Method for extracting betacyanin with high antioxidant activity from pitaya peel

Abstract

The invention discloses a method for extracting betacyanin with high antioxidant activity from pitaya peel. Fresh pitaya peel is used as a raw material, the betacyanin is extracted by adopting an ethanol extraction combined ultrasonic method, powder is obtained through dilution, suction filtration, centrifugation, rotary evaporation and vacuum freeze drying, and the betacyanin with the content of about 133mg / 100g is extracted; the obtained betacyanin has high oxidation resistance and can effectively replace artificially synthesized pigments. The method provides theoretical basis and technical support for efficient extraction of natural pigments, resource utilization of pitaya byproducts and functional development of betacyanin.

Description

Technical Field

[0001] The invention belongs to the field of natural pigment extraction and development, and particularly relates to a method for extracting betalain with high antioxidant activity from pitaya peel. Background Art

[0002] As a byproduct of pitaya processing, pitaya peel is often discarded, resulting in a waste of resources. Extracting betalain from pitaya peel, which is rich in natural betalain, can effectively utilize resources, increase the overall economic value of pitaya, and meet market demand for high-quality natural pigments.

[0003] Betalain is a vibrant natural pigment with excellent water solubility and coloring power. As a safe and healthy pigment source, betalain can replace some synthetic pigments, reducing potential health risks. Therefore, it is widely used in food, cosmetics, and pharmaceuticals.

[0004] Efficiently separate betacyanin from discarded pitaya peels and transform it from waste into a high-value natural pigment resource by optimizing the extraction conditions, laying a solid foundation for the in-depth development of pitaya peel resources and the widespread application of betacyanin. At present, the methods used to extract pigments include organic solvent extraction, pressurized liquid extraction, microwave-assisted extraction, ultrasonic-assisted extraction, supercritical fluid extraction, microbial fermentation and enzyme reaction extraction, and combined assisted extraction. However, there are reports on the extraction of pitaya betacyanin, but its separation technology still needs comprehensive, systematic and in-depth research. How to efficiently obtain pitaya peel betacyanin is a prerequisite for in-depth research and comprehensive utilization of pitaya betacyanin. Summary of the Invention

[0005] In response to the above-mentioned shortcomings of the prior art, the present invention aims to provide a method for extracting betalain with high antioxidant activity from pitaya peel. The extraction method of the present invention can increase the extraction content of betalain to a certain extent, obtain betalain with good water solubility, and have certain antioxidant capacity.

[0006] The first object of the present invention is to provide a method for extracting betalain from pitaya peel, comprising the following steps:

[0007] S1. The fresh pitaya peel was crushed and freeze-dried to obtain pitaya peel powder;

[0008] S2. Take pitaya peel powder and place it in a volume fraction of 38%-42% ethanol aqueous solution, the solid-liquid ratio is 1g: 58-62mL, the pH value of the mixture is adjusted to 6.8-7.2, and the mixture is oscillated at 35 ℃-40 ℃ and an ultrasonic power of 240-260W for 20min to obtain a crude extract of betalain;

[0009] S3. Filter the crude betacyanin extract to remove insoluble solids, centrifuge the filtrate, evaporate and concentrate the supernatant, freeze it, and then vacuum freeze-dry it to obtain betacyanin.

[0010] Preferably, the step S2 comprises: placing pitaya peel powder in a 40% ethanol aqueous solution by volume, mixing the mixture at a solid-liquid ratio of 1 g:60.62-61 mL, adjusting the pH value of the mixture to 7, and oscillating the mixture at 36° C.-36.45° C. and an ultrasonic power of 244.71-250 W for 20 minutes to obtain a crude betalain extract.

[0011] Preferably, the pitaya peel is the pitaya peel with scales removed.

[0012] Preferably, the freeze drying in step S1 is freeze drying to a moisture content of ≤7%.

