Leaf vegetable high-temperature water-holding fresh-keeping method

Abstract

The invention belongs to the technical field of fruit and vegetable fresh-keeping, and particularly relates to a leaf vegetable high-temperature water-holding fresh-keeping method. According to the method, the phytic acid and the gamma-aminobutyric acid are coupled through multi-frequency ultrasound to construct a compound system for humidifying the leaf vegetables, and the cost is low. The quality loss of the leaf vegetables in the storage period can be relieved in a high-temperature storage environment, the quality reduction of the leaf vegetables in the storage period is avoided, the appearance quality of the leaf vegetables is maintained, the senescence of the leaf vegetables after picking is delayed, the edible value and the commodity value of the leaf vegetables are ensured, and the leaf vegetable preservative can be applied to the preservation of various leaf vegetables in high-temperature storage.

Description

Technical Field

[0001] The invention belongs to the technical field of fruit and vegetable preservation, and particularly relates to a high-temperature moisture retention and preservation method for leafy vegetables. Background Art

[0002] With the advent of the new consumer era, the pre-prepared meal industry has entered a fast-paced development phase. The industry chain includes three major links: upstream (raw materials), midstream (pre-prepared meal processing and production), and downstream (sales). The midstream is the pre-prepared meal production and processing industry, primarily responsible for the production and processing of raw vegetables, clean vegetables, and semi-finished products. After production and processing, raw vegetables are transported to the downstream industry through logistics. During transportation, temperature is closely related to the quality of raw vegetables. Currently, there is a gap between the cold chain transportation construction and system of the pre-prepared meal industry and the requirements of industry development. Temperature monitoring at every stage of the transportation process cannot be guaranteed, and transportation often faces large temperature fluctuations. Temperature fluctuations have a significant impact on the quality of raw vegetables. High temperatures and temperature fluctuations within a short period of time lead to severe water loss, wilting, leaf shrinkage, and stem softening of raw vegetables, seriously affecting their edible quality and value.

[0003] Leafy vegetables are an essential part of the vegetable crop. Current methods for preserving leafy vegetables primarily focus on post-harvest storage through refrigeration, controlled atmosphere (CA) storage, modified atmosphere packaging (MAP), and chemical preservation. These methods, designed to extend the shelf life of vegetables, require specialized equipment and are costly. Preserving leafy vegetables often requires a constant low temperature of 4°C. However, in real-world production and transportation, where cold chains are not fully implemented, high temperatures or temperature fluctuations can easily cause dehydration, wilting, and softening of leaves and stems. While CN201810621910.X and CN201610481327.4 can extend the shelf life of shallots and spinach, they require soaking in a solution followed by draining or blotting with absorbent paper before packaging in perforated fresh-keeping bags and storing at a low temperature of 3-5°C. While these methods can maintain freshness, they require low temperatures.

[0004] And with the development of the logistics and transportation industry and the pre-prepared food industry, although the time required for vegetables to be picked and served on the table is decreasing, the current problem faced by companies is the loss of vegetables during transportation. Foam boxes are often used for transportation. The temperature of the environment in which vegetables are located is high and the temperature fluctuates greatly. Therefore, vegetables usually lose weight, wilt, and rot during transportation, which seriously affects the commercial value of vegetables and causes serious economic losses to companies. At present, special storage and transportation boxes are mainly used to preserve vegetables to address the problems faced by vegetables during transportation. Although CN202020545369.1 uses special storage and transportation boxes to achieve the purpose of preservation, current companies usually supply them in quantity according to the quantity required by each store. The storage and transportation boxes require special specifications, which makes it difficult for companies to flexibly implement the supply-on-quantity model. In addition, refrigerants, dry ice, etc. are required inside the storage and transportation boxes to maintain the storage and transportation environment of the storage and transportation boxes. Refrigerants and dry ice greatly increase the transportation costs of companies. Therefore, there is an urgent need for a technology that can retain water and preserve leafy vegetables in a high temperature environment. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for high-temperature moisture retention and freshness preservation of leafy vegetables, and the technical solution adopted is:

[0006] A method for retaining moisture and keeping leafy vegetables fresh at high temperature comprises the following steps:

[0007] 1) Sorting leafy vegetables;

[0008] 2) Using multi-frequency ultrasound to humidify a mixed solution of phytic acid and γ-aminobutyric acid on leafy vegetables;

[0009] 3) Store the processed leafy vegetables.

