阅读说明：本技术 一种仙草黑色素及其制备方法 (Mesona chinensis benth melanin and preparation method thereof ) 是由 田玉庭 王志翱 陈新良 于 2021-06-28 设计创作，主要内容包括：本发明涉食品加工技术领域,具体涉及一种仙草黑色素及其制备方法。其包括以下依次进行的步骤：将新鲜仙草加入米曲霉和黑曲霉的混合菌堆垛发酵3～5天；经过碱水浸提、醇成除胶制得仙草黑色素。其通过黑曲霉和米曲霉的复合菌发酵和碱水浸提的方法,使所得到的仙草黑色素的热稳定性和色阶更高,并且所得到的仙草黑色素为水溶性黑色素。(The invention relates to the technical field of food processing, and particularly relates to mesona chinensis benth melanin and a preparation method thereof. The method comprises the following steps of: adding fresh mesona chinensis benth into mixed bacteria of aspergillus oryzae and aspergillus niger, stacking and fermenting for 3-5 days; leaching with alkaline water, and removing gelatin with alcohol to obtain Mesona chinensis Benth melanin. The obtained mesona chinensis benth melanin has higher heat stability and color level through the method of composite bacteria fermentation and alkaline water leaching of aspergillus niger and aspergillus oryzae, and is water-soluble melanin.)

1. The preparation method of mesona chinensis benth melanin is characterized by comprising the following steps of:

s1, adding fresh Mesona chinensis Benth into a mixed bacterium of Aspergillus oryzae and Aspergillus niger, stacking and fermenting for 3-5 days, and naturally airing to obtain dry Mesona chinensis Benth;

s2 the Mesona chinensis Benth melanin is prepared by leaching dry Mesona chinensis Benth with alkaline water.

2. The method for producing Mesona chinensis Benth melanin according to claim 1, wherein: in the mixed bacteria, the ratio of the effective bacterial number of aspergillus niger to the effective bacterial number of aspergillus oryzae is 2:1, and the concentration of the mixed bacteria is 10⁸～10⁹cfu/mL, the weight volume ratio of the fresh Mesona chinensis Benth to the sprayed mixed bacteria is 3-5 per mill.

3. The method for preparing Mesona procumbens melanin as claimed in claim 1, wherein the step S1 further comprises the following substeps: after the mixed bacteria are added into the fresh Mesona chinensis Benth, culturing for 16-20 h at 28-30 ℃, and then performing stacking fermentation.

4. The method for producing Mesona chinensis Benth melanin according to claim 1, wherein: the temperature of the stack fermentation is 30-33 ℃, and the humidity is 30-35%.

5. The method for producing Mesona chinensis Benth melanin according to claim 1, wherein: the alkaline water is a NaOH aqueous solution with the mass concentration of 0.10-0.15, the addition amount of the alkaline water is 45-50 times of the mass of the dry Mesona chinensis Benth, the leaching temperature of the alkaline water is 90-98 ℃, and the leaching time is 1.5-2.5 h;

preferably, the alkaline leaching is carried out in a jacketed kettle.

6. The method for producing Mesona procumbens melanin as claimed in claim 1 or 5, wherein: leaching with alkaline water, and filtering with plate frame to obtain leaching solution.

7. The method for producing Mesona procumbens melanin according to claim 1, further comprising the steps of: s3, adding absolute ethyl alcohol into the leaching liquor after the alkaline water leaching for alcohol precipitation, and collecting filtrate to obtain the mesona chinensis benth melanin.

8. The method for producing Mesona chinensis Benth melanin of claim 7, wherein: in step S3, adding HCl into the leaching liquor to adjust the pH value of the solution to 6.8-7.2, then carrying out alcohol precipitation, and collecting filtrate; and carrying out electrodialysis desalination treatment on the filtrate to obtain the mesona chinensis benth melanin.

9. The method for producing Mesona procumbens melanin according to claim 7 or 8, further comprising the step of S4: and (3) carrying out nanofiltration concentration on the obtained filtrate, or carrying out nanofiltration concentration on the obtained filtrate after electrodialysis desalination treatment, setting the aperture of a membrane to be 100Da, and concentrating to obtain the mesona chinensis benth melanin.

