorbance during the reaction time, V is the total volume of the reaction system, and ε is H 2 O 2 Molar extinction coefficient (4.36×10 4 L / mol / cm), d is the cuvette light path (1cm), Vsample is the volume of sample added; Vsampletotal is the volume of extract added, T is the reaction time, and W is the fresh weight of the sample. The CAT calculation formula is as follows:

[0065] CAT (nmol / min / g fresh weight) = [ΔA × V total ÷ (ε × d) × 109] ÷ (W × V sample ÷ V total) ÷ ​​T = 678 × ΔA ÷ W

[0066] 2.4 Data Statistics and Plotting

[0067] SPSS software was used for data collation and statistical analysis, and Prism software was used for drawing. The measured values ​​of various physiological and biochemical indices were expressed as "mean ± standard error (SE)", and the variance analysis was performed using the Duncan's new multiple range test (DMRT).

[0068] 3. Results Analysis

[0069] 3.1 Effect on pineapple peel chromaticity

[0070] The phenotypes of pineapple fruits after different treatments and storage for different days (1d, 3d, 5d, 7d, 9d) are as follows Figure 1 As shown. Figure 2 It can be seen that the chromaticity L* and saturation C* of the pineapple peel after harvest gradually increase to the late stage of maturity and then slowly decrease, while the hue h° gradually decreases during the entire storage period. The chromaticity and saturation of the pineapple treated with fruit wax coating and mixed coating increase slower than those of the control group 2 (the pineapple fruit is washed with clean water, sterilized and dried, CK2, the same below); its hue decreases slower than that of the control group 2. Analysis shows that the fruit wax coating and mixed coating treatment can delay the yellowing and ripening of pineapples, and the mixed coating treatment has the best effect and can achieve the best preservation effect.

[0071] 3.2 Effect on pineapple pulp hardness

[0072] Depend on Figure 3 It can be seen that the changes in the flesh hardness of pineapples treated with fruit wax coating, melatonin and mixed coating in the late storage period were not much different among the treatments, but in the middle storage period, the fruit hardness of the fruit treated with fruit wax coating, melatonin and mixed coating was greater than that of the control group 2. This shows that the fruit wax coating, melatonin and mixed coating treatments can maintain the hardness of pineapple fruit to a certain extent.

[0073] 3.3 Effect on pineapple fruit weight loss rate

[0074] The weight loss rate can directly reflect the quality changes and wilting degree of fruits and vegetables. The weight loss rate of pineapple fruit gradually increased during storage, but the growth rate was different. Figure 4 It can be seen that starting from the 6th day, the weight loss rate of pineapple fruit in the control group 2 was significantly higher than that in the fruit wax coating, melatonin and mixed coating treatment groups. Among them, the weight loss rate of the mixed coating treatment group was the lowest, and was significantly lower than the weight loss rate of the fruit wax coating or melatonin treatment. Therefore, it can be concluded that the fruit wax coating, melatonin and mixed coating treatments can all delay the weight loss of pineapples, and the mixed coating treatment has the best effect in reducing the weight loss rate and can achieve the best preservation effect.

[0075] 3.4 Effects on ethylene release from pineapple fruit

[0076] Depend on Figure 5It can be seen that among all treatment groups, the group with the lowest ethylene release was the fruit wax coating treatment group. The ethylene release of the fruit wax coating and melatonin treatment groups was significantly lower than that of the control group 2, while the ethylene release of the mixed coating treatment group was higher than that of the control group 2. The analysis showed that the fruit wax coating and melatonin treatments could effectively reduce the ethylene release during pineapple storage, while the mixed coating treatment could achieve a better preservation effect not because of the reduction in ethylene release, but because it enhanced the response of ethylene to aging stress.

