Chitosan composite sweet potato protective film solution based on plant essential oil and traditional Chinese medicine extract and preparation method of chitosan composite sweet potato protective film solution

Abstract

The invention belongs to the technical field of plant protection, and relates to a chitosan composite sweet potato protective film solution based on plant essential oil and traditional Chinese medicine extracts and a preparation method thereof. Through the combination of a natural compound antibacterial system and a refined preparation process, the purposes of replacing chemical preservatives with pure natural components and eliminating chemical residue hazards are achieved, the organic agriculture requirements are met, multiple pathogens such as bacteria and fungi are covered through multi-component synergistic bacteriostasis, the inhibition rate of the sweet potato black spot is remarkably increased, the storage fresh-keeping period of the sweet potato black spot is remarkably prolonged, and the application prospect is wide. The stepped extraction process maximally retains the activity of thermosensitive components, the nano-emulsification technology overcomes the essential oil-chitosan compatibility problem, the film-forming flexibility and barrier property reach the practical-grade standard, the raw materials are efficiently utilized, the production cost is reduced, and the green solvent is free of toxic waste emission in the whole process.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of plant protection, and relates to a chitosan composite sweet potato protective film solution based on plant essential oil and traditional Chinese medicine extract and a preparation method thereof. BACKGROUND

[0002] Traditional protective films (such as chitosan-based films) often add chemical preservatives (such as sodium benzoate, sulfite) or synthetic bacteriostatic agents (such as imidazoles), and chemical residues are generated after use, which is harmful to human health, does not meet the trend of green agriculture, and easily leads to drug resistance of microorganisms and decreases the bacteriostatic effect after long-term use.

[0003] Existing plant essential oil protective film agents mostly use single plant essential oil (such as tea tree oil) or single traditional Chinese medicine extract, have narrow bacteriostatic spectrum, are difficult to cover various pathogens (such as sweet potato black spot and soft rot), and are prone to volatilization and oxidation inactivation, resulting in poor stability and short shelf life.

[0004] The extraction method (such as steam distillation and solvent extraction) of conventional plant essential oil or traditional Chinese medicine extract has simple parameter control, high extraction temperature and long extraction time, volatile components (such as eugenol and limonene) are easily decomposed at high temperature, the yield of effective components is low, the impurity content is high, and the extraction efficiency is low (such as terpene by-products).

[0005] When the essential oil and chitosan solution in the existing film-forming matrix are directly mixed, they are easily layered due to the difference in hydrophobicity, resulting in large emulsion particle size, poor film flexibility, and difficulty in adhering to the surface of fruits and vegetables, and even the film is easily broken after film formation, resulting in decreased barrier performance. SUMMARY

[0006] In order to solve the above problems, the present application provides a chitosan composite sweet potato protective film solution based on plant essential oil and traditional Chinese medicine extract and a preparation method thereof, which specifically comprises the following steps:

[0007] Step one, the clove flower bud powder with a water content of less than or equal to 8% is crushed to a fineness of 50-60 meshes, and then supercritical CO2 extraction is performed at 20-45℃ and 10-35MPa for 2-2.5h, the CO2 flow rate is 20-25L / h, the collected fraction is frozen at (-30)-(-20)℃ for 22-26h, filtered, and the filter residue is removed to obtain clove essential oil.

[0008] Preferably, the extraction is first performed at 20-25℃ and 10-15MPa for 20-30min, and then performed at 40-45℃ and 30-35MPa for 1.5-2h.

[0009] Step 2: Cinnamon bark is crushed into 5×5 mm pieces (not crushed to avoid clogging the steam channel), mixed with distilled water at a mass ratio of 1:(10-12), soaked at 35-45° C. for 3-3.5 hours, and then steam distilled at 110-120° C. for 90-100 minutes, with a condensation temperature of 8-10° C. The distillate is allowed to stand for stratification, and the lower aqueous phase is removed, leaving the upper oil phase as cinnamon bark essential oil.

[0010] Preferably, during distillation, from 0 to 30 minutes: control the steam volume so that the distillate flow rate is 0.05 to 0.1 mL / s; from 30 to 90 (or 100) minutes: increase the steam volume so that the distillate flow rate is 0.15 to 0.3 mL / s; and stop distillation after 90 (or 100) minutes to avoid distillation of high molecular weight terpenes.