[0010] In some embodiments of the present invention, the leafy vegetables include spinach, lettuce, romaine lettuce, cabbage, water spinach, amaranth, coriander, lettuce leaves, kale, celery, broccoli, cauliflower, pea sprouts, and broccoli.

[0011] In some embodiments of the present invention, the leafy vegetables are mature, free of pests and diseases, and free of mechanical damage.

[0012] In some embodiments of the present invention, in the mixed solution of phytic acid and γ-aminobutyric acid, the concentration of phytic acid is 10-100 mg / L, and the concentration of γ-aminobutyric acid is 5-20 mmol / L; further, the concentration of phytic acid is 40-60 mg / L, and the concentration of γ-aminobutyric acid is 12-18 mmol / L.

[0013] In some embodiments of the present invention, the preparation method of the phytic acid and γ-aminobutyric acid mixed solution is:

[0014] The phytic acid solution is prepared by mixing 10-100 mg / L phytic acid solution and 5-20 mmol / L gamma-aminobutyric acid solution in a volume ratio of 1:(1-5).

[0015] In some embodiments of the present invention, the multi-frequency ultrasound is dual-frequency ultrasound.

[0016] In some embodiments of the present invention, frequency 1 of the dual-frequency ultrasound is 20-60 KHz, and frequency 2 is 40-100 KHz.

[0017] In some embodiments of the present invention, the frequency of the dual-frequency ultrasound can be specifically selected from any combination of 20+40KHz, 20+60KHz, 20+80KHz, 40+80KHz, 40+60KHz, and 80+60KHz.

[0018] In some embodiments of the present invention, the multi-frequency ultrasound is intermittent ultrasound.

[0019] In some embodiments of the present invention, the ratio of the ultrasound time to the intermittent time of the intermittent ultrasound is (1-5) s / s; further (1-2) s / s.

[0020] In some embodiments of the present invention, the total treatment time of the multi-frequency ultrasound is 1 to 10 minutes; further 4 to 6 minutes.

[0021] In some embodiments of the present invention, the dosage of the phytic acid and γ-aminobutyric acid mixed solution is 20 to 40 mL sprayed per 250 g of vegetables.

[0022] In some embodiments of the present invention, the storage temperature is 16-40°C; further, 25-35°C.

[0023] The method of the present invention can keep leafy vegetables fresh in an environment of normal temperature (about 25°C) or even high temperature (above 30°C), but the good preservation effect of the present invention at higher temperatures does not mean that the method of the present invention cannot be used for low-temperature preservation. The high temperature advantage of this solution cannot be used as a temperature condition limitation of the present invention. The method of the present invention can be applied at conventional preservation temperatures in this field.

[0024] Compared with the existing technology, the purpose of the present invention is to alleviate the quality of leafy vegetables under high temperature conditions to ensure the edible value and commercial value of leafy vegetables. It has the following advantages and positive effects:

[0025] The present invention discloses a method for effectively maintaining the moisture content, firm stems, and fresh, crisp leaves of leafy vegetables in a high-temperature environment. The method can effectively maintain the freshness and quality of leafy vegetables in high-temperature and variable-temperature environments. The steps are as follows: a composite system is constructed by coupling multi-frequency ultrasound with phytic acid, gamma-aminobutyric acid, etc., and the leafy vegetables are humidified to enhance the microphase solids in the composite system to be evenly and firmly attached to the surface of the leafy vegetables. During storage at a relatively high temperature (30°C), the vegetable stems are maintained firm and the leaves are fresh and crisp, achieving a water-retaining and fresh-keeping effect. The stirring intensity generated by multi-frequency ultrasound on the solution is much greater than that of mechanical stirring and ordinary immersion treatment. It can not only make the solid phase particles in the solution evenly dispersed at the microscopic scale, but also further make them firmly attached to the surface of the vegetables. At the same time, gamma-aminobutyric acid can reduce the generation of reactive oxygen species by increasing the activity of free radical scavenging system enzymes such as superoxide dismutase, catalase, and glutathione reductase, reduce the damage to cell membranes caused by the accumulation of hydrogen peroxide and malondialdehyde, maintain the stability of the cell membrane structure under high-temperature adversity, and reduce water loss. Phytic acid inhibits gas exchange in harvested vegetables, reducing respiration, slowing cell aging, reducing water loss, and improving the storage quality of leafy vegetables. This invention offers a simple process and significant commercial benefits, effectively maintaining the firmness and appearance of leafy vegetables at elevated temperatures, slowing their mass loss, and extending their shelf life. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0027] Figure 1 Graph showing the mass loss rate of spinach in Example 1 and Comparative Examples 1 and 2.

[0028] Figure 2 Graph showing mass loss rates of Chinese cabbage in Examples 2 and 3 and Comparative Example 4.

[0029] Figure 3 It is the overall appearance picture of Example 1 and Comparative Examples 1 and 2 (spinach).

[0030] Figure 4 It is the appearance vertical figure (spinach) of Example 1 and Comparative Examples 1 and 2.

[0031] Figure 5 This is the overall appearance of Examples 2 and 3 and Comparative Examples 3, 4, and 5 (Chinese cabbage heart) (the red circle is the yellowing area of ​​the leaves).

[0032] Figure 6 It is the vertical figure of the appearance of Example 2, 3 and comparative example 2 (Chinese cabbage heart).

[0033] Figure 7 Softening index diagram of Example 1 and Comparative Examples 1 and 2 (spinach).

[0034] Figure 8 The yellowing index diagram of Examples 2, 3 and Comparative Example 3 (Chinese cabbage). DETAILED DESCRIPTION

[0035] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0036] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the materials and reagents used are commercially available reagents and materials unless otherwise specified.

[0037] The definitions of relevant standards and formulas are as follows:

[0038] 1. Quality loss rate

[0039] The mass loss rate was determined by weighing method and calculated according to formula (1).

[0040]

[0041] Where: m1 represents the initial weight of vegetables treated with preservatives / g; m2 represents the mass of vegetables at the end of storage / g.

[0042] 2. Appearance quality

[0043] 3 to 6 vegetables were randomly selected as the subjects for appearance photography, and the appearance quality of leafy vegetables was recorded in a studio under fixed light intensity, color temperature, angle and the same photography equipment conditions.

[0044] 3. Yellowing index

[0045] Thirty vegetables were randomly selected for grading in each treatment, and the yellowing index of the leaves was calculated. The yellowing degree of each vegetable leaf was divided into 5 levels according to the size of the yellowing area:

[0046] Level 0 leaves, no yellowing leaves;

[0047] Level 1 leaves, yellowing area accounts for 0%-25% of the total leaves

[0048] Level 2 leaves: yellowing area accounts for 25%-50% of the total leaves;

[0049] Level 3 leaves: yellowing area accounts for 50%-75% of the total leaves;

[0050] Level 4 leaves, the yellowing area accounts for 75%-100% of the total leaves.

[0051] The calculation formula (2) for leaf yellowing index is:

[0052] Yellowing index (%) = ∑ (yellowing level × number of leaves in this level) / (total number of leaves × highest level representative value) (2)

[0053] 4 Softening index

[0054] A total of 60 spinach plants were selected for evaluation in each treatment group. The softening level was determined based on the grading index, and the proportion of leafy vegetables in each level to the total number of plants in the survey treatment was calculated.

