Preparation method of cumin essential oil / soybean protein isolate microcapsule and application of cumin essential oil / soybean protein isolate microcapsule in improvement of kraft paper performance and preservation of cherry tomatoes

Abstract

The invention belongs to the field of microcapsule preparation, and particularly relates to a preparation method of a cumin essential oil / soybean protein isolate microcapsule and application of the cumin essential oil / soybean protein isolate microcapsule in improvement of kraft paper performance in cherry tomato preservation. The cumin essential oil (CEO) / soybean protein isolate (SPI) microcapsules are prepared through a coacervation method, the performance of the microcapsules is optimized, the microcapsules are added into konjac glucomannan (KGM) to serve as a coating solution, and the physical and chemical performance of kraft paper is enhanced through a coating method. The release behavior, the antibacterial property and the fresh-keeping effect of CEO are studied. Results show that when the wall-core ratio is 7: 3, the highest encapsulation efficiency can reach 92.20 + / -0.43%. The shelf life of the cherry tomatoes treated by the microcapsule is prolonged by more than 7 days. Therefore, the CEO / SPI microencapsulation and KGM coating has the potential of being used for preserving the cherry tomatoes. According to the preparation method, the cumin essential oil / soybean protein isolate microcapsule microencapsulation is combined with konjac glucomannan to be used for the kraft paper coating, the packaging material with antibacterial and fresh-keeping performance is developed, and a new solution is provided for cherry tomato fresh-keeping.

Description

Technical Field

[0001] The present invention belongs to the field of microcapsule preparation, and specifically relates to a preparation method of cumin essential oil / soybean protein isolate microcapsules and their application in improving the performance of kraft paper for cherry tomato preservation. Background Art

[0002] Cherry tomatoes ( Solanum lycopersicum var. cerasiforme ), as a popular small tomato variety, occupy an important position in the fruit and vegetable market due to their rich nutritional value, unique taste and bright appearance. They are rich in various antioxidant substances such as vitamin C, vitamin E, lycopene, etc., which have many benefits for human health and are deeply loved by consumers. However, cherry tomatoes have a high water content and relatively thin peels, and are extremely vulnerable to microbial infection at room temperature after harvest, resulting in rot and deterioration, leading to a decline in quality and economic losses.

[0003] At present, there are various preservation methods for cherry tomatoes, mainly including physical, biological and chemical preservation. Physical preservation methods such as low-temperature refrigeration and controlled atmosphere preservation can extend the preservation period to a certain extent, but there are problems such as high equipment costs and large energy consumption. Biological preservation uses beneficial microorganisms or their metabolites to inhibit the growth of harmful microorganisms. However, its effect is greatly affected by environmental factors and its stability is poor. Chemical preservation mainly relies on food additives and chemical fungicides. Although it can effectively inhibit the reproduction of microorganisms, long-term use may lead to pesticide residues, endangering human health and polluting the environment. Therefore, the development of safe and efficient natural preservation technologies has become a research hotspot in the field of cherry tomato preservation.

[0004] Plant essential oils, as natural antibacterial agents, have broad-spectrum antibacterial activity and can effectively inhibit the growth of various post-harvest pathogenic microorganisms of fruits and vegetables, delaying fruit rot. Cumin essential oil, as a kind of plant essential oil, contains various active ingredients such as cuminaldehyde and p-cymene, and has strong antibacterial and antioxidant properties. However, cumin essential oil has strong volatility and poor stability, and there are certain limitations in directly applying it to fruit and vegetable preservation. In the prior art, there are few records of using cumin essential oil for cherry tomato preservation. Summary of the Invention

[0005] In view of the problems existing in the prior art, the present invention provides a preparation method of cumin essential oil / soybean protein isolate microcapsules.

[0006] The present invention also provides a cumin essential oil / soybean protein isolate microcapsule prepared by the above preparation method.

[0007] Another object of the present invention is to provide the application of the above cumin essential oil / soybean protein isolate microcapsules in improving the performance of kraft paper for cherry tomato preservation.

[0008] The technical solution adopted by the present invention for the above purpose is as follows: The present invention provides a method for preparing cumin essential oil / soybean protein isolate microcapsules, comprising the following steps: (1) Adjust the pH value of the soybean protein isolate (SPI) solution, add 2 ml of Tween-80, and stir to obtain the SPI solution system; (2) Slowly drop the cumin essential oil ethanol solution into the SPI solution system, continuously stir, and after the stirring ends, let it stand, and then conduct vacuum freeze-drying to obtain the cumin essential oil / soybean protein isolate microcapsules.