10. Mesona chinensis melanin extracted by the method for preparing Mesona chinensis melanin according to any one of claims 1-5, 7 or 8.

Technical Field

The invention relates to the technical field of food processing, and particularly relates to mesona chinensis benth melanin and a preparation method thereof.

Background

Mesona chinensis Benth, also known as Mesona chinensis Benth or Mesona chinensis Benth, is an annual herb of Labiatae, is an important plant resource for both medicine and food, and is mainly distributed in Fujian, Guangdong, Taiwan and other places in China. The Mesona chinensis Benth is a natural green food in plants, has high nutritive and medicinal values, and has effects of cooling, relieving summer-heat, clearing heart fire and removing pathogenic fire. Mesona chinensis Benth is an annual herbaceous plant in the genus of Mesona in the family of Labiatae, and is an important plant resource for both medicine and food. The whole Mesona chinensis Benth dried sample contains about 70% Mesona chinensis Benth carbohydrate, a small amount of protein, fat, pigment, etc., and also contains more mineral elements. Has wide medicinal application, and has effects of clearing summer heat, relieving fever and promoting diuresis. Can be used for treating heatstroke, toxic heat, diabetes, hypertension, nephropathy, diabetes, arthralgia, myalgia, and gonorrhea. The flavonoids in the components of the Mesona Procumbens Hemsl have the effects of inhibiting cancer cell growth and lowering blood pressure; the polysaccharide has the effects of enhancing and improving organism immunity; the essence has effects of tranquilizing, refreshing, removing toxic substance, and promoting diuresis; the microelements have effects of inhibiting free radical formation, resisting aging, and resisting cancer; vitamins can regulate and enhance physiological functions, etc.

The melanin is an active substance existing in a large amount in the dry Mesona chinensis Benth, so that the research on Mesona chinensis Benth melanin has very important practical value and theoretical significance for high-added-value comprehensive utilization and deep processing development of Mesona chinensis Benth.

At present, the extraction and preparation research of Mesona chinensis Benth melanin is rarely reported at home and abroad. Cutting and crushing mesona chinensis benth, and extracting the crushed mesona chinensis benth for 90min in a room-temperature water bath (pH 14) by Cao Chong river and the like, wherein the pigment yield is 12.44%, and the extraction time is shortened only by adopting microwave or ultrasonic extraction, so that the extraction rate of the mesona chinensis benth pigment is not increased (extraction research and development of the mesona chinensis benth pigment in Cao Chong river, Liu Xiao Heng, Wang Jun. food research and development, 2007,128: 64-67). The mesona blume contains a large amount of colloid (the main component is acidic polysaccharide), and if the colloid is not removed, the purity of the mesona blume melanin product is reduced, and the light transmittance of the product is influenced; in addition, fresh Mesona chinensis Benth is naturally dried to obtain dried Mesona chinensis Benth which can be used for extracting and preparing melanin, and sometimes the dried Mesona chinensis Benth is packaged and stored for more than half a year for treatment, otherwise the color value of melanin is affected.

Disclosure of Invention

Technical problem to be solved

In view of the above disadvantages and shortcomings of the prior art, the present invention provides a novel method for preparing mesona chinensis benth melanin, which comprises fermenting Aspergillus niger and Aspergillus oryzae with compound bacteria, and leaching with alkaline water to obtain mesona chinensis benth melanin with higher color level, better light transmittance, and more stable heat, wherein the obtained mesona chinensis benth melanin is water-soluble melanin.

Correspondingly, the invention also provides mesona chinensis benth melanin.

(II) technical scheme

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

in a first aspect, the present invention provides a method for preparing mesona chinensis benth melanin, which comprises the following steps in sequence:

s1, adding fresh Mesona chinensis Benth into a mixed bacterium of Aspergillus oryzae and Aspergillus niger, stacking and fermenting for 3-5 days, and naturally airing to obtain dry Mesona chinensis Benth;

s2 is extracted with alkaline water to obtain Mesona chinensis Benth melanin.

