Method for prolonging fresh-keeping period of fruits by using controlled atmosphere fresh-keeping box

Abstract

According to the method for prolonging the fresh-keeping period of the fruits by using the controlled atmosphere fresh-keeping box, the controlled atmosphere fresh-keeping box is prepared by improving the sealing performance of a common fresh-keeping box and covering a certain area of the common fresh-keeping box with a film, and the fruits are put into the box to be stored. When the area of the covering film is 20%, the lotus seeds are stored in a box, and 1-methylcyclopropene can be added; when the area of the covering film is 34.8%, the longan is placed in a box to be stored. Compared with the control, the modified atmosphere preservation box treatment can reduce the weight loss rate and browning degree of the lotus seeds and maintain the contents of Vc, amylose, total phenols and soluble solids; compared with a control group, the modified atmosphere preservation box treatment can inhibit browning of longan peel, delay reduction of soluble solids, acidity and vitamin C, inhibit increase of malondialdehyde content, reduce peroxidase activity and improve catalase activity and glutathione content. According to the technology, the shelf life of the fruits can be effectively prolonged, and the problems that an existing fresh-keeping method is tedious and short in fresh-keeping period are solved.

Description

Technical Field

[0001] The invention belongs to the field of post-harvest fruit preservation, and in particular relates to a method for extending the shelf life of fruits by utilizing a controlled atmosphere fresh-keeping box. Background Art

[0002] Lotus seeds have a history of about three thousand years. So far, there are 22 known species of lotus seeds in China, which are mainly grown in Fujian, Zhejiang, Hunan and Hubei provinces. Lotus seeds are usually oval or spherical in shape, but different species vary in size. Peeled lotus seeds can be eaten directly or dried and stored. Lotus seeds are a rich source of protein, carbohydrates and fats. They are also rich in a variety of nutrients. The ingredients of this substance include amino acids, vitamins B1, B2, B6, C, E, and trace elements such as phospholipids, calcium, iron, zinc, phosphorus, etc. In addition, it also contains a variety of biologically active substances such as water-soluble polysaccharides, alkaloids, flavonoids and superoxide dismutase (SOD). Therefore, lotus seeds are a food with extremely high nutritional value. They can be eaten not only as daily fruits and vegetables, but also as functional health products. Studies have shown that lotus seeds have a variety of effects such as treating chronic indigestion, hematuria, enteritis, insomnia, tissue inflammation, palpitations, cancer, improving appetite and memory, and enhancing immunity, so they are often used in the fields of medicine and health food. The high temperature period from July to September each year is the main harvest period for fresh lotus seeds. At this stage, the respiratory activity and physiological metabolic processes of lotus seed cells are relatively more active. However, as the hardness of the peel and pulp gradually increases, the sweetness of lotus seeds will also decrease accordingly. This will cause lotus seeds to deteriorate very quickly during storage, thereby increasing the difficulty of keeping them fresh. The pulp of fresh lotus seeds is its main edible part, and the flavor components in it have a significant impact on the taste of lotus seeds. In the low maturity stage, the basic flavor of lotus seeds is mainly sweet and umami, while in the high maturity stage, the main flavor of lotus seeds is astringent. The taste of fresh lotus seeds shows significant differences at different maturity stages. Therefore, ensuring the freshness of lotus seeds is very critical to their commercial potential. For the preservation of fresh lotus seeds, there are many studies on the use of preservatives. However, the method of using preservatives to preserve lotus seeds is not only cumbersome to operate, but also has a relatively short shelf life.

[0003] Longan (Dimocarpus longan Lour.), also known as longan and round eye, is an evergreen fruit tree of the genus Longan in the Sapindaceae family. It is native to southern my country and is mainly distributed in tropical and subtropical climate zones such as Guangdong, Guangxi, and Fujian. Its fruit is rich in sugar, vitamin C, and a variety of amino acids, and has high nutritional and medicinal value. It has been regarded as a tonic since ancient times and is praised as the "small ginseng in the south". The harvest period of longan fruit is usually between summer and autumn. Due to the strong physiological metabolism after picking, the quality deterioration, such as browning, rotting, and mildew, limits its market sales and processing value. Therefore, how to effectively extend the shelf life of longan fruit has become an important research direction. Longan fruit is a non-respiratory climacteric fruit. The physiological metabolism after picking is extremely strong, and the fruit has strong respiration. The shelf life of longan fruit picked at room temperature is only 3 to 4 days. Its preservation method can start from reducing respiration. Traditional methods for preserving longan fruits mainly include low-temperature storage, drying and sulfur treatment. Studies have found that when "Songfengben" longan is stored at room temperature (25±0.5)℃ and low temperature (3±0.5)℃, low temperature can effectively extend the shelf life of "Songfengben" longan. The existing technology studied the effects of three different drying treatments on longan, and the results showed that freeze-drying can effectively reduce the loss of antioxidant activity of longan. Other studies have mentioned that SO2 fumigation treatment is a key method for preserving imported and exported longan, but the aril may have a "sulfur smell", which affects the taste. In addition, studies have found that post-harvest preservation technology of zinc-doped carbon quantum dots and chlorogenic acid (Zn-CQDs / CGA) composites can inhibit the browning of longan and maintain the quality of longan. Some researchers have prepared a sodium alginate (SA) film combined with brewer's yeast (SE) and sucrose (SU), which has a positive effect on the antioxidant properties of longan and can significantly improve the browning of the longan peel. These methods can delay the quality deterioration of longan fruit to a certain extent, but still fail to achieve the expected better shelf life. Summary of the invention

[0004] The invention provides a method for extending the shelf life of fruits by utilizing a controlled atmosphere fresh-keeping box. The method comprises improving the sealing property of an ordinary fresh-keeping box and coating a certain area with a film to prepare the controlled atmosphere fresh-keeping box. Fruits are stored in the box, which can effectively extend the shelf life. The method solves the problems in the prior art of fruit preservation methods that the operation is complicated, the fresh-keeping period is short, and it is difficult to achieve an expected better shelf life.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for extending the freshness period of fruits by using a controlled atmosphere fresh-keeping box comprises the following steps: cutting off part of the cover of an ordinary fresh-keeping box and coating it with a film to prepare a controlled atmosphere fresh-keeping box, and storing the fruits in the box.