[0009] Preferably, in step (1), the concentration of the soybean separation solution is 5% (m / v); the pH is adjusted to 10 with 1.0 mol / l NaOH solution; the addition amount of Tween-80 accounts for 2% of the volume of the soybean protein isolate solution.

[0010] Preferably, in step (2), the mass ratio of the cumin essential oil to the soy protein isolate is 9-1:1-9.

[0011] Preferably, in step (2), the concentration of the cumin essential oil ethanol solution is 0.01 g / ml; the stirring time is 4 h; the standing is carried out at -20 °C for 24 hours.

[0012] The present invention also provides cumin essential oil / soybean protein isolate microcapsules prepared by using the above preparation method.

[0013] The present invention further provides the application of the above cumin essential oil / soybean protein isolate microcapsules in improving the performance of kraft paper for the fresh-keeping of cherry tomatoes.

[0014] Preferably, the cumin essential oil / soybean protein isolate microcapsules and konjac glucomannan are used in combination; the concentration of the cumin essential oil / soybean protein isolate microcapsules in the konjac glucomannan solution is 1-5%.

[0015] Preferably, the concentration of the konjac glucomannan (KGM) solution is 1.5% (w / v).

[0016] The present invention prepares cumin essential oil (CEO) / soybean protein isolate (SPI) microcapsules by the coacervation method and optimizes their performance. The microcapsules are added to konjac glucomannan (KGM) as a coating solution to enhance the physical and chemical properties of kraft paper through the coating method. The release behavior, antibacterial properties, and fresh-keeping effect of CEO are studied. The results show that when the wall-core ratio is 7:3, the encapsulation rate can reach up to 92.20 ± 0.43%. The shelf life of cherry tomatoes treated with the microcapsules is extended by more than 7 days. Therefore, CEO / SPI microencapsulation and KGM coating have the potential for the fresh-keeping of cherry tomatoes.

[0017] The present invention microencapsulates cumin essential oil / soybean protein isolate microcapsules and combines them with konjac glucomannan for use in kraft paper coatings, developing a packaging material with antibacterial and fresh-keeping properties, providing a new solution for the preservation of cherry tomatoes.

[0018] The beneficial effects of the present invention are as follows: (1) The method provided by the present invention has strong controllability, and the prepared microcapsules have a high encapsulation rate and excellent stability; (2) It reaches 92.20 ± 0.43%. The microcapsule-coated paper provided by the present invention has a good fresh-keeping effect on cherry tomatoes, can effectively extend the shelf life, and maintain the fruit quality and nutritional value. Therefore, cumin essential oil / soybean protein isolate microcapsules and konjac glucomannan-coated kraft paper have broad application prospects in the field of cherry tomato preservation. However, this technology needs further research in aspects such as preparation process optimization and practical application to promote its commercial application. Description of the Drawings

[0019] Figure 1 TEM image of the microcapsules prepared with a wall-core ratio of 7:3; Figure 2 . (A) Stability of the microcapsules at high temperatures. (B) XRD spectra of SPI, CEO, SPI-CEO, and KGM. (C) Differential scanning calorimetry curves of CEO, SPI, and SPI-CEO. (D) FTIR spectra of SPI, CEO, SPI-CEO, KGM, and coated paper; Figure 3 X-ray diffraction of the microcapsules prepared with a wall-core ratio of 7:3; Figure 4 DSC analysis result diagram of the microcapsules prepared with a wall-core ratio of 7:3; Figure 5 . (A) Release curve of CEO microcapsules; (B) The corresponding fitting curve follows the first order; (C) Higuchi and (D) Korsemeyer-Peppas models; Figure 6 Antibacterial zone comparison diagram of circular coated paper containing different concentrations of CEO microcapsules; Figure 7 Comparison diagram of circular coated paper containing different concentrations of CEO microcapsules; In Figure 8, (A) time-lapse photos, (B) in vivo changes at 12 d; In Figure 9. (A) Decay rate (B) hardness (C) pH (D) weight loss rate. Detailed Embodiments

[0020] The technical solution of the present invention will be further explained and illustrated through specific embodiments below.