[0055] Grading standards for the softening degree of leafy vegetables:

[0056] Level 0: leaves are bright green and not softened;

[0057] Level 1: The outermost leaves become soft;

[0058] Level 2: The second layer of the leaves begins to soften;

[0059] Level 3: The inner layer of the leaf becomes soft;

[0060] Level 4: The leaves of the entire plant become soft and rotten.

[0061] The calculation formula of softening index is:

[0062] Example 1 Effect of multi-frequency ultrasound coupled phytic acid and γ-aminobutyric acid composite system on high temperature storage of spinach

[0063] Spinach was selected and sorted according to the standards of uniform size, maturity, freedom from pests and diseases, mechanical damage, and rot. 250 g of the sorted spinach was humidified using a multi-frequency ultrasound-coupled phytic acid and γ-aminobutyric acid composite system.

[0064] A phytic acid and γ-aminobutyric acid mixed solution was prepared by mixing γ-aminobutyric acid solution (content: 15 mmol / L) and phytic acid solution (content: 50 mg / L) at a ratio of 1:3 (v / v). The solution was then ultrasonically treated.

[0065] Multi-frequency ultrasonic treatment conditions: 20 + 80 kHz frequency combination, 2 seconds on, 1 second off, for 5 minutes. After treatment, spray 20 mL of the mixed solution per 250 g of vegetables, applying even pressure to the surface of the leafy vegetables to ensure the solvent adheres evenly and firmly to the spinach surface.

[0066] After treatment, the spinach was stored at 30°C for 24 hours. During storage, the spinach mass loss rate, appearance quality, and softening index at 24 hours were measured.

[0067] Example 2 Effect of multi-frequency ultrasound coupled phytic acid and γ-aminobutyric acid composite system on high temperature storage of Chinese cabbage

[0068] The Chinese cabbage was selected and sorted according to the standards of uniform size, maturity, freedom from pests and diseases, mechanical damage and rot. 250 g of the sorted Chinese cabbage was taken and humidified using a multi-frequency ultrasound coupled phytic acid and γ-aminobutyric acid composite system.

[0069] A phytic acid and γ-aminobutyric acid mixed solution was prepared by mixing γ-aminobutyric acid solution (content: 15 mmol / L) and phytic acid solution (content: 50 mg / L) at a ratio of 1:3 (v / v). The solution was then ultrasonically treated.

[0070] Multi-frequency ultrasonic treatment conditions: Combined frequency of 20 + 80 kHz, pulse on for 2 seconds, rest for 1 second, and process for 5 minutes. After treatment, spray 40 mL of the mixed solution per 250 g of vegetables, applying even pressure to the surface of leafy vegetables to ensure that the solvent adheres evenly and firmly to the surface of the vegetable heart.

[0071] After treatment, the spinach was stored at 30°C for 24 hours. During storage, the spinach mass loss rate, appearance quality, and yellowing index at 24 hours were measured.

[0072] Example 3 Effect of multi-frequency ultrasound coupled phytic acid and γ-aminobutyric acid composite system on high temperature storage of Chinese cabbage

[0073] This embodiment is consistent with embodiment 2, except that the multi-frequency ultrasonic frequency is adjusted as follows:

[0074] The Chinese cabbage was selected and sorted according to the standards of uniform size, maturity, freedom from pests and diseases, mechanical damage, and rot. 250 g of the sorted Chinese cabbage was taken and humidified using a multi-frequency ultrasound-coupled phytic acid and γ-aminobutyric acid composite system.

[0075] A phytic acid and γ-aminobutyric acid mixed solution was prepared by mixing γ-aminobutyric acid solution (content: 15 mmol / L) and phytic acid solution (content: 50 mg / L) at a ratio of 1:3 (v / v). The solution was then ultrasonically treated.