[0007] Preferably, the area of ​​the film is 20%, and a controlled atmosphere fresh-keeping box is prepared, and the pre-cooled lotus seeds are stored at room temperature (25° C.) in the box.

[0008] Specifically, choose a cover area of ​​153.94cm 2 A standard fresh-keeping box was used, and after calculation, a cover with a length of 6.2 cm and a width of 5.0 cm was cut off and covered with film so that the covering area was 20%, and the pre-cooled lotus seeds were placed in the box at a weight of 250.0 g for storage.

[0009] More preferably, 1-methylcyclopropene (1-MCP) is also added into the box.

[0010] Preferably, the area of ​​the coating is about 34.8%, and a controlled atmosphere fresh-keeping box is prepared, and the harvested fresh longan is stored in the box at 4°C.

[0011] Specifically, a fresh-keeping box with a cover of 15.2 cm×11.2 cm is selected, and the cover is cut off and coated with film after calculation, so that the area of ​​the film is about 34.8%, and 500 g of fresh longan after harvest is placed in the box for storage.

[0012] Preferably, the film is a cling film.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] Lotus seeds have a long history and are rich in nutrients. However, lotus seeds are mainly in a high temperature period during the harvest stage, and their physiological metabolism is active, making them very easy to rot and deteriorate. In order to study the effect of post-harvest controlled atmosphere fresh-keeping box treatment on the quality of lotus seeds during storage, fresh lotus seeds were used as test materials, and treated with a 20% film-coated controlled atmosphere fresh-keeping box (T1), and a 20% film-coated controlled atmosphere fresh-keeping box plus 1-methylcyclopropene co-treatment (T2), and a common fresh-keeping box was used as a reference (CK). The results showed that compared with CK, both T1 and T2 treatments could significantly reduce the weight loss rate and browning degree of lotus seeds, and maintain the content of nutrients such as Vc, amylose, total phenols, and soluble solids. Under the condition of 7 days of room temperature storage of lotus seeds, the weight loss of CK was 16.4%, the weight loss of T1 was 3.4%, and the weight loss of T2 was 4.0%. The total phenolic contents of CK, T1 and T2 were 5.453 mg / g, 9.210 mg / g and 10.916 mg / g, respectively; the Vc contents of T1 and T2 groups were 0.41 mg / 100 g and 0.84 mg / 100 g higher than those of the control group, and the amylose contents were 0.856 mg / g and 1.438 mg / g higher than those of the control group, respectively. The results showed that the T1 and T2 treatments had good effects on reducing the consumption of nutrients in lotus seeds and maintaining color, and the effect of the T2 treatment was more obvious than that of the T1 treatment. This provides a reference for the development of post-harvest preservation technology for fresh lotus.

[0015] In order to explore the effect of using controlled atmosphere fresh-keeping box treatment (cut off part of the cover of the fresh-keeping box and cover it with film) on the preservation effect of post-harvest longan fruit, the longan fruit without film treatment was used as the control group under refrigeration at 4℃. Samples were taken on the 0th, 1st, 3rd, 5th, 10th and 15th days of storage, and relevant physical and chemical indexes were analyzed. The results showed that compared with the control group, the treatment of controlled atmosphere fresh-keeping box (the film covering area accounted for about 34.8% of the surface area) could significantly inhibit the browning of longan peel. On the 15th day, the peel of the control group was severely browned, while the peel of the treatment group did not change significantly; this treatment method can significantly delay the decline of soluble solids (TSS), acidity and vitamin C. For example, on the 5th day of storage, the TSS and acidity contents of the treatment group were 21.30% and 1.49%, respectively, while those of the control group were 20.03% and 1.16%. On the 3rd day of storage, the vitamin C content of the treatment group was 37.78mg*(100g) -1 , while the control group was 31.67mg*(100g) -1 . In addition, the modified atmosphere fresh-keeping box treatment technology can also effectively inhibit the increase in malondialdehyde (MDA) content. For example, on the 15th day of refrigeration, the content of the control group was as high as 31.02nmol / g, while that of the treatment group was only 22.83nmol / g. Further research found that this technology can significantly affect the activity of antioxidant enzymes in longan pulp, reduce the activity of peroxidase (POD), and increase the activity of catalase (CAT) and glutathione (GSH) content. Therefore, this modified atmosphere fresh-keeping box treatment can effectively extend the shelf life of longan fruit and maintain its good quality and nutritional value, providing a practical technology for longan preservation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The effect of treatments T1 and T2 in Example 1 on the hardness of post-harvest lotus seeds.

[0017] Figure 2 This is the effect of T1 and T2 treatments in Example 1 on the weight loss of post-harvest lotus seeds.

[0018] Figure 3 These are photos of lotus seeds harvested after treatment with T1 and T2 in Example 1.

[0019] Figure 4 The effect of the T1 and T2 treatments in Example 1 on the chromaticity of post-harvest lotus seeds.

[0020] Figure 5 The effect of treatments T1 and T2 in Example 1 on TSS and acidity of post-harvest lotus seeds.

[0021] Figure 6 This is the effect of the T1 and T2 treatments in Example 1 on the respiration of post-harvest lotus seeds.

[0022] Figure 7This is the effect of T1 and T2 treatments in Example 1 on the Vc content of post-harvest lotus seeds.

[0023] Figure 8 The effect of the T1 and T2 treatments in Example 1 on the amylose content of postharvest lotus seeds.

[0024] Fig. 9 This is the effect of the T1 and T2 treatments in Example 1 on the total phenol content of post-harvest lotus seeds.

[0025] Fig.10 The following are the changes in the appearance of longan fruits during storage at 4°C under the two treatments in Example 2.

[0026] Fig.11 The results are as follows: The pulp quality changes of longan fruits stored at 4°C for 3 to 15 days under the two treatments in Example 2.

