Method for preparing nano-crystalline cellulose based on cumin straws and application of nano-crystalline cellulose in Pickering emulsion

Abstract

The invention belongs to the field of cellulose preparation, and particularly relates to a method for preparing nano cellulose based on cumin straw and application of the method in Pickering emulsion. According to the method, agricultural waste cumin straw is taken as a raw material, nano-crystalline cellulose (CSNc) is prepared through a multi-stage process of alkali treatment, oxidation bleaching and acid hydrolysis, and the effect of the nano-crystalline cellulose on stabilizing cumin oil Pickering emulsion is researched. A sulfuric acid hydrolysis process is optimized through a single factor experiment and a response surface method (Box-Behnken design), the optimal conditions are determined as follows: the sulfuric acid concentration is 60%, the temperature is 50 DEG C, the time is 55 min, and the CSNc yield reaches 5.57 + / -0.21% at the moment. TEM characterization shows that CSNc is of a rod-like nanostructure, the average width is 16.93 nm, the length is 253.06 nm, the absolute value of surface Zeta potential is high (zeta is equal to 45.6 mV), and it is indicated that CSNc has good colloidal stability. The CSNc is applied to a cumin oil emulsion system, the oil-in-water (O / W) Pickering emulsion is successfully prepared, and the particle sizes of liquid drops of the emulsion are uniform.

Description

Technical Field

[0001] This invention belongs to the field of cellulose preparation, specifically relating to a method for preparing nanocellulose based on cumin straw and its application in Pickering emulsion. Background Technology

[0003] In recent years, nanocellulose (Nc) has become a research hotspot in materials science due to its unique physicochemical properties (such as high specific surface area, biodegradability, mechanical strength, and interfacial stability). Traditional nanocellulose is mostly extracted from wood or cotton, but its production relies on forest resources, posing an ecological burden. In contrast, extracting nanocellulose from agricultural waste (such as cumin straw) can reduce raw material costs and turn waste into treasure. However, the lignocellulose fibers in cumin straw are highly stable, and existing straw processing methods involve cumbersome pretreatment processes, high costs, and are difficult to effectively handle. Currently, there are no records of preparing nanocellulose from cumin straw.

[0004] On the other hand, cumin oil, as the essential extract of cumin seeds, is rich in active ingredients such as cuminaldehyde, and has antioxidant and antibacterial effects in the food, health product, and pharmaceutical fields. However, the poor water solubility and low chemical stability of cumin oil limit its application range. Traditional emulsion stabilizers (such as synthetic surfactants) have drawbacks such as safety controversies or limited functionality. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method for preparing nanocellulose based on cumin straw.

[0006] This invention also provides the application of the nanocellulose prepared by the above method in Pickering emulsion.

[0007] The technical solution adopted by the present invention to achieve the above objectives is as follows: This invention provides a method for preparing nanocellulose based on cumin straw, comprising the following steps: (1) After the cleaned cumin stalks are dried, they are crushed and sieved to obtain cumin stalk powder; (2) Add cumin straw powder to NaOH solution, stir to react, then centrifuge to collect the precipitate, wash the precipitate, dry the precipitate to obtain alkaline washed precipitate; (3) Add the dried alkaline-washed precipitate to the bleaching solution, stir to react, then centrifuge to collect the precipitate, wash and filter until the pH of the filtrate is neutral, dry, and obtain cumin straw cellulose. (4) Weigh the dried cumin straw cellulose and disperse it in sulfuric acid solution. Hydrolyze it in a water bath. After the hydrolysis is complete, add cold ultrapure water to terminate the reaction. Centrifuge the reaction solution to collect the lower precipitate and dialyze it until the pH is neutral to obtain cumin straw nanocellulose.

[0008] Preferably, in step (1), the mesh size of the sieve is 80.

[0009] Preferably, in step (2), the ratio of cumin straw to NaOH solution is 1:25 (w / v); the concentration of NaOH solution is 4% (w / v); and the stirring reaction is carried out continuously for 2 hours in a 90°C water bath.

