Method for extracting chitosan from hermetia illucens at high value

Abstract

The invention belongs to the field of natural product extraction, and particularly relates to a method for extracting chitosan by using hermetia illucens in a high-valued manner. According to the method, the ionic liquid is introduced while the chitosan is extracted by adopting a deep eutectic solvent method, the deep eutectic solvent can form strong interaction with chitin molecules, the ionic liquid can further enhance specific recognition of the chitin molecules, and the ionic liquid and the deep eutectic solvent have a synergistic effect, so that solubility and recognizability of the chitin are improved; protein and salt are efficiently removed, meanwhile, glucosidic bonds of a chitin macromolecular main chain are prevented from being hydrolyzed and broken, and the extraction rate and purity of chitosan are remarkably improved. According to the method, the extraction condition is mild, the eutectic solvent can be recycled and reused, the extraction process flow of the chitosan is simplified, and the method is environment-friendly.

Description

Technical Field

[0001] The invention belongs to the field of natural product extraction, and particularly relates to a method for extracting chitosan by utilizing black soldier flies in a high-value manner. Background Art

[0002] Chitosan, also known as deacetylated chitin, polyglucosamine and soluble chitin, is the only alkaline polysaccharide among natural polysaccharides and the only cationic alkaline polysaccharide. As a natural polymer, chitosan has natural advantages in terms of edibility, biodegradability, biocompatibility, safety and non-toxicity, and is widely used in food, medical and health, agriculture and other industries.

[0003] Chitosan is usually extracted from the shells of marine organisms such as shrimp, crab, and shellfish. However, the chitin content in shrimp and crab shells is low and the inorganic salt content is high (greater than 30%). The extraction yield and quality of chitosan are unstable, and the extraction cost is high, which is not conducive to promotion and application. The black soldier fly (Hermetia illucens) is a unique insect that can produce fertilizers, proteins, and fats, and can also serve as a source of other important biologically active substances such as chitin, chitosan, and melanin. The chitosan content in the black soldier fly is different in different insect stages (larval stage, prepupal stage, pupal stage, and mature stage). According to the literature (CN115260339A), the chitosan content in the insect shell of the prepupal stage is the highest, and the extraction rate is also the highest at this time, which can be maximized. Secondly, in the prepupal stage, chitosan is mainly enriched in the insect shell, and the visceral fat is mainly protein, which can be made into feed for pets, poultry, etc. The insect shell and viscera are separated, the former is used to extract chitosan, and the latter is used to make feed, which can maximize the economy.

[0004] At present, the main processes for extracting chitosan from black soldier flies include acid-base extraction, microwave-assisted extraction, and enzymatic hydrolysis.

[0005] CN102585035A discloses a preparation method for extracting chitosan from black soldier flies, which comprises demineralization with dilute acid, deproteinization with dilute alkali, depigmentation with sodium hypochlorite, and deacetylation with concentrated alkali. However, since concentrated alkali needs to be used and the temperature is relatively high, under such conditions, the concentrated alkali solution can not only promote the hydrolysis of acetyl groups, but also hydrolyze and break the glycosidic bonds of the main chain of the macromolecule, thereby reducing the relative molecular mass and the extraction rate.

[0006] CN106832054A uses black soldier fly adults as raw materials to extract chitosan. The deacetylation process is combined with microwave-assisted method and enzymolysis. The microwave-assisted method first removes part of the acetyl group, while activating the chemical bond and the substitution site, and then reacts under the action of chitin deacetylase, greatly improving the deacetylation degree, which is as high as 95.6-97.3%, and obtaining good quality chitosan, avoiding the hydrolysis and cleavage of the glycosidic bond of the chitosan macromolecular main chain, and avoiding the pollution and waste caused by the use of high-concentration alkali solution. However, the microwave-assisted method has the disadvantages of using too high sodium hydroxide concentration and too long microwave heating time, and the source of deacetylase is not easy, and the disadvantage of large enzyme amount required to achieve a higher deacetylation degree is large. Summary of the invention

