A method for preparing Pickering emulsion using esterified starch and its application in food preservation

Abstract

The present invention provides a method for preparing Pickering emulsion with esterified starch and its application in food preservation, belonging to the technical field of preparation of granular emulsifiers and their application. Corn starch is dissolved in dimethyl sulfoxide, 3,6-dimethylphthalic anhydride is added with stirring, reacted, eluted, dried, crushed and sieved to obtain esterified corn starch; esterified corn starch is used as a granular stabilizer to prepare an aqueous suspension, an oil phase is added, and homogenization is performed to obtain a Pickering emulsion that can remain stable after storage for 50 days, which can significantly reduce the particle size of starch particles, and provide a modification method for stabilizing Pickering emulsion with modified starch, which has a simple process, a wide source of raw materials, and a low cost, and the emulsion has good emulsification performance and high stability. In addition, the Pickering emulsion prepared with esterified starch is applied to food preservation, especially in food cling film or preservatives. The food cling film can extend the shelf life of fresh pork to 10 days at 4°C, which provides an effective prerequisite for food safety.

Description

Technical Field

[0001] The invention relates to a method for preparing a Pickering emulsion, in particular to a method for preparing a Pickering emulsion by using esterified starch and application thereof in food preservation, belonging to the technical field of preparation of granular emulsifiers and application thereof. Background Art

[0002] More than a century ago, solid particles were used as stabilizers for oil droplets in water (Binks, BP (2002). Particles as surfactants-similarities and differences. Current Opinion in Colloid & Interface Science, 7 , 21-41.). In the past two decades, a lot of research has been conducted to replace traditional molecular-based emulsifiers by using inorganic particles such as metal hydroxides, silica, and clay. These solid particles adsorb on the oil-water interface to form a mechanical barrier that effectively prevents droplet merging (Cui, F., Zhao, S., Guan, X., McClements, DJ, Liu, X., Liu, F., & Ngai, T. (2021). Polysaccharide-based Pickering emulsions: Formation, stabilization and applications. Food Hydrocolloids, 119.). However, due to hydrophobic and electrostatic interactions, emulsions stabilized by these solid particles are relatively easy to aggregate or precipitate. In addition, although some inorganic particles are approved for limited use in food, medicine, and cosmetics, they are still unacceptable and avoided due to problems such as irritation, tissue damage, and environmental impact (Berton-Carabin, CC, & Schroen, K. (2015). Pickeringemulsions for food applications: background, trends, and challenges. Annu RevFood Sci Technol, 6, 263-297.). In view of this, finding renewable, sustainable, clean-label, and environmentally friendly biopolymer particles is a current challenge and research trend.

[0003] So far, various protein- and polysaccharide-based particulate emulsifiers, such as zein, soy protein, β-lactoglobulin, cellulose derivatives, chitin nanoparticles, etc., have played a key role, including improving emulsion stability, controlling, releasing, enhancing bioactive ingredients in food and medicine, and regulating lipid digestion. In addition, starch granules are widely used in the preparation and application of Pickering emulsions due to their GRAS (generally recognized as safe), non-allergenicity, abundant content, and low price.

[0004] Starch is a natural polysaccharide with abundant sources. Corn, rice, wheat, potatoes, cassava, etc. all contain different amounts of starch. Among them, corn is the largest source of starch. At the same time, corn is one of the three major food crops in the world. Its grains contain nutrients that are essential to human health, such as starch (70%), protein (12%) and some trace elements.

[0005] Natural corn starch is not hydrophobic and difficult to adsorb at the oil-water interface to form a stable emulsion (Yu, ZY, Jiang, SW, Zheng, Z., Cao, XM, Hou, ZG, Xu, JJ, Wang, HL, Jiang, ST, & Pan, LJ (2019). Preparation and properties of OSA-modified tarostarches and their application for stabilizing Pickering emulsions. Int JBiol Macromol, 137, 277-285.). Therefore, physical and chemical modifications are often used to increase its hydrophobicity so that it has a higher affinity at the oil-water interface. Among them, the commonly used chemical modifications are: esterification, etherification, oxidation, acid treatment, hydroxypropylation and cross-linking (Agama-Acevedo, E., & Bello-Perez, LA (2017). Starch as an emulsionsstability: the case of octenyl succinic anhydride (OSA) starch. Current Opinion in Food Science, 13, 78-83.).

