A ternary natural eutectic solvent and its application in the extraction of purple cabbage anthocyanins and the preparation of chitosan composite films
Patent Information
- Application Number
- CN202611452422.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-09-18
- Publication Date
- 2026-10-30
AI Technical Summary
[0006]本发明针对现有技术中二元低共熔溶剂萃取效率不稳定、花青素提取液需纯化冻干后才能制膜、复合膜力学性能与紫外屏蔽性能不足等问题，提供一种三元天然低共熔溶剂及其在紫甘蓝花青素提取与壳聚糖复合膜制备中的应用
[0023]本发明以甜菜碱为氢键受体，1,2-丙二醇与乳酸为双氢键供体构建三元天然低共熔溶剂。三种组分之间形成稳定的多重氢键网络。其中，甜菜碱提供季铵阳离子骨架，乳酸提供强氢键相互作用和弱酸性环境，有利于花青素黄烊盐阳离子的稳定存在。1,2-丙二醇的加入并不是简单增加氢键供体数量，而是通过调节三元体系的黏度与极性，使甜菜碱-乳酸二元体系形成的氢键网络结构适度疏松，从而降低传质阻力，提高花青素向溶剂中的扩散速率。该协同效应是二元体系所不具备的。实施例结果表明，三元体系对紫甘蓝花青素的萃取含量最高可达31.84 mg/g，远优于乙醇对照的6.96 mg/g。
Smart Images
Figure CN122998790A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of natural product extraction and biopolymer membrane materials technology, specifically to a ternary natural eutectic solvent and its application in the extraction of anthocyanins from purple cabbage and the preparation of chitosan composite membranes. Background Technology
[0002] With the increasing environmental pollution caused by petroleum-based plastic packaging waste, the development of biodegradable food packaging films has become a research hotspot in this field. Chitosan, with its wide availability, non-toxicity, good biocompatibility, biodegradability, and excellent film-forming properties, is considered one of the ideal substrates to replace traditional plastics. However, pure chitosan films suffer from drawbacks such as strong hydrophilicity, insufficient mechanical strength and flexibility, and limited UV shielding capabilities, which restrict their practical applications. Anthocyanins are natural water-soluble pigments widely found in plants, possessing a conjugated polyphenol structure and combining antioxidant activity with UV absorption capacity. Introducing them into a chitosan matrix is expected to improve the mechanical properties, flexibility, and UV shielding performance of the film. Purple cabbage is rich in anthocyanins, and the raw material is inexpensive and readily available, making it an ideal source of raw materials for preparing anthocyanin-modified chitosan composite films.
[0003] Currently, anthocyanin extraction primarily utilizes organic solvents such as methanol, ethanol, and acetone, or acidified aqueous solutions. These methods suffer from drawbacks including high solvent consumption, high toxicity risks, limited extraction efficiency, and easy oxidative degradation of anthocyanins. Eutectic solvents, as a novel type of green solvent, offer advantages such as low vapor pressure, high designability, good biodegradability, and strong solubility, and are increasingly being used for the extraction of natural active ingredients. However, existing eutectic solvents for anthocyanin extraction are mostly binary systems, generally exhibiting high viscosity, limited hydrogen bond network control, unstable extraction efficiency, and insufficient selectivity for anthocyanins, making it difficult to balance high extraction efficiency with compatibility in subsequent membrane formation.
[0004] Furthermore, the preparation of existing anthocyanin-modified chitosan membranes typically requires purifying and freeze-drying the anthocyanin extract to obtain anthocyanin powder, which is then mixed with a chitosan matrix to form the membrane. This process is cumbersome, time-consuming, and energy-intensive. Additionally, anthocyanins are prone to oxidative degradation during purification and drying, leading to loss of activity and decreased composite membrane performance, while also increasing production costs. Therefore, current technology lacks a method for directly preparing chitosan composite membranes using a eutectic solvent to extract the supernatant.
[0005] In summary, how to construct a ternary natural eutectic solvent with natural raw materials, low toxicity and biodegradability, stable hydrogen bond network and high extraction efficiency for purple cabbage anthocyanins, and how to directly blend its extraction supernatant with chitosan matrix to form a membrane without purification, while improving the light transmittance, UV shielding performance and mechanical flexibility of the composite membrane, is a technical problem that urgently needs to be solved in this field. Summary of the Invention
[0006] This invention addresses the problems in existing technologies, such as unstable extraction efficiency of binary eutectic solvents, the need for purification and freeze-drying of anthocyanin extracts before membrane fabrication, and insufficient mechanical and UV shielding properties of composite membranes. It provides a ternary natural eutectic solvent and its application in the extraction of anthocyanins from purple cabbage and the preparation of chitosan composite membranes.
