Stevia rebaudiana extract as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of plant extracts, and provides a stevia rebaudiana extract and a preparation method and application thereof.The preparation method comprises the following steps that 1, stevia rebaudiana leaves are taken, dried, smashed and sieved, and stevia rebaudiana powder is obtained; step 2, adding stevia rebaudiana powder into pure water, heating to 60-70 DEG C, stirring and extracting, and filtering to obtain filtrate I; step 3, adding a precipitant into the filtrate I, heating to 80-85 DEG C, stirring for 0.5-1 hour, adjusting the pH value, continuously stirring for 0.5-1 hour, keeping the temperature, standing for 4.0-4.5 hours, cooling to room temperature, and carrying out suction filtration to obtain filtrate II; step 4, adsorbing and eluting the filtrate II through macroporous adsorption resin to obtain an eluent; the preparation method of the stevia rebaudiana extract has the advantages that the operation is simple, the purity of the obtained stevia rebaudiana is high, and the stevia rebaudiana extract is suitable for large-scale production.

Description

Technical Field

[0001] The present invention belongs to the technical field of plant extracts, and in particular relates to a stevia extract and a preparation method and application thereof. Background Art

[0002] Stevioside, also known as stevioside, is a perennial herbaceous plant substance of the Asteraceae family originating from eastern Paraguay in South America. It is also known as "sweet grass". Stevioside has been successfully cultivated in China and Southeast Asia. The stevioside contained in stevioside extract is 300 times sweeter than sucrose, while the heat energy is only one-ninetieth of sucrose. Although only 60-70g of stevioside can be extracted from 1kg of leaves, it is still a highly respected natural sugar source that is safe for consumption. Stevioside not only has the characteristics of high sweetness, low energy, non-toxicity, and no side effects, but is also rich in flavonoids, alkaloids, water-soluble chlorophyll, lutein, neutral water-soluble oligosaccharides, free sugars, amino acids, lipids, etc.

[0003] At present, the common extraction methods for the extraction of steviol glycosides usually use water extraction, ethanol extraction, organic solvent extraction and high-pressure solvent extraction. The specific method of the water extraction method is: dry stevia powder is mixed with water in a certain proportion, heated to boiling and kept warm for a period of time (such as 60-90 minutes), then cooled and filtered to obtain an extract. This method is low in cost, but the extraction efficiency and purity are relatively low, and subsequent multiple purification processes are required. The specific method of the ethanol extraction method is: using ethanol as a solvent, extracting steviol glycosides by reflux extraction or ultrasound-assisted extraction. For example: stevia powder is mixed with ethanol in a certain proportion, refluxed and extracted for multiple times at 70-90°C, and the extract is concentrated after membrane filtration and ion exchange resin desalting and decolorization. Ultrasonic-assisted extraction can further improve the extraction rate and purity by treating the extract at a certain temperature with an ultrasonic device. Extraction using organic solvents such as methanol and ethyl acetate usually requires subsequent purification in combination with precipitation, filtration and recrystallization. The above methods are all costly, low in purity, and complicated in subsequent processing.

[0004] Therefore, how to develop an optimal extraction method and process for stevia to obtain high-purity stevioside is a technical problem that needs to be solved urgently. Summary of the invention

[0005] The purpose of the present invention is to provide a stevia extract and a preparation method and application thereof, so as to solve the problem of low extraction efficiency of stevia extract in the prior art.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] The first aspect of the present invention provides a method for preparing a stevia extract, comprising the following preparation steps:

[0008] Step 1: Take stevia leaves, dry them, crush them and sieve them to obtain stevia powder.

[0009] Step 2: Add the stevia powder into pure water, heat it to 60 - 70 °C and stir for extraction, then filter to obtain filtrate I.

[0010] Step 3: Add a precipitant into filtrate I, heat it to 80 - 85 °C, stir for 0.5 - 1 h, adjust the pH value, continue to stir for 0.5 - 1 h, keep warm and stand for 4.0 - 4.5 h, cool to room temperature, and filter by suction to obtain filtrate II.

[0011] Step 4: Adsorb and elute filtrate II through macroporous adsorption resin to obtain an eluate; then desalt, decolorize, vacuum concentrate, dry, and recrystallize the eluate to obtain a stevia extract.