[0021] Materials: Cherry tomatoes were purchased from a local vegetable planting base; Pseudomonas aeruginosa was purchased from the China Center for Type Culture Collection; Cuminum cyminum essential oil was purchased from a spice company in Xinjiang; Soy protein isolate (SPI) was purchased from Shanghai Xingtai Industrial Co., Ltd.; Konjac glucomannan was purchased from Henan Wanbang Industrial Co., Ltd.

[0022] Example 1 (1) A 5% (m / v) soy protein isolate (SPI) solution has good stability, and a 5% SPI emulsion was selected. (2) The pH value of the SPI solution was adjusted to 10 with 1.0 mol / l NaOH solution, and 2 ml of Tween - 80 (2%) was added, and stirred for 5 minutes to obtain a stable solution system. (3) 0.1 g of Cuminum cyminum essential oil was dissolved in 10 ml of absolute ethanol, and then slowly added dropwise to the SPI solution, and continuously stirred for 4 hours to uniformly disperse the essential oil in the SPI solution.

[0023] The ratios of Cuminum cyminum essential oil to SPI (core: wall) were set to 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, 3:7, 2:8, and 1:9 (w / w), respectively. The obtained mixture was placed at -20°C for 24 hours, and then vacuum freeze-dried for 48 hours to obtain Cuminum cyminum essential oil / soy protein isolate microcapsules.

[0024] Effect Example 1 Physical properties of CEO microcapsules The encapsulation efficiency (EE) refers to the percentage of the mass of the essential oil encapsulated in the microcapsules in the total mass of the essential oil in the microcapsules. Accurately weigh 0.1 g of microcapsules, wash them thoroughly with 10 ml of absolute ethanol to remove the unencapsulated essential oil on the surface of the microcapsules. Then, the washed microcapsules were made up to 100 ml with absolute ethanol, centrifuged at 8000 rpm for 15 minutes, and the supernatant was taken to measure the concentration of free Cuminum cyminum essential oil (C1) at a wavelength of 287 nm. Then, the microcapsules were placed in absolute ethanol and ultrasonically oscillated at a power of 100 W and a temperature of 30°C for 30 minutes to fully release the essential oil in the microcapsules. Again, it was made up to 100 ml with absolute ethanol and centrifuged at 8000 r / min for 15 minutes to measure the total concentration of Cuminum cyminum essential oil (C2) in the solution at this time.

[0025] There are significant differences in the encapsulation efficiency of CEO microcapsules prepared with different wall - core ratios. When the wall - core ratio is 7:3, the encapsulation rate of the microcapsules is the highest, reaching 91.89 ± 0.59%. With the further increase of the wall material ratio or the core material ratio, the encapsulation rate shows a downward trend. When the wall - core ratio is relatively low (such as 9:1), due to the relatively small amount of wall material, it is unable to completely wrap the core material, resulting in some cumin essential oil not being effectively encapsulated, thus reducing the encapsulation rate; while when the wall - core ratio is relatively high (such as 1:9), too much wall material may affect the formation of microcapsules, leading to unstable structure and also reducing the encapsulation rate. Therefore, the wall - core ratio of 7:3 is the optimal ratio for preparing CEO microcapsules with high encapsulation rate.

[0026] In the following effect example part, cumin essential oil / soybean protein isolate microcapsules prepared with a wall - core ratio of 7:3 were selected for detection.

[0027] Effect Example 2 (I) Physicochemical property analysis of CEO microcapsules A 0.25% (w / v) anhydrous ethanol solution of CEO microcapsules was carefully dropped onto a silicon nitride transmission electron microscope (TEM) grid (SimPore Inc.) to prepare samples, and a transmission electron microscope (JEOL JEM - 2100F, Japan) was used to observe and analyze the microstructure of the microcapsules. At the same time, a scanning electron microscope (SEM) (Hitachi, S - 3400 N, Japan) was used to observe the appearance morphology of the microcapsules to understand their surface characteristics and overall morphology.

[0028] Transmission electron microscope (TEM) images ( Figure 1 ) showed that the CEO microcapsules were spherical, with a relatively uniform particle size distribution, and the average particle size was about 200 - 300 nm. The cumin essential oil inside the microcapsules was tightly wrapped by the SPI wall material, forming a relatively stable structure.

[0029] (II) Particle size and zeta potential of microcapsules The CEO microcapsules prepared by vacuum drying were ground into powder with a mortar, and then diluted with anhydrous ethanol at a ratio of 1:20. A laser particle size analyzer (Zeta Sizer Nano ZS90, Malvern Co., Worcestershire, UK) was used to accurately measure the average particle size, polydispersity index (PDI), and zeta potential of the microcapsules. The average particle size reflects the size of the microcapsules, the PDI is used to evaluate the uniformity of the microcapsule particle size distribution, and the zeta potential can reflect the stability of the microcapsules in solution.