[0011] Step 3: lemon fruit is mixed with 45-55°C water in a mass ratio of 1:(1-2), soaked for 0.5-1.5 minutes, immediately cooled to 4-5°C with 2-4°C water, squeezed at 0.3-0.5 MPa, collected the outflowing mixture, filtered to remove the residue, centrifuged the filtrate at 8000-10000 rpm for 10-15 minutes, collected the supernatant, and allowed to stand at (-5)-(-3)°C for 2-2.5 days, collected the supernatant to obtain lemon essential oil.

[0012] Step 4: The rhizome of Coptis chinensis and the wormwood leaf are mixed in a mass ratio of (6-7): (3-4), quick-frozen in liquid nitrogen at -196°C for 5-6 minutes, crushed to a particle size of 40-50 mesh, and then mixed with the extractant in a mass ratio of 1: (8-10), extracted at 35-45°C and 100-120rpm for 1-1.5h, 55-65°C and 200-250rpm for 1-1.5h, and 65-75°C and 150-200rpm for 0.5-1h. The extract is filtered, the filter residue is removed, and the filtrate is concentrated to 1 / 5-1 / 4 of the original volume to obtain the Coptis chinensis-wormwood leaf extract.

[0013] Preferably, the extractant is an ethanol solution with a volume fraction of 45-55%.

[0014] Step 5: chitosan powder with a deacetylation degree of ≥85% is mixed with an organic acid solution in a mass ratio of (2-3):(8-10), allowed to stand at 3-5°C for 2-2.5 hours, and then placed in a water bath at 550-650 rpm and 40-50°C for 1-1.5 hours to obtain a chitosan base solution.

[0015] Preferably, the organic acid solution comprises lactic acid, citric acid and water in a mass ratio of (0.5-1):(1-2):(200-220).

[0016] Step six, mix clove essential oil, cinnamon essential oil, lemon essential oil and emulsifier, stir at 40-50 DEG C, 300-400 rpm for 15-20 min, then 90-100 MPa cycle homogenization 3-4 times, get nano emulsion;

[0017] Under the condition of stirring at 700-800 rpm, add the nano emulsion into the chitosan base liquid at a rate of 0.5-1 L / min, after the system is uniform, add the coptis and mugwort extract at a rate of 300-500 mL / min, finally add the plasticizer and water, and adjust the pH to 5.8-6.2 with sodium bicarbonate solution, continue to stir for 20-30 min, then filter to remove the residue, and obtain the protective film solution.

[0018] Preferably, the mass ratio of the clove essential oil, cinnamon essential oil, lemon essential oil, coptis and mugwort extract, emulsifier, plasticizer, chitosan base liquid and water is (2-4):(3-5):(2-4):(7-9):(1-2):(1-2):(180-220):(700-750).

[0019] Preferably, the emulsifier is Tween 80, the plasticizer is glycerol, and the concentration of the sodium bicarbonate solution is 0.1-0.2 mol / L.

[0020] The present application has the following advantages:

[0021] (1) The present application constructs a broad-spectrum bacteriostatic network by compounding clove essential oil (strong phenolic), cinnamon essential oil (aldehyde), lemon essential oil (terpene) and coptis and mugwort extract (alkaloid + flavonoid), replaces chemical preservatives, eliminates residual toxicity risk, and significantly expands the bacteriostatic spectrum through synergistic effect, which can simultaneously and efficiently inhibit common pathogens such as sweet potato black spot and soft rot.

[0022] (2) The present application optimizes the extraction process according to the characteristics of different raw materials, supercritical CO2 extraction of clove essential oil in stages, captures volatile components at low temperature and low pressure first, and then purifies heat-stable substances at high pressure, dynamically adjusts the steam flow rate during the distillation process of cinnamon essential oil to avoid the mixing of high molecular terpene impurities, and extracts coptis and mugwort extract after liquid nitrogen quick freezing and gradient temperature rise to protect heat-sensitive alkaloids, which significantly improves the extraction purity of key active ingredients (such as eugenol and coptis berberine), reduces impurities, and ensures the stability of the film-forming solution.

