Composite fresh-keeping method for keeping postharvest storage flavor of flat peaches

Abstract

The invention belongs to the technical field of postharvest preservation of fruits and vegetables, and particularly relates to a composite preservation method for keeping the postharvest storage flavor of flat peaches. The method comprises the following steps: pre-cooling fresh-picked flat peaches, and fumigating the flat peaches with 10-20L / L of NO; after the flat peaches are fumigated, packaging the flat peaches with packaging bags to realize spontaneous controlled atmosphere of the fruits; and then placing in a phase temperature library for programmed cooling treatment. The fresh-keeping method disclosed by the invention is easy to implement, simple to operate, short in treatment time, green and safe; the shelf life of the fruits can be prolonged, the loss of aromatic volatile matters can be slowed down, and relatively good commodity value and edible value of the fruits are kept.

Description

Technical Field

[0001] The invention belongs to the technical field of post-harvest preservation of fruits and vegetables, and particularly relates to a composite preservation method for maintaining the flavor of post-harvest storage peaches. Background Art

[0002] Xinjiang is a superior fruit and forest base. Peach is one of Xinjiang's superior specialty fruits. It is loved by consumers for its rich nutritional value and unique flavor. The flavor of fruit is mainly reflected in taste (sugar and acid) and smell (aromatic volatiles). However, peach matures in the hot summer, and the fruit is very easy to rot and deteriorate after harvest, which seriously restricts storage, transportation and sales. In production, low temperature refrigeration is often used to extend the shelf life. However, peach is a cold-sensitive fruit. After long-term refrigeration, the fruit is prone to chilling damage, which is manifested as browning of the flesh, flocculation, rapid loss of aromatic flavor, and quality decline, causing the industry problem of increasing production but not increasing income for fruit farmers, restricting the large-scale development of the industry. Although the current preservation technology in production can achieve the effect of extending the shelf life of peach fruit, the fruit loses a lot of aromatic substances after about 20 days of refrigeration, and loses the commercial value and edible value of the fruit. Therefore, it is urgent to find a preservation method that can both extend the shelf life of peach fruit and delay the loss of aroma volatiles in the fruit.

[0003] Low temperature regulation is a commonly used preservation technology that can effectively reduce the chilling damage of fruits. It is a technology that keeps low-temperature sensitive plant tissues at a technical chilling damage threshold range slightly above the known temperature, induces fruit tolerance and subsequently reduces the temperature. Slow cooling, also known as programmed cooling, is a cooling method in LTC. It is a technical method that plans to cool fruits and vegetables in multiple steps until the required storage temperature is reached after pre-cooling. The research team's previous research found that programmed cooling can effectively slow down the loss of aroma volatiles during the cold storage of peaches and maintain the good flavor of the fruit, but the disadvantage is that the ripening and aging of the fruit will be appropriately accelerated. Based on this, a study on the effect of NO synergistic programmed cooling treatment on the aroma volatiles of peaches was carried out.

[0004] Nitric oxide (NO) is a regulator of various physiological processes, participating in various physiological processes such as seed germination, root and plant growth and development, stomatal movement and aging, and affecting their functions by interacting with different macromolecules (proteins, lipids and nucleic acids). Under low temperature conditions, short-term application of low-concentration NO can effectively alleviate low-temperature damage. In plants, NO has complex biological functions, which can be either a cytotoxin or a cell protector. The dual function of NO as a strong oxidant or an effective antioxidant depends mainly on its concentration and environmental state. When used at a high concentration, NO significantly interferes with the normal metabolism of plants. However, NO promotes the normal growth and development of plants at lower concentrations. A large number of studies have shown that the appropriate NO treatment concentration can not only maintain the quality of fruit refrigeration and extend the shelf life of the fruit, but also maintain the high nutritional value and flavor quality of the fruit. These effects have far-reaching significance for the commercial value of fruits and human health. In order to achieve both the extension of the shelf life of flat peaches and the maintenance of the good aromatic flavor of flat peaches. The aroma substances give flat peaches a unique flavor, which determines the consumer's perception and satisfaction.

[0005] At present, chemical treatments such as 1-MCP preservation and biological preservation methods are often used in production to extend the shelf life of flat peaches. Although 1-MCP preservation technology can extend the cold storage period of flat peaches and maintain good hardness of the fruit, high concentrations of 1-MCP treatment will greatly inhibit the release of aroma volatiles of flat peaches, especially after storage for about 15 days, the unique flavor of flat peaches (aroma volatiles and sugar acid) is lost, which greatly reduces the commercial value and edible value of the fruit. However, biological preservation technology only stays in the experimental stage, and the cost is high, which is not easy to achieve in production. At present, there is no specific preservation technology in production that can not only extend the shelf life of flat peaches, maintain good sensory quality, but also maintain the good aroma and flavor of flat peaches. This study aims to use composite preservation technology to achieve post-harvest antiseptic and antibacterial effects of flat peaches, and maintain post-harvest physiological quality and flavor quality, so as to achieve the purpose of extending the post-harvest shelf life of fruits under the condition of maintaining the physiological quality and flavor quality of fruits. Summary of the invention

[0006] In order to overcome the deficiencies in the prior art, the present invention provides a composite preservation method for maintaining the flavor of peaches after harvest, thereby solving the problem that the current technology cannot both extend the shelf life of peaches after harvest and maintain their good flavor.

