Dragon fruit flower dry powder and microwave and hot air drying combined preparation method thereof

Abstract

The invention discloses pitaya flower dry powder and a preparation method of the pitaya flower dry powder by combining microwaves with hot air drying. The preparation method comprises the following steps: chopping fresh pitaya flowers, carrying out microwave and oven drying treatment, and crushing the dried pitaya flowers to obtain dried pitaya flower powder. Compared with a traditional drying mode, the fresh pitaya flowers are dried through the microwave and hot air combined drying technology, the drying efficiency of the pitaya flowers is greatly improved, enzymes in the pitaya flowers are rapidly inactivated, and the flavor and quality of the product are improved. According to the method, microwave treatment time and microwave power are taken as test factors, polyphenol content, carotenoid content and vitamin E content in the pitaya flowers are taken as evaluation indexes, and the optimal process conditions for microwave and hot air combined drying of the pitaya flowers are as follows: the microwave treatment time is 8 minutes, the microwave power is 1260 W, the total phenol content is 3.30 mg GAE / g DW, and the total phenol content is 3.30 mg GAE / g DW. The content of phenolic substances identified by high performance liquid chromatography is 5.74 mg / g DW, the content of total carotenoids is 24.89 mu g / g DW, and the content of total vitamin E is 33.58 mu g / g DW.

Description

Technical Field

[0001] The present invention relates to the technical field of pitaya flower drying, and particularly relates to a pitaya flower dry powder and a preparation method thereof by combining microwave and hot air drying. Background Art

[0002] The pitaya flower, also known as the Hylocereus undatus Britt. & Rose flower, is the flower of Hylocereus undatus Britt. & Rose of the genus Hylocereus in the family Cactaceae.

[0003] The single pitaya flower weighs about 250 g, with a funnel-shaped flower type, white petaloid perianth segments, and yellowish-green flower buds.

[0004] During the cultivation of pitaya, each branch can grow more than a dozen flowers. To enable the plant to grow better and produce high-quality fruits, it is necessary to thin the flowers of the pitaya plant, remove the excess flower buds, and retain 1 - 2 flowers on each branch, thus generating a large amount of agricultural waste.

[0005] The pitaya flower has a sweet fragrance and delicious taste. It is often used for making soup or tea in South China. It is rich in nutritional and medicinal components, including amino acids, polysaccharides, polyphenols, vitamins, saponins, and trace elements, and has functions such as relieving cough and reducing phlegm, clearing heat and moistening the lungs, anti-inflammatory, antioxidant, regulating the intestinal flora, and immune regulation.

[0006] The pitaya flower is a veritable natural health food. However, due to the high water content of fresh flowers, it is not conducive to storage, transportation, and processing. Drying has become a common preservation method for pitaya flowers, and the drying method and conditions are the main factors affecting the quality of pitaya flowers.

[0007] Currently, there are two common types of flower drying technologies, such as microwave drying and hot air drying. Although each has its own advantages, there are certain defects and deficiencies when operating alone. However, if the process parameters cannot be well controlled when the two processes are combined, not only the expected quality improvement effect cannot be achieved, but the quality will even decline. Therefore, when technicians in this field perform flower drying treatment, they usually use microwave drying or hot air drying alone.

[0008] The microwave radiation generated during microwave drying causes rapid internal heating of the flowers, greatly improving the drying efficiency, quickly inactivating the enzymes in the pitaya flowers, and improving the flavor and quality of the products. The disadvantage is that the process parameters of microwave treatment need to be strictly controlled. If the treatment time is too long, it will affect the sensory quality of the pitaya flowers.

[0009] The technology of drying pitaya flowers by hot air has the advantages of simple operation, large production capacity, and low cost, but it also has defects such as long processing time, low thermal efficiency, difficulty in removing internal moisture, and difficulty in controlling other conditions.

[0010] However, how to organically integrate the two drying processes, overcome the disadvantages of the two processes when used alone, and at the same time accelerate the drying efficiency, improve the flavor and quality of the product, and make the operation simple and easy to implement are issues that need to be studied and solved.

[0011] In the existing technical inventions regarding the drying of pitaya flowers, the evaluation indicators are usually sensory quality, rehydration ability, and Vc retention rate, lacking the evaluation of the content of active ingredients in pitaya flowers.