[0076] Multi-frequency ultrasonic treatment conditions: Combined frequency of 20 + 40 kHz, pulse on for 2 seconds, rest for 1 second, and process for 5 minutes. After treatment, spray 40 mL of the mixed solution per 250 g of vegetables, applying even pressure to the surface of leafy vegetables to ensure that the solvent adheres evenly and firmly to the surface of the vegetable heart.

[0077] After treatment, the vegetables were stored at 30°C for 24 h. During storage, the mass loss rate, appearance quality, and yellowing index at 24 h were measured.

[0078] Comparative Example 1: High temperature storage of spinach without any treatment

[0079] Select spinach that is uniform in size, mature, free of pests and diseases, mechanical damage, and rot. Take 250g of spinach without any treatment and store it at 30℃ for 24h.

[0080] The mass loss rate, appearance quality and softening index of spinach at 24 h were measured during storage.

[0081] Comparative Example 2 Effect of single-frequency ultrasound coupled phytic acid and γ-aminobutyric acid composite system on high-temperature storage of spinach

[0082] Select spinach that is uniform in size, mature, free of pests and diseases, mechanical damage, and rot. Take 250g of spinach and humidify it using a single-frequency ultrasound coupled with a phytic acid and γ-aminobutyric acid composite system.

[0083] A phytic acid and γ-aminobutyric acid mixed solution was prepared by mixing γ-aminobutyric acid solution (content: 15 mmol / L) and phytic acid solution (content: 50 mg / L) at a ratio of 1:3 (v / v). The solution was then ultrasonically treated.

[0084] Single-frequency ultrasonic treatment conditions: 40 kHz frequency, 2-second pulse on, 1-second off, 5-minute treatment. After treatment, spray 20 mL of the mixed solution per 250 g of vegetables, applying even pressure to the surface of the leafy vegetables to ensure the solvent adheres evenly and firmly to the spinach surface.

[0085] After treatment, the spinach was stored at 30°C for 24 hours. During storage, the spinach mass loss rate, appearance quality, and softening index at 24 hours were measured.

[0086] Comparative Example 3 Effect of multi-frequency ultrasound coupled citric acid system on high temperature storage of Chinese cabbage

[0087] Select choy sum that is uniform in size, mature, free of pests, diseases, mechanical damage, and rot. Take 250g of choy sum and treat it with multi-frequency ultrasound coupled with citric acid humidification. The citric acid content is 1 wt%.

[0088] Multi-frequency ultrasonic treatment conditions: Combined frequency of 20 + 80 kHz, pulse on for 2 seconds, rest for 1 second, and process for 5 minutes. After treatment, spray 40 mL of the mixed solution per 250 g of vegetables, applying even pressure to the surface of leafy vegetables to ensure that the solvent adheres evenly and firmly to the surface of the vegetable heart.

[0089] After treatment, the vegetables were stored at 30°C for 24 h. During storage, the mass loss rate, appearance quality, and yellowing index at 24 h were measured.

[0090] Comparative Example 4 High-temperature storage of Chinese cabbage treated with phytic acid

[0091] Select spinach that is uniform in size, mature, and free of pests, diseases, mechanical damage, or rot. Take 250g of choy sum and treat it with a 50mg / L phytic acid solution using a multi-frequency ultrasound coupled with 20kHz and 80kHz combined frequency, 2s pulses on, 1s off, for 5 minutes.

[0092] Store at 30℃ for 24h.

[0093] The mass loss rate and appearance quality of spinach were measured during storage.

[0094] Comparative Example 5 High-temperature storage of Chinese cabbage treated with γ-aminobutyric acid

[0095] Select choy sum that is uniform in size, mature, and free of pests, diseases, mechanical damage, or rot. 250g of choy sum was humidified using a multi-frequency ultrasound coupled with a γ-aminobutyric acid solution. The γ-aminobutyric acid solution concentration was 15 mmol / L. The multi-frequency ultrasound treatment conditions were: a combined frequency of 20 + 80 kHz, a 2-second pulse cycle followed by a 1-second pause, and a treatment time of 5 minutes.

