Pickering emulsion based on dialdehyde cellulose nanofibers modified soy protein isolate, its preparation method and application

Abstract

This invention discloses a Pickering emulsion based on dialdehyde cellulose nanofibers modified with soy protein isolate, its preparation method, and its application, relating to the fields of food science and bio-based functional materials technology. A pH-adjusted aqueous dispersion of carboxylated cellulose nanofibers is reacted with an oxidant under light-protected conditions. After termination with a terminator, the reaction is completed by alcohol precipitation, washing, and drying to obtain dialdehyde cellulose nanofibers. A pH-adjusted aqueous solution of soy protein isolate is stirred, hydrated, and heat-treated, then cooled to obtain a soy protein isolate solution. The obtained dialdehyde cellulose nanofibers are dispersed in water and then mixed with the soy protein isolate solution to form a composite particle dispersion. Carvacrol is slowly added to this dispersion, and after dispersion treatment, a carvacrol-loaded Pickering emulsion is constructed. This emulsion, when applied to the surface of fruits, can significantly inhibit the growth of pathogenic microorganisms, delay fruit spoilage, and improve the appearance quality and shelf life during storage.

Description

Technical Field

[0001] This invention relates to a Pickering emulsion based on dialdehyde cellulose nanofiber modified soybean protein isolate, its preparation method and application, belonging to the field of food science and bio-based functional materials technology. Background Technology

[0002] Soy protein isolate (SPI) is widely used as a food emulsifier and a substrate for edible films due to its abundant sources and good biodegradability. However, SPI's natural conformation is compact, and hydrophobic groups are buried in its secondary structure, resulting in poor solubility and limited emulsion stability, which restricts its application in functional carriers and active packaging. Existing SPI modification methods include physical treatment (high pressure, ultrasound), enzymatic hydrolysis, and chemical cross-linking (such as glutaraldehyde). Although these methods can improve its function to some extent, they suffer from high energy consumption, toxic cross-linking agents, or uncontrollable reactions, hindering its widespread application in food contact materials. Based on this, current research utilizes green polysaccharides for composite modification, such as carboxymethyl cellulose (CMC), chitosan, pectin, and alginate. However, these methods mainly rely on electrostatic interactions, hydrogen bonds, or hydrophobic interactions. While they can improve dispersibility and emulsification, the binding force is limited, and the emulsions or films are prone to instability under storage, heating, or ionic interference, limiting their application in complex food environments.

[0003] In recent years, Pickering emulsions have attracted attention in the food and preservation industries due to their high stability and lack of surfactant residue. However, designing natural particles that combine good interfacial activity with the ability to load active substances remains a challenge in this field. Carvacrol, as a monoterpene phenolic natural compound, has significant antibacterial and antioxidant activities, but its hydrophobicity and volatility limit its direct application in fruit preservation.

[0004] Therefore, there is an urgent need for a green, stable and efficient SPI modification strategy that can be used as a stabilizer for Pickering emulsions and loaded with carvacrol, thereby developing a novel fruit preservative with both structural stability and antibacterial and preservative functions. Summary of the Invention

[0005] One objective of this invention is to provide a method for preparing Pickering emulsion based on dialdehyde cellulose nanofiber modified soy protein isolate, specifically including the following steps:

[0006] (1) Preparation of dialdehyde cellulose nanofibers: Adjust the pH value of the aqueous dispersion of carboxylated cellulose nanofibers (preferably with 0.1 mol / L H2SO4 aqueous solution to adjust the pH value), and then carry out an oxidation reaction between the aqueous dispersion of carboxylated cellulose nanofibers with an oxidant. After the reaction is completed, a mixture is obtained. Then, a terminator (preferably ethylene glycol) is added to the mixture to terminate the reaction and induce precipitation in the mixture after the reaction is terminated. The precipitate is filtered, washed and dried to obtain dialdehyde cellulose nanofibers (DCNFs).

[0007] (2) Synthesis of dialdehyde cellulose nanofiber-soy protein isolate composite particles: The pH value of the soy protein isolate aqueous solution was adjusted (preferably by adjusting the pH value with 0.1 mol / L NaOH aqueous solution), followed by stirring, hydration, heat treatment and cooling to obtain a soy protein isolate solution. Dialdehyde cellulose nanofibers were dispersed in water to form a dialdehyde cellulose nanofiber dispersion. Then, the soy protein isolate solution and the dialdehyde cellulose nanofiber dispersion were mixed and reacted to obtain a dialdehyde cellulose nanofiber-soy protein isolate composite particle (DCNF-SPI) dispersion.

[0008] (3) Pickering emulsion construction: The oil phase was added to the dispersion of dialdehyde cellulose nanofiber-soy protein isolate composite particles, and then dispersed (preferably in an ultrasonic cell disruptor) to construct the Pickering emulsion.

[0009] Preferably, the mass percentage concentration of the carboxylated cellulose nanofiber aqueous dispersion in step (1) is 1.0-2.0%; and the pH value of the carboxylated cellulose nanofiber aqueous dispersion after adjustment is 3-5.

[0010] More preferably, the mass percentage concentration of the carboxylated cellulose nanofiber aqueous dispersion in step (1) is 2.0%; and the pH value of the carboxylated cellulose nanofiber aqueous dispersion after adjustment is 4.

[0011] Preferably, in step (1), the oxidant is added to the aqueous dispersion after pH adjustment at a molar ratio of 1:(0.5-2) of carboxylated cellulose nanofibers to oxidant; the oxidant is sodium periodate; the oxidation reaction conditions are: under light-protected conditions, 30-60℃, reaction for 3-7 hours; the mixture after the reaction is terminated produces a precipitate by alcohol precipitation, specifically by adding anhydrous ethanol to the mixture after the reaction is terminated at a volume ratio of 1:4 and letting it stand for 1-2 hours.

[0012] More preferably, the oxidation reaction in step (1) is carried out at 45°C for 5 hours under light-protected conditions.

[0013] Preferably, the mass percentage concentration of the soy protein isolate aqueous solution in step (2) is 1.0-4.0%; the pH value of the soy protein isolate aqueous solution after adjustment is 9-11; the stirring time is 0.5-2h; the hydration conditions are 4℃ hydration for 2-10h; and the heat treatment conditions are 80-100℃ heat treatment for 5-30min.

