Pickering emulsion based on dialdehyde cellulose nanofiber modified soybean protein isolate as well as preparation method and application of Pickering emulsion

Abstract

The invention discloses Pickering emulsion based on dialdehyde cellulose nanofiber modified soybean protein isolate as well as a preparation method and application of the Pickering emulsion, and relates to the technical field of food science and bio-based functional materials. Reacting the carboxylated cellulose nanofiber aqueous dispersion with an oxidizing agent under a dark condition after the pH is adjusted, terminating through a terminating agent, and performing alcohol precipitation, washing and drying to obtain dialdehyde cellulose nanofibers; carrying out stirring, hydration and heat treatment on the soybean protein isolate aqueous solution after pH adjustment, and cooling to obtain a soybean protein isolate solution; dispersing the obtained dialdehyde cellulose nanofibers in water, and then mixing with a soybean protein isolate solution for reaction to form a composite particle dispersion liquid; the carvacrol is slowly added into the dispersion liquid, and a carvacrol loaded Pickering emulsion is constructed through dispersion treatment; the emulsion is applied to fruit surface film formation, can significantly inhibit the growth of pathogenic microorganisms, delays fruit spoilage, and improves the appearance quality in the storage period and the shelf life.

Description

TECHNICAL FIELD

[0001] The present application relates to a Pickering emulsion based on dialdehyde cellulose nanofiber modified soy protein isolate and a preparation method and application thereof, and belongs to the technical field of food science and bio-based functional materials. BACKGROUND

[0002] Soy protein isolate (SPI) is often used as a food emulsifier and edible film substrate due to its abundant source and good degradability. However, the natural conformation of SPI is tight, and the hydrophobic groups in the secondary structure are buried, resulting in poor solubility and limited emulsion stability, which limits 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), which can improve its function to some extent, but have problems such as high energy consumption, toxic cross-linking agent or uncontrollable reaction, which is not conducive to the popularization and application of food contact materials. On this basis, existing research uses green polysaccharides for composite modification, such as carboxymethyl cellulose (CMC), chitosan, pectin and alginate. However, these methods mainly rely on electrostatic interaction, hydrogen bonding or hydrophobic interaction, which can improve dispersibility and emulsification, but the binding force is limited, and the emulsion or film is easy to lose stability under storage, heating or ion interference, which limits its application in complex food environments.

[0003] In recent years, Pickering emulsion has attracted attention in the field of food and preservation due to its high stability and no surfactant residues. However, how to design natural particles with good interfacial activity and active substance loading capacity is still a difficult problem in this field. Carvacrol, as a natural compound of monoterpenoid phenols, has significant antibacterial and antioxidant activity, 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 emulsion and load carvacrol, so as to develop a new type of fruit preservative with structural stability and antibacterial preservation function. SUMMARY

[0005] One of the purposes of the present application is to provide a Pickering emulsion preparation method based on dialdehyde cellulose nanofiber modified soy protein isolate, which specifically comprises the following steps: (1) Preparation of dialdehyde cellulose nanofiber: adjust the pH value of the carboxylated cellulose nanofiber aqueous dispersion (preferably adjust the pH value with 0.1 mol / L H2SO4 aqueous solution), then the carboxylated cellulose nanofiber aqueous dispersion after adjusting the pH value is subjected to an oxidation reaction with an oxidizing agent, a mixed solution is obtained after the reaction is completed, then a terminating agent (preferably ethylene glycol) is added to the mixed solution to terminate the reaction, and the mixed solution after the reaction is terminated is induced to produce a precipitate, and the precipitate is subjected to suction filtration, washing, and drying to obtain dialdehyde cellulose nanofiber (DCNFs).

[0006] (2) Synthesis of dialdehyde cellulose nanofiber-soy protein isolate composite particles: adjust the pH value of the soy protein isolate aqueous solution (preferably adjust the pH value with 0.1 mol / L NaOH aqueous solution), then obtain the soy protein isolate solution by stirring, hydration, heat treatment, and cooling, disperse the dialdehyde cellulose nanofiber in water to form a dialdehyde cellulose nanofiber dispersion, then mix the dialdehyde cellulose nanofiber dispersion with the soy protein isolate solution to obtain a dialdehyde cellulose nanofiber-soy protein isolate composite particle (DCNF-SPI) dispersion.

[0007] (3) Construction of Pickering emulsion: add the oil phase to the dialdehyde cellulose nanofiber-soy protein isolate composite particle dispersion, then perform dispersion treatment (preferably dispersion treatment in an ultrasonic cell pulverizer) to construct a Pickering emulsion.

[0008] 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.

[0009] 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.

[0010] Preferably, the oxidizing agent is added to the water dispersion after adjusting the pH value in step (1) at a molar ratio of carboxylated cellulose nanofiber to oxidizing agent of 1:(0.5-2), the oxidizing agent is sodium periodate, the oxidation reaction conditions are: in the dark, 30-60°C, for 3-7 h, and the precipitate of the reaction termination mixed solution is obtained by alcohol precipitation, and the specific method is: add anhydrous ethanol to the reaction termination mixed solution at a volume ratio of 1:4 and stand for 1-2 h.

[0011] More preferably, the oxidation reaction conditions in step (1) are: in the dark, 45°C for 5 h.

[0012] Preferably, the mass percentage concentration of the soybean protein isolate aqueous solution in step (2) is 1.0-4.0%; the adjusted pH value of the soybean protein isolate aqueous solution is 9-11; the stirring time is 0.5-2h; the hydration condition is 4℃ for 2-10h; and the heat treatment condition is 80-100℃ for 5-30min.

