Fresh-keeping method applied to fresh-cut broccoli

Abstract

The invention relates to a fresh-keeping method applied to fresh-cut broccoli, which comprises the following steps: (1) preparing dodecenyl succinic anhydride esterified starch nanocrystals (DSN) by taking starch nanocrystals (SNC) and dodecenyl succinic anhydride (DDSA) as raw materials; (2) preparing a herba houttuyniae essential oil Pickering emulsion (DSN / HEO) with stable DSN (Digital Substitute Nitrogen); and (3) adsorbing the DSN / HEO on filter paper, and putting the filter paper into a perforated preservation box filled with the fresh-cut broccoli, wherein the addition amount of the DSN / HEO is 0.1% of the mass of the broccoli. By means of the method, slow and continuous release of the herba houttuyniae essential oil is achieved, and the phytotoxicity effect on the broccoli caused by mass release of the essential oil is avoided in the process of prolonging the quality of the fresh-cut broccoli.

Description

TECHNICAL FIELD

[0001] The application is a vegetable preservation technology, specifically using fishy grass essential oil emulsion prepared by dodecyl succinic anhydride starch nanocrystals as fumigant to preserve fresh-cut broccoli. BACKGROUND

[0002] Fumigation technology is a highly effective postharvest treatment, especially in terms of insecticidal sterilization and inhibition of sprouting. However, its serious defects (including chemical residues, health hazards, environmental damage, the risk of phytotoxicity to vegetables, and technical limitations) have severely limited its application. Essential oils are safe and efficient bacteriostatic and antioxidant agents, but due to their rapid evaporation speed, they often lead to excessive essential oil concentration in the air of the storage environment. When used for fruit and vegetable preservation, the excessive essential oil concentration in the air of the storage environment can cause phytotoxicity to fruits and vegetables.

[0003] In the paper "Inhibition of Plum Pathogens and Preservation Effect of Carvacol Delivery System Based on Casein Nanocarriers", plums were soaked in nanometer casein-stabilized carvacol emulsion to achieve preservation. However, the contact between casein, carvacol, and plums may cause residues of carvacol and other substances on the surface of plums, and liposoluble carvacol is not easy to clean, which may pose a risk of food safety problems. In the paper "Antibacterial and Disease Resistance Effect of Pogostemonis Herba Essential Oil on Mango Anthracnose and Preservation Application of Compound Chitosan", it has been confirmed that fumigation treatment with Pogostemonis Herba essential oil has an inhibitory effect on anthracnose fungi, but in order to avoid the phytotoxicity of Pogostemonis Herba essential oil to mangoes, the essential oil is compounded in chitosan to prepare a coating solution to treat mangoes, which still causes food safety risks due to the base.

[0004] Houttuynia cordata is a plant used in traditional medicine that is widely used in East and Southeast Asia for its heat-clearing and detoxifying and anti-inflammatory effects. Houttuynia cordata essential oil is its main bioactive component, which is usually extracted from fresh stems and leaves by steam distillation or supercritical CO2 extraction. Chemical analysis shows that Houttuynia cordata essential oil contains more than 70 compounds, including methyl nonyl ketone, decanal, alpha-pinene, and limonene, thus showing inhibitory properties against a variety of microorganisms, including Escherichia coli, Staphylococcus aureus, Streptococcus hemolyticus, Trichoderma viride, Aspergillus niger, and Saccharomyces cerevisiae. This natural safety and broad-spectrum antibacterial properties determine its ability as a viable alternative to synthetic preservatives in food preservation. However, as a volatile substance, Houttuynia cordata essential oil faces challenges such as reduced bioavailability, short duration of drug efficacy, and increased cost due to rapid evaporation. Traditional slow-release techniques, such as emulsions based on surfactants, often encounter limitations, including low encapsulation efficiency, poor interfacial stability, and potential toxicity of chemical additives.

