A composite method for protecting the green color of stuffed leafy vegetables

Abstract

This invention discloses a method for preserving the green color of leafy green vegetables used in fillings. The method involves first irradiating fresh leafy vegetables with alternating low-intensity pulsed light and ultraviolet C rays to maintain the integrity of the chloroplasts. Next, the irradiated leafy vegetables are subjected to enzyme inactivation and sterilization. Then, the vegetables are soaked in a solution of maltodextrin and sodium caseinate, dried, and finally cut, seasoned, stuffed, steamed, packaged, and refrigerated at 4°C to obtain a pre-prepared dish containing green vegetables. Vegetables processed using this method show a particularly significant improvement in green preservation after reheating following one week of refrigeration at 0°C–4°C. The preparation method provided by this invention is simple, uses pollution-free and inexpensive raw materials that are readily available, and solves the problem of yellowing and softening of leafy green vegetables during processing and storage, demonstrating its feasibility for application.

Description

Technical Field

[0001] This invention discloses a composite method for protecting the green color of leafy green vegetables with fillings, which belongs to the field of food processing technology. Background Technology

[0002] Pre-cooked meals refer to finished or semi-finished dishes made from agricultural products such as livestock, poultry, aquatic products, fruits and vegetables, and various auxiliary ingredients, which are pre-processed in factories. Consumers can eat them directly after purchasing them or they only need to be heated or cooked before consumption. They generally need to be stored, transported and sold under cold chain conditions.

[0003] Green vegetables in pre-cooked dishes are typically prepared by blanching at high temperatures. The "green" color of these vegetables is primarily due to their high chlorophyll content, which coexists with protein within them. During blanching, the chlorophyll-protein complex breaks down, releasing chlorophyll. High temperatures also cause the vegetable cells to produce a slightly acidic environment. Enzymes such as pheophytinase exhibit higher catalytic activity in this acidic environment (around 60-80℃), making it easier for chlorophyll to convert to pheophytin, causing the vegetable color to change from green to yellow. Furthermore, oxygen is a crucial factor for the chlorophyll-degrading enzymes to function. Under the influence of oxygen and enzymes, the porphyrin macrocycle in the chlorophyll molecule is destroyed, generating colorless molecules, leading to a deterioration in the vegetable's appearance. This severely impacts product quality and consumer appetite, and results in significant waste of vegetables. Therefore, addressing the problem of green vegetables turning yellow and soft during processing and storage in the catering industry is of substantial significance in improving food quality and reducing resource waste.

[0004] Sun Hongnan et al. (2023) disclosed a method for improving chlorophyll stability (Publication No.: CN115843960A). This invention, through the use of high hydrostatic pressure treatment technology, mixes chlorophyll solution with zinc acetate solution, effectively improving the color and antioxidant activity of chlorophyll, and increasing the zinc ion replacement rate. However, within the limits allowed by national standards, single Zn... 2+ The effect on leafy green vegetables was not significant.

[0005] Liu Dequan et al. (2021) proposed a novel sterilizing refrigerator lamp and refrigerator (Publication No.: CN212538450U). This invention connects ultraviolet lamp groups and lighting lamp groups in parallel to kill bacteria entering the refrigerator and extend the shelf life. Each group of lights is provided by LED lights. Although ultraviolet light can kill microorganisms well, excessive dosage will cause problems such as dehydration and tissue deterioration of fruits and vegetables, while insufficient dosage will not achieve the sterilization effect. Moreover, the lighting lamp group does not have a sterilization function. Therefore, its application to fruits and vegetables needs to be combined with other methods.

[0006] Han et al. (2023) disclosed an underwater ultraviolet lamp sterilization and color protection device for fresh-cut fruits and vegetables (publication number: CN220441831U). The ultraviolet lamp sterilization and color protection device proposed in this invention improves the cleaning effect of fruit and vegetable washing machines and ensures food safety. However, ultraviolet light has poor penetration in water. If the water flow rate is larger, more ultraviolet light is needed to achieve the same disinfection effect, and the cost will also increase accordingly.

