A highly stable and antioxidant compound essential oil antibacterial agent and its application

Abstract

This invention provides a highly stable and antioxidant compound essential oil antibacterial agent and its application, belonging to the field of food-grade emulsion technology. This invention uses ultrasonic technology to prepare an oil-in-water essential oil emulsion. The combination and encapsulation of lemon and ginger essential oils significantly improves the stability of single essential oil emulsions. Furthermore, the combination of the two essential oils has a significant synergistic effect in enhancing the DPPH free radical scavenging ability of the emulsion. In addition, this invention also provides applications of the compound essential oil emulsion prepared by the above method in antibacterial applications in food coating preservation and in preventing whitening of fresh-cut fruits and vegetables.

Description

Technical Field

[0001] This invention belongs to the field of food-grade emulsion technology, specifically relating to a compound essential oil emulsion, its preparation method, and its application. Background Technology

[0002] Plant essential oils are secondary metabolites of plants, a class of natural plant active substances with aromatic odors. For example, lemon essential oil, extracted from lemon peel, is a pale yellow oil containing various volatile components such as terpenes, aldehydes, and lipids, and possesses antioxidant and antibacterial activities. Ginger essential oil, obtained primarily from the rhizomes of ginger, also exhibits antioxidant and antibacterial effects. Plant essential oils generally possess advantages such as biodegradability and low residue, making them promising for applications in the food processing industry. However, due to their low water solubility, strong odor, and high volatility, essential oils are difficult to maintain stably in food, resulting in a low practical application rate.

[0003] To mask the odor of plant essential oils and improve their high volatility, extensive research by scholars both domestically and internationally has shown that encapsulating essential oils in emulsion form is an effective measure to address the problems of high volatility and low solubility. CN114009775A discloses a method for preparing protein-polysaccharide complex emulsions using sequential step-gap ultrasonic technology. This method involves adding pectin to sodium caseinate to construct the protein-polysaccharide complex through electrostatic interactions. During the preparation of the sodium caseinate-pectin complex, a step-gap ultrasonic processing device is used instead of heating. The physical force generated by the cavitation effect of ultrasound promotes the interaction between proteins and polysaccharides to form the complex, altering the physicochemical structure of the complex, reducing the particle size by 10.2%, and improving emulsifiability by 32.3%. However, if the essential oil is directly emulsified using the above method, unstable phenomena such as small droplets coalescing into large droplets and forming flocculation and precipitation often occur. Currently, a common method is to add Auschwitz ripening inhibitors (such as medium-chain triglycerides, MCT, corn oil, etc.) to encapsulate the essential oil, masking its odor and improving its high volatility. However, introducing other oil phases during emulsion preparation can weaken the antioxidant and antibacterial activities of essential oil emulsions, and the emulsifier's ability to encapsulate the oil phase is limited. Summary of the Invention

[0004] In view of the problems of high volatility, low solubility and low stability of essential oils, the purpose of this invention is to provide a compound essential oil antibacterial agent that can be applied to the field of fruit and vegetable preservation and has high stability and high antioxidant activity.

[0005] To achieve the above-mentioned technical objectives, the inventors conducted extensive experiments and research, and finally determined a suitable ratio of packaging materials and oil phase. By combining lemon essential oil and ginger essential oil, the stability and functional properties of the essential oil emulsion were significantly improved.

[0006] Specifically, the method for preparing a highly stable and antioxidant compound essential oil emulsion provided by the present invention includes the following steps:

[0007] (1) Prepare a pectin solution of 8-12 mg / mL using ultrapure water and citrus pectin powder for later use; prepare a sodium caseinate solution of 8-12 mg / mL using ultrapure water and sodium caseinate for later use.

[0008] (2) The sodium caseinate solution is added dropwise to the pectin solution, with a mass ratio of pectin to sodium caseinate of (0.5-2):1. The mixture is magnetically stirred for 0.5-2 hours to obtain a pectin-sodium caseinate composite solution for later use.

[0009] (3) Add compound essential oil to the pectin-sodium caseinate solution obtained in step (2), wherein the mass ratio of lemon essential oil to ginger essential oil is (0.5~2):1, and homogenize for 2~4 min at 8000r / min~15000r / min to obtain crude essential oil emulsion.

