CN115154555A

CN115154555A - Green and sustainable millet polyphenol extraction method and application

Info

Publication number: CN115154555A
Application number: CN202210823148.XA
Authority: CN
Inventors: 王晓闻; 张宏丽; 荆旭; 王敏; 白涛; 付丽红
Original assignee: Shanxi Agricultural University
Current assignee: Shanxi Agricultural University
Priority date: 2022-07-13
Filing date: 2022-07-13
Publication date: 2022-10-11
Anticipated expiration: 2042-07-13
Also published as: CN115154555B

Abstract

The invention relates to a method for continuously extracting millet polyphenol and application thereof, belonging to the technical field of extraction and processing. The method comprises the steps of carrying out ultrahigh pressure pretreatment on millet, using a hydrophilic eutectic solvent with convertible property as an extracting agent, and carrying out auxiliary grinding by beta-cyclodextrin to extract millet polyphenol, so as to greatly improve the extraction yield of the millet polyphenol. And then, the characteristic of the convertible eutectic solvent is utilized to convert the hydrophilic eutectic solvent into hydrophobic property, so that the recovery of the millet polyphenol is realized. And finally, converting the recovered hydrophobic eutectic solvent into hydrophilic solvent, and repeatedly extracting a new millet sample to realize the cyclic utilization of the eutectic solvent. The method has the advantages of simple and quick operation, low cost, environmental protection, high efficiency, sustainable recycling of the extractant and great saving of the production cost.

Description

Green and sustainable millet polyphenol extraction method and application

Technical Field

The invention relates to a method for green sustainable extraction of millet polyphenol and application thereof, belonging to the technical field of extraction and processing.

Background

Millet is an important cereal crop and is cultivated in arid and semiarid tropical regions, and more than 25 countries in asia and africa use millet as a staple food. Millet is rich in polyphenol, protein, dietary fiber and micronutrients, so that millet is more nutritious than common grains such as rice, wheat and the like. There are studies reporting that millet polyphenols have many beneficial health properties, such as antioxidant, anti-inflammatory, antiviral, anticancer and platelet aggregation inhibiting activities. The research on the extraction of the millet polyphenol has important significance on the research on the application of bioactive compounds of natural plant materials.

In the extraction of the active substance, conventional organic solvents are often used as extractants, such as methanol, ethanol, acetone, etc. However, the extraction rate of millet polyphenol by using the traditional organic solvent is low, the toxicity is high, the biodegradability is poor, and a large amount of the organic solvent is used to cause environmental pollution, so that how to effectively extract millet polyphenol without toxicity is a technical problem to be solved urgently.

Because of low cost, greenness, good biodegradability and high yield, the eutectic solvent is being used as a substitute solvent of an organic solvent in natural product extraction. However, the vapor pressure of the eutectic solvent is low, and the extracted compound cannot be separated from the eutectic solvent by the conventional reduced pressure concentration method. Currently, in the prior art, macroporous resin column chromatography is often applied to the separation of target compounds. However, the macroporous resin has high production cost, complex operation and time consumption. Therefore, the development of the eutectic solvent which can realize green and high-efficiency extraction of the bioactive compound and can simply, quickly and efficiently recover the target compound from the extractant as the extractant has important practical significance.

Disclosure of Invention

Technical problem to be solved

The invention provides a method for green sustainable extraction of millet polyphenol, aiming at solving the problems that the prior extracting agent has low extraction yield, higher toxicity and poor biodegradability, can possibly cause environmental pollution, and the extract is not easy to recover from the extracting agent.

(II) technical scheme

In order to achieve the purpose, the invention adopts the main technical scheme that:

a green sustainable extraction method of millet polyphenol comprises the following steps:

s1, mixing millet and water, placing a mixed sample in an ultrahigh pressure container, performing ultrahigh pressure pretreatment, drying, crushing by a crusher, and sieving;

s2, adding the sieved millet powder into a hydrophilic switchable eutectic solvent containing beta-cyclodextrin, extracting, centrifuging once, and collecting supernatant to obtain a millet polyphenol extracting solution;

and S3, adding the millet polyphenol extracting solution into an acid solution, carrying out secondary centrifugation to separate two phases, wherein the upper layer is a hydrophobic eutectic solvent phase, the lower layer is a water phase containing millet polyphenol, and collecting and freeze-drying the lower layer to obtain the millet polyphenol solid.