[0007] Ma et al. (2019) disclosed a compound blanching and color-protecting agent for cabbage and its application (Publication No.: CN110140859A). This invention involves immersing cabbage in the compound color-protecting agent under different blanching methods to maximally inhibit enzymatic browning and maintain the natural color of the product. However, high-temperature blanching results in significant loss of nutrients in vegetables, making it unsuitable for processed fruit and vegetable products.

[0008] Li Miaoyun et al. (2022) disclosed a method for color preservation and freshness protection of pre-cooked dishes containing green vegetables (Publication No.: CN115444027A). The color-protecting agent A described in this invention is an aqueous solution containing baking soda and copper sulfate. It maintains the green color by replacing magnesium ions in the chlorophyll porphyrin ring with metal ions and then saponifying it under alkaline conditions to form a relatively stable chlorophyll metal salt. However, copper sulfate does not meet the requirements of GB / T 2760-2014, and the metal ion replacement rate is too low, resulting in an insignificant green-protecting effect.

[0009] Zhang Xiuling et al. (2020) disclosed the preparation and application of a compound greening agent for pointed peppers (Publication No.: CN202011144031.6). The greening agent is composed of an aqueous solution of sodium isoascorbate, sodium bicarbonate, and zinc gluconate. It effectively protects the chlorophyll in pointed peppers by maintaining their green color for 20–60 minutes at 40°C. However, zinc gluconate is expensive and not suitable for large-scale use in factories. Summary of the Invention

[0010] To overcome the shortcomings of the prior art, this invention provides a composite method for protecting the green color of leafy green vegetables with fillings. By combining two light treatments, the integrity of chloroplasts is maintained. The chlorophyll is encapsulated by maltodextrin and sodium caseinate solution, which improves the stability of chlorophyll in vegetables. This solves the problem of yellowing of vegetable hearts under high-temperature steaming, improves the quality of catering food, enhances the consumer's eating experience, and reduces resource waste.

[0011] The technical solution of the present invention is as follows:

[0012] A method for protecting the green color of leafy green vegetables with fillings, comprising the following steps:

[0013] (1) Initial processing of vegetables: After washing the fresh green leafy vegetables, remove the roots and yellow leaves;

[0014] (2) Light pretreatment: The leafy green vegetables that have been pretreated in step (1) are placed in a lighting system that can provide ultraviolet C rays (UVC), low-intensity pulsed white light and green light.

[0015] (3) Ultrasonic heat treatment: The leafy green vegetables that have undergone light pretreatment in step (2) are immersed in an ultrasonic bath (DL-360E), and the temperature and time of the ultrasound are designed for enzyme inactivation treatment.

[0016] (4) Embedding: The green leafy vegetables obtained by ultrasonic heat treatment in step (3) are immersed in the prepared maltodextrin and sodium caseinate embedding solution, then removed and dried.

[0017] (5) Filling preparation: Cut the dried green leafy vegetables from step (4) into granules, add genetically modified soybean oil, salt, monosodium glutamate, and white sugar seasoning to make filling, and then steam it.

[0018] (6) Packaging and refrigeration: The semi-finished product in step (5) is packaged in a retort pouch filled with nitrogen and sealed. After sterilization, it is placed in a refrigerated environment at 4°C.

[0019] (7) Reheating: After the water boils, reheat it.

[0020] Furthermore, in step (2), low-intensity pulsed white light and green light are provided by fluorescent lamps, and ultraviolet C rays are provided by unfiltered bactericide emitting lamps (ultraviolet germicidal lamp tubes). In order to irradiate fresh vegetables with green light, a filter is placed between the fluorescent lamp and the leafy green vegetables.

[0021] Furthermore, in step (2), the intensity of low-intensity pulsed white light and green light is 20-25 μmol m. -2 s -1 Each irradiation lasts 1.5-3 hours, while each irradiation with ultraviolet C rays lasts 4-8 minutes. The wavelength of ultraviolet C rays is 254nm (ultraviolet light at 254nm has the strongest inactivation effect). Low-intensity pulsed white light and green light are alternated with ultraviolet C rays, and the total irradiation time is 8-10 hours.

