A dry processing method of purple leaf mustard with high anthocyanin retention rate

Abstract

The application discloses a high anthocyanin retention rate dry processing method of purple leaf mustard, and comprises the following steps: (1) anthocyanin antioxidant color protection pretreatment of purple leaf mustard: fresh purple leaf mustard is selected, washed with clean water, and then surface water is drained, and then an oil-in-water emulsion of a vitamin compound antioxidant is sprayed on the surface of the purple leaf mustard; (2) blanching and drying integrated treatment of the purple leaf mustard: the purple leaf mustard subjected to the anthocyanin antioxidant color protection pretreatment is placed on a screen, and then placed in a convection hot air in an electric heating air drying oven to blanch the purple leaf mustard with a center temperature greater than or equal to 85 DEG C; then the hot air is discharged, and the temperature in the drying oven is lowered to dry the purple leaf mustard. The anthocyanin retention rate of the purple leaf mustard dry product obtained by the method can reach more than 90%.

Description

Technical Field

[0001] This invention relates to a vegetable processing method, and more particularly to a method for processing dried purple mustard greens with high anthocyanin retention rate. Background Technology

[0002] Mustard greens (Brassica juncea) are a plant belonging to the Brassicaceae family and the Brassica genus. They are an important specialty vegetable in my country, consumed fresh and processed. Mustard greens are highly nutritious, rich in various amino acids, minerals, dietary fiber, soluble sugars, and vitamin C, polyphenols, flavonoids, and other nutrients and bioactive components. They offer a variety of physiological benefits, including boosting immunity, maintaining cardiovascular health, promoting intestinal motility, preventing constipation, and lowering cholesterol and blood sugar levels.

[0003] Besides the common green mustard greens, purple mustard greens have also entered the consumer market in recent years. Purple mustard greens have an anthocyanin layer evenly distributed on both the upper and lower epidermis of their leaves, giving them their purple color. Anthocyanins are secondary metabolites in plants and possess various functional activities such as anti-oxidation, anti-inflammatory and anti-allergic effects, regulating blood lipids, enhancing blood vessel elasticity, improving the circulatory system, anti-tumor effects, and delaying aging. Therefore, compared to green mustard greens, purple mustard greens offer a wider range of health benefits.

[0004] Dried vegetables are a common processed vegetable product. The drying process significantly reduces the water content and increases the solids content of vegetables, effectively inhibiting microbial growth and enzyme activity, greatly extending the shelf life of vegetables at room temperature. Simultaneously, the significantly reduced volume and weight of dried vegetables make them easier to transport. Furthermore, after being pulverized, dried vegetables can be used in aleurone-based nutritional foods, Chinese pastries, baked goods, and cold drinks, making them a highly adaptable raw material for food processing. Therefore, processing fresh purple mustard greens into dried purple mustard greens is an effective way to improve their economic benefits and contribute to enriching the food market.

[0005] The existing vegetable drying process includes two processing units: blanching pretreatment and drying treatment. Although drying treatment is the main processing unit, blanching is also an important pretreatment unit for vegetable drying. It can effectively kill the activity of biological enzymes such as polyphenol oxidase and peroxidase in fresh vegetables, reduce the respiration rate, inhibit enzymatic browning of vegetables during the drying process, and reduce nutrient loss. It can also remove air from the vegetable tissue, delay the oxidation of its nutrient-active components during the drying process, and reduce the number of microorganisms on the surface of vegetables, thus improving food safety.

[0006] Existing blanching pretreatment methods include traditional hot water and steam blanching, and newer methods such as gas jet impact, microwave, infrared, and radio frequency blanching. Traditional blanching methods are the most widely used in industry. Hot water blanching provides uniform heating and is simple to operate, requiring no complex equipment, but it can lead to significant loss of water-soluble nutrients and active ingredients, softening of the texture, and environmental problems related to wastewater treatment. Steam blanching is beneficial for nutrient retention and texture maintenance, but it suffers from uneven heating and high energy consumption. New blanching technologies have begun to be applied in recent years, but they have not yet been widely adopted, mainly due to high equipment investment and difficulty in controlling process parameters. Among them, gas jet impact blanching is highly efficient and produces excellent quality, but the equipment is complex and can easily lead to excessive surface drying. Microwave blanching is instantaneously efficient and results in minimal nutrient loss, but it suffers from uneven heating and limited penetration. Infrared blanching has strong surface treatment capabilities and is energy-saving, but its penetration is weak and can easily cause surface burns. Radio frequency blanching has strong penetration and uniform heating, making it suitable for continuous production, but the equipment is expensive and the technical parameters are difficult to set.

