阅读说明：本技术 一种鼠李糖脂复合表面活性剂的制备方法和应用 (Preparation method and application of rhamnolipid composite surfactant ) 是由 李泽勇 李秋如 吴海龙 刘康 于 2021-08-09 设计创作，主要内容包括：本发明属于表面活性剂技术领域,公开了一种鼠李糖脂复合表面活性剂的制备方法和应用。所述制备方法包括：往发酵完成的鼠李糖脂发酵液中加入溶菌酶,在温度为45～50℃,pH为5～7的条件下搅拌反应,所得发酵液冷却至室温,然后加入APG搅拌洗涤,再加入聚合氯化铝进行絮凝沉淀,离心,取上清液浓缩干燥,得到鼠李糖脂-APG复合表面活性剂。本发明的制备方法采用溶菌酶处理发酵液,配合采用APG进行洗涤,可以显著提高鼠李糖脂的得率；并采用聚合氯化铝对溶菌处理后的发酵液进行絮凝沉淀,提高产物纯度。所得产物具有良好的表面活性,应用于日化洗涤用品中具有天然、环保、无刺激、生物可降解的优势。(The invention belongs to the technical field of surfactants, and discloses a preparation method and application of a rhamnolipid composite surfactant. The preparation method comprises the following steps: and adding lysozyme into the rhamnolipid fermentation liquor after fermentation is finished, stirring and reacting under the conditions that the temperature is 45-50 ℃ and the pH value is 5-7, cooling the obtained fermentation liquor to room temperature, adding APG (ammonium polyphosphate G), stirring and washing, adding polyaluminium chloride for flocculation precipitation, centrifuging, taking supernate, concentrating and drying to obtain the rhamnolipid-APG composite surfactant. The preparation method adopts lysozyme to treat fermentation liquor, and is matched with APG for washing, so that the yield of rhamnolipid can be obviously improved; and the polyaluminium chloride is adopted to carry out flocculation precipitation on the fermentation liquor after the bacteriolysis treatment, thereby improving the purity of the product. The obtained product has good surface activity, and has the advantages of naturalness, environmental protection, no irritation and biodegradability when being applied to daily chemical washing products.)

1. A preparation method of a rhamnolipid composite surfactant is characterized by comprising the following preparation steps:

(1) adding lysozyme into the fermented rhamnolipid fermentation liquor, and stirring for reaction at the temperature of 45-50 ℃ and the pH of 5-7;

(2) cooling the fermentation liquor subjected to the bacteriolysis treatment in the step (1) to room temperature, and then adding APG (ammonium peroxyphosphate) to stir and wash;

(3) and (3) adding polyaluminium chloride into the fermentation liquor washed in the step (2) for flocculation and precipitation, centrifuging, taking the supernatant, concentrating and drying to obtain the rhamnolipid-APG composite surfactant.

2. The method for preparing a rhamnolipid composite surfactant according to claim 1, wherein the rhamnolipid fermentation broth in step (1) is a fermentation broth obtained by culturing pseudomonas aeruginosa as a production strain in a fermentation medium; the content of rhamnolipid in the fermentation liquor is 5-70 g/L.

3. The method for preparing a rhamnolipid complex surfactant according to claim 2, wherein the fermentation medium includes a carbon source, a nitrogen source, and inorganic salts; the carbon source comprises at least one of soybean oil, palm oil, peanut oil, glycerol, glucose and molasses, the nitrogen source comprises at least one of yeast powder, peptone, nitrate and ammonium salt, and the inorganic salt comprises at least one of sodium salt, potassium salt, magnesium salt and calcium salt.

4. The method for preparing a rhamnolipid composite surfactant according to claim 1, wherein the amount of lysozyme added in step (1) is 0.02-0.08% of the mass of rhamnolipid fermentation broth; the stirring reaction time is 1-4 h.

5. The method for preparing rhamnolipid complex surfactant according to claim 1, wherein the amount of APG added in step (2) is 0.5-5% of the mass of the fermentation broth after bacteriolysis.