[0022] Further, in step (3), the ultrasonic treatment conditions are: ultrasonic frequency of dual frequency 40-60kHz, amplitude of 90%-95%, temperature of 85-90℃, and time of 60-150s.

[0023] Further, in step (4), the maltodextrin and sodium caseinate are dissolved in deionized water and stirred at room temperature (25°C) for 3-4 hours using a magnetic stirrer until homogeneous. The mixed solution is then placed in a refrigerator at 4°C overnight to allow the polymer molecules to be completely hydrated, resulting in a hydrated wall material solution. Then, 1-2% (w / v) of Tween 80 is added to the hydrated wall material solution and stirred vigorously at room temperature until completely dissolved, yielding a maltodextrin and sodium caseinate encapsulation solution.

[0024] Further, in step (4), the maltodextrin in the maltodextrin and sodium caseinate encapsulation solution has a mass fraction of 2%-6%, and the sodium caseinate in the maltodextrin and sodium caseinate encapsulation solution has a mass fraction of 1%-3%; the leafy green vegetables are soaked in the maltodextrin and sodium caseinate encapsulation solution for 60-90 minutes.

[0025] Further, in step (5), the leafy green vegetables are cut into 0.5-1mm particles. Based on 100 parts of leafy green vegetables, the weight ratio of genetically modified soybean oil, edible salt, monosodium glutamate and white sugar seasoning is (6-8): (2-4): (0.4-0.6): (5-7). The steaming time is 3-5 minutes.

[0026] Furthermore, in step (6), the material of the retort bag is a polyamide / polypropylene (PA / CPP) composite material.

[0027] Furthermore, in step (6), a vacuum must be drawn before nitrogen filling and packaging, wherein the nitrogen purity is above 99.9%; in step (7), the re-evaporation time is 4-6 minutes.

[0028] This invention utilizes a combination of low-intensity pulsed white / green light and ultraviolet C-rays to maintain the integrity of chloroplasts. Low-intensity ultraviolet treatment preserves a higher level of natural chlorophyll a, thereby increasing the chlorophyll content in leafy green vegetables during illumination and reducing browning during processing. In this invention, the pulsed light is provided by fluorescent lamps, and inert gases are used instead of preservatives, resulting in no biochemical residues and ensuring environmental safety. Fluorescent lamps have a longer lifespan than LED lamps, making them suitable for prolonged illumination, and are relatively inexpensive and provide more uniform lighting. The combination of these two methods better controls quality changes in leafy green vegetables during storage, delaying the degradation of chlorophyll and proteins.

[0029] This invention utilizes maltodextrin and sodium caseinate to enhance the stability of chlorophyll in leafy green vegetables during processing and storage, thereby achieving a color-protecting effect. The added sodium caseinate, with its hydrophobic and hydrophilic groups, may contribute to electrostatic and steric stability. Chlorophyll is captured within the sodium caseinate dispersion through hydrogen bonds and van der Waals forces, thus improving the water solubility and stability of chlorophyll in food. Due to the heat-protective properties of maltodextrin, this invention uses it as a heat protectant during processing and storage. The added Tween 80, combined with maltodextrin, enhances its emulsifying ability. The synergistic treatment of maltodextrin and sodium caseinate more effectively reduces chlorophyll degradation and enhances chlorophyll storage stability.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The greening protection compound method for leafy green vegetables with fillings proposed in this invention adopts the following steps: first, low-intensity pulsed light and ultraviolet light are combined for irradiation, then ultrasonic-assisted blanching is performed, and finally maltodextrin and sodium caseinate are used for encapsulation treatment to protect chlorophyll. This reduces the loss of nutrients and enzymatic browning of chlorophyll in leafy green vegetables during subsequent processing, and better maintains the initial color of leafy green vegetables.