[0007] The main drying methods for processed dried vegetables include natural sun-drying, hot air drying, microwave drying, and vacuum freeze-drying. Currently, traditional natural sun-drying and hot air drying remain the primary methods used in the domestic agricultural product processing industry for dried vegetable processing. Natural sun-drying is low-cost but highly susceptible to weather conditions, time-consuming, and results in significant nutrient loss and unstable product quality. Hot air drying is currently the most common and economical method in industrialized dried vegetable processing, but it faces problems such as a decline in the color, aroma, and sensory quality of vegetables due to high temperatures, as well as the loss of heat-sensitive nutrients and active ingredients. Newer technologies such as microwave drying and vacuum freeze-drying have not yet been widely applied in the dried vegetable processing industry. While microwave drying has seen advancements in equipment technology, it suffers from uneven heating and surface charring, affecting the product's edibility and nutrient retention. Vacuum freeze-drying, while better preserving the color, aroma, flavor, and nutrients and active ingredients of vegetables, significantly increases product brittleness and alters textural properties. Furthermore, its high equipment investment, energy consumption, and production costs limit its widespread adoption in the industrialized production of dried vegetables.

[0008] In general, traditional methods for processing dried vegetables are mature but prone to nutrient loss and quality decline, and are inefficient and environmentally unfriendly. New technologies have advantages in energy saving and quality improvement, but they also have technical bottlenecks, high costs, and complex process control, making it difficult to replace traditional processes. Therefore, in practical applications, it is necessary to select and optimize the appropriate processing methods according to the material characteristics of different types of vegetables and different product quality requirements. The processing methods for different types of dried vegetables and different quality requirements cannot be substituted for each other.

[0009] Purple mustard greens are rich in anthocyanins. Natural anthocyanins are not only easily soluble in water and lost, but also have poor stability and are easily oxidized. They are prone to degradation and fading under high temperature, alkaline conditions, ultraviolet radiation, and long-term light exposure. Reducing anthocyanin loss, maintaining anthocyanin stability, and improving anthocyanin retention are key issues that need to be addressed in the processing of dried purple mustard greens. The existing blanching methods and other drying methods besides freeze-drying all easily cause anthocyanin loss in purple mustard greens. In particular, the widely used traditional blanching and drying methods are even more detrimental to the retention and stability of anthocyanins in dried purple mustard greens.

[0010] This invention provides a method for processing dried purple mustard greens that effectively protects anthocyanins, thereby improving the anthocyanin retention rate. Furthermore, this method combines the blanching pretreatment and drying processes, achieving integrated blanching and drying operations and significantly improving production efficiency. In particular, it can utilize conventional drying equipment, resulting in low production costs and easy application, providing a new pathway for the high-value, intensive processing of purple mustard greens. Summary of the Invention

[0011] The purpose of this invention is to provide a processing method for dried purple mustard greens that can retain a large amount of anthocyanins from fresh purple mustard greens, with a high anthocyanin retention rate.

[0012] The objective of this invention is achieved through the following technical means: a processing method for dried purple mustard greens, comprising the following steps:

[0013] (1) Pretreatment of purple mustard greens with anthocyanins for antioxidant and color protection

[0014] Select fresh purple mustard greens, wash them with clean water and hang them to drain the surface moisture. Then, spray the surface of the purple mustard greens with a water-in-oil (O / W) emulsion of vitamin complex antioxidants to complete the anthocyanin antioxidant and color protection pretreatment of purple mustard greens.