[0007] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions: A composite preservation method for maintaining the flavor of peaches after harvesting and storage, comprising the following steps: (1) Precool the freshly picked peaches to a core temperature of 20 ± 0.5 °C and use NO fumigation; (2) After the peaches are fumigated, they are packaged in sealing bags to achieve spontaneous atmosphere control of the fruit; (3) Place the packaged peaches in a phase temperature storage for programmed cooling.

[0008] Preferably, the precooling method in step (1) is as follows: the precooling temperature is 0 ± 0.5 °C, and the NO fumigation experiment is carried out when the fruit core temperature drops to 20 ± 0.5 °C.

[0009] Preferably, the NO fumigation method in step (1) is to use a concentration of 10 - 20 µL L -1 NO gas was used for fumigation. A 5 mL syringe was used to draw NO gas from the NO gas bottle and injected into a closed container containing pre-cooled peaches. The fumigation environment temperature was 20 ± 1 ℃ and the relative humidity was 90 ± 4% to allow the gas to diffuse rapidly and evenly. After fumigation for 2 h, the fruit was placed at a room temperature of 20 ± 5 ℃.

[0010] Further preferably, in step (1), 10 µL L -1 NO fumigation is performed.

[0011] Preferably, after fumigation in step (2), a layer of absorbent paper is placed on the upper layer of the peaches, and a layer of fresh-keeping paper is placed on the absorbent paper, wherein the fresh-keeping paper contains 62.5% Na2S2O5, 4.1% 1-MCP, 1.25% ClO2 and 32.15% base material, and is sealed and packaged in a 0.02 mm PE bag to achieve spontaneous gas conditioning of the fruit.

[0012] The steps for making the fresh-keeping paper refer to the preparation method of 1-MCP fresh-keeping paper in the following literature, except that the fresh-keeping agent used is the fresh-keeping agent described in this application: Ma Xiuyu, et al. Preparation of 1-MCP fresh-keeping paper and its application in nectarine preservation [J]. Journal of Packaging, 2017, 9 (1): 79-84. Preferably, the programmed cooling operation in step (3) is as follows: precooling at 15°C for 24 hours, cooling to 8°C and maintaining for 24 hours on the first day; on the second day, cooling to 5°C and maintaining for 24 hours; on the third day, cooling to 3°C and maintaining for 24 hours; on the fourth day, cooling to 1°C and refrigerating to a temperature of 1±0.5°C and a humidity of 80-90%.

[0013] The flat peaches described in the present invention are uniform in size, free from pests and diseases, free from mechanical damage, with a hardness of >6.8 N and a solidity of 13.5%. The foamed net single fruit is packed in a 2 kg plastic turnover basket and transported back to the cold storage of the Institute of Agricultural Product Processing of Xinjiang Academy of Agricultural Sciences for fumigation experiments.

[0014] The peaches of uniform size, similar maturity and the same number were divided into 24 groups and placed in polyethylene bags, with 15 peaches in each bag. The surface of the peaches was covered with absorbent paper, and the prepared fresh-keeping pad was gently placed on the absorbent paper and sealed. The fruit was placed at room temperature for three days, and the basic physical and chemical indicators of fruit hardness, titratable acid, soluble solids and weight loss rate were measured within three days. The best fresh-keeping paper was selected, which contained 62% Na2S2O5, 4% 1-MCP and 1.2% ClO2.