[0014] More preferably, in step (2), the mass percentage concentration of the soy protein isolate aqueous solution is 2%; the pH value of the soy protein isolate aqueous solution after adjustment is 10; the stirring conditions are: stirring at room temperature for 1 hour; the hydration conditions are: hydration at 4°C for 6 hours; and the heat treatment conditions are: heat treatment at 95°C for 15 minutes.

[0015] Preferably, in step (2), the mass percentage concentration of the dialdehyde cellulose nanofiber dispersion is 0.25-4%; the soybean protein isolate solution and the dialdehyde cellulose nanofiber dispersion are mixed in equal volumes and reacted; the reaction conditions are: reaction at 30-60℃ for 1-2 hours.

[0016] More preferably, the mixing reaction conditions in step (2) are: reacting at 30°C for 2 hours.

[0017] Preferably, in step (3), the oil phase is carvacrol; the dispersion treatment time is 3-10 min; and the volume percentage of the oil phase in the Pickering emulsion is 1-20%.

[0018] The second objective of this invention is to provide a Pickering emulsion prepared using the method of this invention.

[0019] The third objective of this invention is to provide an application of the Pickering emulsion prepared by this invention in fruit preservation.

[0020] Mechanism of the invention:

[0021] The functional Pickering emulsion constructed in this invention covalently crosslinks dialdehyde cellulose nanofibers (DCNFs) and soy protein isolate (SPI) via an aldehyde-amino Schiff base reaction, forming composite particles that possess both chemical stability and nano-scaffold reinforcement. These particles efficiently adsorb and stabilize carvacrol oil droplets at the oil-water interface, allowing carvacrol to be effectively loaded through hydrophobic interactions and hydrogen bonding. The controlled release of carvacrol is achieved through the synergistic effect of the composite particle barrier and the cellulose network structure. When the emulsion is coated onto the surface of fruit, it forms a protective film that combines physical barrier and biological activity. This film reduces water evaporation and exogenous contamination while continuously releasing carvacrol to inhibit the growth of pathogenic microorganisms and delay fruit oxidation and softening, thereby significantly extending the storage and shelf life of the fruit and achieving a green, safe, and sustainable preservation effect.

[0022] The beneficial effects of this invention are:

[0023] (1) Stable covalent bonding: Unlike the modification of CMC and pectin that rely on non-covalent interactions, this invention makes the SPI structure more stable through the aldehyde-amino covalent crosslinking of DCNF.

[0024] (2) Dual enhancement mechanism: DCNFs not only improve the molecular structure of SPI as a crosslinking agent, but also enhance the physical stability of the emulsion with nanofiber skeleton.

[0025] (3) High-efficiency loading and sustained release: DCNF-SPI particles can form a stable interface network, effectively loading carvacrol and prolonging its antibacterial action time.

[0026] (4) Excellent fruit preservation performance: The emulsion produced achieves the slow-release and controlled release of carvacrol through the synergistic effect of the composite particle barrier and cellulose mesh structure, which can significantly inhibit the growth of microorganisms. During the 11-day test period, mangoes can achieve low spoilage rate or even no spoilage, with slow decrease in hardness and reduced weight loss, thus maintaining the appearance and nutritional quality of the fruit.

[0027] (5) Green and environmentally friendly: DCNF is derived from natural cellulose, is degradable and non-toxic, avoids the safety hazards of harmful crosslinking agents such as glutaraldehyde, and meets the application requirements of food contact materials; the present invention has the advantages of natural raw material source, simple process, environmental friendliness, and safety and non-toxicity. Attached Figure Description

[0028] Figure 1 This is a comparison chart of the macroscopic storage stability of the emulsions in Examples 1-6 of the present invention.

[0029] Figure 2 This is a comparison chart of the antioxidant capacity of the emulsions in Examples 1-6 of the present invention.

[0030] Figure 3This is a comparison chart of the antibacterial ability of the emulsions in Examples 1-6 of the present invention.

[0031] Figure 4 The images show a comparison of the effects of emulsion preservation on mangoes in Examples 1-6 and Comparative Example 1 of the present invention.

[0032] Figure 5 This is a graph showing the weight loss rate during the emulsion preservation of mangoes in Examples 1-6 and Comparative Example 1 of the present invention.

[0033] Figure 6 The diagram shows the hardness analysis of mangoes preserved by emulsion in Examples 1-6 and Comparative Example 1 of this invention.

[0034] Figure 7 This is a graph showing the spoilage rate analysis of mangoes preserved by emulsion in Examples 1-6 and Comparative Example 1 of the present invention. Detailed Implementation

[0035] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0036] Example 1

[0037] A method for preparing Pickering emulsion based on dialdehyde cellulose nanofiber modified soy protein isolate, specifically including the following steps:

[0038] (1) Preparation of dialdehyde cellulose nanofibers: The pH of a 2% (w / w) carboxylated cellulose nanofiber aqueous dispersion was adjusted to 4 using a 0.1 mol / L H2SO4 aqueous solution. Then, the pH-adjusted carboxylated cellulose nanofiber aqueous dispersion was reacted with sodium periodate in a constant-temperature water bath at 45°C for 5 hours under light-protected conditions. Sodium periodate was added to the pH-adjusted aqueous dispersion at a molar ratio of 1:1.5. After the reaction was complete, a mixed solution was obtained. Subsequently, the mixture was prepared with a molar ratio of sodium periodate to ethylene glycol of 1:1.5. Ethylene glycol was added to the mixture at a ratio of 1:2 to terminate the reaction. Anhydrous ethanol was added to the mixture at a volume ratio of 1:4 to terminate the reaction, and the mixture was allowed to stand for 1 hour to allow the precipitate to fully separate. The precipitate was collected by filtration and washed with mixtures of anhydrous ethanol and deionized water at volume ratios of 7:3, 5:5, and 3:7 to remove residual reactants. Finally, the washed precipitate was dried in a freeze dryer for 24 hours to obtain dialdehyde cellulose nanofibers.

