Ultrasonic preparation of Lotus root starch Pickering emulsion and application thereof as functional food

Abstract

The present invention relates to the technical field of Pickering emulsion preparation, and in particular, to a method for ultrasonic preparation of a Pickering emulsion containing lotus root starch a

Description

TECHNICAL FIELD The present disclosure relates to the technical field of producing Pickering emulsion, and specifically to a method for preparing a Pickering emulsion using lotus root starch and xanthan gum, employing an energy-gathered ultrasonic technology. The process involves utilizing lotus root starch and xanthan gum as the primary ingredients and incorporating fish oil to produce functional food. BACKGROUND Pickering emulsions usually refer to emulsions stabilized by solid particles acting as emulsifiers or by colloidal particles. The traditional surfactants are the hydrophilic part, which extends into the water phase at the oil-water interface, and the lipophilic part, which extends into the oil phase, thus producing spatial repulsion to stabilize the emulsion. In Pickering emulsion, solid particles are irreversibly adsorbed at the oil-water interface to form a three-dimensional barrier to stabilize the emulsion. In comparison to traditional emulsions, Pickering emulsion offers several advantages. It requires a smaller amount of emulsifier, making it more cost-effective. Additionally, it is less toxic, resulting in fewer side effects on the human body and causing fewer environmental concerns. The emulsion demonstrates excellent stability and remains unaffected by various environmental factors, including pH, salt ions, and system temperature. Over the past two decades, synthetic polymer and inorganic particle emulsifiers have become the focus of research because of the controllability of their shape, size, and surface properties. However, the biocompatibility, biodegradability, and sustainability of synthetic polymers and inorganic particles are poor, and their applications in food, biomedicine, cosmetics, and other fields are limited. In the last five years, there has been a growing tendency to use naturally sourced biomaterials to prepare granular emulsifiers that can stabilize Pickering emulsions. So far, there have been many research reports on the preparation of Pickering emulsions from cellulose, starch, protein, pectin, etc. as natural sources of solid particles. The use of natural biological materials to prepare new solid particles for stabilizing Pickering emulsion and preparing related functional materials can promote the prevention of environmental pollution and save resources. Starch has gained significant attention as a raw material of natural origin, thanks to its numerous advantages, including its abundant sources and cost-effectiveness. China has a wide variety of starch types, including cereal starch, bean starch, potato starch, and other sources of starch. Currently, high-purity starch and its derivatives have been extensively utilized in various industries, including food, biomedicine, chemicals, papermaking, agriculture, and more. Thus, starch-based granule emulsifiers hold promising potential for various applications. Nelumbo nucifera gaertn, commonly, also referred to as lotus root, is a perennial plant belonging to the Nymphaeaceae family. It is primarily found in the Yangtze River, Yellow River, and Pearl River basins in China, particularly in Jiangsu, Zhejiang, Hunan, Hubei, and other provinces. Lotus root is packed with a variety of nutrients that are beneficial for human health, including starch, protein, vitamins, iron, calcium, alkaloids, and more. This crop is highly valued for its edible and medicinal properties, making it a popular choice in the aquatic industry. As per the "Compendium of Materia Medica," lotus root is described as having a sweet and cooling nature. This product has the ability to cool the blood, stop bleeding, eliminate heat, and clear the stomach. Thus, it possesses the capabilities of promoting blood circulation, reducing heat, quenching thirst, alleviating digestive issues, and providing relief from alcohol consumption. Experienced ones are known for their delightful and comforting qualities. They have the ability to support the spleen, promote digestion, enhance blood health, and provide nourishment to the heart. As a result, they are commonly used to support the well-being of the body's internal organs. Lotus root starch is a high-quality powder product created through a meticulous process that involves peeling, cutting, color protection, homogenization, filtration, drying, grinding, and other advanced techniques. This ensures that the lotus root starch maintains the original color and flavor of the lotus root meat while preserving its natural components, including starch, flavonoids, vitamins, minerals, and aspartate. The fresh lotus root is known for its exceptional flavor and high nutritional value. The lotus root starch contains approximately 25% to 30% amylose and about 65% amylopectin, making up the total starch composition. The role of amylopectin in starch particles is to serve as a structural support, forming radial extensions that create microcrystalline fiber bundles. Amylose is commonly found in the form of double-helix crystals, which are evenly distributed. Xanthan gum is a kind of extracellular polysaccharide produced by the fermentation of Xanthomnas campestris. It is an anionic hydrophilic colloid composed of a glucose main chain and a tri sugar side chain. When dissolved in water, the side chain can be reversed and wound around the main chain of the fiber to form the primary structure of xanthan gum; the double helix structure is formed by hydrogen bonding between molecules, which is the secondary structure of xanthan gum; furthermore, the double helical structures intertwine with each other to form a network of three-dimensional tertiary conformations. This unique molecular conformation determines that it has good emulsification, thickening, thixotropy, pseudoplasticity, and other properties and can interact with other polysaccharides (such as starch), but also safe, non-toxic, green substances, making it one of the most superior hydrophilic colloids in the food industry at home and abroad. At present, the application of starch particles as Pickering emulsion stabilizer mainly stems from the modification of starch particles so as to reduce their size and improve their hydrophobicity. Common preparation methods for starch nanoparticles include mechanical grinding, antisolvent precipitation, octenyl succinic anhydride (OSA) modification, acid hydrolysis, and enzymatic hydrolysis. These methods have more or less high energy consumption, cumbersome operation, the use of chemical reagents and other problems. It is urgent to develop a green preparation method with simple operation, a stable product, and no chemical reagents. As for the preparation technology of emulsion, high-energy emulsification technologies such as high-pressure homogenization, high-pressure microjets, and high-speed shear before high-pressure homogenization are mainly used to make protein molecules closely arranged at the oil-water interface and reduce the interfacial tension of the two phases to prepare emulsion. However, the above emulsification technology equipment is expensive; high maintenance costs, small sample processing capacity, complex operation, and high requirements for operators limit its application in the field of food. The spoilage caused by oil oxidation can have a significant impact on the appearance and taste of food during the processing and storage of emulsions. Although the current research primarily centers around the inclusion and delivery of bioactive substances, there is a limited amount of research on the antioxidant properties of fats and unsaturated fatty acids in Pickering emulsion. This emulsion's oxidation primarily takes place at the interface between oil and water. The nano-starch-based Pickering emulsion forms a robust physical barrier at this interface, thanks to the arrangement of micro-starch particles. This barrier effectively prevents oxygen from entering. Additionally, xanthan gum acts as a chelator for metal ions and eliminates free radicals, significantly boosting the oils' antioxidant properties. To address the aforementioned issues, the present disclosure utilizes a pressure-heat recovery method for the production of starch nanoparticles and employs energy-gathered ultrasonic technology for producing a lotus root starch / xanthan gum-stabilized Pickering emulsion. An efficient and environmentally friendly method is employed to produce the lotus root starch-xanthan gum Pickering emulsion, ensuring a smaller particle size and enhanced stability. An investigation was conducted to study the oxidation stability and protection of Pickering emulsion when loaded with herring oil, specifically against docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). SUMMARY The above problems are addressed by preparing lotus root starch nanoparticles using the pressing heat recovery method and treating the lotus root starch xanthan gum Pickering emulsion with energy-gathered ultrasonic technology. An investigation is conducted to analyze the alterations in the physical and chemical properties, as well as the structural characteristics of the nanoparticles. Additionally, the impact on the stability of the Pickering emulsion was examined. A fish oil-loaded antioxidant emulsion was prepared by substituting the oil phase with fish oil. The preparation of starch nanoparticles in lotus root is achieved using the pressing heat recovery method. The structure of starch particles can be compromised by high temperature and pressure, leading to the dissolution of amylose and the formation of starch nanoparticles through recrystallization. The