[0013] More preferably, the mass percentage concentration of the soybean protein isolate aqueous solution in step (2) is 2%; the adjusted pH value of the soybean protein isolate aqueous solution is 10; the stirring condition is room temperature for 1h; the hydration condition is 4℃ for 6h; and the heat treatment condition is 95℃ for 15min.

[0014] Preferably, the mass percentage concentration of the dialdehyde cellulose nanofiber dispersion liquid in step (2) is 0.25-4%; the soybean protein isolate solution and the dialdehyde cellulose nanofiber dispersion liquid are mixed in equal volume for reaction; and the mixing reaction condition is 30-60℃ for 1-2h.

[0015] More preferably, the mixing reaction condition in step (2) is 30℃ for 2h.

[0016] Preferably, the oil phase in step (3) is carvacol; the dispersion treatment time is 3-10min; and the volume percentage of the oil phase in the Pickering emulsion is 1-20%.

[0017] The second object of the present application is to provide a Pickering emulsion prepared by the preparation method of the present application.

[0018] The third object of the present application is to provide an application of the Pickering emulsion prepared by the present application in fruit preservation.

[0019] The mechanism of the present application is as follows: The functional Pickering emulsion constructed by the present application is covalently crosslinked by aldehyde-amino Schiff base reaction between dialdehyde cellulose nanofiber (DCNFs) and soybean protein isolate (SPI), forming a composite particle with both chemical stability and nanoskeleton enhancement effect. The particle can efficiently adsorb and stabilize carvacol oil droplets at the oil-water interface, so that carvacol is effectively loaded through hydrophobic interaction and hydrogen bonding, and realizes sustained release and controlled release under the synergistic effect of the composite particle barrier and the cellulose network structure. After the emulsion is coated on the surface of fruits, a protective film with both physical barrier and biological activity can be formed, which can not only reduce water evaporation and external pollution, but also continuously release carvacol to inhibit the growth of pathogenic microorganisms and delay the oxidation and softening of fruits, thereby significantly prolonging the storage period and shelf life of fruits, and realizing green, safe and sustainable preservation effect.

[0020] Advantages of the present application: (1) Stable covalent binding: Unlike the modification of CMC and pectin-dependent non-covalent interaction, the present application covalently crosslinks SPI structure through aldehyde-amino crosslinking of DCNFs.

[0021] (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 as a nanofiber skeleton.

[0022] (3) High loading and slow release: DCNF-SPI particles can form a stable interface network, effectively loading carvacol and prolonging its antibacterial effect.

[0023] (4) Excellent fruit preservation performance: The prepared emulsion realizes the slow release of carvacol through the synergistic effect of the composite particle barrier and the cellulose grid structure, can significantly inhibit the growth of microorganisms, and can realize low spoilage rate or even no spoilage of mangoes within 11 days of test period, slow hardness decrease, and low weight loss rate, maintaining the appearance and nutritional quality of the fruit.

[0024] (5) Green and environmentally friendly: DCNFs are derived from natural cellulose and are biodegradable and non-toxic, avoiding the safety hazards of harmful crosslinking agents such as glutaraldehyde, and meeting the application requirements of food contact materials; The present application has the advantages of natural raw material source, simple process, environmental friendliness, safety and non-toxicity. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The figure is a comparison chart of the macroscopic storage stability of the emulsion of examples 1-6 of the present application.

[0026] Figure 2 The figure is a comparison chart of the antioxidant capacity of the emulsion of examples 1-6 of the present application.

[0027] Figure 3 The figure is a comparison chart of the antibacterial capacity of the emulsion of examples 1-6 of the present application.

[0028] Figure 4 The figure is a comparison chart of the effect of the emulsion of examples 1-6 and comparative example 1 in preserving mangoes.

[0029] Figure 5 The figure is a weight loss rate analysis chart of the emulsion of examples 1-6 and comparative example 1 in preserving mangoes.

[0030] Figure 6 The figure is a hardness analysis chart of the emulsion of examples 1-6 and comparative example 1 in preserving mangoes.

[0031] Figure 7A graph for analyzing the rate of spoilage during the preservation of mangoes using the emulsion of Examples 1 to 6 and Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0032] In order to better illustrate the purpose, technical scheme and advantages of the present application, the present application will be further described below in conjunction with specific examples.

[0033] Example 1

[0034] A Pickering emulsion preparation method based on dialdehyde cellulose nanofiber modified soybean protein isolate, specifically comprising the following steps: (1) Preparation of dialdehyde cellulose nanofiber: adjust the pH value of a 2% carboxylated cellulose nanofiber water dispersion to 4 using 0.1 mol / L H2SO4 aqueous solution, then add sodium periodate to the pH-adjusted carboxylated cellulose nanofiber water dispersion under light-proof conditions at a molar ratio of 1:1.5, and perform oxidation reaction at 45℃ constant temperature water bath for 5h, then add ethylene glycol to the mixture at a molar ratio of 1:2 to terminate the reaction, and then add anhydrous ethanol to the reaction-terminated mixture at a volume ratio of 1:4 and stand for 1h to precipitate the product in the reaction-terminated mixture, collect the precipitated product by suction filtration, and then wash the precipitated product with a mixture of anhydrous ethanol and deionized water at a volume ratio of 7:3, 5:5 and 3:7, respectively, to remove residual reactants, and finally dry the washed precipitated product in a freeze dryer for 24h to obtain dialdehyde cellulose nanofiber.