[0006] Esterification is a good method for modifying starch granules for stabilizing Pickering emulsions. The reactants for esterification modification include octenyl succinic anhydride (OSA), dodecenyl succinic anhydride, acetic anhydride, phthalic anhydride and fatty acids, among which OSA is the most widely used. OSA modification is highly efficient in improving hydrophobicity, and the modified products are safe and reliable, but the US Food and Drug Administration (FDA) limits the content of OSA to 3% (w / w starch base) (Wang, J., Su, L., & Wang, S. (2010). Physicochemical properties of octenyl succinic anhydride-modified potato starch with different degrees of substitution. J Sci Food Agric, 90(3), 424-429.). Moreover, for most starch granules, OSA-modified starch (≤3%, w / w starch base) cannot be used to prepare stable Pickering emulsions (Song, X., Pei, Y., Qiao, M., Ma, F., Ren, H., & Zhao, Q. (2015). Preparation and characterizations of Pickering emulsions stabilizedby hydrophobic starch particles. Food Hydrocolloids, 45, 256-263.), thus limiting its application in food and medicine.

[0007] In addition, the prior art CN106832350A discloses a "method for preparing a Pickering emulsion stabilized by starch nanoparticles", which includes selecting starch with a linear content of 20-40%, titrating with anhydrous ethanol after gelatinization, centrifuging, freeze-drying the precipitate to obtain starch nanoparticles, and adding the starch nanoparticles to an oil-water mixture to prepare a Pickering emulsion. CN110358759A discloses a "Pickering emulsion encapsulating lipase and a preparation method thereof", wherein modified starch is used as a particle stabilizer, specifically esterification modification of the gelatinized starch by 3,6-dimethylphthalic anhydride, granulation, to obtain esterified nanoparticles; then coupling reaction with methoxysilane to perform hydrophobic modification; then dispersing it in an organic solution as an oil phase, mixing it with the water phase of the lipase solution, and stirring to obtain a stable Pickering emulsion.

[0008] However, the prior art still has the following technical problems: the emulsification performance of the prepared Pickering emulsion cannot be guaranteed, and its stability is poor. Summary of the invention

[0009] The present invention aims to overcome the shortcomings of the prior art and proposes a method for preparing Pickering emulsion with esterified starch and its application in food preservation. This technical solution can significantly reduce the particle size of natural starch, ensure simple process, wide source of raw materials, low cost, and the emulsion stabilized by the esterified modified corn starch can have an emulsification index of up to 100% and a storage stability of 50 days. In addition, the Pickering emulsion prepared with esterified starch is used in food preservation, especially in chitosan active film (food cling film) or preservatives. The food cling film can extend the shelf life of fresh pork to 10 days at 4°C, which provides an effective prerequisite for food safety.

[0010] In order to achieve the above technical objectives, the following technical solutions are proposed:

[0011] On the one hand, the present technical solution provides: a method for preparing Pickering emulsion by esterifying starch, comprising the following steps:

[0012] 1) Dissolution: corn starch is used as raw material and dissolved in dimethyl sulfoxide solvent to obtain a corn starch-dimethyl sulfoxide solution with a mass fraction of 10-15%;

[0013] 2) Esterification: add esterification modifier 3,6-dimethylphthalic anhydride to corn starch-dimethyl sulfoxide solution, stir at 85-95°C, react for 1-3h, cool to 30-40°C, wash, dry, crush and sieve to obtain esterified corn starch particles;

[0014] 3) Preparation: The obtained esterified corn starch particles are dissolved in deionized water to prepare a water suspension with a mass fraction of 0.5-3.0%; then, an oil phase is added and homogenized to obtain a Pickering emulsion.

[0015] Preferably, in step 2), the amount of 3,6-dimethylphthalic anhydride added is 2.5-7.5% (w / w) based on the dry weight of corn starch.

[0016] Preferably, in step 2), the stirring speed is 175-225 rpm / min.

[0017] Preferably, in step 2), the degree of substitution of the esterified corn starch granules is 0.036-0.072, and more preferably, the degree of substitution of the esterified corn starch granules is 0.072.