[0039] (2) Synthesis of dialdehyde cellulose nanofiber-soy protein isolate composite particles: The pH value of a 2% (w / w) soy protein isolate aqueous solution was adjusted to 10 using a 0.1 mol / L NaOH aqueous solution. Then, the solution was stirred at room temperature for 1 h. After that, the stirred soy protein isolate aqueous solution was hydrated at 4 °C for 6 h in a refrigerator. Then, the hydrated soy protein isolate aqueous solution was heat-treated in an oil bath at 95 °C for 15 min. Finally, it was cooled to room temperature to obtain a soy protein isolate solution. Dialdehyde cellulose nanofibers were dispersed in deionized water and stirred to obtain a 1% (w / w) dialdehyde cellulose nanofiber dispersion. Then, the soy protein isolate solution and the dialdehyde cellulose nanofiber dispersion were mixed in equal volumes and reacted at 30 °C for 2 h to allow the two to fully crosslink and combine, thus obtaining a dialdehyde cellulose nanofiber-soy protein isolate composite particle dispersion.

[0040] (3) Construction of Pickering emulsion: using carvacrol as the oil phase, carvacrol was slowly added to the dispersion of dialdehyde cellulose nanofiber-soy protein isolate composite particles, and then dispersed in an ultrasonic cell disruptor for 10 min to make the oil phase uniformly dispersed in the aqueous phase, thus constructing a carvacrol-loaded Pickering emulsion (SDC-1), in which the volume percentage of carvacrol in the Pickering emulsion was 1%.

[0041] The weight loss analysis chart during the Pickering emulsion preservation of mangoes in this embodiment is shown in the figure below. Figure 5 As shown, the hardness analysis chart is as follows: Figure 6 As shown in the corruption rate analysis chart... Figure 7 As shown.

[0042] Example 2

[0043] A method for preparing Pickering emulsion based on dialdehyde cellulose nanofiber modified soy protein isolate, specifically including the following steps:

[0044] (1) Preparation of dialdehyde cellulose nanofibers: The pH of a 2% (w / w) carboxylated cellulose nanofiber aqueous dispersion was adjusted to 4 using a 0.1 mol / L H2SO4 aqueous solution. Then, the pH-adjusted carboxylated cellulose nanofiber aqueous dispersion was reacted with sodium periodate in a constant-temperature water bath at 45°C for 5 hours under light-protected conditions. Sodium periodate was added to the pH-adjusted aqueous dispersion at a molar ratio of 1:1.5. After the reaction was complete, a mixed solution was obtained. Subsequently, the mixture was prepared with a molar ratio of sodium periodate to ethylene glycol of 1:1.5. Ethylene glycol was added to the mixture at a ratio of 1:2 to terminate the reaction. Anhydrous ethanol was added to the mixture at a volume ratio of 1:4 to terminate the reaction, and the mixture was allowed to stand for 1 hour to allow the precipitate to fully separate. The precipitate was collected by filtration and washed with mixtures of anhydrous ethanol and deionized water at volume ratios of 7:3, 5:5, and 3:7 to remove residual reactants. Finally, the washed precipitate was dried in a freeze dryer for 24 hours to obtain dialdehyde cellulose nanofibers.

[0045] (2) Synthesis of dialdehyde cellulose nanofiber-soy protein isolate composite particles: The pH value of a 2% (w / w) soy protein isolate aqueous solution was adjusted to 10 using a 0.1 mol / L NaOH aqueous solution. Then, the solution was stirred at room temperature for 1 h. After that, the stirred soy protein isolate aqueous solution was hydrated at 4 °C for 6 h in a refrigerator. Then, the hydrated soy protein isolate aqueous solution was heat-treated in an oil bath at 95 °C for 15 min. Finally, it was cooled to room temperature to obtain a soy protein isolate solution. Dialdehyde cellulose nanofibers were dispersed in deionized water and stirred to obtain a 1% (w / w) dialdehyde cellulose nanofiber dispersion. Then, the soy protein isolate solution and the dialdehyde cellulose nanofiber dispersion were mixed in equal volumes and reacted at 30 °C for 2 h to allow the two to fully crosslink and combine, thus obtaining a dialdehyde cellulose nanofiber-soy protein isolate composite particle dispersion.

[0046] (3) Construction of Pickering emulsion: using carvacrol as the oil phase, carvacrol was slowly added to the dispersion of dialdehyde cellulose nanofiber-soy protein isolate composite particles, and then dispersed in an ultrasonic cell disruptor for 10 min to make the oil phase uniformly dispersed in the aqueous phase, thus constructing a carvacrol-loaded Pickering emulsion (SDC-3), in which the volume percentage of carvacrol in the Pickering emulsion was 3%.

[0047] The weight loss analysis chart during the Pickering emulsion preservation of mangoes in this embodiment is shown in the figure below. Figure 5 As shown, the hardness analysis chart is as follows: Figure 6 As shown in the corruption rate analysis chart... Figure 7 As shown.

[0048] Example 3

[0049] A method for preparing Pickering emulsion based on dialdehyde cellulose nanofiber modified soy protein isolate, specifically including the following steps:

[0050] (1) Preparation of dialdehyde cellulose nanofibers: The pH of a 2% (w / w) carboxylated cellulose nanofiber aqueous dispersion was adjusted to 4 using a 0.1 mol / L H2SO4 aqueous solution. Then, the pH-adjusted carboxylated cellulose nanofiber aqueous dispersion was reacted with sodium periodate in a constant-temperature water bath at 45°C for 5 hours under light-protected conditions. Sodium periodate was added to the pH-adjusted aqueous dispersion at a molar ratio of 1:1.5. After the reaction was complete, a mixed solution was obtained. Subsequently, the mixture was prepared with a molar ratio of sodium periodate to ethylene glycol of 1:1.5. Ethylene glycol was added to the mixture at a ratio of 1:2 to terminate the reaction. Anhydrous ethanol was added to the mixture at a volume ratio of 1:4 to terminate the reaction, and the mixture was allowed to stand for 1 hour to allow the precipitate to fully separate. The precipitate was collected by filtration and washed with mixtures of anhydrous ethanol and deionized water at volume ratios of 7:3, 5:5, and 3:7 to remove residual reactants. Finally, the washed precipitate was dried in a freeze dryer for 24 hours to obtain dialdehyde cellulose nanofibers.