[0012] As a further scheme of the present invention, in Step 1, the mesh number during the sieving process is 120 - 160 meshes. After the stevia leaves are dried, crushed and sieved, stevia powder particles with uniform particle size and larger specific surface area are obtained, which can provide favorable conditions for subsequent reactions, increase the contact area with the solvent, accelerate the dissolution and diffusion processes, and thus improve the extraction efficiency.

[0013] As a further scheme of the present invention, in Step 2, the dosage of pure water is 15 - 30 times the mass of the stevia powder, and the extraction time is 2 - 3 h. If the dosage of pure water is too small, the extraction rate of stevioside will be relatively low; if the dosage of pure water is too large, the extraction cost will be too high.

[0014] As a further scheme of the present invention, the precipitant in Step 3 comprises the following raw materials in parts by weight: 30 - 45 parts of modified activated carbon, 3 - 3.5 parts of ferrous sulfate, and 5 - 6 parts of calcium hydroxide.

[0015] As a further scheme of the present invention, the modified activated carbon is prepared through the following steps:

[0016] Add activated carbon and chitosan into acetic acid solution, ultrasonically disperse for 1.0 - 1.5 h, under a nitrogen atmosphere, add 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide, continue to stir for 8 - 12 h, filter and wash, and obtain modified activated carbon after vacuum drying.

[0017] As a further scheme of the present invention, the dosage ratio of activated carbon, chitosan, acetic acid solution, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide is 0.2 - 0.3 g : 0.25 - 0.35 g : 100 mL : 0.60 - 0.62 g : 0.80 - 0.84 g.

[0018] As a further solution of the present invention, the dosage of the precipitating agent in step 3 is 5-15% of the volume of filtrate I.

[0019] As a further solution of the present invention, the pH value is adjusted to 10.0-10.5 in step 3.

[0020] As a further solution of the present invention, the macroporous adsorption resin in step 4 is one of LX-T28 resin, LX-T81 resin, D101 resin and AB-8 resin.

[0021] The second aspect of the present invention provides a stevia extract obtained by the preparation method described in the first aspect above.

[0022] The third aspect of the present invention provides the application of the stevia extract described in the second aspect above in food.

[0023] Advantages of the present invention:

[0024] The preparation method of a stevia extract (i.e., stevioside) of the present invention, after drying, crushing and sieving stevia leaves to obtain stevia leaf powder with uniform particle size, then through water extraction, treatment with a precipitating agent, macroporous adsorption resin, and vacuum concentration, drying and recrystallization, obtains stevioside with high extraction efficiency and high purity, improves the quality of the product, and reduces costs. At the same time, the obtained stevioside has the advantages of high sweetness and low calories, and is widely used in food.

[0025] The precipitating agent used in the preparation process of a stevia extract in the present invention is composed of modified activated carbon, ferrous sulfate and calcium hydroxide mixed according to a weight ratio. The modified activated carbon is obtained by coating chitosan on the surface of activated carbon through an amidation reaction. Activated carbon has excellent adsorption capacity and can effectively perform adsorption separation and decolorization treatment. Crosslinking and coating chitosan on the surface of activated carbon can significantly increase the hydrophilicity of activated carbon and enable it to be evenly dispersed in the solution; on the other hand, chitosan can adsorb some proteins. At the same time, the chitosan coated on the surface of activated carbon has good mechanical properties, and thus is not easily washed away in the solution, the action effect is prolonged, and the precipitation and flocculation effect is excellent. Among them, ferrous sulfate can remove some impurities such as proteins, colored substances and other miscellaneous odor substances, and calcium hydroxide can remove colloidal impurities in the leaching solution, effectively prevent the deterioration of macroporous resin and reduce the consumption of macroporous adsorption resin, thereby further reducing production costs and saving economy.

[0026] The preparation method of a stevia extract of the present invention is convenient to operate, the process is simple, and it is suitable for large-scale production. Specific embodiments

[0027] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0028] Example 1

[0029] This example provides a preparation method of stevia extract, and the preparation steps are as follows:

[0030] Step 1: Take stevia leaves, dry them and then crush and sieve them through a 120-mesh sieve to obtain stevia powder;

[0031] Step 2: Add the stevia powder to pure water with a dosage 15 times that of the stevia powder, heat it to 60 °C and stir and extract for 2 h. After filtration, obtain filtrate I;

[0032] Step 3: Add a precipitant with a dosage of 5% of the volume of filtrate I to filtrate I, heat it to 80 °C and stir for 0.5 h, adjust the pH value to 10.0, continue to stir for 0.5 h, keep warm and stand for 4.0 h, cool to room temperature, and filter by suction to obtain filtrate II;

[0033] Among them, the precipitant includes the following raw materials in parts by weight: 30 parts of modified activated carbon, 3 parts of ferrous sulfate, and 5 parts of calcium hydroxide.