[0035] (2) Synthesis of dialdehyde cellulose nanofiber-soybean protein isolate composite particles: adjust the pH value of a 2% soybean protein isolate aqueous solution to 10 using 0.1 mol / L NaOH aqueous solution; then stir at room temperature for 1h, then hydrate the stirred soybean protein isolate aqueous solution in a refrigerator at 4℃ for 6h, then heat treat the hydrated soybean protein isolate aqueous solution in a 95℃ oil bath for 15min, and finally cool to room temperature to obtain a soybean protein isolate solution, disperse dialdehyde cellulose nanofiber in deionized water to obtain a 1% dialdehyde cellulose nanofiber dispersion, then mix the soybean protein isolate solution and the dialdehyde cellulose nanofiber dispersion in equal volumes, and react at 30℃ for 2h to allow them to crosslink and combine, to obtain a dialdehyde cellulose nanofiber-soybean protein isolate composite particle dispersion.

[0036] (3) Pickering emulsion construction: taking carvacol as the oil phase, the carvacol was slowly added into the dialdehyde cellulose nanofiber-soy protein isolate composite particle dispersion liquid, and then dispersed in the ultrasonic cell pulverizer for 10 min, so that the oil phase was uniformly dispersed in the water phase, and the carvacol-loaded Pickering emulsion (SDC-1) was constructed, wherein the volume percentage of carvacol in the Pickering emulsion was 1%.

[0037] The weight loss rate analysis diagram of the Pickering emulsion fresh-keeping mango in the process of the embodiment is shown in Figure 5 , the hardness analysis diagram is shown in Figure 6 , and the corruption rate analysis diagram is shown in Figure 7 .

[0038] Example 2

[0039] A Pickering emulsion preparation method based on dialdehyde cellulose nanofiber modified soy protein isolate, specifically comprising the following steps: (1) Preparation of dialdehyde cellulose nanofiber: the pH value of the 2% carboxylated cellulose nanofiber water dispersion liquid was adjusted to 4 by using 0.1 mol / L H2SO4 aqueous solution, and then the adjusted pH value of the carboxylated cellulose nanofiber water dispersion liquid was added to sodium periodate under light shielding conditions at 45°C constant temperature water bath oxidation reaction for 5h, wherein the sodium periodate was added to the adjusted pH value of the water dispersion liquid in a proportion of 1:1.5 of carboxylated cellulose nanofiber and sodium periodate, and then the reaction was terminated by adding ethylene glycol to the mixed liquid in a proportion of 1:2 of sodium periodate and ethylene glycol, and the reaction terminated mixed liquid was added with anhydrous ethanol in a proportion of 1:4 of the reaction terminated mixed liquid and anhydrous ethanol by volume ratio and placed for 1h, so that the precipitated product in the reaction terminated mixed liquid was analyzed and discharged, the precipitated product was collected by suction filtration, and the precipitated product was washed with a mixed liquid prepared by mixing anhydrous ethanol and deionized water in a proportion of 7:3, 5:5 and 3:7 by volume ratio, respectively, to remove residual reactants, and finally the washed precipitated product was dried in a freeze dryer for 24h to obtain dialdehyde cellulose nanofiber.

[0040] (2) Synthesis of dialdehyde cellulose nanofiber-soy protein isolate composite particles: 2% (w / v) soy protein isolate aqueous solution was adjusted to pH 10 using 0.1 mol / L NaOH aqueous solution; then the solution was stirred at room temperature for 1 h, and then the stirred soy protein isolate aqueous solution was hydrated in a refrigerator at 4°C for 6 h, and then the hydrated soy protein isolate aqueous solution was heat-treated at 95°C for 15 min, and finally cooled to room temperature to obtain a soy protein isolate solution. Dialdehyde cellulose nanofiber was dispersed in deionized water to obtain a 1% (w / v) 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 them to crosslink and combine, thereby obtaining a dialdehyde cellulose nanofiber-soy protein isolate composite particle dispersion.

[0041] (3) Pickering emulsion construction: carvacol was used as the oil phase, and carvacol was slowly added to the dialdehyde cellulose nanofiber-soy protein isolate composite particle dispersion, and then dispersed in an ultrasonic cell crusher for 10 min to uniformly disperse the oil phase in the water phase, thereby constructing a carvacol-loaded Pickering emulsion (SDC-3), wherein the volume percentage of carvacol in the Pickering emulsion was 3%.

[0042] The weight loss rate analysis chart of the Pickering emulsion fresh-keeping mango in the process is shown in Figure 5 , the hardness analysis chart is shown in Figure 6 , and the spoilage rate analysis chart is shown in Figure 7 .

[0043] Example 3

[0044] A Pickering emulsion preparation method based on dialdehyde cellulose nanofiber modified soy protein isolate, specifically comprising the following steps: (1) Preparation of dialdehyde cellulose nanofiber: 0.1 mol / L H2SO4 aqueous solution was used to adjust the pH value of 2% carboxylated cellulose nanofiber water dispersion to 4, then the carboxylated cellulose nanofiber water dispersion after adjusting the pH value was added with sodium periodate under light-proof condition, and the oxidation reaction was carried out at 45℃ constant temperature water bath for 5h, wherein the sodium periodate was added into the water dispersion after adjusting the pH value at a molar ratio of carboxylated cellulose nanofiber to sodium periodate of 1:1.5, the mixed solution was obtained after the reaction was completed, then glycol was added into the mixed solution at a molar ratio of sodium periodate to glycol of 1:2 to terminate the reaction, and through alcohol precipitation method, dehydrated alcohol was added into the mixed solution after the reaction was terminated at a volume ratio of 1:4, and the mixed solution was allowed to stand for 1h, so that the precipitated product in the mixed solution after the reaction was terminated was analyzed and removed, the precipitated product was collected by suction filtration, and the mixed solution prepared by dehydrated alcohol and deionized water at a volume ratio of 7:3, 5:5 and 3:7 was used to wash the precipitated product in turn to remove residual reactants, and finally the washed precipitated product was dried in a freeze dryer for 24h to obtain dialdehyde cellulose nanofiber.

