A method for preserving salted duck eggs using a low-temperature plasma gas flow combined with a chiral nanocoating

Abstract

This invention provides a method for preserving salted duck eggs using a low-temperature plasma-assisted chiral nano-coating, which solves the problems of poor barrier properties and lack of antibacterial function in traditional packaging, leading to fat oxidation and microbial growth. The method is characterized by: (1) Plasma pretreatment: Salted duck eggs are treated in a plasma flow of 250-350V and 3-8A for 1-3 minutes, with a total treatment time of 2-6 minutes; (2) Chiral nano-coating: L-cysteine-modified nano-SiO2 (particle size 20-50 nm) is cross-linked with PVA to prepare a chiral nano-SiO2-modified PVA-based composite coating material; (3) Coating preservation: Salted duck eggs pretreated with plasma are immersed in the composite coating solution for 1-2 minutes, air-dried, and the coating and air-drying processes are repeated once. Beneficial effects: After 70 days of storage at 25℃, the total bacterial count in the synergistic treatment group was <300 CFU / g, significantly enhancing the antibacterial effect compared to the single coating group (>500 CFU / g) and the blank group (>3000 CFU / g); the shelf life was extended to over 70 days; the quality deterioration process was effectively slowed down, the pH change was reduced by more than 50%, and the sensory score was ≥8 points. This invention achieves long-term preservation of salted duck eggs through the synergistic effect of plasma activation and chiral nano-coating.

Description

Technical Field

[0001] This invention belongs to the field of food preservation materials and processes, specifically relating to a method for preserving salted duck eggs using a low-temperature plasma airflow synergistic chiral nano-coating, which is particularly suitable for extending the shelf life and stabilizing the quality of salted duck eggs. Background Technology

[0002] Traditional salted duck eggs are often packaged in vacuum-sealed plastic containers (such as polyethylene PE and polypropylene PP) after pickling. However, these materials have insufficient barrier properties, making it difficult to effectively isolate oxygen and moisture, and they lack active antibacterial function, leading to fat oxidation, rancidity, microbial growth, and spoilage. To address these issues, existing technologies have made some improvements but still have limitations: nano-SiO2 composite packaging (such as SiO2 / chitosan systems) can improve antibacterial properties by reducing oxygen permeability (but...). E. coli While it boasts an antibacterial rate of approximately 70%, it faces inherent limitations such as nanoparticle aggregation and poor substrate compatibility, hindering its large-scale application. Furthermore, a single material cannot simultaneously address the synergistic challenges of oxidation and microbial growth. On the other hand, although low-temperature plasma technology can achieve immediate surface sterilization, its effect is short-lived and cannot provide a long-term protection mechanism, failing to meet the core requirement of extended shelf life. Summary of the Invention

[0003] This invention proposes an innovative solution: by modifying nano-SiO2 with L-cysteine ​​chiral molecules, the antibacterial activity of nano-SiO2 is significantly enhanced. At the same time, a dense network structure is constructed by crosslinking PVA with citral. Combined with low-temperature plasma gas flow pretreatment to activate the eggshell surface, both primary sterilization and coating adhesion are achieved. Subsequently, a coating preservation material modified with chiral SiO2 is used for PVA-based coating. In the later storage process, it can not only effectively sterilize but also prevent moisture loss, forming a dual synergistic barrier of "physical barrier-chemical antibacterial".

[0004] A method for preserving salted duck eggs using a low-temperature plasma gas flow synergistic with a chiral nanocoating, characterized by comprising the following steps: (1) Preparation of chiral nano-SiO2 modified PVA-based composite coating material: L-cysteine-modified nano-SiO2 was stirred and dispersed in water, PVA was added to dissolve it, the pH was adjusted to 2-6 and then citral was added, and the crosslinking reaction was carried out at 60-75℃ for 1-1.5 hours. (2) Low-temperature plasma airflow sterilization: Place the salted duck eggs in a tray and place them in a double dielectric barrier discharge plasma airflow device. Treat them for 1 to 3 minutes at a distance of 10 to 15 cm from the airflow outlet, a current of 3 to 8 A, and a voltage of 250 to 350 V. Turn the salted duck eggs over and repeat the treatment once. The total treatment time is 2 to 6 minutes. (3) Coating for preservation: Soak the salted duck eggs treated in step (2) in the composite coating liquid prepared in step (1) for 1 to 2 minutes, take them out and air dry at room temperature for 1.5 to 2 hours, and repeat the coating and air drying operation once.