composite nanoparticles are prepared by fully hydrating them with xanthan gum. A dual-frequency energy-gathered ultrasonic device is used to prepare the Pickering emulsion. This ultrasonic device effectively overcomes the issue of standing waves that can occur with single-frequency ultrasonic technology, allowing for optimal emulsification. Furthermore, the oxidation of grease in the emulsion has consistently posed a challenging issue. The emulsion made from fish oil, which is prone to oxidation, is chosen to create an antioxidant emulsion containing fish oil. The lotus root starch-xanthan gum composite nanoparticles of the present disclosure are prepared from the following mass portions of raw materials: 1-20 parts by weight of lotus root starch; 1-20 parts by weight of xanthan gum; and 600-1000 parts by weight of water. The preferred lotus root starch-xanthan gum composite nanoparticles are prepared from the following weight parts of raw materials: 8 parts by weight of lotus root starch; 2.4 parts by weight of xanthan gum; and 800 parts by weight of water. The lotus root starch / xanthan gum stabilized Pickering emulsion of the present disclosure is prepared from the following ingredients by weight: 1-20 parts by weight of lotus root starch; 1-20 parts by weight of xanthan gum; 100-300 parts by weight of soy bean oil; and 600-1000 parts by weight of water. The preferred lotus root starch-xanthan gum Pickering emulsion is prepared from the following weight parts of raw materials: 8 parts by weight of lotus root starch; 2.4 parts by weight of xanthan gum; 200 parts by weight of soybean oil; and 800 parts by weight of water. The lotus root starch-xanthan gum Pickering emulsion loaded with the fish oil in the present disclosure is prepared from the following weight parts of raw materials: 1-20 parts by weight of lotus root starch; 1-20 parts by weight of xanthan gum; 150-200 parts by weight of herring oil; 10-50 parts by weight of orange essential oil; and 600-1000 parts by weight of water. The preferred lotus root starch-xanthan gum Pickering emulsion loaded with fish oil is prepared from the following weights of raw materials: 8 parts by weight of lotus root starch; 2.4 parts by weight of xanthan gum; 160 parts by weight of herring oil; 40 parts by weight of orange essential oil; and 800 parts by weight of water. The preparation method of lotus root starch xanthan gum composite nanoparticles is carried out according to the following steps: (1) dispersing lotus root starch in distilled water at a concentration of 1-5 wt%, to obtain a starch dispersion liquid; (2) pre-gelatinizing the starch dispersion in boiling water for 5 min and stirring continuously to ensure uniform dispersion. (3) immediately transferring a pre-gelatinized starch dispersion from the step (2) to a sterilization pot for pressure-heat treatment; (4) taking out a pressure-heat treated dispersion from the step (3), cooling naturally to room temperature, and then transferring to a refrigerator at 4°C for recrystallization; (5) dissolving xanthan gum in distilled water at a concentration of 0.2 wt% to 1 wt% with stirring overnight on a magnetic stirrer for complete dissolution; and (6) mixing a starch nanoparticle dispersion prepared in the step (4) with a xanthan gum solution from the step (5) to obtain composite nanoparticles, where a preferred dispersion concentration described in the step (1) is 2 wt%; the pressure-heat treatment condition described in the step (3) is 121°C for 20 min; a time for recrystallization described in the step (4) is 8 to 12 h, and a preferred recrystallization time is 9 h; a preferred concentration of the xanthan gum solution described in the step 5 is 0.6 wt%; and a mass ratio of the lotus root starch to the xanthan gum in the composite nanoparticles described in the step (6) is 10:1 to 10:5, and preferably 10:3. Lotus root starch-xanthan gum Pickering emulsion is prepared according to the following steps: (1) dispersing lotus root starch in distilled water at a concentration of 2 wt%, to obtain a starch dispersion; (2) pre-gelatinizing the starch dispersion in boiling water for 5 min with constant stirring to ensure uniform dispersion; (3) immediately transferring a pre-gelatinized starch dispersion from the step (2) to a sterilization pot for pressure-heat treatment at 121 °C for 20 min; (4) taking out a pressure-heat treated dispersion from the step (3), naturally cooling to room temperature, and then transferring to a refrigerator at 4°C for recrystallization for 9 h; (5) dissolving xanthan gum in distilled water at a concentration of 0.6 wt% and placing on a magnetic stirrer for overnight stirring for complete dissolution; (6) mixing a starch nanoparticle dispersion prepared in the step (4) with a xanthan gum solution in the step (5), at a mass ratio of the lotus root starch to the xanthan gum of 10:3, to obtain a composite nanoparticle solution; (7) preparation of a crude emulsion: according to a mass ratio of soybean oil to the lotus root starch of 25:1, adding the soybean oil to the composite nanoparticle solution from the step (6) dispersing with a high-speed shear disperser at a rotation speed of 12,000 rpm for 2 min to form the crude emulsion; and (8) ultrasonic emulsification: subjecting the crude emulsion prepared from the step (7) to emulsification using a dual-frequency concentrated energy ultrasonic device; where ultrasonic treatment conditions include: an ultrasonic frequency of 20 kHz, 40 kHz, or 20 / 40 kHz, an ultrasonic power of 400 W / L-2000 W / L, an ultrasonic treatment time of 2 min-10 min, to obtain a final product of the lotus root starch xanthan gum pickering emulsion. Where the preferred ultrasonic treatment conditions in the step (8) include the ultrasonic frequency of 20 / 40 kHz, the ultrasonic power of 1200 W / L, and the ultrasonic treatment time of 4 min. A method of preparing the lotus root starch-xanthan gum Pickering emulsion loaded with fish oil is carried out according to the following steps: (1) dispersing lotus root starch in distilled water at a concentration of 2 wt%, to obtain a starch dispersion liquid; (2) pre-gelatinizing the starch dispersion in boiling water for 5 min with constant stirring to ensure uniform dispersion; (3) immediately transferring a pre-gelatinized starch dispersion from the step (2) to a sterilization pot for pressure-heat treatment at 121°C for 20 min; (4) taking out a pressure-heat treated dispersion from the step (3), naturally cooling to room temperature, and then transferring to a refrigerator at 4°C for recrystallization, where a regeneration time is 9 h; (5) dissolving xanthan gum in distilled water at a concentration of 0.6 wt% and placing on a magnetic stirrer overnight for complete dissolution; (6) mixing a starch nanoparticle dispersion prepared in the step (4) with a xanthan gum solution from the step 5, at a mass ratio of the lotus root starch to the xanthan gum of 10:3, to obtain a composite nanoparticle solution; (7) preparation of a crude emulsion: adding herring oil and orange essential oil to the composite nanoparticle solution from the step (6), and dispersing by a high-speed shear disperser at a rotation speed of 12,000 rpm for 2 min to form the crude emulsion, where a mass ratio of the herring oil to the lotus root starch is 22.5:1-12.5:1 and a mass ratio of the orange essential oil to the lotus root starch is 2.5:1-12.5:1; and (8) ultrasonic emulsification: subjecting the crude emulsion prepared from the step (7) to emulsification using a dual-frequency concentrated energy ultrasonic device, where the ultrasonic treatment conditions include: an ultrasonic frequency of 20 kHz, 40 kHz, or 20 / 40 kHz; an ultrasonic power of 400 W / L-2000 W / L; and an ultrasonic treatment time of 2 min-10 min, to obtain a final product of the Lotus root starch and the Xanthan gum Pickering emulsion. Where a preferred ratio of the herring oil to the lotus root starch in the step (7) is 20:1. Where a preferred ratio of the orange essential oil to the lotus root starch in the step (7) is 5:1. Where preferred ultrasonic treatment conditions in the step (8) include the ultrasonic frequency of 20 / 40 kHz, the ultrasonic power of 1200 W / L, and the ultrasonic treatment time of 4 min. The application of the lotus root starch-xanthan gum Pickering emulsion can be used in the preparation of food, functional food, special medical food, health care products, pharmaceuticals, and cosmetics. The application of lotus root starch-xanthan gum Pickering emulsion loaded with the fish oil can be used in the preparation of food, functional food, special medical food, health care products, pharmaceuticals, and cosmetics. The beneficial effects of the present disclosure are: (1) The present disclosure prepares lotus root starch nanoparticles by the pressure-heat regeneration method, which is a green preparation method with easy operation, a stable product, and no chemical reagents. (2) The present disclosure adds xanthan gum to the starch nanoparticles as a Pickering emulsion stabilizer, which can significantly improve the Pickering emulsion stability. Both are polysaccharides of natural origin that are safe and reliable for consumption. (3) Compared with the expensive high-pressure homogenization method and the micro-jet method, the ultrasonic emulsification method has a simple process operation, low maintenance costs, is suitable for industrial production, and the raw materials and equipment are inexpensive. (4) The lotus root starch nanoparticles of the present disclosure have a particle size of about 243 nm, and the lotus root starch-xanthan gum composite nanoparticles have a particle size of about 486 nm and a potential of -35 mV and have the advantages of small particle size, uniform particle size distribution, good stability, and good biocompatibility. (5) The lotus root starch-xanthan gum Pickering emulsion of the present disclosure has good storage stability, is less affected by environmental conditions such as temperature, pH, ionic strength, etc., and was found to be very stable during storage. However, it can be applied in many fields, such as food, health products, drugs, and cosmetics. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the structure diagram of the dual-frequency concentrated energy type ultrasonic treatment equipment of the present disclosure, where 1 is the controller, 2 is the indicator light, 3 is the ultrasonic generator, 4 is the temperature controller, 5 is the concentrated energy type ultrasonic probe, 6 is the feed liquid outlet, 7 is the constant temperature water inlet, 8 is the thermometer, 9 is the constant temperature water outlet, 10 is the feed liquid inlet, and 11 is the peristaltic pump. FIGS. 2-3 shows the changes in particle size and polydispersion index of lotus root starch in the present disclosure with concentration and time, respectively. Note: Different lowercase English letters in the same index in the figure indicate significant differences between data in the same group (p<0.05). FIG. 4 shows the variations in particle size, poly dispersion index, and £ potential of lotus root starch-xanthan gum composite nanoparticles with the ratio of the two. Note: Different lowercase letters in the figure for the same index indicate significant differences between data in the same group (p<0.05). FIGS. 5A-5E show the scanning electron microscope and transmission electron microscope images of each raw material in the present disclosure. FIG. 6 shows the infrared spectrum diagram of each raw material in the present disclosure. FIG. 7 shows the X-ray diffraction pattern of each raw material in the present disclosure. FIGS. 8A-10B show the particle size and potential diagram of Pickering emulsion under different ultrasonic frequencies, powers, and times. Note: Different lowercase English letters in the same index in the figure indicate significant differences between data in the same group (p<0.05); FIG. 8A, FIG. 9A, and FIG. 10A show the emulsion particle size diagram, and FIG. 8B, FIG. 9B, and FIG. 10B show the emulsion potential diagram. FIGS. 11 A-l ID show optical microscope images of different Pickering emulsions in the present disclosure. FIG. 12 shows confocal laser microscope images of different Pickering emulsions in the present disclosure. FIGS. 13-14 show optical microscope images and appearance images of Pickering emulsion under different conditions of the present disclosure. FIGS. 15A-15B show the particle size and potential diagram of fish oil-loaded Pickering emulsion under different amounts of essential oil in the present disclosure. Note: Different lowercase English letters in the same index in the figure indicate significant differences between data in the same group (p<0.05); FIG. 15A is the emulsion particle size diagram, and FIG. 15B is the emulsion potential diagram. FIG. 16 shows the content of secondary oxidation products after accelerated oxidation of different fish oil Pickering emulsions in the present disclosure. Note: T80-emulsion represents the emulsion stable to Tween 80 in ratio 2; HO-emulsion represents the fish oil-loaded Pickering emulsion stable to ratio 3 of lotus root starch to xanthan gum; HO / MO-emulsion represents the lotus root starch-Xanthan gum stabilized fish oil / orange essential oil Pickering emulsion in Example 11. DETAILED DESCRIPTION OF THE EMBODIMENTS The terms used in the present disclosure are generally understandable by those skilled in the art, unless otherwise specified. The present disclosure is described in further detail with reference to the data. It is hereby clarified that these embodiments are only to illustrate the present disclosure by example and do not limit the scope of the present disclosure in any way. FIG. 1 shows the dual-frequency energy-gathered ultrasonic processing device of the present disclosure. This device can set ultrasonic working parameters (ultrasonic power density, frequency, pulse working time, intermittent time, and total processing time) by controller 1, and the probe of different ultrasonic wave frequencies (20 kHz, 28 kHz, 35 kHz, 40 kHz, and 50 kHz) can be selected when working. Different ultrasonic generators are connected, and single-frequency and dual-frequency ultrasonic processing can be realized. Before ultrasonic treatment with an open thermostat, constant-temperature water is pumped in from a constant-temperature water inlet by peristaltic pump 11, and constant-temperature water outlet 9 is pumped out. During the processing, the feed liquid that needs to be processed is pumped into the treatment tank through the peristaltic pump 11 from the feed liquid inlet 10 and pumped out from the feed liquid outlet 6 to achieve cyclic uniform treatment. The temperature in the treatment tank can be monitored in real time through the thermometer. The lotus root starch used in the present disclosure can be extracted by the lotus root itself, or the finished lotus root starch can be purchased on the market. The extraction method for lotus root starch is as follows: (1) Pretreatment of lotus root: The fresh lotus root is quickly washed, sanded, peeled, weighed, cut into pieces, and soaked in a mixture of 1% NaCl and 0.2% NaHSCh. (2) Beating (the ratio of material to liquid is 1:6) and filtration: the filter slag is soaked in a 0.05% NaOH solution for 40 min, then filtered, and the filtrate is obtained. Then the filter residue is washed with water twice and the filtrate is taken. (3) All the obtained filtrate is centrifuged at 4500 rpm for 10 min to obtain a white solid at the bottom of the centrifuge cup and scrape away the dark impurities on the surface. The cleaning is repeated three times to obtain wet starch, then the wet starch is placed in a 50°C-oven drying for 12 hours, and then grinding with a pulverizer to get lotus root starch. Example 1: The lotus root starch nanoparticles were developed using the following method: (1) Lotus root starch was dispersed in distilled water with concentrations of 1 wt%, 2 wt%, 3 wt%, 4 wt%, and 5 wt%, respectively. (2) The LS suspension was then heated in a boiling water bath for 5 min with constant stirring to ensure uniform dispersion. (3) The LS suspension in step (2) was immediately transferred to the autoclave and kept at 121°C for 20 min. (4) The autoclaved starch paste in step (3) was allowed to cool to room temperature and stored at 4°C for 10 h. Determination method: The particle size and poly dispersion index of lotus root starch nanoparticles were measured by a Litesizer 500 nanoparticle size analyzer. The sample to be measured was diluted 50 times with distilled water and mixed well, and the particle size of the sample was measured at 25°C in a disposable sample cell with a sample refractive index of 1.53 and a solvent refractive index of 1.33. Each sample was measured three times continuously. The particle size and poly dispersity index were used to optimize the concentration of lotus root starch nanoparticle dispersion solution, and the results in FIG. 2 show that with the increase of lotus root starch concentration, the particle size of starch nanoparticles showed a trend of first decreasing and then increasing, and the poly dispersity index was all less than 30%, indicating good dispersion during the test. When the starch concentration was 2 wt%, the particle size and polydispersion index were the smallest, so it was selected to prepare lotus root starch nanoparticles. Example 2: The method of preparing lotus root starch nanoparticles was carried out according to the following steps: (1) Lotus root starch was dispersed in distilled water at a concentration of 2 wt%. (2) The LS suspension was then heated in a boiling water bath for 5 min with constant stirring to ensure uniform dispersion. (3) Immediately transfer the pre-gelatinized starch dispersion in step (2) to a sterilization pot for sterilization treatment under the condition of 121°C for 20 min. (4) The autoclaved starch paste in step (3) was allowed to cool to room temperature and stored at 4°C for 9 h for recrystallization; the time was 8 h, 9 h, 10 h, 11 h, and 12 h, respectively. Determination method: the same as that in Example 1. Particle size and polydispersion index were used to optimize the preparation recovery time of lotus root starch nanoparticles, and the results in FIG. 3 show that the recovery time increases, the particle size of starch nanoparticles decreases first and then increases, and the polydispersion index is less than 30%, indicating good dispersion during the test. When the regeneration time was 9 h, the particle size of the nanoparticles was the smallest, so the regeneration time was 9 h to prepare lotus root starch nanoparticles. Example 3: The method of preparing lotus root starch / xanthan gum nanoparticles was carried out according to the following steps: (1) Lotus root starch (1 g) was dispersed in 300 ml of distilled water. (2) The LS suspension was then heated in a boiling water bath for 5 min with constant stirring to ensure uniform dispersion. (3) The LS suspension in step (2) was immediately transferred to the autoclave and kept at 121 °C for 20 min. (4) The autoclaved starch paste in step (3) was allowed to cool to room temperature and stored at 4°C for 9 hours. (5) Xanthan gum (1 g) was dissolved in 300 mL of distilled water and stirred with a magnetic stirrer overnight for complete dissolution. (6) The 300-mL starch nanoparticle dispersion prepared in step (4) was mixed with 300-mL xanthan gum in step (5) to obtain a composite nanoparticle solution. Example 4: The method of preparing lotus root starch / xanthan gum nanoparticles was prepared according to the following steps: (1) Lotus root starch (20 g) was