[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:
[0008] In a first aspect, the present invention provides a ternary natural eutectic solvent, with betaine as a hydrogen bond acceptor and 1,2-propanediol and lactic acid as hydrogen bond donors, wherein the molar ratio of betaine, 1,2-propanediol and lactic acid is 1:1:1 to 1:1:4.
[0009] Furthermore, the preparation method of the ternary natural eutectic solvent includes the following steps:
[0010] S1: Betaine, 1,2-propanediol and lactic acid were pretreated by vacuum drying.
[0011] S2: Pretreated betaine, 1,2-propanediol and lactic acid are mixed in the molar ratio described above, stirred at 50-80 °C until a homogeneous and transparent solution is formed, cooled to room temperature and then vacuum dried to obtain a ternary natural eutectic solvent.
[0012] Preferably, the vacuum drying temperature in step S1 is 55 ℃ and the drying time is 24 h; the stirring speed in step S2 is 400 r / min and the stirring time is 2 h; the vacuum drying temperature is 55 ℃ and the drying time is 72 h.
[0013] Secondly, this invention provides the application of the above-mentioned ternary natural eutectic solvent in the preparation of purple cabbage anthocyanin extract, and the specific extraction operation is as follows:
[0014] Purple cabbage was freeze-dried and then pulverized to obtain purple cabbage powder; the purple cabbage powder was mixed with the ternary natural eutectic solvent at a solid-liquid ratio of 1:10-1:50 and ultrasonically extracted at 20-60 ℃ for 5-80 min; the extracted mixture was centrifuged and the supernatant was collected to obtain anthocyanin extract.
[0015] Preferably, the freeze-drying temperature is -30 ℃; the centrifugation speed is 10000 r / min, and the centrifugation time is 10 min.
[0016] Thirdly, the present invention provides the application of the above-mentioned anthocyanin extract in the preparation of chitosan composite membranes, comprising the following steps:
[0017] S1: Add chitosan powder to a 2% (v / v) aqueous solution of glacial acetic acid, stir to dissolve, centrifuge, collect the clear supernatant, and obtain a chitosan stock solution.
[0018] S2: Add the anthocyanin extract to the chitosan stock solution, mix well and degas to obtain a film-forming solution;
[0019] S3: The film-forming liquid is poured, spread, and dried to obtain a chitosan composite film.
[0020] Preferably, the anthocyanin extract added in step S2 accounts for 1%-5% of the chitosan powder mass; the drying temperature in step S3 is 50 ℃ and the drying time is 4 h.
[0021] Fourthly, the present invention provides a chitosan composite membrane prepared by the above method, wherein the tensile strength of the composite membrane is ≥50 MPa and the elongation at break is ≥45%.
[0022] Compared with the prior art, the present invention has the following beneficial effects:
[0023] This invention constructs a ternary natural eutectic solvent using betaine as a hydrogen bond acceptor and 1,2-propanediol and lactic acid as double hydrogen bond donors. A stable multi-hydrogen bond network is formed among the three components. Betaine provides the quaternary ammonium cation framework, while lactic acid provides strong hydrogen bond interactions and a weakly acidic environment, which is conducive to the stable existence of anthocyanin flavonoid cations. The addition of 1,2-propanediol does not simply increase the number of hydrogen bond donors, but rather adjusts the viscosity and polarity of the ternary system, making the hydrogen bond network structure formed by the betaine-lactic acid binary system moderately loose, thereby reducing mass transfer resistance and increasing the diffusion rate of anthocyanins into the solvent. This synergistic effect is not present in binary systems. The results of the examples show that the ternary system can extract up to 31.84 mg / g of anthocyanins from purple cabbage, far superior to the 6.96 mg / g of the ethanol control.
[0024] Betaine, 1,2-propanediol, and lactic acid are all natural or biodegradable green components. The preparation process is simple and inexpensive, avoiding the use of traditional organic solvents, and meeting the requirements of green chemistry and sustainable development.