According to the scheme, stacking and fermenting the fresh mesona chinensis benth by the mixed bacteria of aspergillus oryzae and aspergillus niger is beneficial to improving the color gradation of water-soluble mesona chinensis benth melanin; aspergillus oryzae and Aspergillus niger have a significant synergistic effect on the color gradation of highly water-soluble Mesona melanin. Preferably, aspergillus niger is aspergillus niger AS3.324 and aspergillus oryzae is aspergillus oryzae AS 3.042. The invention creatively adopts a stacking fermentation mode, and can improve the color gradation and the yield of the water-soluble mesona chinensis benth melanin. Naturally drying, and avoiding sun exposure.

In an optional scheme of the preparation method of the mesona blume melanin, the ratio of the effective bacterial count of aspergillus niger to the effective bacterial count of aspergillus oryzae in mixed bacteria is 2:1, and the concentration of the mixed bacteria is 10⁸～10⁹cfu/mL。

The weight volume ratio of the fresh Mesona chinensis Benth to the sprayed mixed bacteria is 3-5 per mill.

In an optional embodiment of the method for preparing mesona chinensis benth melanin of the present invention, step S1 further includes the following substeps: after the mixed bacteria are added into the fresh Mesona chinensis Benth, culturing for 16-20 h at 28-30 ℃, and then performing stacking fermentation.

In the optional scheme of the preparation method of mesona chinensis benth melanin, the temperature of stacking fermentation is 30-33 ℃, and the humidity is 30-35%.

In an optional scheme of the preparation method of the mesona blume melanin, the alkaline water is a NaOH aqueous solution with the mass concentration of 0.12-0.15%, the addition amount of the alkaline water is 45-50 times of the mass of the dry mesona blume, the leaching temperature of the alkaline water is 90-98 ℃, and the leaching time is 1.5-2.5 hours; wherein, the pH value of the NaOH aqueous solution is more than 12, and the invention adopts the alkaline water leaching mode with higher pH value, so that the yield of the water-soluble melanin is higher and the color level is higher.

Preferably, the alkaline water leaching is carried out in a jacketed kettle, the jacketed kettle is adopted to ensure that the heating is more uniform, the temperature in the leaching process is stably kept at 90-98 ℃, and the industrialization is facilitated.

In the optional scheme of the preparation method of the mesona chinensis benth melanin, the leaching liquor is obtained by adopting plate-and-frame filtration after alkaline water leaching.

In an optional scheme of the preparation method of the mesona chinensis benth melanin, the preparation method further comprises the following steps of: s3 adding absolute ethanol into the leaching solution after the alkaline water leaching for alcohol precipitation, and collecting the filtrate to obtain the mesona chinensis benth melanin. The alcohol precipitation of the invention can further remove the glue and improve the purity of the water-soluble pigment. Adding absolute ethyl alcohol into the leaching liquor until the concentration is 48% -53%, and collecting filtrate by adopting a tubular centrifugal separation method.

In an optional scheme of the preparation method of the mesona chinensis benth melanin, in step S3, HCl is added into the leaching liquor to adjust the pH of the solution to 6.8-7.2, then alcohol precipitation is carried out, and filtrate is collected; and carrying out electrodialysis desalination treatment on the filtrate to obtain the mesona chinensis benth melanin. According to the invention, the pH value of the solution is adjusted to 6.8-7.2 by HCl, then alcohol precipitation is carried out, impurities are removed by tube-type centrifugal separation, and the obtained water-soluble mesona chinensis benth melanin has the lowest turbidity.

In an optional scheme of the preparation method of mesona chinensis benth melanin, the preparation method further comprises the step of S4: and (3) carrying out nanofiltration concentration on the obtained filtrate, or carrying out nanofiltration concentration on the obtained filtrate after electrodialysis desalination treatment, setting the aperture of a membrane to be 100Da, and obtaining the mesona chinensis benth melanin after concentration, wherein the mesona chinensis benth melanin is more efficient and lower in consumption compared with vacuum evaporation concentration or other concentration modes.