[0007] In view of the shortcomings of the prior art, the present invention aims to provide a method for extracting chitosan using black soldier flies, which has mild extraction conditions for chitosan, high extraction rate and high chitosan purity. In order to achieve the above purpose, the present invention adopts the following technical scheme: A method for extracting chitosan by utilizing black soldier flies in a high-value manner comprises the following steps: Step 1) preparing black soldier fly pupa shell powder: taking black soldier fly pupa shells, washing with water, washing with alcohol, washing with water, drying, grinding, and sieving to obtain black soldier fly pupa shell powder; Step 2) Preparation of defatted black soldier fly pupa shell powder: Mix the black soldier fly pupa shell powder prepared in step 1) with a solvent, perform Soxhlet extraction at 35-65°C for 8-15h, filter, desolventize the liquid component at 35-65°C to obtain oil and recovered solvent respectively, repeatedly wash the oil with the recovered solvent, dry the obtained solid component, and obtain defatted black soldier fly pupa shell powder. The solvent is one or more of petroleum ether, acetone, and toluene; the mass volume ratio of black soldier fly pupa shell powder to solvent is 1g:20-40mL.

[0008] Step 3) preparing a low eutectic solvent: mixing a hydrogen bond acceptor and a hydrogen bond donor, stirring and heating to obtain a low eutectic solvent; the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:2-4; Step 4) preparing an ionic liquid solution: dissolving the ionic liquid in ethanol, stirring and heating to obtain an ionic liquid solution; the ionic liquid is selected from one or more of 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium sulfonate, and 1-ethyl-3-methylimidazolium tetrafluoroborate; Step 5) preparing chitosan: mixing the defatted black soldier fly pupa shell powder prepared in step 2) with the low eutectic solvent prepared in step 3) and the ionic liquid solution prepared in step 4), reacting in a water bath at 65-85° C. for 3-5 hours, filtering, centrifuging the filtrate to obtain a precipitate, washing, drying, adding H2O2 aqueous solution at a ratio of 1 g: 20-40 mL and mixing evenly, adjusting the pH value to 7.5, decolorizing, standing, centrifuging, washing, and drying to obtain chitosan; Step 6) Preparation of chitosan: The chitosan prepared in step 5) is mixed with a 35 wt% NaOH aqueous solution, deacetylated at 80-120° C. for 3-5 h, filtered, washed, and dried to obtain chitosan.

[0009] In some embodiments, the hydrogen bond donor in step 3) is one or more of lactic acid, urea, acetamide, methyl urea, imidazole, pyridine, glycerol, butanediol, amino acid and glucose, and the hydrogen bond acceptor is one or more of choline chloride and betaine.

[0010] In some embodiments, in step 3), the hydrogen bond donor is lactic acid and imidazole, and the hydrogen bond acceptor is choline chloride; the molar ratio of choline chloride to lactic acid and imidazole is 1:1:1-3.

[0011] In some embodiments, in step 3), the hydrogen bond donor is lactic acid and imidazole, and the hydrogen bond acceptor is betaine; the molar ratio of betaine to lactic acid and imidazole is 1:1:1-3.

[0012] In some embodiments, in step 4), the solid-liquid ratio of the ionic liquid to ethanol is 1 g: 100-200 mL.

[0013] In some embodiments, in step 5), the solid-to-liquid ratio of the defatted black soldier fly pupa shell powder to the low eutectic solvent and ionic liquid solution is 1 g: 10-30 mL: 5-15 mL.

[0014] Compared with the prior art, the present invention has the following beneficial effects: 1) The present invention introduces ionic liquid while extracting chitosan using a deep eutectic solvent method, wherein the deep eutectic solvent can form a strong interaction with the chitosan molecules, and the ionic liquid can further enhance the specific recognition of the chitosan molecules, thereby improving the solubility and recognition of chitosan. The synergistic effect of the two makes the chitosan in the black soldier fly have high solubility and selectivity, efficiently removes protein and salt, and significantly improves the extraction rate and purity of chitosan.

[0015] 2) The present invention adopts two specific hydrogen bond donors, lactic acid and imidazole, and a hydrogen bond acceptor to form a low eutectic solvent, which interacts with the ionic liquid. The low eutectic solvent and the ionic liquid have the same imidazole, carboxyl and other groups, and can form a stable eutectic solution to exert a synergistic effect. Through intermolecular forces such as hydrogen bonds, a strong interaction is formed with the chitin molecules, which can not only efficiently remove proteins and salts, but also avoid the hydrolysis and breakage of the glycosidic bonds of the main chain of the chitin macromolecule, thereby significantly improving the extraction rate and purity of chitosan.