[0010] Preferably, in step (3), the ratio of the alkaline precipitate to the bleaching solution is 1:25 (w / v); the stirring reaction is carried out by continuous stirring in an 80°C water bath environment for 2 hours.

[0011] Preferably, in step (3), the bleaching solution consists of: 1.7% (w / v) NaClO2, 2.7% (w / v) NaOH, 7.5% (v / v) glacial acetic acid, with the remainder being water.

[0012] Preferably, in step (4), the ratio of cumin straw cellulose to sulfuric acid solution is 1:15 (w / v); the concentration of sulfuric acid solution is 30-70%.

[0013] Preferably, in step (4), the water bath hydrolysis is performed at 20-60℃ for 20-60 minutes; the dialysis is performed using a 3000 Da dialysis bag.

[0014] The present invention also provides an application of nanocellulose prepared by the above method in Pickering emulsion.

[0015] Preferably, the Pickering emulsion is prepared by: weighing a certain amount of cumin straw nanocellulose powder, adding deionized water to dissolve it, and obtaining an aqueous CSNc solution; mixing cumin oil with the aqueous phase and ultrasonically emulsifying it to obtain a cumin oil Pickering emulsion.

[0016] Preferably, the final concentration of the CSNc solution is 1%; the ratio of cumin oil to water is 3:7; and the ultrasonic emulsification is performed using an ultrasonic cell disruptor at 500 W for 3 minutes.

[0017] This invention uses cumin straw, an agricultural waste, as raw material to prepare nanocellulose (CSNc) through a multi-stage process of alkali treatment, oxidative bleaching, and acid hydrolysis, and investigates its role in stabilizing cumin oil Pickering emulsions. The sulfuric acid hydrolysis process was optimized through single-factor experiments and Box-Behnken response surface methodology, determining the optimal conditions to be a sulfuric acid concentration of 60%, a temperature of 50℃, and a time of 55 min, at which the CSNc yield reached 5.57 ± 0.21%. TEM characterization showed that the CSNc exhibited a rod-like nanostructure with an average width of 16.93 nm and a length of 253.06 nm, and a high absolute value of the surface zeta potential (|ζ| = 45.6 mV), indicating its good colloidal stability. Applying CSNc to the cumin oil emulsion system successfully prepared an oil-in-water (O / W) Pickering emulsion with uniform droplet size.

[0018] The beneficial effects of this invention are as follows: (1) The method provided by this invention provides a new strategy for the high-value utilization of agricultural waste, and at the same time lays a theoretical foundation for the development of delivery systems for natural active ingredients, promoting green technology innovation in the food and pharmaceutical industries.

[0019] (2) This invention optimized the preparation process of cumin straw nanocellulose using response surface methodology, achieving a yield of 5.57% under optimal conditions. The obtained CSNc possesses nanoscale characteristics, high surface charge, and good dispersibility, effectively stabilizing O / W type cumin oil Pickering emulsions with uniform droplet distribution and excellent stability. The results indicate that CSNc can serve as a natural emulsifier to replace traditional synthetic stabilizers, providing technical support for the resource utilization of agricultural waste and the development of functional emulsion systems. Further research is needed to explore its specific application performance and industrial feasibility in the food, pharmaceutical, and other fields. Attached Figure Description