[0015] Compared with the prior art, the present invention has the following technical effects: (1) The preservation method of the present invention is easy to implement, simple to operate, and has a short processing time; (2) The preservation method of the present invention is green and safe; (3) The preservation method of the present invention can not only extend the shelf life of the fruit but also slow down the loss of aromatic volatiles, thereby maintaining a good commercial value and edible value of the fruit. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the PCA analysis diagram of storage quality and aroma substances of fruits under direct refrigeration and programmed cooling; Figure 2 Cluster analysis diagram of storage quality, aroma substances and fatty acids of fruits stored in direct refrigeration and programmed cooling; Figure 3A This is the effect of NO treatment on total aldehydes during storage of peaches under programmed cooling; Figure 3B This is the effect of NO treatment on total alcohol during storage of peaches under programmed cooling; Figure 3C This is the effect of NO treatment on total esters during storage of peaches under programmed cooling; Figure 3D This is the effect of NO treatment on total lactones during storage of peaches under programmed cooling; Figure 4 A is a graph showing the effect of NO treatment on ADH activity during storage of flat peaches under programmed cooling; Figure 4 B is a graph showing the effect of NO treatment on HPL activity during storage of flat peaches under programmed cooling; Figure 4 C shows the effect of NO treatment on LOX activity during storage of flat peaches under programmed cooling; Figure 4 D is the effect of NO treatment on AAT activity during storage of flat peaches under programmed cooling; FIG5A is a graph showing the effect of NO treatment on the content of palmitic acid in the fatty acids of peaches during cold storage under programmed cooling; Figure 5 B is a graph showing the effect of NO treatment on the stearic acid content in the fatty acids of peaches during cold storage under programmed cooling; Figure 5 C shows the effect of NO treatment on the oleic acid content in the fatty acids of peaches during cold storage under programmed cooling; Figure 5 D is a graph showing the effect of NO treatment on the linoleic acid content in the fatty acids of peaches during cold storage under programmed cooling; Figure 5 E is a graph showing the effect of NO treatment on the content of linolenic acid in the fatty acids of peaches during cold storage under programmed cooling; Figure 6 A is the GO map of differentially expressed genes; Figure 6 B is the KEGG enriched pathway and classification diagram; Fig. 7A This is the effect of different NO fumigation concentrations on the relative conductivity of peach fruit at room temperature; Figure 7B This is the effect of different NO fumigation concentrations on the relative conductivity of peach fruit during cold storage; Figure 7C This is the effect of different NO fumigation concentrations on the relative conductivity of peach fruit under programmed cooling; Fig. 8A This is the effect of different NO fumigation concentrations on PPO of peach fruit at room temperature; Figure 8B This is the effect of different NO fumigation concentrations on PPO of peach fruit during cold storage; Figure 8C This is the effect of different NO fumigation concentrations on PPO of peach fruit under programmed cooling; Fig. 9A This is the effect of different NO fumigation concentrations on the vitamin C content of peach fruit at room temperature; Fig. 9B This is the effect of different NO fumigation concentrations on the vitamin C content of peach fruit during cold storage; Fig. 9C This is the effect of different NO fumigation concentrations on the vitamin C content of peach fruit under programmed cooling; Fig. 10A This is the effect of different NO fumigation concentrations on the firmness of peach fruit at room temperature; Fig. 10B This is the effect of different NO fumigation concentrations on the firmness of peach fruits during cold storage; Fig. 10C This is the effect of different NO fumigation concentrations on the firmness of peach fruit under programmed cooling; Fig.11 This is a graph showing the effect of different preservation treatments on the sucrose content of peaches during the cold storage period and shelf life; Fig.12 This is the effect of different preservation treatments on the glucose content of peaches during the cold storage period and shelf life; Fig.13 This is the effect of different preservation treatments on the fructose content of peaches during the cold storage period and shelf life; Fig.14 This is the effect of different preservation treatments on the malic acid content of peaches during the cold storage period and shelf life; Fig.15 This is the effect of different preservation treatments on the quinic acid content of peaches during the refrigeration period and shelf life; Fig.16 This graph shows the effects of different preservation treatments on the citric acid content of peaches during the refrigeration period and shelf life. DETAILED DESCRIPTION

[0017] The present invention will be further described below in conjunction with specific embodiments, and the advantages and features of the present invention will become clearer as the description proceeds. However, the embodiments are exemplary only and do not constitute any limitation to the scope of the present invention. It should be understood by those skilled in the art that the details and forms of the technical solution of the present invention may be modified or replaced without departing from the spirit and scope of the present invention, but these modifications and replacements all fall within the scope of protection of the present invention.

[0018] Preparation and screening process of fresh-keeping paper: select 1g, 2g, 3g, 4g, 5g or 15g of Na2S2O5, 0.1g or 0.06g of ClO2, and 0.1g or 0.33g of 1-MCP, three solid granular preservatives, respectively, mix them evenly in a total of 24 groups of different mass combinations, and obtain 24 groups of preservatives with different formulas. The 24 groups of preservatives are respectively used for the production of fresh-keeping paper. The production process is as described above, and 24 different fresh-keeping papers are obtained.

[0019] The peaches of uniform size, similar maturity and the same number are divided into 24 groups, respectively placed in polyethylene bags, 15 peaches are placed in each bag, the surface of the peaches is covered with absorbent paper, and the prepared fresh-keeping pad is gently placed on the absorbent paper and sealed. Placed at room temperature for three days, the basic physical and chemical indicators of fruit hardness, titratable acid, soluble solids and weight loss rate within three days are measured. The best fresh-keeping paper (preservative component: 5g Na2S2O5, 0.1g ClO2, 0.33g 1-MCP; the others are base materials) is screened out, that is, containing 62.5% Na2S2O5 by mass, 4.1% 1-MCP by mass and 1.25% ClO2 by mass, and the fresh-keeping paper of this specification is used as the fresh-keeping paper used in all embodiments.

[0020] Example 1 A composite preservation method for maintaining the flavor of peaches after harvesting and storage, comprising the following steps: (1) Select fruits of uniform size, free of pests and diseases, and mechanical damage, with a hardness of >6.8 N and a solidity of about 13.5%. The fruit is packed in a 2 kg plastic turnover basket and transported back to the cold storage of the Institute of Agricultural Products Processing of Xinjiang Academy of Agricultural Sciences for fumigation experiments. The fruit precooling temperature is 0 ± 0.5 ℃, and the NO fumigation experiment is carried out when the fruit core temperature drops to 20 ± 0.5 ℃. The concentration used is 10 µL L -1 NO gas was used for fumigation. A 5 mL syringe was used to draw NO gas from the NO gas bottle and injected into a sealed container. The fumigation environment temperature was 20 ± 1 ℃ and the relative humidity was 90 ± 4%. A small fan was blown for 15 minutes at the beginning of fumigation to make the gas diffuse quickly and evenly. After fumigation for 2 hours, the room temperature treatment was placed at 20 ± 5 ℃.