The method as described above preferably further comprises step S4 of adding an alkali to the upper hydrophobic eutectic solvent phase in step S3 to convert the upper hydrophobic eutectic solvent phase into a hydrophilic switchable eutectic solvent, which can be recycled.

In the method described above, preferably, in step S1, the millet and water are mixed in a mass ratio of 1.

In the method, preferably, in step S1, the ultrahigh pressure pretreatment is performed under a pressure of 300 to 500MPa for 5 to 20min.

Further, the millet and the water are mixed according to the mass ratio of 1.

In the method, preferably, in step S2, the switchable eutectic solvent is a mixed solution of caprylic acid and linalool, nonanoic acid and linalool, or decanoic acid and linalool, and the mixing ratio is 3-1: 1-3, and the hydrophilic property means that the pH value is 8.5-9.5. Preferably, the mixing ratio is in a molar ratio of 2.

Further, the switchable eutectic solvent is most preferably a mixture of caprylic acid and linalool in a molar ratio of 1.

In the method as described above, preferably, in step S2, the concentration of the β -cyclodextrin in the switchable eutectic solvent is 10 to 30g/L. Further, the concentration of beta-cyclodextrin is preferably 12 to 20g/L, most preferably 16g/L.

In the method as described above, preferably, in step S2, the extraction is performed by grinding or water bath, the frequency of the grinding is 30HZ, and the time of the grinding is 60 to 120S; the temperature of the water bath is 50 ℃ and the time is 120min.

Further, the extraction is preferably carried out for a milling time of 80s.

The method as described above, preferably, in step S2, the millet powder and the switchable eutectic solvent are performed in a ratio of 1;

the first centrifugation is 5000-7000 rpm, and the centrifugation lasts for 1-3 min.

Further, it is preferable that the millet powder and the switchable eutectic solvent are performed in a ratio of 1.

In the method, preferably, in step S3, the acid solution is hydrochloric acid or sulfuric acid or carbonic acid solution, so that the pH is 6 to 7, and the secondary centrifugation is 7000 to 10000rpm for 2 to 10min.

Further preferably, in step S3, the addition amount of the hydrochloric acid solution is made low in hydrophobicityAdding the volume ratio of the eutectic solvent to the hydrochloric acid solution of 1mol L ^-1 ；

In the method as described above, preferably, in step S4, a solid or solution of a base, such as sodium hydroxide, ammonia water, sodium bicarbonate, potassium hydroxide, is added to the resultant switchable eutectic solvent solution, and the pH is adjusted to 8.5 to 9.5, i.e., converted into a hydrophilic switchable eutectic solvent.

Further preferably, in step S4, the alkali is a NaOH solution, and is added in a volume ratio of the hydrophobic eutectic solvent to the NaOH solution of 1 ^-1 。

The application of the mixed solvent of caprylic acid and linalool in extracting millet polyphenol.

As described above, preferably, the mixture of caprylic acid and linalool is mixed according to the following ratio of 2,1 or 1.

(III) advantageous effects

The invention has the beneficial effects that:

the invention provides a method for continuously extracting millet polyphenol, which adopts a physical non-thermal processing technology, namely an ultrahigh pressure technology, to carry out ultrahigh pressure pretreatment on millet, so that the cell structure of the millet is destroyed, polyphenol substances in the millet are easier to dissolve out, a hydrophilic switchable eutectic solvent is used as an extracting agent, beta-cyclodextrin is used as an auxiliary extracting agent, millet polyphenol is ground and extracted, the yield of the millet polyphenol is greatly improved, the method is more than ten times of the traditional ethanol extraction method, and the extraction efficiency is greatly improved.

According to the green sustainable extraction method of millet polyphenol, provided by the invention, the eutectic solvent with convertible property is used as the extractant, and the conversion of the hydrophilicity and the hydrophobicity of the extractant can be realized only by converting the pH of the solution, so that the extractant extracts the millet polyphenol in the hydrophilic state, the separation of a water phase and the eutectic solvent phase occurs in the hydrophobic state, and the polyphenol is separated and recovered from the extractant, and the problems that the vapor pressure of the low eutectic solvent is low in the traditional method, and the extracted compound cannot be separated from the eutectic solvent by a conventional reduced pressure concentration method are solved.