[0013] Preferably, the centrifugation conditions in step S3 are temperature 25° C., 6500 rpm, and 15 min.

[0014] Preferably, the step S3 comprises: appropriately diluting the crude betacyanin extract, filtering to remove insoluble solids, centrifuging the filtrate, evaporating and concentrating the supernatant at 40°C to reduce the volume of the solution to 1 / 4-1 / 5 of the original volume, freezing at -20°C for 4 hours, then freezing at -80°C overnight, and freeze-drying at -80°C in a vacuum to obtain betacyanin.

[0015] Preferably, the dilution is 5 times dilution with a 40% by volume ethanol aqueous solution.

[0016] The second object of the present invention is to provide betalain extracted according to any one of the methods described.

[0017] The beneficial effects of the present invention are as follows:

[0018] The present invention uses fresh pitaya peel as raw material, adopts ethanol extraction combined with ultrasonic method to extract betalain, and obtains powder after dilution, suction filtration, centrifugation, rotary evaporation, and vacuum freeze drying. The extracted betalain content is about 133mg / 100g. Ultrasound-assisted technology is used to break up pitaya peel cells. By optimizing the ethanol concentration (40%), material-liquid ratio (1:61g / mL), pH conditions (pH 7) and ultrasonic parameters (250W, 36℃), combined with the cavitation effect, cell permeability is significantly improved, and efficient extraction is achieved under mild conditions, avoiding the damage of high temperature to the pigment structure; the obtained betalain has high antioxidant capacity and can effectively replace artificial synthetic pigments. Its high water solubility can improve the coloring performance of products in the fields of food, cosmetics, etc., while reducing the waste of waste peel resources. The present invention provides a new direction for improving the extraction rate of betalain, provides a theory and method for the development and application of betalain in various fields, and provides a theoretical basis and technical support for the efficient extraction of natural pigments, the resource utilization of pitaya by-products and the functional development of betalain. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the ultraviolet absorption spectrum of betalain.

[0020] Figure 2 This is the standard curve of betalain.

[0021] Figure 3 The effect of ethanol concentration on the betalain content in pitaya peel.

[0022] Figure 4 The effect of pH value on the betalain content in pitaya peel.

[0023] Figure 5 This is the effect of ultrasonic power on the betalain content in pitaya peel.

[0024] Figure 6 The effect of temperature on the betalain content in pitaya peel.

[0025] Figure 7 This is the effect of material-liquid ratio on the betacyanin content in pitaya peel.

[0026] Figure 8 The effect of ultrasonic power and temperature on betalain content.

[0027] Figure 9 The effects of ultrasonic power and material-liquid ratio on betalain content.

[0028] Figure 10 The effects of temperature and material-liquid ratio on betalain content.

[0029] Figure 11The color changes of betalain under different storage conditions; from left to right, the storage conditions are 4°C, room temperature away from light, and room temperature without light.

[0030] Figure 12 is the retention rate of betalain under different storage conditions.

[0031] Figure 13 is the △E value of betalain stored for 5 days under different conditions.

[0032] Figure 14 Analysis of the antioxidant activity of betalain; A is the DPPH scavenging rate, B is the hydroxyl radical scavenging rate, C is the ABTS free radical scavenging ability, and D is the FRAP free radical scavenging ability. DETAILED DESCRIPTION

[0033] The following examples are provided to further illustrate the present invention, but are not intended to limit the present invention.

[0034] Example 1

[0035] 1 Materials and Methods

[0036] 1.1 Materials and Reagents

[0037] Fresh pitaya peel was purchased from Guangdong Meichen Biotechnology Co., Ltd.; anhydrous ethanol (AR) was purchased from Guangdong Guanghua Science and Technology Co., Ltd.; ultrapure water; sodium hydroxide (AR) was purchased from Xilong Science Co., Ltd.; pH buffer solution was purchased from Shanghai Yidian Scientific Instrument Co., Ltd.; betalain analytical standard was purchased from Shanghai Mengcheng Technology Co., Ltd.; 2,2-biphenyl-1-picrylhydrazyl was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.; hydroxyl free radical test kit and total antioxidant capacity (T-AOC) test kit (ABTS method, FRAP method) were purchased from Nanjing Jiancheng Bioengineering Institute.