[0034] The modified activated carbon is prepared by the following steps:

[0035] Add 0.2 g of activated carbon and 0.25 g of chitosan to 100 mL of acetic acid solution (volume fraction of 25%), ultrasonically disperse for 1.0 h, under a nitrogen atmosphere, add 0.60 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 0.80 g of N-hydroxysuccinimide, continue to stir for 8 h, filter and wash, and place it in a vacuum drying oven at 40 °C for drying for 24 h to obtain modified activated carbon.

[0036] Step 4: Adsorb and elute filtrate II through D101 resin to obtain an eluate; then desalt, decolorize, vacuum concentrate, dry, and recrystallize the eluate to obtain stevia extract.

[0037] The stevia extract is obtained by the above steps.

[0038] Example 2

[0039] The difference from Example 1 is only that the preparation steps of the modified activated carbon are different:

[0040] This example provides a preparation method of stevia extract, and the preparation steps are as follows:

[0041] Step 1: Take stevia leaves, dry them, crush and sieve them through a 120-mesh sieve to obtain stevia powder.

[0042] Step 2: Add the stevia powder to pure water at a dosage 15 times that of the stevia powder, heat up to 60°C, stir and extract for 2 h, and after filtration, obtain filtrate I.

[0043] Step 3: Add a precipitant at a dosage of 5% of the volume of filtrate I to filtrate I, heat up to 80°C, stir for 0.5 h, adjust the pH value to 10.0, continue to stir for 0.5 h, keep warm and stand for 4.0 h, cool to room temperature, and perform suction filtration to obtain filtrate II.

[0044] The precipitant includes the following raw materials in parts by weight: 30 parts of modified activated carbon, 3 parts of ferrous sulfate, and 5 parts of calcium hydroxide.

[0045] The modified activated carbon is prepared through the following steps:

[0046] Add 0.25 g of activated carbon and 0.30 g of chitosan to 100 mL of acetic acid solution (volume fraction 25%), perform ultrasonic dispersion for 1.0 h, under a nitrogen atmosphere, add 0.60 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 0.80 g of N-hydroxysuccinimide, continue to stir for 8 h, filter and wash, and place in a vacuum drying oven at 40°C for drying for 24 h to obtain the modified activated carbon.

[0047] Step 4: Adsorb and elute filtrate II through D101 resin to obtain an eluate; then desalt, decolorize, perform vacuum concentration, drying, and recrystallization on the eluate to obtain the stevia extract.

[0048] The stevia extract is obtained through the above steps.

[0049] Example 3

[0050] It is only different from Example 1 in that the preparation steps of the modified activated carbon are different:

[0051] This example provides a preparation method of a stevia extract, and the preparation steps are as follows:

[0052] Step 1: Take stevia leaves, dry them, crush and sieve them through a 120-mesh sieve to obtain stevia powder.

[0053] Step 2: Add the stevia powder to pure water at a dosage 15 times that of the stevia powder, heat up to 60°C, stir and extract for 2 h, and after filtration, obtain filtrate I.

[0054] Step 3: Add a precipitant with a dosage of 5% of the volume of Filtrate I to Filtrate I, heat to 80°C, stir for 0.5 h, adjust the pH value to 10.0, continue stirring for 0.5 h, keep warm and stand for 4.0 h, cool to room temperature, and perform suction filtration to obtain Filtrate II;

[0055] Among them, the precipitant includes the following raw materials in parts by weight: 30 parts of modified activated carbon, 3 parts of ferrous sulfate, and 5 parts of calcium hydroxide.

[0056] The modified activated carbon is prepared through the following steps:

[0057] Add 0.3 g of activated carbon and 0.35 g of chitosan to 100 mL of acetic acid solution (volume fraction of 25%), perform ultrasonic dispersion for 1.0 h, under a nitrogen atmosphere, add 0.62 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 0.84 g of N-hydroxysuccinimide, continue stirring for 8 h, filter and wash, and place in a vacuum drying oven at 40°C for drying for 24 h to obtain the modified activated carbon.

[0058] Step 4: Adsorb and elute Filtrate II through D101 resin to obtain an eluate; then desalt, decolorize, perform vacuum concentration, drying, and recrystallization on the eluate to obtain a stevia extract.