[0025] This invention directly blends the supernatant obtained from eutectic solvent extraction with chitosan matrix to form a membrane, eliminating the complex processing steps of anthocyanin purification and freeze-drying in traditional processes, shortening the processing cycle, reducing production costs, and avoiding oxidative degradation of anthocyanins during purification and drying.
[0026] The conjugated π-electron skeleton of anthocyanin molecules in the composite film can effectively absorb ultraviolet light, giving the film a significant ultraviolet shielding effect in the 200-400nm ultraviolet range, which can slow down the oxidation of photosensitive fruits under light exposure; at the same time, it still maintains a certain light transmittance in the visible light range, with little impact on the appearance of the fruit, and has broad application prospects in the field of photosensitive fruit packaging. Attached Figure Description
[0027] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.
[0028] Figure 1 The anthocyanin standard curve for Example 1;
[0029] Figure 2 The infrared spectrum of [Bet:PG:3LA] prepared in Example 3;
[0030] Figure 3 Thermogravimetric curve of [Bet:PG:3LA] prepared in Example 3;
[0031] Figure 4 XRD patterns of purple cabbage powder before and after [Bet:PG:3LA] extraction in Example 3;
[0032] Figure 5 SEM images of purple cabbage powder before and after [Bet:PG:3LA] extraction were prepared for Example 3;
[0033] Figure 6 Here is a photograph of the appearance of the composite membrane prepared in Example 5;
[0034] Figure 7 The mechanical property test curves of the pure chitosan membrane and the composite membrane prepared in Example 5 are shown.
[0035] Figure 8 The UV-Vis transmittance curves are for the pure chitosan membrane and the composite membrane prepared in Example 5. Detailed Implementation
[0036] The present invention will be further described below with reference to specific embodiments. The core of the present invention lies in constructing a ternary natural eutectic solvent and directly using it to extract anthocyanins from purple cabbage to prepare a chitosan composite membrane. The key steps, the reasons for parameter settings, and the mechanism of action will be explained first, followed by specific embodiments.
[0037] I. Construction principle and parameter setting of ternary natural eutectic solvent
[0038] This invention selects betaine as the hydrogen bond acceptor and 1,2-propanediol and lactic acid as hydrogen bond donors. Betaine is a natural, non-toxic, and biodegradable quaternary ammonium salt compound. Its molecule contains both quaternary ammonium cations and carboxyl anions, providing strong hydrogen bond acceptance. Lactic acid contains hydroxyl and carboxyl groups, serving as a strong hydrogen bond donor and providing a weakly acidic environment conducive to the stable existence of the anthocyanin flavonoid cation. 1,2-propanediol contains two hydroxyl groups, acting as an auxiliary hydrogen bond donor, effectively regulating the viscosity and polarity of the ternary system and improving the solvent's permeability to plant cell walls. The combination of these three compounds forms a stable ternary hydrogen bond network, with a hydrogen bond density and adjustable polarity range superior to that of a binary system, thus achieving highly efficient extraction of anthocyanins from purple cabbage.
[0039] The structural formulas of the above-mentioned betaine, 1,2-propanediol, and lactic acid are shown below:
[0040]
[0041] This invention limits the molar ratio of betaine, 1,2-propanediol, and lactic acid to a range of 1:1:1 to 1:1:4. The 1,2-propanediol ratio is fixed at 1, while the lactic acid ratio is adjusted between 1 and 4. If the lactic acid ratio is too low, there are insufficient hydrogen bond donors in the system, making it difficult to form a stable eutectic solvent, thus reducing extraction efficiency. If the lactic acid ratio is too high, the system becomes too acidic, which may lead to the degradation of anthocyanin structures, and simultaneously increases viscosity, which is detrimental to mass transfer. Experiments show that a molar ratio of 1:1:3 provides the best extraction effect for anthocyanins from purple cabbage; therefore, this invention preferably uses a 1:1:3 ratio.
[0042] In step S1, betaine, 1,2-propanediol, and lactic acid are dried separately in a vacuum drying oven at 55 °C for 24 h. This condition effectively removes moisture from the raw materials, preventing moisture from interfering with the formation of hydrogen bond networks. Furthermore, 55 °C is below the decomposition temperature of each component, thus preventing deterioration of the raw materials.