[0051] (2) Synthesis of dialdehyde cellulose nanofiber-soy protein isolate composite particles: The pH value of a 2% (w / w) soy protein isolate aqueous solution was adjusted to 10 using a 0.1 mol / L NaOH aqueous solution. Then, the solution was stirred at room temperature for 1 h. After that, the stirred soy protein isolate aqueous solution was hydrated at 4 °C for 6 h in a refrigerator. Then, the hydrated soy protein isolate aqueous solution was heat-treated in an oil bath at 95 °C for 15 min. Finally, it was cooled to room temperature to obtain a soy protein isolate solution. Dialdehyde cellulose nanofibers were dispersed in deionized water and stirred to obtain a 1% (w / w) dialdehyde cellulose nanofiber dispersion. Then, the soy protein isolate solution and the dialdehyde cellulose nanofiber dispersion were mixed in equal volumes and reacted at 30 °C for 2 h to allow the two to fully crosslink and combine, thus obtaining a dialdehyde cellulose nanofiber-soy protein isolate composite particle dispersion.

[0052] (3) Construction of Pickering emulsion: using carvacrol as the oil phase, carvacrol was slowly added to the dispersion of dialdehyde cellulose nanofiber-soy protein isolate composite particles, and then dispersed in an ultrasonic cell disruptor for 10 min to make the oil phase uniformly dispersed in the aqueous phase, thus constructing a carvacrol-loaded Pickering emulsion (SDC-5), in which the volume percentage of carvacrol in the Pickering emulsion was 5%.

[0053] The weight loss analysis chart during the Pickering emulsion preservation of mangoes in this embodiment is shown in the figure below. Figure 5 As shown, the hardness analysis chart is as follows: Figure 6 As shown in the corruption rate analysis chart... Figure 7 As shown.

[0054] Example 4

[0055] A method for preparing Pickering emulsion based on dialdehyde cellulose nanofiber modified soy protein isolate, specifically including the following steps:

[0056] (1) Preparation of dialdehyde cellulose nanofibers: The pH of a 2% (w / w) carboxylated cellulose nanofiber aqueous dispersion was adjusted to 4 using a 0.1 mol / L H2SO4 aqueous solution. Then, the pH-adjusted carboxylated cellulose nanofiber aqueous dispersion was reacted with sodium periodate in a constant-temperature water bath at 45°C for 5 hours under light-protected conditions. Sodium periodate was added to the pH-adjusted aqueous dispersion at a molar ratio of 1:1.5. After the reaction was complete, a mixed solution was obtained. Subsequently, the mixture was prepared with a molar ratio of sodium periodate to ethylene glycol of 1:1.5. Ethylene glycol was added to the mixture at a ratio of 1:2 to terminate the reaction. Anhydrous ethanol was added to the mixture at a volume ratio of 1:4 to terminate the reaction, and the mixture was allowed to stand for 1 hour to allow the precipitate to fully separate. The precipitate was collected by filtration and washed with mixtures of anhydrous ethanol and deionized water at volume ratios of 7:3, 5:5, and 3:7 to remove residual reactants. Finally, the washed precipitate was dried in a freeze dryer for 24 hours to obtain dialdehyde cellulose nanofibers.

[0057] (2) Synthesis of dialdehyde cellulose nanofiber-soy protein isolate composite particles: The pH value of a 2% (w / w) soy protein isolate aqueous solution was adjusted to 10 using a 0.1 mol / L NaOH aqueous solution. Then, the solution was stirred at room temperature for 1 h. After that, the stirred soy protein isolate aqueous solution was hydrated at 4 °C for 6 h in a refrigerator. Then, the hydrated soy protein isolate aqueous solution was heat-treated in an oil bath at 95 °C for 15 min. Finally, it was cooled to room temperature to obtain a soy protein isolate solution. Dialdehyde cellulose nanofibers were dispersed in deionized water and stirred to obtain a 1% (w / w) dialdehyde cellulose nanofiber dispersion. Then, the soy protein isolate solution and the dialdehyde cellulose nanofiber dispersion were mixed in equal volumes and reacted at 30 °C for 2 h to allow the two to fully crosslink and combine, thus obtaining a dialdehyde cellulose nanofiber-soy protein isolate composite particle dispersion.

[0058] (3) Construction of Pickering emulsion: using carvacrol as the oil phase, carvacrol was slowly added to the dispersion of dialdehyde cellulose nanofiber-soy protein isolate composite particles, and then dispersed in an ultrasonic cell disruptor for 10 min to make the oil phase uniformly dispersed in the aqueous phase, thus constructing a carvacrol-loaded Pickering emulsion (SDC-10), in which the volume percentage of carvacrol in the Pickering emulsion was 10%.

[0059] The weight loss analysis chart during the Pickering emulsion preservation of mangoes in this embodiment is shown in the figure below. Figure 5 As shown, the hardness analysis chart is as follows: Figure 6 As shown in the corruption rate analysis chart... Figure 7 As shown.

[0060] Example 5

[0061] (1) Preparation of dialdehyde cellulose nanofibers: The pH of a 2% (w / w) carboxylated cellulose nanofiber aqueous dispersion was adjusted to 4 using a 0.1 mol / L H2SO4 aqueous solution. Then, the pH-adjusted carboxylated cellulose nanofiber aqueous dispersion was reacted with sodium periodate in a constant-temperature water bath at 45°C for 5 hours under light-protected conditions. Sodium periodate was added to the pH-adjusted aqueous dispersion at a molar ratio of 1:1.5. After the reaction was complete, a mixed solution was obtained. Subsequently, the mixture was prepared with a molar ratio of sodium periodate to ethylene glycol of 1:1.5. Ethylene glycol was added to the mixture at a ratio of 1:2 to terminate the reaction. Anhydrous ethanol was added to the mixture at a volume ratio of 1:4 to terminate the reaction, and the mixture was allowed to stand for 1 hour to allow the precipitate to fully separate. The precipitate was collected by filtration and washed with mixtures of anhydrous ethanol and deionized water at volume ratios of 7:3, 5:5, and 3:7 to remove residual reactants. Finally, the washed precipitate was dried in a freeze dryer for 24 hours to obtain dialdehyde cellulose nanofibers.