[0032] (2) Experiments show that, according to the application method proposed in this invention, after the leafy green vegetables are reheated after refrigeration, the vegetables are still bright green, the chlorophyll is effectively protected, and the nutritional quality is significantly improved.

[0033] (3) The greening compound method for leafy green vegetables with fillings proposed in this invention will not affect the original smell and taste of the food, and will maintain the quality of the vegetables to the greatest extent. Attached Figure Description

[0034] Figure 1 These are the color difference effect images of small Chinese cabbage treated with light-induced synergistic molecular encapsulation in Embodiment 1 and Comparative Examples 1-1 to 1-4 of the present invention;

[0035] Figure 2 These are the effects of light-induced synergistic molecular encapsulation treatment on chlorophyll content in Chinese cabbage in Embodiment 1 and Comparative Examples 1-1 to 1-4 of the present invention.

[0036] Figure 3 This is a comparison chart of chlorophyll content between Examples 1, 2, and 3 of the present invention and Comparative Examples 1, 2, and 3;

[0037] Figure 4 This is a comparison diagram between the molecular encapsulation treatment examples in Example 1 of the present invention, wherein the encapsulation solution is a maltodextrin and sodium caseinate encapsulation solution; the mixed solution is a mixed solution of maltodextrin and sodium caseinate that has not undergone complete hydration or other subsequent operations. Detailed Implementation

[0038] To better understand the present invention and demonstrate its greening effects, further detailed descriptions are provided below with reference to specific embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0039] Preparation methods of all maltodextrin and sodium caseinate encapsulation solutions in the examples and comparative examples: The maltodextrin and sodium caseinate were dissolved in deionized water and stirred at room temperature (25°C) for 3 hours using a magnetic stirrer (stirring speed 800 rpm) until homogeneous. The mixed solution was then incubated overnight at 4°C to allow the polymer molecules to fully hydrate and obtain a hydrated wall material solution. Then, 1.5% (w / v) of Tween 80 was added to the hydrated wall material solution, and the mixture was vigorously stirred at room temperature (stirring speed 800 rpm) for 15 minutes to ensure complete dissolution and obtain the maltodextrin and sodium caseinate encapsulation solution.

[0040] Example 1

[0041] A method for preserving the green color of bok choy filling, the steps are as follows:

[0042] (1) Initial processing of vegetables: Select fresh bok choy with uniform color, no wilting or yellowing, no mechanical damage, and no insect infestation. Remove the roots and stems, wash the bok choy thoroughly, drain the water and set aside.

[0043] (2) Light pretreatment: The bok choy pretreated in step (1) is placed in a lighting system for illumination. The lighting system can provide ultraviolet C-rays (UVC) (model TUV 15W G15 T8, Philips), low-intensity pulsed white light and green light (fluorescent lamp model TL-D 36W / 29-530 1SL / 25, Phillips; the filter used is a bandpass narrowband filter); the intensity of the low-intensity pulsed white light and green light is 22 μmol / m². -2 s -1 Each irradiation lasts for 2 hours, and each irradiation with ultraviolet C rays lasts for 6 minutes. The wavelength of ultraviolet C rays is 254nm. Low-intensity pulsed white light and green light are alternated with ultraviolet C rays, and the total irradiation time is 8 hours.

[0044] (3) Ultrasonic heat treatment: The green vegetables after the light pretreatment in step (2) are immersed in an ultrasonic bath (DL-360E). The ultrasonic frequency is designed to be 40kHz dual frequency, the amplitude is 95%, the temperature is 90℃, and the time is 60s, in order to carry out enzyme inactivation treatment.

[0045] (4) Encapsulation: The small green vegetables obtained by ultrasonic treatment in step (3) are soaked in the prepared maltodextrin and sodium caseinate encapsulation solution for 60 minutes, then removed and dried. The mass fraction of maltodextrin in the maltodextrin and sodium caseinate encapsulation solution is 4%, and the mass fraction of sodium caseinate is 2%.