According to the green sustainable extraction method of millet polyphenol provided by the invention, the used solvent utilizes the convertible property of the extractant, so that the extractant is recovered from the extracting solution and is used for extracting a new millet sample, the cycle is repeated for five times, the polyphenol yield of the extractant is not obviously reduced, the problem of recycling the extractant is realized, and the production cost is greatly saved.

Drawings

FIG. 1 shows the effect of different pressure of ultra-high pressure pretreatment on the yield of millet polyphenols;

FIG. 2 shows the effect of different times of ultra-high pressure pretreatment on the yield of millet polyphenols;

FIG. 3 shows the effect of different types of extractants on the yield of millet polyphenols;

FIG. 4 shows the effect of different eutectic solvent molar ratios on the yield of millet polyphenols;

FIG. 5 shows the effect of different feed liquid ratios on the yield of millet polyphenols;

FIG. 6 shows the effect of different extraction methods on the yield of millet polyphenols;

FIG. 7 shows the effect of different extraction times on the yield of millet polyphenols;

FIG. 8 shows the effect of different concentrations of beta-cyclodextrin on the yield of millet polyphenols;

fig. 9 shows the yield of millet polyphenols extracted from the new and recovered eutectic solvents.

Detailed Description

According to the invention, a large number of experimental researches show that the millet is subjected to ultrahigh pressure pretreatment, a convertible eutectic solvent synthesized by caprylic acid and linalool is selected as an extracting agent, and beta-cyclodextrin assists in grinding and extracting millet polyphenol, so that the extraction yield of polyphenol is improved. And then, the characteristic of the convertible eutectic solvent is utilized to convert the hydrophilic eutectic solvent into hydrophobic property, so that the recovery of the millet polyphenol is realized. And finally, converting the recovered hydrophobic eutectic solvent into hydrophilic solvent, and repeatedly extracting a new millet sample to realize the cyclic utilization of the eutectic solvent.

The method adopts the switchable eutectic solvent and combines the ultrahigh pressure pretreatment to extract and recover the millet polyphenol, and recovers and reuses the switchable eutectic solvent. The invention creatively establishes that the extractant can realize the conversion of hydrophilic property and hydrophobic property under the condition of changing the pH value of the extractant, so that the extractant can extract the millet polyphenol in a hydrophilic state, the millet polyphenol and the extractant are separated in a hydrophobic state, the polyphenol is recovered, the extractant is recovered and can be extracted and utilized in a new round, and finally the extraction of the millet polyphenol by sustainable utilization is realized. Solves the problems of high extraction cost, no green color, low yield and incapability of separating the extracted compound from the eutectic solvent by a conventional reduced pressure concentration method in the prior art.

The invention provides a method for green and sustainable extraction of millet polyphenol by combining ultrahigh pressure pretreatment with switchable eutectic solvent, which comprises the following steps:

s1, sample pretreatment: mixing semen Setariae and distilled water, and sealing in polyethylene plastic bag with vacuum sealing machine. Then placing the mixed sample in an ultrahigh pressure container, carrying out ultrahigh pressure pretreatment, then freeze-drying, crushing by a crusher, and sieving;

s2, extracting millet polyphenol: adding the sieved millet powder into a hydrophilic eutectic solvent containing beta-cyclodextrin, grinding and extracting by using a grinder, performing first centrifugation, and collecting supernatant to obtain a millet polyphenol extracting solution;

s3, adding an acid solution into the millet polyphenol extracting solution to convert a hydrophilic eutectic solvent into hydrophobicity so as to realize two-phase separation, wherein the pH value of an upper hydrophobic phase ranges from 6 to 7, performing second centrifugation, converting the eutectic solvent into hydrophobicity, separating the two phases, wherein the upper hydrophobic eutectic solvent phase is the upper hydrophobic eutectic solvent phase, the lower aqueous phase is the lower aqueous phase, recovering the millet polyphenol in the extracting solution into the aqueous phase, and performing vacuum freeze drying on the lower aqueous phase to obtain a millet polyphenol solid;

s4, recycling the extractant: and taking the hydrophobic eutectic solvent on the upper layer recovered by the phase separation in the third step, continuously adding alkali to ensure that the eutectic solvent is in an alkaline condition, preferably has a pH value of 8.5-9.5, converting the eutectic solvent into a hydrophilic eutectic solvent which can be used for extracting a new millet sample, and then continuously recovering the extractant and repeating the extraction test to realize recovery and reuse.

