A quinoa polyphenol extraction method based on a deep eutectic solvent and ultrasonic assistance

Abstract

The application belongs to the technical field of food industry, and specifically discloses a quinoa polyphenol extraction method based on a eutectic solvent and ultrasonic assistance, which comprises the following steps: quinoa pretreatment; preparation of a eutectic solvent by using a heating stirring method; and intermittent ultrasonic extraction of polyphenols in the quinoa by using the prepared eutectic solvent. The quinoa polyphenol extraction method provided by the application not only has excellent stability and safety, but also realizes a higher quinoa polyphenol extraction rate with smaller energy consumption, and has the advantages of high extraction rate, strong selectivity, energy saving, low cost, high efficiency and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of food industry, and relates to a quinoa polyphenol extraction method, in particular to a quinoa polyphenol extraction method based on a deep eutectic solvent and ultrasonic assistance. BACKGROUND

[0002] Chenopodium quinoa Willd. is originally from the Andes in South America and is an annual herbaceous plant of the Chenopodiaceae family, which has been cultivated for more than 5,000 years. Quinoa is a pseudo-cereal with high nutritional value, rich in protein, lipids, fiber, vitamins, and minerals. The Food and Agriculture Organization of the United Nations considers quinoa to be the only single plant that can meet the basic nutritional needs of the human body, and officially recommends quinoa as the perfect nutritional food most suitable for human consumption and one of the top ten nutrients in the world. In addition, quinoa is also rich in active substances such as polyphenols, flavonoids, saponins, and phytosterols, and has various health benefits. Studies have shown that quinoa contains at least 23 kinds of polyphenols, and the polyphenols contained in quinoa have various functional activities such as antioxidant, antibacterial, and immune regulation, and have broad application prospects in the fields of food, medicine, and health care products.

[0003] Large-scale application of quinoa polyphenols first requires the polyphenols to be fully extracted from quinoa. Most of the existing research on quinoa polyphenol extraction processes use ethanol-water solution as the extraction agent. For example, the team of You Xin-yong, see the published literature

You Xin-yong, Cui Li-hua, Zhou Ya-li, et al. Optimization of polyphenol extraction process from quinoa seeds by response surface method [J]. Food industry, 2020, 41(10): 118-122

Wang Ruo-lan, Guo Ya-peng. Optimization of ultrasonic-assisted extraction of quinoa polyphenols by response surface method [J]. Grain and oil, 2020, 33(09): 1-7

[0004] Deep eutectic solvents (DESs) are a new type of green solvent developed in recent years, which are formed by two components that can form hydrogen bonds, one of which is a hydrogen bond donor (HBD), and the other is a hydrogen bond acceptor (HBA). DESs have many advantages, such as low volatility, high thermal stability, non-toxic or low toxicity, recyclability, low cost, easy preparation, adjustable solubility, etc. They show great advantages in natural product extraction, organic synthesis, etc.

[0005] For example, the prior art provides cases of extracting polyphenols from different plant bodies using deep eutectic solvents. See the publication: Wang Xiaoyi, Li Peikun, Li Jinhong, et al. Ultrasonic-assisted deep eutectic solvent extraction of rose polyphenols and its antioxidant activity [J]. Food Research and Development, 2022, 43(8): 8. The publication discloses that the ultrasonic-assisted DES method is used to extract polyphenols from rose flowers quickly and efficiently, and is compared with the traditional ethanol extraction method. Through the optimization of single-factor experiments, the optimal process conditions for extracting rose polyphenols by the DES method are obtained as follows: the chlorocholine lactate (molar ratio 1:2) with a water content of 30% is the best extractant, the solid-liquid ratio is 1:40 (g / mL), the ultrasonic time is 10 min, the ultrasonic power is 400 W, the ultrasonic temperature is 50℃, and the extraction is performed twice. Under the above conditions, the extraction amount of rose polyphenols is 136.20±1.23 mg / g.

[0006] However, the structures and components of different plants are different, and the types and content ratios of polyphenols contained are also different, so the deep eutectic solvent formula and extraction conditions suitable for extracting polyphenols from different plants are not consistent, and there is obvious individual difference. Currently, there is no published scheme for extracting polyphenols from quinoa using a deep eutectic solvent.