[0012] Therefore, in view of the above problems, it is necessary to propose a preparation process for drying pitaya flowers by combining microwave and hot air drying, with the content of polyphenols, carotenoids, and vitamin E in pitaya flowers as the evaluation indicators. Summary of the Invention

[0013] The purpose of the present invention is to solve the disadvantages and deficiencies existing when the existing drying processes are used alone, and to provide a dry powder of pitaya flowers with simple and easy operation, high drying efficiency, and high nutritional value of the product, as well as a preparation method by combining microwave and hot air drying.

[0014] The present invention is achieved through the following technical solutions:

[0015] A preparation method for dry powder of pitaya flowers by combining microwave and hot air drying, comprising the following steps:

[0016] S1: Screening and chopping the freshly collected pitaya flowers;

[0017] S2: Microwave drying the chopped pitaya flowers;

[0018] S3: Placing the microwave-treated pitaya flowers in an oven for drying;

[0019] S4: Crushing the dried pitaya flowers to obtain dry powder of pitaya flowers, and storing it sealed at room temperature.

[0020] In step S1, the screening and chopping means removing the diseased tissues of the freshly collected pitaya flowers and chopping them into petal fragments and / or granular forms; the petal fragments and / or granular forms mean chopping the pitaya flowers with removed diseased tissues into petal fragments with side lengths less than 0.5 cm and / or granular forms with particle sizes less than 0.5 cm.

[0021] In step S2, the microwave drying means spreading the pitaya flowers screened and chopped in step S1 on a microwave drying tray for microwave treatment. The microwave treatment parameters are: microwave power is 360 - 1260 W, and the microwave treatment time is 8 - 14 min.

[0022] The drying in step S3 means hot air drying at 75 - 80 °C for 15 - 20 h; the thickness of the pitaya flowers spread is 1 - 1.5 cm.

[0023] The origin of the pitaya flower described in step S1 is Guizhou Province.

[0024] The optimal power obtained from the single-factor experiment on microwave power in step S2 is 1260 W, and the optimal treatment time obtained from the single-factor experiment on microwave treatment time is 10 min; combining all the experimental results, the optimal conditions for microwave treatment are: 1260 W, 8 min.

[0025] Compared with the prior art, the present invention has the following advantages and effects:

[0026] The dry powder of the pitaya flower of the present invention is first treated with microwave and then immediately dried by oven heat. During the treatment process, by optimizing and controlling the key parameters, the drying processes of different principle types are organically connected and integrated, overcoming the disadvantages and deficiencies existing when the existing processes are used alone. In the dried sample of the pitaya flower prepared by the method of organic integration of the present invention, not only the polyphenol content has been greatly improved compared with the fresh sample, but also the carotenoid content and the vitamin E content have been greatly improved compared with the fresh sample.

[0027] The present invention organically integrates microwave drying and oven drying, overcoming the technical problem in the traditional process that when the two are combined, if the process parameters cannot be well controlled, not only the expected quality improvement effect cannot be achieved, but on the contrary, the quality will decline.

[0028] The preparation process of the present invention is simple and easy to operate, has strong operability, high drying efficiency, and good sensory quality.

[0029] Taking the microwave treatment time and microwave power as experimental factors, and the polyphenol content, carotenoid content and vitamin E content in the pitaya flower as evaluation indicators, the optimal process conditions for drying the pitaya flower by combining microwave and hot air are: microwave treatment time 8 min, microwave power 1260 W, the total phenol content is 3.30 mg GAE / g DW, the content of phenolic substances identified by high performance liquid chromatography is 5.74 mg / g DW, the total carotenoid content is 24.89 μg / g DW, and the total vitamin E content is 33.58 μg / g DW. Description of the Drawings

[0030] Figure 1 It is a graph showing the effect of microwave power on the total phenol content of pitaya flower; different letters on the bar graph indicate that the values are significantly different (p < 0.05).

[0031] Figure 2 It is a graph showing the effect of microwave treatment time on the total phenol content of pitaya flower; different letters on the bar graph indicate that the values are significantly different (p < 0.05). Detailed Embodiments

[0032] The present invention discloses a preparation method for dried pitaya flower powder by combining microwave and hot air drying. The present invention will be further described in detail with specific embodiments below.

[0033] Example 1:

[0034] Step (1): Remove the diseased tissues of the freshly collected pitaya flowers and chop them into petal fragments with side lengths less than 0.5 cm and particles with particle sizes less than 0.5 cm.