[0043] In step S2, the mixing temperature is set at 50-80 °C. Below 50 °C, the components are difficult to melt and form a homogeneous liquid phase; above 80 °C, lactic acid is easily volatilized, and betaine may decompose slightly. The stirring speed is 400 r / min, and the stirring time is 2 h to ensure sufficient contact between the components and the formation of a homogeneous, transparent eutectic solvent. Subsequently, the sample is dried in a vacuum drying oven at 55 °C for 72 h to remove residual moisture and ensure the purity of the eutectic solvent. The resulting sample is stored under a nitrogen atmosphere to prevent moisture absorption and oxidation.
[0044] II. Key parameters and mechanisms of anthocyanin extraction from purple cabbage
[0045] This invention limits the solid-liquid ratio to a range of 1:10-1:50 (g / mL). When the solid-liquid ratio is below 1:10, the solvent volume is insufficient, the purple cabbage powder cannot be fully wetted, and anthocyanins are not completely dissolved. When the solid-liquid ratio is above 1:50, the anthocyanin concentration is too low, requiring the addition of a large amount of extract during subsequent film formation, which affects the film quality. This invention preferably uses a solid-liquid ratio of 1:10.
[0046] The extraction temperature range is 20-60 °C. At too low a temperature, molecular motion is slow, resulting in a low anthocyanin dissolution rate; at too high a temperature, anthocyanins are easily oxidized and degraded. The ultrasonic extraction time is 5-80 min. The ultrasonic cavitation effect can effectively disrupt the cell wall structure of purple cabbage, promoting the diffusion of anthocyanins into the solvent. Too short an extraction time leads to incomplete extraction, while too long an extraction time may cause anthocyanin degradation. The preferred extraction temperature in this invention is 50 °C, and the ultrasonic extraction time is 40 min.
[0047] The extraction mixture was centrifuged at 10,000 r / min for 10 min to achieve rapid solid-liquid separation. The supernatant was collected as the anthocyanin extract. Under these conditions, cell residues were fully separated from the solvent, and the supernatant was clear and could be directly used for subsequent membrane fabrication.
[0048] The ternary natural eutectic solvent, rich in hydroxyl and carboxyl groups, can form multiple hydrogen bonds with cellulose, hemicellulose, and pectin in the cell walls of purple cabbage, disrupting the ordered structure of the cell walls and causing them to swell and tear. Simultaneously, the eutectic solvent forms hydrogen bonds and solvates anthocyanin molecules, reducing the chemical potential of anthocyanins in the solid phase and promoting their diffusion into the liquid phase. Scanning electron microscopy and X-ray diffraction results show that after treatment with the eutectic solvent, the original blocky structure of the purple cabbage residue disappears, and the crystallinity decreases, confirming the above extraction mechanism.
[0049] III. Key Parameters and Mechanisms for the Preparation of Chitosan Composite Membranes
[0050] Chitosan powder was added to a 2% (v / v) aqueous solution of glacial acetic acid. Glacial acetic acid protonates the amino groups in the chitosan molecules, thus dissolving them in water. If the acetic acid concentration is too low, the chitosan will not dissolve completely; if the concentration is too high, the solution viscosity will be too high, which is not conducive to subsequent degassing and spreading. The stirring speed was 600 r / min, and the stirring time was 4 h to ensure complete dissolution of the chitosan. Subsequently, the solution was centrifuged at 10000 r / min for 10 min to remove insoluble residues, and the clear supernatant was collected to obtain the chitosan stock solution.
[0051] Based on the mass of dried chitosan powder, the anthocyanin extract added accounts for 1%-5% of the total mass. When the addition amount is less than 1%, the improvement effect of anthocyanins on the performance of the composite membrane is not significant; when the addition amount is greater than 5%, the flexibility of the composite membrane decreases, and anthocyanin precipitation may occur. The preferred addition amount in this invention is 2.5%.
[0052] After the film-forming solution is poured and spread, it is dried at 50 ℃ for 4 h. Too high a drying temperature will cause anthocyanin degradation and the film to become brittle, while too low a temperature will result in incomplete drying and the film will easily stick together. At 50 ℃, the moisture evaporates slowly, which is conducive to the formation of a uniform and dense composite film.
[0053] Anthocyanin molecules contain multiple phenolic hydroxyl groups, which can form hydrogen bonds with the amino and hydroxyl groups in chitosan molecules. Simultaneously, the conjugated π-electron backbone of anthocyanins interacts electrostatically with the chitosan chains, creating a dense cross-linked network within the composite film. This significantly improves tensile strength and elongation at break. Furthermore, the conjugated structure of anthocyanins absorbs ultraviolet light in the 200-400 nm wavelength range, endowing the composite film with excellent UV shielding properties, while maintaining a certain degree of transmittance in the visible light region.
