A quick-freezing and fresh-keeping process for broccoli

Abstract

The present application relates to the technical field of food preservation, and specifically discloses a quick-freezing preservation process for broccoli. A quick-freezing preservation process for broccoli comprises the following steps: S1 pre-cooling: after the broccoli is packaged with a plastic wrap material, water is sprayed on the plastic wrap material to pre-cool it, thereby obtaining the pre-cooled broccoli; S2 freezing: the pre-cooled broccoli is frozen at a constant temperature to obtain the frozen broccoli; S3 thawing: water is sprayed on the plastic wrap material, and then low-frequency ultrasonic thawing is performed to obtain the thawed broccoli; the plastic wrap material is a sponge soaked in a preservative mixture; the preservative mixture includes water, a gelling agent, a coagulant and a film-forming substance; the film-forming substance includes one or two of carboxymethyl chitosan and hydroxypropyl starch. The quick-freezing preservation process of the present application can not only effectively reduce the metabolic function of broccoli, but also replenish water to the broccoli, which can effectively extend the shelf life of the broccoli and improve the preservation effect of the broccoli.

Description

Technical Field

[0001] The present application relates to the technical field of food preservation, and more specifically, to a quick-freezing and preservation process for broccoli. Background Art

[0002] Vegetables are plants or fungi that can be cooked and made into food. They provide essential nutrients such as vitamins and minerals, making them an essential part of our daily diet. Broccoli, in particular, is rich in protein, carbohydrates, fat, minerals, vitamin C, and carotene. Consuming it not only promotes growth and development but also has cancer-preventing properties, making it a popular vegetable.

[0003] However, after harvesting, broccoli will easily rot and spoil if it is not preserved due to physiological aging, pathogens, and mechanical damage. Although low-temperature refrigeration can inhibit the metabolic function of broccoli and delay its aging, broccoli is still prone to aging after a period of low-temperature refrigeration because it is still metabolizing. Summary of the Invention

[0004] In order to improve the preservation effect of broccoli, the present application provides a quick-freezing preservation process for broccoli.

[0005] A quick-freezing and fresh-keeping process for broccoli comprises the following steps:

[0006] S1 pre-cooling: After the broccoli is packaged with a plastic wrap material, the plastic wrap material is sprayed with water for pre-cooling to obtain the pre-cooled broccoli;

[0007] S2 freezing: freezing the pre-cooled broccoli at a constant temperature to obtain frozen broccoli;

[0008] S3 thawing: spraying water on the plastic wrap material, and then performing low-frequency ultrasonic thawing to obtain thawed broccoli;

[0009] The preservative film material is a sponge soaked in a preservative mixture;

[0010] The preservative mixture comprises water, a gelling agent, a coagulant and a film-forming substance;

[0011] The film-forming substance comprises one or both of carboxymethyl chitosan and hydroxypropyl starch.

[0012] By adopting the above technical solution, the film layer formed by the film-forming material when dissolved in water has certain water absorption and water retention properties. Therefore, after soaking the sponge in the preservative mixture, the resulting plastic wrap material has certain water absorption and water retention properties. On the one hand, during the pre-cooling process S1, the water contained in the plastic wrap material quickly evaporates, absorbing heat from the surrounding environment of the broccoli, thereby rapidly lowering the temperature of the surrounding environment. This helps shorten the pre-cooling time, reduce water loss in the broccoli, and improve the freshness of the broccoli. On the other hand, when the frozen broccoli is thawed by low-frequency ultrasonic wave, the vibrations generated will increase the temperature of the broccoli, thereby achieving thawing. At this time, the water-sprayed plastic wrap material contains a certain amount of water, which not only prevents overheating and localized heating of the broccoli, but also provides a certain amount of moisture, which helps reduce water loss and improves the physical properties of the broccoli after thawing, thereby maintaining the freshness of the broccoli. Furthermore, because the freezing temperature is lower than the refrigeration temperature, it effectively reduces the metabolic function of the broccoli, extending its shelf life. Since plastic frames are generally used to hold broccoli in the pre-cooling process of large-scale broccoli, the present invention can wrap the plastic wrap material on the surface of the plastic frame and cover the top of the plastic frame to minimize the contact between the plastic wrap material and the broccoli before pre-cooling.