[0059] The stevia extract is obtained through the above steps.

[0060] Example 4

[0061] It is only different from Example 1 in that the mesh size is different during the crushing and sieving process in Step 1:

[0062] This example provides a preparation method of a stevia extract, and the preparation steps are as follows:

[0063] Step 1: Take stevia leaves, dry them and then crush and sieve them with a mesh size of 160 meshes to obtain stevia powder;

[0064] Step 2: Add stevia powder to pure water with a dosage of 15 times that of stevia powder, heat to 60°C, stir and extract for 2 h, and after filtration, obtain Filtrate I;

[0065] Step 3: Add a precipitant with a dosage of 5% of the volume of Filtrate I to Filtrate I, heat to 80°C, stir for 0.5 h, adjust the pH value to 10.0, continue stirring for 0.5 h, keep warm and stand for 4.0 h, cool to room temperature, and perform suction filtration to obtain Filtrate II;

[0066] Among them, the precipitant includes the following raw materials in parts by weight: 30 parts of modified activated carbon, 3 parts of ferrous sulfate, and 5 parts of calcium hydroxide.

[0067] The modified activated carbon is prepared through the following steps:

[0068] Add 0.2 g of activated carbon and 0.25 g of chitosan to 100 mL of acetic acid solution (volume fraction 25%), ultrasonically disperse for 1.0 h, under a nitrogen atmosphere, add 0.60 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 0.80 g of N-hydroxysuccinimide, continue stirring for 8 h, filter and wash, and place in a vacuum drying oven at 40 °C for drying for 24 h to obtain modified activated carbon.

[0069] Step 4: Adsorb the filtrate II through D101 resin, elute to obtain an eluate; then desalt, decolorize, vacuum concentrate, dry, and recrystallize the eluate to obtain a stevia extract.

[0070] The stevia extract is prepared by the above steps.

[0071] Example 5

[0072] It is only different from Example 1 in that the amount of pure water used in Step 2 is different:

[0073] This example provides a preparation method of a stevia extract, and the preparation steps are as follows:

[0074] Step 1: Take stevia leaves, dry them and then crush and sieve them through a 120-mesh sieve to obtain stevia powder.

[0075] Step 2: Add the stevia powder to 28 times the amount of pure water of the stevia powder, heat up to 60 °C and stir for extraction for 2 h, filter to obtain filtrate I.

[0076] Step 3: Add a precipitant with a dosage of 5% of the volume of filtrate I to filtrate I, heat up to 80 °C and stir for 0.5 h, adjust the pH value to 10.0, continue stirring for 0.5 h, keep warm and stand for 4.0 h, cool to room temperature, and filter by suction to obtain filtrate II.

[0077] The precipitant includes the following raw materials in parts by weight: 30 parts of modified activated carbon, 3 parts of ferrous sulfate, and 5 parts of calcium hydroxide.

[0078] The modified activated carbon is prepared by the following steps:

[0079] Add 0.2 g of activated carbon and 0.25 g of chitosan to 100 mL of acetic acid solution (volume fraction 25%), ultrasonically disperse for 1.0 h, under a nitrogen atmosphere, add 0.60 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 0.80 g of N-hydroxysuccinimide, continue stirring for 8 h, filter and wash, and place in a vacuum drying oven at 40 °C for drying for 24 h to obtain modified activated carbon.

[0080] Step 4: Adsorb the filtrate II with D101 resin, elute it to obtain an eluate; then desalt, decolorize, concentrate under vacuum, dry, and recrystallize the eluate to obtain a stevia extract.

[0081] The stevia extract is prepared by the above steps.

[0082] Example 6

[0083] It is only different from Example 1 in that the dosage of the precipitant in step 3 is different:

[0084] This example provides a method for preparing a stevia extract, and the preparation steps are as follows:

[0085] Step 1: Take stevia leaves, dry them and then crush and sieve them through a 120-mesh sieve to obtain stevia powder.

[0086] Step 2: Add the stevia powder to pure water with a dosage 15 times that of the stevia powder, heat to 60°C and stir for extraction for 2 h, and after filtration, obtain filtrate I.

[0087] Step 3: Add a precipitant with a dosage of 15% of the volume of filtrate I to filtrate I, heat to 80°C and stir for 0.5 h, adjust the pH value to 10.0, continue to stir for 0.5 h, keep warm and stand for 4.0 h, cool to room temperature, and filter by suction to obtain filtrate II.