[0096] Store at 30℃ for 24h.

[0097] The mass loss rate and appearance quality of Chinese cabbage were measured during storage.

[0098] Effect Example 1: Spinach Effect Comparison

[0099] Example 1 Treatment results are as follows Figures 1 to 3 、 Figure 6 As shown, the results of Comparative Examples 1 and 2 are as follows Figure 1 、 3 , 4, and 7, comparative example 2.

[0100] Figure 1 The figure shows the mass loss rate of spinach in Example 1 and Comparative Examples 2 and 3. The mass loss rate is an important indicator of vegetable quality. The larger the value, the more serious the water loss in the vegetable. Although the mass loss rate of Example 1 increases with the extension of storage time, it is only 4.79% at 8 hours and 7.55% at 16 hours. The mass loss rate reaches the maximum at 10.25% after 24 hours of storage. In Comparative Example 1, the mass loss rate reaches 10.29% after only 8 hours of storage and reaches 21.61% at 24 hours, indicating serious water loss. The mass loss rate of Example 1 during storage is much lower than that of Comparative Examples 1 and 2. This shows that the treatment method of Example 1 can effectively maintain the moisture of spinach under high-temperature storage.

[0101] Figure 3 and Figure 4They are the overall appearance diagram and vertical diagram of Example 1 and Comparative Examples 1 and 2 respectively. It can be seen from the overall diagram that during the 24-hour storage period, most of the spinach leaves of Example 1 remained plump and crisp, and only a few leaves had slightly wilted edges. However, the spinach leaves of Comparative Example 1 that were not treated in any way began to shrink and curl at 8 hours. At 24 hours, the leaves of the spinach were severely wrinkled and wilted, and the overall volume was reduced. The vertical diagram can intuitively show the degree of softening of the spinach stems. The spinach of Comparative Example 3 began to show slight wrinkling and curling of leaves at 16 hours. At 24 hours, some leaves were wrinkled and wilted. From Figure 3 It can be seen that the treatment method of Example 1 can effectively maintain the firmness of the spinach stems during storage, while the stems of Comparative Examples 1 and 2 softened after 24 hours of storage. The stems of the spinach in Comparative Example 1 softened severely, and most of them could no longer support the leaves to stand upright. The spinach in Comparative Example 2 softened partially after 24 hours of storage, and some stems could not stand upright. The softening index was 32.22%. Combined with the softening index ( Figure 6 ). The softening index of spinach treated with the method of Example 1 after 24 hours was only 24.54%, lower than that of Comparative Example 1 (63.16%) and Comparative Example 2 (32.22%). This indicates that the method of Example 1 can effectively maintain the freshness of spinach after 24 hours of storage at 30°C, locking in moisture and reducing wilting and softening. It also maintains a firm stem and plump leaves. Therefore, the treatment method of Example 1 is the optimal treatment condition.

[0102] The treatment method in Comparative Example 2 was inferior to Example 1 in maintaining spinach water loss, leaf wilting, and stem softening, but still superior to Comparative Example 1. The spinach's freshness could not be maintained after 24 hours of storage at 30°C. This indicates that the cavitation effect produced by single-frequency ultrasound at 40 kHz is weaker than that produced by dual-frequency ultrasound, resulting in a less tight and uneven adhesion of the phytic acid and GABA mixture to the spinach, leading to poor preservation of the spinach treated with the method in Comparative Example 2.

[0103] Effect Example 2: Comparison of the Effects of Choy Sum

[0104] The processing results of Examples 2 and 3 are as follows: Figure 2 、 Figure 5 、 Figure 6 and Figure 8 shown.