In a second aspect, the invention further provides the mesona chinensis benth melanin extracted by the preparation method of the mesona chinensis benth melanin in any one of the above schemes.

(III) advantageous effects

The invention has the beneficial effects that: according to the preparation method of the mesona chinensis benth melanin, the aspergillus niger and aspergillus oryzae mixed bacteria are adopted to carry out stacking fermentation treatment on the fresh mesona chinensis benth, so that the color value of the obtained water-soluble mesona chinensis benth melanin is higher; the water-soluble mesona chinensis benth melanin product has good thermal stability and good stability within the pH range of 5-12.

The invention further adopts a combined method of alkaline water extraction and alcohol precipitation glue removal, reduces the turbidity of the mesona chinensis benth melanin, and further improves the light transmittance.

Drawings

FIG. 1 is a UV-visible band scan of an aqueous solution of water-soluble Mesona chinensis melanin according to example 1 of the present invention;

FIG. 2 is a graph showing the change of absorbance with pH value of water-soluble Mesona chinensis Benth melanin in example 1 of the present invention.

Detailed Description

For a better understanding of the present invention, reference will now be made in detail to the present invention by way of specific embodiments thereof.

The preparation method of mesona chinensis benth melanin provided by the embodiment of the invention creatively adopts the stacking fermentation treatment of aspergillus niger and aspergillus oryzae mixed bacteria in the field of pigment extraction to improve the extraction rate of water-soluble melanin, and after fermentation, the mixture is extracted by using high-alkaline water. The water-soluble mesona chinensis benth melanin product has good thermal stability and good stability within the pH range of 5-12.

In order to better understand the above technical solutions, exemplary embodiments of the present invention will be described in more detail below. While the following shows exemplary embodiments of the invention, it should be understood that the invention may be embodied in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

Example 1

The preparation method of the mesona chinensis benth melanin comprises the following steps:

s1 Stacking fermentation

Picking fresh Mesona chinensis Benth in field, spreading naturally, spraying mixed suspension of Aspergillus niger AS3.324 and Aspergillus oryzae AS3.042 with effective strain ratio of 2:1 to obtain mixed suspension with concentration of 4.6 × 10⁸cfu/mL, the weight volume ratio of the fresh Mesona chinensis Benth to the sprayed mixed bacterial suspension is 3 per mill; culturing at 30 deg.C for 18h, then transferring to sealed space for stacking fermentation for 3 days at 33 deg.C and 33% humidity, and naturally drying after stacking fermentation to avoid sun exposure to obtain dry Mesona chinensis Benth;

alkaline leaching of S2

Placing the Mesona chinensis Benth after stacking fermentation in the step S1 into a jacketed pan, adding NaOH aqueous solution with mass concentration of 0.12% 45 times of the mass of the dry Mesona chinensis Benth, leaching at 95 deg.C for 2h, and press-filtering with a plate frame to obtain alkaline water leaching liquor;

s3 alcohol precipitation degumming

Cooling the obtained alkaline water leaching liquor to room temperature, adjusting the pH of the solution to 7 by HCl, adding absolute ethyl alcohol to the concentration of 50.8%, performing tubular centrifugal separation, and collecting filtrate;

s4 electrodialysis desalination

And desalting the obtained filtrate by electrodialysis, wherein the operating parameters are as follows: operating pressure 1.5kg/cm²An operating voltage of 220V and an operating current of 2.5A;

s5 nanofiltration concentration

Carrying out nanofiltration concentration on the desalted filtrate, wherein the operating parameters are as follows: the aperture of the sulfonated polysulfone membrane is 100Da, the feeding temperature is less than 50 ℃, the working pressure is 0.5MPa, the feeding flow is 250L/h, and a concentrated solution is obtained after concentration;

s6 vacuum drying

Vacuum drying the concentrated extract to obtain water soluble Mesona chinensis Benth melanin.