[0018] Preferably, in step 2), an excess of anhydrous ethanol is used for elution 3-4 times, and the mixture is freeze-dried at -50°C for 24-36 hours, crushed, and passed through a 100-mesh sieve.

[0019] Preferably, in step 3), the oil phase is cinnamon essential oil, and the volume fraction of the oil phase is 10%.

[0020] Preferably, in the homogenization of step 3), the speed is 11000-21000 rpm / min, and the homogenization time is 1-3 min.

[0021] On the other hand, the technical solution provides: application of Pickering emulsion prepared with esterified starch in food preservation.

[0022] Preferably, the application includes using the Pickering emulsion to prepare food preservative film or preservative.

[0023] The preferred method for preparing the food preservative film comprises:

[0024] Dissolve chitosan in acetic acid solution, remove bubbles, add glycerol and Pickering emulsion, stir, and form a film-forming solution;

[0025] The bubbles are removed again, and then the film-forming solution is cast on a mold by a casting method and dried to obtain a food preservative film.

[0026] In the present technical solution, the prepared Pickering emulsion has an emulsification index of 34.69-100%, a uniform droplet size distribution, D [4,3] of 8.50-15.79 μm, and remains stable after storage for 50 days.

[0027] In the present technical solution, the corn starch involved is natural corn starch.

[0028] The beneficial technical effects brought about by adopting this technical solution are:

[0029] 1. The present invention uses 3,6-dimethylphthalic anhydride to esterify corn starch. Compared with other modification methods, this modification method can significantly reduce the particle size of corn starch, ensuring that the corn starch particles with smaller particle sizes are conducive to stabilizing the particles, that is, improving the stability of the Pickering emulsion; at the same time, it can significantly improve the hydrophobicity of corn starch, that is, improve the emulsification performance of starch. In addition, the present invention controls the addition amount of 3,6-dimethylphthalic anhydride to 2.5-7.5% of the dry weight of corn starch to obtain esterified corn starch particles with a degree of substitution of 0.036-0.072, and obtains a stable Pickering emulsion with good emulsification performance and high stability. For example, the esterified corn starch particles with a degree of substitution of 0.084 will produce a large amount of foam in the prepared stable Pickering emulsion, that is, the esterified corn starch particles with a high degree of substitution are more likely to self-aggregate in water, resulting in incomplete contact at the oil-water interface, etc.;

[0030] Second, in the present invention, the raw material corn starch involved is abundant in source, cheap and low in cost;

[0031] 3. The present invention relates to a simple process, good Pickering emulsion emulsification performance (emulsification index is 34.69-100%), D[4,3] is 8.50-15.79 μm, droplet size distribution is uniform, and stability is strong. The Pickering emulsion can be stored at room temperature for 50 days and still remain stable;

[0032] 4. In the present invention, the prepared Pickering emulsion is used for food preservation, especially in the application in chitosan active film (food cling film) or preservative. The food cling film can extend the shelf life of fresh pork to 10 days at 4°C, which provides an effective prerequisite for food safety. In the preparation method of the food cling film, chitosan has good film-forming properties and is expected to replace plastic (which has great environmental problems) for food packaging, but its limited antibacterial activity hinders practical application. For this reason, the present invention adds active antibacterial substances to chitosan to increase the antibacterial properties. Among them, cinnamon essential oil (CEO) is safe and non-toxic, and has good antibacterial and antioxidant activities, but cinnamon essential oil is volatile and hydrophobic, while chitosan is hydrophilic. Therefore, cinnamon essential oil is embedded in Pickering emulsion to improve the dispersibility of cinnamon essential oil in chitosan film, and to enhance compatibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The infrared spectra of esterified corn starch granules and native corn starch;

[0034] Figure 2 is the particle size distribution diagram of esterified corn starch particles and native corn starch;

[0035] Figure 3 The three-phase contact angle diagram of esterified corn starch particles and native corn starch;

[0036] Figure 4 The effect of the addition amount of 3,6-dimethylphthalic anhydride on the degree of substitution of esterified corn starch particles (a: 0.0066; b: 0.019; c: 0.036, d: 0.072);

[0037] Figure 5 The infrared spectra of esterified corn starch particles with different degrees of substitution (where natural corn starch is used as a control);

[0038] Figure 6 The three-phase contact angle diagram of esterified corn starch particles with different degrees of substitution (where natural corn starch is used as a control);