[0015] (2) Integrated blanching and drying process for purple leaf mustard greens

[0016] Purple mustard greens that have undergone anthocyanin antioxidant and color-protecting pretreatment are spread on a sieve and then placed in a hot air convection drying oven to blanch them at a center temperature ≥85℃. The hot air is then exhausted, and the temperature inside the drying oven is lowered to dry the purple mustard greens. This process yields dried purple mustard greens with a high anthocyanin retention rate, exceeding 90%.

[0017] The optimized method involves atomizing the vitamin complex antioxidant emulsion in water for 5-10 minutes until the emulsion evenly covers the surface of the purple mustard leaves.

[0018] Furthermore, the preparation process of the emulsion is as follows:

[0019] ① Preparation of aqueous phase of emulsion: Weigh an appropriate amount of sodium caseinate and prepare a sodium caseinate solution with a mass fraction (unless otherwise specified, all concentrations below are mass fractions) of 2.0~2.5% with room temperature purified water. Then add a certain amount of vitamin C and stir gently to dissolve it, so that the concentration of vitamin C in the above solution reaches 0.10~0.15%. Control the pH of the mixture at 5.5~5.8, which is higher than the isoelectric point of sodium caseinate (pI≈4.6). This can avoid flocculation and precipitation caused by charge neutralization near the isoelectric point, thereby ensuring its interfacial adsorption and stabilizing effect as an emulsifier in O / W emulsions. The amount of VC added is such that it provides a certain amount of VC with antioxidant activity in the system, and also keeps the pH of the aqueous phase away from the isoelectric point of sodium caseinate, thus balancing the functionality of VC and the emulsion stability; ② Preparation of the oil phase of the emulsion: Weigh an appropriate amount of VE and dissolve it in edible vegetable oil (corn oil, soybean oil, rapeseed oil, peanut oil, etc. are all acceptable) to prepare a vegetable oil solution with a VE concentration of 0.5~1.0%; ③ Emulsification: According to the mass ratio of 1 part of the oil phase to 9 parts of the aqueous phase, slowly add the above emulsion oil phase to the aqueous phase and mix evenly. Then, place it in a shear homogenizer and a high-pressure homogenizer for homogenization treatment to obtain the VC / VE complex vitamin O / W emulsion. The average droplet size of the VC / VE complex vitamin O / W emulsion is 100~300 nm, which is a nanoemulsion, as determined by a laser particle size analyzer.

[0020] The optimized method involves first homogenizing the sample in a shear homogenizer at 6000–8000 r / min for 3–5 min, followed by high-pressure homogenization at 60–100 MPa 2–3 times.

[0021] The optimized method involves spreading purple mustard greens on a sieve and then placing them in an electric heating drying oven preheated to 95-100°C, where they are kept in convective hot air for 2-5 minutes. The convective hot air is provided by the circulating fan of the electric heating drying oven and the temperature inside the oven is maintained at 95-100°C by electric heating.

[0022] The optimized drying process involves lowering the temperature inside the drying chamber to 50-60°C to dry the purple mustard greens, maintaining this temperature and continuously blowing air until the moisture content of the purple mustard greens drops to 8-10%.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] 1. In the pretreatment process of anthocyanin antioxidant color protection in purple mustard, the vitamin complex antioxidant O / W emulsion is atomized and sprayed onto the purple mustard. The atomized spraying method replaces the traditional soaking method, which significantly reduces the dissolution loss of anthocyanins in the aqueous phase and effectively improves the anthocyanin retention rate.

[0025] 2. Vitamin C and Vitamin E, which have both nutritional fortification and antioxidant functions, were combined to prepare an O / W type composite antioxidant emulsion for anthocyanin protection during the processing of purple mustard greens. This achieved multiple beneficial effects: ① Utilizing the synergistic antioxidant mechanism of VC and VE, VE preferentially captures free radicals and is then oxidized, while VC reduces and regenerates them, resulting in a cyclical synergistic effect that significantly prolongs the duration of antioxidant activity. The anthocyanin protection effect is superior to that of VC or VE used alone; ② An O / W emulsion biphase delivery system was constructed, dispersing water-soluble VC in the aqueous phase and fat-soluble VE in the oil phase, enabling the stable coexistence and simultaneous application of two antioxidants with different properties in the same system, simplifying the process; ③ By leveraging the interfacial activity of the emulsifier, the spreadability, wettability, and permeability of the emulsion droplets on hydrophobic leaf surfaces were improved, prolonging the residence time on the liquid surface and promoting the penetration of VC and VE into the leaf mesophyll tissue, further enhancing the anthocyanin protection effect.