[0020] Figure 1 The image shows the physical product prepared in Example 1; where (A) is cumin straw powder, (B) is cumin straw cellulose, and (C) is cumin straw nanocellulose. Figure 2 TEM image of cumin straw nanocellulose; Figure 3 The (A) length and (B) width size distribution of cumin straw nanocellulose; Figure 4 Zeta potential diagram; CSc: cumin straw cellulose; CSNc: cumin straw nanocellulose; Figure 5 The effect of hydrolysis time on the yield of nanocellulose; Figure 6 The effect of sulfuric acid concentration on the yield of nanocellulose; Figure 7 Effect of hydrolysis temperature on the yield of nanocellulose; Figure 8 Contour lines and response surfaces showing the effects of extraction temperature and sulfuric acid concentration on cellulose extraction rate; Figure 9 Contour lines and response surfaces showing the effects of extraction time and sulfuric acid concentration on cellulose extraction rate; Figure 10 Contour lines and response surfaces showing the effects of extraction time and extraction temperature on cellulose extraction rate; Figure 11 Appearance and types of cumin oil emulsion stabilized by nanocellulose from cumin straw. a: Nanocellulose solution; b: Cumin oil; c: Cumin oil emulsion (containing nanocellulose); d: Cumin oil-water mixture; e: Cumin oil emulsion (without nanocellulose); f: Cumin oil emulsion dispersed in water; g: Cumin oil emulsion dispersed in oil; Figure 12 Microscopic observation of cumin oil emulsion; Figure 13 (A) Particle size distribution and (B) Zeta potential of cumin oil emulsion. Detailed Implementation

[0021] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0022] Example 1 1. Materials and Methods 1.1 Experimental Materials 1.1.1 Main Reagents Cumin stalks, cumin oil, concentrated sulfuric acid, sodium hydroxide, sodium chlorite, glacial acetic acid 1.1.2 Main Instruments Thermostatic magnetic stirrer, electronic balance, pH meter, ultrasonic cell disruptor, freeze dryer, optical microscope, transmission electron microscope, high-speed centrifuge, particle size analyzer 1.2 Experimental Methods 1.2.1 Preparation of cumin straw nanocellulose Select fresh, pest-free, and mold-free cumin stalks and carefully rinse them with clean water to remove impurities such as sand and stones. Dry the washed stalks in an oven at 60℃ for 12 hours until constant weight to obtain dried cumin stalks. Crush the cumin stalks using a pulverizer, pass them through an 80-mesh sieve to obtain stalk powder, and seal it in a sealed bag for later use. Add the stalk powder to a 4% (w / v) NaOH solution at a material-to-liquid ratio of 1:25. Stir continuously in a 90℃ water bath for 2 hours, then centrifuge (8000 r / min, 10 min) to collect the precipitate. Wash the precipitate with deionized water to remove excess alkali; repeat this alkali washing process four times. After alkali washing, place the precipitate in a 50℃ oven overnight to dry. Then, perform bleaching treatment by adding the dried alkali-washed precipitate to a bleaching solution at a material-to-liquid ratio of 1:25. The bleaching solution consisted of 1.7% (w / v) NaClO2, 2.7% (w / v) NaOH, and 7.5% (v / v) glacial acetic acid. The solution was continuously stirred in an 80℃ water bath for 2 h, followed by centrifugation (8000 r / min, 10 min) to collect the precipitate. This rinsing process was repeated twice. Finally, the solution was repeatedly washed and filtered with deionized water until the pH of the filtrate was neutral, and then dried in a 50℃ oven. The dried cumin straw cellulose was weighed and dispersed in a 60% sulfuric acid solution at a material-to-liquid ratio of 1:15 (w / v), and hydrolyzed in a 50℃ water bath for 55 min. After hydrolysis, 10 times the volume of cold ultrapure water was added to terminate the reaction. The reaction solution was centrifuged (8000 r / min, 10 min) to collect the lower precipitate. The precipitate was then dialyzed in a 3000 Da dialysis bag until the pH was neutral to obtain cumin straw nanocellulose (CSNc).

[0023] Products such as Figure 1 As shown. Cumin straw powder ( Figure 1 A) It is light green in color. After alkali treatment and purification, the cumin straw cellulose obtained is ( Figure 1 B) is pure white. Using straw cellulose as raw material, and through an optimized sulfuric acid hydrolysis process, cumin straw nanocellulose (…) was prepared. Figure 1 C) It is also a pure white powder.

[0024] like Figure 2 As shown, after acid hydrolysis, cumin nanocellulose exhibits a rod-shaped or long-fiber structure. This phenomenon is due to the hydrolysis of straw cellulose by sulfuric acid, which breaks down the large-sized cellulose structure, resulting in nano-sized CSNc.

