Fresh-keeping method suitable for stem brassica vegetables

Abstract

The invention belongs to the technical field of vegetable preservation, and particularly relates to a preservation method suitable for stem brassica vegetables. The stem brassica vegetables are pretreated, the composite preservative is sprayed to leaves and brassica stems, and a W / O / W emulsion formed by the composite preservative can form a transparent and flexible thin film, has good barrier property and moisture retention, can slow down the loss of moisture on the surfaces of the leaves and the surfaces of the brassica stems, remarkably reduces the respiration rate of the vegetables, and improves the quality of the brassica vegetables. The used green bacteriostatic preservative is active substances including rosemary extract, melissa extract, clausena lansium peel extract and loquat leaf extract and can effectively inhibit bacteria, beewax with a certain concentration forms a film at a cut, and nutrient substance loss and water loss are reduced; according to the invention, through the combination of spraying and soaking of different preservatives, the fresh-keeping agent has the fresh-keeping effects of moisture retention, respiration rate reduction, bacteriostasis, anti-oxidation protection and energy supply.

Description

Technical Field

[0001] The present invention belongs to the technical field of vegetable preservation, and particularly relates to a preservation method applicable to stem-type Brassica vegetables. Background Art

[0002] Stem-type Brassica vegetables mainly take the flower stalk as the edible part. Typical examples are flowering Chinese cabbage (Brassica rapa sp. parachinesis), Chinese kale (Brassica oleracea var. alboglabra), purple-stemmed flowering Chinese cabbage (Brassica rapa var. purpuraria), and rape stalk (Brassica napus var. oleifera DC.), which are all typical vegetables that can be eaten with stems, leaves, and flowers. They are rich in nutrients such as organic acids, flavonoids, and minerals, and have a fresh and fragrant taste, being deeply loved by consumers. Hongshan flowering Chinese cabbage and Jiuhua red flowering Chinese cabbage are geographical indication products with distinct characteristics. Flowering Chinese cabbage and Chinese kale are among the vegetables with the largest cultivation scale in South China, and the cultivation area of flowering Chinese cabbage reaches 10 million mu. It is a typical vegetable supplied to Hong Kong. Such vegetables are becoming a unique product group and a new growth point in China's vegetable industry.

[0003] There are mainly four problems with stem-type Brassica vegetables after harvest during shelf life and storage: (1) large leaf surface area, high water content, and the leaves quickly turn yellow and wilt; (2) bolting and flowering, flower dropping, and the stalk bending; (3) the cut part of the stem is prone to lignification and quickly extends upwards, causing the stem to age, increase in hardness, and become hollow in the center; (4) the cut is easily infected by microorganisms and rots. Currently, researchers have conducted extensive and in-depth studies on the regulation mechanisms of the senescence and quality deterioration of post-harvest flowering Chinese cabbage leaf tissues from multiple aspects such as chlorophyll degradation, hormone signal regulation, and transcriptional modification regulation. Plant hormones such as methyl jasmonate (MeJA), CPPU, 1-MCP, gibberellin (GA), melatonin (MT), etc., vacuum precooling, modified atmosphere packaging, and low-temperature storage can delay leaf yellowing and lignification. However, there is less attention paid to the research on the hollowness and cut rot of this type of Brassica stalk vegetables during storage and their preservation methods. The hollowness of the stalk is caused by the continuous consumption and loss of stored nutrients after detaching from the plant. The crispness and tenderness of the stalk are severely reduced, and at the same time, it accelerates leaf senescence and flower dropping, resulting in faster quality deterioration. When harvesting, the cut surface has damaged cells, and rot occurs, losing its commercial value. Therefore, developing preservatives and preservation methods for stem-type Brassica vegetables to slow down the hollowness of the stalk and inhibit cut rot is of great significance for the storage and preservation of stalk vegetables. Summary of the Invention

[0004] Aiming at the above problems, the purpose of the present invention is to provide a preservation method applicable to stem-type Brassica vegetables.

[0005] The technical content of the present invention is as follows:

[0006] The present invention provides a fresh-keeping method applicable to stem Brassica vegetables, comprising the following steps:

[0007] 1) Vegetable pretreatment: Pick fresh vegetables, remove plants with diseases, pests and mechanical damage, and then perform precooling until the temperature of the stem is ≤10°C;

[0008] 2) Fresh-keeping treatment: Spray a composite fresh-keeping agent on the stem and leaf parts, and soak the cut with an antibacterial fresh-keeping agent;

[0009] The composite fresh-keeping agent consists of: ascorbic acid, adenosine triphosphate (ATP), chondroitin sulfate, pullulan polysaccharide, trehalose, guar gum and water. By mass fraction of concentration, the concentrations of each component are 0.1% - 0.5% ascorbic acid, 0.2% - 0.5% adenosine triphosphate (ATP), 0.4% - 0.6% chondroitin sulfate, 1% - 1.5% pullulan polysaccharide, 0.5% - 1% trehalose, 0.5% - 1% guar gum;

[0010] The preparation of the composite fresh-keeping agent comprises the following steps:

[0011] 1) Preparation of W / O emulsion: Mix adenosine triphosphate (ATP) and water as the internal aqueous phase, emulsify edible corn oil and an emulsifier to form an oil phase, slowly inject the internal aqueous phase into the oil phase, and stir and homogenize under ice bath conditions to form a W / O emulsion;