[0039] Figure 7 The appearance of the Pickering emulsion stability stabilized by esterified corn starch particles with different mass fractions;

[0040] Figure 8The emulsification index diagram of Pickering emulsion stabilized by esterified corn starch particles with different mass fractions;

[0041] Fig. 9 The particle size distribution diagram of Pickering emulsion stabilized by esterified corn starch particles with different mass fractions;

[0042] Fig.10 Confocal microscopy images of Pickering emulsions stabilized by esterified corn starch particles with different mass fractions;

[0043] Fig.11 Apparent viscosity diagram of Pickering emulsion stabilized by esterified corn starch particles with different mass fractions;

[0044] Fig.12 This is the change diagram of volatile basic nitrogen content of fresh pork with different treatments during storage;

[0045] Fig.13 This is a graph showing changes in total colony count during storage of fresh pork with different treatments. DETAILED DESCRIPTION

[0046] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] Example 1

[0048] This embodiment proposes a method for preparing a Pickering emulsion stabilized by esterified corn starch particles, comprising:

[0049] Preparation of esterified modified corn starch granules: 50 g corn starch (purchased directly from Xi'an Guowei Starch Co., Ltd., China) was dissolved in a 12.5% ​​mass fraction of dimethyl sulfoxide aqueous solution, and 3,6-dimethylphthalic anhydride (the addition amount was 7.5% of the dry weight of corn starch) was added while stirring. The stirring speed was controlled at 200 rpm / min. Under the condition of a water bath temperature of 85°C, the reaction time was 1 hour, and the mixture was cooled to 40°C. After elution, drying, crushing and sieving, hydrophobic esterified corn starch granules with a degree of substitution of 0.068 were obtained.

[0050] Preparation of Pickering emulsion: The esterified corn starch particles obtained by esterification modification were dissolved in deionized water to prepare 18 mL of water suspension (the mass fraction of esterified corn starch was 0.5%), 2 mL of cinnamon essential oil was added as the oil phase, and homogenized for 1 min at a rotation speed of 11000 rpm / min to obtain Pickering emulsion.

[0051] Example 2

[0052] This embodiment proposes a method for preparing a Pickering emulsion stabilized by esterified corn starch particles, comprising:

[0053] Preparation of esterified modified corn starch granules: 50 g corn starch (purchased directly from Xi'an Guowei Starch Co., Ltd., China) was dissolved in a 12.5% ​​mass fraction of dimethyl sulfoxide aqueous solution, and 3,6-dimethylphthalic anhydride (the addition amount was 7.5% of the dry weight of corn starch) was added while stirring. The stirring speed was controlled at 200 rpm / min. The reaction time was 2 h under a water bath temperature of 85 °C. The mixture was cooled to 35 °C, eluted, dried, crushed and sieved to obtain hydrophobic esterified corn starch granules with a degree of substitution of 0.070.

[0054] Preparation of Pickering emulsion: The esterified corn starch particles obtained by esterification modification were dissolved in deionized water to prepare 18 mL of water suspension (the mass fraction of esterified corn starch was 1.0%), 2 mL of cinnamon essential oil was added as the oil phase, and homogenized for 2 min at a rotation speed of 16000 rpm / min to obtain Pickering emulsion.

[0055] Example 3

[0056] This embodiment proposes a method for preparing a Pickering emulsion stabilized by esterified corn starch particles, comprising:

[0057] Preparation of esterified modified corn starch granules: 50 g corn starch (purchased directly from Xi'an Guowei Starch Co., Ltd., China) was dissolved in a 12.5% ​​mass fraction of dimethyl sulfoxide aqueous solution, and 3,6-dimethylphthalic anhydride (the addition amount was 7.5% of the dry weight of corn starch) was added while stirring. The stirring speed was controlled at 200 rpm / min. The reaction time was 2 h under a water bath temperature of 90 ° C. The mixture was cooled to 30 ° C. After elution, drying, crushing and sieving, hydrophobic esterified corn starch granules with a degree of substitution of 0.066 were obtained.

[0058] Preparation of Pickering emulsion: The esterified corn starch particles obtained by esterification modification were dissolved in deionized water to prepare 18 mL of water suspension (the mass fraction of esterified corn starch was 2.0%), 2 mL of cinnamon essential oil was added as the oil phase, and homogenized for 3 min at a rotation speed of 21000 rpm / min to obtain Pickering emulsion.