[0026] 3. Using sodium caseinate, a natural protein, to replace synthetic emulsifiers to prepare a VC / VE complex vitamin O / W emulsion for the protection of anthocyanins in purple mustard greens not only avoids the food safety risks caused by synthetic emulsifiers, but also enhances the nutritional value of dried purple mustard greens.

[0027] 4. The integrated blanching and drying process for purple-leaf mustard greens achieves the following beneficial effects: ① Replacing traditional hot water and steam blanching with high-temperature hot air avoids the loss of anthocyanins and other water-soluble nutrients and active ingredients by dissolving in the blanching hot water and steam condensate, and eliminates the generation of blanching wastewater. This not only improves the anthocyanin retention rate but also meets the requirements of green and clean production. ② By adjusting the process parameters, the high-temperature hot air is quickly converted to medium-low temperature drying conditions after a short period of treatment. Blanching and drying can be continuously completed in the same blower drying equipment, simplifying the process operation unit, reducing energy consumption, and reducing the thermal degradation of anthocyanins caused by high-temperature drying by maintaining medium-low temperature drying conditions, thereby improving the anthocyanin retention rate and nutritional quality of dried purple-leaf mustard greens.

[0028] 5. Compared with processes using new equipment such as gas jet impact, microwave, infrared, radio frequency scalding or microwave, vacuum freeze drying, the present invention only requires conventional electric heating blower drying equipment to achieve integrated scalding and drying, which significantly reduces equipment investment and production costs and facilitates promotion and application. Detailed Implementation

[0029] Example 1

[0030] To prepare a type of dried purple mustard greens with high anthocyanin retention rate, follow these steps:

[0031] 1. Preparation of water-in-oil (O / W) emulsion of vitamin complex antioxidant

[0032] The vitamin complex antioxidant O / W emulsion used in this invention is a VC / VE complex vitamin O / W emulsion, using sodium caseinate, a natural protein with good emulsifying properties, as the emulsifier. The preparation method is as follows: ① Emulsion aqueous phase preparation: Weigh an appropriate amount of sodium caseinate and prepare a 2.2% sodium caseinate solution with room temperature purified water. Then add a certain amount of VC and stir gently to dissolve it, so that the VC concentration in the above solution reaches 0.12%. ② Emulsion oil phase preparation: Weigh an appropriate amount of VE and dissolve it in corn oil to prepare a corn oil solution with a VE concentration of 0.8%. ③ Emulsification: According to a mass ratio of 1:9, slowly add the above emulsion oil phase to the aqueous phase, mix evenly, and then place it in a shear homogenizer at 7000 r / min for 4 min. Then, it is homogenized three times under high pressure at 70 MPa to obtain the VC / VE complex vitamin O / W emulsion. The average particle size of the emulsion droplets was measured by a laser particle size analyzer to be 220±5.0 nm, which is a nanoemulsion.

[0033] 2. Anthocyanin Antioxidant and Color-Protecting Pretreatment of Purple Leaf Mustard

[0034] Select fresh purple mustard greens that are free from rot and pests, wash them with running water and hang them to drain. Then, spray the above-mentioned vitamin complex antioxidant O / W emulsion onto the surface of the purple mustard greens using a medical nebulizer for 8 minutes until the emulsion evenly covers the surface of the purple mustard green leaves.

[0035] 3. Integrated blanching and drying process for purple-leaf mustard greens

[0036] The purple mustard greens, having undergone the anthocyanin antioxidant and color-protecting pretreatment, were quickly and evenly spread on a sieve and then placed in an electrically heated drying oven preheated to 98°C. The oven fan was turned on, and the temperature was maintained by electric heating for 4 minutes in forced convection hot air until the core temperature of the purple mustard greens reached 86°C. This process killed the activity of enzymes such as polyphenol oxidase and peroxidase in the fresh mustard greens, achieving the purpose of hot air blanching. Subsequently, the hot air was quickly discharged, and the temperature inside the drying oven was lowered to 55°C to enter the drying stage of the purple mustard greens. This temperature was maintained, and the air was continuously blown until the moisture content of the purple mustard greens dropped to 8.5%, resulting in dried purple mustard greens with a high anthocyanin retention rate of 93.16±2.63%.