[0027] Fig.12 The figure shows the changes in vitamin C content of longan pulp treated with two methods in Example 2.

[0028] Fig.13 The MDA content of longan pulp after two treatments in Example 2 is changed.

[0029] Fig.14 The following are the effects of the two treatments in Example 2 on GSH, POD and CAT in longan pulp, wherein (A) is the effect on GSH content; (B) is the effect on POD activity; and (C) is the effect on CAT activity. DETAILED DESCRIPTION

[0030] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] Example 1 Storage and preservation of fresh lotus seeds using a controlled atmosphere fresh-keeping box and 1-MCP treatment

[0032] The structure of the common fresh-keeping box was improved, and a modified atmosphere fresh-keeping box was prepared by improving the sealing and coating with 20%. Under normal temperature, the lotus seeds packed in the 20% coating (T1), 20% coating + 1-methylcyclopropane treatment (T2) and the common fresh-keeping box (CK) were compared in terms of hardness, color, respiration, weight loss, soluble solids (TSS), acidity, Vc, total phenols (TP) and the content of amylose in lotus seeds, and an in-depth systematic analysis was conducted to observe the changes in physiological indicators of fresh lotus seeds during the storage stage after harvest, providing a simple, healthy and beneficial packaging option for the preservation of fresh lotus seeds.

[0033] 1. Materials and Methods

[0034] 1.1 Experimental Materials

[0035] Select a cover area of ​​153.94cm 2 The standard fresh-keeping box was used, and according to its area, the cover with a length of 6.2 cm and a width of 5.0 cm was cut off and coated. The pre-cooled lotus seeds were placed in a standard fresh-keeping box at a weight of 250.0 g. The experiment set up three different treatment groups: CK, 20% film coating (T1), and 20% film coating + 1-methylcyclopropene (T2). Each group contained 10 parallel treatment groups and was stored at room temperature of 25°C. Samples were taken once a day for each treatment, and samples were taken on days 0, 1, 2, 3, 4, 5, and 7. After completing each random sample collection and the corresponding basic indicators, the shells and cores were removed, and the pulp was quickly frozen with liquid nitrogen and stored at -80°C for subsequent indicator determination.

[0036] 1.2 Experimental methods

[0037] 1.2.1 Determination of fruit respiration intensity

[0038] The Li-6262CO2 / H2O analyzer (LI-COR Inc LincolnNE USA) was used for the determination using infrared carbon dioxide analysis. When sampling, fruits of similar quality were selected and placed in a 2.5L sealed plastic fresh-keeping box, the ventilation port of which was directly connected to the interface of the analyzer. The analyzer was started, the air pump was started, and the values ​​were recorded every 60 seconds for a total of 5 times.

[0039] 1.2.2 Determination of weight loss rate

[0040] The weighing method is used for determination and the calculation formula is

[0041]

[0042] Where a is the mass before storage, and b is the mass on the Nth day of storage.

[0043] 1.2.3 Determination of fruit chromaticity

[0044] The measurements were performed using a MinoIta Chroma Meter CR-400. In each treatment group, we randomly selected the side of the lotus seed for measurement and divided its side into three levels. Measurements were made at intervals to obtain a * Value, b * Value and L * The average value of the value. Here, +a * Represents red, -a *Represents green, +b * Represents yellow, -b * stands for blue, and L * The value represents the brightness. A Sony zve10 camera (Sony, China) was used to take photos of fresh lotus seeds, and the browning phenomenon of fresh lotus seeds under various processing environments and different storage times was observed and recorded in detail.

[0045] 1.2.4 Determination of pulp hardness

[0046] Ten lotus seeds were randomly selected from different treatment groups. After carefully peeling the lotus seed skin (ensuring that the flesh was not damaged), the hardness tester (GY-64 China Aideburg) was used to measure the hardness, and the data of each treatment group were recorded and averaged.

[0047] 1.2.5 Determination of soluble solids (TSS) and acidity in pulp

[0048] The measurement was performed using an ATAGO portable fruit sugar meter (PAL-BX Japan). 15 lotus seeds were selected from each treatment group, peeled and cored, and then the juice was squeezed out manually using 40% gauze. After standing for 20 minutes, 0.1 ml of the juice was dropped into the ATAGO portable fruit sugar meter to determine its soluble solids, and then 4.90 ml of deionized water was added for dilution determination of acidity.

[0049] 1.2.6 Determination of Vitamin C content in fruits

[0050] Vitamin C test kit (Nanjing Jiancheng Bioengineering Institute, Nanjing, China) was used for relevant detection. The specific detection steps are detailed in the kit.

[0051] 1.2.7 Determination of total phenolic content in fruits

[0052] The Solebao plant total phenol (TP) content detection kit (Beijing Solebao Technology Co., Ltd., Beijing, China) was used for detection. Please refer to the kit for specific operation steps.

[0053] 1.2.8 Determination of fruit amylose content

[0054] The amylose content kit (Nanjing Jiancheng Bioengineering Institute, Nanjing, China) was used for detection, and the detailed steps are shown in the kit.

[0055] 1.2.9 Data Processing

[0056] Excel 2019 statistics and SPSS Statistics 21 were used for variance analysis and one-way ANOVA analysis, and P < 0.05 indicated a significant difference. Origin 2021 was used for drawing.

[0057] 1.3 Results and Analysis

[0058] 1.3.1 Effects of T1 and T2 treatments on postharvest lotus seed hardness

[0059] The change in the hardness of fresh lotus seeds during storage reveals to some extent the degree of aging of the lotus seeds. Figure 1 As shown in the figure, with the gradual extension of storage time, the hardness of the pulp of both the control group and the two treatment groups showed a trend of first increasing and then decreasing. In the control group, the hardness reached a peak value (31.253 kg / cm 2 ), but then began to gradually decrease. On the fifth day of storage, the control group and the T1 treatment group showed a significant difference in pulp hardness (p<0.05). The difference between the groups treated with T1 and T2 was not significant. During the ripening stage of lotus seeds, sugar is converted into starch. The accumulation of this starch significantly increases the hardness of the pulp, but as the storage time increases, the starch begins to gradually decompose, resulting in a gradual decrease in hardness. On the whole, the hardness of the two treatment groups, T1 and T2, showed a stable fluctuation within a smaller range, and the amplitude of the change was smaller than that of the control group. The results show that under the treatments of T1 and T2, the crispness of lotus seeds was effectively maintained.