[0012] The rotation speed of the stirring and homogenizing is 3000 - 5000 rpm, and the time is 2 - 3 min;

[0013] 2) Preparation of W / O / W emulsion: Disperse pullulan polysaccharide and guar gum in hot water at 80°C, stir magnetically for 1 h until completely dissolved, then add chondroitin sulfate and trehalose, stir and dissolve at 40°C, finally cool to room temperature, add ascorbic acid, stir in the dark, filter to form the external aqueous phase, and slowly drop the W / O emulsion into the external aqueous phase, stir and homogenize to form a W / O / W emulsion;

[0014] The rotation speed of the stirring and homogenizing is 3000 - 5000 rpm, and the time is 2 - 3 min;

[0015] The prepared composite preservative is a double emulsion, namely W / O / W emulsion. By separating ATP and ascorbic acid through the W / O / W structure, it can effectively avoid the degradation of ATP caused by acid-base imbalance, as well as the moisture absorption and moisturizing of chondroitin sulfate. Trehalose fixes water through vitrification transition. After compounding, it can prevent condensation in high-humidity environments and reduce water loss in low-humidity environments. In addition, the flexibility of pullulan polysaccharide and the adhesiveness of guar gum are combined to form a dense composite film with adjustable air permeability. And for the formed W / O / W emulsion, the outer aqueous phase first contacts the stem and leaf parts of the stem, and the middle oil phase can prevent the oxidation of the outer aqueous phase components, and ATP provides energy to jointly delay cell death, extend the preservation time, and improve the stability of the preservative.

[0016] The composition of the antibacterial preservative includes: rosemary extract with a concentration of 1% - 1.5% by mass percentage, lemon balm extract with a concentration of 1% - 1.5%, wampee peel extract with a concentration of 1% - 2%, loquat leaf extract with a concentration of 1% - 2%, 1% - 3% beeswax and water;

[0017] The preparation methods of the rosemary extract, lemon balm extract, wampee peel extract, and loquat leaf extract include: respectively collecting fresh rosemary, lemon balm, wampee peel, and loquat leaves, quickly freezing them in liquid nitrogen, and quickly grinding them into powders. Then add 70 - 95% (volume ratio) ethanol-aqueous solution for extraction, and perform ultrasonic extraction at 50 - 70 °C and a power of 400 - 650 W for 1 - 3 h, repeating 2 - 3 times;

[0018] The mass-to-volume ratios of rosemary, lemon balm, wampee peel, and loquat leaves to the ethanol solution are each 1:(20 - 60).

[0019] The preparation method of the rosemary extract is more preferably as follows: After crushing the fresh rosemary plants under liquid nitrogen grinding, add 70% ethanol-aqueous solution according to a solid-liquid ratio of 1:30, perform ultrasonic extraction at 55 °C and a power of 400 W for 2 h, repeat 3 times, collect the extract, centrifuge and filter, and concentrate the collected filtrate by rotary evaporation of the extract to obtain the rosemary extract.

[0020] The preparation method of the lemon balm extract is more preferably as follows: Add 75% ethanol by volume according to a solid-liquid ratio of 1:40, perform ultrasonic extraction at 60 °C and a power of 450 W for 3 h, repeat 3 times, collect the extract, centrifuge and filter, and concentrate the collected filtrate by rotary evaporation of the extract to obtain the lemon balm extract.

[0021] The preparation method of the wampee peel extract is more preferably as follows: Add 90% ethanol by volume according to a solid-liquid ratio of 1:60, perform ultrasonic extraction at 65 °C and a power of 650 W for 3 h, repeat 3 times, collect the extract, centrifuge and filter, and concentrate the collected filtrate by rotary evaporation of the extract to obtain the wampee peel extract.

[0022] The preparation method of the loquat leaf extract more preferably includes: adding ethanol with a volume fraction of 85% according to a solid-liquid ratio of 1:50, performing ultrasonic extraction at 70°C and a power of 600W for 2.5h, repeating 3 times, collecting the extract, centrifuging and filtering, and rotary evaporating the collected filtrate to concentrate the extract to obtain the loquat leaf extract.

[0023] The spraying amount of the composite preservative is to spray until all the leaves and stems are wrapped and a small amount of water drips.

[0024] The soaking time of the green antibacterial preservative is 5 - 10 min, and the soaking part is 2 - 5 cm at the cut.

[0025] After spraying the composite preservative and soaking the green antibacterial preservative, dry the surface moisture at room temperature of 15°C.

[0026] 3) Packaging treatment: Use a modified atmosphere packaging bag for packaging.

[0027] 4) Storage: Store at a low temperature of 2 - 5°C or at a shelf life of 12 - 15°C.