[0010] (4) The crude essential oil emulsion obtained in step (3) is subjected to ultrasonic treatment to obtain an essential oil emulsion.

[0011] More preferably, in the preparation method of the compound essential oil emulsion as described above, the concentration of the pectin solution prepared in step (1) is 10 mg / mL.

[0012] More preferably, in the preparation method of the compound essential oil emulsion as described above, the concentration of the sodium caseinate solution prepared in step (1) is 10 mg / mL.

[0013] More preferably, in the method for preparing the composite essential oil emulsion as described above, the pectin-sodium caseinate composite solution prepared in step (3) has a mass ratio of pectin to sodium caseinate of 1:1.

[0014] More preferably, in the preparation method of the compound essential oil emulsion as described above, the total amount of lemon essential oil and ginger essential oil added in step (3) is 10 wt% of the pectin-sodium caseinate solution.

[0015] The experimental results show that the compound essential oil emulsion exhibits a smaller particle size and PDI than the single essential oil emulsion, and the particle size distribution is more uniform, indicating that the essential oil blending conditions created by this invention can improve the stability of the emulsion. Specifically, when the blending ratio of lemon essential oil and ginger essential oil is 1:1, the PDI value of the emulsion is significantly lower than that of the single essential oil emulsion, and the compound essential oil emulsion exhibits the highest stability at this point. Therefore, more preferably, in the preparation method of the compound essential oil emulsion as described above, the mass ratio of lemon essential oil to ginger essential oil in step (3) is 1:1.

[0016] More preferably, in the preparation method of the composite essential oil nanoemulsion as described above, the homogenization condition in step (3) is 10000 r / min.

[0017] More preferably, in the preparation method of the composite essential oil nanoemulsion as described above, the ultrasonic treatment power in step (4) is 300W and the time is 12min.

[0018] The experimental results also showed that the DPPH free radical scavenging ability of lemon essential oil emulsion was only 9.77±0.82%, while that of ginger essential oil emulsion was as high as 88.42±0.47%. The two essential oil composite systems created in this invention (with the same total essential oil concentration as the single essential oil mentioned above) can significantly improve the DPPH free radical scavenging ability of the emulsions. The DPPH free radical scavenging abilities of all three composite emulsions were greater than 60%, with the 2:1 group at 64.95±0.55%, the 1:1 group at 75.13±0.23%, and the 1:2 group at 81.86±0.69%. The DPPH free radical scavenging ability of the emulsions increased with the increase of the proportion of ginger essential oil, and the iron reducing ability of the emulsions also showed this trend. Since the essential oil emulsions prepared by the method of this invention not only possess good stability and antioxidant capacity, but also have application potential in the preservation of fresh-cut fruits and vegetables, this invention also provides the application of the composite essential oil emulsions prepared by the above method in food coating preservation.

[0019] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0020] (1) The present invention significantly improves the stability and antioxidant properties of the compound essential oil emulsion by combining lemon essential oil and ginger essential oil.

[0021] (2) The compound essential oil emulsion of the present invention with an oil phase ratio of 10% and a pectin-sodium caseinate ratio of 1:1 has the highest stability. After 14 days of storage, the emulsion does not show obvious stratification.

[0022] (3) This invention uses ultrasonic technology to prepare water-in-oil type essential oil emulsions. Based on the encapsulation method, essential oils from different sources are compounded, which can significantly improve the processing stability of single essential oils. At the same time, the compounding of essential oils has a synergistic effect in improving the DPPH free radical scavenging ability of the emulsion. Attached Figure Description

[0023] Figure 1 The study investigated the effect of the pectin-sodium caseinate blend ratio on the storage stability of emulsions. Among them, A-1: ​​fresh ginger essential oil emulsion, A-2: ginger essential oil emulsion stored for 14 days; B-1: fresh lemon essential oil emulsion, B-2: lemon essential oil emulsion stored for 14 days; the numerical ratios (e.g., 2:1) all refer to the blend ratio of pectin and sodium caseinate.