[0045] (2) Synthesis of dialdehyde cellulose nanofiber-soy protein isolate composite particles: 0.1 mol / L NaOH aqueous solution was used to adjust the pH value of 2% soy protein isolate aqueous solution to 10; then the stirred soy protein isolate aqueous solution was hydrated in a refrigerator at 4℃ for 6h, and then the hydrated soy protein isolate aqueous solution was heat treated in an oil bath at 95℃ for 15min, and finally cooled to room temperature to obtain a soy protein isolate solution, dialdehyde cellulose nanofiber was dispersed in deionized water to obtain a 1% dialdehyde cellulose nanofiber dispersion, then the soy protein isolate solution and the dialdehyde cellulose nanofiber dispersion were mixed in equal volume, and the two were crosslinked and combined at 30℃ for 2h to obtain dialdehyde cellulose nanofiber-soy protein isolate composite particle dispersion.

[0046] (3) Construction of Pickering emulsion: carvacol was used as oil phase, and the carvacol was slowly added into the dialdehyde cellulose nanofiber-soy protein isolate composite particle dispersion, then the oil phase was uniformly dispersed in the water phase by dispersing treatment in an ultrasonic cell pulverizer for 10min to construct a carvacol-loaded Pickering emulsion (SDC-5), wherein the volume percentage of carvacol in the Pickering emulsion was 5%.

[0047] The weight loss rate analysis chart of the Pickering emulsion fresh-keeping mango in the process is shown in Figure 5 , the hardness analysis chart is shown in Figure 6 , and the corruption rate analysis chart is shown in Figure 7 .

[0048] Example 4

[0049] A Pickering emulsion preparation method based on dialdehyde cellulose nanofiber modified soybean protein isolate, specifically comprising the following steps: (1) Preparation of dialdehyde cellulose nanofiber: adjust the pH value of 2% carboxylated cellulose nanofiber water dispersion to 4 using 0.1 mol / L H2SO4 aqueous solution, then add sodium periodate to the adjusted pH value of the water dispersion in a molar ratio of 1:1.5 (carboxylated cellulose nanofiber to sodium periodate) under light-proof conditions and constant temperature water bath at 45°C for oxidation reaction for 5h, then add ethylene glycol to the mixed solution in a molar ratio of 1:2 (sodium periodate to ethylene glycol) to terminate the reaction, and then add anhydrous ethanol to the reaction-terminated mixed solution in a volume ratio of 1:4 (reaction-terminated mixed solution to anhydrous ethanol) and stand for 1h to precipitate the product in the reaction-terminated mixed solution, collect the precipitated product by suction filtration, and then wash the precipitated product with a mixed solution prepared by mixing anhydrous ethanol and deionized water in a volume ratio of 7:3, 5:5, and 3:7, respectively, to remove residual reactants, and finally dry the washed precipitated product in a freeze dryer for 24h to obtain dialdehyde cellulose nanofiber.

[0050] (2) Synthesis of dialdehyde cellulose nanofiber-soybean protein isolate composite particles: adjust the pH value of 2% soybean protein isolate aqueous solution to 10 using 0.1 mol / L NaOH aqueous solution, then stir for 1h at room temperature, then hydrate the stirred soybean protein isolate aqueous solution in a refrigerator at 4°C for 6h, then heat treat the hydrated soybean protein isolate aqueous solution in a 95°C oil bath for 15min, and finally cool to room temperature to obtain a soybean protein isolate solution, disperse dialdehyde cellulose nanofiber in deionized water to obtain a 1% dialdehyde cellulose nanofiber dispersion, then mix the soybean protein isolate solution and the dialdehyde cellulose nanofiber dispersion in equal volumes, and crosslink and combine them at 30°C for 2h to obtain a dialdehyde cellulose nanofiber-soybean protein isolate composite particle dispersion.

[0051] (3) Pickering emulsion construction: use carvacol as the oil phase, slowly add carvacol to the dialdehyde cellulose nanofiber-soybean protein isolate composite particle dispersion, then disperse in an ultrasonic cell crusher for 10min to uniformly disperse the oil phase in the water phase to construct a carvacol-loaded Pickering emulsion (SDC-10), wherein the volume percentage of carvacol in the Pickering emulsion is 10%.