[0046] (5) Filling preparation: Cut the dried green leafy vegetables from step (4) into 0.5-1mm particles, add genetically modified soybean oil, edible salt, monosodium glutamate and white sugar seasoning to make filling (the percentage of vegetable weight is 6:2:0.4:5 respectively), and then steam for 5 minutes;

[0047] (6) Packaging and refrigeration: The semi-finished jade shumai from step (5) is packaged in PA / CPP retort pouches filled with nitrogen and sealed, with nitrogen purity of 99.9% or higher. After sterilization, it is refrigerated at 4°C.

[0048] (7) Reheat: After the water boils, steam for 4 minutes.

[0049] Comparative Example 1-1: Traditional hot water blanching treatment. Blanching conditions: blanching temperature 90℃, blanching time 60s, material-to-liquid mass ratio 1:20. (Alternative to step 3, except for steps 2 and 4, all other steps are the same as steps 1, 5, 6, and 7 of Example 1).

[0050] Comparative Examples 1-2: Ultrasonic heat treatment. (Except for steps 2 and 4, the other steps are the same as steps 1, 3, 5, 6, and 7 of Example 1).

[0051] Comparative Examples 1-3: Only composite light treatment was performed, without embedding treatment. (Except for step 4, the other steps are the same as steps 1, 2, 3, 5, 6, and 7 of Example 1).

[0052] Comparative Examples 1-4: Embedding treatment, but without light exposure. (Except for step 2, all other steps are the same as steps 1, 3, 4, 5, 6, and 7 of Example 1).

[0053] The vegetables prepared above were refrigerated for one week and then reheated. Their color difference and chlorophyll content were then measured to evaluate their quality. Figure 3 As shown in Example 1 and Comparative Example 1-1, the chlorophyll retention rate of the treated bok choy was significantly improved under the same environment.

[0054] Furthermore, in the verification experiment of this invention, the total chlorophyll content of Comparative Examples 1-1, 1-2, 1-3, 1-4, and Example 1 after re-distillation was measured respectively. A comparison was also made between the encapsulation solution of maltodextrin and sodium caseinate and the mixed solution of maltodextrin and sodium caseinate (without complete hydration or subsequent operations, i.e., the maltodextrin and sodium caseinate were dissolved in deionized water and stirred at room temperature (800 rpm) for 3 hours using a magnetic stirrer until uniformly dissolved; the mass fraction of maltodextrin in the encapsulation solution was 4%, and the mass fraction of sodium caseinate was 2%). The results showed that the mixed solution of maltodextrin and sodium caseinate without complete hydration exhibited poor chlorophyll retention and color. This may be because the untreated mixed solution had poor dispersibility and unstable properties, leading to uneven chlorophyll encapsulation. Figure 4 Comparative Example 1-1 showed the lowest chlorophyll retention rate, while Comparative Example 1-2 relatively increased chlorophyll content but the effect was still not ideal. Comparative Examples 1-3 and 1-4 were able to maintain or even increase the chlorophyll content of leafy green vegetables better, while the treatment in Example 1 (maltodextrin and sodium caseinate encapsulation combined with light) retained chlorophyll to a greater extent. Figure 2 Furthermore, its color difference diagram also shows the same trend as chlorophyll retention; when both are treated together, a* is significantly reduced, as shown in the results. Figure 1 This demonstrates that the greening compound method of the present invention can better improve the color of vegetables.

[0055] Example 2

[0056] A method for preserving the green color of spinach filling, the steps are as follows:

[0057] (1) Initial processing of vegetables: Select fresh spinach with uniform color, no wilting or yellowing, no mechanical damage, and no insect infestation. Remove the roots and stems, wash the spinach thoroughly, drain the water and set aside.

[0058] (2) Light pretreatment: The fresh spinach pretreated in step (1) was placed in a lighting system for illumination. The lighting system was capable of providing ultraviolet C-rays (UVC) (model TUV 15W G15 T8, Philips), low-intensity pulsed white light, and green light (fluorescent lamp model TL-D 36W / 29-530 1SL / 25, Phillips; the filter used was a bandpass narrowband filter). The intensity of the low-intensity pulsed white light and green light was 22 μmol / m². -2 s -1 Each irradiation lasts for 2 hours, and each irradiation with ultraviolet C rays lasts for 6 minutes. The wavelength of ultraviolet C rays is 254nm. Low-intensity pulsed white light and green light are alternated with ultraviolet C rays, and the total irradiation time is 8 hours.