[0088] The precipitant includes the following raw materials in parts by weight: 30 parts of modified activated carbon, 3 parts of ferrous sulfate, and 5 parts of calcium hydroxide.

[0089] The modified activated carbon is prepared by the following steps:

[0090] Add 0.2 g of activated carbon and 0.25 g of chitosan to 100 mL of acetic acid solution (volume fraction of 25%), ultrasonically disperse for 1.0 h, under a nitrogen atmosphere, add 0.60 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 0.80 g of N-hydroxysuccinimide, continue to stir for 8 h, filter and wash, and place in a vacuum drying oven at 40°C for drying for 24 h to obtain the modified activated carbon.

[0091] Step 4: Adsorb the filtrate II with D101 resin, elute it to obtain an eluate; then desalt, decolorize, concentrate under vacuum, dry, and recrystallize the eluate to obtain a stevia extract.

[0092] The stevia extract is prepared by the above steps.

[0093] Example 7

[0094] It is only different from Example 1 in that the pH value in step 3 is different:

[0095] This embodiment provides a method for preparing a stevia extract, and the preparation steps are as follows:

[0096] Step 1: Take stevia leaves, dry them, crush them and sieve them through a 120-mesh sieve to obtain stevia powder;

[0097] Step 2: Add the stevia powder to pure water at a dosage of 15 times that of the stevia powder, heat it to 60 °C, stir and extract for 2 h, and after filtration, obtain filtrate I;

[0098] Step 3: Add a precipitant at a dosage of 5% of the volume of filtrate I to filtrate I, heat it to 80 °C, stir for 0.5 h, adjust the pH value to 10.5, continue to stir for 0.5 h, keep warm and stand for 4.0 h, cool to room temperature, and perform suction filtration to obtain filtrate II;

[0099] The precipitant includes the following raw materials in parts by weight: 30 parts of modified activated carbon, 3 parts of ferrous sulfate, and 5 parts of calcium hydroxide.

[0100] The modified activated carbon is prepared through the following steps:

[0101] Add 0.2 g of activated carbon and 0.25 g of chitosan to 100 mL of acetic acid solution (volume fraction of 25%), ultrasonically disperse for 1.0 h, under a nitrogen atmosphere, add 0.60 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 0.80 g of N-hydroxysuccinimide, continue to stir for 8 h, filter and wash, and place in a vacuum drying oven at 40 °C for drying for 24 h to obtain the modified activated carbon;

[0102] Step 4: Adsorb and elute filtrate II through D101 resin to obtain an eluate; then desalt, decolorize, vacuum concentrate, dry, and recrystallize the eluate to obtain the stevia extract.

[0103] The stevia extract is obtained through the above steps.

[0104] Example 8

[0105] It is only different from Example 1 in that the dosage of the precipitant raw materials in Step 3 is different:

[0106] This embodiment provides a method for preparing a stevia extract, and the preparation steps are as follows:

[0107] Step 1: Take stevia leaves, dry them, crush them and sieve them through a 120-mesh sieve to obtain stevia powder;

[0108] Step 2: Add the stevia powder to pure water at a dosage of 15 times that of the stevia powder, heat it to 60 °C, stir and extract for 2 h, and after filtration, obtain filtrate I;

[0109] Step 3: Add a precipitating agent accounting for 5% of the volume of filtrate I to filtrate I, heat up to 80°C, stir for 0.5 h, adjust the pH value to 10.0, continue stirring for 0.5 h, keep warm and stand for 4.0 h, cool to room temperature, and perform suction filtration to obtain filtrate II;

[0110] Among them, the precipitating agent includes the following raw materials in parts by weight: 40 parts of modified activated carbon, 3.3 parts of ferrous sulfate, and 5.5 parts of calcium hydroxide.

[0111] The modified activated carbon is prepared through the following steps:

[0112] Add 0.2 g of activated carbon and 0.25 g of chitosan to 100 mL of acetic acid solution (volume fraction of 25%), perform ultrasonic dispersion for 1.0 h, under a nitrogen atmosphere, add 0.60 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 0.80 g of N-hydroxysuccinimide, continue stirring for 8 h, filter and wash, and place in a vacuum drying oven at 40°C for drying for 24 h to obtain modified activated carbon;

[0113] Step 4: Adsorb and elute filtrate II through D101 resin to obtain an eluate; then desalt, decolorize, vacuum concentrate, dry, and recrystallize the eluate to obtain a stevia extract.