6. The method for preparing rhamnolipid complex surfactant according to claim 1, wherein the amount of the polyaluminium chloride added in the step (3) is 0.1-0.5% of the mass of the washed fermentation broth.

7. The method for preparing rhamnolipid composite surfactant according to claim 1, wherein the flocculation is performed at a pH of 5-7.

8. The method for preparing rhamnolipid complex surfactant according to claim 1, wherein the supernatant of step (3) is washed with organic solvent to remove impurities before concentration and drying; the organic solvent is a mixed solvent of cyclohexane and ethyl acetate.

9. The application of the composite surfactant prepared by the method of any one of claims 1 to 8 in daily chemical washing products.

10. The use of claim 9, wherein the daily chemical washing product comprises a shampoo, a body wash, a face wash, a laundry detergent, a washing powder, a hand sanitizer, a liquid detergent, a soap powder or a soap.

Technical Field

The invention belongs to the technical field of surfactants, and particularly relates to a preparation method and application of a rhamnolipid composite surfactant.

Background

The rhamnolipid is a biosurfactant which has the longest research time and the most mature application technology. It is produced mainly by fermentation of pseudomonas or burkholderia species or other suitable microorganisms. However, the resulting fermentation mixture or "fermentation broth" must be further processed to isolate/purify rhamnolipids. The fermentation broth components of rhamnolipid producing bacteria are complex, and other fermentation broth components include incompletely reacted feed substrates such as triglycerides, diglycerides and monoglycerides, as well as fatty acids, as well as cellular components and sugars, etc. The extraction of rhamnolipid from fermentation liquor is high in cost and difficult. High recovery and purification costs are major obstacles to be overcome for large-scale commercialization of rhamnolipids. At present, methods for extracting rhamnolipid from fermentation liquor mainly comprise chloroform-methanol extraction, silica gel column chromatography and the like. However, the above method has problems in that a toxic solvent is used and the cost is high.

Patent CN 107405537 a discloses a method for separating rhamnolipids from fermentation broth, comprising: (a) mixing an inert adsorption carrier with the rhamnolipid mixture; (b) dissolving the mixture in an organic solvent at a temperature above 31 ℃ and a pressure above 73 bar; (c) isolating at least one fatty compound; (d) adding a co-solvent to the organic solvent; (e) changing the temperature and/or pressure; (f) isolating a first rhamnolipid compound; and (g) isolating a second rhamnolipid compound. The patent mainly adopts an adsorption carrier for adsorption and uses supercritical CO₂Dehydration/degreasing and treatment with supercritical CO₂And a fractionation step with increasing proportions of co-solvent to remove mono-and di-rhamnolipid compounds. The process control difficulty is high, and the cost is high.

Patent CN 108191930 a discloses a method for extracting rhamnolipid product in fermentation broth, comprising: 1) pretreatment: heating the fermentation liquid, cooling, and centrifuging to remove insoluble substances such as thallus and denatured protein; 2) flocculation and concentration: adding appropriate amount of chitosan into the supernatant, stirring, naturally settling at appropriate temperature, and removing the upper layerA liquid phase; 3) and (3) elution: washing with distilled water to remove residual fermentation liquid in precipitate, adding NaHCO solution with proper concentration₃Eluting rhamnolipid in the precipitate by using a solution, and collecting eluent; 4) obtaining: adjusting the pH value of the eluent, standing for precipitation and centrifuging to obtain a rhamnolipid product. The technology of the patent adopts chitosan to flocculate and settle rhamnolipid products, and then adopts NaHCO₃Eluting with water solution, and precipitating with acid solution to obtain rhamnolipid product. However, in practical operation, the problem of low product purity and yield exists in the flocculation and sedimentation of the rhamnolipid product by using chitosan.

Patent CN 112225763 a discloses a method for separating and purifying rhamnolipid, which comprises the following steps: preparing graphene oxide; performing cation modification on the graphene oxide to obtain cation-modified graphene oxide; and adding the cation modified graphene oxide into fermentation liquor for adsorption to obtain the rhamnolipid adsorption amount. The technology adopts the cation modified graphene oxide to adsorb rhamnolipid, and has the problems of high preparation cost and low yield.