[0059] (3) Ultrasonic heat treatment: The spinach that has been pretreated by light in step (2) is immersed in an ultrasonic bath (DL-360E). The ultrasonic frequency is designed to be 40kHz dual frequency, the amplitude is 90%, the temperature is 85℃, and the time is 150s to carry out enzyme inactivation treatment.

[0060] (4) Encapsulation: The spinach obtained by ultrasonic treatment in step (3) was soaked in the prepared maltodextrin and sodium caseinate encapsulation solution for 80 minutes, then removed and dried. The mass fraction of maltodextrin in the maltodextrin and sodium caseinate encapsulation solution was 2%, and the mass fraction of sodium caseinate was 2%.

[0061] (5) Filling preparation: Cut the dried green leafy vegetables from step (4) into 0.5-1mm particles, add genetically modified soybean oil, edible salt, monosodium glutamate and white sugar seasoning to make filling (the percentage of vegetable weight is 6.5:3:0.4:6 respectively), and then steam for 5 minutes;

[0062] (6) Packaging and refrigeration: The semi-finished product from step (5) is packaged in PA / CPP retort pouches filled with nitrogen and sealed, with nitrogen purity of 99.9% or higher. After sterilization, it is refrigerated at 4°C.

[0063] (7) Reheating: After the water boils, reheat for 4 minutes. At the same time, conduct a blank control experiment without using the green protection composite method of the present invention while keeping other operations consistent. After reheating, take samples to test their color difference value and chlorophyll content.

[0064] Comparative Example 2-1: Traditional hot water blanching treatment. Blanching conditions: blanching temperature 93℃, blanching time 50s, material-to-liquid mass ratio 1:20. (Alternative to step 3, except for steps 2 and 4, all other steps are the same as steps 1, 5, 6, and 7 of Example 1).

[0065] Comparative Example 2-2: Ultrasonic heat treatment. (Except for steps 2 and 4, the other steps are the same as steps 1, 3, 5, 6, and 7 of Example 1).

[0066] Comparative Examples 2-3: Only composite light treatment was performed, without embedding treatment. (Except for step 4, the other steps are the same as steps 1, 2, 3, 5, 6, and 7 of Example 1).

[0067] Comparative Examples 2-4: Embedding treatment, but without light exposure. (Except for step 2, all other steps are the same as steps 1, 3, 4, 5, 6, and 7 of Example 1).

[0068] The vegetables prepared above were refrigerated for one week and then reheated. Their color difference and chlorophyll content were then measured to evaluate their quality. Figure 3 As shown in Example 2 and Comparative Example 2-1, the chlorophyll retention rate of the treated spinach was significantly improved under the same environment.

[0069] Example 3

[0070] A method for preserving the green color of bok choy filling, the steps are as follows:

[0071] (1) Initial processing of vegetables: Select small bok choy with uniform color, no wilting or yellowing, no mechanical damage, and no insect infestation. Remove the roots and stems, wash the bok choy thoroughly, drain the water and set aside.

[0072] (2) Light pretreatment: The fresh bok choy pretreated in step (1) is placed in a lighting system for illumination. The lighting system can provide ultraviolet C rays (UVC) (model TUV 15W G15 T8, Philips), low-intensity pulsed white light and green light (fluorescent lamp model TL-D 36W / 29-530 1SL / 25, Phillips; the filter used is a bandpass narrowband filter); the intensity of low-intensity pulsed white light and green light is 22 μmol / m². -2 s -1 Each irradiation lasts for 2 hours, and each irradiation with ultraviolet C rays lasts for 6 minutes. The wavelength of ultraviolet C rays is 254nm. Low-intensity pulsed white light and green light are alternated with ultraviolet C rays, and the total irradiation time is 8 hours.