dispersed in 500 ml of distilled water. (2) The LS suspension was then heated in a boiling water bath for 5 min with constant stirring to ensure uniform dispersion. (3) The LS suspension in step (2) was immediately transferred to the autoclave and kept at 121°C for 20 min. (4) The autoclaved starch paste in step (3) was allowed to cool to room temperature and stored at 4°C for 9 hours. (5) Xanthan gum (20 g) was dissolved in 500 ml of distilled water and stirred with a magnetic stirrer overnight for complete dissolution. (6) The 500-ml starch nanoparticle dispersion prepared in step (4) was mixed with 500-ml xanthan gum in step (5) to obtain a composite nanoparticle solution. Example 5: The preparation method of lotus root starch / xanthan gum nanoparticles was prepared according to the following steps: (1) Lotus root starch (8 g) was dispersed in 400 ml of distilled water. (2) The LS suspension was then heated in a boiling water bath for 5 min with constant stirring to ensure uniform dispersion. (3) The LS suspension in step (2) was immediately transferred to the autoclave and kept at 121°C for 20 min. (4) The autoclaved starch paste in step (3) was allowed to cool to room temperature and stored at 4°C for 9 h. (5) Xanthan gum, 2.4 g, was dissolved in 400 ml of distilled water and stirred with a magnetic stirrer overnight for complete dissolution. (6) The 400-ml starch nanoparticle dispersion prepared in step (4) was mixed with 400-ml xanthan gum in step (5) to obtain a composite nanoparticle solution. Determination method: particle size determination of lotus root starch nanoparticles: The particle size, polydispersion index, and zeta potential of lotus root starch and xanthan gum nanoparticles were measured by the Litesizer 500 nanoparticle size analyzer. The sample to be measured was diluted 50 times with distilled water and mixed well, and the particle size of the sample was measured at 25°C in a disposable sample cell with a sample refractive index of 1.53 and a solvent refractive index of 1.33. Each sample was measured three times continuously. The zeta potential was measured with an Omega II cell, the solvent refractive index was 1.33, and each sample was measured three times continuously. The ratio of starch to xanthan gum in lotus root was optimized by particle size, polydispersion index, and zeta potential, and the results are shown in FIG. 4. With the increase in xanthan gum, the particle size of composite nanoparticles showed an increasing trend, which may be due to the fact that xanthan gum attached to the outside of starch nanoparticles and formed a coating layer. The polydispersion index was lower than 30%, indicating that the particle dispersion was good during the test. The absolute value of the zeta potential of all samples was greater than 30 mV, and there was a large enough repulsion between the particles, indicating that the prepared composite nanoparticles had good stability. With the increase in xanthan gum, the absolute value of the zeta potential of the composite nanoparticles increases first and then decreases. When the ratio of lotus root starch to xanthan gum is 10:3, the absolute value of zeta potential reaches its maximum, and the composite nanoparticles are the most stable. Therefore, the ratio of lotus root starch to xanthan gum was 10:3 to prepare lotus root starch-xanthan gum composite nanoparticles. Experiment Example 1: Characterization of nanoparticles Structure analysis and characterization of lotus root starch, lotus root starch nanoparticles and lotus root starch-Xanthan gum composite nanoparticles: The preparation methods of lotus root starch nanoparticles and lotus root starch-xanthan gum composite nanoparticles in this experiment were carried out according to the steps of Examples 2 and 5, respectively. (1) Scanning electron microscope and transmission electron microscope analysis The silicon wafers were picked up with tweezers and placed on the sample table with conductive glue. The freshly prepared samples were dropped on the silicon wafers and then sprayed with gold for 5 min after air drying. Lotus root starch, lotus root starch nanoparticles and lotus root starch-xanthan gum composite nanoparticles were observed by scanning electron microscopy at 5 kV and 15 kV, respectively. The diluted sample dispersion was dropped on the copper net coated with ultra-thin carbon supporting film, and the excess liquid was absorbed by filter paper. After drying, the lotus root starch nanoparticles and the lotus root starch-xanthan gum composite nanoparticles were observed under transmission electron microscopy at an accelerated voltage of 100 kV. As can be seen from FIGS. 5A-5E, the original lotus root starch is columnar in shape and has a large particle size of about 35 pm. The electron microscopy of lotus root starch nanoparticles showed that the starch nanoparticles with a particle size of 250 nm were successfully obtained by pressure-heat treatment, which also proved the test results of the particle size analyzer. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images of lotus root starch-xanthan gum composite nanoparticles showed that xanthan gum formed a relatively tight network structure among the particles. (2) Fourier transform infrared spectral analysis The infrared spectrum analysis of the sample was performed in the wave number range of 4000 to 500 cm'1 with a resolution of 4 cm'1 and 32 scanning times. The test results were processed and analyzed using OMNIC offline software. As can be seen from FIG. 6, in the FT-IR spectrum of the original lotus root starch, the absorption peak at 3420 cm’1 is mainly caused by the stretching vibration of -OH, the absorption peak at 2931 cm’1 can be attributed to the stretching vibration of -CH2, and the absorption peak at 1648 cm’1 is caused by the bending vibration of the bound water. The absorption peak at 1367 cm’1 is caused by the bending vibration of C-H. In the FT-IR spectra of lotus root starch nanoparticles, the absorption peak was basically consistent with that of the original lotus root starch, but the absorption peak formed by the stretching vibration of the OH moved from 3420 cm’1 to 3412 cm’1 and the peak strength was enhanced. In addition, the absorption peak in the fingerprint region also moved to the short-wave direction, obviously. This suggests that a more stable hydrogen bond interaction may be formed in the lotus root starch nanoparticles. For the FT-IR map of xanthan gum, the characteristic peak appeared at 1732 cm’1, which was the characteristic absorption peak of uronic acid. Compared with the FT-IR spectra of lotus root starch nanoparticles and xanthan gum respectively, the FT-IR spectra of lotus root starch / xanthan gum composite nanoparticles showed no new absorption peaks, indicating that the composite nanoparticles prepared by physical methods did not produce new groups. In addition, in the FT-IR spectra of composite nanoparticles, the absorption peak (3408) caused by the stretching vibration of -OH moved to a shorter wavelength direction than that of lotus root starch nanoparticles (3412) and xanthan gum (3446), indicating that hydrogen bond interaction is the main force between lotus root starch and xanthan gum in the composite nanoparticles. (3) X-ray diffraction analysis The sample was placed in the center of the sample table, pressed, and then tested by X-ray diffraction (XRD) under the test conditions of 5-45° and 5° / min. As can be seen from FIG. 7, the original lotus root starch appeared with crystal peaks at 15°, 17°, 18°, and 23° and was A-type starch. After pressure-heat treatment, starch transforms into type B and peak strength decreases, indicating that pressure-heat treatment can collapse the starch particle structure, destroy the internal crystalline structure, and form nanoscale particles, which supports the observation results of scanning electron microscopy. In addition, xanthan gum has a strong peak at about 12°, but this peak does not appear at the corresponding position of the diffraction pattern of lotus root starch-xanthan gum composite nanoparticles, which may prove the interaction between lotus root starch and xanthan gum and the formation of composite nanoparticles. Example 6: The method of preparing lotus root starch-xanthan gum Pickering emulsion was carried out according to the following steps: (1) Lotus root starch (8 g) was dispersed in 400 ml of distilled water; (2) The LS suspension was then heated in a boiling water bath for 5 min with constant stirring to ensure uniform dispersion. (3) The LS suspension in step (2) was immediately transferred to the autoclave and kept at 121°C for 20 min. (4) The autoclaved starch paste in step (3) was allowed to cool to room temperature and stored at 4°C for 9 hours. (5) Xanthan gum, 2.4 g, was dissolved in 400 ml of distilled water and stirred with a magnetic stirrer overnight for complete dissolution. (6) The 400-ml starch nanoparticle dispersion prepared in step (4) was mixed with 400-ml xanthan gum in step (5) to obtain a composite nanoparticle solution. (7) Preparation of crude emulsions: Soybean oil 200 g was added to 800 ml of the composite nanoparticle solution obtained in step (6) and dispersed with a high-speed disperser at 12,000 rpm for 2 min to form a crude emulsion; (8) Ultrasonic emulsification: The crude emulsion in step (7) was placed in a dual-frequency polygraphic ultrasonic device for emulsification to obtain the final product, Lotus root starch-xanthan gum Pickering emulsion. The ultrasonic power was 800 W / L and the ultrasonic treatment time was 6 min. Optimization of parameters for ultrasonic frequencies of 20 kHz, 40 kHz, and 20 / 40 kHz. Determination method: An apparatus called the Mastersizer 3000 was employed to determine the mean droplet size of the created emulsions. Water served as the dispersant and a generalized