[0035] Step (2): Spread the chopped pitaya flowers on a microwave drying tray and perform microwave treatment. The microwave power is set to 360 W, and the microwave treatment time is 8 min.

[0036] Step (3): Place the microwave-treated pitaya flowers in an oven and dry them with hot air at 80 °C for 20 h.

[0037] Step (4): Grind the dried pitaya flowers to obtain dried pitaya flower powder, and store it sealed at room temperature.

[0038] Example 2:

[0039] Step (1): Remove the diseased tissues of the freshly collected pitaya flowers and chop them into petal fragments with side lengths less than 0.5 cm and particles with particle sizes less than 0.5 cm.

[0040] Step (2): Spread the chopped pitaya flowers on a microwave drying tray and perform microwave treatment. The microwave power is set to 900 W, and the microwave treatment time is 8 min.

[0041] Step (3): Place the microwave-treated pitaya flowers in an oven and dry them with hot air at 80 °C for 20 h.

[0042] Step (4): Grind the dried pitaya flowers to obtain dried pitaya flower powder, and store it sealed at room temperature.

[0043] Example 3:

[0044] Step (1): Remove the diseased tissues of the freshly collected pitaya flowers and chop them into petal fragments with side lengths less than 0.5 cm and particles with particle sizes less than 0.5 cm.

[0045] Step (2): Spread the chopped pitaya flowers on a microwave drying tray and perform microwave treatment. The microwave power is set to 1260 W, and the microwave treatment time is 8 min.

[0046] Step (3): Place the microwave-treated pitaya flowers in an oven and dry them with hot air at 80 °C for 20 h.

[0047] Step (4): Crush the dried pitaya flowers to obtain dried pitaya flower powder, and store it sealed at room temperature.

[0048] Example 4:

[0049] Step (1): Remove the diseased tissues of the freshly collected pitaya flowers and chop them into petal fragments with side lengths less than 0.5 cm and particles with particle sizes less than 0.5 cm;

[0050] Step (2): Spread the chopped pitaya flowers on a microwave drying tray and perform microwave treatment. The microwave power is set to 900 W, and the microwave treatment time is 10 min;

[0051] Step (3): Place the microwave-treated pitaya flowers in an oven and dry them with hot air at 80 °C for 20 h;

[0052] Step (4): Crush the dried pitaya flowers to obtain dried pitaya flower powder, and store it sealed at room temperature.

[0053] Example 5:

[0054] Step (1): Remove the diseased tissues of the freshly collected pitaya flowers and chop them into petal fragments with side lengths less than 0.5 cm and particles with particle sizes less than 0.5 cm;

[0055] Step (2): Spread the chopped pitaya flowers on a microwave drying tray and perform microwave treatment. The microwave power is set to 900 W, and the microwave treatment time is 12 min;

[0056] Step (3): Place the microwave-treated pitaya flowers in an oven and dry them with hot air at 80 °C for 20 h;

[0057] Step (4): Crush the dried pitaya flowers to obtain dried pitaya flower powder, and store it sealed at room temperature.

[0058] Example 6:

[0059] Step (1): Remove the diseased tissues of the freshly collected pitaya flowers and chop them into petal fragments with side lengths less than 0.5 cm and particles with particle sizes less than 0.5 cm;

[0060] Step (2): Spread the chopped pitaya flowers on a microwave drying tray and perform microwave treatment. The microwave power is set to 900 W, and the microwave treatment time is 14 min;

[0061] Step (3): Place the microwave-treated pitaya flowers in an oven and dry them with hot air at 80 °C for 20 h;

[0062] Step (4): Crush the dried pitaya flowers to obtain dried pitaya flower powder, and store it sealed at room temperature.

[0063] Extract polyphenols from the dried pitaya flower samples obtained by the preparation methods described in the above Examples 1-6. The specific method steps are as follows:

[0064] (1) Weigh 2 g of the dried pitaya flower powder sample;

[0065] (2) Add approximately 30 mL of 80% ice acetone solution (v / v) and extract;

[0066] (3) Perform ultrasonic thermal extraction, centrifuge, and take the supernatant;

[0067] (4) Vacuum-rotate and dry the supernatant with a rotary evaporator, make the volume up to 10 mL with methanol, and store it in a -20 °C refrigerator.