[0052] The weight loss rate analysis chart of the Pickering emulsion in the process of preserving mangoes is shown in Figure 5 The hardness analysis chart is shown in Figure 6 The corruption rate analysis chart is shown in Figure 7

[0053] Example 5

[0054] (1) Preparation of dialdehyde cellulose nanofiber: 0.1 mol / L H2SO4 aqueous solution was used to adjust the pH value of 2% carboxylated cellulose nanofiber water dispersion to 4, and then the carboxylated cellulose nanofiber water dispersion after adjusting the pH value was mixed with sodium periodate under light-proof conditions at 45°C constant temperature water bath for oxidation reaction for 5h, wherein the sodium periodate was added to the water dispersion after adjusting the pH value in a proportion of 1:1.5 of carboxylated cellulose nanofiber to sodium periodate, the mixed solution was obtained after the reaction was completed, and then the reaction was terminated by adding ethylene glycol to the mixed solution in a proportion of 1:2 of sodium periodate to ethylene glycol, and the reaction-terminated mixed solution was precipitated by alcohol precipitation method, and deionized water was added to the reaction-terminated mixed solution in a proportion of 1:4 of reaction-terminated mixed solution to anhydrous ethanol and was left for 1h, so that the precipitated product in the reaction-terminated mixed solution was analyzed and removed, the precipitated product was collected by suction filtration, and the precipitated product was washed with a mixed solution prepared by mixing anhydrous ethanol and deionized water in a proportion of 7:3, 5:5 and 3:7 by volume, respectively, to remove residual reactants, and finally the washed precipitated product was dried in a freeze dryer for 24h to obtain dialdehyde cellulose nanofiber.

[0055] (2) Synthesis of dialdehyde cellulose nanofiber-soy protein isolate composite particles: 0.1 mol / L NaOH aqueous solution was used to adjust the pH value of 2% soy protein isolate aqueous solution to 10; then the stirred soy protein isolate aqueous solution was hydrated in a refrigerator at 4°C for 6h, and then the hydrated soy protein isolate aqueous solution was heat-treated in a 95°C oil bath for 15min, and finally cooled to room temperature to obtain a soy protein isolate solution, dialdehyde cellulose nanofiber was dispersed in deionized water to obtain a 1% dialdehyde cellulose nanofiber dispersion, and then the soy protein isolate solution and the dialdehyde cellulose nanofiber dispersion were mixed in equal volume, and the two were crosslinked and combined at 30°C for 2h to obtain a dialdehyde cellulose nanofiber-soy protein isolate composite particle dispersion.

[0056] ​(3) Pickering emulsion construction: with carvacol as the oil phase, carvacol was slowly added into the dispersion liquid of the dialdehyde cellulose nanofiber-soy protein isolate composite particles, and then dispersed in an ultrasonic cell pulverizer for 10 min, so that the oil phase was uniformly dispersed in the water phase, and a carvacol-loaded Pickering emulsion (SDC-15) was constructed, wherein the volume percentage of carvacol in the Pickering emulsion was 15%.

[0057] The weight loss rate analysis diagram of the Pickering emulsion fresh-keeping mango in the process is shown in Figure 5 , the hardness analysis diagram is shown in Figure 6 , and the spoilage rate analysis diagram is shown in Figure 7 .

[0058] Example 6

[0059] A Pickering emulsion preparation method based on dialdehyde cellulose nanofiber modified soy protein isolate, specifically comprising the following steps: (1) Preparation of dialdehyde cellulose nanofiber: the pH value of a 2% mass percentage carboxylated cellulose nanofiber water dispersion liquid was adjusted to 4 using 0.1 mol / L H2SO4 aqueous solution, and then the adjusted pH value carboxylated cellulose nanofiber water dispersion liquid was added to sodium periodate under light shielding conditions at 45°C constant temperature water bath oxidation reaction for 5 h, wherein the sodium periodate was added to the adjusted pH value water dispersion liquid at a sodium periodate to carboxylated cellulose nanofiber molar ratio of 1:1.5, the reaction was terminated by adding ethylene glycol to the mixed liquid at a sodium periodate to ethylene glycol molar ratio of 1:2, and the reaction terminated mixed liquid was precipitated by alcohol precipitation method, the reaction terminated mixed liquid was added with anhydrous ethanol at a volume ratio of 1:4, and the precipitated product in the reaction terminated mixed liquid was analyzed and removed after standing for 1 h, the precipitated product was collected by suction filtration, and the precipitated product was washed with a mixed liquid prepared by mixing anhydrous ethanol and deionized water at a volume ratio of 7:3, 5:5, and 3:7, respectively, to remove residual reactants, and finally the washed precipitated product was dried in a freeze dryer for 24 h to obtain dialdehyde cellulose nanofiber.

[0060] (2) Synthesis of dialdehyde cellulose nanofiber-soy protein isolate composite particles: 2% (w / v) soy protein isolate aqueous solution was adjusted to pH 10 using 0.1 mol / L NaOH aqueous solution; then the soy protein isolate aqueous solution was stirred at room temperature for 1 h, and then the stirred soy protein isolate aqueous solution was hydrated in a refrigerator at 4°C for 6 h, and then the hydrated soy protein isolate aqueous solution was heat-treated at 95°C for 15 min, and finally cooled to room temperature to obtain a soy protein isolate solution. Dialdehyde cellulose nanofiber was dispersed in deionized water to obtain a 1% (w / v) 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 them to crosslink and combine, thereby obtaining a dialdehyde cellulose nanofiber-soy protein isolate composite particle dispersion.

[0061] (3) Pickering emulsion construction: carvacol was used as the oil phase, and carvacol was slowly added to the dialdehyde cellulose nanofiber-soy protein isolate composite particle dispersion, and then dispersed in an ultrasonic cell crusher for 10 min to uniformly disperse the oil phase in the water phase, thereby constructing a carvacol-loaded Pickering emulsion (SDC-20), wherein the volume percentage of carvacol in the Pickering emulsion was 20%.