[0054] The present invention will be further illustrated by specific embodiments below.
[0055] Example 1
[0056] Preparation of a ternary natural eutectic solvent with a molar ratio of 1:1:1 and its application in extracting anthocyanins from purple cabbage
[0057] S1 Raw material pretreatment: Betaine, 1,2-propanediol and lactic acid were placed in a vacuum drying oven and dried at 55 °C for 24 h to obtain high-purity samples.
[0058] Preparation of S2 ternary natural eutectic solvent: Pretreated betaine, 1,2-propanediol, and lactic acid were added to a beaker in a molar ratio of 1:1:1 and stirred at 400 r / min for 2 h at 80 ℃. After cooling to room temperature, a homogeneous and transparent solution was formed. The solution was placed in a vacuum drying oven and dried at 55 ℃ for 72 h to obtain the ternary natural eutectic solvent, named [Bet:PG:LA], which was stored under a nitrogen atmosphere.
[0059] S3 Purple Cabbage Pretreatment: After washing, the purple cabbage is placed in a freeze dryer and freeze-dried at -30 ℃. After pulverizing, purple cabbage powder is obtained and stored at room temperature under sealed conditions.
[0060] S4 Anthocyanin Extraction: Purple cabbage powder and [Bet:PG:LA] were added to a reaction vessel at a solid-liquid ratio of 1:10 (g / mL), and extracted by ultrasonication at 50 °C for 40 min. The extract was then centrifuged at 10000 r / min for 10 min, and the supernatant was collected as the anthocyanin extract. Anhydrous ethanol was used as a control group, and extraction was performed under the same conditions.
[0061] S5 Anthocyanin Content Determination: Anthocyanin content was determined using the pH differential method. 1.0 mg of cyanidin-3-O-glucoside standard was accurately weighed, dissolved in methanol, and diluted to volume to prepare a standard stock solution. This stock solution was then diluted to different concentrations. The solutions were diluted with pH 1.0 and pH 4.5 buffers, respectively, and the absorbance was measured at 530 nm and 700 nm. The absorbance was calculated using the formula A = (A...). 530 -A 700 ) pH1.0 -( A 530 -A 700 ) pH4.5 Calculate the absorbance and plot a standard curve. Calculate the anthocyanin concentration in the extract based on the standard curve, and then calculate the anthocyanin content using the formula.
[0062] This embodiment uses the pH differential method to determine anthocyanin content. Accurately weigh 1.0 mg of cyanidin-3-O-glucoside standard, dissolve it in methanol, and dilute to 5 mL to prepare a standard stock solution. Transfer the stock solution to prepare standard solutions of different concentrations, and dilute to 5 mL with pH 1.0 buffer and pH 4.5 buffer, respectively. Measure the absorbance at 530 nm and 700 nm wavelengths. The absorbance is calculated using the formula A = (A...). 530 -A 700 ) pH1.0 -( A 530 -A 700 ) pH4.5 Calculate the actual absorbance. Plot a standard curve with cyanidin-3-O-glucoside concentration on the x-axis and absorbance on the y-axis. The results are as follows: Figure 1 As shown.
[0063] Figure 1 This indicates that, within the measured concentration range, there is a good linear relationship between anthocyanin concentration and absorbance, with a linear correlation coefficient R0. 2 A value greater than 0.999 indicates that the standard curve can be used to accurately quantify the anthocyanin content in the extract. Based on this standard curve, the anthocyanin content extracted from purple cabbage using [Bet:PG:LA] in this example was calculated to be 28.64 mg / g, compared to 6.96 mg / g in the ethanol control group. The extraction efficiency of the ternary eutectic solvent is approximately 4.1 times that of ethanol.
[0064] Example 2
[0065] Preparation of a ternary natural eutectic solvent with a molar ratio of 1:1:2 and its application in extracting anthocyanins from purple cabbage.
[0066] The preparation method was the same as in Example 1, except that the molar ratio of betaine, 1,2-propanediol, and lactic acid was 1:1:2, and the resulting ternary natural eutectic solvent was named [Bet:PG:2LA]. The extraction conditions were the same as in Example 1.
[0067] Results: The anthocyanin content extracted from purple cabbage was 30.4 mg / g, and the anthocyanin content extracted with ethanol was 6.96 mg / g.