[0060] 1.3.2 Effects of T1 and T2 treatments on weight loss of postharvest lotus seeds

[0061] from Figure 2 We can observe that the weight loss of lotus seeds during storage gradually increases, and the weight loss of the control group is the most serious. On the seventh day of storage, the weight loss rate rose to 16.4%. The weight loss rate of the group treated with T1 was relatively low, reaching 3.4%, and the weight loss rate of the group treated with T2 was 4.0% on the seventh day. The weight loss rate of lotus seeds in the two treatment groups of T1 and T2 was much lower than that of the control group. The results show that the use of T1 and T2 treatments can effectively slow down the weight loss of fresh lotus seeds during storage.

[0062] 1.3.3 Effects of T1 and T2 treatments on chromaticity of postharvest lotus seeds

[0063] The color of the fruit peel is mainly due to two key pigments: green chlorophyll and yellow carotenoids. These two pigments play a decisive role in the coloring of the ripe fruit of most species and cultivars. Anthocyanins belong to the third class of pigments, whose main color range extends from red to purple. The commercial value of lotus seeds is directly affected by their appearance color. During storage, the color of its peel will gradually change over time, from tender green to yellow-green, and finally completely turn brown. Figure 3The preservation effect of different treatment methods on the color of fresh lotus seeds is shown. The control group began to show obvious browning on the second day of storage, the T1 treatment group showed slight browning on the fourth day of storage, and the T2 treatment group showed slight browning on the fifth day of storage. However, in the control group on the fifth day, most of the fresh lotus seeds had serious browning and were no longer of commercial value. * 、a * and b * is a key indicator of color change, such as Figure 4 As shown in the figure, the overall brightness between the control group and the treatment group showed a gradual decrease. The brightness of the control group began to decrease on the second day, and the yellowing phenomenon intensified, which may be related to the chlorophyll degradation process. During the 4-7 days of storage, L * The difference in the values ​​was significant (P<0.05), but the difference between the T1 treatment group and the T2 treatment group was not so obvious (P>0.05). The rate of color brightness decline in the T1 and T2 groups was significantly lower than that in the control group. * The values ​​showed a gradual downward trend. During the storage period of 0-4 days, the b * The value did not change significantly. However, during the storage period of 5-7 days, the b value between the control group and the treatment group * There were significant differences in the values ​​(P<0.05). It is worth noting that during the entire storage process, the two treatment groups * The decreasing speed of the value was always lower than that of the control group. * The values ​​continued to rise, while the control group * The values ​​were always higher than those in the treatment group, which means that the green degree of fresh lotus seeds is gradually decreasing. The results show that the use of T1 and T2 treatments can effectively maintain the color stability of fresh lotus seeds and further extend their shelf life.

[0064] 1.3.4 Effects of T1 and T2 treatments on TSS and acidity of postharvest lotus seeds

[0065] The change in the content of total soluble solids (TSS) in lotus seeds can intuitively show the fluctuation of the maturity and quality of lotus seeds. Sugar is the dominant factor affecting the sweetness of lotus seeds. Organic acid is the key factor affecting the taste quality of fresh lotus seeds. As the storage time gradually increases, the soluble solids between the control group and the treatment group generally show an increasing trend. Figure 5As shown in the figure, in the control group, the soluble solids began to increase gradually on the second day of storage and reached a peak of 14.15 on the seventh day. Under the treatments of T1 and T2, the growth rate of soluble solids was relatively slow, and the difference between the two was not significant (P>0.05). After 3-7 days of storage, the difference between the control group and the treatment group was significant (P<0.05). After 3 days of storage, the soluble solids content of the T2 treatment group was significantly lower than that of the control group. On the 2nd, 3rd, 4th and 7th days, the soluble solids content of the T2 treatment group was reduced by 1.5, 2.4, 2.55 and 3.6 respectively compared with the control group, and on the 3rd, 4th and 7th days, the T1 treatment group was reduced by 2.3, 1.7 and 3.6 compared with the control group. We observed significant differences between the control group and the treatment group (P<0.05), which means that during storage, the lotus seeds can be significantly slowed down by the treatment of T1 and T2, which can significantly slow down the consumption of nutrients and reduce the accumulation of soluble solids. During the whole storage process, the acidity of fresh lotus seeds was relatively stable, fluctuating within a range of about 2%. The control group had a slight increase on the seventh day of storage, which was higher than the two treatment groups ( Figure 5 ).

[0066] 1.3.5 Effects of T1 and T2 treatments on respiration of postharvest lotus seeds

[0067] The respiratory activity of fresh lotus seeds is one of the key indicators to measure their maturity and aging degree after harvest. Since fresh lotus seeds have active respiration after harvest, they age quickly after harvest and lose their market value. Figure 6 As shown, during the storage process, the respiration rate first increased rapidly, and then gradually decreased. At 2-4 days of storage, the difference between the control group and the treatment group was significant (P<0.05). The respiration rate of fresh lotus seeds increased rapidly on the first day, and then decreased rapidly on the second day of storage. Among them, the control group had the most significant decline rate, rapidly decreasing from 537.957 mgCO2 (kg.h) to 246.953 mgCO2 (kg.h), while the T1 treatment group decreased from 815.417 mgCO2 (kg.h) to 764.973 mgCO2 (kg.h), and the T2 treatment decreased from 943.763 mgCO2 (kg.h) to 690.380 mgCO2 (kg.h), and the decline was significantly lower than that of the control group. The results show that adding T1 and T2 can effectively slow down the decrease in the respiration rate of fresh lotus seeds, slow down the loss of nutrients, and help delay its aging process ( Figure 6 ).