Color number E of the Water-soluble Mesona chinensis Benth melanin obtained in this example^1％＝8.8。

Example 2

The preparation method of the mesona chinensis benth melanin comprises the following steps:

s1 Stacking fermentation

Picking fresh Mesona chinensis Benth in field, spreading naturally, spraying mixed suspension of Aspergillus niger AS3.324 and Aspergillus oryzae AS3.042 with effective strain ratio of 2:1 to obtain mixed suspension with concentration of 6.2 × 10⁸cfu/mL, the weight volume ratio of the fresh Mesona chinensis Benth to the sprayed mixed bacterial suspension is 5 per mill; culturing at 28 deg.C for 16h, then transferring to sealed space for stacking fermentation for 5 days at 35 deg.C and 30% humidity, and naturally drying to avoid sun exposure to obtain dry Mesona chinensis Benth;

alkaline leaching of S2

Placing the Mesona chinensis Benth after stacking fermentation in the step S1 into a jacketed pan, adding NaOH aqueous solution with mass concentration of 0.12% 45 times of the mass of the dry Mesona chinensis Benth, leaching at 95 deg.C for 2h, and press-filtering with a plate frame to obtain alkaline water leaching liquor;

s3 alcohol precipitation degumming

Cooling the obtained alkaline water leaching liquor to room temperature, adding HCl to adjust the pH value of the solution to 7, then adding absolute ethyl alcohol to the solution until the concentration reaches 50.5%, then performing tubular centrifugal separation, and collecting filtrate;

s4 electrodialysis desalination

The obtained filtrate is desalted by electrodialysis, and the operating parameters are as follows: operating pressure 2.0kg/cm²An operating voltage of 220V and an operating current of 2.5A;

s5 nanofiltration concentration

And (3) carrying out nanofiltration concentration on the desalted filtrate, wherein the operation parameters are as follows: the aperture of the sulfonated polysulfone membrane is 100Da, the feeding temperature is less than 50 ℃, the working pressure is 0.7MPa, and the feeding flow is 280L/h;

s6 vacuum drying

Vacuum drying the concentrated extract to obtain water soluble Mesona chinensis Benth melanin.

Color number E of the Water-soluble Mesona chinensis Benth melanin obtained in this example^1％＝8.6。

Example 3

The preparation method of the mesona chinensis benth melanin comprises the following steps:

s1 Stacking fermentation

The fresh Mesona chinensis Benth is picked in the field and spread naturally,spraying mixed suspension of Aspergillus niger AS3.324 and Aspergillus oryzae AS3.042 with effective strain ratio of 2:1 to the suspension at a concentration of 8.1 × 10⁸cfu/mL, the weight volume ratio of the fresh Mesona chinensis Benth to the sprayed mixed bacterial suspension is 4 per mill; culturing at 30 deg.C for 20h, then transferring to sealed space for stacking fermentation for 4 days, controlling temperature at 32 deg.C and humidity at 35%, and naturally drying to avoid sun exposure to obtain dry Mesona chinensis Benth;

alkaline leaching of S2

S1, placing the stacking fermented mesona blume into a jacketed kettle, adding NaOH aqueous solution with the concentration of 0.13 percent and the mass of 48 times of that of the dry mesona blume, leaching for 1.8h at 97 ℃, and then performing plate-and-frame filter pressing to obtain alkaline water leaching liquor;

s3 alcohol precipitation degumming

Cooling the obtained alkaline water leaching liquor to room temperature, adding HCl to adjust the pH value of the solution to 7, then adding absolute ethyl alcohol to the solution until the concentration reaches 50.2%, then performing tubular centrifugal separation, and collecting filtrate;

s4 electrodialysis desalination

The obtained filtrate is desalted by electrodialysis, and the operating parameters are as follows: operating pressure 1.8kg/cm²An operating voltage of 220V and an operating current of 2.5A;

s5 nanofiltration concentration

And (3) carrying out nanofiltration concentration on the desalted filtrate, wherein the operation parameters are as follows: the aperture of the sulfonated polysulfone membrane is 100Da, the feeding temperature is less than 50 ℃, the working pressure is 0.7MPa, and the feeding flow is 280L/h;

s6 vacuum drying

Vacuum drying the concentrated extract to obtain water soluble Mesona chinensis Benth melanin.