[0030] The measurement results of the laser particle size analyzer showed that the average particle size of the CEO microcapsules was 188.57 ± 22.53 nm, and the polydispersity index (PDI) was 0.22 ± 0.06. The smaller PDI value indicated that the particle size distribution of the microcapsules was relatively uniform, which was beneficial to ensuring the consistency of the microcapsule performance. The zeta potential of the microcapsules was – 10.77 ± 0.26 mV. The higher negative potential value made the microcapsules repel each other in the solution and not easily agglomerate, thus improving their stability in the system.

[0031] (III) Fourier Transform Infrared Spectroscopy The samples were subjected to spectral analysis using a Fourier transform infrared spectrometer (Suzhou Leighton Scientific Instruments Co., Ltd., Suzhou, China). The measurement wavelength range was set to 4000 - 650 cm⁻¹, the resolution was 4 cm⁻¹, and the scanning sampling time was 32 s. By analyzing the spectral characteristics, the chemical bond vibrations of each component in the microcapsules were understood to judge whether there was an interaction between cumin essential oil and SPI and the structural characteristics of the microcapsules.

[0032] Fourier transform infrared spectroscopy analysis results ( Figure 2 ) showed that SPI corresponded to the characteristic absorption peaks of amide I band and amide II band at 1627.07 cm -1 and 1515.25 cm -1 respectively. In the spectrum of the CEO / SPI microcapsules, these characteristic peaks still existed. At the same time, an absorption peak related to the carbonyl group in cumin essential oil appeared at 1742.63 cm -1 , indicating that cumin essential oil was successfully encapsulated in the SPI wall material, and there might be a certain interaction between SPI and cumin essential oil, such as hydrogen bond interaction or van der Waals force, thus stabilizing the structure of the microcapsules.

[0033] (IV) X-ray Diffraction of Microcapsules X-ray diffraction analysis of cumin essential oil, SPI, CEO / SPI microcapsules, KGM, and coated paper was carried out using an X-ray diffractometer (Bruker D8 Venture, Germany) in the scanning range (2θ = 5° - 90°). By comparing the diffraction patterns of different samples, the crystal structure changes of the microcapsules were studied to further determine whether cumin essential oil was successfully encapsulated in the SPI wall material and the influence of microencapsulation on its structure.

[0034] X-ray diffraction analysis ( Figure 2B) The results showed that SPI presented typical amorphous characteristics with broad and low-intensity diffraction peaks. Cumin essential oil had obvious crystalline diffraction peaks. In the diffraction pattern of the CEO / SPI microcapsules, the intensity of the crystalline peaks of cumin essential oil decreased significantly, and some new diffraction peaks appeared, indicating that during the microencapsulation process, the crystalline state of cumin essential oil changed, and some essential oil molecules were embedded in the amorphous structure of SPI, further confirming that cumin essential oil was successfully encapsulated in the SPI wall material, and the microencapsulation changed the crystal structure of the essential oil, improving its stability.

[0035] (V) Differential Scanning Calorimetry (DSC) DSC (STARe System DSC 3, Mettler Toledo) was used to evaluate the thermal stability of the wall material, cumin essential oil, SPI, and CEO-SPI. All samples (about 6 mg) were accurately weighed and added to the sample chamber. Under a nitrogen atmosphere, the temperature was increased from 20 °C to 600 °C at a heating rate of 10 °C / min, and the nitrogen flow rate was set at 50 ml / min. At the same time, an empty aluminum crucible was used as a control. By analyzing the DSC curves, the enthalpy change of the samples during heating was understood to evaluate the improvement effect of microencapsulation on the thermal stability of cumin essential oil.

[0036] The results of DSC analysis ( Figure 4 ) showed that SPI had an endothermic peak at about 195.8 °C, corresponding to its glass transition temperature. Cumin essential oil had multiple endothermic peaks between 150 - 250 °C, which was related to the evaporation of its volatile components. In the DSC curve of the CEO / SPI microcapsules, the glass transition temperature of SPI increased slightly, and the endothermic peaks of cumin essential oil became less obvious, indicating that the microencapsulation process enhanced the interaction between SPI and cumin essential oil, changed the thermal behavior of the essential oil, significantly improved its thermal stability, and thus reduced the volatile loss of the essential oil during storage and application.