[0062] The weight loss rate analysis chart of the Pickering emulsion fresh-keeping mango in this example is shown in Figure 5 , the hardness analysis chart is shown in Figure 6 , and the spoilage rate analysis chart is shown in Figure 7 .

[0063] Example 7

[0064] A Pickering emulsion preparation method based on dialdehyde cellulose nanofiber modified soy protein isolate, specifically comprising the following steps: (1) Preparation of dialdehyde cellulose nanofiber: 0.1 mol / L H2SO4 aqueous solution was used to adjust the pH value of 1% carboxylated cellulose nanofiber water dispersion to 3, then the carboxylated cellulose nanofiber water dispersion after adjusting the pH value was added with sodium periodate under light-proof condition, and the mixture was reacted at 60°C for 3h, wherein the sodium periodate was added into the water dispersion after adjusting the pH value at a molar ratio of carboxylated cellulose nanofiber to sodium periodate of 1:0.5, and the reaction was terminated by adding ethylene glycol into the mixture at a molar ratio of sodium periodate to ethylene glycol of 1:2. The reaction-terminated mixture was precipitated by alcohol, and deionized water was added into the reaction-terminated mixture at a volume ratio of 1:4, and the mixture was left to stand for 2h to precipitate the product. The precipitate was collected by suction filtration, and was washed with a mixture of deionized water and anhydrous ethanol at a volume ratio of 7:3, 5:5 and 3:7, respectively, to remove residual reactants. Finally, the washed precipitate was dried in a freeze dryer for 24h to obtain dialdehyde cellulose nanofiber.

[0065] (2) Synthesis of dialdehyde cellulose nanofiber-soy protein isolate composite particles: 0.1 mol / L NaOH aqueous solution was used to adjust the pH value of 4% soy protein isolate aqueous solution to 11, and the mixture was stirred at room temperature for 0.5h, and then was hydrated in a refrigerator at 4°C for 10h. The hydrated soy protein isolate aqueous solution was heated at 100°C for 5min, and then was cooled to room temperature to obtain a soy protein isolate solution. Dialdehyde cellulose nanofiber was dispersed in deionized water to obtain a 0.25% dialdehyde cellulose nanofiber dispersion. The soy protein isolate solution and the dialdehyde cellulose nanofiber dispersion were mixed in equal volume, and were crosslinked at 60°C for 1h to obtain dialdehyde cellulose nanofiber-soy protein isolate composite particle dispersion.

[0066] (3) Construction of Pickering emulsion: carvacrol was used as oil phase, and was slowly added into the dialdehyde cellulose nanofiber-soy protein isolate composite particle dispersion. The mixture was dispersed in an ultrasonic cell crusher for 3min to obtain carvacrol-loaded Pickering emulsion, wherein the volume percentage of carvacrol in the Pickering emulsion was 20%.

[0067] Example 8

[0068] A Pickering emulsion preparation method based on dialdehyde cellulose nanofiber modified soy protein isolate, specifically comprising the following steps: (1) Preparation of dialdehyde cellulose nanofiber: 0.1 mol / L H2SO4 aqueous solution was used to adjust the pH value of 1.5% carboxylated cellulose nanofiber water dispersion to 5, then the carboxylated cellulose nanofiber water dispersion after adjusting the pH value was added with sodium periodate under light-proof condition, and the oxidation reaction was carried out at 30℃ constant temperature water bath for 7h, wherein the sodium periodate was added into the water dispersion after adjusting the pH value at a molar ratio of carboxylated cellulose nanofiber to sodium periodate of 1:2, the mixed solution was obtained after the reaction was completed, then glycol was added into the mixed solution at a molar ratio of sodium periodate to glycol of 1:2 to terminate the reaction, and through alcohol precipitation method, dehydrated alcohol was added into the mixed solution after the reaction was terminated at a volume ratio of 1:4, and the mixed solution was allowed to stand for 1.5h, so that the precipitated product in the mixed solution after the reaction was terminated was analyzed and removed, the precipitated product was collected by suction filtration, and the mixed solution prepared by dehydrated alcohol and deionized water at a volume ratio of 7:3, 5:5 and 3:7 respectively was used to wash the precipitated product in turn to remove residual reactants, and finally the washed precipitated product was dried in a freeze dryer for 24h to obtain dialdehyde cellulose nanofiber.

[0069] (2) Synthesis of dialdehyde cellulose nanofiber-soy protein isolate composite particles: 0.1 mol / L NaOH aqueous solution was used to adjust the pH value of 1% soy protein isolate aqueous solution to 9; then the stirred soy protein isolate aqueous solution was hydrated in a refrigerator at 4℃ for 2h, and then the hydrated soy protein isolate aqueous solution was heat treated at 80℃ oil bath for 30min, and finally cooled to room temperature to obtain soy protein isolate solution. Dialdehyde cellulose nanofiber was dispersed in deionized water to obtain 4% dialdehyde cellulose nanofiber dispersion. Then the soy protein isolate solution and the dialdehyde cellulose nanofiber dispersion were mixed in equal volume, and crosslinked and combined at 45℃ for 1.5h to obtain dialdehyde cellulose nanofiber-soy protein isolate composite particle dispersion.

[0070] (3) Construction of Pickering emulsion: carvacol was used as oil phase, and carvacol was slowly added into dialdehyde cellulose nanofiber-soy protein isolate composite particle dispersion, then dispersed and treated in an ultrasonic cell pulverizer for 7min to uniformly disperse the oil phase in the water phase, and a carvacol-loaded Pickering emulsion was constructed, wherein the volume percentage of carvacol in the Pickering emulsion was 20%.