Disclosure of Invention

Aiming at the defects and shortcomings of the prior art, the invention aims to provide a preparation method of a rhamnolipid composite surfactant. The preparation method adopts lysozyme to treat fermentation liquor, and adopts alkyl glycoside (APG) for washing, so that the yield of rhamnolipid can be obviously improved; and the polyaluminium chloride is adopted to carry out flocculation precipitation on the fermentation liquor after the bacteriolysis treatment, so that solid parts, cells and proteins after the bacteriolysis treatment are removed, and unfavorable impurity components are reduced. The obtained composite surfactant of rhamnolipid and APG has good surface activity and biodegradability.

The invention also aims to provide the application of the composite surfactant prepared by the method in daily chemical washing products.

The purpose of the invention is realized by the following technical scheme:

a preparation method of a rhamnolipid composite surfactant comprises the following preparation steps:

(1) adding lysozyme into the fermented rhamnolipid fermentation liquor, and stirring for reaction at the temperature of 45-50 ℃ and the pH of 5-7;

(2) cooling the fermentation liquor subjected to the bacteriolysis treatment in the step (1) to room temperature, and then adding APG (ammonium peroxyphosphate) to stir and wash;

(3) and (3) adding polyaluminium chloride into the fermentation liquor washed in the step (2) for flocculation and precipitation, centrifuging, taking the supernatant, concentrating and drying to obtain the rhamnolipid-APG composite surfactant.

Further, the rhamnolipid fermentation liquor in the step (1) refers to fermentation liquor obtained by culturing pseudomonas Aeruginosa (aeroginosa) serving as a production strain through a fermentation medium; the rhamnolipid content in the fermentation liquor (after the thalli are removed by centrifugation) is 5-70 g/L.

Further preferably, the fermentation medium comprises a carbon source, a nitrogen source and inorganic salts; the carbon source comprises at least one of soybean oil, palm oil, peanut oil, glycerol, glucose and molasses, the nitrogen source comprises at least one of yeast powder, peptone, nitrate and ammonium salt, and the inorganic salt comprises at least one of sodium salt, potassium salt, magnesium salt and calcium salt.

Further, the adding amount of the lysozyme in the step (1) is 0.02-0.08% of the mass of the rhamnolipid fermentation liquor.

Further, the stirring reaction time in the step (1) is 1-4 h.

Further, the addition amount of the APG in the step (2) is 0.5-5% of the mass of the fermentation liquor after the bacteriolysis treatment.

Further, the adding amount of the polyaluminium chloride in the step (3) is 0.1-0.5% of the mass of the washed fermentation liquor. The verification proves that the adding amount of the polyaluminium chloride has obvious influence on the yield and the purity of the obtained product. Under the condition of adding amount less than 0.1%, the flocculation precipitation effect is poor, and the product purity is reduced; under the condition of adding amount higher than 0.5%, part of rhamnolipid and APG are flocculated and precipitated, and the yield of the product is reduced.

Further, the flocculation precipitation in the step (3) is carried out under the condition that the pH value is 5-7. The pH condition of the flocculation precipitation of the invention has obvious influence on the yield and the purity of the obtained product. Under the acidic condition that the pH is lower than 5, the flocculation precipitation effect is poor, and the product purity is reduced; under the alkaline condition that the pH is higher than 7, partial rhamnolipid and APG can be flocculated and precipitated, and the product yield is reduced.

Further, the supernatant in the step (3) is washed by an organic solvent to remove impurities before concentration and drying. Preferably, the organic solvent is a mixture of cyclohexane and ethyl acetate. Through organic solvent washing, the non-flocculated and precipitated lipophilic components such as glyceride, fatty acid and the like can be further extracted and removed, and the adverse effect on the foaming performance of the obtained composite surfactant is reduced.

The composite surfactant prepared by the method is applied to daily chemical washing products.