[0021] (2) After fumigation, place a layer of absorbent paper on the top of the peaches, place a homemade fresh-keeping mat on the absorbent paper, and use a 0.02 mm PE bag to seal the packaging to achieve spontaneous gas conditioning of the fruit.

[0022] (3) After packaging, the fruit is placed in a phase temperature storage for programmed cooling as follows: precooling at 15°C for 24 hours, cooling to 8°C on the first day and keeping it for 24 hours; on the second day, cooling to 5°C and keeping it for 24 hours; on the third day, cooling to 3°C and keeping it for 24 hours; on the fourth day, cooling to 1°C and refrigerating to a temperature of 1±0.5°C and a humidity of 80-90%.

[0023] Example 2 A composite preservation method for maintaining the flavor of peaches after harvest, wherein the operation steps are different from steps (1), (2), and (3) in Example 1 in that the NO concentration is 20 μL L -1 .

[0024] Comparative Example 1 A composite preservation method for maintaining the flavor of peaches after harvesting, which is different from Example 1 in that there is no 10µLL -1 NO fumigation treatment, only programmed cooling treatment.

[0025] Comparative Example 2 A composite preservation method for maintaining the flavor of peaches after harvest, which is different from Example 1 in that the NO concentration is 30 μL L -1 .

[0026] Comparative Example 3 Compared with Example 1, there is neither NO treatment nor programmed temperature reduction treatment, and the peaches are stored at room temperature.

[0027] By comparing 10µL L -1 , 20µL -1, 30 µL -1 Effects of NO fumigation on storage quality and aroma volatiles content -1 NO fumigation concentration has a better effect on maintaining the quality of fruits at room temperature and shelf life, as well as the richness and content of aroma volatiles. Finally, 10 µL L -1 The NO concentration is used as the fumigation concentration for subsequent composite preservation.

[0028] The following analysis experiments were performed on the peach fruits treated by the preservation methods of the above embodiments and comparative examples: (1) HS-SPME-GC-MS (Headspace Solid Phase Microextraction) was used to determine the room temperature shelf life of Comparative Example 1 (CK) and Example 1 (10 µL L -1 NO) and Example 2 (20 µL L -1 The contents of aroma volatiles in peach fruits of NO on the 0th, 2nd and 4th days. SPSS software was used to analyze the significance of aroma volatiles under different treatments. The results are shown in Table 1. -1 The aldehydes, alcohols and esters under NO treatment were significantly higher than those in the control group and 20 μL L -1 NO treatment group (P<0.05). The conclusion showed that 10μL L -1 NO can maintain the rich and high content of aldehydes, alcohols, esters, and lactones in the fruit during the shelf life at room temperature, delaying the loss of fruit aroma substances. -1 NO inhibited the release of aroma substances during shelf life.

[0029] Table 1 Effect of NO on volatile aroma compounds of peaches during storage at room temperature

[0030] (2) The main storage quality of peaches during direct refrigeration and programmed cooling, including hardness, VC, MDA, relative conductivity, and the principal component analysis of aroma substances such as total aldehydes, total alcohols, total esters, total lactones, and fatty acids SA, PA, OA, LA, and LeA. Figure 1 As shown in , the indicators are mainly limited to the first two components PC1 and PC2, and the total explanation rate of the two components reaches 100%, which is very good. Figure 1 It can be seen that there is an obvious separation between the direct refrigeration group and the programmed cooling group, indicating that the NO regulation method at different storage temperatures has a significant effect on the storage quality and aroma metabolism of the fruit.

[0031] Cluster analysis was performed on the aroma substances, main physiological qualities, and fatty acids of flat peach fruits during storage under direct refrigeration, programmed cooling, and NO treatment. Figure 2 As shown in the figure, it can be seen that the direct refrigeration and programmed cooling storage on the 6th, 12th, and 18th days are clustered into one group; while the storage on the 24th, 30th, and 36th days are clustered into another group; this shows that the regulation mechanism of NO on the quality of fruits under direct refrigeration and programmed cooling during the same storage period is basically the same. Figure 2 It can be seen that under programmed cooling, the fruit firmness and VC content were higher, the aldehyde and alcohol content were higher, and the fatty acid content was higher on the 6th and 12th days of storage; but on the 18th day of storage, the alcohol and ester content was higher under direct refrigeration. On the 24th day of storage, except for the alcohol and SA content in the programmed cooling group, which were lower than those in the direct refrigeration group, the content of other substances was significantly higher than that in the direct refrigeration group. On the 30th day of storage, the VC, SA, PA, OA, and LA contents in the programmed cooling group were higher than those in the programmed cooling group. Overall, the programmed cooling group was able to maintain higher nutritional quality and higher fatty acid content of the fruit, and maintain better overall quality of the fruit. Next, we will mainly discuss the effect of 10 µL L -1 Effect of NO treatment on aroma metabolism of Duopan peaches during cold storage.