[0028] The beneficial effects of the present invention are as follows:

[0029] The preservation method of the present invention applicable to stem-type Brassica vegetables, through pretreatment of stem-type Brassica vegetables, spraying a composite preservative on the leaves and stems, the formed W / O / W emulsion can form a transparent and flexible film, which has good barrier properties and moisture retention properties, can slow down the loss of water on the leaf surface and the stem epidermis, significantly reduce the respiration rate of vegetables, and at the same time the polysaccharide substances also have significant antibacterial properties, can form a protective layer on the surface of fruits and vegetables, reduce the invasion of exogenous microorganisms, ascorbic acid can scavenge free radicals, protect nutrients such as fat and protein in fruits and vegetables from oxidative damage, adenosine triphosphate can provide the energy required by fruit and vegetable cells, and improve various physiological functions such as antioxidant and anti-aging of fruits and vegetables. Water loss, microbial invasion, and nutrient loss occur at the cut at the base of stem-type Brassica vegetables. The green antibacterial preservative used is rosemary extract, lemon balm extract, wampee peel extract, and active substances of loquat leaf extract, which can effectively inhibit bacteria, and a certain concentration of beeswax forms a film at the cut to reduce nutrient loss and water loss; the present invention combines spraying and soaking different preservatives, and has the preservation effects of water retention: reducing the respiration rate, antibacterial effect, antioxidant protection, and energy supply. It has the advantages of high-efficiency preservation: significantly extending the preservation period of vegetables, reducing stem hollowness and cut rot, green environmental protection: using natural polysaccharides and plant extracts, safe and non-toxic, multi-functionality: solving problems such as water loss, microbial invasion, and oxidative damage at the same time, and simple operation: combining spraying and soaking, easy to scale up for application. Description of the Drawings

[0030] Figure 1 This is a schematic diagram of the preservation process of the present invention for stem-type Brassica vegetables;

[0031] Figure 2 It shows the influence of different treatment methods on the phenotypic changes of flowering Chinese cabbage stored at 4°C for 30 days;

[0032] Figure 3 It shows the influence of different treatment methods on the quality changes of flowering Chinese cabbage stored at 4°C for 30 days;

[0033] Figure 4 It shows the influence of different treatment methods on the phenotypic changes of Chinese kale stored at 15°C for 12 days;

[0034] Figure 5 It shows the influence of different treatment methods on the nutritional quality changes of Chinese kale stored at 15°C for 12 days;

[0035] Figure 6 It shows the influence of different treatment methods on the phenotypic changes of flowering Chinese cabbage stored at 20°C for 4 days;

[0036] Figure 7 It shows the influence of different treatment methods on the nutritional quality changes of flowering Chinese cabbage stored at 20°C for 4 days. Specific embodiments

[0037] The present invention will be further described in detail below through specific implementation cases and accompanying drawings. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the protection scope of the present invention. After reading the present invention, various equivalent modifications made by those skilled in the art fall within the scope defined by the appended claims of this application.

[0038] Unless otherwise specified, all raw materials and reagents of the present invention are raw materials and reagents on the conventional market.

[0039] The preparation methods of the rosemary extract, lemon balm extract, wampee peel extract, and loquat leaf extract used in the present invention include: respectively collecting fresh rosemary, lemon balm, wampee peel, and loquat leaf, quickly freezing them in liquid nitrogen, quickly grinding them into powder, adding 70-95% (volume ratio) ethanol-aqueous solution for extraction, performing ultrasonic extraction at 50-70°C and a power of 400-650W for 1-3h, and repeating 2-3 times;

[0040] The mass-volume ratio of the rosemary, lemon balm, wampee peel, and loquat leaf to the ethanol solution is 1:(20-60);

[0041] Preferably, the preparation method of the rosemary extract comprises: pulverizing fresh rosemary plants by grinding in liquid nitrogen, adding 70% ethanol-aqueous solution according to a solid-liquid ratio of 1:30, performing ultrasonic extraction at 55 °C and a power of 400 W for 2 h, repeating 3 times, collecting the extraction solution, centrifuging and filtering, and concentrating the collected filtrate by rotary evaporation of the extraction solution to obtain the rosemary extract.

[0042] Preferably, the preparation method of the lemon balm extract comprises: adding ethanol with a volume fraction of 75% according to a solid-liquid ratio of 1:40, performing ultrasonic extraction at 60 °C and a power of 450 W for 3 h, repeating 3 times, collecting the extraction solution, centrifuging and filtering, and concentrating the collected filtrate by rotary evaporation of the extraction solution to obtain the lemon balm extract.

[0043] Preferably, the preparation method of the wampee pericarp extract comprises: adding ethanol with a volume fraction of 90% according to a solid-liquid ratio of 1:60, performing ultrasonic extraction at 65 °C and a power of 650 W for 3 h, repeating 3 times, collecting the extraction solution, centrifuging and filtering, and concentrating the collected filtrate by rotary evaporation of the extraction solution to obtain the wampee pericarp extract.

[0044] Preferably, the preparation method of the loquat leaf extract comprises: adding ethanol with a volume fraction of 85% according to a solid-liquid ratio of 1:50, performing ultrasonic extraction at 70 °C and a power of 600 W for 2.5 h, repeating 3 times, collecting the extraction solution, centrifuging and filtering, and concentrating the collected filtrate by rotary evaporation of the extraction solution to obtain the loquat leaf extract.

[0045] Example 1

[0046] The preparation of the composite preservative comprises the following steps:

[0047] 1) Preparation of the W / O emulsion: Mix purine nucleoside triphosphate (ATP) and water as the inner aqueous phase, emulsify edible corn oil and an emulsifier to form an oil phase, slowly inject the inner aqueous phase into the oil phase, and perform stirring and homogenization under ice bath conditions at a rotation speed of 4000 rpm for 2.5 min to form a W / O emulsion;

[0048] 2) Preparation of the W / O / W emulsion: Disperse pullulan polysaccharide and guar gum in hot water at 80 °C, stir magnetically for 1 h until completely dissolved, then add chondroitin sulfate and trehalose, stir and dissolve at 48 °C, finally cool to room temperature, add ascorbic acid, stir in the dark, and filter to form the outer aqueous phase. Slowly drop the W / O emulsion into the outer aqueous phase at a rotation speed of 3000 rpm for 3 min, and stir and homogenize to form a W / O / W emulsion, which is the composite preservative;

[0049] In the prepared composite preservative, it contains ascorbic acid at a concentration of 0.5%, adenosine triphosphate (ATP) at 0.5%, chondroitin sulfate at 0.6%, pullulan polysaccharide at 1.5%, trehalose at 1%, guar gum at 1% and water.