[0023] (3) The present application uses high-pressure homogenization (90-100 MPa) to reduce the particle size of the essential oil emulsion to nanoscale (<100 nm), realizes uniform fusion with the chitosan base liquid, accurately adjusts the pH to the vicinity of the isoelectric point of chitosan (5.8-6.2), optimizes the intermolecular binding force, makes the protective film solution stable and non-layered for a long time, and greatly improves the flexibility and barrier property after film formation, which tightly adheres to the surface of sweet potato and is not easy to break.

[0024] (4) Eugenol destroys the cell membrane of pathogens, berberine alkaloids inhibit energy metabolism, and mugwort flavonoids block oxidative stress, forming a multi-defense mechanism of synergistic antibacterial effects. Glycerol plasticization improves membrane elasticity, and Tween 80 emulsification reduces interfacial tension, thereby doubling the antibacterial effect and significantly extending the shelf life of sweet potatoes. The film layer has excellent moisture barrier properties, and the weight loss rate during storage is significantly reduced.

[0025] (5) Lemon essential oil is extracted by direct pulp extrusion to improve the utilization rate of raw materials. Coptis chinensis-artemisia argyi extraction uses low-concentration ethanol, which can be recycled, reducing production costs and avoiding organic solvent pollution. The entire process complies with food safety standards and is suitable for large-scale application. DETAILED DESCRIPTION

[0026] The following is a clear and complete description of the technical solutions in the embodiments of the invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0027] Example 1

[0028] Step 1: Clove buds with a moisture content of 8% or less are crushed to a 55-mesh fineness, and then subjected to supercritical CO2 extraction, first at 23°C and 12 MPa for 25 minutes, then at 42°C and 33 MPa for 1.75 hours, with a CO2 flow rate of 24 L / h. The collected fractions are frozen at -25°C for 24 hours, filtered, and the filter residue is removed to obtain clove essential oil.

[0029] The second step comprises crushing cinnamon bark into 5×5 mm pieces, mixing the pieces with distilled water at a mass ratio of 1:10, and soaking the pieces at 40° C. for 3 hours. During distillation, the steam volume is controlled to achieve a distillate flow rate of 0.08 mL / s from 0 to 30 minutes, and the steam volume is increased to achieve a distillate flow rate of 0.2 mL / s from 30 to 90 minutes. The distillation is stopped after 90 minutes, the condensation temperature is 8° C., the distillate is allowed to stand for stratification, the lower aqueous phase is removed, and the upper oil phase is cinnamon bark essential oil.

[0030] Step 3: lemon fruit is mixed with 50°C water in a mass ratio of 1:1.5, soaked for 1 minute, immediately cooled to 4°C with 3°C water, squeezed at 0.4 MPa, collected the outflowing mixture, filtered to remove the residue, centrifuged the filtrate at 9000 rpm for 12 minutes, took the supernatant, and let it stand at -4°C for 2 days, took the supernatant to obtain lemon essential oil.

[0031] Step 4: Mix the rhizome of Coptis chinensis and Artemisia argyi in a mass ratio of 7:3, quick-freeze with liquid nitrogen at -196°C for 5 minutes, crush to a 45-mesh particle size, and then mix with a 50% volume fraction ethanol solution in a mass ratio of 1:9, extract at 40°C and 110rpm for 1.25h, extract at 60°C and 230rpm for 1.5h, and extract at 70°C and 180rpm for 0.75h. Filter the extract, remove the residue, and concentrate the filtrate to 1 / 5 of the original volume to obtain the Coptis chinensis-Artemisia argyi extract.

[0032] Step 5: chitosan powder with a deacetylation degree of 85% or higher was mixed with an organic acid solution (lactic acid, citric acid and water, with a mass ratio of 0.7:1.2:200) at a mass ratio of 3:10, allowed to stand at 4°C for 2 hours, and then placed in a water bath at 600 rpm and 45°C for 1.5 hours to obtain a chitosan base solution.

[0033] Step 6: clove essential oil, cinnamon essential oil, lemon essential oil and Tween 80 were mixed, stirred at 45° C. and 350 rpm for 18 min, and then circulated and homogenized at 95 MPa for 3 times to obtain a nanoemulsion;

[0034] Under stirring conditions of 750 rpm, the nanoemulsion was added to the chitosan base liquid at a rate of 0.8 L / min. After the system was homogenized, the coptis chinensis-artemisia argyi extract was added at a rate of 400 mL / min. Finally, glycerol and water were added, and the pH was adjusted to 5.8-6.2 with 0.1 mol / L sodium bicarbonate solution. After continuing stirring for 25 minutes, the mixture was filtered and the residue was removed to obtain a protective film solution.