[0016] 3) The extraction conditions of the present invention are mild, and the low eutectic solvent can be recycled and reused, which simplifies the extraction process of chitosan, is environmentally friendly, and is suitable for industrial production. DETAILED DESCRIPTION

[0017] The following non-limiting examples can enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way. The following content is merely an exemplary description of the scope of the present invention, and those skilled in the art can make various changes and modifications to the present invention based on the disclosed content, which should also fall within the scope of the present invention. The present invention is further described below in the form of specific embodiments.

[0018] Chitosan extraction rate = extracted chitosan mass / chitosan mass in black soldier fly shell x 100%; Chitosan purity = mass of chitosan in the extract / mass of the extract x 100%.

[0019] The content of chitosan was determined by ninhydrin colorimetry.

[0020] Example 1 A method for extracting chitosan by utilizing black soldier flies in a high-value manner comprises the following steps: Step 1) preparing black soldier fly pupa shell powder: taking black soldier fly pupa shells, washing with water, washing with alcohol, washing with water, drying, grinding, and passing through a 60-mesh sieve to obtain black soldier fly pupa shell powder; Step 2) preparing defatted black soldier fly pupa shell powder: mixing the black soldier fly pupa shell powder prepared in step 1) with petroleum ether at a solid-liquid ratio of 1 g: 40 mL, performing Soxhlet extraction at 50° C. for 12 h, filtering, and desolventizing the liquid component at 50° C. to obtain oil and recovered solvent, respectively, repeatedly washing the oil with the recovered solvent, and drying the obtained solid component to obtain defatted black soldier fly pupa shell powder; Step 3) preparing a low eutectic solvent: mixing hydrogen bond donor lactic acid and imidazole and hydrogen bond acceptor choline chloride, stirring evenly at 75° C. to obtain a transparent liquid; wherein the molar ratio of choline chloride to lactic acid and imidazole is 1:1:1.5; Step 4) preparing an ionic liquid solution: dissolving 1-ethyl-3-methylimidazolium acetate in ethanol and stirring the mixture at 50° C. to obtain an ionic liquid solution; the solid-liquid ratio of the 1-ethyl-3-methylimidazolium acetate to ethanol is 1 g:100 mL; Step 5) Extracting chitosan: Mix the defatted black soldier fly pupa shell powder prepared in step 2) with the low eutectic solvent prepared in step 3) and the ionic liquid solution prepared in step 4), wherein the solid-liquid ratio of the defatted black soldier fly pupa shell powder to the low eutectic solvent and the ionic liquid solution is 1 g:25 mL:5 mL, react in a 75°C water bath for 4 hours, filter, centrifuge the filtrate to obtain a precipitate, wash, dry, add a 20 wt% H2O2 aqueous solution in a ratio of 1 g:20-40 mL, mix evenly, adjust the pH value to 7.5, perform decolorization, let stand, centrifuge and wash, and dry to obtain chitosan; Step 6) Preparation of chitosan: The chitosan prepared in step 5) is mixed with a 35 wt % NaOH aqueous solution, deacetylated at 80° C. for 3 h, filtered, washed, and dried to obtain chitosan.

[0021] Example 2 A method for extracting chitosan by utilizing black soldier flies in a high-value manner comprises the following steps: Step 1) preparing black soldier fly pupa shell powder: taking black soldier fly pupa shells, washing with water, washing with alcohol, washing with water, drying, grinding, and passing through a 60-mesh sieve to obtain black soldier fly pupa shell powder; Step 2) preparing defatted black soldier fly pupa shell powder: mixing the black soldier fly pupa shell powder prepared in step 1) with petroleum ether at a solid-liquid ratio of 1 g: 40 mL, performing Soxhlet extraction at 50° C. for 12 h, filtering, and desolventizing the liquid component at 50° C. to obtain oil and recovered solvent, respectively, repeatedly washing the oil with the recovered solvent, and drying the obtained solid component to obtain defatted black soldier fly pupa shell powder; Step 3) preparing a low eutectic solvent: mixing hydrogen bond donor lactic acid and hydrogen bond acceptor choline chloride, stirring evenly at 75° C. to obtain a transparent liquid; wherein the molar ratio of choline chloride to lactic acid is 1:2.5; Step 4) preparing an ionic liquid solution: dissolving 1-ethyl-3-methylimidazolium acetate in ethanol and stirring the mixture at 50° C. to obtain an ionic liquid solution; the solid-liquid ratio of the 1-ethyl-3-methylimidazolium acetate to ethanol is 1 g:100 mL; Step 5) Extracting chitosan: Mix the defatted black soldier fly pupa shell powder prepared in step 2) with the low eutectic solvent prepared in step 3) and the ionic liquid solution prepared in step 4), wherein the solid-liquid ratio of the defatted black soldier fly pupa shell powder to the low eutectic solvent and the ionic liquid solution is 1 g:25 mL:5 mL, react in a 75°C water bath for 4 hours, filter, centrifuge the filtrate to obtain a precipitate, wash, dry, add a 20 wt% H2O2 aqueous solution in a ratio of 1 g:20-40 mL, mix evenly, adjust the pH value to 7.5, perform decolorization, let stand, centrifuge and wash, and dry to obtain chitosan; Step 6) Preparation of chitosan: The chitosan prepared in step 5) is mixed with a 35 wt % NaOH aqueous solution, deacetylated at 80° C. for 3 h, filtered, washed, and dried to obtain chitosan.