[0025] The length and width of cumin straw nanocellulose in TEM were measured using ImageJ software, and the results are as follows: Figure 3As shown, the cumin straw nanocellulose has a small size, with a width of approximately 16.93 nm and a length of 253.06 nm, both of which are at the nanoscale.

[0026] like Figure 4 As shown, cumin straw nanocellulose prepared by acid hydrolysis exhibits a high Zeta potential (ζ = -45.6 mV). This phenomenon is mainly determined by its surface chemical properties and microstructure, and also brings significant advantages to its practical applications. During sulfuric acid hydrolysis, the sulfonic acid groups (-SO3H) of sulfuric acid (H2SO4) undergo esterification with the hydroxyl groups (-OH) on the cellulose molecular chain to form sulfonate groups (-OSO3⁻). These negatively charged sulfonic acid groups are fixed on the surface of nanocellulose, significantly increasing the surface charge density and leading to an increase in the absolute value of the Zeta potential. The high absolute value of the Zeta potential indicates the existence of strong electrostatic repulsion between particles, which can effectively prevent the agglomeration of nanocellulose and form a long-term stable colloidal dispersion system in the liquid phase. This characteristic makes it promising for applications in food, medicine, and environmental protection materials.

[0027] Example 1 (a) Yield of cumin straw nanocellulose The extraction rate of CSNc is calculated using the following formula: In the formula: C is the extraction rate of CSNc, % M1 is the dry weight of CSNc, in g; M2 is the dry weight of straw powder, in grams.

[0028] (II) Optimization of the preparation process of cumin straw nanocellulose Single-factor experiments were conducted to select three factors that significantly affected the CSNc extraction rate by sulfuric acid hydrolysis: sulfuric acid concentration (%), treatment temperature (°C), and hydrolysis time (min). The effects of each factor on the CSNc extraction rate were investigated separately, providing corresponding factor reference levels for the experimental design of response surface methodology and optimization of the CSNc extraction process.

[0029] (1) Effect of hydrolysis time on the yield of nanocellulose Five 1.00 g portions of cumin straw powder were weighed and a 60% sulfuric acid solution was prepared. The solutions were heated at 50°C for 20 min, 30 min, 40 min, 50 min, and 60 min, respectively. After extraction, the solutions were cooled to room temperature and dried to obtain the mass of CSNc and the extraction rate was calculated.

[0030] (2) Effect of sulfuric acid concentration on the yield of nanocellulose Five 1.00 g portions of cumin straw powder were weighed and sulfuric acid solutions were prepared at concentrations of 30%, 40%, 50%, 60%, and 70%, respectively. The solutions were heated at 50°C for 40 min. After extraction, the solutions were cooled to room temperature, dried, and the mass of CSNc was obtained. The extraction rate was then calculated.

[0031] (3) Effect of hydrolysis temperature on the yield of nanocellulose Five 1.00 g portions of cumin straw powder were weighed and a 60% sulfuric acid solution was prepared. The solutions were heated at 20℃, 30℃, 40℃, 50℃, and 60℃ for 50 min, respectively. After extraction, the solutions were cooled to room temperature, dried, and the mass of CSNc was obtained. The extraction rate was then calculated.

[0032] (III) Design of response surface methodology experiments Response surface methodology (RSM) is a collection of mathematical and statistical techniques based on fitting polynomial equations to experimental data. It is used to describe the behavior of datasets and aims to make statistical predictions. RSM is widely used to optimize experimental conditions, selecting the optimal experimental conditions with the shortest number of trials and time. This experiment utilizes the principle of the Box-Behnken central composite experiment to optimize the CSNc extraction process parameters. Based on the results of the single-factor experiments, using Design-Expert 13 response surface design analysis software, sulfuric acid concentration, time, and temperature were selected as important process parameters. With the CSNc extraction rate as the response value, a three-factor, three-level Box-Behnken response surface experiment was designed to determine the optimal CSNc extraction process parameters. The specific experimental design parameter levels are shown in Table 1, where X1, X2, and X3 represent sulfuric acid concentration (%), extraction temperature (°C), and extraction time (min), respectively, and -1, 0, and 1 represent the low, medium, and high level coding values ​​of the three variables, respectively.