[0114] The stevia extract is prepared through the above steps.

[0115] Comparative Example 1

[0116] It is only different from Example 1 in that the precipitating agent raw materials do not contain modified activated carbon:

[0117] A preparation method of a stevia extract, and the preparation steps are as follows:

[0118] Step 1: Take stevia leaves, dry and then crush and sieve them, with a sieve mesh of 120 meshes, to obtain stevia powder;

[0119] Step 2: Add stevia powder to pure water 15 times the amount of stevia powder, heat up to 60°C, stir and extract for 2 h, and after filtration, obtain filtrate I;

[0120] Step 3: Add a precipitating agent accounting for 5% of the volume of filtrate I to filtrate I, heat up to 80°C, stir for 0.5 h, adjust the pH value to 10.0, continue stirring for 0.5 h, keep warm and stand for 4.0 h, cool to room temperature, and perform suction filtration to obtain filtrate II;

[0121] Among them, the precipitating agent includes the following raw materials in parts by weight: 3 parts of ferrous sulfate and 5 parts of calcium hydroxide.

[0122] Step 4: Adsorb and elute the filtrate II through D101 resin to obtain an eluate; then desalt, decolorize, vacuum concentrate, dry, and recrystallize the eluate to obtain a stevia extract.

[0123] The stevia extract is prepared by the above steps.

[0124] Comparative Example 2

[0125] It is only different from Example 1 in that the mesh size is different in the grinding and sieving process in Step 1:

[0126] A preparation method of a stevia extract, the preparation steps are as follows:

[0127] Step 1: Take stevia leaves, dry them and then crush and sieve them with a mesh size of 100 meshes to obtain stevia powder;

[0128] Step 2: Add the stevia powder to pure water with a dosage of 15 times that of the stevia powder, heat to 60 °C and stir for extraction for 2 h, and after filtration, obtain filtrate I;

[0129] Step 3: Add a precipitant with a dosage of 5% of the volume of filtrate I to filtrate I, heat to 80 °C and stir for 0.5 h, adjust the pH value to 10.0, continue to stir for 0.5 h, keep warm and stand for 4.0 h, cool to room temperature, and filter by suction to obtain filtrate II;

[0130] The precipitant includes the following raw materials in parts by weight: 30 parts of modified activated carbon, 3 parts of ferrous sulfate, and 5 parts of calcium hydroxide.

[0131] The modified activated carbon is prepared by the following steps:

[0132] Add 0.2 g of activated carbon and 0.25 g of chitosan to 100 mL of acetic acid solution (volume fraction of 25%), ultrasonically disperse for 1.0 h, under a nitrogen atmosphere, add 0.60 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 0.80 g of N-hydroxysuccinimide, continue to stir for 8 h, filter and wash, and place in a vacuum drying oven at 40 °C for drying for 24 h to obtain modified activated carbon.

[0133] Step 4: Adsorb and elute the filtrate II through D101 resin to obtain an eluate; then desalt, decolorize, vacuum concentrate, dry, and recrystallize the eluate to obtain a stevia extract.

[0134] The stevia extract is prepared by the above steps.

[0135] Comparative Example 3

[0136] It is only different from Example 1 in that the dosage of pure water in Step 2 is different:

[0137] A preparation method of stevia extract, the preparation steps are as follows:

[0138] Step 1: Take stevia leaves, dry them, crush and sieve them through a 120-mesh sieve to obtain stevia powder;

[0139] Step 2: Add the stevia powder to pure water with a dosage 10 times that of the stevia powder, heat to 60°C, stir and extract for 2 h, filter to obtain filtrate I;

[0140] Step 3: Add a precipitant with a dosage of 5% of the volume of filtrate I to filtrate I, heat to 80°C, stir for 0.5 h, adjust the pH value to 10.0, continue to stir for 0.5 h, keep warm and stand for 4.0 h, cool to room temperature, and filter by suction to obtain filtrate II;

[0141] The precipitant includes the following raw materials in parts by weight: 30 parts of modified activated carbon, 3 parts of ferrous sulfate, and 5 parts of calcium hydroxide.

[0142] The modified activated carbon is prepared by the following steps:

[0143] Add 0.2 g of activated carbon and 0.25 g of chitosan to 100 mL of acetic acid solution (volume fraction 25%), ultrasonically disperse for 1.0 h, under a nitrogen atmosphere, add 0.60 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 0.80 g of N-hydroxysuccinimide, continue to stir for 8 h, filter and wash, and place in a vacuum drying oven at 40°C for 24 h to obtain modified activated carbon.