[0007] In summary, it is very meaningful to develop a new solvent that meets the needs of industrial production, establish a new type of quinoa polyphenol extraction process with high extraction rate, low cost and safety, and lay a foundation for the development and utilization of quinoa polyphenol resources. SUMMARY

[0008] The purpose of the present application is to provide a quinoa polyphenol extraction method based on a deep eutectic solvent and ultrasonic assistance, which can solve the problems of low efficiency and the use of solvents with flammability, volatility, high toxicity, poor stability and selectivity in traditional quinoa polyphenol extraction processes.

[0009] Technical scheme: In order to solve the above problems, the present application provides a quinoa polyphenol extraction method based on a deep eutectic solvent, which comprises the following steps:

[0010] The deep eutectic solvent solution, i.e. the DES solution, is added to the quinoa powder, wherein the liquid-solid ratio of the DES solution and the quinoa powder is (8-92) mL: 1 g; after the quinoa powder and the DES solution are mixed, ultrasonic treatment is performed, followed by centrifugation and vacuum filtration. The filtrate obtained by the vacuum filtration is the quinoa polyphenol extraction liquid;

[0011] The ultrasonic extraction temperature of the ultrasonic treatment is 20-70 DEG C, the time is 20-60 min, the power is 150-450 W, and the ultrasonic treatment mode is intermittent ultrasonic, that is, the ultrasonic mode is "open N seconds-off N seconds-open N seconds-off N seconds", that is, the ultrasonic is opened for N seconds, then stopped for N seconds, and then opened for N seconds, and so on, wherein the value of N is 0.5-3.0.

[0012] The quinoa powder has a mesh number of at least 80 meshes, and is obtained by drying, crushing and sieving fresh quinoa.

[0013] The DES solution is prepared by mixing a hydrogen bond donor HBD and a hydrogen bond acceptor HBA after vacuum drying, respectively, according to a molar ratio of (1-5):(1-5), dissolving by heating and stirring, and then vacuum drying, adding distilled water and stirring.

[0014] Further, the amount of distilled water added is 5-55% of the total volume of the DES solution; further preferably, the amount of distilled water added is 41% of the total volume of the DES solution.

[0015] Further, the DES solution is specifically obtained by vacuum drying the hydrogen bond donor HBD and the hydrogen bond acceptor HBA for 24 h, mixing, heating and stirring at 80 DEG C for 6 h to dissolve, vacuum drying overnight to obtain DES, and mixing the DES with distilled water in a volume ratio of 41:59.

[0016] Further, the drying of fresh quinoa is specifically placing the quinoa in a constant temperature drying oven.

[0017] Further, the quinoa powder needs to be stored at a temperature of 4 DEG C.

[0018] Further, the hydrogen bond donor HBD is any one of glycerol, levulinic acid and lactic acid.

[0019] Further, the hydrogen bond acceptor HBA is any one of betaine and L-proline.

[0020] Further, considering the accuracy and convenience of the intermittent time control of the intermittent ultrasonic mode, and considering the overall quinoa polyphenol extraction efficiency of the extraction method, the value of N is 1, 2 or 3.

[0021] Beneficial effects: the quinoa polyphenol extraction method based on the low eutectic solvent and ultrasonic assistance provided by the application has the characteristics of high thermal stability, non-flammability and non-volatility compared with traditional organic solvents, so that the process has excellent stability and safety. At the same time, the low eutectic solvent is low in price and simple in preparation method, so that the process has the advantage of low cost; and the hydrogen bond formed between the hydrogen bond donor and the hydrogen bond acceptor in the low eutectic solvent makes it more conducive to extracting polyphenols from quinoa, and it has higher specificity than water and other solvents, and higher extraction rate than traditional solvents. The quinoa polyphenol extraction method provided by the application extracts quinoa polyphenols from quinoa, and the extraction rate can reach 6.078±0.025mg / g. In addition, based on the low eutectic solvent, the intermittent ultrasonic mode provided by the application can improve the efficiency of the low eutectic solvent in extracting quinoa polyphenols and reduce the loss of the instrument. At the same time, the intermittent ultrasonic power of the quinoa polyphenol extraction method provided by the application is 150-450W, and the ultrasonic power of 150W in the preferred embodiment of the application can achieve better quinoa polyphenol extraction efficiency. Compared with other quinoa polyphenol extraction methods assisted by ultrasonic in the prior art, the power consumption is low, so that the quinoa polyphenol extraction method provided by the application realizes higher extraction rate with smaller energy consumption, saves energy and cost, further improves the efficiency, and also has the advantages of safety, good stability and strong selectivity of the low eutectic solvent. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The polyphenol content determination standard curve graph in test example 1;