[0013] Preferably, the preservative mixture comprises the following components in parts by weight:

[0014] 50-70 parts water;

[0015] 1-3 parts of gel;

[0016] 0.4-0.8 parts of coagulant aid;

[0017] 50-75 parts of film-forming substance.

[0018] By adopting the above technical solution, the film-forming substance, the gelling agent and the coagulant aid are added to water according to the above weight proportions, so as to form a paste-like preservative mixture with good fluidity, which is convenient for penetrating and filling in the sponge to form a film layer, thereby improving the water retention of the obtained preservative film material, thereby facilitating the reduction of water loss of broccoli during the pre-cooling and thawing process, and improving the preservation effect of broccoli.

[0019] Preferably, the film-forming substance is composed of a mixture of carboxymethyl chitosan and hydroxypropyl starch, and the weight ratio of carboxymethyl chitosan to hydroxypropyl starch is 1:(0.82-1.25).

[0020] By adopting the above technical solution, carboxymethyl chitosan has excellent film-forming and antibacterial properties. Carboxymethyl chitosan and hydroxypropyl starch are dissolved in water as film-forming substances. The resulting plastic wrap material not only hydrates broccoli but also has a certain antibacterial effect on broccoli, which helps to extend the shelf life of broccoli.

[0021] Preferably, the preservative mixture further comprises bamboo fiber.

[0022] By adopting the above technical solution, bamboo fiber has excellent antibacterial and water absorption properties. By dispersing the bamboo fiber in an aqueous solution of a film-forming substance and then soaking a sponge, the resulting plastic wrap material can improve its water absorption and antibacterial properties. This not only helps shorten the pre-cooling time of broccoli, but also prevents overheating and localized heating of the broccoli, allowing the broccoli to be thawed evenly, reducing water loss and rotting, thereby improving the preservation effect of the broccoli.

[0023] Preferably, the particle size of the bamboo fiber is 150-200 mesh.

[0024] By adopting the above technical solution, 150-200 mesh bamboo fiber has good dispersibility in a mixture of film-forming substances, gelling agents, water and other raw materials. Therefore, after soaking the sponge in a preservative mixture containing bamboo fiber, the water retention of the obtained preservative film material can be improved, which is beneficial to reducing the water loss of broccoli.

[0025] Preferably, the gelling agent is one or more of xanthan gum, carrageenan and gellan gum.

[0026] By adopting the above technical solution, the above-mentioned types of gelling agents are mixed with film-forming substances, coagulant aids and water to form a gel, which is beneficial to improving the film-forming property of the preservative solution and further improving the water retention capacity of the final preservative film material.

[0027] Preferably, the preparation method of the cling film material is: add a gelling agent, a coagulant, bamboo fiber, and a film-forming substance into water at 68 to 78° C., stir and mix for 1 to 2 hours, add a sponge, and let it stand at 20 to 25° C. for 3 to 5 hours to obtain the cling film material.

[0028] By adopting the above technical solution, raw materials such as gelling agent and coagulant are added into water at 68-78°C and stirred and mixed. The obtained preservative mixture has good fluidity, is conducive to penetrating and adhering to the sponge, and improves the water retention capacity of the obtained preservative film material, thereby improving the water replenishing effect of the preservative film material on broccoli and improving the preservative effect on broccoli.

[0029] Preferably, in the S1 pre-cooling, the pre-cooling temperature is -2 to 0°C, the pressure is 0.5 to 0.9 kPa, and the time is 20 to 40 minutes.

[0030] By adopting the above technical solution, the broccoli packaged with plastic wrap material is pre-cooled in the above pressure and temperature environment. Since the water loss of the plastic wrap material can quickly reduce the temperature around the broccoli, the pre-cooling time is shortened to 20 to 40 minutes, which effectively reduces the water loss of the broccoli and is conducive to improving the preservation effect of the broccoli.