[0105] from Figure 2It can be seen that as the storage time increases, the mass loss rate of the Chinese cabbage treated by the method of Example 2 is lower than that of Example 3 and Comparative Example 3 during storage. The mass loss rate of the Chinese cabbage treated by the method of Example 2 is 5.83% after 6 hours of storage, 7.91% after 16 hours of storage, and only 10.57% after 24 hours of storage. The mass loss rate of the Chinese cabbage treated by the method of Example 3 is 12.04% after 24 hours of storage, while the mass loss rate of the Chinese cabbage treated by the method of Comparative Example 3 reaches 12.54% after 16 hours of storage and 16.50% after 24 hours of storage. This shows that the effect of maintaining the moisture content of the Chinese cabbage is: Example 2 > Example 3 > Comparative Example 3. The treatment method of Example 2 can effectively maintain the moisture content of the Chinese cabbage and reduce mass loss during storage. It is superior to Example 3 and Comparative Example 3 in terms of water retention effect.

[0106] Depend on Figure 5 It can be seen that the Chinese cabbage treated by the method of Example 2 maintained a bright color and full leaves during storage, and the Chinese cabbage did not shrink in size. The treatment method of Example 3 was also able to maintain a bright and full leaf color within 24 hours of storage. A small number of leaves showed slight curling at the edges, but the whole remained relatively fresh. The Chinese cabbage treated by the method of Comparative Example 3 began to show curling and shrinking at the edges of the leaves after 8 hours of storage. After 24 hours, the leaves were severely curled and shrunken, and the Chinese cabbage was wilted as a whole. And from the vertical graph ( Figure 6 ) It can be seen that during the 24-hour storage period, the stalks of the Chinese cabbage treated by the method of Example 2 remained upright and firm, with very few stalks softening. The stalks of the Chinese cabbage treated by the method of Example 3 began to soften at 8 hours, but most of the stalks were still relatively firm at 24 hours. In Comparative Example 2, most of the leaves had softened and could not stand upright after 24 hours of storage.

[0107] Figure 8 It is a graph of the yellowing index of Examples 2, 3 and Comparative Example 3 after 24 hours of storage. The yellowing index represents the degree of yellowing of the Chinese cabbage as a whole. The higher the yellowing index, the more yellowed the Chinese cabbage is and the more serious the yellowing is. The yellowing index of Example 2 at 24 hours is 0.64, which is significantly lower than that of Example 3 (1.37) and Comparative Example 3 (2.21). The results show that the treatment method of Example 2 can effectively maintain the moisture content of the Chinese cabbage stored at a high temperature of 30°C, maintain the appearance quality of the Chinese cabbage, and maintain the freshness of the Chinese cabbage leaves and the firmness of the stems. The yellowing index of Example 3 is 1.37, which is lower than that of Comparative Example 3.

[0108] The choy sum treated with the method in Example 3 remained relatively fresh for 24 hours at 30°C. The water retention was better than that of Control Example 3 but weaker than that of Example 2. This may be because the combined frequency of the dual-frequency ultrasound in the composite system of Example 3 is 20+40 kHz, and the cavitation effect generated by ultrasound is weaker than that of 20+80 kHz. As a result, the solvent in the mixed solution failed to firmly adhere to the surface of the choy sum, resulting in a less favorable preservation effect than that of Example 2.

[0109] The effects of the Chinese cabbage treated with the method of Control Example 3 in reducing water loss, maintaining firm stems, and reducing the degree of yellowing of the Chinese cabbage were worse than those of Examples 2 and 3. This may be because citric acid mainly inhibits bacterial growth, resists oxidation, and prevents browning in the preservation of fruits and vegetables, while the γ-aminobutyric acid and phytic acid composite preservative not only plays a role in inhibiting bacterial growth but also regulates the energy metabolism and active oxygen metabolism of fruits and vegetables, which can more effectively ensure the quality of fruits and vegetables during storage.