Preparation of switchable eutectic solvents as described above: preferably, three saturated fatty acids, namely caprylic acid, pelargonic acid and capric acid, are used as hydrogen bond acceptors, linalool is used as a hydrogen bond donor, the three saturated fatty acids are mixed according to a proper molar ratio, and the mixture is stirred by a magnetic stirrer to become uniform, transparent and clear liquid, so that three switchable eutectic solvents (caprylic acid-linalool, pelargonic acid-linalool and capric acid-linalool) are prepared. Adding solid or solution of alkali such as sodium hydroxide, ammonia water, sodium bicarbonate, potassium hydroxide, etc. into the synthesized convertible eutectic solvent solution, adjusting pH to 8.5-9.5, converting the solution into uniform water phase without phase separation, indicating that the hydrophobic eutectic solvent is converted into hydrophilic, and further preferably adding 1mol L ^-1 According to the ratio of the hydrophobic eutectic solvent: sodium hydroxide solution was added at a volume ratio of 1 ^-1 Beta-cyclodextrin.

For the purpose of better explaining the present invention and to facilitate understanding, the present invention will be described in detail by way of specific embodiments with reference to the accompanying drawings.

EXAMPLE 1 ultra high pressure pretreatment Condition optimization

A. Optimization of pretreatment pressure

(1) The experimental method comprises the following steps: millet sample (300 g) was mixed with distilled water (300 g) and sealed in a polyethylene plastic bag using a vacuum sealer. The mixed sample was then placed in an ultra-high pressure vessel and pretreated at a pressure of (0, 300, 400, 500, 600 MPa) for 15min. Vacuum freeze drying (24 h), pulverizing, and sieving with 40 mesh sieve.

Accurately weighing 0.1g of the sieved millet powder after the treatment in a 2mL centrifuge tube, and adding an extracting agent: containing the active ingredient in a concentration of 16mg mL ^-1 Extracting with a mill (grinding frequency of 30 Hz) for 80s in 1mL of hydrophilic eutectic solvent of beta-cyclodextrin, centrifuging at 7000rpm for 2min, and collectingSupernatant fluid is obtained to obtain millet polyphenol extracting solution, and finally gallic acid is used as a standard substance, and the yield of polyphenol in the extracting solution is determined by adopting a Folin phenol method.

The preparation method of the extracting agent (hydrophilic eutectic solvent) comprises the steps of mixing caprylic acid and linalool according to the molar ratio of 1. Taking 1mL of the synthesized eutectic solvent, and adding 16mg of beta-cyclodextrin into the eutectic solvent to ensure that the concentration of the beta-cyclodextrin is 16mg mL ^-1 。

Previously, through preliminary experiments, studies found that eutectic solvents synthesized with menthol, terpineol, citronellol, geraniol as hydrogen bond donors do not have convertible properties; hydroxypropyl-beta-cyclodextrin can affect the determination of the folin phenol method, and cannot be used for extracting millet polyphenol. Researches find that the yield of the millet polyphenol without adding the beta-cyclodextrin is lower than that with adding the beta-cyclodextrin.

The detailed operation of the Fulinfen method determination:

adding 50 mu L of millet polyphenol extract into a colorimetric tube, adding 50 mu L of Folin phenol reagent, shaking uniformly, standing in the dark for 2min, adding 100 mu L of 12% sodium carbonate solution, diluting with distilled water to a constant volume of 5mL, standing in the dark for 2h, preparing a blank control by the same method, and finally detecting the light absorption value at the wavelength of 760 nm.

Accurately weighing gallic acid standard 5.0mg, dissolving with extractant, and making into gallic acid standard solutions (0.1, 0.2,0.3,0.4,0.5,1.0mg mL) with different concentrations ^-1 ) Taking 50 mu L of gallic acid standard solutions with different concentrations respectively, performing the steps of the determination, and finally detecting the light absorption value at the wavelength of 760nm, and taking the concentration of the gallic acid as a horizontal coordinate and the light absorption as a vertical coordinate to prepare a gallic acid standard curve. Substituting the absorbance value of the sample to be detected into a gallic acid standard curve to obtain the mass concentration of the polyphenol, and calculating according to a formula (1) to obtain the polyphenol yield.