[0144] Step 4: Adsorb and elute filtrate II through D101 resin to obtain an eluate; then desalt, decolorize, vacuum concentrate, dry, and recrystallize the eluate to obtain stevia extract.

[0145] The stevia extract is obtained by the above steps.

[0146] Comparative Example 4

[0147] It is only different from Example 1 in that the dosage of the precipitant in Step 3 is different:

[0148] Step 1: Take stevia leaves, dry them, crush and sieve them through a 120-mesh sieve to obtain stevia powder;

[0149] Step 2: Add the stevia powder to pure water with a dosage 15 times that of the stevia powder, heat to 60°C, stir and extract for 2 h, filter to obtain filtrate I;

[0150] Step 3: Add a precipitant with a dosage of 3% of the volume of filtrate I to filtrate I, heat to 80°C, stir for 0.5 h, adjust the pH value to 10.0, continue to stir for 0.5 h, keep warm and stand for 4.0 h, cool to room temperature, and filter by suction to obtain filtrate II;

[0151] Among them, the precipitant includes the following raw materials in parts by weight: 30 parts of modified activated carbon, 3 parts of ferrous sulfate, and 5 parts of calcium hydroxide.

[0152] The modified activated carbon is prepared by the following steps:

[0153] Add 0.2 g of activated carbon and 0.25 g of chitosan into 100 mL of acetic acid solution (volume fraction is 25%), ultrasonically disperse for 1.0 h, under a nitrogen atmosphere, add 0.60 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 0.80 g of N-hydroxysuccinimide, continue to stir for 8 h, filter and wash, place in a vacuum drying oven at 40 °C and dry for 24 h to obtain the modified activated carbon.

[0154] Step 4: Adsorb and elute the filtrate II through D101 resin to obtain an eluate; then desalt, decolorize, vacuum concentrate, dry, and recrystallize the eluate to obtain the stevia extract.

[0155] The stevia extract is obtained by the above steps.

[0156] Comparative Example 5

[0157] It is only different from Example 1 in that the dosage of the precipitant raw materials in Step 3 is different:

[0158] A preparation method of stevia extract, the preparation steps are as follows:

[0159] Step 1: Take stevia leaves, dry and then crush and sieve them, with a sieve mesh of 120 meshes, to obtain stevia powder;

[0160] Step 2: Add stevia powder to pure water with a dosage of 15 times that of stevia powder, heat up to 60 °C and stir for extraction for 2 h, filter to obtain filtrate I;

[0161] Step 3: Add a precipitant with a dosage of 5% of the volume of filtrate I to filtrate I, heat up to 80 °C and stir for 0.5 h, adjust the pH value to 10.0, continue to stir for 0.5 h, keep warm and stand for 4.0 h, cool to room temperature, and filter by suction to obtain filtrate II;

[0162] Among them, the precipitant includes the following raw materials in parts by weight: 20 parts of modified activated carbon, 3 parts of ferrous sulfate, and 5 parts of calcium hydroxide.

[0163] The modified activated carbon is prepared by the following steps:

[0164] Add 0.2 g of activated carbon and 0.25 g of chitosan to 100 mL of acetic acid solution (volume fraction 25%), ultrasonically disperse for 1.0 h, under a nitrogen atmosphere, add 0.60 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 0.80 g of N-hydroxysuccinimide, continue stirring for 8 h, filter and wash, and place in a vacuum drying oven at 40 °C for drying for 24 h to obtain modified activated carbon.

[0165] Step 4: Adsorb the filtrate II through D101 resin, elute to obtain an eluate; then desalt, decolorize, vacuum concentrate, dry, and recrystallize the eluate to obtain a stevia extract.

[0166] The stevia extract is prepared by the above steps.

[0167] Comparative Example 6

[0168] It is only different from Example 1 in that the dosage of the precipitant raw materials in Step 3 is different:

[0169] A preparation method of a stevia extract, the preparation steps are as follows:

[0170] Step 1: Take stevia leaves, dry and then crush and sieve through a 120-mesh sieve to obtain stevia powder;

[0171] Step 2: Add the stevia powder to pure water with a dosage 15 times that of the stevia powder, heat to 60 °C and stir for extraction for 2 h, filter to obtain filtrate I;

[0172] Step 3: Add a precipitant with a dosage of 5% of the volume of filtrate I to filtrate I, heat to 80 °C and stir for 0.5 h, adjust the pH value to 10.0, continue stirring for 0.5 h, keep warm and stand for 4.0 h, cool to room temperature, and filter to obtain filtrate II;

[0173] The precipitant includes the following raw materials in parts by weight: 30 parts of modified activated carbon, 1.5 parts of ferrous sulfate, and 4 parts of calcium hydroxide.