[0037] Example 2

[0038] To prepare a type of dried purple mustard greens with high anthocyanin retention rate, follow these steps:

[0039] 1. Preparation of water-in-oil (O / W) emulsion of vitamin complex antioxidant

[0040] The vitamin complex antioxidant O / W emulsion used in this invention is a VC / VE complex vitamin O / W emulsion, using sodium caseinate, a natural protein with good emulsifying properties, as the emulsifier. The preparation method is as follows: ① Emulsion aqueous phase preparation: Weigh an appropriate amount of sodium caseinate and prepare a 2.5% sodium caseinate solution with room temperature purified water. Then add a certain amount of VC and stir gently to dissolve it, so that the VC concentration in the above solution reaches 0.10%. ② Emulsion oil phase preparation: Weigh an appropriate amount of VE and dissolve it in rapeseed oil to prepare a rapeseed oil solution with a VE concentration of 0.5%. ③ Emulsification: According to a mass ratio of 1:9, slowly add the above emulsion oil phase to the aqueous phase, mix evenly, and then place it in a shear homogenizer at 8000 r / min for 3 min. Then, homogenize it twice under high pressure at 100 MPa to obtain the VC / VE complex vitamin O / W emulsion. The average particle size of the emulsion droplets was measured by a laser particle size analyzer to be 180±6.0 nm, which is a nanoemulsion.

[0041] 2. Anthocyanin Antioxidant and Color-Protecting Pretreatment of Purple Leaf Mustard

[0042] Select fresh purple mustard greens that are free from rot and pests, wash them with running water, hang them to drain the surface moisture, and then spray the above-mentioned vitamin complex antioxidant O / W emulsion onto the surface of the purple mustard greens using a medical nebulizer. The spraying time is 10 minutes, until the emulsion evenly covers the surface of the purple mustard green leaves.

[0043] 3. Integrated blanching and drying process for purple-leaf mustard greens

[0044] The purple mustard greens, having undergone the anthocyanin antioxidant and color-protecting pretreatment, were quickly and evenly spread on a sieve and then placed in an electrically heated drying oven preheated to 95°C. The oven fan was turned on, and the temperature was maintained by electric heating for 5 minutes in forced convection hot air until the core temperature reached 88°C. This process killed the activity of enzymes such as polyphenol oxidase and peroxidase in the fresh mustard greens, achieving the purpose of hot air blanching. Subsequently, the hot air was quickly discharged, and the temperature inside the drying oven was lowered to 50°C to enter the drying stage of the purple mustard greens. This temperature was maintained, and the air was continuously blown until the moisture content of the purple mustard greens dropped to 9.2%, resulting in dried purple mustard greens with a high anthocyanin retention rate of 93.82±2.71%.

[0045] Example 3

[0046] To prepare a type of dried purple mustard greens with high anthocyanin retention rate, follow these steps:

[0047] 1. Preparation of water-in-oil (O / W) emulsion of vitamin complex antioxidant

[0048] The vitamin complex antioxidant O / W emulsion used in this invention is a VC / VE complex vitamin O / W emulsion, using sodium caseinate, a natural protein with good emulsifying properties, as the emulsifier. The preparation method is as follows: ① Emulsion aqueous phase preparation: Weigh an appropriate amount of sodium caseinate and prepare a 2.0% sodium caseinate solution with room temperature purified water. Then add a certain amount of VC and stir gently to dissolve it, so that the VC concentration in the above solution reaches 0.15%. ② Emulsion oil phase preparation: Weigh an appropriate amount of VE and dissolve it in soybean oil to prepare a soybean oil solution with a VE concentration of 0.9%. ③ Emulsification: At a mass ratio of 1:9, slowly add the above emulsion oil phase to the aqueous phase, mix evenly, and then place it in a shear homogenizer at 6500 r / min for 5 min. Then, homogenize it three times under high pressure at 60 MPa to obtain the VC / VE complex vitamin O / W emulsion. The average particle size of the emulsion droplets was measured by a laser particle size analyzer to be 260±8.0 nm, which is a nanoemulsion.