Yield of millet polyphenol (mg g) ^-1 )＝nCV/M (1)

In the formula: n is the dilution multiple; in this example, n is 100;

c is the mass concentration of polyphenol, mg mL ^-1 ；

V is the volume of the extracting solution, mL;

m is the mass of the millet flour, g. (2) experimental results: as shown in fig. 1.

The results illustrate the effect of different pressure conditions (0, 300, 400, 500, 600 MPa) of the ultra-high pressure pretreatment on the yield of millet polyphenols. When the pressure is continuously increased, the millet polyphenol yield is continuously increased, and the pressure reaches 500MPa, the millet polyphenol yield reaches the highest value, and the pressure is continuously increased, so that the yield is reduced. This is because the ultra-high pressure destroys the cell structure of millet, and makes polyphenols in millet more easily dissolved out, but the ultra-high pressure may degrade polyphenols. Therefore, the ultrahigh pressure is preferably 500MPa.

B. Optimization of pretreatment time

(1) The experimental method comprises the following steps: the same method as A in example 1 was used except that the ultrahigh pressure pretreatment was carried out for different periods of time (0,5, 10, 15, 20 min) at an ultrahigh pressure of 500MPa.

(2) The experimental results are as follows: as shown in fig. 2.

The results show that the yield of millet polyphenol increases with the increase of the processing time, and the yield begins to be kept unchanged at 15min. This is because the cell structure of the millet flour is more largely destroyed with the continuation of the ultrahigh pressure treatment time, and the cell structure is sufficiently destroyed by further extending the treatment time, and the dissolution of the target substance is not further promoted. Therefore, the ultrahigh pressure time is preferably 15min.

Example 2 optimization of switchable eutectic solvent extraction conditions

A. Kinds of extracting agents

(1) The experimental method comprises the following steps: the same method as A in example 1, except that different kinds of extractants are respectively used, and the extractants are respectively selected from three switchable eutectic solvents (caprylic acid-linalool, pelargonic acid-linalool, capric acid-linalool, all synthesized according to a molar ratio of 3.

(2) The experimental results are as follows: as shown in fig. 3.

The result shows that the eutectic solvent is obviously higher than the yield of millet polyphenol extracted by ethanol, and the octoate-linalool extract has the strongest capacity of extracting the millet polyphenol. This may be related to the strength of the hydrogen bonding interaction and hydrophilicity of the switchable eutectic solvent. Thus, beta-cyclodextrin containing linalool-octanoate is preferred as the extractant.

B. Molar ratio of eutectic solvent

(1) The experimental method comprises the following steps: the same procedure as in a in example 1, except that the eutectic solvent was synthesized using different molar ratios of octanoic acid and linalool (3.

(2) The experimental results are as follows: as shown in fig. 4.

The results show that with octanoic acid in the eutectic solvent: the mol ratio of linalool is continuously reduced, the yield is gradually increased, and when the mol ratio is 1: the yield was highest at 1 and then decreased. This is probably because the molar ratio affects the surface tension of the eutectic solvent and the degree of dissociation during extraction. Thus, caprylic acid was selected: linalool is 1:1 in a molar ratio.

C. Optimization of feed-liquid ratio

(1) The experimental method comprises the following steps: the same procedure as in A in example 1 was followed, except that different feed-to-liquid ratios (i.e., millet flour and hydrophilic eutectic solvent in g: mL) were used at 500MPa in each case of 1:5,1:10,1:20,1:30,1:40,1:50 extracting the millet polyphenol.

(2) The experimental results are as follows: as shown in fig. 5.

The result shows that the yield of the millet polyphenol is continuously increased along with the increase of the feed-liquid ratio, and the ratio of the millet polyphenol to the feed-liquid ratio is 1:10g mL ^-1 Highest, then not significantly improved, 1. 1, 40, but from the viewpoint of cost saving, the ratio of the millet flour to the hydrophilic eutectic solvent is preferably 1:10g mL ^-1 。

D. Optimization of extraction mode

(1) The experimental method comprises the following steps: the same procedure as in A in example 1 was followed except that different extraction methods were used at a pressure of 500MPa (milling extraction: 80s, ultrasonic extraction: 50 ℃ C., 15min, water bath extraction: 50 ℃ C., 120 min).