[0023] Figure 2 The polyphenol content graph of quinoa extract obtained by different solvent extraction methods determined in test example 1;

[0024] Figure 3 The residual diagnosis result graph of the factorial design quinoa polyphenol extraction rate fitting model in the verification example, wherein A is the normal probability graph; B is the scatter plot of the residual with respect to the fitted predicted value of the response variable as the horizontal axis; C is the histogram; D is the scatter plot of the residual with respect to the observation value order as the horizontal axis;

[0025] Figure 4 The main influencing factor graph of quinoa polyphenol extraction rate, wherein A is the standardized effect normal graph; B is the Pareto graph of standardized effect;

[0026] Figure 5 The influence situation graph of the water content of DES solution and the liquid-solid ratio on the quinoa polyphenol extraction rate, wherein A is the contour graph; B is the response surface graph;

[0027] Figure 6Figure for the influence of the water content of DES solution and ultrasonic temperature on the extraction rate of quinoa polyphenols, wherein A is the contour plot; B is the response surface plot;

[0028] Figure 7 Figure for the main factors affecting the extraction rate of quinoa polyphenols;

[0029] Figure 8 Figure for the interaction of factors affecting the extraction rate of quinoa polyphenols;

[0030] Figure 9 Figure for the polyphenol content in quinoa extract under different ultrasonic modes. DETAILED DESCRIPTION

[0031] In order to better understand the content of the present application, the embodiments of the present application are described in detail below. The embodiments are implemented on the premise of the technical solutions of the present application, and detailed implementation modes and specific operation processes are given. However, the content of the present application is not limited to the examples described below.

[0032] The reagents, materials and instruments involved in the embodiments of the present application are as follows:

[0033] Reagents and materials: The quinoa used is mature and unhulled seed produced in Qinghai-Tibet Plateau. Betaine (Bet, 98%), L-proline (Pro, 99%), glycerol (Gly, 99%), DL-lactic acid (La, ACS, ≥85%), levulinic acid (Lev, 99%), and the above reagents are purchased from Shanghai Aldrich Biochemical Technology Co., Ltd. Anhydrous ethanol is purchased from Shanghai Titan Chemical Co., Ltd. Methanol is purchased from Wuxi Yasheng Chemical Co., Ltd. Gallic acid is purchased from Shanghai Solabio Technology Co., Ltd. Anhydrous sodium carbonate is purchased from Shanghai Lingfeng Chemical Reagent Co., Ltd. Folin phenol is purchased from Shanghai Maikelin Biochemical Technology Co., Ltd. The above reagents are all of analytical purity unless otherwise specified.

[0034] Main instruments: Pulverizer (Wenling Lin, DFY-500), ultrasonic cell pulverizer (Ningbo Xinzhi, JY92-IIDN), centrifuge (Shanghai Anting, LXJ-IIB), ultraviolet spectrophotometer (Shanghai Jinghua, 754PC).

[0035] Table 1 Types of DES solvents used in the present application

[0036] Number Combination Abbreviation Molar ratio 1 Betaine:glycerol BetGly 1：2 2 Betaine:lactic acid BetLa 1：2 3 Betaine:levulinic acid BetLev 1：2 4 L-proline:glycerol ProGly 2：5 5 L-proline:lactic acid ProLa 1：2 6 L-proline:levulinic acid ProLev 1：1

[0037] Example 1

[0038] The fresh quinoa was put into a constant temperature drying oven at 50°C and dried for 48h, then crushed by a pulverizer, and sieved through an 80 mesh sieve to obtain quinoa powder, which was stored in a 4°C refrigerator for standby. L-proline and glycerol were vacuum dried for 24h, then 2mol L-proline was mixed with 5mol glycerol, heated and stirred at 80°C for 6h to dissolve, and vacuum dried overnight to obtain DES ProGly. 59mL ProGly was mixed with 41mL distilled water to obtain a DES solution ProGly solution. 1.28g quinoa powder was added into 100mL of the above ProGly solution for extraction, and an ultrasonic cell pulverizer was used for intermittent ultrasonic treatment at an ultrasonic power of 150W and a temperature of 59°C, with an intermittent ultrasonic mode of "on 1.0s-off 1.0s-on 1.0s-off 1.0s". After 60min of extraction, centrifugation was performed at 4000rpm for 10min, vacuum filtration was performed, and the filtrate was the quinoa polyphenol extract, which had a quinoa polyphenol content of 6.078±0.025mg / g.