analytical mode was employed using the following partial parameters: particles' refractive index of 1.47, particles' absorbance of 0.001, dispersant's refractive index of 1.330, and stirrer speed of 3000 r / min. Three consecutive measurements were taken for each sample. The Zetasizer Nano ZS90 instrument with an Omega II cuvette was used to measure the zeta potential of the emulsion sample, utilizing a solvent refractive index of 1.33. Three consecutive measurements were taken for each sample. The data presented in FIGS. 8A-8B shows that the blank emulsion had the largest average particle size of 19.83±0.55 pm before ultrasonic treatment. However, the emulsion particle size was significantly reduced by ultrasound treatment, particularly when the particle size of the emulsions treated with dual-frequency ultrasound reached a minimum value of 10,50=0,56 pm, which may be due to the ability of dual-frequency ultrasound to overcome the standing wave phenomenon caused by single-frequency ultrasound so that the role of ultrasonic waves can be fully utilized. The particle size distribution graph of the emulsions reveals a small peak at approximately 3 pm after ultrasonic treatment, implying that more small oil droplets appeared in the emulsions, among which the emulsions treated by dual-frequency ultrasonic waves of 20 / 40 kHz had the largest small peak at 3 pm, indicating that the emulsions treated by dual-frequency ultrasonic waves had the largest number of small droplets and the best treatment effect. The stability of an emulsion can be characterized by its ^-potential; the higher the absolute potential, the stronger the repulsive force between droplets, which results in higher spatial potential resistance and greater stability of the emulsion. From FIGS. 8A-8B, we can see that all the emulsions showed negative charging and that the ultrasound treatment resulted in a significant increase in the absolute potential of the emulsions, with the highest absolute potential of 29.90 ± 0.59 mV obtained by the treatment with dual-frequency ultrasound waves, at which time the repulsive force present in the emulsion was the largest and the emulsion was the most stable. Example 7: The method of preparing lotus root starch-xanthan gum Pickering emulsion was carried out according to the following steps: (1) Lotus root starch (8 g) was dispersed in 400 ml of distilled water. (2) The LS suspension was then heated in a boiling water bath for 5 min with constant stirring to ensure uniform dispersion. (3) The LS suspension in step (2) was immediately transferred to the autoclave and kept at 121 °C for 20 min. (4) The autoclaved starch paste in step (3) was allowed to cool to room temperature and stored at 4°C for 9 hours. (5) Xanthan gum, 2.4 g, was dissolved in 400 ml of distilled water and placed on a magnetic stirrer overnight for complete dissolution. (6) The 400-ml starch nanoparticle dispersion prepared in step 4 and the 400-ml xanthan gum solution in step 5 were mixed to obtain the composite nanoparticle solution. (7) Preparation of crude emulsions: Soybean oil 200 g was added to 800 ml of the composite nanoparticle solution obtained in step (6) and dispersed with a high-speed disperser at 12,000 rpm for 2 min to form a crude emulsion. (8) Ultrasonic emulsification: The crude emulsion in step (7) was placed in a dual-frequency polygraphic ultrasonic device for emulsification to obtain the final product, Lotus root starch-xanthan gum Pickering emulsion. The ultrasonic frequency was 20 / 40 kHz, the ultrasonic treatment time was 6 min, and the parameters were optimized for ultrasonic power of 400 W / L, 800 W / L, 1200 W / L, 1600 W / L, and 2000 W / L. Determination method was the same as that in in Example 6. As can be seen from FIGS. 9A-9B, the blank emulsion without ultrasonic treatment has the largest average particle size of 18.53±1.52 pm, and all the emulsions after ultrasonic treatment have a significant reduction in the particle size of the emulsions. The particle size of the emulsions decreases with the increase in the ultrasonic power, which may be due to the fact that with the increase in ultrasonic power, the greater the energy propagated through the treatment tank, which is able to cause more droplets to break up, thus decreasing the particle size of the emulsions. In addition, it can be seen from the particle size distribution graph of the emulsions that a small peak appeared at about 3 pm after ultrasonic treatment, indicating that more smaller oil droplets appeared in the emulsions, among which the distribution of the emulsions treated with 1600 W / L and 2000 W / L had the largest small peak at 3 pm, when the emulsions had the most small droplets, which matched the results of the average particle size test of the emulsions. The (^-potential test results show that all emulsions are negatively charged, and the absolute potential of an emulsion first increases and then decreases with the increase of ultrasonic power. When the ultrasonic power is 1200 W / L, the absolute potential of the emulsion is the largest, reaching 32.58 ± 0.33 mV. At this time, the emulsion has the largest repulsive force, and the emulsion is the most stable. The research shows that when the absolute potential of the emulsion is greater than 30 mV, it can be stable for a long time. Example 8: The method of preparing lotus root starch-xanthan gum Pickering emulsion was carried out according to the following steps: (1) Lotus root starch (8 g) was dispersed in 400 ml of distilled water; (2) The LS suspension was then heated in a boiling water bath for 5 min with constant stirring to ensure uniform dispersion. (3) The LS suspension in step (2) was immediately transferred to the autoclave and kept at 121 °C for 20 min. (4) The autoclaved starch paste in step (3) was allowed to cool to room temperature and stored at 4°C for 9 hours. (5) Xanthan gum, 2.4 g, was dissolved in 400 ml of distilled water and placed on a magnetic stirrer overnight for complete dissolution. (6) The 400-ml starch nanoparticle dispersion prepared in step 4 and the 400-ml xanthan gum solution in step 5 were mixed to obtain the composite nanoparticle solution. (7) Preparation of crude emulsions: Soybean oil 200 g was added to step (6) to obtain 800 mL of composite nanoparticle solution and dispersed with a high-speed disperser at 12,000 rpm for 2 min to form a crude emulsion; (8) Ultrasonic emulsification: The crude emulsion in step (7) was placed in a dual-frequency polygraphic ultrasonic device for emulsification to obtain the final product, Lotus root starch-xanthan gum Pickering emulsion. The ultrasonic frequency was 20 / 40 kHz and the ultrasonic power was 1200 W / L. The parameters were optimized for ultrasonic treatment time of 2 min, 4 min, 6 min, 8 min, and 10 min. Determination method was the same as that in Example 6. As can be seen from FIGS. 10A-10B, the blank emulsion without ultrasonic treatment has the largest average particle size of 19.20±0.66 pm, and all the emulsions after ultrasonic treatment have a significant reduction in the particle size of the emulsions. The particle size of the emulsions decreases with the increase of the ultrasonic treatment time, which may be due to the fact that with the increase in ultrasonic time, it is able to cause more droplets to be broken, which in turn reduces the particle size of the emulsions. In addition, it can be seen from the particle size distribution graph of the emulsions that a small peak appeared at about 3 pm after ultrasonic treatment, indicating that more smaller oil droplets appeared in the emulsions, among which the distribution of the emulsions treated for 8 min and 10 min had the largest small peak at 3 pm, when the emulsions had the smallest droplets, which matched the results of the average particle size test of the emulsions. The (^-potential test results show that all emulsions are negatively charged, and the absolute potential of the emulsion first increases and then decreases with the extension of the ultrasonic treatment time. When the ultrasonic treatment time is 4 min, the absolute potential of the emulsion is the largest, reaching 35.38 ± 0.62 mV. At this time, the emulsion has the largest repulsive force, and the emulsion is the most stable. This may be because prolonged ultrasonic treatment may destroy the gel network structure between particles, reducing the absolute potential and stability of the emulsion. Therefore, in summary, the preferred ultrasonic conditions are 20 / 40 kHz, 1200 W / L, and 4 min. Comparative Example 1: The method of preparing lotus root starch-xanthan gum Pickering emulsion was carried out according to the following steps: (1) Lotus root starch (8 g) was dispersed in 400 ml of distilled water; (2) The LS suspension was then heated in a boiling water bath for 5 min with constant stirring to ensure uniform dispersion. (3) The LS suspension in step (2) was immediately transferred to the autoclave and kept at 121 °C for 20 min. (4) The autoclaved starch paste in step (3) was allowed to cool to room temperature and stored at 4°C for 9 hours. (5) Preparation of crude emulsions: Soybean oil 100 g was added to 400 ml of the composite nanoparticle solution obtained in step (4) and dispersed with a high-speed disperser at 12,000 rpm for 2 min to form a crude emulsion. (6) Ultrasonic emulsification: The crude emulsion in step (5) was placed in a dual-frequency polygraphic ultrasonic device for emulsification to obtain the final product, Lotus root starch Pickering emulsion. The ultrasonic frequency was 20 / 40 kHz, the ultrasonic power was 1200 W / L, and the ultrasonic treatment time was 4 min. Experiment Example 2: Optical microscope observation The preparation method of lotus root starch Pickering emulsion was the same as that in Comparative Example 1. The preparation method of lotus root starch-xanthan gum Pickering emulsion was the same as that in Example 8. 