[0038] 1.2 Instruments and Equipment

[0039] DFY-500 swing mill (Wenling Linda Machinery Co., Ltd.); UW220H electronic balance (Shimadzu Corporation, Japan); pH meter (Shanghai Yidian Scientific Instrument Co., Ltd.); KQ-500DB CNC ultrasonic cleaning machine (Kunshan Ultrasonic Instrument Co., Ltd.); GM-0.33A diaphragm vacuum pump (Tianjin Jinteng Experimental Equipment Co., Ltd.); JIDI-20R desktop high-speed refrigerated centrifuge (Guangzhou Jidi Instrument Co., Ltd.); N-4000 rotary evaporator (Tokyo Rika Instrument Co., Ltd.); LGJ-10 vacuum freeze dryer (Beijing Songyuan Huaxing Technology Development Co., Ltd.); HL-6 digital display constant temperature water bath (Changzhou Aowa Instrument Co., Ltd.); UV-1900i ultraviolet-visible spectrophotometer (Shimadzu Corporation, Japan); Varioskan Flash fully automatic microplate reader (Thermo Scientific, USA).

[0040] 1.3 Experimental methods

[0041] 1.3.1 Raw material pretreatment

[0042] The pulp and scales of fresh pitaya peel are removed, the pulp is crushed into pulp by a grinder, and the pulp is freeze-dried to a moisture content of ≤7% to obtain pitaya peel powder, which is sealed and stored for later use.

[0043] 1.3.2 Single-factor process optimization for betalain extraction

[0044] Extraction process route: Take pitaya peel powder and place it in ethanol and water solution, adjust the pH value of the mixture, and subject the mixture to ultrasonic oscillation reaction at a certain temperature for 20 minutes to obtain a crude betalain extract.

[0045] Specifically, the process optimization is as follows: 1g of pitaya peel powder was weighed, and the extraction conditions were optimized by exploring the effects of ethanol concentration, pH value, ultrasonic power, extraction temperature, and solid-liquid ratio on the amount of betalain extracted. The effects of different ethanol aqueous solution volume fractions (0%, 20%, 40%, 60%, 80%), pH values (5, 6, 7, 8, 9), ultrasonic power (200W, 250W, 300W, 350W, 400W), temperature (20℃, 30℃, 40℃, 50℃, 60℃), and solid-liquid ratios (1:30, 1:40, 1:50, 1:60, 1:70 g / mL) on the extraction content of betalain from pitaya peel were investigated.

[0046] 1.3.3 Response surface design

[0047] On the basis of single factor experiment, response surface analysis (Box-Behnken) was used to optimize the extraction process parameters of betalain from pitaya peel with ultrasonic power (A), temperature (B) and material-liquid ratio (C) as the investigation factors and the extraction content as the response value. The factor levels are shown in Table 1.

[0048] Table 1 Response surface analysis optimization experimental design for betalain extraction from pitaya peel

[0049]

[0050] 1.3.4 Dilution treatment

[0051] The crude betalain extract was diluted to 5 times with a 40% ethanol aqueous solution to obtain a betalain diluted solution.

[0052] 1.3.5 Filtration treatment

[0053] The betalain dilution solution is filtered to remove insoluble solids.

[0054] 1.3.6 Centrifugation

[0055] The filtered betalain dilution was poured into a 50 mL centrifuge tube and placed in a centrifuge at 25°C and 6500 rpm for 15 minutes.

[0056] 1.3.7 Absorbance determination

[0057] After centrifugation, the supernatant was collected and its absorbance value A at 536 nm was measured. The betalain content was calculated according to formula 1.