[0005] Pickering emulsion systems utilize nanoparticles such as silica and cellulose nanocrystals as interfacial stabilizers to form irreversible adsorbed mechanical barriers at the boundary between oil and water. This 3D network structure effectively hinders the evaporation pathway, significantly reducing the Ostwald ripening and volatile diffusion rate of droplets. However, the use of inorganic nanoparticles such as titanium dioxide and silicon dioxide in food and pharmaceuticals is limited due to complex synthesis, high cost, poor biocompatibility, and possible toxic effects. Natural solid particles have become a promising alternative to stabilize Pickering emulsions.

[0006] Starch nanocrystals (SNCs) are a semi-crystalline material characterized by the formation of an onion-like structure through acid hydrolysis. During acid hydrolysis, the amorphous regions of starch are preferentially degraded, while the crystalline domains remain intact, resulting in SNCs with high crystallinity. This high crystallinity confers excellent acid resistance, enhanced mechanical properties, and small particle size (30-200 nm) - properties that are lacking in native starch. Despite its biodegradability and non-toxicity, which offer better performance than traditional nanoparticles, the apparent hydrophilicity of SNCs limits their application in hydrophobic systems. To address this issue, hydrophobic groups can be introduced onto the surface of SNCs, thereby enhancing their hydrophobicity and possibly conferring amphiphilicity. Dodecenyl succinic anhydride (DDSA) can be used as an esterifying agent to increase the hydrophobicity of polymers, and no organic acid byproducts are produced during the esterification process. Through esterification with DDSA, the long alkenyl chains replace the hydroxyl groups on the anhydroglucose units of SNCs, which can improve hydrophobicity. SUMMARY

[0007] The purpose of the present invention is to use the fishy grass essential oil emulsion prepared by dodecenyl succinic anhydride starch nanocrystals as a fumigant, which is added dropwise on filter paper and then used for vegetable preservation.

[0008] The present invention is a preservation method for fresh-cut broccoli, comprising the following steps: Step (1) Preparation of potato starch nanocrystals (SNCs): Mix 250 g of potato starch with 1000 mL of sulfuric acid solution (3.16 M) and stir at 200 r / min for 14 d at 40°C; after hydrolysis, centrifuge at 8000 rpm and 4°C for 10 min to obtain the precipitate; wash the precipitate with distilled water until the washing liquid reaches pH 7, and freeze-dry to obtain SNCs; Step (2) preparation of dodecyl succinic anhydride esterified starch nanocrystal (DSN): take 2g of prepared potato starch nanocrystal (SNC), add 60 mL of 50% ethanol solution, and obtain SNC suspension by ultrasonic oscillation in water bath for 30 min; 1g of dodecyl succinic anhydride (DDSA) is dissolved in 5 mL volumetric flask with anhydrous ethanol to prepare a DDSA-ethanol solution with a concentration of 0.2g / mL; 4mL of the DDSA-ethanol solution is added dropwise to the SNC suspension, and stirred at 35℃ and 200r / min for 3h; during the whole process, 0.1mol / L NaOH is used to adjust the pH, so that the pH is maintained between 8.5-9.5; after 3h, the reaction is completed by adjusting the pH to 6.8 with 0.1mol / L HCl; after the reaction is completed, the dodecyl succinic anhydride starch nanocrystal (DSN) precipitate is obtained by centrifugation, and washed with 70% ethanol and anhydrous ethanol for 3 times respectively, and then freeze-dried to obtain DSN particles; Step (3) preparation of Houttuynia cordata slow-release emulsion: mix 3mL of distilled water, 3mL of Houttuynia cordata essential oil and 0.3g of DSN, and then homogenize for 3min at 10000rpm; Step (4) preparation of slow-release filter paper: drop 300μL of Houttuynia cordata Pickering emulsion on the filter paper, and let the emulsion be completely absorbed on the filter paper; Step (5) preparation of broccoli packaging box: select a 2L polypropylene box, the box cover can be sealed, and 3-4 round holes with a diameter of 5-6mm are punched on the box cover; Step (5) preservation of fresh-cut broccoli: select uniform size, fresh, no mechanical damage and disease-free broccoli, and cut with a sterile blade; then put the segmented small flower heads into a 2L perforated polypropylene packaging box, about 300±30g of fresh-cut broccoli is put into each container; then the slow-release filter paper is placed in the PP container containing the broccoli, and the box cover is sealed for preservation at 25℃ for 7 days.