[0031] Preferably, in the thawing step S3, after water is sprayed onto the cling film material, the thawing frequency is 20 to 40 kHz and the power is 300 to 450 W.

[0032] By adopting the above technical solution, the frozen broccoli is thawed by low-frequency ultrasonic treatment under the above frequency and power conditions, so that the broccoli can be evenly heated and the ice crystals in the broccoli are quickly melted, which is conducive to shortening the thawing time of the broccoli and allowing the broccoli after thawing to maintain good color and hardness.

[0033] In summary, this application has the following beneficial effects:

[0034] 1. Since the sponge impregnated with the preservative mixture used in this application has good water retention and water absorption, it can not only shorten the pre-cooling time, but also replenish water for the broccoli, thereby reducing the water loss of the broccoli and improving the preservation effect of the broccoli;

[0035] 2. The bamboo fiber in the preservative mixture of the present application has good water absorption and antibacterial properties, which can improve the hydration and antibacterial effects of the obtained preservative film material on broccoli, thereby extending the shelf life of broccoli;

[0036] 3. The present application shortens the pre-cooling process time by controlling the temperature and pressure of the pre-cooling process, which is beneficial to reducing the loss of water in the broccoli and improving the preservation effect of the broccoli. DETAILED DESCRIPTION

[0037] The present application is further described in detail below with reference to the embodiments.

[0038] Performance testing

[0039] Weight loss rate test: First, weigh three broccoli florets freshly picked on a sunny morning and record the weight of the broccoli florets before pre-cooling. Then, treat the broccoli florets using the quick-freezing preservation process of the embodiment of the present application or the preservation process of the comparative example, and weigh the broccoli florets after thawing. Finally, calculate the weight loss rate using the following formula: Weight loss rate = (weight of broccoli florets before pre-cooling - weight of broccoli florets after thawing) / weight of broccoli florets before pre-cooling. The final recorded weight loss rate result is the average weight loss rate of the three broccoli florets.

[0040] Sensory evaluation test: One head of broccoli freshly picked on a sunny morning was treated with the quick-freezing preservation process of the embodiment of the present application or the preservation process of the comparative example. Five trained sensory evaluators were selected to visually inspect the color and texture of the broccoli and then score it according to the scoring criteria in the table below (the score can be quantified according to the actual situation, for example, 5.5 points). The final score was averaged.

[0041]

[0042] Preparation Example

[0043] Preparation Example 1

[0044] A fresh-keeping film material is a sponge soaked in a preservative mixture.

[0045] The preservative mixture, its components and their corresponding weights (kg) are shown in the following table.

[0046]

[0047] In the preparation example of this application, the gelling agent is gellan gum; the coagulant aid is potassium chloride;

[0048] The film-forming material is composed of a mixture of carboxymethyl chitosan and hydroxypropyl starch, with a weight ratio of carboxymethyl chitosan to hydroxypropyl starch of 1:1.05. Carboxymethyl chitosan, item number 255, and hydroxypropyl starch, item number 563, were purchased from Shandong Fengtai Biotechnology Co., Ltd.

[0049] Bamboo fiber, with a particle size of 150 mesh, was purchased from Lingshou County Lixin Mineral Products Co., Ltd.

[0050] The preparation method of the above-mentioned cling film material is as follows: adding a gelling agent, a coagulant aid, bamboo fiber, and a film-forming substance into 68°C water, stirring and mixing for 2 hours, adding a sponge, and standing at 20-25°C for 3 hours to obtain the cling film material.

[0051] Preparation Examples 2-3

[0052] A cling film material, which is different from Preparation Example 1 in that the components and their corresponding weights (kg) are shown in the following table.

[0053]

[0054] Preparation Example 4

[0055] A fresh-keeping film material is different from Preparation Example 1 in that the film-forming substance is composed of a mixture of carboxymethyl chitosan and hydroxypropyl starch, and the weight ratio of carboxymethyl chitosan to hydroxypropyl starch is 1:0.82.