[0077] 3.5 Effects on the respiration rate of pineapple fruit

[0078] Depend on Figure 6 It can be seen that the respiration rate of pineapple fruits in the control group 2 gradually increased during storage, while the respiration rates of pineapples in the fruit wax coating treatment group and the mixed coating treatment group were lower than that in the control group 2. Analysis showed that both the fruit wax coating treatment and the mixed coating treatment inhibited the respiration rate of pineapples, and the respiration rate of pineapples treated with the mixed coating was always at a low level and significantly lower than that of pineapples in the fruit wax coating treatment group, indicating that the mixed coating treatment has a better effect on inhibiting the respiration rate of pineapples and can effectively delay fruit maturation and senescence.

[0079] 3.6 Effect on the malondialdehyde (MDA) content in pineapple fruit

[0080] The content of malondialdehyde (MDA) reflects the degree of cell membrane lipid peroxidation. Excessive accumulation of MDA may cause damage to the plasma membrane of pineapple fruit cells.

[0081] Depend on Figure 7 It can be seen that the MDA content of pineapples in each treatment group increased in the early stage of storage, but the MDA content of pineapple fruits in the mixed coating treatment group and melatonin treatment group was significantly lower than that in the control group 2. Analysis showed that melatonin treatment or mixed coating treatment of pineapple fruits can effectively inhibit the accumulation of malondialdehyde, inhibit the peroxidation of pineapple cell membranes, and delay fruit senescence. Among them, the mixed coating treatment group had the best effect in inhibiting malondialdehyde.

[0082] 3.7 Effects on peroxidase (POD) activity in pineapple fruit

[0083] POD and CAT are important for scavenging ROS and decomposing H 2 O 2 The increase of antioxidant enzyme activity and its coordination function can reduce lipid peroxidation and delay senescence in crops. Melatonin treatment can induce an increase in POD activity in pineapple fruit to a certain extent, which is similar to the effect of melatonin coating on POD content in apples.

[0084] Depend on Figure 8It can be seen that the peroxidase activity of pineapples in the treatment group and the control group 2 showed an upward trend. Compared with the control group 2, the POD of the melatonin treatment group was higher on the 6th and 9th days, and there was no difference at other time points, while the POD activity of pineapple fruits in the fruit wax coating treatment group and the mixed coating treatment group was lower than that in the control group 2 in the middle and late storage, which may be related to the lower superoxide in the body, resulting in lower MDA content and lower degree of membrane lipid oxidation in the fruit.

[0085] 3.8 Effects on catalase (CAT) activity in pineapple fruit

[0086] Catalase (CAT) is widely present in plants and is an oxidoreductase. CAT is a protective enzyme that plays an important role in the ripening and aging of fruits. It can effectively remove free radicals and protect cell membrane structures. Catalase is the main defense enzyme in plant tissues. In the active oxygen scavenging enzyme metabolic system, catalase can degrade H 2 O 2 .

[0087] Depend on Fig. 9 It can be seen that in the early stage of storage, the catalase activity of both the treatment group and the control group 2 increased. There was basically no difference in the CAT activity in the pineapple fruits between the melatonin treatment and the control group 2, while the mixed coating treatment and the fruit wax coating treatment could inhibit the activity of the CAT enzyme to a certain extent, which may be related to the lower active oxygen concentration in the fruit, resulting in a lower MDA content and a lower degree of membrane lipid oxidation in the fruit.

Claims

1. A preservative, characterized in that: The active ingredients of the preservative include fruit wax and melatonin.

2. The preservative according to claim 1, characterized in that The concentration of the fruit wax is 65g·L -1 The concentration of melatonin is 600 μmol·L -1 .

3. A composite fresh-keeping method for pineapple, characterized in that: The following steps are involved: S1. Wash the harvested pineapple with water to remove surface dirt, sterilize it, and dry it; S2. Soak the pineapple in the preservative described in any one of claims 1-2 and dry it.

4. The method according to claim 3, characterized in that: The sterilization is carried out using 50 mg·L -1 Soak in chlorine dioxide for 10 min and then dry it. -1 of prochloraz and 500mg·L -1 Soak in the solution of cyprodinil for 1 min.

5. The method according to claim 3, characterized in that: The method of soaking the pineapple in the preservative according to claim 1 is to soak the pineapple in the preservative according to claim 1 for 30 minutes.

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