[0033] Table 1. Experimental Factors and Levels (iv) Preparation of Pickering emulsion for cumin straw-stabilized cumin oil Weigh a certain amount of CSNc powder and dissolve it in 10 mL of deionized water to make the final concentration of the CSNc solution 1%. Mix cumin oil and water in a 3:7 ratio and emulsify using an ultrasonic cell disruptor at 500 W for 3 min to obtain cumin oil Pickering emulsion.

[0034] (v) Optical microscopic observation of emulsion morphology A drop of emulsion sample was placed on a glass slide, covered with a coverslip, and observed under an optical microscope. Images were taken using the microscope's camera. All measurements were performed at 25°C.

[0035] (vi) Determination of emulsion particle size The particle size distribution of cumin oil Pickering emulsion droplets was measured using a laser particle size analyzer and dynamic light scattering (DLS) method.

[0036] (vii) Determination of Zeta potential of emulsion The zeta potential (ζ) of cumin oil Pickering emulsion droplets was measured using a laser particle size analyzer.

[0037] Results and Analysis (I) Optimization of the preparation process of cumin straw nanocellulose (1) Effect of hydrolysis time on CSNc yield like Figure 5 As shown, five hydrolysis times of 20, 30, 40, 50, and 60 min were set. The results showed that the yield of cumin straw nanocellulose increased with the extension of treatment time. When the hydrolysis time reached 40 min, the yield of CSNc no longer increased. When the hydrolysis time continued to increase, reaching 60 min, the change in CSNc yield was not significant; however, the color of the reaction solution darkened at this time, possibly due to partial carbonization of cellulose caused by excessively long acid treatment time. Therefore, to ensure the quality and yield of cumin straw CSNc, the hydrolysis time was set to 50 min for subsequent experiments.

[0038] (2) Effect of sulfuric acid concentration on CSNc yield By varying the concentration of the sulfuric acid solution, the optimal acid concentration for hydrolyzing cumin straw cellulose was screened. The results are as follows: Figure 6 As shown, the CSNc yield initially increases and then decreases with increasing sulfuric acid concentration. When the sulfuric acid concentration in the hydrolysate is below 60%, the straw cellulose contains many large, unreacted cellulose particles due to incomplete hydrolysis. With increasing sulfuric acid concentration, the degree of cellulose hydrolysis increases, and the yield also increases. When the sulfuric acid concentration exceeds 70%, the solution color darkens after hydrolysis, possibly due to cellulose particle agglomeration caused by partial coking, leading to a decrease in CSNc yield. Therefore, a sulfuric acid concentration of 60% was chosen for subsequent experiments.

[0039] (3) Effect of hydrolysis temperature on CSNc yield like Figure 7As shown, changing the acid hydrolysis temperature revealed that the CSNc yield initially increased and then decreased with increasing temperature. Within the hydrolysis temperature range of 20-50℃, the reaction rate increased with rising temperature, the degree of cellulose hydrolysis gradually improved, and thus the CSNc yield gradually increased as well. However, when the temperature was further increased to 60℃, the cellulose might undergo charring due to the excessively high temperature, reducing the yield. In conclusion, 50℃ is the suitable temperature for sulfuric acid hydrolysis of straw cellulose.

[0040] (II) Results and Analysis of Box-Behnken Experimental Design (1) Establishment of model equations and significance experiment This study used sulfuric acid hydrolysis to extract nanocellulose from cumin straw and optimized the extraction process conditions using Box-Behnken experimental design. Seventeen experimental schemes with three factors and three levels (extraction time, sulfuric acid concentration, and extraction temperature) were set up, as shown in Table 2.