[0049] 2. Anthocyanin Antioxidant and Color-Protecting Pretreatment of Purple Leaf Mustard

[0050] Select fresh purple mustard greens that are free from rot and pests, wash them with running water, hang them to drain the surface moisture, and then spray the above-mentioned vitamin complex antioxidant O / W emulsion onto the surface of the purple mustard greens using a medical nebulizer. The spraying time is 6 minutes, until the emulsion evenly covers the surface of the purple mustard green leaves.

[0051] 3. Integrated blanching and drying process for purple-leaf mustard greens

[0052] The purple mustard greens, having undergone the anthocyanin antioxidant and color-protecting pretreatment, were quickly and evenly spread on a sieve and then placed in an electrically heated drying oven preheated to 100°C. The oven fan was turned on, and the temperature was maintained by electric heating for 3 minutes in forced convection hot air until the core temperature reached 90°C. This process killed the activity of polyphenol oxidase, peroxidase, and other biological enzymes in the fresh mustard greens, achieving the purpose of hot air blanching. Subsequently, the hot air was quickly discharged, and the temperature inside the drying oven was lowered to 60°C to enter the drying stage of the purple mustard greens. This temperature was maintained, and the air was continuously blown until the moisture content of the purple mustard greens dropped to 8.1%, resulting in dried purple mustard greens with a high anthocyanin retention rate of 92.03±1.97%.

[0053] Experimental Example 1

[0054] To investigate the effectiveness of the vitamin complex antioxidant O / W emulsion atomization spraying method of the present invention in improving the anthocyanin retention rate of purple mustard, in the experiment of Example 1, a control group (hereinafter referred to as the soaking control group) was set up to be treated with vitamin complex antioxidant O / W emulsion soaking. The soaking time was the same as the spraying time in Example 1, and other treatment conditions were the same as in Example 1. Purple mustard dried with the same degree of dryness (moisture content) was prepared, and its subsequent drying time and anthocyanin retention rate were investigated. The results are shown in Table 1.

[0055] Table 1

[0056] Drying time (min) 310 420 Anthocyanin retention rate (%) 93.16±2.63 68.42±1.85

[0057] As shown in Table 1, the anthocyanin retention rate in the soaking control group was only 68.42±1.85%, while the subsequent drying time for the purple mustard greens with the same degree of dryness (moisture content) as in Example 1 was 420 min. This indicates that soaking increased the dissolution loss of anthocyanins in the aqueous phase and also promoted the absorption of water by the purple mustard greens, leading to a prolonged drying time and exacerbating anthocyanin degradation. The results in Table 1 demonstrate that the composite antioxidant O / W emulsion atomization spraying method significantly improved the anthocyanin retention rate of purple mustard greens, increasing it by 24.74% compared to the soaking treatment.

[0058] Experimental Example 2

[0059] To investigate the effectiveness of the vitamin complex antioxidant O / W emulsion of the present invention in synergistic antioxidant protection of anthocyanins in purple mustard, in the experiment of Example 1, O / W emulsions with no added VC, no added VE, and no added VC and VE were prepared for the pretreatment of purple mustard. Other treatment conditions were the same as in Example 1. Dry control samples of purple mustard with the same degree of drying (moisture content) were prepared to investigate their anthocyanin retention rate. The results are shown in Table 2.

[0060] Table 2

[0061] Anthocyanin retention rate (%) 93.16±2.63 75.31±1.92% 81.27±1.84% 62.74±1.56

[0062] As shown in Table 2, the anthocyanin retention rate was lowest when purple mustard greens were pretreated with an O / W emulsion without the addition of VC and VE. Pretreatment with O / W emulsions containing VC or VE improved the anthocyanin retention rate, indicating that VC and VE have a certain antioxidant protective effect on the anthocyanins of purple mustard greens. However, the anthocyanin retention rates of these two control samples were still significantly lower than those of Example 1 of this invention, indicating that Example 1 significantly improved the anthocyanin retention rate of purple mustard greens through the synergistic effect of VC and VE.