[0050] Example 2

[0051] The preparation of the composite preservative includes the following steps:

[0052] 1) Preparation of W / O emulsion: Mix adenosine triphosphate (ATP) and water as the inner aqueous phase, emulsify edible corn oil and an emulsifier to form an oil phase, slowly inject the inner aqueous phase into the oil phase, and perform stirring and homogenization under ice bath conditions at a rotation speed of 5000 rpm for 2 minutes to form a W / O emulsion;

[0053] 2) Preparation of W / O / W emulsion: Disperse pullulan polysaccharide and guar gum in hot water at 82 °C, stir magnetically for 1 h until completely dissolved, then add chondroitin sulfate and trehalose, stir and dissolve at 40 °C, finally cool to room temperature, add ascorbic acid, stir in the dark, filter to form the outer aqueous phase, slowly drop the W / O emulsion into the outer aqueous phase, at a rotation speed of 4000 rpm for 2.5 minutes, stir and homogenize to form a W / O / W emulsion, which is the composite preservative;

[0054] In the prepared composite preservative, it contains ascorbic acid at a concentration of 0.1%, adenosine triphosphate (ATP) at 0.2%, chondroitin sulfate at 0.4%, pullulan polysaccharide at 1%, trehalose at 0.5%, guar gum at 0.5% and water.

[0055] Example 3

[0056] The preparation of the composite preservative includes the following steps:

[0057] 1) Preparation of W / O emulsion: Mix adenosine triphosphate (ATP) and water as the inner aqueous phase, emulsify edible corn oil and an emulsifier to form an oil phase, slowly inject the inner aqueous phase into the oil phase, and perform stirring and homogenization under ice bath conditions at a rotation speed of 3000 rpm for 3 minutes to form a W / O emulsion;

[0058] 2) Preparation of W / O / W emulsion: Disperse pullulan polysaccharide and guar gum in hot water at 85 °C, stir magnetically for 1 h until completely dissolved, then add chondroitin sulfate and trehalose, stir and dissolve at 41 °C, finally cool to room temperature, add ascorbic acid, stir in the dark, filter to form the outer aqueous phase, slowly drop the W / O emulsion into the outer aqueous phase, at a rotation speed of 3000 rpm for 2 minutes, stir and homogenize to form a W / O / W emulsion, which is the composite preservative;

[0059] In the prepared composite preservative, it contains ascorbic acid with a concentration of 0.3%, adenosine triphosphate (ATP) with a concentration of 0.25%, chondroitin sulfate with a concentration of 0.5%, pullulan with a concentration of 1.25%, trehalose with a concentration of 0.75%, guar gum with a concentration of 0.75% and water.

[0060] Example 4

[0061] A preservation method applicable to stem Brassica vegetables

[0062] 1) Vegetable pretreatment: Pick fresh vegetable hearts to remove pests, diseases and mechanically damaged plants, and then pre-cool them in a 4°C cold storage until the temperature of the stem is ≤10°C;

[0063] 2) Preservation treatment: Spray the composite preservative of Example 1 on the stem and leaf parts until the leaves and stems are completely wrapped and there is a small amount of dripping water. Immerse the cut end in the antibacterial preservative. The immersion part is 2 cm from the cut end and immerse for 10 minutes;

[0064] After spraying the composite preservative and immersing in the green antibacterial preservative, dry the surface moisture in a treatment room at room temperature of 15°C;

[0065] The composition of the antibacterial preservative includes: 1.5% rosemary extract, 1.5% lemon balm extract, 2% wampee peel extract, 2% loquat leaf extract, 3% beeswax and water;

[0066] 3) Packaging treatment: Package with a self - regulating modified atmosphere packaging bag

[0067] The thickness of the self - regulating modified atmosphere preservation bag is 30μm, made of PE material, and the oxygen transmission rate is 5625 cm 3 / m 2 ·24h·0.1Mpa;

[0068] 4) Storage: Store at 4°C in a low - temperature environment

[0069] The results show that after 30 days of storage of the vegetable hearts, there are no yellow leaves and no rotting in the whole vegetable hearts. The stems show good performance, and there is a small amount of hollowness after cutting the cross - section.

[0070] As Figure 1 shown, it is a flow chart of the preservation method for stem Brassica vegetables of the present invention, which has a good preservation effect on vegetables.

[0071] Example 5

[0072] A preservation method applicable to stem Brassica vegetables

[0073] 1) Vegetable pretreatment: Pick fresh Chinese kale to remove pests, diseases and mechanically damaged plants, and then pre - cool them in a 4°C cold storage until the temperature of the stem is ≤10°C;

[0074] 2) Fresh-keeping treatment: Spray the compound fresh-keeping agent of Example 2 for inhibiting leaf yellowing and stem hollowness on the stem and leaf parts until the leaves and stems are completely covered and a small amount of water drips. Immerse the cut end in the antibacterial fresh-keeping agent at a position 2 cm from the cut end for 10 minutes.