[0056] Preparation Example 5

[0057] A fresh-keeping film material is different from Preparation Example 1 in that the film-forming substance is composed of a mixture of carboxymethyl chitosan and hydroxypropyl starch, and the weight ratio of carboxymethyl chitosan to hydroxypropyl starch is 1:1.25.

[0058] Preparation Example 6

[0059] A fresh-keeping film material, which is different from Preparation Example 1 in that the film-forming substance is hydroxypropyl starch.

[0060] Preparation Example 7

[0061] A fresh-keeping film material, which is different from Preparation Example 1 in that the bamboo fiber has a particle size of 200 meshes.

[0062] Preparation Example 8

[0063] A plastic wrap material, which is different from Preparation Example 1 in that bamboo fiber has a particle size of 80 mesh and is purchased from Lingshou County Lixin Mineral Products Co., Ltd.

[0064] Preparation Example 9

[0065] A plastic wrap material, which is different from Preparation Example 1 in that bamboo fiber has a particle size of 400 mesh and is purchased from Lingshou County Lixin Mineral Products Co., Ltd.

[0066] Preparation Example 10

[0067] A cling film material is different from Preparation Example 1 in that the preparation method of the cling film material is: adding a gelling agent, a coagulant aid, bamboo fiber, and a film-forming substance into water at 78°C, stirring and mixing for 1 hour, adding a sponge, and standing at 20-25°C for 5 hours to obtain the cling film material.

[0068] Preparation Example 11

[0069] A fresh-keeping film material, which differs from Preparation Example 1 in that it does not contain a preservative mixed liquid.

[0070] Preparation Example 12

[0071] A fresh-keeping film material is different from Preparation Example 1 in that an aqueous solution of a vegetable preservative (mainly composed of sodium benzoate) of equal weight model number KLY3360 is used instead of the preservative mixture.

[0072] Preparation Example 13

[0073] A fresh-keeping film material, which is different from Preparation Example 1 in that the film-forming aid is hydroxypropyl starch.

[0074] Example

[0075] Example 1

[0076] A quick-freezing and fresh-keeping process for broccoli comprises the following steps:

[0077] S1 precooling: After the broccoli is packaged with a plastic wrap material, the water content of the plastic wrap material is adjusted to 60% by spraying water, and then precooled for 30 minutes at a temperature of -2 to 0°C and a pressure of 0.7 kPa to obtain precooled broccoli;

[0078] S2 freezing: freezing the pre-cooled broccoli at a constant temperature of -18°C for 15 days to obtain frozen broccoli;

[0079] S3 thawing: The water content of the plastic wrap material is adjusted to 40% by spraying water, and then low-frequency ultrasonic thawing is performed at a frequency of 30 kHz and a power of 350 W to a temperature of 0-1° C. to obtain thawed broccoli;

[0080] The cling film material adopts the cling film material prepared in Preparation Example 1.

[0081] Examples 2 to 10

[0082] A quick-freezing and fresh-keeping process for broccoli is different from that of Example 1 in that the fresh-keeping film material adopts the fresh-keeping film material prepared by the preparation example in the following table.

[0083]

[0084]

[0085] The broccoli obtained in Examples 1 to 10 of the present application were tested for weight loss rate and sensory evaluation. The test results are shown in the following table.

[0086]

[0087] By analyzing the data in the table above, it can be seen that the quick-freezing and fresh-keeping processes of Examples 1 to 10 of the present application were used to quickly freeze and preserve broccoli, and the weight loss rate of the broccoli was as low as 0.9 to 2.9%, and the sensory evaluation score was as high as 4.8 to 5.9 points. This shows that the quick-freezing and fresh-keeping processes of Examples 1 to 10 of the present application have a good fresh-keeping effect on broccoli.