[0022] Example 3 A method for extracting chitosan by utilizing black soldier flies in a high-value manner comprises the following steps: Step 1) preparing black soldier fly pupa shell powder: taking black soldier fly pupa shells, washing with water, washing with alcohol, washing with water, drying, grinding, and passing through a 60-mesh sieve to obtain black soldier fly pupa shell powder; Step 2) preparing defatted black soldier fly pupa shell powder: mixing the black soldier fly pupa shell powder prepared in step 1) with petroleum ether at a solid-liquid ratio of 1 g: 40 mL, performing Soxhlet extraction at 50° C. for 12 h, filtering, and desolventizing the liquid component at 50° C. to obtain oil and recovered solvent, respectively, repeatedly washing the oil with the recovered solvent, and drying the obtained solid component to obtain defatted black soldier fly pupa shell powder; Step 3) preparing a low eutectic solvent: mixing a hydrogen bond donor imidazole and a hydrogen bond acceptor choline chloride, stirring them uniformly at 75° C. to obtain a transparent liquid; wherein the molar ratio of choline chloride to imidazole is 1:2.5; Step 4) preparing an ionic liquid solution: dissolving 1-ethyl-3-methylimidazolium acetate in ethanol and stirring the mixture at 50° C. to obtain an ionic liquid solution; the solid-liquid ratio of the 1-ethyl-3-methylimidazolium acetate to ethanol is 1 g:100 mL; Step 5) Extracting chitosan: Mix the defatted black soldier fly pupa shell powder prepared in step 2) with the low eutectic solvent prepared in step 3) and the ionic liquid solution prepared in step 4), wherein the solid-liquid ratio of the defatted black soldier fly pupa shell powder to the low eutectic solvent and the ionic liquid solution is 1 g:25 mL:5 mL, react in a 75°C water bath for 4 hours, filter, centrifuge the filtrate to obtain a precipitate, wash, dry, add a 20 wt% H2O2 aqueous solution in a ratio of 1 g:20-40 mL, mix evenly, adjust the pH value to 7.5, perform decolorization, let stand, centrifuge and wash, and dry to obtain chitosan; Step 6) Preparation of chitosan: The chitosan prepared in step 5) is mixed with a 35 wt % NaOH aqueous solution, deacetylated at 80° C. for 3 h, filtered, washed, and dried to obtain chitosan.