Furthermore, the daily chemical washing products comprise shampoo, shower gel, facial cleanser, laundry detergent, washing powder, liquid soap, liquid detergent, soap powder or perfumed soap.

The principle of the invention is as follows: firstly, rhamnolipid fermentation liquor is treated by lysozyme, so that rhamnolipid in a bacterium body is further dissolved out, then APG is added, stirring and washing are carried out, the APG has a molecular structure similar to that of the rhamnolipid, the solubility of the APG in water is high, the desorption of the rhamnolipid can be further promoted, the rhamnolipid can enter water for dissolution, and the yield of the rhamnolipid can be remarkably improved in the two aspects. The method comprises the steps of adding polyaluminium chloride for flocculation precipitation, adjusting the adding amount of the polyaluminium chloride and the pH condition of the flocculation precipitation to realize preferential selective adsorption of the suspended matters, the protein colloids and the inorganic salt components, having little influence on the highly water-soluble rhamnolipid and APG components, and then performing centrifugal separation to realize separation and purification of the rhamnolipid and APG composite components.

Compared with the prior art, the invention has the beneficial effects that:

(1) the preparation method of the invention can achieve equivalent or even higher yield and purity of rhamnolipid under the condition of not using or reducing the use of organic solvent.

(2) The product obtained by the invention is a compound of rhamnolipid and APG, has rich and fine foam, strong compatibility, no toxicity, no harm, no stimulation to skin, and rapid and thorough biodegradation, can be directly applied to daily chemical washing products, and has better foaming performance (foaming power, foaming stability and foam fineness) compared with a pure rhamnolipid component.

(3) The method adopts lysozyme to treat fermentation liquor, and adopts alkyl glycoside (APG) for washing, so that the yield of rhamnolipid can be obviously improved; in the subsequent process of flocculating and precipitating the fermentation liquor after the bacteriolysis treatment by adopting the polyaluminium chloride, although a small amount of rhamnolipid can be adsorbed to cause the yield to be reduced, the overall yield is equivalent to or better than the organic solvent extraction yield after the thalli is centrifugally separated in the prior art.

Detailed Description

The present invention will be described in further detail with reference to examples, but the embodiments of the present invention are not limited thereto.

The rhamnolipid fermentation broth used in the following examples is a fermentation broth obtained by using pseudomonas Aeruginosa (aeromonas) as a production strain and continuously feeding and culturing the pseudomonas Aeruginosa in a fermentation medium (6% of soybean oil, 0.5% of yeast powder, 0.4% of sodium dihydrogen phosphate, 0.5% of dipotassium hydrogen phosphate, 0.03% of magnesium sulfate, 0.003% of calcium chloride and the balance of water, wherein the pH value is 7); the rhamnolipid content in the fermentation liquor (after the thalli are removed by centrifugation) is 35.3 g/L.

The APG used in the following examples is a commercially available low-degree of polymerization pale yellow oil (96.7% purity).

Example 1

The preparation method of the rhamnolipid composite surfactant comprises the following preparation steps:

(1) adding lysozyme into the rhamnolipid fermentation liquor, adjusting the adding amount of the lysozyme to be 0.01%, 0.02%, 0.04%, 0.08% and 0.10% of the mass of the rhamnolipid fermentation liquor respectively, and stirring and reacting for 2 hours under the conditions that the temperature is 45-50 ℃ and the pH value is adjusted to be 5.5-6.5 by phosphoric acid. And fermentation broth without lysozyme was used as a blank control.

(2) And (2) cooling the fermentation liquor subjected to the bacteriolysis treatment in the step (1) to room temperature, adding APG, stirring and washing, wherein the addition amount of the APG is 3.5% of the mass of the fermentation liquor subjected to the bacteriolysis treatment.

(3) And (3) adding polyaluminium chloride into the fermentation liquor washed in the step (2) for flocculation and precipitation, maintaining the pH of a system to be about 6 by the flocculation and precipitation, wherein the adding amount of the polyaluminium chloride is 0.35 percent of the mass of the washed fermentation liquor, centrifuging, taking supernate, concentrating and drying until the moisture content is lower than 1 percent, and obtaining the brown viscous rhamnolipid-APG composite surfactant.