[0075] After spraying the compound fresh-keeping agent and immersing in the green antibacterial fresh-keeping agent, dry the surface moisture in a treatment room at room temperature of 15°C.

[0076] The composition of the antibacterial fresh-keeping agent includes: 1% rosemary extract, 1% lemon balm extract, 1% wampee pericarp extract, 1% loquat leaf extract, 1% beeswax and water.

[0077] 3) Packaging treatment: Package with a modified atmosphere packaging bag

[0078] The thickness of the modified atmosphere fresh-keeping bag is 30 μm, made of PE material, and the oxygen transmission rate is 5625 cm 3 / m 2 ·24 h·0.1 Mpa;

[0079] 4) Storage: Store at a low temperature of 4°C

[0080] The results show that after the packaged Chinese kale is stored at 15°C for 12 days, a small amount of yellow leaves appear on the outer layer of the Chinese kale, there is no rot, and there is no hollowness after the stem cross-section is cut.

[0081] Example 6

[0082] A fresh-keeping method applicable to stem-type Brassica vegetables

[0083] 1) Vegetable pretreatment: Pick fresh vegetable hearts to remove pests, diseases and mechanically damaged plants, and then pre-cool in a 4°C cold storage until the stem temperature ≤ 10°C;

[0084] 2) Fresh-keeping treatment: Spray the compound fresh-keeping agent of Example 1 on the stem and leaf parts until the leaves and stems are completely covered and a small amount of water drips. Immerse the cut end in the antibacterial fresh-keeping agent at a position 2 cm from the cut end for 10 minutes;

[0085] After spraying the compound fresh-keeping agent and immersing in the green antibacterial fresh-keeping agent, dry the surface moisture in a treatment room at room temperature of 15°C;

[0086] The composition of the antibacterial fresh-keeping agent includes: 0.75% rosemary extract, 0.75% lemon balm extract, 1.5% wampee pericarp extract, 1.5% loquat leaf extract, 2% beeswax and water;

[0087] 3) Packaging treatment: Package with a modified atmosphere packaging bag

[0088] The thickness of the self - regulating modified atmosphere fresh - keeping bag is 30μm, made of PE material, and the oxygen transmission rate is 5625cm 3 / m 2 ·24h·0.1Mpa;

[0089] 4) Storage: Store at a low temperature of 4℃

[0090] The results show that after 4 days of storage of the flowering Chinese cabbage, there are no yellow leaves and no rot in the whole plant. The stem shows good performance, and there is a small amount of hollowness after cutting the cross - section.

[0091] Comparative Example 1

[0092] As the control group of Example 4, in Comparative Example 1, the base of the stem is not soaked with the green antibacterial fresh - keeping agent, and other conditions remain unchanged. The packaged flowering Chinese cabbage is stored at 4℃. The results show that after 30 days of storage, there are a few yellow leaves on the outermost layer of the flowering Chinese cabbage, no rot, the cut of the stem has a rotten appearance, and there is a large amount of hollowness after cutting the cross - section.

[0093] Comparative Example 2

[0094] As the control group of Example 4, in Comparative Example 2, the leaves and stems are not sprayed with the composite fresh - keeping agent, and other conditions remain unchanged. The packaged flowering Chinese cabbage is stored at 4℃. After 30 days of storage, there are more yellow leaves on the flowering Chinese cabbage, no rot, a large amount of hollowness appears after cutting the cross - section of the stem, and there is spoilage.

[0095] Comparative Example 3

[0096] As the control group of Example 4, the composite fresh - keeping agent in Comparative Example 3 is directly mixed with 0.5% ascorbic acid, 0.5% adenosine triphosphate (ATP), 0.6% chondroitin sulfate, 1.5% pullulan, 1% trehalose, 1% guar gum and water, and other conditions remain unchanged. The packaged flowering Chinese cabbage is stored at 4℃. After 30 days of storage, there are a small number of yellow leaves on the flowering Chinese cabbage, no rot, a little hollowness appears after cutting the cross - section of the stem, and there is slight rot.

[0097] Comparative Example 4

[0098] Pick fresh flowering Chinese cabbage for selection and pre - cooling, and directly pack it with ordinary plastic packaging bags. The packaged flowering Chinese cabbage is stored at 4℃. After 30 days of storage, the whole flowering Chinese cabbage has all turned yellow, started to rot, the cut of the stem has rot, and a large amount of hollowness and spoilage appear after cutting the cross - section of the stem.

[0099] Comparative Example 5

[0100] As the control group of Example 5, in Comparative Example 3, the base of the stem is not soaked with the green antibacterial fresh - keeping agent, and other conditions remain unchanged. The packaged Chinese kale is stored at 15℃. After 12 days of storage, the whole Chinese kale has all turned yellow, the leaves are rotten and moldy, and there is hollowness after cutting the cross - section of the stem.

[0101] Comparative Example 6

[0102] As the control group of Example 5, in Comparative Example 4, the compound preservative was not sprayed on the leaves and stems, and other conditions remained unchanged; the packaged Chinese kale was stored at 15°C. After 12 days of storage, all the whole plants of Chinese kale turned yellow, the leaves did not rot or grow mold, and there were many hollows after cutting the cross-section of the stem.