[0005] In the technical solution of the present invention: the particle size of nano-SiO2 in step (1) is 20~50 nm, the modification concentration of L-cysteine ​​is 10~40 mmol / L, and the mass ratio of L-cysteine ​​to SiO2 is 2~5.

[0006] In the technical solution of this invention: the mass percentage of each component in step (1) is: chiral nano-SiO2 0.5%~2%; PVA 1%~5%; citral 0.5%~4% and the remainder is water.

[0007] In the technical solution of this invention: during the plasma gas flow treatment in step (2), the salted duck egg is 12-15 cm away from the gas flow outlet, the current is 5-6A, and the voltage is 280-320V.

[0008] In the technical solution of the present invention: the soaking time of salted duck eggs in step (3) is 1 minute, and the air drying time is 1.5 hours. The beneficial effects of this invention are:

[0009] (1) The synergistic antibacterial effect is significantly enhanced: Compared with the single coating treatment group and the blank group, the total number of colonies on the surface of salted duck eggs that are pretreated with low temperature plasma gas flow and then coated with chiral nano-SiO2 modified PVA coating can be controlled below 500 CFU / g after being stored at 25℃ for 70 days. This is because plasma surface activation promotes uniform coating adhesion, while L-cysteine ​​chiral modified SiO2 targets and destroys bacterial cell membranes through thiol (-SH), forming a dual synergistic barrier of "physical sterilization-chemical inhibition".

[0010] (2) Extended shelf life: Compared with the untreated group (shelf life ≤ 30 days), the salted duck eggs treated with plasma synergistic coating have a shelf life of more than 70 days at 25°C. At the same time, the sensory evaluation (color, flavor, texture) is good, breaking through the problem of spoilage and dehydration caused by insufficient oxygen barrier in traditional packaging.

[0011] (3) Effective delay in quality deterioration: Compared with the untreated group, the single coating group and the single plasma treatment group, the salted duck eggs treated with the same method showed the smallest change in pH value (6.5→7.2 vs 6.5→8.0, taking Example 1 as an example), and the stability of protein structure properties was significantly improved. This is because the densification of the plasma cross-linked coating network inhibited the quality deterioration process. Attached Figure Description

[0012] Figure 1: Changes in total bacterial count of salted duck eggs over time during storage. Figure 2: Changes in mold count of salted duck eggs over time during storage. Figure 3: Weight loss rate of salted duck eggs during storage period over time. Figure 4: Changes in pH value of salted duck egg yolk over time during storage. Figure 5: Sensory rating of salted duck eggs after 70 days of storage Detailed Implementation

[0013] The present invention will be further described below with reference to embodiments, but the scope of protection of the present invention is not limited thereto: The experiment consisted of four groups: Blank group: Unprocessed salted duck eggs; Comparative Example 1: Coated film only (chiral nano-SiO2 modified PVA film). Comparative Example 2: Plasma treatment only (2 minutes / side); Examples 1-3: Plasma treatment (1 / 2 / 3 minutes / side) + chiral nano-SiO2 modified PVA coating. Example 1

[0014] Preparation of chiral nano-SiO2: 10 g of nano-SiO2 with a particle size of 30 nm was dispersed in 500 mL of anhydrous ethanol, and 2.5 g of L-cysteine ​​(modification concentration of about 40 mmol / L, mass ratio of L-cysteine ​​to SiO2 of 2.5) was added. The mixture was ultrasonically dispersed for 30 min, refluxed at 60 °C for 12 h, centrifuged, washed and dried to obtain L-cysteine-modified chiral nano-SiO2.

[0015] Salted duck eggs were treated with plasma gas flow (300V, 5A, 15cm from the gas outlet) for 1.5 minutes on each side. Then, a chiral nano-SiO2 modified PVA-based composite membrane solution was prepared: 0.62g of chiral nano-SiO2 (30nm particle size) was weighed into 100mL of distilled water and dispersed by stirring at room temperature for 30 minutes; 5g of PVA was added and stirred at 90℃ for 1 hour to dissolve into a homogeneous solution. The solution was then sonicated at 100W and 25℃ for 30 minutes. The pH of the solution was then adjusted to 2.0 with hydrochloric acid, and 3.93mL of citral was added. The solution was crosslinked with PVA at 60℃ for 1.5 hours to obtain a homogeneous membrane solution. After cooling to room temperature, each egg was immersed for 1 minute, air-dried at 25℃ for 60 minutes, and then immersed again for 1 minute and air-dried. The samples were stored at 25℃, and sensory evaluation was performed every 10 days, measuring the total bacterial count, mold count, pH value of egg white and yolk, and weight loss rate. Example 2