[0009] The advantages of the present application are: (1) the safe plant essential oil is used to replace the traditional harmful fumigant, and the food safety hidden danger is avoided; (2) the Pickering emulsion is used as a slow-release mode, which slows down the release process of Houttuynia cordata essential oil, avoids the phytotoxicity of high-concentration essential oil, and achieves long-term antibacterial and antioxidant effects; (3) the Pickering emulsion is dropped on the filter paper, and then put into the packaging box, which does not affect the slow-release process, expands the application scenario, and avoids the defects of inconvenient transportation of liquid. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 is the implementation process diagram of the method of the present application, Figure 2 is the laser scanning confocal microscope photo of the DSN stabilized Houttuynia cordata essential oil, Figure 3It is the cumulative release rate of the emulsion. Figure 4 DPPH clearance rate of emulsion Figure 5 It is the ABTS clearance rate. Figures 6-8 These are photos of bacterial colonies taken on different days. Figure 9 It is the diameter of the colony. Figure 10 Photos showing the effect of houttuynia cordata essential oil emulsion on the storage quality of broccoli. Figures 11-20 The effects of Houttuynia cordata essential oil emulsion on the storage quality of broccoli include respiration rate, brightness (L), chroma a, and chroma b curves; bar charts of chlorophyll a, b, total chlorophyll, and carotenoid content; and bar charts of weight loss and firmness. Figures 21-23 This is a photo showing the antibacterial effect of houttuynia cordata essential oil emulsion. Figures 24-27 These are microscopic images and particle size distributions of different emulsions after 0 days and 7 days of storage. Figure 28 This refers to the encapsulation efficiency of the emulsion. Different lowercase letters (ab) indicate differences within groups, while different uppercase letters (AC) indicate differences between groups. p <0.05). Detailed Implementation

[0011] The key points of this invention are: 1. Using dodecenyl succinic anhydride esterified starch nanocrystals, a naturally sourced and safe organic nanocrystal, to replace inorganic nanoparticles in the preparation of Pickering emulsion.

[0012] 2. Use a houttuynia cordata essential oil emulsion stabilized by dodecenyl succinic anhydride esterified starch nanocrystals as a slow-release fumigant.

[0013] 3. The combination of slow-release fumigant, filter paper, and packaging box achieves the effects of preservation and antibacterial properties.

[0014] like Figure 1 As shown, this invention is a method for preserving fresh-cut broccoli. (1) Dodecenyl succinic anhydride esterified starch nanocrystals (DSN) are prepared using starch nanocrystals (SNC) and dodecenyl succinic anhydride (DDSA) as raw materials; (2) DSN-stabilized Houttuynia cordata essential oil Pickering emulsion (DSN / HEO) is prepared; (3) DSN / HEO is adsorbed onto filter paper and then placed in a perforated preservation box containing fresh-cut broccoli. The amount of DSN / HEO added is 1‰ of the broccoli mass. Through the above method, the slow and continuous release of Houttuynia cordata essential oil is achieved, thus avoiding the phytotoxic effects on broccoli caused by the large release of essential oil during the process of prolonging the quality of fresh-cut broccoli. Example 1:

[0015] The present invention provides a method for preserving fresh-cut broccoli, comprising the following steps: Step (1) Preparation of potato starch nanocrystals (SNC): 250g of potato starch was mixed with 1000mL of sulfuric acid solution (3.16M) and stirred at 200r / min at 40℃ for 14 days; after hydrolysis, the mixture was centrifuged at 8000prm at 4℃ for 10min to obtain the precipitate; the precipitate was repeatedly washed with distilled water until the pH of the washing solution was 7, and then freeze-dried to obtain SNC; Step (2) Preparation of dodecenyl succinic anhydride esterified starch nanocrystals (DSN): Take 2g of the prepared potato starch nanocrystals (SNC), add 60 mL of 50% ethanol solution, and sonicate in a water bath for 30 min to obtain SNC suspension; add 1g of dodecenyl succinic anhydride (DDSA) to a 5mL volumetric flask and dilute with anhydrous ethanol to prepare a DDSA-ethanol solution with a concentration of 0.2g / mL; add 4mL of DDSA-ethanol solution dropwise to the SNC suspension, and stir at 200r / min at 35℃ for 3h. During the process, adjust the pH with 0.1mol / L NaOH to maintain the pH between 8.5 and 9.5; after 3h, the reaction ends, and adjust the pH to 6.8 with 0.1mol / L HCl to end the reaction; after the reaction, centrifuge to obtain dodecenyl succinic anhydride starch nanocrystals (DSN) precipitate, and wash with 70% ethanol and anhydrous ethanol 3 times respectively, and freeze-dry to obtain DSN particles; Step (3) Preparation of Houttuynia cordata sustained-release emulsion: Mix 3 mL of distilled water, 3 mL of Houttuynia cordata essential oil and 0.3 g of dodecenyl succinic anhydride esterified starch nanocrystals (DSN) and homogenize at 10000 rpm for 3 min. Step (4) Preparation of sustained-release filter paper: Add 300 μL of Houttuynia cordata Pickering emulsion to the filter paper and allow the emulsion to be completely absorbed onto the filter paper; Step (5) Preparation of broccoli packaging box: Select a 2L polypropylene box with a sealable lid and drill 2-3 round holes with a diameter of 5-6mm in the lid. Step (5) Preservation of fresh-cut broccoli: Select broccoli that is uniform in size, fresh, and free from mechanical damage and disease, and cut it with a sterile blade; then put the cut florets into a 2L perforated polypropylene packaging box, with about 300±30g of fresh-cut broccoli in each container; then place the slow-release filter paper in the PP container containing the broccoli, seal the box lid and store it at 25℃ for 7 days.

[0016] In the preservation method described above, the starch nanocrystals are potato-derived starch nanocrystals, and after modification with dodecenyl succinic anhydride, the degree of substitution is between 0.039 and 0.052.

[0017] The preservation method described above, the preparation of the slow-release emulsion refers to the fact that the essential oil source used in step (3) is houttuynia cordata essential oil, and the ratio of the added amount is houttuynia cordata essential oil: distilled water: DSN = 10: 10: 1.

[0018] In the preservation method described above, the slow-release filter paper used in step (4) is No. 1 qualitative filter paper with a pore size of 11μm, and 300μL of emulsion of slow-release emulsion is dropped onto the filter paper.

[0019] In the above-described preservation method, the packaging box material used in step (5) is polypropylene (PP), and the diameter of the perforation on the box lid is 5-6 mm, and the number is 2-3.

[0020] In the preservation method described above, the weight of broccoli in each 2L packaging box in step (6) is 300g ± 30g. Example 2:

[0021] Steps (1) to (4) are the same. Step (5) will be grown on PDA medium until day 4. Fusarium fujikuroi, Fusarium incarnatum, and Alternaria brassicicola These three fungi were prepared at a concentration of 10. 8 / mL of spore suspension; Step (6) Select fresh, disease-free broccoli, take 5 mL of each of the three spore suspensions prepared in step (5) and spray them onto the surface of the broccoli; Step (7) Place the inoculated broccoli into a 6-liter plastic container with a petri dish lid containing 0.1% (w / w) of the broccoli mass of DSN / HEO emulsion; Step (8) Seal the container with a perforated PE film and store it at 28°C and 60% humidity. After 3 days of storage, photograph and observe the colonies on the surface of the broccoli.

[0022] In the antibacterial method described above, the starch nanocrystals are potato-derived starch nanocrystals, and after modification with dodecenyl succinic anhydride, the degree of substitution is between 0.039 and 0.052.

[0023] The antibacterial method described above, the preparation of the DSN / HEO emulsion refers to the fact that the essential oil source required in step (3) is houttuynia cordata essential oil, and the ratio of the added amount is houttuynia cordata essential oil: distilled water: DSN = 10:10:1.