[0063] The anthocyanin retention rate in the above embodiments and experimental examples was obtained by the following determination and calculation methods: the anthocyanin content of fresh purple leaf mustard raw material and dried purple leaf mustard was determined by pH differential method (both on a dry basis). The anthocyanin retention rate was calculated by dividing the anthocyanin content of dried purple leaf mustard by the anthocyanin content of fresh purple leaf mustard raw material as a percentage. The average value was taken after three repeated experiments.

[0064] The above examples illustrate different implementation processes of the present invention in detail. However, the implementation methods of the present invention are not limited thereto. Those skilled in the art can achieve the purpose of the present invention based on the content disclosed in the present invention. Any improvements and modifications made based on the concept of the present invention fall within the protection scope of the present invention. The specific protection scope is subject to the claims.

Claims

1. A method for processing dried purple mustard greens with high anthocyanin retention rate, characterized in that... Includes the following steps: (1) Pretreatment of purple mustard greens with anthocyanins for antioxidant and color protection Select fresh purple mustard greens, wash them with clean water and drain the surface water, then spray the surface of the purple mustard greens with a water-in-oil emulsion of vitamin complex antioxidants. (2) Integrated blanching and drying process for purple leaf mustard greens The purple mustard greens that have undergone anthocyanin antioxidant and color-protecting pretreatment are spread on a sieve and then placed in a hot air convection drying oven to blanch them at a center temperature ≥85℃. After that, the hot air is discharged and the temperature inside the drying oven is lowered to dry the purple mustard greens.

2. The processing method for dried purple mustard greens with high anthocyanin retention rate according to claim 1, characterized in that: The vitamin complex antioxidant water-in-oil emulsion is atomized and sprayed for 5-10 minutes until the emulsion evenly covers the surface of the purple mustard leaves.

3. A method for processing dried purple mustard greens with high anthocyanin retention rate according to claim 1 or 2, characterized in that: The preparation process of the vitamin complex antioxidant water-in-oil emulsion is as follows: ① Prepare a sodium caseinate solution with a mass percentage of 2.0~2.5% using room temperature purified water, then add vitamin C and stir gently to dissolve it, so that the mass percentage concentration of vitamin C in the sodium caseinate solution reaches 0.10~0.15%. Control the pH of the mixture at 5.5~5.8 to obtain the emulsion aqueous phase. ② Dissolve vitamin E in edible vegetable oil to obtain a vegetable oil solution with a vitamin E mass percentage concentration of 0.5~1.0%, and prepare an emulsion oil phase; ③ Add the above oil phase to the water phase at a mass ratio of 1 part oil phase to 9 parts water phase, mix evenly, and then place the mixture in a shear homogenizer and a high-pressure homogenizer for homogenization to obtain the vitamin complex antioxidant water-in-oil emulsion.

4. The processing method for dried purple mustard greens with high anthocyanin retention rate according to claim 3, characterized in that: First, place the sample in a shear homogenizer and shear homogenize it at 6000-8000 r / min for 3-5 min, then homogenize it in a high-pressure homogenizer at 60-100 MPa 2-3 times.

5. The processing method for dried purple mustard greens with high anthocyanin retention rate according to claim 3, characterized in that: The edible vegetable oil is corn oil, soybean oil, rapeseed oil, or peanut oil.

6. The processing method for dried purple mustard greens with high anthocyanin retention rate according to claim 1, characterized in that: Spread the purple mustard greens on a sieve and then place them in an electric hot air drying oven preheated to 95-100℃, and keep them in the convective hot air for 2-5 minutes.

7. The processing method for dried purple mustard greens with high anthocyanin retention rate according to claim 6, characterized in that: The convective hot air is provided by the circulating fan of the electric heating drying oven, and the temperature inside the oven is maintained at 95-100°C by electric heating.

8. The processing method for dried purple mustard greens with high anthocyanin retention rate according to claim 1, characterized in that: The temperature inside the drying chamber is lowered to 50-60℃ to dry the purple mustard greens. This temperature is maintained and air is continuously blown in until the moisture content of the purple mustard greens drops to 8-10%.