[0059] Example 4

[0060] This embodiment proposes a method for preparing a Pickering emulsion stabilized by esterified corn starch particles, comprising:

[0061] Preparation of esterified modified corn starch granules: 50 g corn starch (purchased directly from Xi'an Guowei Starch Co., Ltd., China) was dissolved in a 12.5% ​​mass fraction of dimethyl sulfoxide aqueous solution, and 3,6-dimethylphthalic anhydride (the addition amount was 7.5% of the dry weight of corn starch) was added while stirring. The stirring speed was controlled at 200 rpm / min. The reaction time was 3 h under a water bath temperature of 95 ° C. The mixture was cooled to 40 ° C. After elution, drying, crushing and sieving, hydrophobic esterified corn starch granules with a degree of substitution of 0.064 were obtained.

[0062] Preparation of Pickering emulsion: The esterified corn starch particles obtained by esterification modification were dissolved in deionized water to prepare 18 mL of water suspension (the mass fraction of esterified corn starch was 3.0%), 2 mL of cinnamon essential oil was added as the oil phase, and homogenized for 1 min at a rotation speed of 16000 rpm / min to obtain Pickering emulsion.

[0063] Example 5

[0064] This embodiment proposes a method for preparing a Pickering emulsion stabilized by esterified corn starch particles, comprising:

[0065] Preparation of esterified modified corn starch granules: 50 g corn starch (purchased directly from Xi'an Guowei Starch Co., Ltd., China) was dissolved in a 12.5% ​​mass fraction of dimethyl sulfoxide aqueous solution, and 3,6-dimethylphthalic anhydride (the addition amount was 7.5% of the dry weight of corn starch) was added while stirring. The stirring speed was controlled at 200 rpm / min. The reaction time was 2 h under a water bath temperature of 90 ° C. The mixture was cooled to 40 ° C. After elution, drying, crushing and sieving, hydrophobic esterified corn starch granules with a degree of substitution of 0.072 were obtained.

[0066] Preparation of Pickering emulsion: The esterified corn starch particles obtained by esterification modification were dissolved in deionized water to prepare 18 mL of water suspension (the mass fraction of esterified corn starch was 0.5%), 2 mL of cinnamon essential oil was added as the oil phase, and homogenized for 1 min at a rotation speed of 11000 rpm / min to obtain Pickering emulsion.

[0067] Example 6

[0068] This embodiment proposes the use of Pickering emulsion prepared with esterified starch in food preservation, wherein the application includes using the Pickering emulsion to prepare food preservative film or preservative.

[0069] The preparation method of the food preservative film involved includes:

[0070] 0.8 g of chitosan (2%, w / v) was dispersed in 40 mL of 1% (v / v) acetic acid solution, and stirred at 30°C at 300 rpm / min for 3 h to fully dissolve the chitosan. The chitosan solution was then ultrasonicated at 30°C for 2 min to remove bubbles, and 0.32 g (40%, w / w) of glycerol was added as a plasticizer. At the same time, 0.5 mL of emulsion (the degree of substitution of modified starch was 0.072, the mass fraction was 3%, and the volume of cinnamon essential oil was 10%) was added, and stirred at 300 rpm / min for 0.5 h at 30°C to form a film-forming solution. After stirring, it was ultrasonicated again for 2 min to remove bubbles. The prepared film-forming solution was cast on a 10 cm×10 cm polytetrafluoroethylene mold by casting and dried at 30°C for 24 h.

[0071] Discussion Example 1

[0072] This discussion example characterizes and compares the prepared esterified corn starch granules with natural corn starch to further illustrate the technical solution.

[0073] 1. Preparation of esterified modified corn starch granules: 50 g corn starch (purchased directly from Xi'an Guowei Starch Co., Ltd., China) was dissolved in a 12.5% ​​by mass dimethyl sulfoxide aqueous solution, and 3,6-dimethylphthalic anhydride (the addition amount was 7.5% of the dry weight of corn starch) was added while stirring. The stirring speed was controlled at 200 rpm / min. The reaction time was 2 h under a water bath temperature of 90 ° C. The mixture was cooled to 40 ° C. After elution, drying, crushing and sieving, esterified corn starch granules with a degree of substitution of 0.072 were obtained.