[0071] Comparative Example 1 This comparative example is a blank control comparative example.

[0072] The weight loss rate analysis diagram of the Pickering emulsion in the preservation process of the mango in the comparative example is as follows: Figure 5As shown, the hardness analysis chart is as shown in FIG. 2. Figure 6 As shown, the corruption rate analysis chart is as shown in FIG. 3. Figure 7

[0073] Comparative Example 2 A modified soybean protein isolate emulsion preparation method, specifically comprising the following steps: (1) Synthesis of carboxylated cellulose nanofiber-soybean protein isolate composite particles: 0.1 mol / L NaOH aqueous solution was used to adjust the pH value of a 2% mass percentage soybean protein isolate aqueous solution to 10; then the soybean protein isolate aqueous solution was stirred at room temperature for 1 h, and then the stirred soybean protein isolate aqueous solution was hydrated in a refrigerator at 4°C for 6 h, and then the hydrated soybean protein isolate aqueous solution was heat-treated in an oil bath at 95°C for 15 min, and finally cooled to room temperature to obtain a soybean protein isolate solution. Carboxylated cellulose nanofiber was dispersed in deionized water to form a 1% mass percentage carboxylated cellulose nanofiber dispersion, and then the soybean protein isolate solution and the carboxylated cellulose nanofiber dispersion were mixed in equal volumes, and crosslinked and combined at 30°C for 2 h to obtain a carboxylated cellulose nanofiber-soybean protein isolate composite particle dispersion.

[0074] (2) Emulsion construction: carvacrol was used as the oil phase, and the carvacrol was slowly added to the carboxylated cellulose nanofiber-soybean protein isolate composite particle dispersion, and then dispersed in an ultrasonic cell crusher for 10 min to uniformly disperse the oil phase in the water phase to construct a carvacrol-loaded emulsion system, wherein the volume percentage of carvacrol in the emulsion system was 1%.

[0075] The emulsion system prepared in this comparative example did not form nanoparticles, the system was not uniformly dispersed and visible flocs were present, and after standing, the system was layered; dynamic light scattering did not show a stable single peak and the polydispersity increased. This result shows that the lack of covalent modification of -CHO / -NH2 and interface construction, DCNF cannot achieve the nanoparticle construction of the present application under this condition, i.e., Pickering emulsion cannot be prepared.

[0076] Comparative Example 3 A soybean protein isolate emulsion preparation method, specifically comprising the following steps: (1) Preparation of a soybean protein isolate solution: 0.1 mol / L NaOH aqueous solution was used to adjust the pH value of a 2% mass percentage soybean protein isolate aqueous solution to 10; then the soybean protein isolate aqueous solution was stirred at room temperature for 1 h, and then the stirred soybean protein isolate aqueous solution was hydrated in a refrigerator at 4°C for 6 h, and then the hydrated soybean protein isolate aqueous solution was heat-treated in an oil bath at 95°C for 15 min, and finally cooled to room temperature to obtain a soybean protein isolate solution.

[0077] ​(2) Emulsion construction: take carvacol as oil phase, slowly add carvacol into soybean protein isolate solution, then disperse in ultrasonic cell pulverizer for 10 min, so that the oil phase is uniformly dispersed in the water phase, and the carvacol-loaded emulsion system is constructed, wherein the volume percentage of carvacol in the emulsion is 1%.

[0078] The emulsion system of the present comparative example only appears transient turbidity, and does not form stable nanoparticles: dynamic light scattering shows multiple peaks and PDI is significantly increased, the absolute value of zeta potential is low, and after standing, phase / sedimentation appears. The reason is that the natural soybean protein isolate molecules are not fully unfolded, the accessibility and nucleophilicity of lysine and other amine groups are insufficient, it is difficult to form effective Schiff base bond with aldehyde group of dialdehyde cellulose nanofiber, and there is lack of heat-induced conformational rearrangement and dehydration curing process, resulting in that the interface cannot be shaped. Pickering emulsion system is not constructed. As can be seen, the alkali treatment and heat treatment of soybean protein isolate are necessary technical features for realizing the construction of nanoparticles of the present application, and the nanoparticles are the basis for the formation of Pickering emulsion.

[0079] The application of a Pickering emulsion based on dialdehyde cellulose nanofiber modified soybean protein isolate in fruit preservation specifically includes the following steps: Uniformly spray the Pickering emulsion prepared in Example 1-6 on the surface of the treated mango after diluting 10 times with deionized water; together with the blank comparative example group of mangoes of Comparative Example 1, place them in a 25℃, 50% relative humidity (RH) environment for 11 days, avoiding direct sunlight. Record the appearance changes of the mangoes regularly during storage, and take fruit hardness, weight loss rate and rot rate as evaluation indexes to systematically analyze the influence of the composite emulsion film on the preservation performance of mangoes.

[0080] Mango weight loss rate determination: before the experiment, weigh the initial mass of the mangoes W0. During storage, take samples at a set time interval, and measure the current mass of the mangoes W i . The weight loss rate of the mangoes is calculated as follows: .

[0081] Mango surface hardness determination: use a Shore fruit hardness tester to measure the surface hardness of the mangoes. The hardness tester probe is vertically pressed into the mango peel until the probe is completely immersed in the peel, and the hardness tester reading is recorded; the hardness is expressed in units of Shore hardness (HSD, Hardness Shore Degree).