E of the Water-soluble Mesona chinensis Benth melanin obtained in this example^1％＝8.7。

Comparative example 1

The preparation method of the mesona chinensis benth melanin comprises the following steps:

the other points are different from example 1 in that in step S1, fresh Mesona chinensis Benth is dried by conventional method. The method specifically comprises the following steps: harvesting fresh Mesona chinensis Benth, directly placing in the field for about 4 days, placing cement terrace in the air for naturally drying, avoiding sun exposure, packaging, storing in storehouse for more than half a year to obtain dry Mesona chinensis Benth.

Comparative example 2

The preparation method of the mesona chinensis benth melanin comprises the following steps:

the other point is that the difference from the example 1 is that the stacking fermentation in the step S1, mixed bacteria are not sprayed, specifically: the method comprises the steps of picking fresh Mesona chinensis Benth in the field, naturally spreading the fresh Mesona chinensis Benth, transferring to a sealed space for stacking fermentation for 3 days, controlling the temperature at 33 ℃ and the humidity at 33%, stacking fermentation, naturally drying, and avoiding sun exposure to obtain the dry Mesona chinensis Benth.

Comparative example 3

The preparation method of the mesona chinensis benth melanin comprises the following steps:

otherwise, the same as example 1, except that the stacking fermentation in step S1 was carried out by spraying only aspergillus oryzae, specifically: picking fresh Mesona chinensis Benth in field, spreading naturally, spraying Aspergillus oryzae AS3.042 suspension with bacteria suspension concentration of 5.3 × 10⁸cfu/mL, culturing fresh Mesona chinensis Benth and sprayed mixed bacterial suspension at 30 ℃ for 18h according to the weight volume ratio of 3 per mill, then transferring to a sealed space for stacking fermentation for 3 days, controlling the temperature at 33 ℃ and the humidity at 33%, and naturally airing after stacking fermentation to avoid sunlight exposure to obtain the dry Mesona chinensis Benth.

Comparative example 4

The preparation method of the mesona chinensis benth melanin comprises the following steps:

otherwise, the same as example 1, except that the stacking fermentation in step S1, only aspergillus niger was sprayed, specifically: picking fresh Mesona chinensis Benth in field, spreading naturally, spraying Aspergillus niger AS3.324 bacterial suspension with concentration of 4.8 × 10⁸cfu/mL, culturing fresh Mesona chinensis Benth and sprayed bacterial suspension at 30 ℃ for 18h according to the weight volume ratio of 3 per mill, then transferring to a sealed space for stacking fermentation for 3 days, controlling the temperature at 33 ℃ and the humidity at 33%, and naturally airing after stacking fermentation to avoid sunlight exposure to obtain the dry Mesona chinensis Benth.

Comparative example 5

The preparation method of the mesona chinensis benth melanin comprises the following steps:

the other points are different from those of embodiment 1 in the stacking of hair in step S1Fermenting, spraying Aspergillus niger and Aspergillus oryzae mixed bacterial suspension with effective strain ratio of 1:1, specifically: picking fresh Mesona chinensis Benth in field, spreading naturally, spraying mixed suspension of Aspergillus niger AS3.324 and Aspergillus oryzae AS3.042 with effective strain ratio of 1:1 to obtain mixed suspension with concentration of 4.9 × 10⁸cfu/mL, culturing fresh Mesona chinensis Benth and sprayed mixed bacterial suspension at 30 ℃ for 18h according to the weight volume ratio of 3 per mill, then transferring to a sealed space for stacking fermentation for 3 days, controlling the temperature at 33 ℃ and the humidity at 33%, and naturally airing after stacking fermentation to avoid sunlight exposure to obtain the dry Mesona chinensis Benth.