[0068] 1.3.6 Effects of T1 and T2 treatments on the content of vitamin C in postharvest lotus seeds

[0069] Vc is a substance with antioxidant properties that can effectively inhibit the generation of superoxide. Figure 7 As shown in the results, the Vc content of fresh lotus seeds generally decreased during storage. The Vc content of the T2 treatment group increased slightly on the first day and then began to decrease. In the treatment groups, the Vc content was significantly higher than that of the control group. Especially at 5 days of storage, the difference between the T1 treatment group and the control group was very significant (P<0.05), while the difference between the T2 treatment group and the control group at 7 days of storage was significant (P<0.05). The results show that the use of T1 and T2 treatments can effectively maintain the Vc content in fresh lotus seeds.

[0070] 1.3.7 Effects of T1 and T2 treatments on the amylose content of postharvest lotus seeds

[0071] Starch is a key nutrient element in fresh lotus seeds. It is mainly composed of amylopectin and amylose molecules. It plays a role in energy storage in plant cells. Lotus seed starch is a highly specific amylose starch, and its aging rate is directly related to the overall quality of lotus seeds. It is also a key functional ingredient in a variety of functional foods and their processing applications. Amylose content is often used to evaluate grain quality, especially as an important indicator of cooking quality and taste. Figure 8 As shown in the figure, during the storage process, the content of amylose showed a trend of first rapidly increasing and then gradually decreasing. The content of amylose in the treatment group was significantly higher than that in the control group. The content of amylose in the T2 treatment group was generally greater than that in the T1 treatment group. There was a significant difference between T1 and T2 from the third to the seventh day of storage. This shows that the use of T1 and T2 can effectively slow down the degradation of amylose in fresh lotus seeds and maintain its original nutritional value, among which the effect of T2 treatment is more significant than that of T1 treatment.

[0072] 1.3.8 Effects of T1 and T2 treatments on total phenolic content in postharvest lotus seeds

[0073] Phenolic compounds play a key role in secondary metabolism in plants, and the browning of fruits is mainly catalyzed by peroxidase, which converts phenolic compounds into quinone compounds, resulting in a brown appearance. Total phenols help eliminate free radicals and have anti-aging and antioxidant properties. Fig. 9 As shown in the results, the total phenolic content of lotus seed pulp showed a downward trend during storage. The total phenolic content of the treatment group was always higher than that of the control group. At the end of storage, the total phenolic content of lotus seed pulp in the control group decreased fastest. The total phenolic content of the treatment group and the control group was T2 (10.916 mg / g), T1 (9.210 mg / g) and the control group (5.453 mg / g), respectively. On the 7th day of storage, there was a significant difference between the control group and the treatment group (P<0.05), and there was a significant difference between T1 and T2 (P<0.05).

[0074] 1.4 Discussion and Conclusion

[0075] During the harvest season, the high temperature and humidity shorten the storage time of lotus seeds and accelerate the loss of nutrients, which greatly reduces their commercial value. Modified atmosphere packaging (MAP) helps slow down the ripening process of fruits and effectively prolongs their shelf life. In this experiment, we used modified atmosphere preservation to preserve lotus seeds. The study found that storing lotus seeds at room temperature and treating them with T1 and T2 can effectively slow down the browning of the lotus seeds' skin, weight loss, and pulp hardness, thereby maintaining the crispness of the pulp. Compared with the control group, the browning time of the treated group was significantly delayed, indicating that the T1 and T2 treatment methods can significantly delay the decomposition of chlorophyll. TSS mainly includes sugars, proteins and organic acids contained in vacuoles. During storage, the TSS of lotus seeds showed a gradual upward trend. On the seventh day of storage, the TSS of the control group increased the most (14.150), followed by T1 (10.583), and the least (9.850) in T2. ​​This phenomenon can be explained by the degradation of cell wall pectin, cellulose and hemicellulose, which leads to the release of some neutral sugars. At high temperatures, the release of soluble polysaccharides is more intense than at low temperatures, and the change in acidity between the treatment group and the control group is relatively small. Vc is an important marker for products to resist oxidative stress. It mainly exists in fresh fruits and vegetables in a reduced form and is an essential nutrient for the human body. Studies have shown that T1 and T2 treatments can effectively maintain the Vc content of fresh lotus seeds during storage. In the processing of lotus seeds, the content of amylose is regarded as a key indicator. It is positively correlated with the hygroscopicity and swelling rate of the lotus seeds after treatment, but negatively correlated with its viscosity and color. In this experimental study, we observed that the content of amylose first increased and then decreased. Compared with the control group, the degradation rate of amylose content in the treated group was relatively slow. This suggests that the use of T1 and T2 treatments can effectively delay the degradation of amylose in lotus seeds, thereby helping to maintain the sweetness and taste of lotus seeds after harvest. Adjusting the gas can maintain high total phenolic content (TPC) levels in fruits. Studies have shown that phenolic compounds can evaluate the maturity of fresh fruits and vegetables, and the content of phenolic compounds and other secondary metabolites in lotus seeds is closely related to the scavenging ability of DPPH free radicals. The antioxidant capacity is also related to the accumulation of phenolic compounds. In this experiment, we observed that the treatments of T1 and T2 can significantly maintain the total phenolic content in lotus seed pulp and help slow down the aging process of lotus seeds after picking.

[0076] According to the findings of this study, the lotus seeds were subjected to T1 and T2 preservation treatments at room temperature (25°C) using the controlled atmosphere preservation method. As the storage time increased, the color of the lotus seeds in the treatment group gradually changed from light green to yellow-green, and finally turned completely brown. *The values, weight loss rate, hardness and TSS all showed an upward trend, and the values ​​of the treatment group were lower than those of the control group. * 、b * , respiration rate, starch content, total phenol content and Vc values ​​all showed a downward trend, and the values ​​of the treatment group were always higher than those of the control group. The treatment effect of T2 was significantly better than that of T1. In summary, T2 treatment had the best effect on maintaining the quality of fresh lotus seeds, followed by T1 treatment, which can be developed and applied as a safe and reliable packaging technology.