[0016] Salted duck eggs were treated with plasma gas flow (300V, 5A, 15cm from the gas outlet) for 2 minutes on each side. Then, a chiral nano-SiO2 modified PVA-based composite membrane solution was prepared: 0.62g of chiral nano-SiO2 (30nm particle size) was weighed into 100mL of distilled water and dispersed by stirring at room temperature for 30 minutes; 5g of PVA was added and stirred at 90℃ for 1 hour to dissolve into a homogeneous solution. The solution was then sonicated at 100W and 25℃ for 30 minutes. The pH of the solution was then adjusted to 2.0 with hydrochloric acid, and 3.93mL of citral was added. The solution was crosslinked with PVA at 60℃ for 1.5 hours to obtain a homogeneous membrane solution. After cooling to room temperature, each egg was immersed for 1 minute, air-dried at 25℃ for 60 minutes, and then immersed again for 1 minute and air-dried. The samples were stored at 25℃, and sensory evaluation was performed every 10 days, measuring the total bacterial count, mold count, pH value of egg white and yolk, and weight loss rate. Example 3

[0017] Salted duck eggs were treated with plasma gas flow (300V, 5A, 15cm from the gas outlet) for 3 minutes on each side. Then, a chiral nano-SiO2-modified PVA-based composite membrane solution was prepared: 0.62g of chiral nano-SiO2 (30nm particle size) was weighed into 100mL of distilled water and dispersed by stirring at room temperature for 30 minutes; 5g of PVA was added and stirred at 90℃ for 1 hour to dissolve into a homogeneous solution. The solution was then sonicated at 100W and 25℃ for 30 minutes. The pH of the solution was then adjusted to 2.0 with hydrochloric acid, and 3.93mL of citral was added. The solution was crosslinked with PVA at 60℃ for 1.5 hours to obtain a homogeneous membrane solution. After cooling to room temperature, each egg was immersed for 1 minute, air-dried at 25℃ for 60 minutes, and then immersed again for 1 minute and air-dried. The samples were stored at 25℃, and sensory evaluation was performed every 10 days, measuring the total bacterial count, mold count, pH value of egg white and yolk, and weight loss rate. Comparative Example 1

[0018] Preparation of chiral nano-SiO2 modified PVA-based composite membrane solution: 0.62 g of chiral nano-SiO2 (particle size 30 nm) was weighed into 100 mL of distilled water and dispersed by stirring at room temperature for 30 minutes; 5 g of PVA was added and stirred at 90 °C for 1 h to dissolve into a homogeneous solution, followed by sonication at 100 W and 25 °C for 30 minutes. Then, the pH of the solution was adjusted to 2.0 with hydrochloric acid, and 3.93 mL of citral was added. The solution was crosslinked with PVA at 60 °C for 1.5 h to obtain a homogeneous membrane solution. After cooling to room temperature, each egg was immersed for 1 minute, air-dried at 25 °C for 60 minutes, and then immersed again for 1 minute and air-dried. The samples were stored at 25 °C, and sensory evaluation was performed every 10 days, and the total bacterial count, mold count, pH value of egg white and yolk, and weight loss rate were measured. Comparative Example 2

[0019] Salted duck eggs were treated with plasma airflow (300V, 5A, 15cm from the airflow outlet) for 2 minutes on each side. The samples were stored at 25 degrees Celsius. Sensory evaluation was performed every 10 days, and the total bacterial count, mold count, pH value of egg white and yolk, and weight loss rate were measured. Blank group

[0020] The control group consisted of untreated salted duck eggs, pickled in the same batch as the examples and stored simultaneously. Sensory evaluation was performed every 10 days, and the total bacterial count, mold count, pH value of egg white and yolk, and weight loss were measured. Performance testing: Analysis of microbial inhibition effect

[0021] Under storage conditions at 25℃, the growth rate of total bacterial count in the synergistic treatment groups (Examples 1-3) was significantly lower than that in the control group (Figure 1). By 70 days, Example 3 had only 175 CFU / g, which was 68.2% lower than Comparative Example 1 (550 CFU / g) and had an inhibition rate of >94% compared to the blank group (>3000 CFU / g*). Examples 2-3 still met the food safety standards (<300 CFU / g, GB 4789.2) after 70 days. Table 1. Changes in total bacterial count

[0022] Mold growth inhibition As shown in Figure 2, in Example 3 (6 minutes), the number of molds after 70 days was <50 CFU / g, which was 84.6% higher than that of Comparative Example 1 (325 CFU / g); the blank group had mold growth (>100 CFU / g) by day 40.