20 pL of the freshly prepared emulsion was dropped on the slide, covered with the cover slide, and placed on the BM2000 optical microscope. The microphotos of the emulsion were taken by the DC6000 camera. As a thermodynamically unstable system, emulsions are usually unstable at different times. Generally speaking, the physical causes of emulsion instability are: milk analysis, flocculation, coalescence, and Oster ripening. Milk precipitation refers to the settlement of milk droplets caused by gravity, which is related to the anti-settlement property of the emulsion system. Stokes' law of sedimentation shows that this gravitational separation can be slowed down by decreasing the particle size of the dispersed phase or increasing the viscosity of the continuous phase. Flocculation is when multiple milk droplets come together to form a floc, but the droplets are still able to maintain their integrity and do not merge, so the phenomenon is reversible. The phenomenon of flocculation occurs when the attractive force between the droplets is greater than the repulsive force, which in the emulsion system is mainly electrostatic force. Coalescence refers to the breakup of the interfacial film of the milk droplet, which changes from several small droplets into one large droplet. This phenomenon is irreversible. In the O / W system, a large agglomeration of droplets eventually forms a separate oil layer on top of the emulsion. Oswald ripening is a phenomenon of coalescence between small droplets and large droplets due to the internal pressure difference between droplets of different sizes. In the phenomenon of emulsion instability, Oswald ripening is one of the reasons that is easily overlooked. In FIGS. 11 A-l ID, sample A is a crude emulsion with stable lotus root starch nanoparticles. As can be seen from the figure, the particle size of the milk droplets is large, and another very obvious feature is the flocculation of the milk droplets. Flocculation between small droplets and small droplets can be seen, as well as multiple small droplets flocculating around large droplets. These flocculations increase the average particle size of the droplets, which enhances gravitational separation and ultimately leads to the stratification of the emulsion. Sample B is a stable emulsion of lotus root starch nanoparticles after ultrasonic treatment. It can be seen from the figure that the particle size of the milk droplets is significantly reduced, which can be attributed to the excellent cavitation and crushing effect of dual-frequency ultrasonic. However, the flocculation phenomenon of the emulsion still exists, which still leads to the rapid stratification of the emulsion. Sample C is a stable, crude emulsion composed of lotus root starch-xanthan gum composite nanoparticles. As can be seen from the figure, the particle size of the milk droplets is still large, but the flocculation phenomenon is significantly improved; the small droplets are more dispersed, and the small droplets and large droplets can also be better dispersed. The reason for this phenomenon may be that the addition of xanthan gum forms a dense three-dimensional network structure in the emulsion system, which can well limit the agglomeration between milk drops, thus improving the flocculation phenomenon of the emulsion and improving the stability of the emulsion. Sample D is the lotus root starch-xanthan Pickering emulsion after ultrasonic treatment. As can be seen from the figure, the particle size of milk droplets has been significantly reduced compared with sample C, and the flocculation phenomenon of milk droplets has been significantly improved, just like in sample C. In summary, the lotus root starch-xanthan gum composite nanoparticles can improve the viscosity of the emulsion and inhibit the phenomenon of milk precipitation caused by gravity. Xanthan gum can also form a three-dimensional network structure in the system, which significantly improves the flocculation phenomenon of milk droplets. Finally, combined with the cavitation crushing effect of the ultrasonic wave, milk droplets with smaller particle sizes are formed, and the stability of Pickering emulsion is greatly improved. Experiment Example 3: Laser confocal microscopy The preparation method of lotus root starch-xanthan gum Pickering emulsion was the same as Example 8. Experimental methods: A Leica TCS SP5 laser confocal system was used to observe the microstructure and interface structure of the emulsion. 5 mg of Nile red and Nile blue were accurately weighed and dissolved in 5 ml of propylene glycol to form a 1 mg / ml staining solution. 50 pL of dye was mixed with 1 ml of freshly prepared emulsion and dyed for 30 min. The 10 pL emulsion sample was dropped on the slide, covered with the cover slide, and sent to the laser confocal system for observation. All images were scanned at a frequency of 200 kHz and a resolution of 1024^ 1024. The excitation wavelength of Nile red was 488 nm and that of Nile blue was 633 nm. In FIG. 12, sample A is a stable, crude emulsion of lotus root starch nanoparticles. It can be seen from the figure that the particle size of the milk droplets is large, which is consistent with the optical microscope observation results. Under a confocal laser microscope, the milk drops are green, and lotus root starch nanoparticles and lotus root starch-xanthan gum composite nanoparticles are red. It can be obviously seen that the red around the green milk droplets in sample A is dark, indicating that the milk droplets adsorb fewer starch nanoparticles. Sample B is a stable emulsion of lotus root starch nanoparticles after ultrasonic treatment, which is consistent with the observation results of optical microscopy. The particle size of the milk droplets is significantly reduced. It is worth noting that the red color around the green milk droplets becomes bright, indicating that more starch nanoparticles are adsorbed by the milk droplets. Sample C was a crude emulsion stabilized by lotus root starch-xanthan gum composite nanoparticles, while sample D was a lotus root starch-xanthan gum Pickering emulsion after ultrasonic treatment. The same phenomenon was repeated in samples C and D. In summary, the laser confocal observation results prove that the dual-frequency ultrasonic wave can not only effectively reduce the particle size of the milk droplet but also enhance the adsorption of particles at the milk droplet interface, so that more particles are gathered on the interface, forming a denser interface film, and avoiding the emulsion instability caused by agglomeration. Experiment Example 4: pH stability analysis The preparation method of lotus root starch-xanthan gum Pickering emulsion was the same as Example 8. Methods: 20 ml of freshly prepared emulsion was taken and the pH 2-8 of the emulsion was adjusted with 0.5 M HC1 and NaOH. The emulsion was stored at room temperature for 30 days, and macro- and micro-monitoring was performed at 1, 7, and 30 days. The optical microscope observation method is the same as that of Embodiment 8. Macro monitoring is recorded by taking photos of mobile phones. FIG. 13 shows that the lotus root starch-Xanthan Pickering emulsion has good stability during the whole 30 days of storage, and no delamination occurs at all pH values. The pH of the freshly prepared emulsion was between 5 and 6. According to the optical microscope observation of the emulsion, the particle size of the lotus root starch-xanthan gum Pickering emulsion has little difference under an acidic condition, but the particle size of the milk drops increases significantly under an alkaline pH of 8, which indicates that an alkaline condition may lead to instability of the emulsion relative to an acidic condition. In addition, the observed results showed that the particle size of milk droplets did not increase significantly at days 1, 7, and 30 of all samples, indicating that the emulsion was very stable, which was attributed to the interfacial adsorption of lotus root starch-xanthan gum composite nanoparticles and the three-dimensional network structure of the system, which effectively overcame the milk precipitation, flocculation, and agglomeration of the emulsion and improved the stability of the emulsion. In addition, dual-frequency ultrasonic treatment can reduce the particle size of the milk droplet, make the emulsion more uniform, and effectively overcome the milk analysis and Oswald curing phenomenon caused by gravity. Experiment Example 5: Analysis of ionic strength stability The preparation method of lotus root starch-xanthan gum Pickering emulsion was the same as Example 8. Methods: NaCl powder was added to freshly prepared emulsions with emulsion ion concentrations of 50 mM, 100 mM, 200 mM, and 300 mM, stored at room temperature for 30 days, and macro- and micro-monitoring was performed at 1, 7, and 30 days. The optical microscope observation method is the same as that of Embodiment 8. Macro monitoring is recorded by taking photos of mobile phones. It can be seen from FIG. 14 that the lotus root starch-Xanthan gum Pickering emulsion has good stability during the whole 30 days of storage, and no stratification phenomenon occurs under all ionic strength conditions. According to the optical microscope observation results of the emulsion, the lotus root starch-xanthan gum Pickering emulsion has a high stability on ionic strength, and the particle size of the milk droplets decreases with the increase in NaCl concentration, indicating that NaCl can improve the stability of the emulsion, which is consistent with the results of other studies. In addition, the observed results showed that the particle size of milk droplets did not increase significantly at days 1, 7, and 30 of all samples, indicating that the emulsion was very