[0068] Determine the total phenolic content of the extracted polyphenols using the Folin-Ciocalteu colorimetric method. The specific method steps are as follows:

[0069] (1) Dissolve gallic acid with ultrapure water to prepare a standard stock solution (0 - 600 μg / mL);

[0070] (2) Respectively pipette 100 μL of the standard stock solution and the pitaya flower polyphenol extract into centrifuge tubes. Sequentially add 400 μL of ultrapure water and 100 μL of Folin-Ciocalteu reagent to all standards and samples, shake well, and let stand at room temperature for 6 min;

[0071] (3) After standing, add 1 mL of Na2CO3 solution (0.7%, w / v) and 0.8 mL of ultrapure water to the centrifuge tubes, mix well, and let stand for another 90 min;

[0072] (4) Detect the absorbance value of each sample at a wavelength of 760 nm;

[0073] (5) Draw a standard curve with the absorbance values of the standard stock solution samples, calculate the total phenolic content in the pitaya flower extract according to the standard curve, and express it in terms of gallic acid equivalents, which is expressed as: milligrams of gallic acid equivalent per gram of fresh weight of pitaya flower (mg gallic acid equivalents (GAE) / g flowers, dry weight: mg GAE / g DW).

[0074] Identify phenolic compounds in the pitaya flower extract using high-performance liquid chromatography (HPLC). The specific method steps are as follows:

[0075] (1) Filter the extract with a 0.22 μm organic phase filter membrane and dilute it to an appropriate concentration with methanol;

[0076] (2) The extract was detected using a high performance liquid chromatograph. In the experiment, a C18 column (4.6×250 mm, 5 μm, Waters, USA) was used for detection on a Waters 2998 detector; the mobile phase was: A: 0.1% trifluoroacetic acid aqueous solution (v / v), B: chromatographic grade acetonitrile. The detection wavelength was: 360 nm.

[0077] (3) The external standard method was used for qualitative and quantitative analysis of phenolic compounds. The experimental results were expressed as: the content of the chemical substances contained in milligrams per gram of dry weight of pitaya flower (mg / g DW).

[0078] Effect of microwave power on the total phenolic content and phenolic compounds in dried pitaya flower samples:

[0079] ① In the microwave treatment of pitaya flower, the microwave treatment time was fixed at 8 min, and the microwave powers were set at 360, 900, and 1260 W, with a total of 3 groups of samples, namely Example 1, Example 2, and Example 3. In addition, fresh samples were used as a control.

[0080] ② The results of the total phenols showed that the total phenolic content of the fresh sample extract was the highest, at 4.19±0.08 mg GAE / gDW. All treatments reduced the total phenolic content in pitaya flower. The average total phenolic content in the dried pitaya flower samples with different microwave power treatments was 3.23 mg GAE / g DW. Among them, the total phenolic content was the highest when the microwave power was 1260 W, at 3.30 mg GAE / gDW. The optimal microwave power was selected as 1260 W, as Figure 1 shown.

[0081] ③ The experimental results of HPLC detection of phenolic compounds in the pitaya flower extract are shown in Table 2. A total of 9 substances were identified, namely: rutin, hyperoside, quercetin 3-O-glucoside, kaempferol-rhamnose-galactoside, kaempferol 3-O-rutinoside and isorhamnetin 3-O-rhamnose-galactoside mixture, narcissin, astragalin, isorhamnetin 3-O-glucoside. The total content of phenolic substances in the fresh sample extract was 3.32±0.34 mg / g DW. There were significant differences in the total content of phenolic substances between different drying groups. Compared with the total content of phenolic substances in the fresh sample extract, the total content of phenolic substances in pitaya flower increased in each drying group. Among them, the total content of phenolic substances in the pitaya flower with the third drying treatment (1260 W, 8 min) was the highest, at 5.74±0.20 mg / g DW. The total content of phenolic substances in the third group was 1.73 times that of the fresh sample. Therefore, the optimal microwave power was selected as 1260 W.

[0082] Effect of microwave treatment time on the total phenolic content and phenolic compounds in dried pitaya flower samples:

[0083] ①In the microwave treatment of pitaya flowers, the microwave power was fixed at 900 W, and the microwave treatment times were set to 8, 10, 12, and 14 min, resulting in a total of 4 groups of samples, namely Example 2, Example 4, Example 5, and Example 6. Additionally, fresh samples were used as a control.