[0074] Second, the esterified corn starch particles obtained above and the native corn starch were subjected to a series of characterizations: infrared spectroscopy analysis (Fourier transform infrared spectrometer, Spectrum Two, PerkinElmer, USA), particle size distribution test (laser particle size analyzer, Mastersizer 2000, Malvern, UK) and three-phase contact angle test (contact angle meter, OCA2, Defei, Germany). The results are as follows: Figure 1-3 shown.

[0075] Among them, from Figure 1 It can be seen that compared with native corn starch, esterified corn starch particles have a -1 and 1690cm -1 New peaks appeared at 1572 cm -1 The peak at 1690 cm -1The peaks are related to the C=O stretching vibration of the ester group. These two additional peaks confirm that the hydroxyl groups in the starch molecules are replaced by the carbonyl groups of 3,6-dimethylphthalic anhydride, proving that the esterification reaction between native corn starch and 3,6-dimethylphthalic anhydride is successful.

[0076] Figure 2 It shows that esterification modification significantly reduces the average particle size of natural corn starch (esterified corn starch particles: 4.67μm, natural corn starch 14.86μm). Particle size plays an important role in the stability of the emulsion. Smaller particles are more easily absorbed at the oil-water interface and have better contact. Therefore, it can be seen that small-sized esterified corn starch particles have the potential to be excellent particles for preparing Pickering emulsions.

[0077] from Figure 3 It can be seen that the three-phase contact angle of natural corn starch is 30.63°, which is hydrophilic. After esterification modification, the contact angle is significantly increased to 63.90°, which improves the hydrophobicity of starch. Appropriate wettability can increase steric hindrance to prevent oil droplets from aggregating, which is conducive to the adsorption of particles at the oil-water interface to form a stable emulsion. This further verifies the potential of it as a stabilizer for Pickering emulsions.

[0078] Discussion Example 2

[0079] This discussion example is based on the dry weight of corn starch, adding 0.5%, 1.0%, 2.5% and 7.5% of 3,6-dimethylphthalic anhydride, and then obtaining esterified corn starch particles with corresponding degrees of substitution to further illustrate the technical solution.

[0080] Specifically include:

[0081] 50g corn starch (purchased directly from Xi'an Guowei Starch Co., Ltd., China) was dissolved in dimethyl sulfoxide solvent, and 3,6-dimethylphthalic anhydride (the addition amount was 0.5%, 1.0%, 2.5% and 7.5% of the dry weight of corn starch) was added while stirring. The stirring speed was controlled at 175rpm / min. The reaction time was 2h under the condition of water bath temperature of 90℃. After cooling to 40℃, elution, drying, crushing and sieving, hydrophobic esterified corn starch particles with substitution degrees of 0.0066, 0.019, 0.036 and 0.072 were obtained. The results are as follows Figure 4-6 shown.

[0082] Among them, from Figure 5 It can be seen that: at about 3378cm -1 A characteristic peak appears at 1572 cm-1, indicating the presence of hydroxyl groups. After esterification, some hydroxyl groups are replaced, and the intensity of the characteristic peak at 3378 cm-1 is weakened. Compared with native corn starch, the esterified corn starch granules samples with different degrees of substitution have a characteristic peak at 1572 cm-1. -1A new peak appeared at 1690 cm-1, which is attributed to the asymmetric stretching vibration of the carboxyl group. In addition, only higher substitution degree (≥0.036) can produce a peak at 1690 cm-1. -1 A new characteristic peak appeared at 1690 cm -1 The peak intensity of esterified corn starch at 1690 cm -1 The peaks observed at are related to the C=O stretching vibration of the ester group. These two additional peaks confirm that the hydroxyl groups in the starch molecules are replaced by the carbonyl groups of 3,6-dimethylphthalic anhydride, proving that the esterification reaction of corn starch granules with 3,6-dimethylphthalic anhydride is successful.