[0024] In the antibacterial method described above, the slow-release filter paper used in step (4) is No. 1 qualitative filter paper with a pore size of 11μm, and 300μL of the emulsion layer of the slow-release emulsion is dropped onto the filter paper.

[0025] In the antibacterial method described above, the diameter of the perforations on the plastic wrap used in step (10) is 5-6 mm, and the number is 2-3.

[0026] To illustrate the effectiveness of the present invention, the following experiments were conducted: 1. Test Methods 1.1 Preparation of dodecenyl succinic anhydride starch nanocrystals (DSN) SNC was prepared by acid hydrolysis. 2 g of pre-prepared starch nanocrystals (SNC) were dispersed in 60 mL of 50% (v / v) ethanol and sonicated for 30 min to form an SNC suspension. 4 mL of a 0.2 g / mL dodecenylsuccinic anhydride (DDSA)-ethanol solution was added dropwise to the SNC suspension. During this process, the mixture was stirred at 200 rpm and 35 °C for 3 h, and the pH was maintained between 8.5 and 9.5 by adding 0.1 mol / L NaOH dropwise. After 3 hours, the pH was adjusted to 6.8 with 0.1 mol / L HCl to stop the reaction. The precipitate obtained by centrifugation was washed three times each with 70% ethanol and anhydrous ethanol, and then freeze-dried to obtain DSN.

[0027] 1.2 Preparation of Houttuynia cordata essential oil emulsion A mixture of 6 mL of distilled water and HEO (volume ratio 1:1) was mixed with 0.3 g of distilled water and DSN, respectively, and then homogenized for 3 minutes. The resulting emulsion samples were named crude emulsion (HEO) and Pickering emulsion (DSN / HEO), respectively. Key parameters of the emulsions were evaluated, including droplet diameter and microstructure.

[0028] 1.3 Properties of Houttuynia cordata essential oil emulsion 1.3.1 Determination of the antifungal properties of the emulsion 2μL Fusarium fujikuroi , Fusarium incarnatum and Alternaria brassicicola spore suspension (10 8 ( / mL) was added dropwise to the center of a PDA culture plate and dried for 30 minutes. Individual filter papers were then soaked in 15 μL of HEO and DSN / HEO emulsion, respectively. After placing them on the plate lid, the plate was inverted and incubated at 28°C. Observations were performed every 2 days to measure colony diameter and photograph colonies.

[0029] The in vivo antifungal properties of the emulsion were assessed by evaluating colony development on broccoli inoculated with the fungus. Fresh, disease-free broccoli was selected, and 5 mL of the emulsion was applied... F. fujikuroi , F. incarnatum and A. brassicicola spore suspension (10 8Spray the inoculum (0.1% (w / w) of the broccoli emulsion onto the surface of the broccoli. Place the inoculated broccoli in a 6-liter plastic container with a petri dish lid containing a 0.1% (w / w) emulsion by weight of the broccoli. Seal the container with a perforated PE film and store it at 28°C and 60% humidity. After 3 days of storage, photograph and observe the colonies on the broccoli surface.

[0030] 1.3.2 Antioxidant properties of emulsions The antioxidant properties of the emulsions were evaluated using DPPH and ABTS free radical scavenging assays. 100 μL, 50 μL, and 25 μL of the emulsion layer were added to 40 mL of prepared ABTS reaction solution and reacted at room temperature in the dark for 30 minutes. Additionally, 20 μL, 40 μL, and 80 μL of the emulsion layer were mixed with 4 mL of DPPH methanol solution (23 mg / L) and shaken at 22 °C in the dark for 1 hour. The absorbance values ​​of the ABTS and DPPH reaction solutions were measured at 734 nm and 517 nm before and after the reaction, respectively. The free radical scavenging rate was calculated using Equation 1.

[0031] Free radical scavenging rate (%) = (A t0 -A t ) / A t0 ×100 (Formula 1) In the formula, A t0 A represents the initial absorbance of the sample. t This indicates the absorbance at the end of the reaction.

[0032] 1.3.3 Cumulative release rate of HEO emulsion Dispense 10 mL of the emulsion sample onto the petri dish lid and maintain at 25°C and 60% relative humidity, recording daily weight measurements. Calculate the cumulative release rate of Houttuynia cordata essential oil using Formula 2.