[0023] Example 4 A method for extracting chitosan by utilizing black soldier flies in a high-value manner comprises the following steps: Step 1) preparing black soldier fly pupa shell powder: taking black soldier fly pupa shells, washing with water, washing with alcohol, washing with water, drying, grinding, and passing through a 60-mesh sieve to obtain black soldier fly pupa shell powder; Step 2) preparing defatted black soldier fly pupa shell powder: mixing the black soldier fly pupa shell powder prepared in step 1) with petroleum ether at a solid-liquid ratio of 1 g: 40 mL, performing Soxhlet extraction at 50° C. for 12 h, filtering, and desolventizing the liquid component at 50° C. to obtain oil and recovered solvent, respectively, repeatedly washing the oil with the recovered solvent, and drying the obtained solid component to obtain defatted black soldier fly pupa shell powder; Step 3) preparing a low eutectic solvent: mixing hydrogen bond donor lactic acid and methyl urea and hydrogen bond acceptor choline chloride, stirring evenly at 75° C. to obtain a transparent liquid; wherein the molar ratio of choline chloride to lactic acid and methyl urea is 1:1:1.5; Step 4) preparing an ionic liquid solution: dissolving 1-ethyl-3-methylimidazolium acetate in ethanol and stirring the mixture at 50° C. to obtain an ionic liquid solution; the solid-liquid ratio of the 1-ethyl-3-methylimidazolium acetate to ethanol is 1 g:100 mL; Step 5) Extracting chitosan: Mix the defatted black soldier fly pupa shell powder prepared in step 2) with the low eutectic solvent prepared in step 3) and the ionic liquid solution prepared in step 4), wherein the solid-liquid ratio of the defatted black soldier fly pupa shell powder to the low eutectic solvent and the ionic liquid solution is 1 g: 25 mL: 5 mL, react in a 75° C. water bath for 4 h, filter, centrifuge the filtrate to obtain a precipitate, wash, dry, add a 20 wt% H2O2 aqueous solution at a ratio of 1 g: 20-40 mL, mix evenly, adjust the pH value to 7.5, perform decolorization, let stand, centrifuge and wash, and dry to obtain chitosan; Step 6) Preparation of chitosan: The chitosan prepared in step 5) is mixed with a 35 wt % NaOH aqueous solution, deacetylated at 80° C. for 3 h, filtered, washed, and dried to obtain chitosan.

[0024] Example 5 A method for extracting chitosan by utilizing black soldier flies in a high-value manner comprises the following steps: Step 1) preparing black soldier fly pupa shell powder: taking black soldier fly pupa shells, washing with water, washing with alcohol, washing with water, drying, grinding, and passing through a 60-mesh sieve to obtain black soldier fly pupa shell powder; Step 2) preparing defatted black soldier fly pupa shell powder: mixing the black soldier fly pupa shell powder prepared in step 1) with petroleum ether at a solid-liquid ratio of 1 g: 40 mL, performing Soxhlet extraction at 50° C. for 12 h, filtering, and desolventizing the liquid component at 50° C. to obtain oil and recovered solvent, respectively, repeatedly washing the oil with the recovered solvent, and drying the obtained solid component to obtain defatted black soldier fly pupa shell powder; Step 3) preparing a low eutectic solvent: mixing hydrogen bond donors lactic acid and pyridine and hydrogen bond acceptor choline chloride, stirring at 75° C. to obtain a transparent liquid; wherein the molar ratio of choline chloride to lactic acid and pyridine is 1:1:1.5; Step 4) preparing an ionic liquid solution: dissolving 1-ethyl-3-methylimidazolium acetate in ethanol and stirring the mixture at 50° C. to obtain an ionic liquid solution; the solid-liquid ratio of the 1-ethyl-3-methylimidazolium acetate to ethanol is 1 g: 100 mL; Step 5) Extracting chitosan: Mix the defatted black soldier fly pupa shell powder prepared in step 2) with the low eutectic solvent prepared in step 3) and the ionic liquid solution prepared in step 4), wherein the solid-liquid ratio of the defatted black soldier fly pupa shell powder to the low eutectic solvent and the ionic liquid solution is 1 g:25 mL:5 mL, react in a 75°C water bath for 4 hours, filter, centrifuge the filtrate to obtain a precipitate, wash, dry, add a 20 wt% H2O2 aqueous solution in a ratio of 1 g:20-40 mL, mix evenly, adjust the pH value to 7.5, perform decolorization, let stand, centrifuge and wash, and dry to obtain chitosan; Step 6) Preparation of chitosan: The chitosan prepared in step 5) is mixed with a 35 wt % NaOH aqueous solution, deacetylated at 80° C. for 3 h, filtered, washed, and dried to obtain chitosan.