[0035] The mass ratio of the clove essential oil, cinnamon essential oil, lemon essential oil, coptis root-artemisia argyi extract, Tween 80, glycerol, chitosan base liquid and water is 3:4:3:8:1.5:1.5:200:725.

[0036] Test Example 1

[0037] 1. Sample Grouping

[0038] Blank group: sweet potatoes were not treated in any way

[0039] Control group 1: Fresh Doctor fruit and vegetable preservative purchased from Hebei Tuohai Biotechnology Co., Ltd. was used to coat the sweet potatoes according to the dosage specified in the instructions.

[0040] Control group 2: chitosan-based liquid was prepared according to the method of Example 1, and sweet potatoes were coated with the chitosan-based liquid.

[0041] Experimental group: Sweet potatoes were coated with the protective film solution prepared by the method of Example 1 (emulsion particle size <100 nm). The film thickness after coating was 32.5±1.8 μm and the water contact angle was 78.6±2.1°.

[0042] Coating treatment: After cleaning and disinfecting the surface of the sweet potato, dry it, soak it in the corresponding solution for 30 seconds, take it out and drain it. The dosage of 1-2 in the experimental group and the control group was the same.

[0043] 2. Antibacterial effect test

[0044] 1) To test the inhibition rate of microbial metabolic activity (respiration intensity method), healthy sweet potato tissue pieces (5 × 5 × 5 mm) were coated as described above. The pieces were then placed in a sealed container (containing a CO2 sensor) and incubated at 25°C for 72 h. The cumulative CO2 release (mg / kg·h) was recorded and the inhibition rate was calculated:

[0045] Inhibition rate (%) = (1-CO2 release amount of experimental group / CO2 release amount of blank group) × 100%.

[0046] 2) Counting the actual storage moldy area: After the sweet potatoes were coated as described above, they were stored for 45 days (15±1°C, 85% humidity). The surface mold area percentage after 45 days was counted, and the following indicators were measured every 5 days:

[0047] Weight loss rate (%) = (initial mass - current mass) / initial mass × 100%.

[0048] Moldy rate (%) = the percentage of sweet potatoes with mold spots on the surface.

[0049] The hardness was measured using a texture analyzer (probe diameter 2 mm, pressing speed 1 mm / s).

[0050] Table 1 Comparison of microbial metabolism inhibition rate and moldy area

[0051] <![CDATA[CO2释放量(mg / kg·h)]]> Bacteriostatic rate (%) Mildew area ratio in 45 days (%) Blank group 38.6±1.8 0 92.5±4.3 Control group 1 24.3±1.2 37.0 35.7±3.1 Control group 2 32.5±1.5 15.8 68.9±5.2 Experimental group 14.7±0.9 61.9 8.3±1.2

[0052] Table 2 Freshness-keeping index of sweet potato after 45 days of storage

[0053]

[0054]

[0055] As shown in Table 1-2, the 61.9% decrease in CO2 emission indicates that microbial respiratory metabolism is suppressed. The only 8.3% moldy area indicates that the compound essential oil (eugenol, cinnamaldehyde) and traditional Chinese medicine alkaloids synergistically destroy the pathogen's living environment. A nanoscale film (<100nm) densely covers the sweet potato surface, blocking oxygen and moisture (contact angle 78.6°). Oil plasticization increases film toughness (no cracking during storage), delaying tissue softening and water loss. Weight loss and mold rate are significantly reduced, while hardness retention is significantly improved. The nanoemulsion has a stable particle size (<100nm) and a uniform film (32.5μm), meeting the requirements for large-scale applications.