[0058]

[0059] Where A is the absorbance, V is the volume of the extract, n is the dilution factor, m is the mass of the pitaya peel used to extract the pigment, 550.46 is the molar molecular mass of standard betalain, and 61600 is the molar extinction coefficient of standard betalain.

[0060] 1.3.8 Rotary evaporation

[0061] The supernatant of the centrifuged betalain dilution solution was taken and concentrated by evaporation at 40°C using a rotary evaporator. When the volume of the solution was reduced to 1 / 4-1 / 5 of the original liquid, the rotary evaporation was stopped to obtain the betalain concentrated solution.

[0062] 1.3.9 Freeze-drying

[0063] Pour the betalain concentrate (obtained in 1.3.8) into a 50 mL centrifuge tube, place it at an angle and freeze it at -20°C for 4 hours, then freeze it at -80°C overnight, and freeze it in a vacuum freeze dryer pre-cooled to -80°C the next day for 48 hours to obtain betalain. Store it in a sealed container away from light.

[0064] 1.3.10 Determination of betalain stability

[0065] The supernatant of the centrifuged betalain dilution was divided into three groups in equal amounts and stored at 4°C, room temperature and dark conditions, and room temperature and non-light conditions for 5 days. The absorbance was measured at a wavelength of 536 nm every 24 hours and the retention rate was calculated according to Formula 2. The color of the betalain was recorded by taking photos every 24 hours and the color value was measured using a colorimeter: L * 、a * and b * The ΔE value was calculated according to Formula 3. Each group was measured three times and the results were averaged.

[0066]

[0067] Where: A is the initial absorbance of betalain dilution; A1 is the absorbance of betalain measured every 24 hours.

[0068]

[0069] Where: L0 * 、a0 * and b0 * Indicates the brightness value, red-green value and yellow-blue value of the solution on day 0, L * 、a * and b * Indicates the brightness value, red-green value, and yellow-blue value of the solution on the 5th day.

[0070] 1.3.11 Determination of DPPH clearance

[0071] Prepare a sample solution of a specific concentration using betalain as the solute and distilled water as the solvent. Mix 2.0 mL of the sample solution with 2.0 mL of a 0.1 mM DPPH solution in anhydrous ethanol. Incubate at room temperature in the dark for 30 minutes. Measure the absorbance at 517 nm. Use vitamin C as a positive control. Repeat the measurement three times for each group, and average the results. Calculate the DPPH scavenging rate using Equation 4.

[0072]

[0073] Where: A sample is the absorbance of 2 mL sample solution + 2 mL DPPH anhydrous ethanol solution; A negative control is the absorbance of 2 mL sample solution + 2 mL distilled water (used to deduct the color interference of the sample itself); A blank is the absorbance of 2 mL DPPH anhydrous ethanol solution + 2 mL distilled water.

[0074] 1.3.1 Determination of 2·OH Scavenging Rate

[0075] Prepare sample solutions of a certain concentration using betalain as the solute and distilled water as the solvent. Detect the ·OH scavenging rate of betalain using vitamin C as the positive control according to the kit's protocol.

[0076] 1.3.13 Determination of ABTS free radical scavenging ability

[0077] Prepare a sample solution of a certain concentration using betalain as the solute and distilled water as the solvent. Detect the ABTS free radical scavenging ability of betalain using the kit's protocol, using vitamin C as the positive control.

[0078] 1.3.14 Determination of FRAP free radical scavenging ability

[0079] Betalain was used as the solute and distilled water as the solvent to prepare a sample solution of a certain concentration. Vitamin C was used as the positive control and the FRAP free radical scavenging ability of betalain was tested according to the kit protocol.

[0080] 1.3.15 Data Statistics and Analysis

[0081] The experiment was repeated three times in parallel, and the experimental data were expressed as mean ± standard deviation (SD). SPSS26.0 software was used to perform statistical analysis on the data results, and GraphPad Prism10.1 and Origin2021 were used to draw charts.