[0033] Cumulative release rate (%) = (1-m) t / m)×100% (Formula 2) In the formula, m t 'm' and 'm' represent the release time and the initial emulsion mass, in grams.

[0034] 1.3.4 Determination of emulsion particle size and encapsulation efficiency After staining with 0.1% Nile blue and 0.1% Nile red, the emulsion structure was observed using a fluorescence microscope at excitation wavelengths of 633 nm and 488 nm, respectively. Encapsulation efficiency was determined by measuring the concentration of essential oil in the supernatant after centrifugation. Specifically, 1 mL of emulsion was centrifuged at 1000 rpm and 4°C for 1, 2, 3, 4, 5, and 6 minutes, and the supernatant was collected and diluted to 5 mL volumetric flasks. The absorbance was measured at 270 nm, and the concentration of essential oil was determined using a standard curve. The encapsulation efficiency was then determined using Equation 3.

[0035] Encapsulation efficiency (%) = (mC × 5) / m × 100 (Formula 3) Where m represents the mass of HEO in the initial emulsion, in g; c is the HEO concentration calculated based on the standard curve, in g / mL; and 5 is the final volume, in mL.

[0036] 1.4 Effects of emulsion on the storage quality and disease control of fresh-cut broccoli Select uniformly sized, fresh broccoli florets free from mechanical damage and disease, and cut them with a sterile blade. Place the cut florets into 2L perforated polypropylene (PP) containers, each containing approximately 300±30g of broccoli. Then, apply 300μL each of distilled water, HEO, and DSN / HEO emulsion to sterile filter paper. Place the filter paper into the PP containers containing the broccoli. The broccoli samples were stored at 25°C and 75% relative humidity. During storage, various storage parameters of the broccoli, including appearance, weight loss, firmness, color, chlorophyll content, and respiration rate, were measured.

[0037] 2. Experimental Results 2.1 Appearance and diameter distribution of the emulsion During the 7-day storage period, the droplets in the DSN / HEO remained uniformly distributed, forming a homogeneous emulsion. Figures 26-27 This contrasts sharply with the distinct stratification observed in HEO. Figures 24-25 ). For example, the interfacial structure of the emulsion in the fluorescence microscope image shows ( Figure 2 The DSN (green) compacts a dense interfacial layer on the surface of the essential oil spherical droplets (red). The high surface potential of the DSN (-30.5mV) causes the interfacial layer formed on the HEO droplet surface to repel the droplets, thereby preventing droplet aggregation and Ostwald ripening, ultimately improving the stability of the emulsion.

[0038] 2.2 Encapsulation efficiency and cumulative release rate of the emulsion The encapsulation efficiency of the emulsion decreased continuously with increasing centrifugation time. However, throughout the entire centrifugation process, the encapsulation efficiency of DSN / HEO remained significantly higher than that of HEO emulsion. Figure 28This may be because the high desorption energy barrier prevents DSN separation at the oil-water interface in the DSN / HEO emulsion. During storage, the evaporation rate of essential oils in the DSN / HEO emulsion remains significantly lower than that in HEO (…). Figure 3 Essential oils are dispersed as droplets throughout the aqueous phase of the Pickering emulsion, reducing the evaporation rate by extending their migration path to the water-air interface. The release of essential oils occurs in three distinct phases, with the release rate steadily decreasing. By day three, the cumulative release rate of essential oils in H2O / HEO reaches 81%, constituting a "burst release." This rate is significantly higher than that in DSN / HEO (39%), indicating that DSN significantly mitigates the initial rapid release of essential oils.