[0024] Figure 2 This is a particle size distribution diagram of emulsions with different essential oil blend ratios;

[0025] Figure 3 This is a particle size distribution diagram of emulsions with different essential oil blend ratios;

[0026] Figure 4 This is a zeta potential diagram of emulsions with different essential oil blend ratios;

[0027] Figure 5 This is a graph showing the polydispersity index (PDI) of emulsions with different essential oil blend ratios;

[0028] Figure 6 This is a graph showing the antioxidant capacity of emulsions with different essential oil blend ratios;

[0029] Figures 2-6 In the illustrations, the numerical ratios (such as 2:1) represent the blending ratio of lemon essential oil and ginger essential oil.

[0030] Figure 7 These are photographs of the appearance of carrot samples from each treatment group in Example 4 after 6 days of storage. The treatment methods shown for the samples, from left to right, are: CK, P+SC, LEO, L+G, and GEO.

[0031] Example 1: Stability Evaluation of Ginger Essential Oil Emulsion

[0032] In this embodiment, the method for preparing ginger essential oil emulsion based on pectin-sodium caseinate compound includes the following steps:

[0033] (1) Prepare a 10 mg / mL pectin solution with ultrapure water and citrus pectin powder, and prepare a 10 mg / mL sodium caseinate solution with ultrapure water and sodium caseinate. Stir magnetically for 10-12 h.

[0034] (2) Add 10 mg / mL sodium caseinate solution dropwise to 10 mg / mL pectin solution and stir magnetically for 1 h to obtain pectin-sodium caseinate composite solution.

[0035] (3) Add to the pectin-sodium caseinate solution in step (2) ginger essential oil The essential oil was added at a rate of 10 wt%, and homogenized at 10,000 rpm for 3 minutes to obtain a crude essential oil emulsion.

[0036] (4) The crude emulsion in step (3) is subjected to ultrasonic treatment. The ultrasonic treatment power is 300W and the time is 12min to obtain ginger essential oil emulsion.

[0037] In this embodiment, the mass ratio of pectin to sodium caseinate is 0:1, 1:2, 1:1, 2:1, and 1:0, respectively.

[0038] Comparative Group 1: Pure pectin ginger essential oil emulsion. The emulsion prepared according to Example 1 is denoted as 1:0.

[0039] Comparative Group 2: Pure sodium caseinate ginger essential oil emulsion, prepared according to Example 1, denoted as 0:1.

[0040] Experimental Group 1: The pectin-sodium caseinate ginger essential oil emulsion prepared in Example 1, with a mass ratio of pectin to sodium caseinate of 2:1, is denoted as 2:1.

[0041] Experimental Group 2: The pectin-sodium caseinate ginger essential oil emulsion prepared in Example 1, with a mass ratio of pectin to sodium caseinate of 1:1, is denoted as 1:1.

[0042] Experimental Group 3: The pectin-sodium caseinate ginger essential oil emulsion prepared in Example 1, with a mass ratio of pectin to sodium caseinate of 1:2, is denoted as 1:2.

[0043] Furthermore, the stability of the pectin-sodium caseinate ginger essential oil emulsion prepared in the above embodiments was tested and verified. The test procedure is as follows: the emulsion was placed in a glass bottle and allowed to stand at 4°C. The state of the emulsion was observed periodically with the naked eye to check whether it was uniform and stable, and photographs were taken and recorded.

[0044] like Figure 1 As shown in A-1 and A-2, except for the 1:2 emulsion group, the other emulsions did not show any demulsification or phase separation within one day of initial preparation. After two weeks of storage, except for the 1:1 group, the other emulsions all showed obvious stratification, indicating that the pectin-sodium caseinate mass ratio of 1:1 is the optimal ratio.

[0045] Example 2: Stability Evaluation of Lemon Essential Oil Emulsion

[0046] In this embodiment, the method for preparing lemon essential oil emulsion based on pectin-sodium caseinate compound includes the following steps:

[0047] (1) Prepare a 10 mg / mL pectin solution with ultrapure water and citrus pectin powder, and prepare a 10 mg / mL sodium caseinate solution with ultrapure water and sodium caseinate. Stir magnetically for 10-12 h.

[0048] (2) Add 10 mg / mL sodium caseinate solution dropwise to 10 mg / mL pectin solution and stir magnetically for 1 h to obtain pectin-sodium caseinate composite solution.

[0049] (3) Add to the pectin-sodium caseinate solution in step (2) Lemon essential oil The essential oil was added at a rate of 10 wt%, and homogenized at 10,000 rpm for 3 minutes to obtain a crude essential oil emulsion.