[0110] Effect Example 3 Comparison of the effects of phytic acid and γ-aminobutyric acid single system

[0111] The mass loss rate of control example 4 was higher than that of example 2 and control example 3 during storage. At 24 hours, the mass loss rate was as high as 21.37%, indicating that the Chinese cabbage without any treatment had a serious water loss when stored at 30℃ for 24 hours. Figure 5 ) It can be seen that the leaves of the Chinese cabbage treated with only phytic acid solution began to shrink and curl at 8 hours. At 24 hours, the leaves of the Chinese cabbage shrank and wilted severely, and the overall volume was reduced. However, the leaves of Example 2 remained fresh and plump after 24 hours of storage, and only some leaves of Control Example 3 shrank and wilted. After 24 hours of storage, the stems of the Chinese cabbage in Comparative Example 4 softened severely, and most of the stems collapsed and could not support the leaves upright, completely losing the commercial value and edible value of the Chinese cabbage itself.

[0112] The mass loss rate of Control Example 5 was higher than that of Example 2 and Control Example 3 during storage. At 24 hours, the mass loss rate was as high as 16.00%, indicating that the Chinese cabbage treated with γ-aminobutyric acid solution alone had a serious water loss when stored at 30°C for 24 hours. Figure 5 ) It can be seen that the leaves of the Chinese cabbage without any treatment began to shrink and curl at 8 hours. At 24 hours, the leaves of the Chinese cabbage shrank and wilted severely, and the overall volume was reduced. However, the leaves of Example 2 remained fresh and plump after 24 hours of storage. Only some leaves of Control Example 3 shrank and wilted. After 24 hours of storage, the stems of the Chinese cabbage softened and the leaves turned yellow severely. Most of the stems were soft and collapsed, unable to support the leaves to stand upright, and the commercial value and edible value of the Chinese cabbage itself were completely lost.

[0113] While the embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to the embodiments described above. Various modifications may be made within the scope of knowledge possessed by a person skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof may be combined with one another unless there is a conflict.

Claims

1. A method for preserving leafy vegetables at high temperature, comprising the following steps: 1) Sorting leafy vegetables; 2) treating the phytic acid and γ-aminobutyric acid mixed solution using multi-frequency ultrasound; 3) Spray the treated phytic acid and γ-aminobutyric acid mixed solution on the surface of leafy vegetables for storage.

2. The method according to claim 1, wherein: In the phytic acid and gamma-aminobutyric acid mixed solution, the concentration of phytic acid is 10-100 mg / L, and the concentration of gamma-aminobutyric acid is 5-20 mmol / L.

3. The method according to claim 2, wherein: The preparation method of the phytic acid and γ-aminobutyric acid mixed solution is as follows: The phytic acid solution is prepared by mixing 10-100 mg / L phytic acid solution and 5-20 mmol / L gamma-aminobutyric acid solution in a volume ratio of 1:(1-5).

4. The method according to claim 1, wherein: The multi-frequency ultrasound is dual-frequency ultrasound; The frequency 1 of the dual-frequency ultrasound is 20-60 KHz, and the frequency 2 is 40-100 KHz.

5. The method according to claim 4, characterized in that: The multi-frequency ultrasound is intermittent ultrasound; The ratio of the ultrasound time to the intermittent time of the intermittent ultrasound is (1-5) s / s.

6. The method according to claim 5, characterized in that: The total treatment time of the multi-frequency ultrasound is 1 to 10 minutes.

7. The method according to claim 6, characterized in that: The dosage of the phytic acid and gamma-aminobutyric acid mixed solution is 20 to 40 mL sprayed on every 250 g of vegetables.

8. The method according to claim 1, wherein: The leafy vegetables include spinach, lettuce, romaine lettuce, cabbage, water spinach, amaranth, coriander, lettuce leaves, kale, celery, broccoli, cauliflower, pea sprouts, and cauliflower.

9. The method according to claim 1, wherein: The storage temperature is 16-35°C.

10. The method according to claim 1, wherein: The leafy vegetables are mature, free of pests and diseases, and free of mechanical damage.

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