[0039] The mechanism of volatile release of houttuynia cordata essential oil from the emulsion was analyzed using a series of mathematical models, and the fitting parameters are shown in Table 1. The Rigter-Peppas model elucidated the diffusion mechanism through the exponential diffusion constant n and described the release curve of the essential oil in the emulsion. r ²>0.91). The release of essential oils in HEO conforms to Fick diffusion kinetics ( ). n <0.45), in the initial stage, the rapid aggregation of essential oil droplets drove concentration gradient-dependent release. In contrast, essential oils released in DSN / HEO exhibited an anomalous transport mechanism (0.45 < n <0.89, controlled by coupled diffusion and polymer relaxation processes. This finding suggests that the interfacial layer formed by DSN restricts droplet diffusion, thus ensuring that the essential oil release rate is not solely dependent on its concentration. Although the zero-order model shows a similar fit in DSN / HEO ( r (²=0.937), but its significant non-zero intercept k0 indicates that the linear relationship is only transient during the observation period, which is consistent with... n The coupling mechanism revealed by (0.58) is consistent.

[0040] Table 1. Model parameters for cumulative release of Houttuynia cordata essential oil in emulsion, mean ± standard deviation.

[0041] Note: C0, K0, K1, K2, K3, and n These are all fitting parameters.

[0042] 2.3 Antioxidant properties of the emulsion HEO had higher DPPH and ABTS clearance rates than DSN / HEO emulsion. Figures 4-5This finding indicates that Pickering emulsions cannot completely eliminate free radicals in a short time because the DSN interface layer around the essential oil droplets hinders their full interaction with DPPH and ABTS. This further illustrates that the DSN encapsulates the essential oils, inhibiting their diffusion.

[0043] 2.4 Antifungal properties of the emulsion By measurement F. fujikuroi , F. incarnatum , A. brassicicola The antifungal activity of emulsions was evaluated by the diameter of fungi. All emulsion samples showed antifungal activity ( ). Figures 6-9 This may be due to the evaporation of antifungal compounds in Houttuynia cordata essential oil, such as β-caryophyllene, p-cymene, and d-limonene. The rapid release of essential oil in HEO leads to a rapid increase in the concentration of antifungal components on the culture plate, effectively inhibiting fungal growth. In contrast, the antifungal efficacy of DSN / HEO weakens in a short period due to the delayed release of essential oil.

[0044] 2.5 Effect of Houttuynia cordata essential oil emulsion on the storage quality of broccoli. DSN / HEO treatment effectively delayed the yellowing of broccoli. Figure 10 , Figures 12-14 ), and maintained a consistent respiratory rate throughout the entire 7-day storage period. Figure 11 Furthermore, this treatment resulted in an increase in chlorophyll a levels. Figure 15 ), total chlorophyll content increased ( Figure 17 ) and increased hardness ( Figure 1 Meanwhile, chlorophyll b ( Figure 16 ) and weight loss rate ( Figure 19 The levels remained low. Different treatments had no significant effect on carotenoid content. Figure 18 However, the rapid release of essential oils in HEO leads to phytotoxic effects, including browning of broccoli florets and root dehydration. Figure 10 DSN / HEO treatment maintains antioxidant activity by gradually releasing essential oils, thereby preserving the post-harvest quality of broccoli and mitigating the phytotoxicity of houttuynia cordata essential oil due to rapid volatilization.

[0045] 2.6 Effect of Houttuynia cordata essential oil emulsion on the antibacterial effect of broccoli During the storage of broccoli, the essential oil emulsion also inhibited the growth of fungi. Figures 21-23 Because the broccoli was not completely sealed in the plastic container, a large amount of essential oil was released in a short period of time, causing it to disperse outside the container. The longer-term release of essential oils in DSN / HEO may provide a more lasting antifungal effect, thus enhancing its antifungal efficacy.

[0046] 3. Conclusion Due to its high absolute delta potential and amphiphilicity, DSN effectively stabilized the DSN / HEO emulsion, improving the encapsulation efficiency of Houttuynia cordata essential oil and thus preventing sudden release while maintaining sustained release. The interfacial stability imparted by DSN transformed the essential oil release kinetics from Fick diffusion to a process controlled by coupled diffusion and polymer relaxation. Therefore, the DSN / HEO emulsion exhibited sustained antioxidant activity and durable antifungal effects. DSN / HEO treatment effectively delayed senescence-related chlorophyll degradation in fresh-cut broccoli, maintained post-harvest quality indicators throughout storage, and avoided phytotoxicity induced by Houttuynia cordata essential oil. In conclusion, enhancing the lipophilicity of potato starch nanocrystals through DDSA esterification is a highly feasible method, providing a promising approach for delaying essential oil volatilization and preserving fresh fruits and vegetables.