[0077] Example 2: Using a controlled atmosphere fresh-keeping box to store and preserve fresh longan

[0078] In this experiment, fresh longan after harvest was taken as the research object. The longan fruits were put into the prepared controlled atmosphere fresh-keeping box (after the longan was put into the fresh-keeping box, the upper surface of the box was coated with film, and the coating area accounted for about 34.8% of the surface area). The fruit not covered with plastic wrap was used as a control to explore the effects of the two packaging methods on the relevant physiological indicators of fresh longan fruit, mainly including soluble solids, vitamin C content, malondialdehyde content, etc., in order to obtain a new technology of controlled atmosphere fresh-keeping box coating and preservation that can be applied to longan.

[0079] 1 Materials and methods

[0080] 1.1 Materials and reagents

[0081] Materials: Fresh longan collected from Guangzhou, 15.2cm×11.2cm fresh-keeping box, and fresh-keeping film. Reagents: 1×PBS, Beijing Xinquan Yongshuo Technology Co., Ltd. The experimental water was distilled water.

[0082] 1.2 Instruments and Equipment

[0083] Li-6262 CO2 / H2O analyzer (LI-COR, Inc, Lincoln, NE, USA); ATAGO portable fruit sugar meter (PAL-BX, Japan).

[0084] 1.3 Test methods

[0085] 1.3.1 Longan sample processing and storage

[0086] Longan fruits of uniform size, without external injuries and insect pests were selected and placed in specific fresh-keeping boxes, each weighing about 500g. The experiment set up a blank control group (the longan was placed in a fresh-keeping box without film covering) and a modified atmosphere fresh-keeping box treatment group (the longan was placed in a fresh-keeping box, and part of the cover of the fresh-keeping box was cut off and covered with film, and the area covered with film accounted for about 34.8% of the surface area), all of which were refrigerated at 4°C. Samples were taken on the 0th (the same day), 1, 3, 5, 10, and 15th day of storage, and the harvested longan fruits were selected from the sample group each time according to the principle of random sampling, and subsequent relevant physical and chemical index analysis was carried out.

[0087] 1.3.2 Determination of respiration intensity of longan samples

[0088] The infrared carbon dioxide analysis method was used (Sun Ying. Post-harvest water loss law and control of Gannan 'Newhall' navel orange [D]. Gannan Normal University, 2023.). The samples in the boxed sample group were placed in a sealed plastic fresh-keeping box with a volume of 2.5L, and a ventilation tube was installed on the fresh-keeping box. The Li-6262CO2 / H2O analyzer (LI-COR, Inc, Lincoln, NE, USA) was used to connect its interface to the ventilation tube of the fresh-keeping box. After the analyzer was started, the measurement began. The measurement time was 60 seconds each time, and each group was recorded 3 times, and the average value was taken.

[0089] 1.3.3 Determination of soluble solids (TSS) and acidity in longan pulp

[0090] Randomly select 10 longan fruits from each sample group, peel and remove the core and place them on 40% gauze. Wrap the pulp in gauze, squeeze the juice manually, and keep the juice in a test tube. Use ATAGO portable fruit sugar meter (PAL-BX, Japan), take 0.1ml juice for measurement, then add 4.9ml distilled water to dilute and measure, and get the measurement readings of soluble solids (TSS) and acidity respectively. Each group is measured 3 times and the average value is taken.

[0091] 1.3.4 Determination of reduced glutathione (GSH) content in longan pulp

[0092] The microplate method was used with a reduced glutathione (GSH) assay kit (Nanjing Jiancheng Bioengineering Institute, Nanjing, China). The specific experimental steps were referred to the kit instructions.

[0093] 1.3.5 Determination of vitamin C (VC) content in longan pulp

[0094] The colorimetric method was used and the vitamin C (VC) / ascorbic acid (AsA) content test kit (Nanjing Jiancheng Bioengineering Institute, Nanjing, China) was used for detection. The detailed test steps refer to the kit instructions.

[0095] 1.3.6 Determination of malondialdehyde (MDA) content in longan pulp

[0096] The microplate method was used to determine the plant malondialdehyde (MDA) assay kit (Nanjing Jiancheng Bioengineering Institute, Nanjing, China). The specific operation steps are shown in the kit manual.

[0097] 1.3.7 Determination of peroxidase (POD) activity in longan pulp

[0098] The colorimetric method was used to determine the activity of POD using the principle that peroxidase (POD) catalyzes hydrogen peroxide reaction. The peroxidase (POD) assay kit (Nanjing Jiancheng Bioengineering Institute, Nanjing, China) was used. The specific operation steps are detailed in the kit manual.

[0099] 1.3.8 Determination of catalase (CAT) activity in longan pulp

[0100] The CAT activity was determined by the ammonium molybdate method and the visible light method using a catalase (CAT) assay kit (Nanjing Jiancheng Bioengineering Institute, Nanjing, China). The detailed operation steps are shown in the kit manual.

[0101] 1.3.9 Data Statistics and Processing

[0102] Microsoft Office 2019 was used for data statistics, SPSS Statistics 27 was used for data processing and statistical analysis, and one-way analysis of variance (ANOVA) was used for significant difference analysis (P<0.05). GraphPadPrism 8.0 was used for drawing.

[0103] 2 Results and discussion

[0104] 2.1 Changes in the appearance of longan fruit during storage

[0105] The physiological metabolism of longan after harvest is very vigorous, which is mainly manifested in the change of its peel color. When the peel turns brown, it loses its commercial value. During the observation of stored longan, it can be clearly seen that the quality of longan fruit decreases. Fig.10 As shown in the figure, it can be seen that the appearance of longan changes with the storage time, and the peel browning phenomenon occurs. On the third day of storage, the peel browning phenomenon is not obvious; on the fifth day, there is a clear color difference between the control group and the treatment group; on the tenth day, the peel browning phenomenon of the control group intensifies, but the treatment group does not significantly increase; on the 15th day, the appearance quality of the control group declines rapidly, the browning is serious, and the treatment group is better. Fig.11 It can be seen that the longan pulp changes during storage. Due to the refrigerated storage, the pulp has no obvious autolysis phenomenon. As can be seen from the figure, there is no obvious difference in the pulp stored on the 3rd day; on the 5th day, the pulp of the control group is slightly yellow; on the 15th day, the color of the pulp of the two is obviously different. The pulp of the control group is yellow and the flesh is slightly soft, while the flesh of the treatment group is firm and elastic, and the flesh is clear. It can be seen that the treatment of the controlled atmosphere fresh-keeping box can significantly inhibit the browning of the longan peel and maintain the freshness of the pulp.