stable, which was attributed to the interfacial adsorption of lotus root starch-xanthan gum composite nanoparticles and the three-dimensional network structure of the system, which effectively overcame the milk precipitation, flocculation, and agglomeration of the emulsion and improved the stability of the emulsion. In addition, dual-frequency ultrasonic treatment can reduce the particle size of the milk droplet, make the emulsion more uniform, and effectively overcome the milk analysis and Oswald curing phenomenon caused by gravity. Example 9: The method of preparing lotus root starch-xanthan gum Pickering emulsion loaded with fish oil was carried out according to the following steps: (1) Lotus root starch (1 g) was dispersed in 300 ml of distilled water. (2) The LS suspension was then heated in a boiling water bath for 5 min with constant stirring to ensure uniform dispersion. (3) The LS suspension in step (2) was immediately transferred to the autoclave and kept at 121 °C for 20 min. (4) The autoclaved starch paste in step (3) was allowed to cool to room temperature and stored at 4°C for 9 hours. (5) Xanthan gum (1 g) was dissolved in 300 ml of distilled water and placed on a magnetic stirrer overnight for complete dissolution. (6) The 300-ml starch nanoparticle dispersion prepared in step 4 and the 300-ml xanthan gum solution in step 5 were mixed to obtain the composite nanoparticle solution. (7) Preparation of crude emulsions: Add 150 g of herring oil and 10 g of orange essential oil to 600 ml of the composite nanoparticle solution in step (6) and disperse with a high-speed shear disperser at 12,000 rpm for 2 min to form a crude emulsion. (8) Ultrasonic emulsification: The crude emulsion in step (7) was placed in a dual-frequency polygraphic ultrasonic device for emulsification to obtain the final product, Lotus root starch-Xanthan gum Pickering emulsion. The ultrasonic frequency was 20 / 40 kHz, the ultrasonic power was 1200 W / L, and the ultrasonic treatment time was 4 min. Example 10: The method of preparing lotus root starch-xanthan gum Pickering emulsion loaded with fish oil was carried out according to the following steps: (1) Lotus root starch (20 g) was dispersed in 500 ml of distilled water. (2) The LS suspension was then heated in a boiling water bath for 5 min with constant stirring to ensure uniform dispersion. (3) The LS suspension in step (2) was immediately transferred to the autoclave and kept at 121°C for 20 min. (4) The autoclaved starch paste in step (3) was allowed to cool to room temperature and stored at 4°C for 9 hours. (5) Xanthan gum (20 g) was dissolved in 500 ml of distilled water and placed on a magnetic stirrer overnight for complete dissolution. (6) The 500-ml starch nanoparticle dispersion prepared in step 4 and the 500-ml xanthan gum solution in step 5 were mixed to obtain the composite nanoparticle solution. (7) Preparation of crude emulsions: Add 200 g of herring oil and 50 g of orange essential oil to 1000 ml of the composite nanoparticle solution in step (6) and disperse with a high-speed shear disperser at 12,000 rpm for 2 min to form a crude emulsion. (8) Ultrasonic emulsification: The crude emulsion in step (7) was placed in a dual-frequency polygraphic ultrasonic device for emulsification to obtain the final product, Lotus root starch-Xanthan gum Pickering emulsion. The ultrasonic frequency was 20 / 40 kHz, the ultrasonic power was 1200 W / L, and the ultrasonic treatment time was 4 min. Example 11: The method of preparing lotus root starch-xanthan gum Pickering emulsion loaded with fish oil was carried out according to the following steps: (1) Lotus root starch (8 g) was dispersed in 400 ml of distilled water. (2) The LS suspension was then heated in a boiling water bath for 5 min with constant stirring to ensure uniform dispersion. (3) The LS suspension in step (2) was immediately transferred to the autoclave and kept at 121°C for 20 min. (4) The autoclaved starch paste in step (3) was allowed to cool to room temperature and stored at 4°C for 9 hours. (5) Xanthan gum, 2.4 g, was dissolved in 400 ml of distilled water and placed on a magnetic stirrer overnight for complete dissolution. (6) The 400-ml starch nanoparticle dispersion prepared in step 4 and the 400-ml xanthan gum solution in step 5 were mixed to obtain the composite nanoparticle solution. (7) Preparation of crude emulsions: Add 160 g of herring oil and 40 g of orange essential oil to 800 ml of the composite nanoparticle solution in step (6) and disperse with a high-speed shear disperser at 12,000 rpm for 2 min to form a crude emulsion. (8) Ultrasonic emulsification: The crude emulsion in step (7) was placed in a dual-frequency polygraphic ultrasonic device for emulsification to obtain the final product, Lotus root starch-Xanthan gum Pickering emulsion. The ultrasonic frequency was 20 / 40 kHz, the ultrasonic power was 1200 W / L, and the ultrasonic treatment time was 4 min. Determination method was the same as that in Example 6. As can be seen from FIGS. 15A-15B, the average particle size of Pickering emulsion increased with the addition of essential oil. However, the absolute potential of the emulsion showed a tendency to increase and then decrease with the increase in the amount of essential oil added, and when the amount of essential oil added was 20% of the total oil phase, the absolute potential of the emulsion was the largest, reaching 39.53=1.31 mV, at which time the repulsive force present in the emulsion was the largest and the emulsion was the most stable. This suggests that essential oils can modulate the physicochemical properties of the emulsion interface and improve the stability of the emulsion. Therefore, the ratio of essential oil to fish oil of 8:2 was chosen to prepare Pickering emulsion. Comparative Example 2: A method of preparing an emulsion stabilized with Tween 80 as a control was as follows: (1) Tween-80 (8 g) was dispersed in 400 ml of distilled water. (2) Preparation of crude emulsion: 100 g of soybean oil was added to 400 ml of Tween-80 solution in step (1) and dispersed with a high-speed disperser at 12000 rpm for 2 min to form a crude emulsion. (3) Ultrasonic emulsification: The crude emulsion from step (2) was placed in a dual-frequency polygraphic ultrasonic device for emulsification to obtain the final finished Lotus root starch Pickering emulsion. The ultrasonic frequency was 20 / 40 kHz, the ultrasonic power was 1200 W / L, and the ultrasonic treatment time was 4 min. Comparative Example 3: The fish oil-loaded lotus root starch-xanthan gum Pickering emulsion without added essential oil as a control was prepared as follows: (1) Lotus root starch (8 g) was dispersed in 400 ml of distilled water. (2) Pregelatinize the starch dispersion in boiling water for 5 min with constant stirring to ensure uniform dispersion. (3) The starch dispersion pre-gelatinized in step (2) was immediately transferred to a sterilizer for pressure-heat treatment at 121 °C for 20 min. (4) The dispersion, which was pressure-heat-treated in step (3), was removed, naturally cooled to room temperature, and then transferred to a 4°C refrigerator for recrystallization, with a regrowth time of 9 hours. (5) Xanthan gum, 2.4 g, was dissolved in 400 ml of distilled water and placed on a magnetic stirrer overnight for complete dissolution. (6) The 400-ml starch nanoparticle dispersion prepared in step 4 and the 400-ml xanthan gum solution in step 5 were mixed to obtain the composite nanoparticle solution. (7) Preparation of crude emulsions: Add 200 g of herring oil to 800 ml of the composite nanoparticle solution in step (6) and disperse with a high-speed shear disperser at 12,000 rpm for 2 min to form a crude emulsion. (8) Ultrasonic emulsification: The crude emulsion in step (7) was placed in a dual-frequency polygraphic ultrasonic device for emulsification to obtain the final product, Lotus root starch-Xanthan gum Pickering emulsion. The ultrasonic frequency was 20 / 40 kHz, the ultrasonic power was 1200 W / L, and the ultrasonic treatment time was 4 min. Experiment Example 6: Determination of oxidation stability The preparation method of the Tween 8 stabilized emulsion was the same as that in Example 2. The preparation method of lotus root starch-xanthan Pickering emulsion loaded with fish oil without adding essential oil was the same as that in Example 3. The preparation method of lotus root starch-xanthan gum Pickering emulsion loaded with fish oil was the same as that in Example 11. The temperature stability of the oil in the emulsion was investigated using the Skal oven method, and the samples of different emulsions were oxidized at 65°C for 24 h. Different emulsion samples were irradiated under an ultraviolet lamp for 24 hours to investigate the light stability of the oil in the emulsion. Samples of different emulsions were left at room temperature for 30 days to investigate the storage stability of the oil in the emulsions. Methods: Determination of oxidation products: Oxidation products are characterized by the content of malondialdehyde (MDA). The 1.0 mL emulsion was mixed with 2.0 mL thiobarbituric acid solution (TBA), heated in a boiling water bath for 20 min, and then centrifuged at 1000 g for 10 min after cooling. The absorption value of the supernatant was measured at 532 nm. The standard curve is drawn using 1, 1,3, and 3-tetraethoxypropane to calculate the TBARS value of the sample. As can be seen from FIG. 16, the oxidation degree of fish oil in the emulsion stabilized by the traditional surfactant TWEEN 80 is the highest under the conditions of heat, light, and storage and is one order of magnitude higher than that in the Pickering emulsion stabilized by lotus root starch-xanthan gum composite nanoparticles. This shows that the lotus root starch-xanthan gum composite nanoparticles form a dense protective