[0082] 2 Results Analysis

[0083] The UV absorption spectrum of betalain Figure 1 As shown, the maximum absorption peak is at 536nm. The standard curve between the mass concentration of betalain standard and absorbance is shown as follows Figure 2 As shown, y = 0.2848x-0.0021, R 2 =0.9996, good linearity.

[0084] 2.1 Extraction content of betalain from pitaya peel under different influencing factors

[0085] 2.1.1 Ethanol concentration

[0086] The results are as follows Figure 3 As shown in the results, the betalain content first increases and then decreases with increasing ethanol concentration. When the ethanol concentration is 40%, the betalain content is the highest, at 129.46 mg / 100 g. In the extraction process of betalain from pitaya peel, ethanol can effectively dissolve and destroy phospholipids and other lipid components in the cell membrane, thus providing favorable conditions for the extraction of betalain. However, due to the water-soluble nature of betalain itself, excessively high concentrations of organic solvents will have a negative impact on the extraction process, manifesting as a certain inhibitory effect.

[0087] 2.1.2 pH value

[0088] The results are as follows Figure 4As shown in the figure, the betalain content first increases and then decreases with increasing pH value. When the pH value is 7, the betalain content is the highest, at 129.51 mg / 100g. This shows that under neutral conditions, the dragon fruit peel pigment is more easily dissolved, and the pigment extraction effect is better. However, in acidic and alkaline environments, the dragon fruit peel red pigment may be destroyed or converted into other pigments, making the pigment unstable.

[0089] 2.1.3 Ultrasonic power

[0090] The results are as follows Figure 5 As shown in the figure, the betalain content first increases and then decreases with increasing ultrasonic power. When the ultrasonic power is 250W, the betalain extractable content is the highest, at 129.46mg / 100g. This phenomenon is due to the cavitation effect induced by ultrasonic vibration. During this process, tiny gas cores (i.e., cavitation bubbles) within the liquid vibrate under the stimulation of the sound waves. When the pressure of the sound waves reaches a certain threshold, these bubbles shrink and burst, forming a dynamic physical process. The cavitation effect can significantly enhance the permeability of most cells. Therefore, with the increase of ultrasonic power, the extractable content of betalain in pitaya peel also increases accordingly. However, the cavitation effect mainly acts on tiny bubbles and dissolved gases in the liquid. When the ultrasonic power exceeds a certain level, the gas in the water is largely removed, causing the cavitation effect to gradually weaken.

[0091] 2.1.4 Temperature

[0092] The results are as follows Figure 6 As shown, betalain content first increases and then decreases with increasing temperature. At 40°C, the betalain content reaches its highest level, at 130.44 mg / 100g. This may be due to the fact that the molecular structure of betalain is sensitive to temperature changes. During the pigment extraction process, excessively high temperatures damage the betalain molecules, accelerating their decomposition.

[0093] 2.1.5 Material-liquid ratio

[0094] The results are as follows Figure 7 As shown, the betalain content first increases and then decreases with increasing solid-liquid ratio. When the solid-liquid ratio is 1:60 (g / mL), the betalain extract reaches its highest content, 132.92 mg / 100 g. This is related to the saturation level of betalain in the ethanol extract. When dissolving the same mass of betalain, a higher concentration of the extract results in a lower concentration of betalain per unit volume, i.e., a lower solubility rate. This decrease in concentration reduces the relative osmotic pressure in the solution, further promoting the transfer of pigment molecules from the solid phase to the liquid phase, thereby promoting the dissolution of the pigment in the extract.