The rhamnolipid yield (the percentage of the rhamnolipid content in the final composite surfactant to the rhamnolipid content in the initial fermentation broth) and the purity (the total percentage of the rhamnolipid and the APG) of the rhamnolipid-APG composite surfactant obtained under the condition of different lysozyme adding amounts in the example were measured, and the results are shown in table 1 below.

TABLE 1

Amount of lysozyme added

Blank control

0.01％

0.02％

0.04％

0.08％

0.10％

Yield of the product

69.3％

80.6％

85.7％

88.6％

90.8％

91.2％

Purity of

90.6％

90.2％

89.7％

88.5％

86.2％

84.3％

As can be seen from the results in Table 1, the yield of rhamnolipid obtained tends to increase with the increase of the addition amount of lysozyme, but the purity tends to decrease. Compared with a blank control group without lysozyme, the method can obviously improve the yield of the rhamnolipid and has higher purity. When the addition amount of the lysozyme is 0.02-0.08 percent, the yield of the rhamnolipid can reach more than 85 percent, and the purity of the obtained composite surfactant can reach more than 86 percent.

Example 2

The preparation method of the rhamnolipid composite surfactant comprises the following preparation steps:

(1) lysozyme is added into the rhamnolipid fermentation liquor, the adding amount of the lysozyme is 0.04 percent of the mass of the rhamnolipid fermentation liquor, and the stirring reaction is carried out for 2 hours under the conditions that the temperature is 45-50 ℃, and the pH value is adjusted to 5.5-6.5 by phosphoric acid.

(2) Cooling the fermentation liquor treated by the bacteriolysis in the step (1) to room temperature, then adding APG, stirring and washing, and adjusting the adding amount of APG to be 0.5%, 1%, 2%, 3.5%, 5% and 7.5% of the mass of the fermentation liquor treated by the bacteriolysis respectively. And fermentation broth washed without APG added was used as a blank.

(3) And (3) adding polyaluminium chloride into the fermentation liquor washed in the step (2) for flocculation and precipitation, maintaining the pH of a system to be about 6 by the flocculation and precipitation, wherein the adding amount of the polyaluminium chloride is 0.35 percent of the mass of the washed fermentation liquor, centrifuging, taking supernate, concentrating and drying until the moisture content is lower than 1 percent, and obtaining the brown viscous rhamnolipid-APG composite surfactant.

The rhamnolipid yield (the percentage of the rhamnolipid content in the final composite surfactant to the rhamnolipid content in the initial fermentation broth) and the purity (the total percentage of the rhamnolipid and the APG) of the rhamnolipid-APG composite surfactant obtained under the condition of different APG addition amounts in this example were determined, and the results are shown in table 2 below.

TABLE 2

APG addition amount

Blank control

0.5％

1％

2％

3.5％

5％

7.5％

Yield of the product

56.6％

81.8％

84.0％

86.9％

89.4％

91.7％

91.2％

Purity of

87.3％

87.7％

88.4％

88.0％

87.6％

86.2％

81.4％

The results in table 2 show that the addition of APG has a significant effect on the yield of rhamnolipid, which indicates that the addition of APG can promote the desorption of rhamnolipid and thalli or protein colloid after bacteriolysis, and can reduce the adsorption of subsequent flocculation precipitation on rhamnolipid, thereby improving the yield. Within a certain range, the purity is not greatly influenced by the addition of the APG, but after the addition amount of the APG exceeds 5 percent, the purity of the product is obviously reduced, and the possibility that the excessive APG can reduce the adsorption of impurities in the flocculation precipitation process, so that the purity of the product is reduced.

Example 3

The preparation method of the rhamnolipid composite surfactant comprises the following preparation steps:

(1) lysozyme is added into the rhamnolipid fermentation liquor, the adding amount of the lysozyme is 0.04 percent of the mass of the rhamnolipid fermentation liquor, and the stirring reaction is carried out for 2 hours under the conditions that the temperature is 45-50 ℃, and the pH value is adjusted to 5.5-6.5 by phosphoric acid.