[0088] Further analysis of the table above shows that, compared to Examples 1 and 2, the weight loss rate of broccoli after preservation using the quick-freezing preservation process of Example 3 significantly increased, and the sensory score significantly decreased. This indicates that in the quick-freezing preservation process of broccoli in this application, the preservative mixture also includes bamboo fiber, which is beneficial for reducing water loss in broccoli after quick-freezing preservation and improving the preservation effect of broccoli. Analysis suggests that the reason for this may be that bamboo fiber improves the water absorption and antibacterial properties of the preservative film material, effectively shortening the pre-cooling time of broccoli, reducing water loss in broccoli, and also having an antibacterial effect on broccoli, reducing broccoli rot and deterioration, thereby improving the preservation effect of broccoli.

[0089] Compared to Examples 1, 4, and 5, after the green cauliflower is preserved by the quick-freezing and fresh-keeping process of Example 6, the weight loss rate is significantly increased, and the sensory score is significantly reduced. This shows that in the quick-freezing and fresh-keeping process of the present application's green cauliflower, the film-forming material is composed of a mixture of carboxymethyl chitosan and hydroxypropyl starch, and the weight ratio of carboxymethyl chitosan and hydroxypropyl starch is 1: (0.82-1.25), which can improve the fresh-keeping effect of the green cauliflower. Analysis of the reason may be that carboxymethyl chitosan has good film-forming and antibacterial properties, and hydroxypropyl starch has good freeze-thaw resistance. The two work synergistically, thereby improving the stability of the preservative film material in a low-temperature environment, and are conducive to hydrating and sterilizing the green cauliflower, thereby extending the shelf life of the green cauliflower.

[0090] Compared with Examples 1 and 7, the weight loss rate of broccoli increased and the sensory score decreased after being preserved using the quick-freezing preservation process of Examples 8 and 9. This shows that in the quick-freezing preservation process of broccoli of the present application, when the particle size of bamboo fiber is 150-200 mesh, the resulting broccoli has good freshness. Analysis shows that the reason may be that 150-200 mesh bamboo fiber has good dispersibility in a mixture of other raw materials such as film-forming substances, gelling agents and water. Therefore, after soaking the sponge in a preservative mixture containing bamboo fiber, the water retention of the resulting preservative film material can be improved, which is beneficial to reduce the water loss of broccoli, thereby improving the hydration effect of broccoli.

[0091] After the broccoli was preserved using the quick-freezing preservation process of Examples 1 and 10, the weight loss rate of the broccoli was as low as 0.9-1.4%, and the sensory evaluation score was as high as 5.7-5.9 points. This shows that in the quick-freezing preservation process of the present application, the preparation method of the preservative film material is as follows: adding a gelling agent, a coagulant, bamboo fiber, and a film-forming substance to water at 68-78°C, stirring and mixing for 1-2 hours, adding a sponge, and standing at 20-25°C for 3-5 hours to obtain the preservative film material; the resulting broccoli has good freshness.

[0092] Example 11

[0093] A quick-freezing and fresh-keeping process for broccoli is different from that of Example 1 in that, in S1 pre-cooling, the pre-cooling temperature is -2 to 0°C, the pressure is 0.5 kPa, and the time is 40 minutes.

[0094] Example 12

[0095] A quick-freezing and fresh-keeping process for broccoli is different from that of Example 1 in that, in S1 pre-cooling, the pre-cooling temperature is -2 to 0°C, the pressure is 0.9 kPa, and the time is 20 minutes.

[0096] The broccoli obtained in Examples 11 to 12 of the present application were tested for weight loss rate and sensory evaluation. The test results are shown in the following table.

[0097]

[0098] By analyzing the data in the above table, it can be seen that the quick-freezing and fresh-keeping process of Examples 1, 11, and 12 of the present application is used to quickly freeze and preserve broccoli, and the weight loss rate of broccoli is as low as 0.9-3.4%, and the sensory evaluation score is as high as 4.5-5.9 points. This shows that in the quick-freezing and fresh-keeping process of broccoli of the present application, when the pre-cooling temperature in S1 is -2-0°C, the pressure is 0.5-0.9kPa, and the time is 20-40min, the broccoli has a good water replenishing effect. The reason for this may be that the broccoli is pre-cooled in the above-mentioned pressure and temperature environment, which effectively reduces the water loss of the broccoli, thereby improving the freshness of the broccoli, so that the broccoli has a smaller weight loss rate after thawing, and has a good sensory effect.