[0073] (3) Ultrasonic heat treatment: The pak choy after light pretreatment in step (2) is immersed in an ultrasonic bath (DL-360E). The ultrasonic frequency is designed to be dual frequency 40kHz, amplitude is 93%, temperature is 87℃, and time is 120s to carry out enzyme inactivation treatment.

[0074] (4) Encapsulation: The Chinese cabbage obtained by ultrasonic treatment in step (3) was soaked in the prepared maltodextrin and sodium caseinate encapsulation solution for 60 minutes, then removed and dried. The mass fraction of maltodextrin in the maltodextrin and sodium caseinate encapsulation solution was 5%, and the mass fraction of sodium caseinate was 3%.

[0075] (5) Filling preparation: Cut the dried green leafy vegetables from step (4) into 0.5-1mm particles, add genetically modified soybean oil, edible salt, monosodium glutamate and white sugar seasoning to make filling (the percentage of vegetable weight is 7:3:0.5:6 respectively), and then steam for 5 minutes;

[0076] (6) Packaging and refrigeration: The semi-finished product from step (5) is packaged in PA / CPP retort pouches filled with nitrogen and sealed, with nitrogen purity of 99.9% or higher. After sterilization, it is refrigerated at 4°C.

[0077] (7) Reheating: After the water boils, reheat for 4 minutes. At the same time, conduct a blank control experiment without using the green protection composite method of the present invention while keeping other operations consistent. After reheating, take samples to test their color difference value and chlorophyll content.

[0078] Comparative Example 3-1: Traditional hot water blanching treatment. Blanching conditions: blanching temperature 95℃, blanching time 30s, material-to-liquid mass ratio 1:20. (Alternative to step 3, except for steps 2 and 4, all other steps are the same as steps 1, 5, 6, and 7 of Example 1).

[0079] Comparative Example 3-2: Ultrasonic heat treatment. (Except for steps 2 and 4, the other steps are the same as steps 1, 3, 5, 6, and 7 of Example 1).

[0080] Comparative Example 3-3: Only composite light treatment was performed, without embedding treatment. (Except for step 4, all other steps are the same as steps 1, 2, 3, 5, 6, and 7 of Example 1).

[0081] Comparative Examples 3-4: Embedding treatment, but without light exposure. (Except for step 2, all other steps are the same as steps 1, 3, 4, 5, 6, and 7 of Example 1).

[0082] The vegetables prepared above were refrigerated for one week and then reheated. Their color difference and chlorophyll content were then measured to evaluate their quality. Figure 3 As shown in Example 3 and Comparative Example 3-1, the chlorophyll retention rate of the treated bok choy was significantly improved under the same environment.

[0083] In the examples and comparative examples, all maltodextrin and sodium caseinate encapsulation solutions are compared with the mixed solutions of maltodextrin and sodium caseinate.

[0084] This invention uses the following methods to detect the color difference value and chlorophyll content of the above-mentioned experimental vegetable samples:

[0085] 1. Measurement of color difference

[0086] The colorimeter was used to measure the color of the samples. Three different parts of the same sample were measured, and the average value was taken as the final result. The results are expressed using spatial coordinate values ​​L*, a*, and b*. L* represents brightness; a larger L* value indicates a brighter color. a* represents red-green value; a smaller a* value indicates a more pronounced green, and a larger a* value indicates a more pronounced red. b* represents yellow-blue value; a smaller b* value indicates a more pronounced blue, and a larger b* value indicates a more pronounced yellow.

[0087] 2. Chlorophyll content

[0088] Chlorophyll content was determined using a colorimetric method. 0.5g of sample leaf was accurately weighed, and a small amount of quartz sand, calcium carbonate powder, and 2-3ml of 95% ethanol were added. The mixture was ground into a homogeneous slurry, then 10ml of ethanol was added, and grinding continued until the tissue turned white. The slurry was filtered into a 25ml brown volumetric flask. Using 95% ethanol as a blank, absorbance was measured at 665nm and 649nm. Each sample was tested in triplicate, and data are expressed as mean ± standard deviation.