[0056] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a chitosan composite sweet potato protective film solution based on plant essential oils and traditional Chinese medicine extracts, characterized in that: The following steps are involved: Step 1: Clove buds are crushed and then subjected to supercritical CO2 extraction at 20-45°C, 10-35MPa, and a CO2 flow rate of 20-25L / h. The collected fractions are frozen and filtered, and the filter residue is removed to obtain clove essential oil; Step 2: Mixing cinnamon bark with distilled water and soaking it, then steam distilling it at 110-120° C. for 90-100 minutes, with a condensation temperature of 8-10° C., allowing the distillate to stand and separate, removing the lower aqueous phase, and the upper oil phase is cinnamon bark essential oil; Step 3: squeeze the lemon fruit, collect the outflowing mixture, filter and remove the filter residue, centrifuge the filtrate, take the upper layer, let it stand, and then take the upper layer to obtain lemon essential oil; Step 4: mixing the rhizome of Coptis chinensis and the wormwood leaf in a mass ratio of (6-7): (3-4), quick-freezing with liquid nitrogen and then crushing, then mixing with the extractant, extracting at 35-75°C and 100-250rpm for 2.5-4h, filtering the extract, removing the filter residue, and concentrating the filtrate to 1 / 5-1 / 4 of the original volume to obtain the Coptis chinensis-wormwood leaf extract; Step 5: chitosan powder and organic acid solution are mixed in a mass ratio of (2-3): (8-10), allowed to stand, and placed in a water bath to obtain a chitosan base solution; Step 6: Clove essential oil, cinnamon essential oil, lemon essential oil and emulsifier are mixed and stirred, and then circulated and homogenized to obtain a nanoemulsion; under stirring conditions, the nanoemulsion is added to the chitosan base liquid at a rate of 0.5-1L / min, and then the coptis chinensis-artemisia argyi extract is added at a rate of 300-500mL / min, and finally a plasticizer and water are added, and the pH is adjusted to 5.8-6.2 with sodium bicarbonate solution, and stirring is continued. Filter and remove the filter residue to obtain a protective film solution; The mass ratio of the clove essential oil, cinnamon essential oil, lemon essential oil, coptis chinensis-artemisia argyi extract, emulsifier, plasticizer, chitosan base liquid and water is (2-4):(3-5):(2-4):(7-9):(1-2):(1-2):(180-220):(700-750).

2. The method for preparing a chitosan composite sweet potato protective film solution based on plant essential oils and Chinese medicine extracts according to claim 1, characterized in that: In step 1, first extract at 20-25° C. and 10-15 MPa for 20-30 min, then extract at 40-45° C. and 30-35 MPa for 1.5-2 h.

3. The method for preparing a chitosan composite sweet potato protective film solution based on plant essential oils and Chinese medicine extracts according to claim 1, characterized in that: During the distillation in step 2, from 0 to 30 minutes, the steam volume is controlled so that the distillate flow rate is 0.05 to 0.1 mL / s. At the end of 30 minutes, the steam volume is increased so that the distillate flow rate is 0.15 to 0.3 mL / s. The distillation is stopped after 90 to 100 minutes.

4. The method for preparing a chitosan composite sweet potato protective film solution based on plant essential oils and Chinese medicine extracts according to claim 1, characterized in that: In step 4, the mixture is first extracted at 35-45° C. and 100-120 rpm for 1-1.5 h, then at 55-65° C. and 200-250 rpm for 1-1.5 h, and finally at 65-75° C. and 150-200 rpm for 0.5-1 h.

5. The method for preparing a chitosan composite sweet potato protective film solution based on plant essential oils and Chinese medicine extracts according to claim 1, characterized in that: The extractant in step 4 is an ethanol solution with a volume fraction of 45-55%.

6. The method for preparing a chitosan composite sweet potato protective film solution based on plant essential oils and Chinese medicine extracts according to claim 1, characterized in that: The organic acid solution in step five comprises lactic acid, citric acid and water in a mass ratio of (0.5-1):(1-2):(200-220).

7. The method for preparing a chitosan composite sweet potato protective film solution based on plant essential oils and Chinese medicine extracts according to claim 1, characterized in that: The emulsifier in step six is ​​Tween 80.

8. The method for preparing a chitosan composite sweet potato protective film solution based on plant essential oils and traditional Chinese medicine extracts according to claim 1, characterized in that: The plasticizer in step six is ​​glycerol.

9. The method for preparing a chitosan composite sweet potato protective film solution based on plant essential oils and traditional Chinese medicine extracts according to claim 1, characterized in that: The concentration of the sodium bicarbonate solution in step 6 is 0.1-0.2 mol / L.

10. The protective film solution prepared by the method according to any one of claims 1 to 9.

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