[0099] At the same time, compared with Example 1, the weight loss rate and sensory evaluation score of the broccoli were significantly changed when the broccoli was quickly frozen and preserved using the quick-freezing preservation process of Examples 11 and 12 of the present application. The reason for this may be that the broccoli loses water during the pre-cooling process. Although the plastic wrap material has a certain hydrating effect on the broccoli, the pressure and time of the pre-cooling process affect the moisture content of the broccoli and the pre-cooling effect, thereby having a significant impact on the preservation effect of the broccoli.

[0100] Example 13

[0101] A quick-freezing and fresh-keeping process for broccoli is different from that of Example 1 in that, in S3 thawing, after water is sprayed onto the fresh-keeping film material, the thawing frequency is 20 kHz and the power is 50 W.

[0102] Example 14

[0103] A quick-freezing and fresh-keeping process for broccoli is different from that of Example 1 in that, in S3 thawing, after water is sprayed onto the fresh-keeping film material, the thawing frequency is 40 kHz and the power is 300 W.

[0104] The broccoli obtained in Examples 13 to 14 of the present application were tested for weight loss rate and sensory evaluation. The test results are shown in the following table.

[0105]

[0106] By analyzing the data in the table above, it can be seen that the broccoli was quickly frozen and preserved using the quick-freezing preservation processes 1, 13, and 14 of the embodiments of the present application. The weight loss rate of the broccoli was as low as 0.9-3.5%, and the sensory evaluation score was as high as 4.4-5.9 points. This shows that in the quick-freezing preservation process of broccoli of the present application, when water is sprayed on the plastic wrap material during thawing in S3, the thawing frequency is 20-40kHz and the power is 300-450W, which has a better preservation effect on the broccoli. Analysis of this may be that the broccoli is thawed by low-frequency ultrasonic waves under the above frequency and power conditions, which allows the broccoli to be heated evenly and shortens the thawing time of the broccoli, thereby improving the preservation effect of the broccoli.

[0107] At the same time, compared to Example 1, the broccoli weight loss rate and sensory evaluation score varied significantly when the broccoli was quick-frozen and preserved using the quick-freezing and preservation processes of Examples 13 and 14 of the present application. This may be due to the fact that the broccoli is heated during the thawing process. Although the plastic wrap material has a certain hydrating effect on the broccoli, the frequency and power of the thawing process affect the uniformity of the heating of the broccoli, thereby affecting the weight loss rate and sensory evaluation of the broccoli after thawing.

[0108] Example 15

[0109] A quick-freezing and fresh-keeping process for broccoli is different from that of Example 1 in that, during the thawing step S3, a spray water replenishing method is used to adjust the water content in the fresh-keeping film material to 60%.

[0110] The broccoli obtained in Example 15 of the present application was tested for weight loss rate and sensory evaluation, and the test results are shown in the following table.

[0111]

[0112] By analyzing the data in the above table, it can be seen that compared with Example 1, the quick-freezing and preservation process of Example 15 of the present application for quick-freezing and preservation of broccoli increased the weight loss rate of broccoli and decreased the sensory evaluation score. Analysis shows that this may be due to the high water content in the plastic wrap material during S3 thawing, which may weaken the effect of low-frequency ultrasonic thawing, resulting in a slower heating rate of the broccoli, thereby weakening the preservation effect of the broccoli.

[0113] Comparative Example

[0114] Comparative Example 1

[0115] A broccoli preservation process is different from Example 1 in that the preservative film material adopts the preservative film material prepared by the preparation example in the following table.