[0039] Examples 2-7

[0040] The DES prepared according to the six formulations in Table 1 was used to extract polyphenols from quinoa, and the extraction conditions of Examples 2-7 were the same except for the DES formulation. The specific operation steps are as follows:

[0041] The fresh quinoa was put into a constant temperature drying oven at 50°C and dried for 48h, then crushed by a pulverizer, and sieved through an 80 mesh sieve to obtain quinoa powder, which was stored in a 4°C refrigerator for standby. The raw materials in Table 1 were vacuum dried for 24h, then mixed, heated and stirred at 80°C for 6h to dissolve, and vacuum dried overnight to obtain DES. 70mL DES was mixed with 30mL distilled water to obtain a DES solution.

[0042] 2g quinoa powder was added into 100mL of the above DES solution for extraction, and an ultrasonic cell pulverizer was used for intermittent ultrasonic treatment at an ultrasonic power of 400W and a temperature of 45°C, with an intermittent ultrasonic mode of "on 1.0s-off 1.0s-on 1.0s-off 1.0s". After 30min of extraction, centrifugation was performed at 4000rpm for 10min, vacuum filtration was performed, and the filtrate was the quinoa polyphenol extract.

[0043] Comparative Examples 1-5

[0044] Five conventional solvents, distilled water, ethanol, 70% ethanol, methanol, and 70% methanol, were used to extract polyphenols from quinoa, and the remaining extraction conditions were the same as those of Example 2.

[0045] Test Example 1: Determination of Polyphenol Content

[0046] 1. Before determining the polyphenol content, a standard curve should be prepared first. The standard curve is prepared as follows: 4 mg of gallic acid is weighed into a 100 mL volumetric flask, and distilled water is added to the mark and shaken to obtain a 0.04 mg / mL gallic acid standard solution. 0 mL, 0.5 mL, 1.0 mL, 1.5 mL, 2.0 mL, 2.5 mL, and 3 mL of the standard solution are respectively taken into 15 mL test tubes, and distilled water is added to 5 mL, then 0.5 mL of Folin-phenol is added, mixed, and incubated at room temperature for 5 min, then 1.0 mL of 10% Na2CO3 solution is added, and placed at room temperature for 1 h in the dark, and the absorbance is measured at 740 nm. The concentration of gallic acid is taken as the abscissa, and the absorbance is taken as the ordinate, and a standard curve is drawn. As shown in Figure 1 , the linear regression equation obtained is: y = 15.62x + 0.0324, R 2 = 0.9995.

[0047] 2. The polyphenol content of the quinoa polyphenol extract samples of Examples 2-7 and Comparative Examples 1-5 is measured according to the method of the standard curve: 1 mL of the sample solution is taken into a 15 mL test tube, 4 mL of distilled water is added, then 0.5 mL of Folin-phenol is added, mixed, and incubated at room temperature for 5 min, then 1 mL of 10% Na2CO3 solution is added, and placed at room temperature for 1 h in the dark, and the absorbance is measured at 740 nm. The polyphenol content in the sample is calculated according to the measured absorbance and the standard curve equation, and the result is expressed in mg gallic acid equivalent (GAE) / g dry weight (DW).

[0048] Polyphenol content calculation formula:

[0049] wherein, is the average of the absorbance measured by three repeated experiments, n is the dilution factor, V is the volume of the extract (mL), and w is the amount of the sample (g).