[0106] 2.2 Effects of two treatments on the respiratory intensity of longan

[0107] Slowing down the respiration rate of fruits is one of the main means of preserving fruits and vegetables. During storage, the respiration rate of longan fruits under both treatments showed a downward trend, indicating that the respiration of both was inhibited under 4°C refrigeration conditions. After the first day of storage, there was an immediate significant difference between the control group and the treatment group (P≤0.001), and the respiration rate of the treatment group was as high as 173.24 mg·(kg·h) -1 , while the control group rapidly dropped to 71.02 mg·(kg·h) -1 On the 3rd, 5th, 10th and 15th days of storage, the respiration intensity of the longan in the treatment group was still higher than that in the control group, with a significant difference (P≤0.001). This is because the longan fruits in the atmosphere-controlled fresh-keeping box are in a sealed space during refrigeration, and when the plastic wrap is removed, their respiration rate will increase sharply. The respiration intensity of the treatment group has been showing a downward trend since the first day of storage. On the 10th day of storage, the respiration intensity of the treatment group has dropped significantly, indicating that the treatment group can effectively slow down the respiration intensity of the longan fruit and maintain the fruit quality.

[0108] Table 1 Respiration intensity of longan treated with controlled atmosphere fresh-keeping box

[0109]

[0110]

[0111] Note: Data are mean ± standard deviation. Different letters indicate that the control group and the treatment group have extremely significant differences (P<0.001) under the same index and time.

[0112] 2.3 Effects of two treatments on TSS and acidity of longan

[0113] As shown in Table 2, the soluble solids (TSS) content of the longan pulp after harvest has a trend of first increasing and then decreasing, and the content of the treatment group is always higher than that of the control group. On the first day of storage, the content of the treatment group increased rapidly, while that of the control group increased slowly, but there was no significant difference; on the 3rd and 10th days, the two showed significant differences (P<0.05); on the 5th and 15th days, the two showed extremely significant differences (P<0.001). According to the above results, it is sufficient to prove that the treatment group can maintain a higher level of TSS content and maintain a better pulp quality of longan.

[0114] During the storage process, the acidity content of both treatments increased first and then decreased; on the first day of storage, the acidity of both the treatment group and the control group increased, and the acidity of the treatment group was 1.1 times that of the control group, showing a very significant difference (P<0.001); on the third day, the acidity content of the treatment group was lower than that of the control group; on the fifth day of storage, the acidity of the control group dropped suddenly to 1.16%, while the acidity of the treatment group dropped slowly to 1.49%, showing a very significant difference (P<0.001); on the 10th to 15th day of storage, the acidity of the treatment group was significantly higher than that of the control group (P<0.05). The results show that the treatment of the modified atmosphere fresh-keeping box can slow down the decrease in the acidity of longan to a certain extent, so that it still has a high level of organic acid nutrients after storage for a period of time.

[0115] Table 2 TSS and acidity content of longan treated with modified atmosphere fresh-keeping box

[0116]

[0117] Note: Data are mean ± standard deviation. Different capital letters indicate that the control group and the treatment group have extremely significant differences (P<0.001) under the same index and time. Different lowercase letters indicate that the control group and the treatment group have significant differences (P<0.05) under the same index and time.

[0118] 2.4 Effects of two treatments on the content of vitamin C (Vc) in longan pulp

[0119] Vitamin C is a common nutrient in fruits and vegetables, and its content changes during storage can effectively reflect the quality changes of fruits and vegetables. Fig.12 It can be seen that during the storage period, the Vc content of the longan pulp of the two treatments continued to decrease; there was no significant difference on the first day of storage; but starting from the third day of storage, the Vc content of the longan pulp of the treated group was significantly higher than that of the control group (P<0.01), and the content of the treated group was 37.78mg*(100g) -1 , the content of the control group was 31.67mg*(100g) -1 On the 5th day, there was a more significant difference (P<0.001), and the Vc content of the treatment group was significantly better than that of the control group. On the 15th day, there was still a significant difference between the two groups (P<0.05). The above results show that the modified atmosphere fresh-keeping box treatment can reduce the loss of vitamin C in longan pulp and effectively maintain the quality and nutrition of longan pulp.

[0120] 2.5 Effects of two treatments on the content of malondialdehyde (MDA) in longan pulp

[0121] Malondialdehyde (MDA) is a hallmark product of oxidative damage to fruit and vegetable tissues and membrane lipid peroxidation, and its content reflects the degree of damage to fruits and vegetables. Fig.13It can be seen that the MDA content of longan pulp treated with controlled atmosphere fresh-keeping boxes was significantly lower than that of the control group. The difference was not obvious on the first day of storage, but there was a very significant difference from the third day of storage (P<0.0001). The MDA content of the treated longan pulp increased slowly, and on the 15th day the content was only 22.83nmol / g, while the control group was as high as 31.02nmol / g. This result shows that the treatment of controlled atmosphere fresh-keeping boxes can effectively reduce the MDA content in longan pulp and delay the aging of longan.