[0025] Comparative Example 1 A method for extracting chitosan by utilizing black soldier flies in a high-value manner comprises the following steps: Step 1) preparing black soldier fly pupa shell powder: taking black soldier fly pupa shells, washing with water, washing with alcohol, washing with water, drying, grinding, and passing through a 60-mesh sieve to obtain black soldier fly pupa shell powder; Step 2) preparing defatted black soldier fly pupa shell powder: mixing the black soldier fly pupa shell powder prepared in step 1) with petroleum ether at a solid-liquid ratio of 1 g:40 mL, performing Soxhlet extraction at 50° C. for 12 h, filtering, and desolventizing the liquid component at 50° C. to obtain oil and recovered solvent, respectively, repeatedly washing the oil with the recovered solvent, and drying the obtained solid component to obtain defatted black soldier fly pupa shell powder; Step 3) preparing a low eutectic solvent: mixing hydrogen bond donor lactic acid and imidazole and hydrogen bond acceptor choline chloride, stirring evenly at 75° C. to obtain a transparent liquid; wherein the molar ratio of choline chloride to lactic acid and imidazole is 1:1:1.5; Step 4) Extracting chitosan: Mix the defatted black soldier fly pupa shell powder prepared in step 2) with the low eutectic solvent prepared in step 3), wherein the solid-liquid ratio of the defatted black soldier fly pupa shell powder to the low eutectic solvent is 1 g:30 mL, react in a water bath at 75° C. for 4 h, filter, centrifuge the filtrate to obtain a precipitate, wash, dry, add a 20 wt% H2O2 aqueous solution at a ratio of 1 g:20-40 mL, mix evenly, adjust the pH value to 7.5, perform decolorization, let stand, centrifuge and wash, and dry to obtain chitosan; Step 5) Preparation of chitosan: The chitosan prepared in step 4) is mixed with a 35 wt % NaOH aqueous solution, deacetylated at 80° C. for 3 h, filtered, washed, and dried to obtain chitosan.

[0026] Comparative Example 2 A method for extracting chitosan by utilizing black soldier flies in a high-value manner comprises the following steps: Step 1) preparing black soldier fly pupa shell powder: taking black soldier fly pupa shells, washing with water, washing with alcohol, washing with water, drying, grinding, and passing through a 60-mesh sieve to obtain black soldier fly pupa shell powder; Step 2) preparing defatted black soldier fly pupa shell powder: mixing the black soldier fly pupa shell powder prepared in step 1) with petroleum ether at a solid-liquid ratio of 1 g: 40 mL, performing Soxhlet extraction at 50° C. for 12 h, filtering, and desolventizing the liquid component at 50° C. to obtain oil and recovered solvent, respectively, repeatedly washing the oil with the recovered solvent, and drying the obtained solid component to obtain defatted black soldier fly pupa shell powder; Step 3) preparing an ionic liquid solution: dissolving 1-ethyl-3-methylimidazolium acetate in ethanol and stirring the mixture at 50° C. to obtain an ionic liquid solution; the solid-liquid ratio of the 1-ethyl-3-methylimidazolium acetate to ethanol is 1 g:100 mL; Step 4) Extracting chitosan: Mix the defatted black soldier fly pupa shell powder prepared in step 2) with the ionic liquid solution prepared in step 3), wherein the solid-liquid ratio of the defatted black soldier fly pupa shell powder to the ionic liquid solution is 1 g:30 mL, react in a water bath at 75° C. for 4 h, filter, centrifuge the filtrate to obtain a precipitate, wash, and dry, add a 20 wt% H2O2 aqueous solution at a ratio of 1 g:20-40 mL, mix evenly, adjust the pH value to 7.5, perform decolorization, let stand, centrifuge, wash, and dry to obtain chitosan; Step 5) Preparation of chitosan: The chitosan prepared in step 4) is mixed with a 35 wt % NaOH aqueous solution, deacetylated at 80° C. for 3 h, filtered, washed, and dried to obtain chitosan.

[0027] Table 1 Extraction results of chitosan using black soldier flies According to the results shown in Table 1, it can be seen from the comparison between Example 1 and Comparative Example 1 and Comparative Example 2 that when using black soldier flies to extract chitosan in Example 1 of the present invention, a low eutectic solvent and an ionic liquid are used at the same time, and the chitosan has a higher extraction rate and the obtained chitosan has a higher purity. This may be because the low eutectic solvent can form a strong interaction with the chitin molecules, and the ionic liquid can further enhance the specific recognition of the chitosan molecules, change the spatial conformation of chitosan, thereby improving the solubility and recognition of chitosan, and the low eutectic solvent and the ionic liquid have the same imidazole, carboxyl and other groups, and the two work synergistically, so that the chitosan in the black soldier fly has high solubility and selectivity, and efficiently removes protein and salt, and significantly improves the extraction rate and purity of chitosan.