[0084] ②The results of total phenols showed that the fresh sample extract had the highest total phenol content, which was 4.19 mg GAE / g DW. All treatments reduced the total phenol content in pitaya flowers. The average total phenol content in the dried samples of pitaya flowers with different microwave treatment times was 3.23 mg GAE / g DW. Among them, the total phenol content was the highest when the microwave treatment time was 10 min, which was 3.26 mg GAE / g DW. However, the differences in total phenol content among the four drying treatment groups were not significant. The optimal microwave treatment time was selected as 10 min, as Figure 2 shown.

[0085] ③The experimental results of detecting phenolic compounds in the pitaya flower extract by HPLC are shown in Table 3. A total of 9 substances were identified, namely: rutin, hyperoside, quercetin 3-O-glucoside, kaempferol-rhamnose-galactoside, kaempferol 3-O-rutinoside and isorhamnetin 3-O-rhamnose-galactoside mixture, narcissin, astragalin, and isorhamnetin 3-O-glucoside. The total content of phenolic substances in the fresh sample extract was 3.32 ± 0.34 mg / g DW. There were significant differences in the total content of phenolic substances among different drying groups. Compared with the total content of phenolic substances in the fresh sample extract, the total content of phenolic substances in pitaya flowers increased in each drying group. Among them, the total content of phenolic substances in the pitaya flowers of the second drying treatment (900 W, 10 min) was the highest, which was 5.02 ± 0.03 mg / g DW. The total content of phenolic substances in the second group was 1.52 times that of the fresh sample. Therefore, the optimal microwave treatment time was selected as 10 min.

[0086] Carotenoids were extracted from the dried pitaya flower samples prepared by the preparation methods described in Examples 1-6. The specific method steps were as follows:

[0087] (1) Weigh 1 g of pitaya flower powder;

[0088] (2) Sequentially add 2 mL of ethanol / water solution (95%, v / v), 1 mL of sodium chloride / water solution (0.3 M), 4 mL of pyrogallic acid / ethanol solution (0.5 M), 1 mL of vitamin C / water solution (1 M), and 2 mL of potassium hydroxide / water solution (600 g / L);

[0089] (3) After mixing, saponify thoroughly in a water bath at 70 °C for 2 h;

[0090] (4) Cool to room temperature and add 0.75 mL of sodium chloride / water solution (3 M);

[0091] (5) Extract with n - hexane / ethyl acetate solution (v / v: 9 / 1), and collect the extract.

[0092] (6) Wash twice with distilled water, and add anhydrous sodium sulfate powder to absorb water.

[0093] (7) Blow - dry the dried extract with nitrogen.

[0094] (8) After drying, redissolve with methyl tert - butyl ether solution containing 0.1% (w / v) 2,6 - di - tert - butyl - 4 - methylphenol, and store in a - 20 °C refrigerator for later measurement.

[0095] For the identification of carotenoids in the pitaya flower extract, high - performance liquid chromatography (HPLC) was used. The specific method steps are as follows:

[0096] (1) Filter the extract with a 0.22 - μm organic - phase filter membrane, and dilute it to an appropriate concentration with methyl tert - butyl ether solution containing 0.1% (w / v) 2,6 - di - tert - butyl - 4 - methylphenol.

[0097] (2) Use high - performance liquid chromatography to determine the carotenoids in pitaya flowers. In the experiment, a C30 column (4.6×250 mm, 5 μm, YMC, JP) was used for detection on a Waters 2998 detector; the mobile phases were: A: 90%A'+10%B', B: 90%B'+10%A', where A' solution was 97% methanol / water solution containing 0.05 M ammonium acetate; B' solution was 100% tert - butyl methyl ether solution; both A' and B' solutions contained 0.1% (w / v) 2,6 - di - tert - butyl - 4 - methylphenol. The detection wavelength was: 450 nm.

[0098] (3) Use the external - standard method for qualitative and quantitative analysis of phenolic compounds. The experimental results were expressed as micrograms per gram of dry weight of pitaya flower (μg / g DW).

[0099] Effect of microwave power on carotenoid components in dry pitaya flower samples:

[0100] ① In the microwave treatment of pitaya flowers, the microwave treatment time was fixed at 8 min, and the microwave powers were set at 360, 900, and 1260 W, with a total of 3 groups of samples, namely Example 1, Example 2, and Example 3. In addition, fresh samples were used as a control.