[0062] (2) Synthesis of dialdehyde cellulose nanofiber-soy protein isolate composite particles: The pH value of a 2% (w / w) soy protein isolate aqueous solution was adjusted to 10 using a 0.1 mol / L NaOH aqueous solution. Then, the solution was stirred at room temperature for 1 h. After that, the stirred soy protein isolate aqueous solution was hydrated at 4 °C for 6 h in a refrigerator. Then, the hydrated soy protein isolate aqueous solution was heat-treated in an oil bath at 95 °C for 15 min. Finally, it was cooled to room temperature to obtain a soy protein isolate solution. Dialdehyde cellulose nanofibers were dispersed in deionized water and stirred to obtain a 1% (w / w) dialdehyde cellulose nanofiber dispersion. Then, the soy protein isolate solution and the dialdehyde cellulose nanofiber dispersion were mixed in equal volumes and reacted at 30 °C for 2 h to allow the two to fully crosslink and combine, thus obtaining a dialdehyde cellulose nanofiber-soy protein isolate composite particle dispersion.

[0063] (3) Construction of Pickering emulsion: using carvacrol as the oil phase, carvacrol was slowly added to the dispersion of dialdehyde cellulose nanofiber-soy protein isolate composite particles, and then dispersed in an ultrasonic cell disruptor for 10 min to make the oil phase uniformly dispersed in the aqueous phase, thus constructing a carvacrol-loaded Pickering emulsion (SDC-15), in which the volume percentage of carvacrol in the Pickering emulsion was 15%.

[0064] The weight loss analysis chart during the Pickering emulsion preservation of mangoes in this embodiment is shown in the figure below. Figure 5 As shown, the hardness analysis chart is as follows: Figure 6 As shown in the corruption rate analysis chart... Figure 7 As shown.

[0065] Example 6

[0066] A method for preparing Pickering emulsion based on dialdehyde cellulose nanofiber modified soy protein isolate, specifically including the following steps:

[0067] (1) Preparation of dialdehyde cellulose nanofibers: The pH of a 2% (w / w) carboxylated cellulose nanofiber aqueous dispersion was adjusted to 4 using a 0.1 mol / L H2SO4 aqueous solution. Then, the pH-adjusted carboxylated cellulose nanofiber aqueous dispersion was reacted with sodium periodate in a constant-temperature water bath at 45°C for 5 hours under light-protected conditions. Sodium periodate was added to the pH-adjusted aqueous dispersion at a molar ratio of 1:1.5. After the reaction was complete, a mixed solution was obtained. Subsequently, the mixture was prepared with sodium periodate and ethylene glycol at a molar ratio of 1:1.5. Ethylene glycol was added to the mixture at a ratio of 2 to terminate the reaction. Anhydrous ethanol was added to the mixture at a volume ratio of 1:4 to terminate the reaction and allowed to stand for 1 hour to allow the precipitate to fully separate. The precipitate was collected by filtration and washed sequentially with mixtures of anhydrous ethanol and deionized water at volume ratios of 7:3, 5:5, and 3:7 to remove residual reactants. Finally, the washed precipitate was dried in a freeze dryer for 24 hours to obtain dialdehyde cellulose nanofibers.

[0068] (2) Synthesis of dialdehyde cellulose nanofiber-soy protein isolate composite particles: The pH value of a 2% (w / w) soy protein isolate aqueous solution was adjusted to 10 using a 0.1 mol / L NaOH aqueous solution. Then, the solution was stirred at room temperature for 1 h. After that, the stirred soy protein isolate aqueous solution was hydrated at 4 °C for 6 h in a refrigerator. Then, the hydrated soy protein isolate aqueous solution was heat-treated in an oil bath at 95 °C for 15 min. Finally, it was cooled to room temperature to obtain a soy protein isolate solution. Dialdehyde cellulose nanofibers were dispersed in deionized water and stirred to obtain a 1% (w / w) dialdehyde cellulose nanofiber dispersion. Then, the soy protein isolate solution and the dialdehyde cellulose nanofiber dispersion were mixed in equal volumes and reacted at 30 °C for 2 h to allow the two to fully crosslink and combine, thus obtaining a dialdehyde cellulose nanofiber-soy protein isolate composite particle dispersion.

[0069] (3) Construction of Pickering emulsion: using carvacrol as the oil phase, carvacrol was slowly added to the dispersion of dialdehyde cellulose nanofiber-soy protein isolate composite particles, and then dispersed in an ultrasonic cell disruptor for 10 min to make the oil phase uniformly dispersed in the aqueous phase, thus constructing a carvacrol-loaded Pickering emulsion (SDC-20), in which the volume percentage of carvacrol in the Pickering emulsion was 20%.

[0070] The weight loss analysis chart during the Pickering emulsion preservation of mangoes in this embodiment is shown in the figure below. Figure 5 As shown, the hardness analysis chart is as follows: Figure 6 As shown in the corruption rate analysis chart... Figure 7 As shown.

[0071] Example 7

[0072] A method for preparing Pickering emulsion based on dialdehyde cellulose nanofiber modified soy protein isolate, specifically including the following steps:

[0073] (1) Preparation of dialdehyde cellulose nanofibers: The pH of a 1% (w / w) carboxylated cellulose nanofiber aqueous dispersion was adjusted to 3 using a 0.1 mol / L H2SO4 aqueous solution. Then, the pH-adjusted carboxylated cellulose nanofiber aqueous dispersion was reacted with sodium periodate in a constant-temperature water bath at 60°C for 3 hours under light-protected conditions. Sodium periodate was added to the pH-adjusted aqueous dispersion at a molar ratio of 1:0.5. After the reaction was complete, a mixed solution was obtained. Subsequently, the mixture was prepared with a sodium periodate to ethylene glycol molar ratio of 1:1. Ethylene glycol was added to the mixture at a ratio of 1:2 to terminate the reaction. Anhydrous ethanol was added to the mixture at a volume ratio of 1:4 to terminate the reaction, and the mixture was allowed to stand for 2 hours to allow the precipitate to fully separate. The precipitate was collected by filtration and washed with mixtures of anhydrous ethanol and deionized water at volume ratios of 7:3, 5:5, and 3:7 to remove residual reactants. Finally, the washed precipitate was dried in a freeze dryer for 24 hours to obtain dialdehyde cellulose nanofibers.