Claims

1. A method for protecting the green color of leafy green vegetables with fillings, characterized in that, Includes the following steps: (1) Initial processing of vegetables: After washing the fresh green leafy vegetables, remove the roots and yellow leaves; (2) Light pretreatment: The leafy green vegetables initially treated in step (1) are placed in a lighting system that provides ultraviolet C-rays, low-intensity pulsed white light, and green light. The low-intensity pulsed white light and green light are provided by fluorescent lamps, and the ultraviolet C-rays are provided by unfiltered bactericide-emitting lamps. A filter is placed between the fluorescent lamps and the leafy green vegetables to irradiate them with green light. The intensity of the low-intensity pulsed white light and green light is 20–25 μmol / m². 2 s 1 Each irradiation lasts 1.5-3 hours, and each irradiation with ultraviolet C rays lasts 4-8 minutes. The wavelength of ultraviolet C rays is 254nm. Low-intensity pulsed white light and green light are alternated with ultraviolet C rays, and the total irradiation time of the two is 8-10 hours. (3) Ultrasonic heat treatment: The green leafy vegetables after the light pretreatment in step (2) are immersed in an ultrasonic bath, and the temperature and time of the ultrasound are designed for enzyme inactivation treatment; the ultrasonic heat treatment conditions are: the ultrasonic frequency is dual frequency 40-60kHz, the amplitude is 90%-95%, the temperature is 85-90℃, and the time is 60-150s. (4) Encapsulation: The green leafy vegetables obtained by ultrasonic heat treatment in step (3) are soaked in the prepared maltodextrin and sodium caseinate encapsulation solution, then removed and dried; the maltodextrin and sodium caseinate are dissolved in deionized water and stirred at room temperature for 3-4 hours to dissolve evenly; the mixed solution is placed in a refrigerator at 4°C overnight to allow the polymer molecules to be completely hydrated to obtain a hydrated wall material solution; then 1-2% w / v Tween 80 is added to the hydrated wall material solution and stirred vigorously at room temperature to dissolve completely to obtain the maltodextrin and sodium caseinate encapsulation solution; (5) Filling preparation: Cut the dried green leafy vegetables from step (4) into granules, add genetically modified soybean oil, salt, monosodium glutamate and white sugar seasoning to make filling, and then steam it; (6) Packaging and refrigeration: The semi-finished product in step (5) is packaged in a retort pouch filled with nitrogen and sealed. After sterilization, it is refrigerated at 4°C. (7) Reheating: After the water boils, reheat it.

2. The greening composite method for leafy green vegetables with fillings according to claim 1, characterized in that, In step (4), the maltodextrin in the maltodextrin and sodium caseinate encapsulation solution has a mass fraction of 2%-6%, and the sodium caseinate in the maltodextrin and sodium caseinate encapsulation solution has a mass fraction of 1%-3%.

3. The greening composite method for leafy green vegetables with fillings according to claim 1, characterized in that, The soaking time for leafy green vegetables in maltodextrin and sodium caseinate encapsulation solution is 60-90 minutes.

4. The greening composite method for leafy green vegetables with fillings according to claim 1, characterized in that, In step (5), leafy green vegetables are cut into 0.5-1mm particles. Based on 100 parts of leafy green vegetables, the weight ratio of genetically modified soybean oil, edible salt, monosodium glutamate and white sugar seasoning is (6~8):(2~4):(0.4~0.6):(5~7). The steaming time is 3-5 minutes.

5. The greening composite method for leafy green vegetables with fillings according to claim 1, characterized in that, In step (6), the retort bag is made of polyamide / polypropylene composite material.

6. The greening composite method for leafy green vegetables with fillings according to claim 1, characterized in that, In step (6), a vacuum must be drawn before nitrogen filling and packaging, with nitrogen purity of 99.9% or higher; in step (7), the re-evaporation time is 4-6 minutes.

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