(2) The experimental results are as follows: as shown in fig. 6.

The results show that the yield of millet polyphenol extracted by grinding is obviously higher than that of ultrasonic extraction and water bath extraction. Grinding extraction can enable the extractant to be in more sufficient contact with the millet sample, has small destructive capacity on the structure of a target object, and is easier to extract quickly and efficiently. Therefore, the millet polyphenol is preferably extracted by grinding extraction.

E. Optimization of extraction time

(1) The experimental method comprises the following steps: the same method as A in example 1 was used except that the time for the attritor extraction was changed to different extraction times (20, 40, 60, 80, 100, 120 s) at a pressure of 500MPa.

(2) The experimental results are as follows: as shown in fig. 7.

The results show that the yield gradually increases with the extension of the extraction time, and the yield is highest when the extraction time is 80s and then is basically kept unchanged. This is because when the polyphenol is sufficiently extracted, the extraction time is further prolonged and the yield is not changed. From the viewpoint of the extraction rate, cost, and the like, the most preferable extraction time is determined to be 80s.

F. Optimization of beta-cyclodextrin concentration

(1) The experimental method comprises the following steps: the same procedure as in A in example 1, under a pressure of 500MPa, except that different β -cyclodextrin concentrations (0, 10, 12, 16, 20, 30mg mL) were used, respectively ^-1 )。

(2) The experimental results are as follows: as shown in fig. 8.

The result shows that the yield is increased along with the increase of the concentration of the beta-cyclodextrin, and the concentration of the beta-cyclodextrin is 16mg mL ^-1 ～30mg mL ^-1 The highest yield is 16mg mL ^-1 Initially and then remains unchanged. Therefore, the preferred concentration of beta-cyclodextrin is 16mg mL ^-1 。

Example 3 recovery of millet polyphenols

In the same manner as in A in example 1, 900. Mu.L of the obtained millet polyphenol extract was put into a centrifuge tube under 500MPa, and 540. Mu.L of 1mol L was added ^-1 The HCl solution (added according to the volume ratio of the extracting solution to the HCl solution being 5). And (4) further centrifuging (8000rpm, 5 min), separating two phases, separating the two phases, wherein the two immiscible phases are generated, the upper layer is insoluble in water and is a hydrophobic phase, the lower layer is a water phase, the polyphenol in the extracting solution is recovered into the water phase, the upper layer and the lower layer are separated, and the water phase is subjected to vacuum freeze drying for 24 hours (the vacuum degree is less than 20Pa, and the temperature of a freeze drying cold trap is-30 to-60 ℃) to obtain the millet polyphenol solid.

EXAMPLE 4 recovery of eutectic solvent and New extraction

(1) The experimental method comprises the following steps: 200. Mu.L of the upper hydrophobic eutectic solvent recovered from the two-phase separation in example 3 was taken out of the centrifuge tube, and 800. Mu.L of 1mol L of the solvent was added ^-1 The addition amount of NaOH (the volume ratio of the hydrophobic eutectic solvent to the NaOH solution is 1 ^-1 ) At this time, the pH was about 9, and the eutectic solvent was changed to a hydrophilic eutectic solvent for extracting a new millet sample (0.1 g), and the above operation was repeated for extracting a new millet sample.

(2) The experimental results are as follows: as shown in fig. 9.

The influence of the use times (1, 2,3,4,5, 6) of the eutectic solvent on the yield of the millet polyphenol is examined in the experiment. The result shows that the yield of the millet polyphenol does not obviously reduce with the increase of the repeated use times of the eutectic solvent. Therefore, the switchable eutectic solvent selected by the experiment is shown to have good recyclability in the millet polyphenol extraction.

Example 5

Millet sample (300 g) was mixed with distilled water (300 g) and sealed in a polyethylene plastic bag using a vacuum sealer. The mixed sample was then placed in an ultra-high pressure vessel and pre-treated at a pressure of 500MPa for 15min. After vacuum freeze drying (24 h), crushing and sieving with a 40-mesh sieve.