[0101] ② The experimental results of detecting carotenoids in the pitaya flower extract by HPLC are shown in Table 5. A total of 6 substances were identified, namely: lutein, zeaxanthin, α-cryptoxanthin, β-cryptoxanthin, α-carotene, and β-carotene. Among the carotenoid extracts from the dried pitaya flower samples with different treatments, the lutein content was the highest, accounting for 71 - 83% of the total carotenoids, followed by zeaxanthin. The total carotenoid content in the fresh sample extract was 17.28 ± 1.78 μg / g DW. The total carotenoids in the three drying groups were significantly higher than those in the fresh sample group. Among them, the total carotenoid content in the pitaya flowers treated by the third drying treatment (1260W, 8 min) was the highest, which was 24.89 ± 0.31 μg / g DW. The total carotenoid content in the third group was 1.44 times that of the fresh sample. Therefore, the optimal microwave power was selected as 1260W.

[0102] Effect of microwave treatment time on carotenoid components in dried pitaya flower samples:

[0103] ① In the microwave treatment of pitaya flowers, the microwave power was fixed at 900W, and the microwave treatment times were set to 8, 10, 12, and 14 min, with a total of 4 groups of samples, namely Example 2, Example 4, Example 5, and Example 6. In addition, the fresh sample was used as a control.

[0104] ② The experimental results of detecting carotenoids in the pitaya flower extract by HPLC are shown in Table 6. A total of 6 substances were identified, namely: lutein, zeaxanthin, α-cryptoxanthin, β-cryptoxanthin, α-carotene, and β-carotene. Among the carotenoid extracts from the dried pitaya flower samples with different treatments, the lutein content was the highest, accounting for 73 - 83% of the total carotenoids, followed by zeaxanthin. The total carotenoid content in the fresh sample extract was 17.28 ± 1.78 μg / g DW. The total carotenoids in the four drying groups were significantly higher than those in the fresh sample group. Among them, the total carotenoid content in the pitaya flowers treated by the fourth drying treatment (900W, 14 min) was the highest, which was 28.27 ± 0.62 μg / g DW. The total carotenoid content in the fourth group was 1.64 times that of the fresh sample. Therefore, the optimal microwave treatment time was selected as 14 min.

[0105] Extract vitamin E from the dried pitaya flower samples obtained by the preparation methods described in Examples 1 - 6. The specific method steps are as follows:

[0106] (1) The extraction steps of vitamin E are the same as those of carotenoids;

[0107] (2) After blowing the extraction liquid to dryness with nitrogen, add a n-hexane solution containing 1% (v / v) isopropanol for reconstitution and store it in a -20°C refrigerator for later measurement.

[0108] The identification of vitamin E in the pitaya flower extract was carried out by high performance liquid chromatography (HPLC). The specific method steps are as follows:

[0109] (1) Filter the extract with a 0.22 μm organic phase filter membrane and dilute it to an appropriate concentration with a n - hexane solution containing 1% (v / v) isopropanol;

[0110] (2) Use high performance liquid chromatography to detect vitamin E in the extract. In the experiment, an Agilent ZORBAX - RX - SIL chromatographic column (4.6×250 mm, 5 μm) was used for detection on a Waters 2475 fluorescence detector. Set the column temperature: 35 °C; excitation wavelength: 290 nm; emission wavelength: 330 nm. The mobile phase composition is n - hexane / isopropanol / acetic acid (98.7:1:0.3, v / v / v).

[0111] (3) Use the external standard method for qualitative and quantitative analysis of the components of vitamin E. The experimental results are expressed in micrograms per gram of dry weight of pitaya flower (μg / g DW).

[0112] Effect of microwave power on vitamin E components in dried pitaya flower samples:

[0113] ① In the microwave treatment of pitaya flowers, the microwave treatment time was fixed at 8 min, and the microwave powers were set at 360, 900, and 1260 W, with a total of 3 groups of samples, namely Example 1, Example 2, and Example 3. In addition, fresh samples were used as a control.

[0114] ② The experimental results of HPLC detection of vitamin E in the pitaya flower extract are shown in Table 7. A total of 3 substances were identified, namely: α - tocopherol, γ - tocopherol, and δ - tocopherol. Among the vitamin E extracts from dried pitaya flower samples with different treatments, α - tocopherol is the vitamin E component with the highest content, followed by γ - tocopherol and δ - tocopherol. The total vitamin E content in the fresh sample extract is 7.86 ± 0.74 μg / g DW. The total vitamin E content in the three drying groups is significantly higher than that in the fresh sample group. Among them, the total vitamin E content in the pitaya flowers with the second drying treatment (900 W, 8 min) is the highest, which is 33.82 ± 1.09 μg / g DW. The total vitamin E content in the second group is 4.30 times that of the fresh sample. Therefore, the optimal microwave power is selected as 900 W.