[0032] (3) Effects of NO treatment on the main aroma volatiles of peaches under programmed cooling Figures 3A-3D shown. Figure 3A The change pattern of total aldehyde content in the two treatment groups during storage of flat peaches was basically the same. Except for the 12th and 18th days, the total aldehyde content in the control group was significantly higher than that in the NO treatment group. During the rest of the storage period, the total aldehyde content in the NO treatment group was significantly higher than that in the control group. On the 36th day of storage, the total aldehyde content of 10 μL L -1 The total aldehyde content in the NO treatment group was 1.4 times that in the control group. NO treatment can delay the loss of aldehydes in peach fruit during the late storage period. Figure 3B The change of total alcohol content during storage is shown in the figure. As shown in the figure, the change pattern of total alcohol content in the two treatment groups is consistent, except for the 10 µLL on the 24th day. -1 The total alcohol content in the NO group was significantly higher than that in the control group. At other storage times, the total alcohol content in the NO-treated group was significantly lower than that in the control group, indicating that NO treatment inhibited the release of alcohol substances in peach fruits. On the 36th day of storage, the total alcohol content in the control group was nearly twice that of the NO group. Figure 3CIt can be seen that during the storage of flat peaches, the esters in both treatment groups reached a peak, the control group reached a peak on the 6th day, and the NO treatment group reached a peak on the 24th day. Before the 18th day of storage, the total ester content in the control group was significantly higher than that in the NO treatment group, and after 18 days, the total ester content in the NO treatment group was significantly higher than that in the control group, indicating that NO combined with programmed cooling treatment can delay the decline of esters in flat peaches that reflect the ripe peach aroma, and can well maintain the aroma of flat peaches in the late storage period. Figure 3D It can be seen that the lactone content in both treatment groups disappeared on the 24th day of storage. On the 12th day of storage, the lactone content in the control group was significantly higher than that in the 10 μL L -1 NO treatment group, and on the 6th and 12th days, the lactone content in the peach fruit of the NO treatment group was significantly higher than that of the control group. On the 36th day of storage, the total lactone content in the NO treatment group was 1.7 times that of the control group.

[0033] Effect of NO treatment on ADH ( Figure 4A ), HPL ( Figure 4B ), LOX ( Figure 4C ), AAT ( Figure 4D ) The results of the influence of activity are as follows Figures 4A-4D As shown in . Figure 4A The results showed that the change trend of ADH enzyme activity in the peach fruit was basically the same in the two treatment groups, which was first increased and then slowly decreased. On the 6th day of storage, the ADH activity in the control group was significantly higher than that in the 10 μLL group. -1 In the NO group, except for the 18th day when the difference between the two groups was not significant, the ADH activity of the NO-treated group was significantly higher than that of the control group from the 12th day. Figure 4B It can be seen that the change trend of HPL activity in the two treatment groups is consistent, but before 18 days of storage, the HPL activity of the control group is significantly greater than that of the NO group, and then the HPL activity of the NO treatment group is significantly higher than that of the control group. Figure 4C As shown in the figure, during the entire storage period, the LOX activity of the NO group was significantly inhibited compared with the control group, and the LOX activity of the control group showed two peaks of activity at the 12th and 24th days of storage, indicating that NO treatment significantly inhibited LOX enzyme activity. Studies have shown that higher LOX will catalyze the increase of peroxidized plasma membrane lipids, thereby changing the fluidity and permeability of the membrane, while lower LOX enzyme activity will maintain the integrity of the fruit cell membrane and maintain better fruit quality. Figure 4D It can be seen that the change pattern of AAT enzyme activity in the two treatment groups is basically the same, but before 24 days of storage, NO treatment significantly inhibited AAT activity compared with the control group, and was significantly lower than the control group. After 24 days, the AAT activity in the NO treatment group was significantly higher than that in the control group.

[0034] (5) Effect of NO treatment on fatty acids (palmitic acid: Figure 5A , stearic acid: Figure 5B , Oleic acid: Figure 5C , Linoleic acid: Figure 5D , linolenic acid: Figure 5E ) content affects Figures 5A-5E As shown in Figure 2, the changes of palmitic acid in the two treatment groups were basically the same, except that on the 6th day of storage, the palmitic acid content in the NO treatment group was lower than that in the control group ( P <0.05), and the palmitic acid content in the NO treatment group was significantly higher than that in the control group at other storage times ( P <0.01), on the 36th day of storage, the content of palmitic acid in the NO treatment group was 1.4 times that of the control group (5A). As shown in 5B, there was no significant difference in the content of stearic acid between the two treatment groups except on the 12th and 18th days. During the other storage periods, the content of stearic acid in the NO group was significantly higher than that in the control group. Figure 5C There was no significant difference in oleic acid content between the two treatment groups before storage on the 30th day. However, on the 30th and 36th days of storage, the oleic acid content in the NO treatment group was significantly higher than that in the control group. Figure 5D As shown in the figure, the changes of linoleic acid in the two treatment groups were basically the same during the entire storage period. Except for the 6th day when the linoleic acid content in the control group was significantly higher than that in the NO treatment group, the oleic acid content in the NO treatment group was significantly higher than that in the control group during the other storage periods ( P <0.01). Figure 5E The linolenic acid content in the control group was significantly higher than that in the NO treatment group except on the 6th day. At other storage times, the NO treatment group was significantly higher than that in the control group ( P <0.01), but there was no significant difference in the linolenic acid content between the two treatment groups at the 36th day of storage.