[0068] Example 3 (Preferred Example)
[0069] Preparation of a ternary natural eutectic solvent with a molar ratio of 1:1:3 and its application in extracting anthocyanins from purple cabbage.
[0070] The preparation method was the same as in Example 1, except that the molar ratio of betaine, 1,2-propanediol, and lactic acid was 1:1:3, and the resulting ternary natural eutectic solvent was named [Bet:PG:3LA]. The extraction conditions were the same as in Example 1.
[0071] Infrared spectroscopy analysis was performed on [Bet:PG:3LA] prepared in Example 3, such as... Figure 2 As shown, the spectrum at 3350 cm⁻¹ -1 The presence of a broad and strong OH stretching vibration absorption peak at 2975 cm⁻¹ indicates the presence of numerous hydrogen bonds in the ternary system; -1 and 2930cm -1 The peaks at 1730 cm⁻¹ are the stretching vibration peaks of CH₃ and CH₂, respectively. -1 The C=O stretching vibration peak appears at 1078 cm⁻¹, originating from the carboxyl group in lactic acid. -1 CN + The stretching vibration peak originates from the quaternary ammonium group in betaine. Figure 2 The results show that the positions of the characteristic peaks are highly consistent with the functional group structure of the target product, and the OH peak is significantly broadened, indicating that a stable multiple hydrogen bond network has been formed between betaine, 1,2-propanediol and lactic acid. This confirms that the ternary natural eutectic solvent [Bet:PG:3LA] has been successfully prepared.
[0072] Thermogravimetric analysis was performed on [Bet:PG:3LA], and the results are as follows: Figure 3 As shown, the sample mass remains essentially unchanged below 100 °C, indicating that the ternary eutectic solvent has good thermal stability within this temperature range and contains no free water. In the 100-300 °C range, the sample mass decreases significantly, corresponding to the decomposition of the organic components. Above 300 °C, the sample mass essentially stops changing, and the residual mass tends to stabilize. In other words, the ternary eutectic solvent exhibits good thermal stability below 100 °C, undergoes significant thermal decomposition in the 100-300 °C range, and its mass essentially stops changing above 300 °C.
[0073] Figure 3This indicates that the ternary natural eutectic solvent has excellent thermal stability below 100 ℃, which can meet the temperature requirements of 50-80 ℃ in the extraction of anthocyanins from purple cabbage, and will not affect the extraction effect due to solvent decomposition.
[0074] Extraction results: The anthocyanin content extracted from purple cabbage was 31.2 mg / g, and the anthocyanin content extracted with ethanol was 6.96 mg / g.
[0075] The original purple cabbage powder and the residue after extraction were characterized by scanning electron microscopy, and the results are as follows: Figure 4 As shown. Figure 4 (a) is the original purple cabbage powder, which shows a relatively complete granular structure, with tightly arranged cells and a complete tissue structure. Figure 4 (b) is the purple cabbage residue after [Bet:PG:3LA] treatment. The original blocky structure of the raw material has basically disappeared, and the cell walls have swollen and torn, generating a large number of loose and curled layered films.
[0076] Figure 4 This indicates that the ternary natural eutectic solvent can effectively disrupt the cell wall structure of purple cabbage, allowing intracellular active substances to be fully exposed and come into contact with the extraction solvent, thus promoting anthocyanin dissolution. These SEM characterization results provide direct microscopic morphological evidence for the mechanism of efficient anthocyanin extraction using eutectic solvents.
[0077] X-ray diffraction analysis was performed on the original purple cabbage powder and the purple cabbage residue after [Bet:PG:3LA] extraction. The results are as follows: Figure 5 As shown, both groups of samples exhibited broad diffraction peaks at 2θ = 20-25°, without sharp crystalline peaks, indicating that the samples are predominantly amorphous and low-crystallinity structures. After extraction with a eutectic solvent, the diffraction peak intensities decreased, and the peak shapes became further broadened.
[0078] Figure 5 This indicates that treatment with a ternary natural eutectic solvent partially disrupts the ordered structure of the purple cabbage raw material, reducing its crystallinity. This is because the eutectic solvent is rich in hydroxyl and carboxyl groups, which can form numerous hydrogen bonds with cell wall components such as cellulose and hemicellulose, resulting in solvation and disrupting the ordered structure of the cell wall, thus facilitating the dissolution of anthocyanins from the cells.