layer on the surface of oil droplets, which can effectively block the contact between oil droplets and oxygen and greatly reduce the oxidation of oil. Some studies have also shown that xanthan gum has the effect of chelating metal ions, which is another important reason for the composite nanoparticles to protect fish oil from oxidation. In addition, the addition of essential oil to the fish oil can further reduce the oxidation products of the emulsion and protect the fish oil from oxidation, which can be attributed to the antioxidant effect of orange essential oil. Experiment Example 7: Determination of DHA and EPA retention The preparation method of the Tween 8 stabilized emulsion was the same as that in Example 2. The preparation method of lotus root starch-xanthan Pickering emulsion loaded with fish oil without adding essential oil is the same as that in Example 3. The preparation method of lotus root starch-xanthan gum Pickering emulsion loaded with fish oil was the same as that in Example 11. The retention rates of DHA and EPA in the emulsion were determined by GC-MS. Extraction of fatty acids from the emulsion: Take 1 mL of emulsion with a pipette and place it in a liposuction bottle; add 10 mL of 65= EC water; shake and dissolve the sample; and disperse the sample evenly. Then add 2 mL of ammonia with a volume fraction of 25%, water bath at 65°C for 15 min, take out slightly oscillating, and cool to room temperature. Then add 10 mL of ethanol to the liposuction bottle, shake well, add 25 mL of ether, cover, and shake. Finally, 25 mL of petroleum ether was added (30°C to 60°C), and the lid was shaken. The upper organic layer is transferred to a ground flask and concentrated to dry by a rotary evaporator. Methyl ester (base catalysis method): Add 30 mL of n-hexane into the flask after spinning; after full oscillation, transfer to a 50 mL volumetric flask with n-hexane at constant volume to obtain the total oil reserve liquid. Take 2 mL of reserve solution into a test tube with a plug, add 0.2 mL of KOH-methanol solution (2 mol / L), fully shake, centrifuge at 5000 rpm for 5 min, and take the upper organic phase. Finally, the sample was added to the temperament sample bottle through a 0.22pm filter membrane and analyzed by GC-MS. GC conditions: inlet temperature is 250°C; the heating procedure is to hold at 50°C for 2 min, start to heat up, rise to 320°C at 7°C / min, and hold for 5 min. The constant speed mode was adopted, the flow rate was 1 mL / min, and the shunt ratio was 1:10. The sample size was 1 pL, the carrier gas was He, and the column name was DB-5 MS. MS condition: ion source temperature 230°C; interface temperature 250°C. The quality scanning range is 50 to 700 m / z, and the solvent delay time is set to 6 min. Component analysis: Qualitative analysis was performed by NIST database searches and comparisons of standard spectrograms to identify DHA and EPA methyl ester components in samples. The area normalization method was used to determine the percentage of DHA and EPA in quantitative analysis. Table 1 Retention rates of DHA and EPA in emulsion treated with accelerated oxidation (65°C, 5 h) Emulsion T80-emulsion HO-emulsion HO / MO-emulsion EPA 87.19% 92.58% 95.88% DHA 89.30% 95.39% 96.14% (The T80-emulsion in the table represents a stable emulsion with a ratio of 2 to Tween 80; HO-emulsion represents a stable herring oil Pickering emulsion with a ratio of 3 medium lotus root starch to xanthan gum; HO / MO-emulsion represents the lotus root starch-Xanthan gum stabilized herring oil / Orange essential oil Pickering emulsion in Example 7.) It can be seen from Table 1 that the fish oil emulsion stabilized by the traditional surfactant T80 has the lowest retention rate of DHA and EPA because it does not have any protection against DHA and EPA. The DHA and EPA retention rates of fish oil Pickering emulsion stabilized by lotus root starch-xanthan gum composite nanoparticles have been significantly improved, which can be attributed to the fact that the composite nanoparticles form a dense shell on the surface of the oil droplets, reducing their contact with oxygen, although at higher temperatures. The retention rate of DHA and EPA in the emulsion can also maintain a high level. When orange essential oil was added to fish oil, the retention rate of DHA and EPA in Pickering emulsion stabilized by lotus root starch-xanthan gum composite nanoparticles was further improved, possibly because orange essential oil was dispersed in the oil phase as an antioxidant, which could further protect DHA and EPA in the emulsion.

Claims

1. A preparation method of a lotus root starch-xanthan gum Pickering emulsion, characterized by comprising the following steps:(1) dispersing lotus root starch in distilled water at a concentration of 2 wt%, to obtain a starch dispersion liquid;(2) pre-gelatinizing the starch dispersion liquid in boiling water for 5 min and constantly stirring to ensure uniform dispersion;(3) immediately transferring a pre-gelatinized starch dispersion from the step (2) to a sterilization pot, to conduct a pressure-heat treatment at 121°C for 20 min;(4) taking out a pressure-heat treated dispersion from the step (3), cooling naturally to room temperature, and then transferring to a refrigerator at 4°C for recrystallization for 9 h;(5) dissolving xanthan gum in distilled water at a concentration of 0.6 wt% with stirring on a magnetic stirrer overnight for complete dissolution;(6) mixing a starch nanoparticle dispersion prepared in the step (4) with a xanthan gum solution from the step (5), at a mass ratio of the lotus root starch to the xanthan gum of 10:3, to obtain a composite nanoparticle solution;(7) preparation of a crude emulsion: according to a mass ratio of soybean oil to the lotus root starch of 25:1, adding the soybean oil to the composite nanoparticle solution from the step (6), dispersing with a high-speed shear disperser at 12000 rpm for 2 min to form the crude emulsion; and(8) ultrasonic emulsification: subjecting the crude emulsion prepared from the step (7) to emulsification using a dual-frequency concentrated energy ultrasonic device, wherein ultrasonic treatment conditions for obtaining a final Pickering emulsion stabilized with the lotus root starch and the Xanthan gum comprise: an ultrasonic frequency of 20 kHz, 40 kHz, or 20 / 40 kHz, an ultrasonic power ranging from 400 W / L to 2000 W / L, and an ultrasonic treatment time ranging from 2 min to 10 min.

2. The preparation method of the lotus root starch-xanthan gum Pickering emulsion according to claim 1, characterized in that, in the step (8), the ultrasonic treatment conditions comprise: the ultrasonic frequency of 20 / 40 kHz, the ultrasonic power of 1200 W / L, and the ultrasonic treatment time of 4 min.

3. A preparation method of a lotus root starch-xanthan Pickering emulsion loaded with fish oil, characterized by comprising the following steps:(1) dispersing lotus root starch in distilled water at a concentration of 2 wt%, to obtain a starch dispersion liquid;(2) pre-gelatinizing the starch dispersion liquid in boiling water for 5 min and constantly stirringto ensure uniform dispersion;(3) immediately transferring a pre-gelatinized starch dispersion from the step (2) to a sterilization pot, to conduct a pressure-heat treatment at 121 °C for 20 min;(4) taking out a pressure-heat treated dispersion from the step (3), cooling to room temperature naturally, and then transferring to a refrigerator at 4°C for recrystallization, wherein a regeneration time is 9 h;(5) dissolving xanthan gum in distilled water at a concentration of 0.6 wt% with stirring on a magnetic stirrer overnight for complete dissolution;(6) mixing a starch nanoparticle dispersion prepared in the step (4) with a xanthan gum solution from the step (5), at a mass ratio of the lotus root starch to the xanthan gum of 10:3, to obtain a composite nanoparticle solution;(7) preparation of a crude emulsion: adding herring oil and orange essential oil into the composite nanoparticle solution from the step (6) and dispersing by a high-speed shear disperser at 12000 rpm for 2 min to form the crude emulsion, wherein a mass ratio of the herring oil to the lotus root starch is 22.5:1-12.5:1, and a mass ratio of the orange essential oil to the lotus root starch is 2.5:1-12.5:1; and(8) ultrasonic emulsification: placing the crude emulsion from the step (7) in a dual-frequency concentrated energy ultrasonic device for an ultrasonic treatment at an ultrasonic frequency of 20 kHz, 40 kHz, or 20 / 40 kHz, an ultrasonic power of 400 W / L-2000 W / L, and an ultrasonic treatment time of 2 min-10 min, to obtain a final Pickering emulsion stabilized with the lotus root starch and the Xanthan gum.

4. The preparation method of the lotus root starch-xanthan Pickering emulsion loaded with the fish oil according to claim 3, characterized in that, a ratio of the herring oil to the lotus root starch in the step (7) is 20:1.

5. The preparation method of the lotus root starch-xanthan Pickering emulsion loaded with the fish oil according to claim 3, characterized in that, a ratio of the orange essential oil to the lotus root starch in the step (7) is 5:1.

6. The preparation method of the lotus root starch-xanthan Pickering emulsion loaded with the fish oil according to claim 3, characterized in that, the ultrasonic frequency in the step (8) is 20 / 407. The preparation method of the lotus root starch-xanthan Pickering emulsion loaded with the fish oil according to claim 3, characterized in that, the ultrasonic power in the step (8) is 1200 W / L.

8. The preparation method of the lotus root starch-xanthan Pickering emulsion loaded with the fish oil according to claim 3, characterized in that, the ultrasonic treatment time in the step (8) is 4 min.

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