[0035] (6) Transcriptome sequencing (RNA-seq) was performed on peach fruits during storage. The results are as follows: Fig. 6A , 6B As shown in . It can be seen that NO treatment under programmed cooling has a significant effect on the mRNA of flat peach fruit during storage. There are 7930 co-expressed genes in flat peach fruit at different storage periods. At 30 days of storage, the up-regulated genes in NO fumigation treatment accounted for 51% of the total DEGs (differential genes), and the down-regulated genes accounted for 49% of the total DEGs. Compared with the 12th day of storage, the up-regulated genes increased by 68.5% and the down-regulated genes increased by 40.1% on the 30th day. The KEGG metabolic pathways related to aroma synthesis are enriched in α-linolenic acid metabolism, linoleic acid metabolism and fatty acid anabolism. Through enrichment metabolic analysis, 12 functional genes related to the aroma synthesis of flat peach fruit were screened.

[0036] (7) Figures 7A-7C It can be seen that the relative conductivity of the fruit increases with the extension of storage time. Fig. 7A It can be seen that under normal temperature conditions, on the second and fourth days of storage, different NO fumigation concentrations had no significant effect on the relative conductivity of the fruit. Compared with the control group, NO treatment could significantly inhibit the increase in the relative conductivity of the fruit ( P <0.05). Figure 7B It can be seen that under direct refrigeration conditions, the CK group and 30μL L -1 The relative conductivity of the NO treatment group increased rapidly, while the 10 and 20 μL L -1 Except for 12 and 18 days, the other storage times in the NO treatment group had no significant effect on the relative conductivity of the fruit. -1 NO fumigation treatment is harmful to the fruit. Figure 7C It can be seen that under programmed cooling conditions, different storage times and different concentrations of NO fumigation treatments had different effects on the relative conductivity of the fruit. -1 The relative conductivity of NO fruit was the highest. On the 36th day of storage, 10, 20 μLL -1 There was no significant difference in the effect of NO treatment on the relative conductivity of the fruit, indicating that these two concentration treatments can effectively inhibit the increase of the relative conductivity of the fruit and maintain good fruit quality.

[0037] (8) Figures 8A-8C As shown, the PPO activity in different treatment groups showed an increasing trend. Fig. 8A It can be seen that NO fumigation treatment at room temperature on the 2nd and 4th day can significantly inhibit the increase of PPO activity and slow down the browning rate of fruit compared with the control group. -1 The effect of NO treatment was the most obvious. Figure 8B As shown in Figure 2, under direct refrigeration conditions, NO fumigation treatment significantly inhibited the increase in PPO activity in the late storage period, and the PPO activity was significantly lower than that in the control group ( P <0.05). During the entire refrigeration process, 10 µL L -1 NO treatment had the most significant effect in inhibiting the increase of PPO. Figure 8C It can be seen that under programmed cooling, NO fumigation has a significantly better effect than the control group in inhibiting the increase of PPO during the entire refrigeration process ( P <0.05), indicating that NO fumigation can slow down the browning of fruits and reduce the problem of fruit browning caused by programmed cooling treatment. -1 NO fumigation treatment was significantly better than 20 µL L -1 NO treatment group.

[0038] (9) VC is one of the key factors in evaluating fruit quality. Figures 9A-9C It can be seen that the VC of peach fruits in all treatment groups showed a downward trend with the extension of storage time. Fig. 9AIt can be seen that on the second day of storage, the CK group and 20, 30μL L -1 There was no significant difference in VC content between the NO treatment groups ( P> 0.05). However, on the second day of shelf life, 10 µL L -1 The NO treatment group could maintain a higher VC content in the fruit, which was 1.5 times that of the control group. -1 The VC content of the fruit in the NO group was significantly lower than that in the other treatment groups ( P <0.05), indicating that high concentration NO treatment had a destructive effect on fruit VC as storage time increased, while 10 μL L -1 The NO group had the best effect in maintaining VC. As shown in Figure 9B, the CK group and 30 µL L -1 There was no significant difference in the VC content between the NO treatment groups ( P> 0.05), 10, 20 µL -1 The VC content of NO was not significantly different on the 6th day of storage, but was significantly different at other storage periods ( P <0.05). Fig. 9C It can be seen that CK and 30 μL L -1 The effects of NO group on VC were not significantly different, 10, 20 μL L -1 The NO group had a better effect in inhibiting the decrease of VC, especially 10 μL L -1 The NO group had the most significant effect in inhibiting the decline of VC ( P <0.05). Figure 9 shows a comprehensive description of 10 µL L -1 The NO treatment group had a better effect on delaying the decline of fruit VC and could maintain a better nutritional quality of the fruit. This was consistent with the results of Saba et al. (2017) that NO treatment could maintain a higher VC content in the fruit compared with the control group.