[0103] Comparative Example 7

[0104] As the control group of Example 5, the compound preservative in Comparative Example 7 was directly mixed with 0.1% ascorbic acid, 0.2% adenosine triphosphate (ATP), 0.4% chondroitin sulfate, 1% pullulan, 0.5% trehalose, 0.5% guar gum and water, and other conditions remained unchanged; the packaged Chinese kale was stored at 15°C. After 12 days of storage, there were some yellow leaves on the Chinese kale, the leaves rotted and grew mold, and there was a hollow after cutting the cross-section of the stem.

[0105] Comparative Example 8

[0106] Fresh Chinese kale was picked, selected and pre-cooled, and then directly packaged in ordinary plastic bags. The packaged Chinese kale was stored at 15°C. After 12 days of storage, all the whole plants of Chinese kale turned yellow, the leaves rotted and grew mold, and there was a hollow and mildew after cutting the cross-section of the stem.

[0107] Comparative Example 9

[0108] As the control group of Example 6, in Comparative Example 5, the green antibacterial preservative was not used to soak the base of the stem, and other conditions remained unchanged; the packaged flowering Chinese cabbage was stored at 20°C for 4 days. The results showed that there were a small number of yellow leaves on the leaves of the flowering Chinese cabbage, the cut surface of the stem began to rot, and there were a large number of hollows after cutting the cross-section.

[0109] Comparative Example 10

[0110] As the control group of Example 6, in Comparative Example 6, the compound preservative was not sprayed on the leaves and stems, and other conditions remained unchanged; the packaged flowering Chinese cabbage was stored at 20°C for 4 days. The results showed that there were a large number of yellow leaves on the leaves of the flowering Chinese cabbage, which began to rot, and there was a small amount of rot on both the cut surface and the surface of the stem, and there were a large number of hollows after cutting the cross-section.

[0111] Comparative Example 11

[0112] As the control group of Example 6, the compound preservative in Comparative Example 11 was directly mixed with 0.3% ascorbic acid, 0.25% adenosine triphosphate (ATP), 0.5% chondroitin sulfate, 1.25% pullulan, 0.75% trehalose, 0.75% guar gum and water, and other conditions remained unchanged; the packaged flowering Chinese cabbage was stored at 20°C for 4 days. The results showed that there were a small number of yellow leaves on the leaves of the flowering Chinese cabbage, the cut surface of the stem showed rot, and there were a small number of hollows after cutting the cross-section.

[0113] Comparative Example 12

[0114] Pick fresh flowering Chinese cabbage hearts for selection and precooling, and directly pack them in ordinary plastic packaging bags. Store the packed flowering Chinese cabbage at 20°C for 4 days. The results show that the leaves of the flowering Chinese cabbage turn yellow throughout the whole plant and start to rot, the cut surface and surface of the stem are both rotten, and a large amount of hollowness appears after cutting the cross-section.

[0115] Characterize the quality of the harvested vegetables:

[0116] 1. Determination of chlorophyll content: Extract leaf chlorophyll with 80% acetone by volume under dark conditions, and use a spectrophotometer to measure the absorbance at wavelengths A663 nm and A645 nm. Calculate the chlorophyll mass concentration (mg / L) according to the formula chlorophyll concentration (mg / L) = 20.29*A645 + 8.05*A663, and then calculate the chlorophyll content (mg / g) according to the formula chlorophyll content (mg / g) = C*V*N / (W*1000), where V is the volume of the extract, mL; N is the dilution factor; W is the fresh weight of the sample, g.

[0117] 2. Determination of the change in Vc content: The 2,4-dinitrophenylhydrazine colorimetric method was used. Weigh 1 g of each sample separately, grind it in liquid nitrogen, add 5 mL of 2,4-dinitrophenylhydrazine solution, and mix well. Place the test tube in a 37°C water bath for 30 minutes. After the reaction ends, add 7 mL of 85% sulfuric acid solution to terminate the reaction and develop color. Place the test tube in a 37°C water bath for 30 minutes. Measure the absorbance of the sample solution with a spectrophotometer at a wavelength of 520 nm. Calculate the content of vitamin C through the standard curve, and the unit is mg·100g -1 。

[0118] The results are as follows:

[0119] Figure 2 It shows the influence of different treatment methods on the phenotypic changes of flowering Chinese cabbage stored at 4°C for 30 days. As can be seen from Figure 2 Among them, after storing at low temperature (4°C) for 30 days, compared with Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4, in Example 4, spraying the leaves and stems with the composite preservative of the present invention and soaking the base of the stems with the green antibacterial preservative, the yellowing of the leaves and the hollowness of the stems of the treated flowering Chinese cabbage are significantly reduced; it shows that this treatment can significantly reduce the senescence and rot of flowering Chinese cabbage during low-temperature storage. The yellowing of the leaves and the hollowness of the stems of the flowering Chinese cabbage in Comparative Example 1 and Comparative Example 2 are also delayed compared with those in Comparative Example 4, indicating that the single treatment of spraying the leaves and stems with the composite preservative or soaking the base of the stems with the green antibacterial preservative can also delay the senescence of the new flowering Chinese cabbage, but the effect is not as good as that in Example 4; and the comparison of the effects between Comparative Example 3 and Example 4 also shows that the composite preservative of the present invention prepared by microencapsulation has a better preservation effect on the stem and leaf parts.