[0074] (2) Synthesis of dialdehyde cellulose nanofiber-soy protein isolate composite particles: The pH value of a 4% (w / w) soy protein isolate aqueous solution was adjusted to 11 using a 0.1 mol / L NaOH aqueous solution. Then, the solution was stirred at room temperature for 0.5 h. After that, the stirred soy protein isolate aqueous solution was hydrated at 4 °C for 10 h in a refrigerator. Then, the hydrated soy protein isolate aqueous solution was heat-treated in an oil bath at 100 °C for 5 min. Finally, it was cooled to room temperature to obtain a soy protein isolate solution. Dialdehyde cellulose nanofibers were dispersed in deionized water and stirred to obtain a 0.25% (w / w) dialdehyde cellulose nanofiber dispersion. Then, the soy protein isolate solution and the dialdehyde cellulose nanofiber dispersion were mixed in equal volumes and reacted at 60 °C for 1 h to allow the two to fully cross-link and combine, thus obtaining a dialdehyde cellulose nanofiber-soy protein isolate composite particle dispersion.

[0075] (3) Construction of Pickering emulsion: using carvacrol as the oil phase, carvacrol was slowly added to the dispersion of dialdehyde cellulose nanofiber-soy protein isolate composite particles, and then dispersed in an ultrasonic cell disruptor for 3 min to make the oil phase uniformly dispersed in the aqueous phase, thus constructing a carvacrol-loaded Pickering emulsion, wherein the volume percentage of carvacrol in the Pickering emulsion was 20%.

[0076] Example 8

[0077] A method for preparing Pickering emulsion based on dialdehyde cellulose nanofiber modified soy protein isolate, specifically including the following steps:

[0078] (1) Preparation of dialdehyde cellulose nanofibers: The pH of a 1.5% (w / w) carboxylated cellulose nanofiber aqueous dispersion was adjusted to 5 using a 0.1 mol / L H2SO4 aqueous solution. Then, the pH-adjusted carboxylated cellulose nanofiber aqueous dispersion was reacted with sodium periodate in a constant-temperature water bath at 30°C for 7 hours under light-protected conditions. Sodium periodate was added to the pH-adjusted aqueous dispersion at a molar ratio of 1:2. After the reaction was complete, a mixed solution was obtained. Subsequently, the mixture was prepared by reacting sodium periodate with ethylene glycol at a molar ratio of 1:2. Ethylene glycol was added to the mixture at a ratio of 2 to terminate the reaction. Anhydrous ethanol was added to the mixture at a volume ratio of 1:4 to terminate the reaction, and the mixture was allowed to stand for 1.5 hours to allow the precipitate to fully separate. The precipitate was collected by filtration and washed sequentially with mixtures of anhydrous ethanol and deionized water at volume ratios of 7:3, 5:5, and 3:7 to remove residual reactants. Finally, the washed precipitate was dried in a freeze dryer for 24 hours to obtain dialdehyde cellulose nanofibers.

[0079] (2) Synthesis of dialdehyde cellulose nanofiber-soy protein isolate composite particles: The pH value of a 1% (w / w) soy protein isolate aqueous solution was adjusted to 9 using a 0.1 mol / L NaOH aqueous solution. Then, the solution was stirred at room temperature for 2 h. After that, the stirred soy protein isolate aqueous solution was hydrated at 4 °C for 2 h in a refrigerator. Then, the hydrated soy protein isolate aqueous solution was heat-treated in an oil bath at 80 °C for 30 min. Finally, it was cooled to room temperature to obtain a soy protein isolate solution. Dialdehyde cellulose nanofibers were dispersed in deionized water and stirred to obtain a 4% (w / w) dialdehyde cellulose nanofiber dispersion. Then, the soy protein isolate solution and the dialdehyde cellulose nanofiber dispersion were mixed in equal volumes and reacted at 45 °C for 1.5 h to allow the two to fully cross-link and combine, thus obtaining a dialdehyde cellulose nanofiber-soy protein isolate composite particle dispersion.

[0080] (3) Construction of Pickering emulsion: using carvacrol as the oil phase, carvacrol was slowly added to the dispersion of dialdehyde cellulose nanofiber-soy protein isolate composite particles, and then dispersed in an ultrasonic cell disruptor for 7 min to make the oil phase uniformly dispersed in the aqueous phase, thus constructing a carvacrol-loaded Pickering emulsion, wherein the volume percentage of carvacrol in the Pickering emulsion was 20%.

[0081] Comparative Example 1

[0082] This comparative example is a blank control comparative example.

[0083] The weight loss analysis of this comparative example of mango preservation using Pickering emulsion is shown in the graph below. Figure 5 As shown, the hardness analysis chart is as follows: Figure 6 As shown in the corruption rate analysis chart... Figure 7 As shown.

[0084] Comparative Example 2

[0085] A method for preparing a modified soy protein isolate emulsion, specifically including the following steps:

[0086] (1) Synthesis of carboxylated cellulose nanofiber-soy protein isolate composite particles: The pH of a 2% (w / w) soy protein isolate aqueous solution was adjusted to 10 using a 0.1 mol / L NaOH aqueous solution. The solution was then stirred at room temperature for 1 h. After that, the stirred soy protein isolate aqueous solution was hydrated at 4 °C for 6 h in a refrigerator. The hydrated soy protein isolate aqueous solution was then heat-treated in an oil bath at 95 °C for 15 min. Finally, it was cooled to room temperature to obtain a soy protein isolate solution. Carboxylated cellulose nanofibers were dispersed in deionized water and stirred to form a 1% (w / w) carboxylated cellulose nanofiber dispersion. The soy protein isolate solution and the carboxylated cellulose nanofiber dispersion were then mixed in equal volumes and reacted at 30 °C for 2 h to allow the two to fully crosslink and combine, thus obtaining a carboxylated cellulose nanofiber-soy protein isolate composite particle dispersion.