[0050] As can be seen from Figure 2 , the quinoa polyphenol extraction rate of the DES (glycerol DES) with alcohol as the HBD is higher than that of the DES (levulinic acid and lactic acid DES) with acid as the HBD, which may be due to the fact that the alcohol DES contains more hydroxyl groups, which have higher similarity with the structure of polyphenols, and thus more polyphenols can be extracted from quinoa. At the same time, the quinoa polyphenol extraction rate of the DES with L-proline as the HBA is higher than that of the corresponding betaine DES, which may be due to the fact that L-proline contains more hydrogen bond acceptors, which is more conducive to the formation of hydrogen bonds. In addition, the quinoa polyphenol extraction rate of ProGly is the highest among all reagents, which may be related to the fact that ProGly forms the most hydrogen bonds. Therefore, ProGly is selected as the extraction agent for subsequent process optimization.

[0051] Verification example: Main factors affecting the extraction rate of quinoa polyphenols

[0052] This invention employs a cubic center point, five-factor, two-level factorial design (2 5 +3) Identify the three most important factors affecting the polyphenol extraction rate. The factor-level table is shown in Table 2. Using Minitab software, analyze the influence of five factors on the quinoa polyphenol extraction rate at high and low levels: DES solution water content, liquid-to-solid ratio, ultrasonic power, ultrasonic time, and ultrasonic temperature. Then, select the three most important factors affecting the quinoa polyphenol extraction rate for subsequent process optimization.

[0053] Table 2 Factorial Design Factors-Level Table

[0054]

[0055] The factorial design of the experiment and the extraction rates of quinoa polyphenols under different combinations of factor levels are shown in Table 3. The results were analyzed using Minitab. The fitted model was: TPC = -2.373 + 0.1013A – 0.01161B + 0.01153D + 0.09292E + 0.000737AB – 0.001483AE, P = 0.000 < 0.05, and the lack of fit test P = 0.776 > 0.05, indicating that the model is effective and there is no lack of fit. 2 =94.16%, R 2 The adj = 92.91% indicates that the model fits well. Figure 3 As shown, in the residual diagnosis results, the residuals in the normal probability plot of Figure A are basically close to a straight line; the residuals in Figure B and the scatter plot of the residuals with the fitted predicted values ​​of the response variable as the horizontal axis and the residuals in Figure D with the order of the observed values ​​as the horizontal axis both fluctuate randomly around 0; the residuals in the histogram of Figure C show a normal distribution, which further proves the usability of the results. Figure 4 This shows the influence of different factors on the extraction rate of quinoa polyphenols. Figure 4 As shown in Figure A of the standardized effect normal plot, factors A (DES solution water content), E (ultrasonic temperature), AB (DES solution water content × liquid-to-solid ratio), B (liquid-to-solid ratio), D (ultrasonic time), and AE (DES solution water content × ultrasonic temperature) have significant effects on the extraction rate of quinoa polyphenols. Furthermore, factors A (DES solution water content), E (ultrasonic temperature), AB (DES solution water content × liquid-to-solid ratio), B (liquid-to-solid ratio), and D (ultrasonic time) are positively correlated with the extraction rate of quinoa polyphenols, while factor AE (DES solution water content × ultrasonic temperature) is negatively correlated with the extraction rate of quinoa polyphenols. The Pareto plot more intuitively illustrates the degree of influence of different factors on the extraction rate of quinoa polyphenols, such as...Figure 4 The influence of factors A (water content of DES solution), E (ultrasonic temperature) and B (liquid-to-material ratio) on the quinoa polyphenol extraction rate is the largest as shown in B of FIG. 1, and thus the three factors are selected for subsequent optimization. In addition, according to the experimental results of the factorial design, the quinoa polyphenol extraction rate at an ultrasonic time of 60 min is higher than that at 20 min and 40 min, and in order to obtain a higher extraction rate, the ultrasonic time is set to 60 min in subsequent experiments. Meanwhile, since the influence of ultrasonic power on the quinoa polyphenol extraction rate is not significant, the ultrasonic power is set to 150 W from the perspective of energy saving.

[0056] Table 3: Factorial design experiment design and results

[0057]

[0058] The central composite circumscribed design (CCC) is used to optimize the three main factors affecting the quinoa polyphenol extraction rate screened out by the factorial design experiment, and the optimal process parameters suitable for quinoa polyphenol extraction are obtained. The CCC factor level table is shown in Table 4.