Comparative example 6

The preparation method of the mesona chinensis benth melanin comprises the following steps:

the other steps are the same as the example 1, and the difference is that the stacking fermentation in the step S1 is carried out, and Aspergillus niger and Aspergillus oryzae mixed bacterial suspension with the effective strain ratio of 1:2 is sprayed, specifically: picking fresh Mesona chinensis Benth in field, spreading naturally, spraying mixed suspension of Aspergillus niger AS3.324 and Aspergillus oryzae AS3.042 with effective strain ratio of 1:2 to obtain mixed suspension with concentration of 5.4 × 10⁸cfu/mL, culturing fresh Mesona chinensis Benth and sprayed mixed bacterial suspension at 30 ℃ for 18h according to the weight volume ratio of 3 per mill, then transferring to a sealed space for stacking fermentation for 3 days, controlling the temperature at 33 ℃ and the humidity at 33%, and naturally airing after stacking fermentation to avoid sunlight exposure to obtain the dry Mesona chinensis Benth.

Comparative example 7

The preparation method of the mesona chinensis benth melanin comprises the following steps:

the other points are that the alcohol precipitation glue removal in the step S3 is performed without adjusting the pH, and specifically: cooling the obtained alkaline water leaching liquor to room temperature, adding absolute ethyl alcohol to the alkaline water leaching liquor to reach the concentration of 50%, performing tubular centrifugal separation, and collecting filtrate;

comparative example 8

The preparation method of the mesona chinensis benth melanin comprises the following steps:

the other points are different from the embodiment 1 in that the alcohol precipitation and glue removal in the step S3 specifically include: cooling the obtained alkaline water leaching liquor to room temperature, adjusting the pH of the solution to 7 by HCl, adding absolute ethyl alcohol to the concentration of 45%, performing tubular centrifugal separation, and collecting filtrate;

comparative example 9

The preparation method of the mesona chinensis benth melanin comprises the following steps:

the other points are different from the embodiment 1 in that the alcohol precipitation and glue removal in the step S3 specifically include: cooling the obtained alkaline water leaching liquor to room temperature, adjusting the pH of the solution to 7 by HCl, adding absolute ethyl alcohol to reach the concentration of 55%, performing tubular centrifugal separation, and collecting filtrate;

to verify the properties of Mesona chinensis Benth melanin of the present invention, the following tests were performed:

test one:

the color gradation of the water-soluble Mesona chinensis Benth melanin obtained in example 1 and comparative examples 1-5 is determined, and the color value is determined by the following method: referring to GB 1886.64-2015 food safety national standard food additive caramel color value method, color value E^1％249nm＝A×100/w。

The measurements gave the data shown in table 1:

table 1: EXAMPLE 1 Melanin color number of Mesona Procumbens obtained in comparative examples 1-6

As can be seen from Table 1, the addition of Aspergillus oryzae or Aspergillus niger to fresh Mesona chinensis in stacking fermentation is beneficial to improving the color value of the water-soluble Mesona chinensis melanin, and when Aspergillus oryzae and Aspergillus niger are added simultaneously in example 1, the color value of the water-soluble Mesona chinensis melanin is the highest and is significantly higher than that in comparative examples 1-6, which shows that Aspergillus oryzae and Aspergillus niger have obvious synergistic effect on improving the color value of the water-soluble Mesona chinensis melanin in the stacking fermentation process of fresh Mesona chinensis and the yield is higher. Compared with the comparative example 1, the comparative example 1 adopts the traditional mode to treat the fresh mesona chinensis benth, although the color value of the product can be improved, the effect is smaller than that of the stacking fermentation treatment, and is obviously smaller than that of the embodiment 1 which adopts aspergillus oryzae and aspergillus niger to cooperate with the stacking fermentation treatment.

FIG. 1 is a scanning diagram of the ultraviolet-visible wavelength band of an aqueous solution of water-soluble Mesona chinensis Benth melanin obtained in example 1 of the present invention, and it can be seen from FIG. 1 that the maximum absorption peak of the water-soluble Mesona chinensis Benth melanin solution is 249 nm.