[0039] (10) As shown in Figure 10 AC, under different storage temperatures, the firmness of flat peach fruit showed a downward trend with the extension of storage time. Fig. 10A The results showed that on the second day at room temperature, the hardness of the NO fumigation group was significantly lower than that of the control group ( P <0.05), while 10 µLL -1 The fruit firmness of NO treatment group was significantly lower than that of 20 and 30 μL L -1 NO treatment group ( P <0.05), indicating that at room temperature on the second day, 10 µL L - 1 NO can effectively delay the decline of fruit firmness, but there is no significant difference in the effect of NO on fruit firmness on the 4th day of storage. Fig. 10B As shown in Figure 2, under direct cold storage conditions, the fruit firmness of the control group was significantly lower than that of the NO treatment group (P <0.05), while 10 µL L -1 The hardness of NO group was significantly higher than that of 20 and 30 μL L -1 NO group ( P <0.05), stored until 30 days, 10-30 µL L -1 The fruit firmness of NO treatment decreased by 25.1%, 33.7% and 41.1%, respectively. Fig. 10C , the fruit firmness of the control group was significantly lower than that of the NO treatment group before 18 days of storage. P <0.05), while after 18 days, the fruit firmness of the control group was similar to that of 30 µL L -1 There was no significant difference between the treatment groups ( P >0.05), while 10 and 20 µL L -1 The NO group had no significant difference in the effect on fruit firmness ( P >0.05), indicating that under programmed cooling conditions, 10, 20 µL L -1 NO fumigation can effectively maintain the firmness of peach fruits.

[0040] (11) Effects of different preservation treatments on the sucrose content of peaches during the cold storage period and shelf life Fig.11 As shown in the figure, direct refrigeration without treatment (DCK), programmed cooling without treatment (LCK), cling film + NO + direct refrigeration (DJN), cling film + NO + programmed cooling (LJN). The sucrose in the fruit can protect plant cells from low temperature stress in a low temperature environment. Therefore, during storage, the fruit is often induced to increase the sucrose content to enhance its cold resistance and prevent cold damage. Fig.11 The sucrose content showed a trend of increasing first and then decreasing during the entire storage and shelf life. The sucrose content accumulated continuously before 12 days and reached a peak on the 12th day of storage. The sucrose contents of LJN, DJN, LCK, and DCK were 76.21 mg / g, 76.21 mg / g, 74.85 mg / g, and 72.72 mg / g, respectively. There were significant differences between the LJN and DJN treatment groups and the control group, indicating that NO and cling film treatment can increase the sucrose level in the early stage of storage. After 12 days, the sucrose content gradually decreased, and LCK and LJN maintained a high sucrose content. At the end of 30 days of cold storage, the sucrose content of each treatment group showed a difference pattern of LJN>DJN>LCK>DCK. The change of sucrose content during the shelf life continued to the late storage period, with LCK and DCK decreasing more sharply, and LJN and DJN decreasing more gently. Compared with the two control groups, the treatment groups had a certain positive effect on maintaining sucrose content, maintaining the quality of flat peaches, extending the shelf life, and preventing chilling injury.

[0041] (12) By Fig.12It can be seen that the glucose content of each treatment group accumulated during the storage period of flat peaches after harvest, but there were certain differences in degree. On the 0th day of storage, the glucose content was 12.15 mg / g. At the end of 30 days of storage, the glucose content of DCK, DJN, LCK, and LJN treatment groups was 19.30 mg / g, 20.80 mg / g, 19.00 mg / g, and 21.18 mg / g, respectively. The glucose content of each treatment group showed a difference pattern of LJN>DJN>DCK>LCK. During the shelf life, the glucose content of each treatment group increased slowly. At the end of the third day of the shelf life, the glucose content of the LJN treatment group was the highest. In the two control groups (LKC, DCK), the content of LCK was higher than that of DCK, indicating that programmed cooling can increase the glucose content.

[0042] (13) By Fig.13 It can be seen that the change trend of fructose content is similar to that of glucose, showing a gradual increase. Before the initial 6 days of storage, the DJN treatment group maintained a high fructose content, but after 12 days, the glucose content of the LJN treatment group was the highest compared with the other three groups until the end of the shelf life. The fructose content of LJN at the end of the storage period and the end of the shelf life was 13.54 mg / g and 15.44 mg / g, respectively, followed by the DJN treatment group, which were 13.00 mg / g and 15.03 mg / g, respectively, indicating that NO+ cling film in the two treatment groups can increase the production of fructose.