Accurately weighing the sieved millet flour after the treatment, and adding the millet flour with the concentration of 16mg mL ^-1 The addition proportion of the hydrophilic eutectic solvent of the beta-cyclodextrin is 1:10 (g: mL), the hydrophilic eutectic solvent is prepared by mixing caprylic acid and linalool according to a molar ratio of 1; and adding beta-cyclodextrin to the solution to make the concentration of the beta-cyclodextrin be 16mg mL ^-1 Extracting at grinding frequency of 30HZ for 80s, centrifuging at 7000rpm for 2min, and collecting supernatant to obtain semen Setariae polyphenol extract.

The concentration of millet polyphenol in the extract was measured by the method of example 1, and the yield of millet polyphenol was calculated according to the formula (1) to obtain a yield of millet polyphenol of 5.4mg g ^-1 。

Comparative example 1

In the prior art, 60% ethanol is generally adopted as an extractant to ultrasonically extract millet polyphenol, and the yield is 0.5mg g ^-1 . The specific operation is as follows:

pulverizing semen Setariae sample, sieving with 40 mesh sieve, accurately weighing 0.1g of powder in 2mL centrifuge tube, adding 60% ethanol solution 1mL, ultrasonic extracting for 15min, and centrifuging at 5000rpm for 2min to obtain semen Setariae polyphenol extractive solution.

The concentration of millet polyphenol in the extract was measured by the method of example 1, and the yield of millet polyphenol was calculated according to the formula (1) to obtain a yield of millet polyphenol of 0.5mg g ^-1 。

It can be seen that the yield of millet polyphenol prepared in the prior art is 0.5mg g ^-1 About, the best yield of the millet polyphenol of the invention is 5.4mg g ^-1 。

The eutectic solvents used in the prior art do not allow for a simple and rapid separation of the target from the extractant, as described in example 1.

Comparative example 2

This comparative example is based on example 5, but does not carry on the ultra-high pressure treatment, the yield of millet polyphenol is 4.2mg g ^-1 . Therefore, the yield of the millet polyphenol can be effectively improved by adopting ultrahigh pressure treatment.

The yield of millet polyphenol extracted by using the traditional ethanol is 0.5mg g ^-1 The method of the invention adopts the convertible eutectic solvent to extract the optimal yield of 5.4mg g ^-1 Therefore, the method greatly improves the extraction efficiency of the millet polyphenol, and the switchable eutectic solvent selected by the invention has good recyclability in the extraction of the millet polyphenol.

While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. However, any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present invention are within the protection scope of the technical solution of the present invention.

Claims

1. A method for green sustainable extraction of millet polyphenol is characterized by comprising the following steps:

2. The method of claim 1, further comprising step S4, adding an alkali to the hydrophobic eutectic solvent phase in the upper layer of step S3 to convert it into a hydrophilic switchable eutectic solvent for re-extraction.

3. The method as claimed in claim 1, wherein the millet and water are mixed in a mass ratio of 1.

4. The method according to claim 1, wherein the ultrahigh pressure pretreatment is performed at a pressure of 300 to 500MPa for 5 to 20min in step S1.

5. The method according to claim 1, wherein in step S2, the switchable eutectic solvent is a mixture of caprylic acid and linalool, pelargonic acid and linalool, or capric acid and linalool, and the mixing ratio is 3-1: 1 to 3, and the hydrophilic property means that the pH value is 8.5 to 9.5.

6. The method of claim 1, wherein in step S2, the concentration of β -cyclodextrin in the switchable eutectic solvent is 10 to 30g/L;

the millet powder and the switchable eutectic solvent are mixed according to the ratio of g to mL of 1;

the extraction is carried out by grinding or water bath;

the primary centrifugation is 5000-7000 rpm, and the centrifugation lasts for 1-3 min.

7. The method according to claim 1, wherein in step S3, the acid solution is hydrochloric acid or sulfuric acid or carbonic acid solution to make pH 6-7,

the secondary centrifugation is 7000-10000 rpm, and the time is 2-10 min.

8. The method of claim 2, wherein in step S4, a solid or solution of a base selected from the group consisting of sodium hydroxide, ammonia, sodium bicarbonate, and potassium hydroxide is added to the resultant switchable eutectic solvent solution, and the pH is adjusted to 8.5 to 9.5, i.e., the base is converted into a hydrophilic switchable eutectic solvent.

9. The application of the mixed solvent of caprylic acid and linalool in extracting millet polyphenol.

10. The use as claimed in claim 9, wherein the mixture of caprylic acid and linalool is mixed at a ratio of 2.