[0023] Pattern of weight loss rate As shown in Figure 3, the weight loss rate of the synergistic treatment group increased the slowest: Example 2 had a weight loss rate of 6.2% after 70 days, which was 62.7% lower than the blank group (16.6%). Comparative Example 2 (plasma only) had a weight loss rate of 18.3% due to damage to surface micropores, which in turn confirms the necessity of the coating's water-blocking properties.

[0024] Egg yolk pH stability As shown in Figure 4, after synergistic treatment with plasma gas flow and modified PVA, the pH increase of the salted duck egg yolks in Examples 1-3 was significantly lower than that in the comparative and blank groups, indicating that the synergistic treatment effectively suppressed pH fluctuations.

[0025] Sensory quality evaluation As shown in Table 1, after 70 days of storage, the sensory qualities of each group showed significant differences: The blank group showed signs of spoilage on day 30 (rancid odor, protein liquefaction), and was completely rotten by day 70 (sensory score <3 / 10). Comparative Examples 1 and 2 showed initial deterioration, with Comparative Example 2 (plasma treatment only) experiencing yellowing and dehydration due to water loss, resulting in a score of 4 / 10. Examples 1-3 all maintained acceptable quality during a 70-day storage period, with Examples 1-2 showing the best performance. There was no yolk breakage, the yolk color was stable, and there was no yolk breakage at all. The egg white was still elastic, and the yolk color was bright and oily. The sensory score was 9.7 / 10.

[0026] In Example 3, the extended plasma treatment time of 6 minutes resulted in slight protein hardening and a score drop to 8.0 / 10, confirming the need for precise control of the plasma dosage. The above data demonstrates that synergistic treatment with plasma pretreatment (1-3 minutes / side) and chiral nanocoating achieves dual stability in both morphology and flavor.

Claims

1. A method for preserving salted duck eggs using a low-temperature plasma gas flow synergistic with a chiral nanocoating, characterized in that, Includes the following steps: (1) Preparation of chiral nano-SiO2 modified PVA-based composite coating material: L-cysteine-modified nano-SiO2 was stirred and dispersed in water, PVA was added to dissolve it, the pH was adjusted to 2-6 and then citral was added, and the crosslinking reaction was carried out at 60-75℃ for 1-1.5 hours. (2) Low-temperature plasma airflow sterilization: Place the salted duck eggs in a tray and place them in a double dielectric barrier discharge plasma airflow device. Treat them for 1 to 3 minutes at a distance of 10 to 15 cm from the airflow outlet, a current of 3 to 8 A, and a voltage of 250 to 350 V. Turn the salted duck eggs over and repeat the treatment once. The total treatment time is 2 to 6 minutes. (3) Coating for preservation: Soak the salted duck eggs treated in step (2) in the composite coating liquid prepared in step (1) for 1 to 2 minutes, take them out and air dry at room temperature for 1.5 to 2 hours, and repeat the coating and air drying operation once.

2. The method according to claim 1, characterized in that: In step (1), the particle size of nano-SiO2 is 20~50 nm, the modification concentration of L-cysteine ​​is 10~40 mmol / L, and the mass ratio of L-cysteine ​​to SiO2 is 2~5.

3. The method according to claim 1, characterized in that: The mass percentage of each component in step (1) is as follows: chiral nano-SiO2 0.5%~2%; PVA 1%~5%; citral 0.5%~4%; and the remainder is water.

4. The method according to claim 1, characterized in that: During step (2) of the ion gas treatment, the salted duck egg is 12-15 cm away from the gas outlet, the current is 5-6A, and the voltage is 280-320V.

5. The method according to claim 1, characterized in that: In step (3), the salted duck eggs are soaked for 1 minute and air-dried for 1.5 hours.

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