[0095] 2.2 Response surface experiment results of betalain extraction

[0096] 2.2.1 Response surface experimental design and results

[0097] The optimized experimental scheme and results of response surface analysis are shown in Table 2, and the variance analysis results are shown in Table 3. Figure 8 The effects of ultrasonic power and material-liquid ratio on betalain content are shown in Figure 9 The effects of temperature and material-liquid ratio on betalain content are shown in Figure 10 .

[0098] Table 2 Response surface analysis optimization test plan and results

[0099]

[0100]

[0101] Table 3 Results of variance analysis

[0102]

[0103] Note: * indicates significant difference (P < 0.05); ** indicates extremely significant difference (P < 0.01).

[0104] Regression fitting was performed on the data in Table 2 to obtain a quadratic polynomial regression equation with betalain content (Y) as the objective function: Y=132.86-0.7825A-2.43B-0.2725C-1.71AB-0.95AC-0.435BC-3.25A2-4.13B2-2.63C2.

[0105] From Table 3, we can see that: Model P < 0.01, indicating that the regression model has reached an extremely significant level; Lack of Fit P > 0.05, not significant; R 2 = 0.9614, indicating that the model has a high degree of fit to the test data and a good fitting effect. Figure 8-10 The influence of various factors on betacyanin content is B>A>C, that is, temperature>ultrasonic power>solid-liquid ratio.

[0106] 2.2.2 Verification Experiment

[0107] The optimal extraction conditions for betalain were determined by fitting a quadratic polynomial regression equation: an ultrasonic power of 244.71 W, a temperature of 36.45°C, and a solid-liquid ratio of 1:60.62 (g / mL). The predicted betalain content at these conditions was 133.202 mg / mL. Considering operational convenience, the process was ultimately adjusted to an ultrasonic power of 250 W, a temperature of 36°C, and a solid-liquid ratio of 1:61 (g / mL). Three validation experiments were conducted under these conditions, resulting in a betalain content of 132.641 mg / 100 g, with a small error from the predicted value, indicating the reliability of the model.

[0108] 2.3 Analysis of betalain stability

[0109] Depend on Figure 11 and 12 It can be seen that the color of the betalain solution gradually changes from purple-red to light yellow as the storage time increases. The retention rate of the solution stored for 5 days under different conditions decreases over time. The color change of the room temperature light-proof group and the room temperature non-light-proof group is more obvious than that of the 4°C group. On the 5th day of storage, the betalain retention rate at 4°C was 91.78%, the retention rate at room temperature light-proof was 43.12%, and the retention rate at room temperature non-light-proof was 42.99%. This shows that the degradation rate of betalain is slower at 4°C, and low temperature can significantly inhibit the decomposition of the pigment. Figure 13 It can be seen that the total color difference between the 0th day and the 5th day of betalain stored at 4°C is 0.4382, which is significantly lower than that of the other two groups, indicating that temperature has a greater impact on betalain, which is consistent with the conclusion drawn by the response surface analysis.

[0110] 2.4 Analysis of antioxidant activity of betalain

[0111] Depend on Figure 14 From A and B in the figure, we can see that as the mass concentration of betalain increases, the scavenging rate of DPPH· and ·OH increases accordingly. When the mass concentration of betalain is 0.5 mg / mL, the scavenging ability of DPPH· reaches the maximum, which is 58.57%; when the mass concentration of betalain is 1 mg / mL, the scavenging ability of ·OH reaches the maximum, which is 71.26%. This may be because as the mass concentration of betalain increases, the content of antioxidants in betalain increases, and these antioxidants can pair with the single electrons of DPPH· and ·OH present in the system, thereby reducing the number of free radicals and showing an enhanced scavenging ability of DPPH· and ·OH. Figure 14 As shown in Figures C and D, the scavenging ability of ABTS and FRAP free radicals increases with the increase of betacyanin concentration. When the concentration of betacyanin is 25 mg / mL, the scavenging ability of ABTS and FRAP free radicals reaches the maximum. This may be because as the concentration of betacyanin increases, the number of active groups per unit volume increases, which is related to the ABTS free radical scavenging ability. + Reacts with Fe3+ to form ABTS + The clearance rate and FRAP reducing ability were enhanced in a dose-dependent manner. The results showed that betalain had certain antioxidant activity in vitro.