[0079] Example 4
[0080] Preparation of a ternary natural eutectic solvent with a molar ratio of 1:1:4 and its application in extracting anthocyanins from purple cabbage.
[0081] The preparation method was the same as in Example 1, except that the molar ratio of betaine, 1,2-propanediol, and lactic acid was 1:1:4, and the resulting ternary natural eutectic solvent was named [Bet:PG:4LA]. The extraction conditions were the same as in Example 1.
[0082] Results: The anthocyanin content extracted from purple cabbage was 31.84 mg / g, and the anthocyanin content extracted with ethanol was 6.96 mg / g.
[0083] Example 5
[0084] A method for preparing a eutectic solvent-anthocyanin-chitosan composite film
[0085] Based on the extraction results of Examples 1-4, [Bet:PG:3LA] and [Bet:PG:4LA] showed better extraction effects. Considering solvent cost and acidity control, the supernatant obtained from the extraction of purple cabbage anthocyanins using [Bet:PG:3LA] was selected as the raw material for preparing the composite membrane.
[0086] Preparation of S1 chitosan solution: Add chitosan powder to a 2% (v / v) aqueous solution of glacial acetic acid and stir at 600 r / min for 4 h to obtain a chitosan mixture. Centrifuge the mixture at 10000 r / min for 10 min to remove insoluble residues and collect the clear supernatant to obtain a chitosan stock solution.
[0087] Preparation of S2 chitosan composite membrane: The purple cabbage anthocyanin extract obtained in Example 3 was added to the chitosan stock solution. Based on the mass of the dried chitosan powder, the mass ratio of the anthocyanin extract added was 2.5%. After thorough mixing, degassing was performed to remove air bubbles from the solution, resulting in the film-forming solution.
[0088] S3 Casting and film formation: The film-forming solution is cast and spread in a petri dish and dried at 50 ℃ for 4 h to obtain a eutectic solvent-anthocyanin-chitosan composite film.
[0089] The 2.5% eutectic solvent-anthocyanin-chitosan composite film prepared in Example 5 was observed in physical samples, and the results are as follows: Figure 6 As shown, the composite membrane is intact and continuous, uniform in shape, without obvious holes, cracks or phase separation, and exhibits good film-forming properties.
[0090] Figure 6 This indicates that the composite membrane prepared by the method of the present invention has a complete and uniform macroscopic structure, and the anthocyanin extract has good compatibility with the chitosan matrix, with no aggregation or precipitation, meeting the basic requirements for subsequent performance testing and application.
[0091] Mechanical properties were tested on the pure chitosan film and the 2.5% eutectic solvent-anthocyanin-chitosan composite film prepared in Example 5. The results are as follows: Figure 7As shown, the tensile strength of the pure chitosan film is 15 MPa, and the maximum elongation at break is 33%; the tensile strength of the composite film is 60 MPa, and the maximum elongation at break is 52%.
[0092] Figure 7 The results show that, compared with pure chitosan film, the composite film has a 300% increase in tensile strength and an approximately 58% increase in elongation at break. The introduction of anthocyanin components creates a dense hydrogen-bonded cross-linked network within the composite film, significantly improving the mechanical properties of the chitosan film. This gives the composite film both high tensile strength and excellent flexibility, meeting the practical needs of biodegradable packaging films.
[0093] The UV-Vis transmittance of pure chitosan film and composite film with 2.5% eutectic solvent-anthocyanin-chitosan was tested, and the results are as follows: Figure 8 As shown, in the 200-400 nm ultraviolet range, the transmittance of the composite film is significantly lower than that of the pure chitosan film; in the visible light range, the composite film still maintains a certain transmittance.
[0094] Figure 8 This indicates that the conjugated π-electron framework of anthocyanin molecules in the composite film can effectively absorb ultraviolet light, giving the film a significant ultraviolet shielding effect and slowing down the oxidation of photosensitive fruits under light exposure. At the same time, the composite film still retains some light transmittance in the visible light region, having minimal impact on the appearance of the fruit, and thus possesses good application potential in the field of photosensitive fruit packaging.
[0095] Comparative Example 1
[0096] Anthocyanins from purple cabbage extracted using a binary natural eutectic solvent
[0097] Under the same pretreatment and extraction conditions as in Example 1, anthocyanins were extracted from purple cabbage using a binary eutectic solvent [Bet:5LA] with betaine as the hydrogen bond acceptor and lactic acid as the hydrogen bond donor, and a binary eutectic solvent [Bet:5PG] with betaine as the hydrogen bond acceptor and 1,2-propanediol as the hydrogen bond donor. The anthocyanin content was determined using the same pH differential method as in Example 1.