[0087] (2) Emulsion construction: using carvacrol as the oil phase, carvacrol was slowly added to the dispersion of carboxylated cellulose nanofiber-soy protein isolate composite particles, and then dispersed in an ultrasonic cell disruptor for 10 min to make the oil phase uniformly dispersed in the aqueous phase, thus constructing a carvacrol-loaded emulsion system, wherein the volume percentage of carvacrol in the emulsion system was 1%.

[0088] The emulsion system prepared in this comparative example did not form nanoparticles; the system exhibited uneven dispersion and visible flocs, and stratification occurred after standing. Dynamic light scattering did not show a stable single peak, and polydispersity increased. These results indicate that without the covalent fixation and interface construction of -CHO / -NH2, DCNF cannot achieve the nanoparticle construction of this invention under these conditions, i.e., it cannot achieve the preparation of Pickering emulsions.

[0089] Comparative Example 3

[0090] A method for preparing a soy protein isolate emulsion, specifically including the following steps:

[0091] (1) Preparation of soy protein isolate solution: The pH value of a 2% (w / w) soy protein isolate solution was adjusted to 10 using a 0.1 mol / L NaOH aqueous solution. Then, the solution was stirred at room temperature for 1 h. After that, the stirred soy protein isolate solution was hydrated in a refrigerator at 4 °C for 6 h. Then, the hydrated soy protein isolate solution was heat-treated in an oil bath at 95 °C for 15 min. Finally, it was cooled to room temperature to obtain the soy protein isolate solution.

[0092] (2) Emulsion construction: using carvacrol as the oil phase, carvacrol was slowly added to the soy protein isolate solution, and then dispersed in an ultrasonic cell disruptor for 10 min to make the oil phase uniformly dispersed in the aqueous phase, thus constructing a carvacrol-loaded emulsion system, wherein the volume percentage of carvacrol in the emulsion was 1%.

[0093] The emulsion system in this comparative example only showed transient turbidity and failed to form stable nanoparticles: dynamic light scattering exhibited multiple peaks and a significantly increased PDI, while the absolute value of the zeta potential was low. After standing, phase separation / precipitation occurred. This is because the natural soy protein isolate molecules did not fully expand, and the accessibility and nucleophilicity of lysine and other amino groups were insufficient, making it difficult to form effective Schiff base bonds with the aldehyde groups of dialdehyde cellulose nanofibers. Furthermore, the lack of thermally induced conformational rearrangement and dehydration solidification processes resulted in an unstable interface. A Pickering emulsion system was not constructed. Therefore, alkali treatment and heat treatment of soy protein isolate are necessary technical features for achieving the nanoparticle construction of this invention, and nanoparticles are the basis for Pickering emulsion formation.

[0094] The application of Pickering emulsion based on dialdehyde cellulose nanofibers modified soy protein isolate in fruit preservation includes the following steps:

[0095] Mangoes of uniform size and ripeness were selected as experimental materials. The surfaces were first rinsed with deionized water and then immersed in a 0.3% sodium hypochlorite aqueous solution for 5 minutes for surface disinfection. Afterward, they were rinsed clean with deionized water and air-dried. The Pickering emulsions prepared in Examples 1-6 were diluted 10 times with deionized water and sprayed evenly onto the treated mango surfaces. Together with the blank control group mangoes from Comparative Example 1, they were placed in an environment of 25°C and 50% relative humidity (RH) for 11 days, avoiding direct sunlight. During storage, changes in the appearance of the mangoes were recorded regularly, and the effects of the composite emulsion film on the preservation performance of mangoes were systematically analyzed using fruit firmness, weight loss rate, and decay rate as evaluation indicators.

[0096] Mango weight loss rate determination: Before the experiment, the initial mass W0 of the mangoes was measured. During storage, samples were taken at set time intervals to determine the current mass W of the mangoes. i The weight loss rate of mangoes is calculated using the following formula:

[0097] .

[0098] Mango surface hardness determination: The surface hardness of mangoes was determined using a Shore hardness tester. The probe of the hardness tester was pressed vertically into the mango peel until it was completely submerged, and the reading was recorded. Hardness is expressed in Shore hardness (HSD).

[0099] Mango spoilage rate determination: During storage, samples were taken periodically to observe and record the spoilage status of the mango surface. The spoilage rate was calculated using the spoilage area method: the ratio of the spoiled area to the total surface area of ​​the fruit was analyzed and estimated, and the average value of each sample was taken as the overall spoilage rate. The spoilage rate was calculated using the following formula:

[0100] .

[0101] Where A0 is the area of ​​decay of a single mango, A i Let n be the total surface area and n be the total number of samples. Mangoes are considered rotten when they show signs of oozing juice or mold.

[0102] like Figure 1 As shown, the Pickering emulsion prepared in the examples maintained a uniform milky white appearance after standing at room temperature, and the system showed no obvious stratification or flocculation, indicating that the obtained emulsion system has good dispersion stability and physical stability. The interfacial composite film constructed by dialdehyde cellulose nanofibers and soy protein isolate in the emulsion can effectively improve the spatial barrier and charge repulsion between emulsion droplets, thereby enhancing the structural stability of the emulsion.

[0103] The free radical scavenging experiments using 2,2'-hydrazine-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) and 1,1-diphenyl-2-trinitrophenylhydrazine (DPPH) showed that (e.g.) Figure 2 As shown in the figures, the Pickering emulsions prepared in the embodiments of the present invention all exhibited certain free radical scavenging activity, indicating that the emulsion system has good antioxidant properties. This property comes from the phenolic hydroxyl structure of the carvacrol molecule itself and the effective loading and sustained release effect of the composite particles on carvacrol, enabling the system to continuously provide antioxidant protection during storage, which helps to delay the oxidative browning of fruits and the degradation of nutrients.

[0104] Antibacterial experiments against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) showed (e.g.) Figure 3As shown in the figure, Pickering emulsion exhibited distinct inhibition zones against both representative bacteria, indicating that the emulsion system possesses certain antibacterial properties. This antibacterial effect mainly stems from the broad-spectrum antibacterial activity of carvacrol and the sustained-release and stabilizing effect of the complex particle network, allowing the active ingredients to maintain an effective concentration over a longer period, thereby achieving sustained antibacterial protection.