[0059] Table 4: CCC factor level table

[0060]

[0061] Result analysis:

[0062] (1) Multiple linear regression and variance analysis

[0063] The CCC experimental design and the quinoa polyphenol extraction rate under different factor level combinations are shown in Table 5. The results are analyzed by Minitab and Design Expert, and the multiple regression equation and the variance analysis results are shown in Table 6. As shown in the table, the model P value is less than 0.05, the lack-of-fit test P value is greater than 0.05, the R 2 value is 0.9778, and the adjusted R 2 value is 0.9616, indicating that the model is significant and the fitting effect is good; the lack-of-fit term is not significant, and there is no lack-of-fit phenomenon. The three factors and their square terms are significant, indicating that the water content of the DES solution, the liquid-to-material ratio and the temperature are all key factors affecting the quinoa polyphenol extraction rate.

[0064] Table 5: CCC experimental design and results

[0065]

[0066]

[0067] Table 6: Variance analysis and multiple regression equation

[0068] Source Sum of squares Degrees of freedom Mean square F value P value Model 28.47 8 3.56 60.54 <0.0001 Significant A - moisture content 14.78 1 14.78 251.47 <0.0001 [R 2 = 0.9778 B - liquid material ratio 0.9743 1 0.9743 16.57 0.0018 [R 2 adj = 0.9616 C - temperature 5.21 1 5.21 88.69 <0.0001 PreR 2 = 0.9089 AB 0.3321 1 0.3321 5.65 0.0367 AC 1.07 1 1.07 18.13 0.0013 A2 5.71 1 5.71 97.12 <0.0001 B2 0.4830 1 0.4830 8.22 0.0153 C2 0.4905 1 0.4905 8.34 0.0147 Loss of fit 0.4144 6 0.0691 1.49 0.3402 Not significant

[0069] TPC (mg GAE / g) = 5.14 + 1.04A + 0.2671B + 0.6179C - 0.6294AB 2 -0.1831

[0070] B 2 -0.1845C 2 +0.2038AB - 0.3650AC.

[0071] (2) The effects of each factor on the extraction rate of polyphenols from quinoa and the interaction between two factors

[0072] The effects of each factor on the extraction rate of polyphenols from quinoa and the interaction between two factors are shown in Figure 5 to Figure 7 .

[0073] From the B graph in Figure 5 , it can be seen that as the water content of the DES solution increases, the extraction rate of polyphenols from quinoa gradually increases, reaches a maximum value when the water content is about 40%, and then begins to decrease as the water content of the DES solution continues to increase. Appropriate water content can adjust the flowability of DES, making it more conducive to the extraction of polyphenols from quinoa; but when the water content exceeds a certain degree, water may destroy the hydrogen bonds between HBA and HBD, thereby reducing the extraction rate.

[0074] At the same time, the extraction rate of polyphenols from quinoa gradually increases as the liquid-to-material ratio increases, and then gradually tends to be constant and decreases when the liquid-to-material ratio is about 75:1 mL / g. This may be because when the liquid-to-material ratio increases, the concentration difference between the solvent and the raw material increases, and the dissolution rate of polyphenols increases, but when the liquid-to-material ratio is too large, the cavitation effect and mechanical vibration of ultrasonic waves are affected, and the polyphenol yield decreases.

[0075] From the B graph in Figure 6 , it can be seen that within a certain range, the extraction rate of polyphenols from quinoa increases as the temperature increases, and when the temperature reaches about 60°C, the extraction rate of polyphenols from quinoa begins to decrease as the temperature increases. As the temperature increases, the diffusion coefficient of polyphenols in the solvent increases, which is conducive to the extraction of polyphenols from quinoa; but when the temperature is too high, the structure of polyphenols may be damaged, thereby reducing the extraction rate of polyphenols.

[0076] The above results can be more intuitively seen from the main factor graph in Figure 7 .

[0077] In addition, as shown in the A graph in Figure 5 and the B graph in Figure 6 , the extraction rate of polyphenols from quinoa increases as the liquid-to-material ratio increases, and then gradually tends to be constant and decreases when the liquid-to-material ratio is about 75:1 mL / g. This may be because when the liquid-to-material ratio increases, the concentration difference between the solvent and the raw material increases, and the dissolution rate of polyphenols increases, but when the liquid-to-material ratio is too large, the cavitation effect and mechanical vibration of ultrasonic waves are affected, and the polyphenol yield decreases.As shown in the A diagram in the figure, the contour lines in the contour diagrams of the effects of DES solution water content and liquid-to-material ratio and DES solution water content and ultrasonic temperature on the quinoa polyphenol extraction rate are all elliptical; and in the interaction diagram, the curves all intersect, indicating that there is interaction between DES solution water content and liquid-to-material ratio and between DES solution water content and ultrasonic temperature, which is consistent with the results of the variance analysis. Figure 8