[0112] Analyzing the results, we found that:

[0113] The betalain extracted in this example showed significant advantages in the DPPH· and ·OH scavenging experiments. When the betalain concentration was 0.5 mg / mL and 1 mg / mL, the DPPH· and ·OH free radical scavenging rates were 58.57% and 71.26%, respectively, which were significantly higher than those of the existing methods (Liu Bing. Study on the Extraction and Antioxidant Protection of Betalain from Pitaya Peel [D]. Jinzhou Medical University, 2018. 0 ) when the mass concentration of betalain was 1 mg / mL, the DPPH· and ·OH scavenging rates were approximately 10% and 29%, respectively.

[0114] The betalain extracted in this embodiment has obvious advantages in scavenging DPPH· and ·OH compared with the existing method (Zhang Lingbang, Shao Ling, Hu Sun, et al. Optimization of the extraction process of two pitaya peel red pigments and their antioxidant activity [J]. Food Industry Science and Technology, 2019, 40(05): 163-169, 175.). Under the condition of the same mass concentration of betalain, the DPPH· free radical scavenging ability of the betalain in this embodiment is about 2 times that of the existing method, and the ·OH free radical scavenging ability is about 3 times that of the existing method.

[0115] The above-mentioned difference in free radical scavenging ability may be due to the low-temperature ultrasonic extraction process under neutral conditions adopted in this example, which effectively retains acid-insensitive and heat-sensitive antioxidant components, while the acid hydrolysis process may cause the destruction of some active groups.

Claims

1. A method for extracting betalain from pitaya peel, characterized in that, The following steps are involved: S1. The fresh pitaya peel was crushed and freeze-dried to obtain pitaya peel powder; S2. Take pitaya peel powder and place it in a volume fraction of 38%-42% ethanol aqueous solution, the solid-liquid ratio is 1g: 58-62mL, the pH value of the mixture is adjusted to 6.8-7.2, and the mixture is oscillated at 35 ℃-40 ℃ and an ultrasonic power of 240-260W for 20min to obtain a crude extract of betalain; S3. Filter the crude betacyanin extract to remove insoluble solids, centrifuge the filtrate, evaporate and concentrate the supernatant, freeze it, and then vacuum freeze-dry it to obtain betacyanin.

2. The method according to claim 1, characterized in that The step S2 comprises: placing pitaya peel powder in a 40% ethanol aqueous solution with a solid-liquid ratio of 1 g:60.62-61 mL, adjusting the pH value of the mixed solution to 7, and oscillating the mixed solution at 36° C.-36.45° C. and an ultrasonic power of 244.71-250 W for 20 minutes to obtain a crude betalain extract.

3. The method according to claim 1, characterized in that The pitaya peel is the pitaya peel with scales removed.

4. The method according to claim 1, wherein The freeze drying in step S1 is freeze drying until the moisture content is ≤7%.

5. The method according to claim 1, wherein The centrifugation conditions in step S3 are temperature 25° C., 6500 rpm, and 15 min.

6. The method according to claim 1, characterized in that The step S3 is as follows: after the crude betacyanin extract is appropriately diluted, the insoluble solids are removed by suction filtration, the filtrate is centrifuged, the supernatant is evaporated and concentrated at 40°C to reduce the volume of the solution to 1 / 4-1 / 5 of the original volume, the solution is frozen at -20°C for 4 hours, then frozen at -80°C overnight, and vacuum freeze-dried at -80°C to obtain betacyanin.

7. The method according to claim 6, characterized in that The dilution is 5 times dilution with a 40% volume fraction ethanol aqueous solution.

8. Betacyanin extracted according to the method according to any one of claims 1 to 7.

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