[0082] Mango rot rate determination: periodically sample during storage, observe and record the rot on the surface of mango. The rot area method is used to calculate the rot rate: the ratio of rot area of fruit to total surface area of fruit is analyzed and estimated, and the average value of each sample is taken as the overall rot rate. The rot rate is calculated as follows: .

[0083] Wherein, A0 is the rot area of a single mango, A i is the total surface area, and n is the total number of samples. When mangoes appear to seep juice, mold spots, they are determined to be rotten.

[0084] As Figure 1 shown, the Pickering emulsion prepared in the examples still maintains a uniform milky white appearance after standing at room temperature, and the system has no obvious layering or flocculation phenomenon, indicating that the obtained emulsion system has good dispersion stability and physical stability. The interface composite film constructed by the dialdehyde cellulose nanofiber and soybean protein isolate in the emulsion can effectively enhance the spatial barrier and charge repulsion between the emulsion droplets, thereby enhancing the structural stability of the emulsion.

[0085] From the 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) and 1,1-diphenyl-2-trinitrobenzene hydrazine (DPPH) free radical scavenging experiments (as Figure 2 shown), the Pickering emulsion prepared in the examples shows certain free radical scavenging activity, indicating that the emulsion system has good antioxidant performance. This performance is derived from the phenolic hydroxyl structure of carvacrol molecules and the effective loading and slow release of carvacrol by composite particles, so that the system can continuously provide antioxidant protection during storage, which helps to delay the oxidation and browning of fruits and the degradation of nutrients.

[0086] The antibacterial experiment of E. coli and S. aureus shows (as Figure 3 shown) that the Pickering emulsion has obvious inhibition zone for the two representative bacteria, indicating that the emulsion system has certain antibacterial performance. The antibacterial effect is mainly due to the broad-spectrum antibacterial activity of carvacrol and the slow release and stabilization effect of the composite particle network, so that the active ingredient maintains an effective concentration for a long time, thereby achieving sustained antibacterial protection.

[0087] In summary, the Pickering emulsion prepared in the present application has good system stability, antioxidant property and antibacterial activity, and can provide a functional protective layer with physical barrier and biological activity for the surface of fruits and vegetables, providing a good foundation for its application in fruit and vegetable preservation.

[0088] The mango preservation effect comparison chart (as Figure 4It can be seen that the sample of Comparative Example 1 obviously lost water during storage, the epidermis rapidly browned and large area of decay appeared, and the mangoes were severely deteriorated on the 5th day. After treatment with the Pickering emulsion prepared in the application, the overall appearance of the mangoes remained intact and good under the same storage conditions.

[0089] The weight loss rate analysis showed that the weight loss rate of the mangoes treated with the Pickering emulsion of Example 1-8 was obviously lower than that of Comparative Example 1 during the whole storage period. The weight loss rate of Comparative Example 1 was 20.05% on the 11th day, and the weight loss rates of the mangoes treated with the Pickering emulsion of Example 1-8 were 18.33%, 17.05%, 14.16%, 12.45%, 11.05%, 10.23%, 13.8% and 9.5%, respectively, indicating that the dense protective film formed on the fruit surface by the emulsion could effectively inhibit water evaporation and slow down respiratory metabolism. The hardness change analysis showed that the hardness of the mangoes in Comparative Example 1 was almost 0 on the 11th day, while the hardness of the mangoes treated with the Pickering emulsion of Example 1-8 decreased obviously slowly, indicating that the system could delay fruit tissue softening and maturation decay to some extent. The decay rate analysis showed that the decay rate of Comparative Example 1 was as high as 98% on the 11th day, the decay rate of the mangoes treated with Example 1 was 37.91%, the decay rate of the mangoes treated with Example 7 was 10%, and the mangoes treated with the Pickering emulsion of Example 2, 3, 4, 5, 6 and 8 did not decay, indicating that the emulsion treatment could significantly inhibit the growth of pathogenic bacteria and the spread of decay, and significantly prolong the shelf life of mangoes.

[0090] The excellent preservation effect of the Pickering emulsion prepared in the application is mainly due to the synergistic effect of the composite structure and function of the Pickering emulsion. The carvacol introduced into the emulsion is firmly adsorbed on the surface of the dialdehyde cellulose nanofiber-soy protein isolate composite particles which have chemical stability and skeleton enhancement effect. Under the synergistic effect of the composite particle barrier and the cellulose network, the carvacol realizes slow release, and continuously plays an antibacterial and antioxidant role. At the same time, the emulsion forms a breathable and dense protective film layer on the surface of the mango, effectively isolates the invasion of external microorganisms and reduces water loss. It can be seen from the above results that the Pickering emulsion of the application has excellent comprehensive preservation performance.

[0091] The above has described various embodiments of the application, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those skilled in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles, practical applications or improvements to the technology in the market of the embodiments, or to enable other ordinary skilled persons 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) Pickering emulsion construction: 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.

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 (1), the mass percentage concentration of the carboxylated cellulose nanofiber aqueous dispersion is 1.0-2.0%; the pH value of the carboxylated cellulose nanofiber aqueous dispersion after adjustment is 3-5.

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 (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.

4. 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.

5. 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.

6. The method for preparing Pickering emulsion based on dialdehyde cellulose nanofiber modified soy protein isolate according to claim 1, characterized in that, 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%.

7. The Pickering emulsion prepared by the method according to any one of claims 1 to 6.

8. The application of the Pickering emulsion according to claim 7 in fruit preservation.

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