[0078] (3) Model prediction and verification

[0079] The model obtained by fitting was used for prediction, and the parameter combination most beneficial to quinoa polyphenol extraction was obtained as follows: DES solution water content of 41.0816%, liquid-to-material ratio of 78.4756 mL: 1 g, and ultrasonic temperature of 59.1974°C. Considering the feasibility of actual operation, the parameter values were rounded, i.e., the conditions set in Example 1 were consistent: DES solution water content was set to 41%, liquid-to-material ratio was 78 mL: 1 g, and ultrasonic temperature was 59°C. Three experiments were performed under these conditions, and the quinoa polyphenol extraction rate obtained was 6.078 ± 0.025 mg / g, which was within the 95% confidence interval, indicating that the model was effective.

[0080] Example 8

[0081] The difference between the quinoa polyphenol extraction step of Example 8 and that of Example 1 is only that the intermittent ultrasonic mode of Example 8 is "on 0.5 s-off 0.5 s-on 0.5 s-off 0.5 s".

[0082] Example 9

[0083] The difference between the quinoa polyphenol extraction step of Example 9 and that of Example 1 is only that the intermittent ultrasonic mode of Example 9 is "on 1.5 s-off 1.5 s-on 1.5 s-off 1.5 s".

[0084] Example 10

[0085] The difference between the quinoa polyphenol extraction step of Example 10 and that of Example 1 is only that the intermittent ultrasonic mode of Example 10 is "on 2.0 s-off 2.0 s-on 2.0 s-off 2.0 s".

[0086] Example 11

[0087] The difference between the quinoa polyphenol extraction step of Example 11 and that of Example 1 is only that the intermittent ultrasonic mode of Example 11 is "on 3.0 s-off 3.0 s-on 3.0 s-off 3.0 s".

[0088] Comparative Example 6

[0089] ​The quinoa polyphenol extraction step of Comparative Example 6 differs from that of Example 1 only in that the continuous ultrasonic mode is used in Comparative Example 6. Specifically, in the continuous ultrasonic mode of Comparative Example 6, the total extraction time and the effective ultrasonic time are controlled to be the same, and the extraction is performed first by continuous ultrasonic extraction for 30 min, and then by ultrasonic extraction with the ultrasonic turned off for 30 min, so that the total extraction time is 60 min and the effective ultrasonic time is 30 min.

[0090] As shown in Table 7, the different ultrasonic modes in Example 1, Examples 8-11 and Comparative Example 6 are compared.

[0091] Table 7

[0092] Number Ultrasonic regime Abbreviation Example 8 Intermittent, "on 0.5 s - off 0.5 s - on 0.5 s - off 0.5 s" mode 0.5 s / 0.5 s Example 1 Intermittent, "on 1.0 s - off 1.0 s - on 1.0 s - off 1.0 s" mode 1.0 s / 1.0 s Example 9 Intermittent, "on 1.5 s - off 1.5 s - on 1.5 s - off 1.5 s" mode 1.5 s / 1.5 s Example 10 Intermittent, "on 2.0 s - off 2.0 s - on 2.0 s - off 2.0 s" mode 2.0 s / 2.0 s Example 11 Intermittent, "on 3.0 s - off 3.0 s - on 3.0 s - off 3.0 s" mode 3.0 s / 3.0 s Comparative Example 6 Continuous Continue