[0098] The results showed that the anthocyanin content extracted from purple cabbage using [Bet:5LA] was 23.35 mg / g, and the anthocyanin content extracted using [Bet:5PG] was 25.87 mg / g. Both were lower than the extraction efficiencies of the ternary natural eutectic solvents [Bet:PG:LA], [Bet:PG:2LA], [Bet:PG:3LA], and [Bet:PG:4LA], which were 28.64 mg / g, 30.4 mg / g, 31.2 mg / g, and 31.84 mg / g, respectively, and significantly higher than the 6.96 mg / g of the ethanol control group.
[0099] The above comparative examples illustrate that when only lactic acid or 1,2-propanediol is used as a single hydrogen bond donor to construct a binary eutectic solvent, its extraction efficiency for purple cabbage anthocyanins is limited. However, in this invention, 1,2-propanediol and lactic acid are used together as double hydrogen bond donors to construct a ternary natural eutectic solvent. A stable multi-hydrogen bond network is formed among the three components, and by adjusting the viscosity and polarity of the system to reduce mass transfer resistance, a synergistic extraction effect not found in binary systems is generated, thereby significantly improving the extraction efficiency of purple cabbage anthocyanins.
[0100] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any improvements and substitutions made by those skilled in the art without departing from the principles of the present invention should be considered to fall within the protection scope of the present invention.
Claims
1. A ternary natural eutectic solvent, characterized in that, The ternary natural eutectic solvent uses betaine as a hydrogen bond acceptor and 1,2-propanediol and lactic acid as hydrogen bond donors, wherein the molar ratio of betaine, 1,2-propanediol and lactic acid is 1:1:1 to 1:1:
4.
2. The method for preparing the ternary natural eutectic solvent according to claim 1, characterized in that, Includes the following steps: S1: Betaine, 1,2-propanediol and lactic acid were pretreated by vacuum drying. S2: Pretreated betaine, 1,2-propanediol and lactic acid are mixed in the molar ratio described above, stirred at 50-80 °C until a homogeneous and transparent solution is formed, cooled to room temperature and then vacuum dried to obtain a ternary natural eutectic solvent.
3. The preparation method according to claim 2, characterized in that, The vacuum drying temperature in step S1 is 55℃ and the drying time is 24 h; the stirring speed in step S2 is 400 r / min and the stirring time is 2 h; the vacuum drying temperature is 55℃ and the drying time is 72 h.
4. The application of the ternary natural eutectic solvent of claim 1 in the preparation of purple cabbage anthocyanin extract.
5. The application according to claim 4, characterized in that, The specific extraction operation is as follows: freeze-dry the purple cabbage and then pulverize it to obtain purple cabbage powder; The purple cabbage powder is mixed with the ternary natural eutectic solvent of claim 1 at a solid-liquid ratio of 1:10-1:50, and ultrasonically extracted at 20-60 ℃ for 5-80 min; the extracted mixture is centrifuged and the supernatant is collected to obtain anthocyanin extract.
6. The application according to claim 5, characterized in that, The freeze-drying temperature is -30 ℃; the centrifugation speed is 10000 r / min, and the centrifugation time is 10 min.
7. The application of the anthocyanin extract obtained in claim 5 in the preparation of chitosan composite membranes.
8. The application according to claim 7, characterized in that, Includes the following steps: S1: Add chitosan powder to a 2% (v / v) aqueous solution of glacial acetic acid, stir to dissolve, centrifuge, collect the clear supernatant, and obtain a chitosan stock solution. S2: Add the anthocyanin extract of claim 5 to the chitosan stock solution, mix evenly and degas to obtain a film-forming solution; S3: The film-forming liquid is poured, spread, and dried to obtain a chitosan composite film.
9. The application according to claim 8, characterized in that, The anthocyanin extract added in step S2 accounts for 1%-5% of the chitosan powder mass; the drying temperature in step S3 is 50 ℃ and the drying time is 4 h.
10. A chitosan composite membrane, characterized in that, The composite membrane prepared by the method described in claim 8 or 9 has a tensile strength ≥ 50 MPa and an elongation at break ≥ 45%.