[0120] FromFigure 3 It can be seen that for flowering Chinese cabbage stored at 4°C for 30 days under different treatment methods, compared with Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4, in Example 4, by spraying the compound preservative on the leaves and bolting stems and combining with soaking the base of the stems with the green antibacterial preservative, the chlorophyll content of the leaves, the Vc content of the leaves, and the Vc content of the bolting stems of the flowering Chinese cabbage treated in this way remained the highest; it shows that this treatment can significantly reduce the decline of chlorophyll and Vc content in the leaves of flowering Chinese cabbage during low-temperature storage. The chlorophyll content of the leaves, the Vc content of the leaves, and the Vc content of the bolting stems of the flowering Chinese cabbage in Comparative Example 1 and Comparative Example 2 were respectively higher than those in Comparative Example 4, indicating that a single treatment of spraying the compound preservative on the leaves and bolting stems or soaking the base of the stems with the green antibacterial preservative can also delay the decline of the quality of flowering Chinese cabbage, but the effect is not as good as that in Example 4; the comparison of the effects between Comparative Example 3 and Example 4 also shows that the compound preservative of the present invention prepared by microencapsulation helps to maintain or improve the quality of flowering Chinese cabbage.

[0121] Figure 4 Shows the effects of different treatment methods on the phenotypic changes of Chinese kale stored at 15°C for 12 days. From Figure 4 It can be seen that after storing at 15°C for 12 days, compared with Comparative Example 5, Comparative Example 6, Comparative Example 7, and Comparative Example 8, in Example 5, by spraying the compound preservative on the leaves and bolting stems and combining with soaking the base of the stems with the green antibacterial preservative, the yellowing of the leaves and the hollowness of the bolting stems of the Chinese kale treated in this way were significantly reduced; it shows that this treatment can significantly reduce the senescence and rot of Chinese kale during low-temperature storage. The yellowing of the Chinese kale and the hollowness of the bolting stems in Comparative Example 5 and Comparative Example 6 were also delayed compared with those in Comparative Example 8, indicating that a single treatment of spraying the compound preservative on the leaves and bolting stems or soaking the base of the stems with the green antibacterial preservative can also delay the senescence of Chinese kale, but the effect is not as good as that in Example 5; and the comparison of the effects between Comparative Example 7 and Example 5 also shows that the compound preservative of the present invention prepared by microencapsulation has a better fresh-keeping effect on the bolting stems and leaf parts.

[0122] From Figure 5 It can be seen that for Chinese kale stored at 15°C for 12 days under different treatment methods, compared with Comparative Example 5, Comparative Example 6, Comparative Example 7, and Comparative Example 8, in Example 5, by spraying the compound preservative on the leaves and bolting stems and combining with soaking the base of the stems with the green antibacterial preservative, the chlorophyll content of the leaves, the Vc content of the leaves, and the Vc content of the bolting stems of the Chinese kale treated in this way remained the highest; it shows that this treatment can significantly reduce the decline of chlorophyll and Vc content in the leaves of Chinese kale during low-temperature storage. The chlorophyll content of the leaves, the Vc content of the leaves, and the Vc content of the bolting stems of the Chinese kale in Comparative Example 5 and Comparative Example 6 were respectively higher than those in Comparative Example 8, indicating that a single treatment of spraying the compound preservative on the leaves and bolting stems or soaking the base of the stems with the green antibacterial preservative can also delay the decline of the quality of Chinese kale, but the effect is not as good as that in Example 5; the comparison of the effects between Comparative Example 7 and Example 5 also shows that the compound preservative of the present invention prepared by microencapsulation helps to maintain or improve the quality of Chinese kale.

[0123] Figure 6 Effect of different treatment methods on the phenotypic changes of flowering Chinese cabbage stored at 20°C for 4 days. As can be seen from Figure 6 it, after 4 days of storage at 20°C, compared with Comparative Example 9, Comparative Example 10, Comparative Example 11 and Comparative Example 12, in Example 6, by spraying the leaves and stem bolts with a composite preservative and soaking the base of the stem with a green antibacterial preservative, the yellowing of the leaves and the hollowness of the stem bolts of the flowering Chinese cabbage treated in this way were significantly alleviated; it shows that this treatment can significantly reduce the senescence and rot of flowering Chinese cabbage during low-temperature storage. The yellowing of the leaves and the hollowness of the stem bolts of the flowering Chinese cabbage in Comparative Example 9 and Comparative Example 10 were also delayed compared with Comparative Example 12, indicating that the single treatment of spraying the leaves and stem bolts with a composite preservative or soaking the base of the stem with a green antibacterial preservative can also delay the senescence of the flowering Chinese cabbage, but the effect is not as good as that of Example 6. The comparison of the effects between Comparative Example 11 and Example 6 also shows that the composite preservative of the present invention prepared by microencapsulation has a better preservation effect on the stem bolt and leaf parts.

[0124] As Figure 7 can be seen, after 4 days of storage at 20°C of the flowering Chinese cabbage with different treatment methods, compared with Comparative Example 9, Comparative Example 10, Comparative Example 11 and Comparative Example 12, in Example 6, by spraying the leaves and stem bolts with a composite preservative and soaking the base of the stem with a green antibacterial preservative, the chlorophyll content of the leaves, the Vc content of the leaves, and the Vc content of the stem bolts of the flowering Chinese cabbage treated in this way remained the highest; it shows that this treatment can significantly reduce the decrease of the chlorophyll and Vc content of the leaves of the flowering Chinese cabbage during low-temperature storage. The chlorophyll content of the leaves, the Vc content of the leaves, and the Vc content of the stem bolts of the flowering Chinese cabbage in Comparative Example 9 and Comparative Example 10 were all higher than those in Comparative Example 12 respectively, indicating that the single treatment of spraying the leaves and stem bolts with a composite preservative or soaking the base of the stem with a green antibacterial preservative can also delay the decline of the quality of the flowering Chinese cabbage, but the effect is not as good as that of Example 6; the comparison of the effects between Comparative Example 11 and Example 6 also shows that the composite preservative of the present invention prepared by microencapsulation helps to maintain or improve the quality of the flowering Chinese cabbage.