[0174] The modified activated carbon is prepared by the following steps:

[0175] Add 0.2 g of activated carbon and 0.25 g of chitosan to 100 mL of acetic acid solution (volume fraction 25%), ultrasonically disperse for 1.0 h, under a nitrogen atmosphere, add 0.60 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 0.80 g of N-hydroxysuccinimide, continue stirring for 8 h, filter and wash, and place in a vacuum drying oven at 40 °C for drying for 24 h to obtain modified activated carbon.

[0176] Step 4: Adsorb and elute the filtrate II through D101 resin to obtain an eluate; then desalt, decolorize, vacuum concentrate, dry, and recrystallize the eluate to obtain a stevia extract.

[0177] The stevia extract is prepared by the above steps.

[0178] The extraction rates and mass fractions of stevia glycosides in the stevia extracts (i.e., steviosides) during the preparation processes in Examples 1 - 8 and Comparative Examples 1 - 6 were detected, and the results are shown in Table 1:

[0179] Table 1

[0180]

[0181] As can be seen from Table 1, compared with Comparative Examples 1 - 6, the preparation method of the stevia extract provided in Examples 1 - 8 and the obtained stevia extract have better extraction rates and mass fractions. Thus, it can be seen that the stevia extract and its preparation method provided by the present invention have the advantages of high extraction efficiency and high purity of the extract, and the preparation method is simple and suitable for large-scale production.

[0182] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device.

[0183] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a stevia extract, characterized in that: The method comprises the following preparation steps: Step 1, taking stevia leaves, drying them, crushing and sieving them to obtain stevia powder; Step 2, adding stevia powder into pure water, heating to 60-70°C for stirring and extraction, filtering to obtain filtrate I; Step 3, add the precipitant to the filtrate I, heat to 80-85°C and stir for 0.5-1h, adjust the pH value, continue stirring for 0.5-1h, keep warm and stand for 4.0-4.5h, cool to room temperature, and filter to obtain filtrate II; Step 4, adsorbing the filtrate II through a macroporous adsorption resin, eluting to obtain an eluate; then desalting, decolorizing, vacuum concentrating, drying, and recrystallizing the eluate to obtain a stevia extract.

2. The method for preparing a stevia extract according to claim 1, characterized in that: The mesh size during the sieving process in step 1 is 120-160 mesh.

3. The method for preparing a stevia extract according to claim 1, characterized in that: In step 2, the amount of pure water used is 15-30 times the mass of stevia powder, and the extraction time is 2-3 hours.

4. The method for preparing a stevia extract according to claim 1, characterized in that: The precipitant in step 3 comprises the following raw materials in parts by weight: 30-45 parts of modified activated carbon, 3-3.5 parts of ferrous sulfate, and 5-6 parts of calcium hydroxide.

5. The method for preparing a stevia extract according to claim 4, characterized in that: The modified activated carbon is prepared by the following steps: Add activated carbon and chitosan to acetic acid solution, ultrasonically disperse for 1.0-1.5 hours, and continue stirring for 8-12 hours with 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide under nitrogen atmosphere. Filter, wash, and vacuum dry to obtain modified activated carbon.

6. The method for preparing a stevia extract according to claim 5, characterized in that: The usage ratio of activated carbon, chitosan, acetic acid solution, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide is 0.2-0.3 g: 0.25-0.35 g: 100 mL: 0.60-0.62 g: 0.80-0.84 g.

7. The method for preparing a stevia extract according to claim 1, characterized in that: The amount of the precipitant used in step 3 is 5-15% of the volume of filtrate I; And / or, in step 3, the pH value is adjusted to 10.0-10.

5.

8. The method for preparing a stevia extract according to claim 1, characterized in that: In step 4, the macroporous adsorption resin is one of LX-T28 resin, LX-T81 resin, D101 resin and AB-8 resin.

9. A stevia extract, characterized in that: The stevia extract includes the stevia extract prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the stevia extract according to claim 9 in food.

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