[0093] The extraction rates of Example 1, Examples 8-11 were determined according to the polyphenol content determination method described in Test Example 1 above, and it was found that Figure 7 that the ultrasonic mode has a significant effect on the extraction rate of quinoa polyphenols, and the extraction effect of intermittent ultrasonic is better than that of continuous ultrasonic. This may be due to the fact that long-term continuous ultrasonic causes a hollow zone around the probe, and the extraction liquid cannot fully contact the probe, resulting in poor ultrasonic effect. At the same time, this operation causes the temperature to rise, and the instrument is damaged. The present application further investigates the effect of different intermittent ultrasonic modes on the extraction rate of quinoa polyphenols, and the results are shown in Table 8. Figure 9 As shown in Table 8, within a certain range, the extraction rate of quinoa polyphenols increases with the extension of ultrasonic / intermittent time, and appropriately extending the ultrasonic working time helps to fully exert the cavitation effect of ultrasonic waves. However, when the continuous ultrasonic working time is further extended, the solution will be hollowed out, causing the instrument to appear almost empty, thereby causing the extraction rate to gradually decrease. In addition, due to the intermittent time compared with continuous ultrasonic, the liquid will return to the probe when the ultrasonic is stopped, and the extraction liquid contacts the probe for a longer time than continuous ultrasonic, so the extraction rate is higher than that of continuous ultrasonic. Compared with Examples 8-11 and Comparative Example 6, the intermittent ultrasonic mode of "on 1.0 s-off 1.0 s-on 1.0 s-off 1.0 s" in Example 1 has the highest extraction rate of quinoa polyphenols. Therefore, it can be concluded that the necessary intermittent time can alleviate the overheating of the instrument caused by continuous work, prevent the solution from appearing hollow, and at the same time, the appropriate continuous working time can fully exert the cavitation effect of ultrasonic waves, thus being most conducive to the extraction of quinoa polyphenols.

[0094] The above description is only a preferred embodiment of the present application, and is not limited to the above-described embodiments, but any equivalent modifications, equivalent replacements and improvements made by those skilled in the art based on the disclosed content of the present application shall be included in the protection scope recited in the claims.

Claims

1. A method for extracting quinoa polyphenols based on a deep eutectic solvent and ultrasonic assistance, characterized by, The method comprises the following steps: A DES solution is added to the quinoa powder, wherein the liquid-solid ratio of the DES solution and the quinoa powder is (8-92) mL:1 g; after mixing the quinoa powder and the DES solution, ultrasonic treatment is performed, followed by centrifugation and vacuum filtration; the filtrate obtained by the vacuum filtration is a quinoa polyphenol extract solution; The ultrasonic treatment is performed at a temperature of 20-70 ℃ for 20-60 min at a power of 150-450 W, and the ultrasonic treatment is intermittent, i.e., the ultrasonic treatment is performed in a mode of "on for N seconds-off for N seconds-on for N seconds-off for N seconds", wherein N is 1-1.5; The quinoa powder has a mesh number of at least 80 meshes, and is obtained by drying, crushing and sieving fresh quinoa; The DES solution is prepared by mixing a hydrogen bond donor (HBD) and a hydrogen bond acceptor (HBA) in a molar ratio of (1-5):(1-5) after vacuum drying, heating and stirring, and then vacuum drying again, and adding distilled water for stirring; The hydrogen bond donor (HBD) is glycerol. The hydrogen bond acceptor (HBA) is L-proline.

2. The quinoa polyphenol extraction method based on deep eutectic solvent and ultrasonic assistance according to claim 1, characterized in that, The amount of distilled water added accounts for 5-55% of the total volume of the DES solution.

3. The quinoa polyphenol extraction method based on deep eutectic solvent and ultrasonic assistance according to claim 2, characterized in that, The amount of distilled water added accounts for 41% of the total volume of the DES solution.

4. The method for quinoa polyphenol extraction based on deep eutectic solvent and ultrasonic assistance according to claim 1, characterized in that, The DES solution is prepared by mixing a hydrogen bond donor (HBD) and a hydrogen bond acceptor (HBA) after vacuum drying for 24 h, heating and stirring at 80 ℃ for 6 h to dissolve, and then vacuum drying overnight to obtain DES, and then mixing the DES with distilled water in a volume ratio of 41:

59. 5.The quinoa polyphenol extraction method based on a deep eutectic solvent and ultrasonic assistance according to claim 1, characterized in that, The fresh quinoa is dried in a constant temperature drying oven.

6. The method for quinoa polyphenol extraction based on deep eutectic solvent and ultrasonic assistance according to claim 5, characterized in that, The fresh quinoa is dried in a constant temperature drying oven at 50 ℃ for 48 h.

7. The method for quinoa polyphenol extraction based on deep eutectic solvent and ultrasonic assistance according to claim 1, characterized in that, The quinoa powder is stored at a temperature of 4 ℃.

Images