[0125] As can be seen from the above results, by using a preservation method for delaying the senescence, stem hollowness and cut rot of stem-type Brassica vegetables provided by the present invention, according to the W / O / W emulsion composite preservative, green antibacterial preservative and soaking time prepared by the present invention, the quality deterioration of stem-type Brassica vegetables during low-temperature and shelf storage can be reduced, and the stem hollowness and cut rot can be alleviated. Therefore, using this method to reduce the senescence rate of flowering Chinese cabbage during postharvest storage and maintain good quality is of great significance for the practical application of postharvest flowering Chinese cabbage production and the development of new preservation technologies.

Claims

1. A fresh-keeping method applicable to stem-type Brassica vegetables, characterized in that, It includes the following steps: 1) Vegetable pretreatment: Pick fresh vegetables, remove plants with diseases, pests and mechanical damage, and then perform precooling until the temperature of the stem is ≤ 10°C; 2) Preservation treatment: Spray a composite preservative on the stem and leaf parts, and soak the cut with a bacteriostatic preservative; The composition of the composite preservative includes: ascorbic acid, adenosine triphosphate, chondroitin sulfate, pullulan, trehalose, guar gum and water; The composition of the bacteriostatic preservative includes: rosemary extract, lemon balm extract, wampee peel extract, loquat leaf extract, beeswax and water; 3) Packaging treatment: Use a modified atmosphere packaging bag for packaging; 4) Storage: Store at a low temperature of 2 - 5°C or store during the shelf life at 12 - 15°C.

2. The fresh-keeping method applicable to stem-type Brassica vegetables according to claim 1, wherein, In the composite preservative, by mass fraction of concentration, the concentrations of each component are 0.1% - 0.5% ascorbic acid, 0.2% - 0.5% adenosine triphosphate, 0.4% - 0.6% chondroitin sulfate, 1% - 1.5% pullulan, 0.5% - 1% trehalose, 0.5% - 1% guar gum.

3. The fresh-keeping method applicable to stem Brassica vegetables according to claim 1, characterized in that, The preparation of the composite preservative includes the following steps: 1) Preparation of W / O emulsion: Mix adenosine triphosphate and water as the internal aqueous phase, emulsify edible corn oil and an emulsifier to form an oil phase, slowly inject the internal aqueous phase into the oil phase, and stir and homogenize under ice bath conditions to form a W / O emulsion; The rotation speed of the stirring and homogenizing is 3000 - 5000 rpm, and the time is 2 - 3 min; 2) Preparation of W / O / W emulsion: Disperse pullulan and guar gum in hot water at 80°C, stir magnetically for 1 h until completely dissolved, then add chondroitin sulfate and trehalose, stir and dissolve at 40°C, finally cool to room temperature, add ascorbic acid, stir in the dark, filter to form the external aqueous phase, slowly drop the W / O emulsion into the external aqueous phase, and stir and homogenize to form a W / O / W emulsion; The rotation speed of the stirring and homogenizing is 3000 - 5000 rpm, and the time is 2 - 3 min.

4. The fresh-keeping method applicable to stem-type Brassica vegetables according to claim 1, characterized in that, In the bacteriostatic preservative, by mass fraction of concentration, the concentrations of each component are 1% - 1.5% rosemary extract, 1% - 1.5% lemon balm extract, 1% - 2% wampee peel extract, 1% - 2% loquat leaf extract, 1% - 3% beeswax.

5. The fresh-keeping method applicable to stem-type Brassica vegetables according to claim 1, characterized in that, The preparation methods of the rosemary extract, lemon balm extract, wampee peel extract and loquat leaf extract include: respectively collect fresh rosemary, lemon balm, wampee peel and loquat leaf, quickly freeze them in liquid nitrogen, quickly grind them into powder, add 70 - 95% (volume ratio) ethanol - aqueous solution for extraction, and perform ultrasonic extraction at 50 - 70°C and a power of 400 - 650 W for 1 - 3 h, repeat 2 - 3 times.

6. The fresh-keeping method applicable to stem Brassica vegetables according to claim 5, characterized in that, The mass - to - volume ratio of rosemary, lemon balm, wampee peel, loquat leaf to the ethanol solution is 1:(20 - 60).

7. The fresh-keeping method applicable to stem-type Brassica vegetables according to claim 1, characterized in that, The spraying amount of the composite preservative is to spray until the leaves and stems are all wrapped and there is a small amount of dripping water.

8. The fresh-keeping method applicable to stem Brassica vegetables according to claim 1, characterized in that, The soaking time of the green bacteriostatic preservative is 5 - 10 min, and the soaking part is 2 - 5 cm from the cut.

9. The fresh-keeping method applicable to stem Brassica vegetables according to claim 1, characterized in that, After spraying the composite preservative and soaking in the green bacteriostatic preservative, dry the surface moisture at room temperature of 15°C.

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