[0122] 2.6 Effects of two treatments on the antioxidant capacity of longan pulp

[0123] Glutathione (GSH) is a non-enzymatic antioxidant found in plants. Fig.14 (A) It can be seen that after 1 day of storage, the GSH content of both treatments showed an upward trend. It is speculated that GSH was produced due to oxidative stress after longan was harvested. At each storage time point, the GSH content of the treatment group was higher than that of the control group; and on the 5th, 10th, and 15th days of storage, the difference in GSH content in the longan pulp after treatment compared with the control group reached a significant level (P<0.01). The data showed that the modified atmosphere fresh-keeping box treatment can maintain the GSH content in the longan pulp. On the 15th day, the control group was 123.96nmol / g, and the treatment group was as high as 235.67nmol / g. The higher content of GSH in the pulp can enhance its antioxidant capacity.

[0124] Peroxidase (POD) plays a key role in enzymatic browning of fruits, which can oxidize phenolic substances in fruits and cause fruit browning. Fig.14 (B) It can be seen that from the first day of storage, the POD activity of both treatments showed an upward trend, and the POD activity of the treatment group was lower than that of the control group; after the third day of storage, the treatment group and the control group showed a very significant difference (P<0.001); after 15 days of storage, the POD activity of the treatment group was 161.93U / g, and that of the control group was 197.33U / g. All of the above prove that the treatment group can effectively inhibit the activity of POD.

[0125] Among antioxidant enzymes, CAT is one of the main ROS scavenging enzymes. Maintaining its high activity can effectively reduce the oxidative damage of post-harvest fruits and vegetables. Fig.14(C) It can be seen that in both treatments, CAT activity decreased with storage time. On the 0th day of storage, the CAT activity was 399.03U / g; on the 1st day of storage, the CAT activity of the control group dropped rapidly to 257.64U / g, a decrease of 141.39U / g compared with the previous day, while the activity of the treatment group on the first day was 336.19U / g, a decrease of only 62.84U / g, and the two showed extremely significant differences (P<0.0001). On the 3rd, 5th, and 15th days of storage, the two showed extremely significant differences (P<0.0001), and on the 10th day, there was a significant difference (P<0.01). The results show that the CAT activity of longan fruit can be effectively maintained after the treatment of the modified atmosphere fresh-keeping box, which delays its post-harvest ripening process, reduces post-harvest oxidative damage, and enhances the antioxidant capacity.

[0126] 3 Results and discussion

[0127] After harvesting, longan peels will turn brown during storage. Studies have shown that peel browning is the main reason for the decline in longan fruit quality, reduced market value, and shortened shelf life. The cause of longan peel browning may be fruit aging and other stress conditions, mainly including energy metabolism, active oxygen metabolism, membrane lipid metabolism, phenolic substance metabolism, etc.

[0128] The enzymatic antioxidant system can effectively remove reactive oxygen species from plant tissues. POD will oxidize polyphenols in the fruit and accelerate enzymatic browning. CAT, as a ROS scavenging enzyme, has a strong ability to remove reactive oxygen species from fruit tissues when it has high activity. This study used a controlled atmosphere fresh-keeping box to treat (the longan was placed in a fresh-keeping box and covered with a film, with a film covering area of ​​about 34.8%). Compared with the control group, the treated group had lower POD activity and higher CAT activity, which effectively regulated the indicators of reactive oxygen metabolism and improved the antioxidant capacity of longan fruit. When the fruit further ages, the cell membrane structure will be destroyed, membrane lipid metabolism will begin to peroxidize, and the MDA content will begin to rise. From the analysis of the results of this study, it can be concluded that after being treated with a controlled atmosphere fresh-keeping box, the MDA content was effectively controlled, the cell membrane structure was stabilized, and the maturation and aging of tissue cells were delayed.

[0129] After being treated with a controlled atmosphere fresh-keeping box, the content of endogenous antioxidant GSH in the longan pulp was also increased compared to the control group. The controlled atmosphere fresh-keeping box treatment can maintain the content of the main non-enzymatic antioxidants in the longan pulp, delaying the browning and aging of the longan. In this study, it can be observed that in the late storage period, the control group has already undergone obvious browning and the flesh has turned yellow, while the treatment group has significantly controlled the browning of its peel and can control the respiration rate to drop significantly.

[0130] In summary, the modified atmosphere fresh-keeping box treatment (the film surface area accounts for about 34.8%) can delay the browning of longan after harvest, maintain low POD activity and MDA content, maintain high CAT activity and GSH content, ensure the overall quality of longan fruit, and delay browning; at the same time, after treatment, the vitamin C content, soluble solids content and acidity of longan pulp are also guaranteed, so that longan has better nutritional content and pulp quality. Therefore, the modified atmosphere fresh-keeping box treatment (the film surface area accounts for about 34.8%) can be used as a safe and healthy preservation technology to preserve longan, and through multiple effects, prolong its normal physiological function and increase its shelf life.

Claims

1. A method for extending the shelf life of fruits by using a controlled atmosphere fresh-keeping box, characterized in that: The following steps are involved: Part of the cover of an ordinary fresh-keeping box is cut off and covered with film to prepare a controlled atmosphere fresh-keeping box, and the fruit is stored in the box.

2. The method according to claim 1, characterized in that The area of ​​the film is 20%, and a controlled atmosphere fresh-keeping box is prepared, and the pre-cooled lotus seeds are placed in the box and stored at room temperature.

3. The method according to claim 2, characterized in that Select a cover area of ​​153.94cm 2 A standard fresh-keeping box is used, and the cover with a length of 6.2 cm and a width of 5.0 cm is cut off and coated so that the coated area is 20%.

4. The method according to claim 3, characterized in that The pre-cooled lotus seeds were placed in a box at a weight of 250.0 g for storage.

5. The method according to claim 2, characterized in that: 1-Methylcyclopropene is also added into the box.

6. The method according to claim 1, characterized in that The area of ​​the film is 34.8%, and a controlled atmosphere fresh-keeping box is prepared, and the harvested fresh longan is placed in the box and stored at 4°C.

7. The method according to claim 6, characterized in that Select a fresh-keeping box with a cover of 15.2 cm×11.2 cm, cut off the cover and coat it with film so that the coated area is 34.8%.

8. The method according to claim 7, characterized in that Store the fresh longan in boxes at a weight of 500g.

9. The method according to any one of claims 1 to 8, characterized in that: The film is a fresh-keeping film.

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