[0041] Table 2. Response Surface Experimental Design and Results A quadratic polynomial regression was performed on the experimental data in the table to obtain the regression equation for the yield of cumin straw nanocellulose (Y) and three factors: sulfuric acid concentration (A), extraction temperature (B), and extraction time (C): Y = 5.56 + 0.72A + 0.65B + 0.35C − 0.28AB − 0.21AC + 0.33BC − 0.45A 2 -0.38B 2 -0.25C 2 The F-test was used to analyze the significance of the model and its coefficients, and the results are shown in Table 3. The F-value of the regression model was high (F-value = 82.95), and P < 0.0001, indicating that the regression model reached a significant level. Furthermore, the P-value for the lack-of-fit term was 0.1863 > 0.05, indicating no significant difference; therefore, the regression model is significant. Additionally, because the model's R² = 0.9907 and the adjusted R² = 0.9782 are close to 1, the correlation between the experimental and predicted values ​​is high.

[0042] The significance test of the regression equation coefficients of the model shows that the linear terms A (sulfuric acid concentration), B (extraction temperature), and C (extraction time) have a significant impact on the yield of nanocellulose, and the square term A... 2 B 2 C 2 The yield of nanocellulose was also significantly affected. Therefore, the effects of various factors on the extraction rate of nanocellulose were not a simple linear relationship. Sulfuric acid concentration (A) had the greatest impact (SS=4.2153), followed by temperature (B) and hydrolysis time (C).

[0043] Table 3. Results of Analysis of Variance for Response Surface Fitting Regression Equations (2) Extracting the interaction effects of various factors on CSNc extraction rate Based on the regression equation, draw the response surface contour lines and response surface plot, such as... Figure 8-10 As shown, the contour plots of the interaction between any two of the three factors—sulfuric acid concentration, extraction temperature, and extraction time—on the yield of cumin straw nanocellulose are all elliptical, indicating that the interaction between any two factors has a significant impact on the CSNc yield.

[0044] (3) Determination and verification of extraction process parameters Table 4. Extraction process parameters and predicted values ​​of cumin straw nanocellulose The optimal extraction parameters for CSNc preparation were obtained through statistical analysis, as shown in Table 4. Based on the statistical analysis and actual operating conditions, the optimal conditions were slightly modified, using a sulfuric acid concentration of 62%, an extraction temperature of 50℃, and an extraction time of 55 min to verify the model results. Under these optimized conditions, the experiment was repeated three times, and the CSNc extraction rate was 5.57±0.21%, which was not significantly different from the software-predicted yield of 5.68%. This indicates that the optimized process conditions for CSNc preparation obtained from response surface methodology are reliable.

[0045] (iii) Cumin oil Pickering emulsion (1) Appearance and emulsion type exist Figure 11 In step a, nanocellulose, after ultrasonic treatment, can be completely dispersed in water to form a uniform gel-like substance. Under ultrasonic emulsification conditions, a uniform cumin oil emulsion is formed. Figure 11 c). On the other hand, cumin oil cannot be mixed with water under simple mixing conditions ( Figure 11 d), and because of its low density, it floats on the water surface. Similarly, without nanocellulose as a surfactant, cumin oil floats to the surface as small particles after ultrasonic treatment. Figure 11 e). Therefore, the preparation of cumin oil Pickering emulsion requires cumin straw nanocellulose and ultrasonic treatment.

[0046] Pickering emulsions come in two types: oil-in-water and water-in-oil. One type consists of water encapsulating oil droplets (oil droplets surrounded by water, abbreviated as O / W type), while the other is the opposite, with water surrounded by an oil phase (water surrounded by oil type, abbreviated as W / O type). The type is identified by adding a small amount of the emulsion to water or oil and observing its diffusion characteristics. The prepared cumin oil emulsion disperses well in water. Figure 11f), cannot be dispersed in oil ( Figure 11 g), proving that the prepared cumin oil emulsion is an oil-in-water (O / W) type emulsion, which can be perfectly used in water-based products, thus solving the problem of poor water solubility of cumin oil.