[0105] In summary, the Pickering emulsion prepared by this invention has good system stability, antioxidant and antibacterial activity, and can provide a functional protective layer with both physical barrier and biological activity for the surface of fruits and vegetables, providing a good foundation for its application in fruit and vegetable preservation.

[0106] Comparison of mango preservation effects (e.g.) Figure 4 As can be seen, the sample in Comparative Example 1 showed significant water loss, rapid browning of the skin, and large-scale rotting during storage, becoming severely spoiled by the 5th day. However, after treatment with the Pickering emulsion prepared in this invention, the mangoes maintained their overall appearance intact and in good condition under the same storage conditions.

[0107] Weight loss analysis showed that the mangoes treated with Pickering emulsion in Examples 1-8 of this invention had a significantly lower weight loss rate throughout the storage period than Comparative Example 1. Comparative Example 1 had a weight loss rate of 20.05% on day 11, while the weight loss rates of mangoes treated with Pickering emulsion in Examples 1-8 were 18.33%, 17.05%, 14.16%, 12.45%, 11.05%, 10.23%, 13.8%, and 9.5%, respectively. This indicates that the dense protective film formed by the emulsion on the fruit surface can effectively inhibit water evaporation and slow down respiration metabolism. Hardness change analysis showed that the mangoes in Comparative Example 1 had almost zero hardness on day 11, while the mangoes treated with Pickering emulsion in Examples 1-8 showed a significantly slower decrease in hardness, indicating that this system can delay fruit tissue softening and ripening to a certain extent. Spoilage rate analysis showed that the comparative example had a spoilage rate as high as 98% on day 11, the mangoes treated in Example 1 had a spoilage rate of 37.91%, the mangoes treated in Example 7 had a spoilage rate of 10%, and the spoilage rates of Examples 2, 3, 4, 5, 6, and 8 were significantly lower. The mangoes treated with Pickering emulsion did not rot, indicating that emulsion treatment can significantly inhibit the growth of pathogens and the spread of spoilage, and significantly extend the shelf life of mangoes.

[0108] The superior preservation effect of the Pickering emulsion prepared by this invention is mainly due to the synergistic effect of its composite structure and function: carvacrol introduced into the emulsion is firmly adsorbed onto the surface of the dialdehyde cellulose nanofiber-soybean protein isolate composite particles, which possess both chemical stability and skeletal reinforcement properties. Under the synergistic effect of the composite particle barrier and the cellulose network, carvacrol achieves slow-release, continuously exerting its antibacterial and antioxidant effects. Simultaneously, the emulsion forms a breathable and dense protective film on the mango surface, effectively isolating exogenous microorganisms and reducing moisture loss. In summary, the Pickering emulsion of this invention exhibits excellent comprehensive preservation performance.

[0109] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for preparing Pickering emulsion based on dialdehyde cellulose nanofiber modified soy protein isolate, characterized in that, Specifically, the following steps are included: (1) Preparation of dialdehyde cellulose nanofibers: Adjust the pH value of the aqueous dispersion of carboxylated cellulose nanofibers, and then carry out an oxidation reaction with an oxidant after adjusting the pH value of the aqueous dispersion of carboxylated cellulose nanofibers. After the reaction is completed, a mixture is obtained. Then, a terminator is added to the mixture to terminate the reaction and induce precipitation in the mixture after the reaction is terminated. The precipitate is filtered, washed and dried to obtain dialdehyde cellulose nanofibers. (2) Synthesis of dialdehyde cellulose nanofiber-soy protein isolate composite particles: The pH value of the soy protein isolate aqueous solution was adjusted, and then stirred, hydrated, heat-treated and cooled to obtain a soy protein isolate solution. Dialdehyde cellulose nanofibers were dispersed in water to form a dialdehyde cellulose nanofiber dispersion. Then the soy protein isolate solution and the dialdehyde cellulose nanofiber dispersion were mixed and reacted to obtain a dialdehyde cellulose nanofiber-soy protein isolate composite particle dispersion. (3) Construction of Pickering emulsion: The oil phase was added to the dispersion of dialdehyde cellulose nanofiber-soy protein isolate composite particles, and then dispersed to construct the Pickering emulsion; The mass percentage concentration of the carboxylated cellulose nanofiber aqueous dispersion in step (1) is 1.0-2.0%; the pH value of the carboxylated cellulose nanofiber aqueous dispersion after adjustment is 3-5. In step (1), the oxidant is added to the aqueous dispersion after pH adjustment at a molar ratio of 1:(0.5-2) of carboxylated cellulose nanofibers to oxidant; the oxidant is sodium periodate; the oxidation reaction conditions are: under light-protected conditions, 30-60℃, reaction for 3-7 hours; the mixture after the reaction is terminated produces a precipitate by alcohol precipitation, specifically by adding anhydrous ethanol to the mixture after the reaction is terminated at a volume ratio of 1:4 and letting it stand for 1-2 hours. In step (3), the oil phase is carvacrol; the dispersion treatment time is 3-10 min; and the volume percentage of the oil phase in the Pickering emulsion is 1-20%.

2. The method for preparing Pickering emulsion based on dialdehyde cellulose nanofiber modified soy protein isolate according to claim 1, characterized in that, In step (2), the mass percentage concentration of the soy protein isolate aqueous solution is 1.0-4.0%; the pH value of the soy protein isolate aqueous solution after adjustment is 9-11; the stirring time is 0.5-2h; the hydration conditions are 4℃ hydration for 2-10h; and the heat treatment conditions are 80-100℃ heat treatment for 5-30min.

3. The method for preparing Pickering emulsion based on dialdehyde cellulose nanofiber modified soy protein isolate according to claim 1, characterized in that, In step (2), the mass percentage concentration of the dialdehyde cellulose nanofiber dispersion is 0.25-4%; the soybean protein isolate solution and the dialdehyde cellulose nanofiber dispersion are mixed in equal volumes and reacted; the reaction conditions are: reaction at 30-60℃ for 1-2 hours.

4. The Pickering emulsion prepared by the method according to any one of claims 1 to 3.

5. The application of the Pickering emulsion according to claim 4 in mango preservation.

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