[0043] (14) Malic acid is the organic acid with the highest proportion of total acid in the ripening process of peaches. Fig.14 As shown in the figure, from the beginning of storage to 12 days, the fruit in the treatment group increased slightly as a whole, while the control group showed a downward trend. The DCK group increased on the 18th day and then decreased. In the middle and late stages of storage, the LJN treatment group was always higher than the other three groups, maintaining a high malic acid content. By the end of the 30-day storage period, the malic acid content was 2.33 mg / g, and the DJN was also 2.33 mg / g. There was no significant difference between the two treatment groups, but it was significantly higher than the two control groups (P < 0.05). During the shelf period, the LJN group decreased more than the DJN group, and DJN showed a more obvious advantage in inhibiting the decline of malic acid. After three days of shelf life, the malic acid content remained at 1.73 mg / g, and the malic acid content of the LJN group was 1.63 mg / g, which was significantly higher than the LJN group.

[0044] (15) From Fig.15It can be seen that after 12 days of storage, the quinic acid content of the fruits in each treatment group was significantly different. As the storage time increased, the acid degradation accelerated. The quinic acid content of the fruit on the 0th day of storage was 1.93 mg / g. On the 30th day of storage, the DCK and LCK contents were 1.00 mg / g and 1.43 mg / g, respectively, which were 0.93 mg / g and 0.50 mg / g lower than the initial storage. The fruit content of the two treatment groups was significantly higher than that of the two control groups. At the end of storage, the LJN and DJN contents were 1.93 mg / g and 1.63 mg / g, respectively. The quinic acid content of the LJN group did not change from the initial storage after 30 days of storage, and the maintenance was still good. When placed at room temperature, the quinic acid content did not drop drastically, but slowly decreased. Among them, the LJN treatment group was still the treatment group with the highest quinic acid content.

[0045] (16) Fig.16 As shown in the figure, the content of citric acid in flat peach fruit is very low. With the change of acid degradation, during the storage period, the treatments gradually showed a certain regularity. DJN, LCK, and DCK reached the citric acid peak at 12 days of storage and then decreased. LJN delayed the peak to 18 days of storage, during which the accumulation of citric acid content increased. The citric acid content of LCK fruit was always higher than that of DCK, and DCK>LCK was shown in the late storage period of 24-30 days, but the difference in citric acid content between the two treatments was small and did not reach a significant level. The citric acid content level of DJN treatment remained relatively stable with a small change range. At the end of storage, the content was 1.07 mg / g, ranking first. There was a very significant difference in the shelf life between the treated group and the control group. The degradation of citric acid may enter an intensified stage due to the increase in temperature. The degradation degree of citric acid content in the fruits of each treatment was different until the end of the three-day shelf life of the fruit. The difference in the degradation degree showed LCK>DCK>LJN>DJN, and the contents were 0.06 mg / g, 0.06 mg / g, 0.23 mg / g, and 0.37 mg / g, respectively.

Claims

1. A composite preservation method for maintaining the flavor of peaches after harvest, characterized in that: The following steps are involved: (1) Precool the freshly picked peaches to a core temperature of 20 ± 0.5 °C and use NO fumigation; (2) After the peaches are fumigated, they are packaged in sealing bags to achieve spontaneous atmosphere control of the fruit; (3) Place the packaged peaches in a phase temperature storage for programmed cooling.

2. A composite preservation method for maintaining the flavor of peaches after harvesting according to claim 1, characterized in that: The precooling method of step (1): the precooling temperature is 0 ± 0.5 °C, and the NO fumigation experiment is carried out when the fruit core temperature drops to 20 ± 0.5 °C.

3. The composite preservation method for maintaining the flavor of peaches after harvesting according to claim 1, characterized in that: Step (1) of the NO fumigation method: use a concentration of 10 ~ 20µL L -1 NO gas was used for fumigation. A 5 mL syringe was used to draw NO gas from the NO gas bottle and injected into a closed container containing pre-cooled peaches. The fumigation environment temperature was 20 ± 1℃ and the relative humidity was 90 ± 4% to allow the gas to diffuse quickly and evenly. After fumigation for 2 h, the fruit was placed at a room temperature of 20 ± 5℃.

4. A composite preservation method for maintaining the flavor of peaches after harvesting according to claim 3, characterized in that: In step (1), 10 µL L -1 NO fumigation is performed.

5. The composite preservation method for maintaining the flavor of peaches after harvesting according to claim 1, characterized in that: After fumigation in step (2), a layer of absorbent paper is placed on the upper layer of the peaches, and a layer of fresh-keeping paper is placed on the absorbent paper, wherein the fresh-keeping paper contains 62.5% Na2S2O5, 4.1% 1-MCP, 1.25% ClO2 and 32.15% base material, and is sealed and packaged in a 0.02 mm PE bag to achieve spontaneous gas conditioning of the fruit.

6. The composite preservation method for maintaining the flavor of peaches after harvesting according to claim 1, characterized in that: The programmed cooling in step (3) is performed as follows: precool at 15°C for 24 h, cool to 8°C on the first day and keep for 24 h; on the second day, cool to 5°C and keep for 24 h; on the third day, cool to 3°C and keep for 24 h; on the fourth day, cool to 1°C and refrigerate to a temperature of 1±0.5°C and a humidity of 80-90%.

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