[0083] Figure 6 It can be seen that the contact angle of natural corn starch is 30.63°, indicating that natural corn starch is mainly hydrophilic and cannot stabilize Pickering emulsion. Different amounts of 3,6-dimethylphthalic anhydride lead to different degrees of modification, and esterified corn starch with different degrees of substitution also show different wettability. Compared with corn starch, the contact angle of esterified corn starch particles is higher. As the degree of substitution increases from 0.0066 to 0.072, the contact angle of esterified corn starch particles increases significantly, from 44.70° to 63.90°, indicating that 3,6-dimethylphthalic anhydride modification promotes the structural change of corn starch, so that the hydroxyl groups in corn starch are replaced by carbonyl groups, which improves the hydrophobicity of starch particles. Appropriate wettability can increase steric hindrance to prevent oil droplets from aggregating, which is conducive to the adsorption of esterified corn starch particles at the oil-water interface to form a stable emulsion. Therefore, esterified corn starch particles are a potential good Pickering emulsion stabilizer.

[0084] Discussion Example 3

[0085] In this discussion example, the stable Pickering emulsion prepared from esterified corn starch particles with different mass fractions (0.5%, 1.0%, 2.0%, 3.0%) was characterized to further illustrate the technical solution.

[0086] 1. Preparation of Pickering emulsion: The esterified corn starch particles obtained by esterification modification in Example 1 were dissolved in deionized water to prepare 18 mL of aqueous suspension, wherein the mass fractions of esterified corn starch in the aqueous suspension were 0.5%, 1.0%, 2.0%, and 3.0%, respectively, and 2 mL of cinnamon essential oil was added as the oil phase, and the mixture was homogenized for 2 min at a rotation speed of 21000 rpm / min to obtain Pickering emulsion;

[0087] Second, in this discussion example, the stable Pickering emulsions prepared with esterified corn starch granules of different mass fractions (0.5%, 1.0%, 2.0%, 3.0%) were characterized as follows: emulsion appearance and storage stability, emulsion volume index, emulsion particle size distribution test (laser particle size analyzer, Mastersizer 2000, Malvern, UK), emulsion microstructure (confocal microscope, STELLARIS 5, Leica, Italy) and apparent viscosity (rheometer, 102e, Anton Paar, Austria). The results are shown in Table 2. Figure 7-11 As shown;

[0088] Figure 7 In the figure, from left to right, the appearance of the emulsions after 24 h, 15 d and 50 d of storage are shown. After 7 d of storage, some Pickering emulsions were stratified, but there was no oil-water separation during the storage time. The Pickering emulsion stabilized by 3% esterified corn starch particles still had good storage stability at 50 d.

[0089] Depend on Figure 8 It can be seen that the emulsification ability of the Pickering emulsion stabilized by esterified corn starch particles is proportional to the mass fraction of esterified corn starch particles. As the mass fraction increases, the emulsification effect is more obvious. Among them, when the mass fraction of esterified corn starch particles is ≥2.0%, the emulsification index reaches the maximum value (100%). When the emulsion with a mass fraction of 3.0% is stored for 50 days, the emulsification index is still 100%, and no stratification or oil-water separation occurs.

[0090] Fig. 9 In the emulsion, D [4,3] decreases with the increase of the mass fraction of esterified corn starch particles, and is 15.79 μm, 14.24 μm, 11.33 μm, and 8.50 μm, respectively. The high density of starch particles is conducive to anchoring at the oil-water interface, making the Pickering emulsion have better stability;

[0091] Fig.10 It can be found through observation that the Pickering emulsion stabilized by esterified corn starch has uniform distribution of emulsion droplets at 1 day; no agglomeration occurs after 15 days, which verifies that the Pickering emulsion stabilized by esterified corn starch has excellent storage stability;

[0092] Fig.11 In the whole shear rate range, all esterified corn starch stabilized Pickering emulsions showed shear thinning behavior and typical non-Newtonian pseudo-plastic characteristics. At lower shear rates, the viscosity of Pickering emulsions was higher, and the viscosity gradually decreased with the increase of shear rate. The non-Newtonian pseudo-plasticity of Pickering emulsions is a typical weak association. The smaller the particle size of the emulsion, the higher the viscosity, the smaller the gravity separation rate of the emulsion droplets, and the more stable the emulsion.

[0093] Discussion Example 4

[0094] In this discussion example, the food preservative film (chitosan active film) prepared in Example 6 is used to preserve cold fresh pork to further illustrate the technical solution.