(2) And (2) cooling the fermentation liquor subjected to the bacteriolysis treatment in the step (1) to room temperature, adding APG, stirring and washing, wherein the addition amount of the APG is 3.5% of the mass of the fermentation liquor subjected to the bacteriolysis treatment.

(3) And (3) adding polyaluminium chloride into the fermentation liquor washed in the step (2) for flocculation and precipitation, maintaining the pH of a system to be about 6 by flocculation and precipitation, respectively adjusting the adding amount of the polyaluminium chloride to be 0.05%, 0.1%, 0.2%, 0.35%, 0.5% and 0.75% of the mass of the washed fermentation liquor, taking the condition without adding the polyaluminium chloride as a blank control, centrifuging, taking the supernatant, concentrating and drying until the water content is lower than 1%, and obtaining the brown viscous rhamnolipid-APG composite surfactant.

The rhamnolipid yield (the percentage of the rhamnolipid content in the final composite surfactant to the rhamnolipid content in the initial fermentation broth) and the purity (the total percentage of the rhamnolipid and the APG) of the rhamnolipid-APG composite surfactant obtained under the condition of different added amounts of polyaluminium chloride in this example were determined, and the results are shown in table 3 below.

TABLE 3

Adding amount of polyaluminium chloride

Blank control

0.05％

0.1％

0.2％

0.35％

0.5％

0.75％

Yield of the product

103.7％

96.2％

94.8％

91.2％

89.0％

81.9％

72.5％

Purity of

49.8％

80.5％

85.9％

87.7％

88.2％

89.8％

92.2％

As is clear from the results in Table 3, in the case of flocculation without adding polyaluminum chloride, it was difficult to remove the impurity components after bacteriolysis by a simple centrifugation. The invention can obviously improve the purity of the product by adding the polyaluminium chloride for flocculation and precipitation. In addition, with the increase of the adding amount of the polyaluminium chloride, the yield of the rhamnolipid is reduced, which indicates that the polyaluminium chloride has a certain adsorption effect on the rhamnolipid. However, the rhamnolipid yield is over 100% under the condition that no polyaluminium chloride is added, which shows that the rhamnolipid content in the treated fermentation broth is obviously improved compared with the measured value in the untreated initial fermentation broth (fermentation broth after thalli is removed by centrifugation) through the processes of lysozyme treatment and APG washing in the early stage of the invention, and the improvement can compensate the reduction effect of the polyaluminium chloride on the rhamnolipid yield, so that under the condition of a certain addition amount (0.1-0.5%) of the polyaluminium chloride, the rhamnolipid yield is kept above 80%, and the product purity is kept above 85%.

Example 4

The preparation method of the rhamnolipid composite surfactant comprises the following preparation steps:

(1) lysozyme is added into the rhamnolipid fermentation liquor, the adding amount of the lysozyme is 0.04 percent of the mass of the rhamnolipid fermentation liquor, and the stirring reaction is carried out for 2 hours under the conditions that the temperature is 45-50 ℃, and the pH value is adjusted to 5.5-6.5 by phosphoric acid.

(2) And (2) cooling the fermentation liquor subjected to the bacteriolysis treatment in the step (1) to room temperature, adding APG, stirring and washing, wherein the addition amount of the APG is 3.5% of the mass of the fermentation liquor subjected to the bacteriolysis treatment.

(3) And (3) adding polyaluminium chloride into the fermentation liquor washed in the step (2) for flocculation and precipitation, adjusting the pH of the system to 4, 5, 6, 7, 8 and 9 in the flocculation and precipitation process respectively, wherein the adding amount of the polyaluminium chloride is 0.35 percent of the mass of the washed fermentation liquor, centrifuging, taking supernate, concentrating and drying until the moisture content is lower than 1 percent, and obtaining the brown viscous rhamnolipid-APG composite surfactant.