And (2) test II:

the water-soluble Mesona chinensis Benth melanin obtained in example 1 and comparative examples 7-9 was prepared into 1 ‰ aqueous solution, and turbidity was measured. The measuring method refers to a method in GB/T5750.4-2006 sensory properties and physical indexes of standard test method for drinking water, and a turbidity analyzer is used for measuring the turbidity of a sample. The measurement results are shown in table 2:

TABLE 2 turbidity of the products obtained by different alcohol precipitation degumming processes

As can be seen from Table 2, the pH value is adjusted to neutral by the alcohol precipitation degumming process, which is beneficial to alcohol precipitation of Mesona chinensis Benth, thereby improving the light transmittance of the water-soluble Mesona chinensis Benth melanin solution. In addition, the optimal concentration of absolute ethyl alcohol in the alcohol precipitation degumming process is 50%, the alcohol precipitation of the mesona blume which is less than 50% is not thorough, and when the concentration is obviously higher than 50%, the effect of improving the light transmittance of the water-soluble mesona blume melanin solution is not great, but the production cost is obviously increased.

And (3) test III:

nanofiltration concentration is carried out on the filtrate after the salt removal in the example 1, and the operation parameters are as follows: the aperture of the sulfonated polysulfone membrane is 100Da, the feeding temperature is less than 50 ℃, the working pressure is 0.7MPa, and the feeding flow is 280L/h;

comparative experiment: the filtrate after desalting in example 1 was concentrated by evaporation in vacuo at 50 ℃ under a vacuum of 0.10MPa, in contrast to the nanofiltration concentration according to the invention. The time required for the two concentration processes to concentrate to different concentration multiples was compared and the results are shown in table 3.

TABLE 3 comparison of the time required for nanofiltration concentration and vacuum evaporation concentration

As can be seen from Table 3, the water-soluble Mesona chinensis Benth melanin solution is concentrated to the same concentration times, and the time required for vacuum evaporation concentration is more than 2.5 times of that of nanofiltration concentration. Nanofiltration concentration is therefore more efficient than vacuum evaporative concentration.

And (4) testing:

the water-soluble Mesona chinensis Benth melanin obtained in the examples 1-3 of the present invention was subjected to thermal stability evaluation and acid-base stability evaluation.

1. Evaluation of thermal stability

The water-soluble Mesona chinensis Benth melanin obtained in examples 1-3 was dried, 0.1g of the water-soluble Mesona chinensis Benth melanin sample was weighed to 0.0001g, diluted 10 times in gradient to 1000 times, 10mL of the diluted water-soluble Mesona chinensis Benth melanin solution was placed in water baths at 25 deg.C, 50 deg.C, 80 deg.C and 100 deg.C for 0h, 1h, 2h and 3h, respectively, and after the water bath was completed, the solution was rapidly cooled to room temperature, and the absorbance at the maximum absorption wavelength of 249nm was measured, with the results shown in Table 4.

TABLE 4 evaluation of thermal stability of melanin

As is clear from Table 4, the absorbance of the water-soluble Mesona chinensis Benth melanin prepared in examples 1-3 of the present invention is not changed at 100 deg.C, which shows that the water-soluble Mesona chinensis Benth melanin prepared in the present invention has good thermal stability in the range of 25-100 deg.C.

2. Evaluation of stability to Melanin acid and alkali

The water-soluble Mesona chinensis Benth melanin obtained in example 1 was dried, 0.1g of melanin sample was weighed to 0.0001g, diluted 10-fold with gradient to 1000-fold (pH of the 1000-fold diluted melanin solution prepared above was adjusted to 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12 with HCI and NaOH solutions), 10mL of the diluted water-soluble Mesona chinensis Benth melanin solution was placed in a 40 ℃ water bath and left to stand for 2 hours, and then absorbance was measured at the maximum absorption wavelength of 249nm, with the results shown in FIG. 2.

As can be seen from FIG. 2, the absorbance of the water-soluble Mesona chinensis Benth melanin prepared in example 1 of the present invention is not substantially changed in the range of pH5-12, and is decreased with the increase of the acidity of the solution in the range of pH 3-5, which shows that the water-soluble Mesona chinensis Benth melanin prepared in the present invention has good stability when the pH is neutral and alkaline.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.