[0047] (2) Microstructure Under an optical microscope, the emulsion exhibits a typical oil-in-water (O / W) structure. The dispersed phase droplets are relatively regular spherical, with most droplets maintaining intact boundaries and showing no obvious aggregation, indicating that cumin straw nanocellulose has good emulsifying ability. No obvious oil precipitation or phase separation was observed in the continuous phase, suggesting that the cumin straw nanocellulose-stabilized cumin oil emulsion system has good stability.

[0048] (3) Particle size and potential The emulsion particle size distribution, measured by a laser particle size analyzer, exhibits a narrow, unimodal distribution, indicating good droplet uniformity. The hydrodynamic diameter is 866 ± 64.98 nm. A low polydispersity index (PDI < 0.3) further demonstrates stable dispersion and the absence of significant aggregation or stratification. The high absolute value of the emulsion surface potential (|ζ| = 61.8 mV) indicates strong electrostatic repulsion between droplets, effectively resisting aggregation and contributing to the system's good physical stability. Overall, this emulsion meets the requirements for long-term storage or functional applications (such as food and pharmaceutical delivery systems).

Claims

1. A method for preparing nanocellulose based on cumin straw, characterized in that, Includes the following steps: (1) After the cleaned cumin stalks are dried, they are crushed and sieved to obtain cumin stalk powder; (2) Add cumin straw powder to NaOH solution, stir to react, then centrifuge to collect the precipitate, wash the precipitate, dry the precipitate to obtain alkaline washed precipitate; (3) Add the dried alkaline-washed precipitate to the bleaching solution, stir to react, then centrifuge to collect the precipitate, wash and filter until the pH of the filtrate is neutral, dry, and obtain cumin straw cellulose. (4) Weigh the dried cumin straw cellulose and disperse it in sulfuric acid solution. Hydrolyze it in a water bath. After the hydrolysis is complete, add cold ultrapure water to terminate the reaction. Centrifuge the reaction solution to collect the lower precipitate and dialyze it until the pH is neutral to obtain cumin straw nanocellulose.

2. The method according to claim 1, characterized in that, In step (1), the mesh size of the sieve is 80.

3. The method according to claim 1 or 2, characterized in that, In step (2), the ratio of cumin straw to NaOH solution is 1:25 (w / v); the concentration of NaOH solution is 4% (w / v); and the stirring reaction is carried out continuously for 2 hours in a 90°C water bath.

4. The method according to claim 1 or 3, characterized in that, In step (3), the ratio of the alkaline precipitate to the bleaching solution is 1:25 (w / v); the stirring reaction is carried out by continuous stirring in an 80°C water bath environment for 2 hours.

5. The method according to claim 4, characterized in that, In step (3), the bleaching solution is composed of: 1.7% (w / v) NaClO2, 2.7% (w / v) NaOH, 7.5% (v / v) glacial acetic acid, and the remainder is water.

6. The method according to any one of claims 1-5, characterized in that, In step (4), the ratio of cumin straw cellulose to sulfuric acid solution is 1:15 (w / v); the concentration of sulfuric acid solution is 30-70%.

7. The method according to claim 1 or 6, characterized in that, In step (4), the water bath hydrolysis is performed at 20-60℃ for 20-60 minutes; the dialysis is performed using a 3000 Da dialysis bag.

8. The application of nanocellulose prepared by the method according to any one of claims 1-7 in Pickering emulsion.

9. The application according to claim 8, characterized in that, The Pickering emulsion is prepared by weighing a certain amount of cumin straw nanocellulose powder, adding deionized water to dissolve it, and obtaining an aqueous CSNc solution; mixing cumin oil with the aqueous phase and ultrasonically emulsifying it to obtain cumin oil Pickering emulsion.

10. The application according to claim 9, characterized in that, The final concentration of the CSNc solution is 1%; the ratio of cumin oil to water is 3:7; the ultrasonic emulsification is performed using an ultrasonic cell disruptor at 500 W for 3 minutes.

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