The rhamnolipid yield (the percentage of the rhamnolipid content in the final composite surfactant to the rhamnolipid content in the initial fermentation broth) and the purity (the total percentage of the rhamnolipid and the APG) of the rhamnolipid-APG composite surfactant obtained under different flocculation precipitation pH conditions in this example were determined, and the results are shown in table 4 below.

TABLE 4

pH of flocculation precipitation

4

5

6

7

8

9

Yield of the product

92.8％

90.7％

88.6％

84.5％

71.5％

23.8％

Purity of

62.9％

85.7％

87.8％

89.3％

92.3％

93.8％

The results in table 4 show that the flocculation precipitation pH condition has significant influence on the rhamnolipid yield and the product purity, and the flocculation effect is poor, part of impurities cannot be effectively removed, and the product purity is low under the acidic condition that the pH value is lower than 5; and under the alkaline condition that the pH value is higher than 7, the yield of the rhamnolipid is obviously reduced, which indicates that the alkaline condition can cause the adsorption and flocculation loss of the rhamnolipid and the yield is reduced.

Example 5

The preparation method of the rhamnolipid composite surfactant comprises the following preparation steps:

(1) lysozyme is added into the rhamnolipid fermentation liquor, the adding amount of the lysozyme is 0.04 percent of the mass of the rhamnolipid fermentation liquor, and the stirring reaction is carried out for 2 hours under the conditions that the temperature is 45-50 ℃, and the pH value is adjusted to 5.5-6.5 by phosphoric acid.

(2) And (2) cooling the fermentation liquor subjected to the bacteriolysis treatment in the step (1) to room temperature, adding APG, stirring and washing, wherein the addition amount of the APG is 3.5% of the mass of the fermentation liquor subjected to the bacteriolysis treatment.

(3) Adding polyaluminium chloride into the fermentation liquor washed in the step (2) for flocculation precipitation, maintaining the pH of a system to be about 6 by the flocculation precipitation, adding the polyaluminium chloride in an amount of 0.35% of the mass of the washed fermentation liquor, centrifuging, taking supernate, adding a mixed solvent of cyclohexane and ethyl acetate in a volume of 1 time (the volume ratio of the cyclohexane to the ethyl acetate is 7:3), and stirring and washing. Standing for layering, and concentrating and drying the aqueous phase until the water content is lower than 1% to obtain brown viscous rhamnolipid-APG composite surfactant.

The yield of the rhamnolipid-APG composite surfactant obtained in the embodiment is 88.2%, the purity of the composite surfactant is 94.2%, and compared with the rhamnolipid yield under the same conditions in the embodiment 1, the yield of the rhamnolipid-APG composite surfactant is not greatly influenced, and the purity is improved to a certain extent. The resulting composite surfactant was subjected to foaming property (foaming power, foaming stability and foam fineness) test. The testing method comprises the steps of preparing 1% aqueous solution by mass concentration, transferring 50mL of test solution into a transparent glass long tube, covering a plug, forcibly shaking the glass tube up and down for 10 times, measuring the height of foam by using a ruler after the foam is generated, recording the result, observing the size of the foam, standing, recording the time until the foam completely disappears, parallelly measuring 3 groups, taking an average value, and comparing by using pure rhamnolipid, wherein the testing result is shown in the following table 5.

TABLE 5

Foaming Properties	Height of foam	Time of disappearance of foam	Size of foam
				Example 5	26cm	43min	Fine foam
Example 1	21cm	35min	Fine foam
				Pure rhamnolipid	16cm	26min	Relatively coarse foam

As can be seen from the results in Table 5, the invention further reduces the content of impurities affecting the foaming performance by further adopting the mixed solvent of cyclohexane and ethyl acetate to wash the clear liquid after flocculation and precipitation, and improves the foaming power and the foaming stability to a certain extent. Compared with the pure rhamnolipid, the rhamnolipid-APG composite surfactant has better foaming performance. And the APG also belongs to a green environment-friendly degradable surfactant, and has the advantages of nature, environmental protection, no stimulation and biodegradability when being applied to daily chemical washing products.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.