[0050] (4) The crude emulsion in step (3) is subjected to ultrasonic treatment. The ultrasonic treatment power is 300W and the time is 12min to obtain lemon essential oil emulsion.

[0051] In this embodiment, the mass ratio of pectin to sodium caseinate is 0:1, 1:2, 1:1, 2:1, and 1:0, respectively.

[0052] Comparative Group 1: Pure pectin lemon essential oil emulsion. The emulsion prepared according to Example 2 is denoted as 1:0.

[0053] Comparative Group 2: Pure sodium caseinate lemon essential oil emulsion. The emulsion prepared according to Example 2 is denoted as 0:1.

[0054] Experimental Group 1: The pectin-sodium caseinate lemon essential oil emulsion prepared in Example 2, with a mass ratio of pectin to sodium caseinate of 2:1, is denoted as 2:1.

[0055] Experimental Group 2: The pectin-sodium caseinate lemon essential oil emulsion prepared in Example 2, with a mass ratio of pectin to sodium caseinate of 1:1, is denoted as 1:1.

[0056] Experimental Group 3: The pectin-sodium caseinate lemon essential oil emulsion prepared in Example 2, with a mass ratio of pectin to sodium caseinate of 1:2, is denoted as 1:2.

[0057] Furthermore, the stability of the pectin-sodium caseinate lemon essential oil emulsion prepared in the above embodiments was tested and verified. The specific experimental method is the same as the experimental procedure described in Example 1. The experimental results are shown below. Figure 1 B-1 and B-2 show that after two weeks of storage, except for the 1:1 group, all other emulsions exhibited obvious stratification.

[0058] Examples 1 and 2 show that, at the same pectin-sodium caseinate blending ratio, ginger essential oil emulsion is more stable than lemon essential oil emulsion. The optimal pectin-sodium caseinate blending ratio is 1:1, at which point the emulsion exhibits the highest stability and shows no obvious layering. The experimental results of Examples 1 and 2 demonstrate that, regardless of the type of essential oil, a 1:1 pectin-sodium caseinate mass ratio is always the optimal ratio.

[0059] Example 3: Characterization and Antioxidant Capacity Evaluation of Compound Essential Oil Emulsion

[0060] In this embodiment, the method for preparing an essential oil emulsion based on a blend of lemon and ginger essential oils includes the following steps:

[0061] (1) Prepare a 10 mg / mL pectin solution with ultrapure water and citrus pectin powder, and prepare a 10 mg / mL sodium caseinate solution with ultrapure water and sodium caseinate. Stir magnetically for 10-12 h.

[0062] (2) Add 10 mg / mL sodium caseinate solution dropwise to 10 mg / mL pectin solution, ensuring that the mass ratio of the two is 1:1, and stir magnetically for 1 h to obtain pectin-sodium caseinate composite solution.

[0063] (3) Add to the pectin-sodium caseinate solution in step (2) Blended essential oils Homogenize at 10,000 rpm for 3 minutes to obtain a crude emulsion of essential oils;

[0064] (4) The crude emulsion in step (3) is subjected to ultrasonic treatment. The ultrasonic treatment power is 300W and the time is 12min to obtain the compound essential oil emulsion.

[0065] In this embodiment, the total amount of essential oil added is fixed at 10 wt%, and the ratios of lemon essential oil and ginger essential oil added are 1:0, 2:1, 1:1, 1:2, and 0:1, respectively.

[0066] Comparative Group 1: Pure ginger essential oil emulsion. The emulsion prepared according to Example 3 is denoted as ginger essential oil.

[0067] Comparative Group 2: Pure lemon essential oil emulsion. The emulsion prepared according to Example 3 is denoted as lemon essential oil.

[0068] Experimental Group 1: The essential oil emulsion prepared in Example 3, with a mass ratio of lemon essential oil to ginger essential oil of 2:1, is denoted as 2:1.

[0069] Experimental Group 2: The essential oil emulsion prepared in Example 3 has a mass ratio of lemon essential oil to ginger essential oil of 1:1, denoted as 1:1.

[0070] Experimental Group 3: The essential oil emulsion prepared in Example 3 has a mass ratio of lemon essential oil to ginger essential oil of 1:2, denoted as 1:2.