[0095] Among them, the blank group (untreated), pure chitosan film group (pure chitosan film for fresh pork preservation), and PE film group (PE film for fresh pork preservation) were used as controls to measure the changes in volatile basic nitrogen (TVB-N) and total bacterial count of fresh pork during the 10-day storage period at 4°C. Figure 12-13 As shown;

[0096] Depend on Fig.12 It can be seen that the TVB-N value in pork gradually increases with the extension of storage time. TVB-N is one of the important indicators reflecting the freshness of meat. On the 8th day, the TVB-N values ​​of pork in the blank group and the PE film group were 20.20 mg / 100g and 20.08 mg / 100g, respectively, indicating that both were corrupt (>20 mg / 100g), while the TVB-N value of pork treated with the food preservative film prepared in Example 6 was only 15.21 mg / 100g on the 10th day, which was in the sub-fresh meat stage (15-20 mg / 100g), proving that the chitosan active film preservation treatment can inhibit the corruption and deterioration of pork.

[0097] Depend on Fig.13 It can be seen that the total colony count in pork gradually increases with the extension of storage time, and the total colony count in pork treated with chitosan active film can be significantly reduced compared with untreated pork, pork treated with PE film and pork treated with pure chitosan film. The total colony counts of the blank group and PE film group on the 8th day were 6.05lgCFU / g and 6.22lgCFU / g, respectively, which exceeded the standard of my country (>6lgCFU / g) and belonged to spoiled meat. On the 10th day, the total colony count of pork treated with chitosan active film was 5.28lgCFU / g, indicating that chitosan active film has a good antibacterial effect.

[0098] The above description is only a preferred example of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing Pickering emulsion using esterified starch, characterized in that: The steps include: 1) Dissolution: corn starch is used as raw material and dissolved in dimethyl sulfoxide solvent to obtain corn starch-dimethyl sulfoxide solution; 2) Esterification: adding 3,6-dimethylphthalic anhydride to a corn starch-dimethyl sulfoxide solution at a concentration of 2.5-7.5% of the dry weight of corn starch, reacting, eluting, drying, crushing and sieving to obtain esterified corn starch particles with a degree of substitution of 0.036-0.072; 3) Preparation: The obtained esterified corn starch particles are dissolved in deionized water to prepare a water suspension with a mass fraction of 0.5-3.0%; then, an oil phase is added and homogenized to obtain a Pickering emulsion.

2. The method for preparing Pickering emulsion using esterified starch according to claim 1, characterized in that: In the corn starch-dimethyl sulfoxide solution of step 1), the mass fraction of corn starch is 10-15%.

3. The method for preparing Pickering emulsion using esterified starch according to claim 2, characterized in that: In step 2), the reaction is stirred at 85-95° C. for 1-3 h, cooled to 30-40° C., and then eluted; wherein the stirring speed is 175-225 rpm / min.

4. The method for preparing Pickering emulsion using esterified starch according to claim 3, characterized in that: In step 2), an excess of anhydrous ethanol is used for elution 3-4 times, and after freeze-drying at -50°C for 24-36 hours, the mixture is crushed and sieved; wherein the sieve mesh number is 100 meshes.

5. The method for preparing Pickering emulsion using esterified starch according to claim 4, characterized in that: In step 2), the degree of substitution of the esterified corn starch particles is 0.

072.

6. The method for preparing Pickering emulsion using esterified starch according to claim 1, characterized in that: In step 3), the oil phase is cinnamon essential oil, and the volume fraction of the oil phase is 10%; the homogenization speed is 11000-21000 rpm / min, and the homogenization time is 1-3 min.

7. The method for preparing Pickering emulsion using esterified starch according to claim 1, characterized in that: The Pickering emulsion has an emulsification index of 34.69-100%, a D[4,3] of 8.50-15.79 μm, and remains stable after storage for 50 days.

8. Use of the Pickering emulsion prepared with esterified starch as claimed in any one of claims 1 to 7 in food preservation, characterized in that the use comprises using the Pickering emulsion to prepare food preservative film or preservative.

9. The use according to claim 8, characterized in that: The preparation method of the food preservative film comprises: Dissolve chitosan in acetic acid solution, remove bubbles, add glycerol and Pickering emulsion, stir, and form a film-forming solution; The bubbles are removed again, and then the film-forming solution is cast on a mold by a casting method and dried to obtain a food preservative film.

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