[0116] Comparative Example Preparation example using plastic wrap material Comparative Example 1 Preparation Example 11 Comparative Example 2 Preparation Example 12 Comparative Example 3 Preparation Example 13

[0117] The broccoli obtained in Comparative Examples 1 to 3 of the present application were tested for weight loss rate and sensory evaluation, and the test results are shown in the following table.

[0118]

[0119] By analyzing the data in the above table, it can be seen that compared with Example 1, the weight loss rate of broccoli for quick freezing and preservation using the preservation processes of Comparative Examples 1 and 2 is as high as 4.6-5.3%, and the sensory evaluation score is as low as 2.8-3.2%. This shows that in the preservation process of broccoli of the present application, the broccoli is packaged with a sponge soaked in a preservative mixture, and then pre-cooled, frozen, and thawed, which not only reduces the metabolic function of the broccoli and prolongs the shelf life of the broccoli, but also helps to replenish the water of the broccoli and improve the freshness of the broccoli.

[0120] Compared with Example 1, the preservation process of Comparative Example 3 was used to quickly freeze and preserve broccoli. The weight loss rate of broccoli was significantly increased, and the sensory evaluation score was significantly reduced. This shows that in the preservation process of broccoli of the present application, the film-forming material includes one or more of carboxymethyl chitosan and hydroxypropyl starch, which can improve the preservation effect of broccoli. Analysis of the reason may be that carboxymethyl chitosan has a bactericidal effect and hydroxypropyl starch has a good freeze-thaw resistance. Therefore, carboxymethyl chitosan and / or hydroxypropyl starch are used as film-forming materials, which have a good antibacterial effect and / or freeze-thaw resistance effect on broccoli, thereby improving the preservation effect of broccoli.

[0121] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A quick-freezing and fresh-keeping process for broccoli, characterized in that: The following steps are involved: S1 pre-cooling: After the broccoli is packaged with a plastic wrap material, the plastic wrap material is sprayed with water for pre-cooling to obtain the pre-cooled broccoli; S2 freezing: freezing the pre-cooled broccoli at a constant temperature to obtain frozen broccoli; S3 thawing: spraying water on the plastic wrap material, and then performing low-frequency ultrasonic thawing to obtain thawed broccoli; The preservative film material is a sponge soaked in a preservative mixture; The preservative mixture comprises water, a gelling agent, a coagulant and a film-forming substance; The film-forming substance is one or both of carboxymethyl chitosan and hydroxypropyl starch; The preservative mixture includes the following components in parts by weight: 50-70 parts water; 1-3 parts of gel; 0.4-0.8 parts of coagulant aid; 50-75 parts of film-forming substance; The gelling agent is one or more of xanthan gum, carrageenan and gellan gum; In the S1 precooling, the precooling temperature is -2 to 0°C, the pressure is 0.5 to 0.9 kPa, and the time is 20 to 40 minutes.

2. The quick-freezing and fresh-keeping process of broccoli according to claim 1, characterized in that: The film-forming substance is composed of a mixture of carboxymethyl chitosan and hydroxypropyl starch, and the weight ratio of the carboxymethyl chitosan to the hydroxypropyl starch is 1:(0.82-1.25).

3. The quick-freezing and fresh-keeping process of broccoli according to claim 1, characterized in that: The preservative mixture also includes bamboo fiber.

4. The quick-freezing and fresh-keeping process of broccoli according to claim 3, characterized in that: The particle size of the bamboo fiber is 150-200 meshes.

5. The quick-freezing and fresh-keeping process of broccoli according to claim 4, characterized in that: The preparation method of the fresh-keeping film material comprises the following steps: adding a gelling agent, a coagulant aid, bamboo fiber and a film-forming substance into water at 68-78° C., stirring and mixing for 1-2 hours, adding a sponge and standing at 20-25° C. for 3-5 hours to obtain the fresh-keeping film material.

6. The quick-freezing and fresh-keeping process of broccoli according to claim 1, characterized in that: In the thawing step S3, after water is sprayed onto the plastic wrap material, the thawing frequency is 20-40 kHz and the power is 300-450 W.

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