[0028] From the comparison between Example 1 and Example 2, Example 3, Example 4, and Example 5, it can be seen that Example 1 of the present invention uses two specific hydrogen bond donors, lactic acid and imidazole, and a hydrogen bond acceptor to form a low eutectic solvent, which interacts with the ionic liquid to exert a synergistic effect, and can form a stable eutectic solution. It forms a strong interaction with the chitin molecules through intermolecular forces such as hydrogen bonds, which can not only efficiently remove protein and salt, but also avoid the hydrolysis and breakage of the glycosidic bonds of the main chain of the chitosan macromolecule, thereby significantly improving the extraction rate and purity of chitosan.

[0029] The above embodiments are merely examples for clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A method for extracting chitosan by utilizing black soldier flies in a high-value manner, characterized in that: The following steps are involved: Step 1) preparing black soldier fly pupa shell powder: taking black soldier fly pupa shells, washing with water, washing with alcohol, washing with water, drying, grinding, and sieving to obtain black soldier fly pupa shell powder; Step 2) preparing defatted black soldier fly pupa shell powder: mixing the black soldier fly pupa shell powder prepared in step 1) with a solvent, performing Soxhlet extraction at 35-65° C. for 8-15 hours, filtering, desolventizing the liquid component at 35-65° C. to obtain oil and recovered solvent respectively, repeatedly washing the oil with the recovered solvent, drying the obtained solid component, and obtaining defatted black soldier fly pupa shell powder; Step 3) preparing a low eutectic solvent: mixing a hydrogen bond acceptor and a hydrogen bond donor, stirring them uniformly and heating them to obtain a low eutectic solvent; the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1: 2-4; Step 4) preparing an ionic liquid solution: dissolving the ionic liquid in ethanol, stirring and heating to obtain an ionic liquid solution; the ionic liquid is selected from one or more of 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium sulfonate, and 1-ethyl-3-methylimidazolium tetrafluoroborate; Step 5) preparing chitosan: mixing the defatted black soldier fly pupa shell powder prepared in step 2) with the low eutectic solvent prepared in step 3) and the ionic liquid solution prepared in step 4), reacting in a water bath at 65-85° C. for 3-5 hours, filtering, centrifuging the filtrate to obtain a precipitate, washing, drying, adding H2O2 aqueous solution at a ratio of 1 g: 20-40 mL and mixing evenly, adjusting the pH value to 7.5, decolorizing, standing, centrifuging, washing, and drying to obtain chitosan; Step 6) Preparation of chitosan: The chitosan prepared in step 5) is mixed with a 35 wt% NaOH aqueous solution, deacetylated at 80-120° C. for 3-5 h, filtered, washed, and dried to obtain chitosan.

2. The method for extracting chitosan by utilizing black soldier flies in high value according to claim 1, characterized in that: In step 2), the solvent is one or more of petroleum ether, acetone, and toluene; the mass volume ratio of the black soldier fly pupa shell powder to the solvent is 1 g: 20-40 mL.

3. The method for extracting chitosan by utilizing black soldier flies in high value according to claim 1, characterized in that: Step 3) The hydrogen bond donor is one or more of lactic acid, urea, acetamide, methyl urea, imidazole, pyridine, glycerol, butanediol, amino acid and glucose, and the hydrogen bond acceptor is one or more of choline chloride and betaine.

4. The method for extracting chitosan by utilizing black soldier flies in high value according to claim 1, characterized in that: Step 3) The hydrogen bond donor is lactic acid and imidazole, and the hydrogen bond acceptor is choline chloride or betaine.

5. The method for extracting chitosan by utilizing black soldier flies in high value according to claim 4, characterized in that: The molar ratio of hydrogen bond acceptor to lactic acid and imidazole was 1:1:1-3.

6. The method for extracting chitosan by utilizing black soldier flies in high value according to claim 1, characterized in that: Step 4) The solid-liquid ratio of the ionic liquid to ethanol is 1 g: 100-200 mL.

7. The method for extracting chitosan by utilizing black soldier flies in high value according to claim 1, characterized in that: Step 4) The ionic liquid is 1-ethyl-3-methylimidazolium acetate.

8. The method for extracting chitosan by utilizing black soldier flies in high value according to claim 1, characterized in that: Step 5) The solid-liquid ratio of the defatted black soldier fly pupa shell powder to the low eutectic solvent and the ionic liquid solution is 1 g: 10-30 mL: 5-15 mL.

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