Claims

1. A method for preserving fresh-cut broccoli, characterized in that, The steps are as follows: Step (1) Preparation of potato starch nanocrystals (SNC): 250g of potato starch was mixed with 1000mL of sulfuric acid solution (3.16M) and stirred at 200r / min at 40℃ for 14 days; after hydrolysis, the mixture was centrifuged at 8000prm at 4℃ for 10min to obtain the precipitate; the precipitate was repeatedly washed with distilled water until the pH of the washing solution was 7, and then freeze-dried to obtain SNC; Step (2) Preparation of dodecenyl succinic anhydride esterified starch nanocrystals (DSN): Take 2g of the prepared potato starch nanocrystals (SNC), add 60 mL of 50% ethanol solution, and sonicate in a water bath for 30 min to obtain SNC suspension; add 1g of dodecenyl succinic anhydride (DDSA) to a 5mL volumetric flask and dilute with anhydrous ethanol to prepare a DDSA-ethanol solution with a concentration of 0.2g / mL; add 4mL of DDSA-ethanol solution dropwise to the SNC suspension, and stir at 200r / min at 35℃ for 3h. During the process, adjust the pH with 0.1mol / L NaOH to maintain the pH between 8.5 and 9.5; after 3h, the reaction ends, and adjust the pH to 6.8 with 0.1mol / L HCl to end the reaction; after the reaction ends, centrifuge to obtain dodecenyl succinic anhydride starch nanocrystal precipitate, and wash with 70% ethanol and anhydrous ethanol 3 times respectively, and freeze-dry to obtain DSN particles; Step (3) Preparation of Houttuynia cordata sustained-release emulsion: Mix 3 mL of distilled water, 3 mL of Houttuynia cordata essential oil and 0.3 g of dodecenyl succinic anhydride esterified starch nanocrystals and homogenize at 10000 rpm for 3 min. Step (4) Preparation of sustained-release filter paper: Add 300 μL of Houttuynia cordata Pickering emulsion to the filter paper and allow the emulsion to be completely absorbed onto the filter paper; Step (5) Preparation of broccoli packaging box: Select a 2L polypropylene box with a sealable lid and drill 2-3 round holes with a diameter of 5-6mm in the lid. Step (5) Preservation of fresh-cut broccoli: Select broccoli that is uniform in size, fresh, and free from mechanical damage and disease, and cut it with a sterile blade; then put the cut florets into a 2L perforated polypropylene packaging box, with about 300±30g of fresh-cut broccoli in each container; then place the slow-release filter paper in the PP container containing the broccoli, seal the box lid and store it at 25℃ for 7 days.

2. The preservation method for fresh-cut broccoli according to claim 1, characterized in that... The starch nanocrystals mentioned are potato-derived starch nanocrystals, and after modification with dodecenyl succinic anhydride, the degree of substitution is between 0.039 and 0.

052.

3. The preservation method for fresh-cut broccoli according to claim 1, characterized in that... The preparation of the sustained-release emulsion refers to the use of houttuynia cordata essential oil in step (3), and the ratio of the amount added is houttuynia cordata essential oil: distilled water: DSN = 10: 10:

1.

4. The preservation method for fresh-cut broccoli according to claim 1, characterized in that... In step (4), the slow-release filter paper used is No. 1 qualitative filter paper with a pore size of 11μm, and 300μL of the emulsion layer of the slow-release emulsion is dropped onto the filter paper.

5. The preservation method for fresh-cut broccoli according to claim 1, characterized in that... The packaging box material used in step (5) is polypropylene, and the diameter of the perforation on the box lid is 5-6mm, and the number is 2-3.

6. The preservation method for fresh-cut broccoli according to claim 1, characterized in that... In step (6), the weight of broccoli in each 2L box is 300g ± 30g.

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