[0071] Furthermore, the compound essential oil emulsion prepared in the above embodiments was characterized and its antioxidant capacity was evaluated. The experimental procedure is as follows.

[0072] Experiment 1: Determination of Emulsion Particle Size and Distribution

[0073] The five samples were measured as follows: a Malvern mastersizer 2000 laser particle size analyzer was used, employing a wet method in general mode. The pump speed was set to 1800 r / min, the background was water, and the laser intensity was greater than 75%. Samples were gradually added dropwise to maintain the sample cell's occlusion between 8% and 12%. The measurement range was 0.04 μm to 2000 μm. The emulsion particle size distribution was measured, and the volume average particle size (D4,3) and area average particle size (D3,2) were recorded.

[0074] from Figure 3 It can be seen that all three experimental emulsion groups exhibited a unimodal distribution, and compared to the two control groups, the peak value shifted to the left. This is consistent with... Figure 2 The smaller particle size values ​​shown in the experimental group also corroborate each other, indicating that the compound essential oil emulsion has higher stability than the single essential oil emulsion.

[0075] Experiment 2: Determination of emulsion zeta potential and polydispersity index

[0076] The five samples were characterized using a Malvern Nano ZS instrument. A polystyrene potentiometric cell was used as the measuring vessel. Essential oil was selected as the dispersed phase, and water as the continuous phase. The measurement temperature was 25°C, and the temperature equilibration time was 15 seconds. To avoid multiple scattering of the emulsion, the fresh emulsion was diluted 600 times with ultrapure water before measurement.

[0077] like Figure 4 As shown, due to the carboxyl groups of pectin at the interface, the Zeta potential of all emulsions is negative; the smaller the PDI value, the better the emulsion dispersibility, such as... Figure 5 As shown, the PDI of the emulsions in both the control group and the experimental group was less than 0.5. When the ratio of lemon essential oil to ginger essential oil was 1:1, the emulsion exhibited the lowest PDI value.

[0078] Experiment 3: Determination of the antioxidant capacity of the emulsion

[0079] Determination of DPPH free radical scavenging capacity: Weigh 2 mg of DPPH and dissolve it in 50 mL of ethanol to obtain a 0.1 mM DPPH solution. Store the solution at 4 °C protected from light and use immediately. Add 1 mL of the test sample to 1 mL of DPPH reaction solution, mix thoroughly, and react in the dark for 30 min. Record the absorbance value A at 517 nm using a microplate reader. sample Blank group A blank Anhydrous ethanol was used instead of DPPH alcohol solution in control group A. control Use distilled water instead of samples, and perform three parallel determinations for each group of samples, taking the average value. Calculate the clearance rate using the formula: Clearance rate = (1 - (A) / 2) sample -A blank ) / A control )×100%

[0080] Determination of FRAP antioxidant capacity: The assay was performed using a kit from Nanjing Jiancheng.

[0081] The results of the antioxidant assay are shown below. Figure 6 It was found that the antioxidant capacity of ginger essential oil emulsion was significantly higher than that of lemon essential oil emulsion. The FRAP values ​​of ginger essential oil emulsion and lemon essential oil emulsion were 1479.12±35.35 (Fe).2+ mmol / L), 77.69±3.05 (Fe 2+ The FRAP value of the emulsion (mmol / L) increased with the increase of the mass ratio of ginger essential oil.

[0082] Ginger essential oil emulsion exhibited a DPPH free radical scavenging capacity as high as 88.42±0.47%, while lemon essential oil emulsion showed a DPPH free radical scavenging capacity of only 9.77±0.82%. By blending the two essential oils, the DPPH free radical scavenging capacity of the emulsions was significantly enhanced. All three blended emulsions showed a DPPH free radical scavenging capacity greater than 60%, with the 2:1 group at 64.95±0.55%, the 1:1 group at 75.13±0.23%, and the 1:2 group at 81.86±0.69%. The blending of essential oils has a synergistic effect in improving the DPPH free radical scavenging capacity of the emulsions.

[0083] Example 4: Application of Compound Essential Oil Emulsion

[0084] The experimental procedure for preserving fresh-cut carrots based on the effect of essential oil emulsion coating is as follows:

[0085] 1) Prepare a 30 mg / mL pectin solution using ultrapure water and citrus pectin powder, and stir magnetically for 10-12 hours;

[0086] 2) Prepare essential oil emulsions according to the method described in Example 3, using lemon essential oil and ginger essential oil in blends of 0:1, 1:1, and 1:0. These three blends were used for subsequent experiments.