[0115] Effect of microwave treatment time on vitamin E components in dried pitaya flower samples:

[0116] ① In the microwave treatment of pitaya flowers, the microwave power was fixed at 900 W, and the microwave treatment times were set at 8, 10, 12, and 14 min, with a total of 4 groups of samples, namely Example 2, Example 4, Example 5, and Example 6. In addition, fresh samples were used as a control.

[0117] ② The experimental results of detecting vitamin E in the pitaya flower extract by HPLC are shown in Table 8. A total of three substances were identified, namely: α-tocopherol, γ-tocopherol, and δ-tocopherol. Among the vitamin E extracts from the dried pitaya flower samples with different treatments, α-tocopherol is the vitamin E component with the highest content, followed by γ-tocopherol and δ-tocopherol. The total vitamin E content in the fresh sample extract is 7.86 ± 0.74 μg / g DW. The total vitamin E contents of the four drying groups are all significantly higher than that of the fresh sample group. Among them, the total vitamin E content in the pitaya flowers treated by the second drying treatment (900W, 10min) is the highest, which is 35.25 ± 1.75 μg / g DW. The total vitamin E content of the second group is 4.48 times that of the fresh sample. Therefore, the optimal microwave treatment time is selected as 10 min.

[0118] Table 1: Effects of microwave power on phenolic substances in pitaya flowers

[0119]

[0120] Table 2: Effects of microwave treatment time on phenolic substances in pitaya flowers

[0121]

[0122] Table 3: Effects of microwave power on carotenoids in pitaya flowers

[0123]

[0124] Table 4: Effects of microwave treatment time on carotenoids in pitaya flowers

[0125]

[0126] Table 5: Effects of microwave power on vitamin E in pitaya flowers

[0127]

[0128] Table 6: Effects of microwave treatment time on vitamin E in pitaya flowers

[0129]

[0130] In the above Tables 1 - 6, different letters in each column indicate that the values have significant differences (p < 0.05).

[0131] The implementation manners of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement manners and are all included in the protection scope of the present invention.

Claims

1. A preparation method of microwave combined with hot air dried pitaya flower dry powder, characterized in that It includes the following steps: S1: Screen and chop the freshly collected pitaya flowers; S2: Microwave-dry the chopped pitaya flowers; S3: Dry the microwave-treated pitaya flowers in an oven; S4: Grind the dried pitaya flowers to obtain pitaya flower dry powder, and store it sealed at room temperature.

2. The preparation method of dragon fruit flower dry powder by microwave combined with hot air drying according to claim 1, characterized in that In step S1, the screening and chopping means removing the diseased tissues of the freshly collected pitaya flowers and chopping them into petal fragments and / or granular forms with a side length less than 0.5 cm.

3. The preparation method of the dried pitaya flower powder by microwave combined with hot air drying according to claim 1, characterized in that In step S2, the microwave drying means spreading the pitaya flowers screened and chopped in step S1 on a microwave drying tray and performing microwave treatment.

4. The preparation method of dried pitaya flower powder by microwave combined with hot air drying according to claim 3, characterized in that The microwave treatment parameter settings are: microwave power is 360 - 1260 W, and the microwave treatment time is 8 - 14 min.

5. The preparation method of dried pitaya flower powder by microwave combined with hot air drying according to claim 1, characterized in that The drying in step S3 means hot air drying at 75 - 80 °C for 15 - 20 h.

6. The preparation method of the dried pitaya flower powder by microwave combined with hot air drying according to claim 3, characterized in that The thickness of the spread pitaya flowers is 1 - 1.5 cm.

7. The preparation method of dried pitaya flower powder by microwave combined with hot air drying according to claim 3, characterized in that The place of origin of the pitaya flowers in step S1 is Guizhou Province.

8. The preparation method of dried pitaya flower powder by microwave combined with hot air drying according to claim 2, characterized in that The petal fragments and / or granular forms with a side length less than 0.5 cm mean chopping the pitaya flowers with removed diseased tissues into petal fragments with a side length less than 0.5 cm and / or granular forms with a particle size less than 0.5 cm.

9. A dried powder of pitaya flower, characterized in that Obtained by using the preparation method described in any one of claims 1 - 9.

Images