[0087] Take 75g of the emulsion prepared in step 2) and 25g of the pectin solution prepared in step 1), mix them together, and then add 2g of glycerin as a plasticizer to the mixture. Stir magnetically for 1 hour to obtain the essential oil coating solution. The coating solution containing lemon essential oil is designated as experimental group LEO, the coating solution containing ginger essential oil is designated as experimental group GEO, and the coating solution containing compound essential oil is designated as experimental group L+G.

[0088] Prepare a 10 mg / mL pectin solution using ultrapure water and citrus pectin powder, and a 10 mg / mL sodium caseinate solution using ultrapure water and sodium caseinate. Stir magnetically for 10-12 hours. Mix the pectin solution and sodium caseinate solution at a mass ratio of 1:1. Take 75 g of the pectin-sodium caseinate solution, 25 g of the pectin solution prepared in step 1), and 2 g of glycerin. Mix well and stir magnetically for 1 hour to obtain the control group coating solution P+SC. Use distilled water as the blank group CK.

[0089] Peel fresh carrots, cut them into small pieces, and soak equal amounts of carrots in each group of coating solutions for 3 minutes. Then remove them, drain them, and store them at 4℃. Periodically measure the changes in the total number of colonies in the samples during storage and take photos to record the changes in the appearance of the samples in each treatment group.

[0090] Table 1. Changes in total bacterial count of carrots in each treatment group during storage.

[0091]

[0092] Note: “—” in the table indicates that the total number of colonies in this group exceeds 10. 6 CFU / mL

[0093] The total bacterial count of carrots in the L+G group and the CK group was compared in the experimental group with the best preservation performance in this invention. The results showed that the preservation effect of carrots treated with compound essential oil emulsion was significantly better than that of carrots treated with distilled water, and also significantly better than that of carrots treated with single essential oil emulsion (LEO and GEO groups).

[0094] Figure 7 The images show the appearance of the samples after 6 days of storage. It can be seen that the samples in the CK and P+SC groups showed obvious whitening, while the samples in the three experimental groups treated with essential oil emulsions maintained their color better. Among them, the LEO group showed the least color change and its color retention was significantly better than the other treatment groups.

[0095] In summary, the essential oil emulsion prepared by this invention not only possesses good stability and antioxidant capacity, but also has application potential in the preservation of fresh-cut fruits and vegetables.

Claims

1. A method for preparing a compound essential oil emulsion, characterized in that, The method includes the following steps: (1) Prepare a pectin solution of 8~12mg / mL with ultrapure water and citrus pectin powder for later use; prepare a sodium caseinate solution of 8~12mg / mL with ultrapure water and sodium caseinate for later use; (2) The sodium caseinate solution is added dropwise to the pectin solution, the mass ratio of pectin to sodium caseinate is 1:1, and the mixture is magnetically stirred for 0.5~2h to obtain a pectin-sodium caseinate composite solution for later use. (3) Add lemon essential oil and ginger essential oil to the pectin-sodium caseinate solution obtained in step (2), with a mass ratio of lemon essential oil to ginger essential oil of 1:

1. Homogenize for 2 to 4 minutes at 8000 r / min to 15000 r / min to obtain crude essential oil emulsion. (4) The crude essential oil emulsion obtained in step (3) is subjected to ultrasonic treatment to obtain a composite essential oil emulsion; In step (3), the total amount of lemon essential oil and ginger essential oil added is 10 wt% of the pectin-casein sodium solution.

2. The method for preparing the compound essential oil emulsion according to claim 1, characterized in that, The concentration of the pectin solution prepared in step (1) is 10 mg / mL.

3. The method for preparing the compound essential oil emulsion according to claim 1, characterized in that, The concentration of the sodium caseinate solution prepared in step (1) is 10 mg / mL.

4. The method for preparing the compound essential oil emulsion according to claim 1, characterized in that, In step (4), the ultrasonic treatment power is 300W and the time is 12min.

5. The application of the composite essential oil emulsion prepared by the method according to any one of claims 1-4 in food coating preservation.

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