[0037] (VI) Retention rate of CEO microcapsules at high temperature The weighing bottle containing a certain mass of microcapsules was placed in an oven at 100 °C, and the weighing bottle was taken out and weighed at 0, 10, 20, 30, 40, 50, 60, and 70 minutes respectively. It was used to investigate the protection ability of the microcapsules for cumin essential oil at high temperature and reflect its thermal stability and anti-volatility performance.

[0038] Under the condition of high temperature of 100 °C, the retention rate of cumin essential oil in CEO microcapsules shows a downward trend with the change of time. In the initial stage (0 - 30 min), the retention rate decreases rapidly, and the retention rate is above 70% at 30 min; after 30 min, the decreasing rate of the retention rate slows down, and the retention rate remains above 60% at 70 min. This indicates that the microcapsules can effectively protect cumin essential oil within a certain period of time and reduce its volatilization loss at high temperature. However, with the extension of time, the protective effect of the microcapsules gradually weakens. This retention rate characteristic at high temperature is of great significance for the preservation of cherry tomatoes during actual storage and transportation, ensuring that the cumin essential oil in the microcapsules can continuously play an antibacterial role within a certain temperature fluctuation range.

[0039] (VII) Release of CEO from Microcapsules The release kinetic curve of CEO from the sample was determined by the dynamic dialysis method. A sample containing 100 mg of CEO was carefully sealed in a dialysis bag (Mw = 200 Da), and then the sealed dialysis bag was immersed in 90 ml of 90% ethanol medium. It was placed in a dark room at 25 °C and incubated with constant shaking at a rotation speed of 100 r / min. At regular time intervals, 5 ml of the solution outside the dialysis bag was taken out regularly, and at the same time, an equal amount of fresh 90% ethanol was immediately added. The concentration of CEO in the taken-out solution was measured using a UV-V spectrophotometer, and the CEO release time curve was plotted accordingly. This experiment aims to study the release law of cumin essential oil from microcapsules, providing a theoretical basis for its practical application in the preservation process of cherry tomatoes, ensuring the continuous release of a sufficient concentration of essential oil within an appropriate time to play an antibacterial and preservation role.

[0040] The release behavior of CEO from microcapsules was studied by the dynamic dialysis method, and the results showed that, as Figure 5 shown, in the initial stage of release (0 - 5 d), the release rate of cumin essential oil was relatively fast, and the release rate reached about 40%, which may be due to the rapid diffusion of a small amount of essential oil adsorbed on the surface of the microcapsules. Subsequently, the release rate gradually slowed down, and at 25 d, the release rate reached 80%. After 30 d, the release tended to be flat, and the final release rate stabilized at about 85%. This slow-release characteristic is beneficial for the continuous release of cumin essential oil for a long time during the preservation of cherry tomatoes, maintaining a certain antibacterial concentration, thereby effectively inhibiting the growth of microorganisms on the fruit surface and extending the preservation period.

[0041] Effect Example 2 (I) Preparation of Coated Paper Cut kraft paper into small pieces of 25 cm×25 cm. Add different amounts of CEO microcapsules to a 1.5% konjac glucomannan (KGM) solution (w / v), and continuously stir at room temperature until evenly mixed. The final contents of CEO microcapsules in the antibacterial coating solution are set to 1%, 2%, 3%, 4% and 5% (w / v) respectively. The pre-experiment results show that when the addition amount exceeds 5%, phenomena such as uneven mixing and precipitation of microcapsules will occur. Use a glass rod to evenly coat 20 ml of the coating solution containing 1%, 2%, 3%, 4% and 5% (w / v) microcapsules on the kraft paper. After calculation, the microcapsule contents on the prepared coated paper are 3.3×10⁻ 4 、6.6×10⁻ 4 、10×10⁻ 4 、13.3×10⁻ 4 and 16.6×10⁻ 4 g / cm². Name the antibacterial papers with different microcapsule contents prepared as AP - 1, AP - 2, AP - 3, AP - 4 and AP – 5 respectively; the KGM group is the 1.5% konjac glucomannan (KGM) solution (w / v) group without microcapsules. Finally, place the coated paper in an environment of 25 ±1℃ and relative humidity of 50 ± 2% for 24 hours to make it fully dry and cured.

[0042] (II) Antibacterial activity of coated paper First, carefully pour 15 ml of sterilized PDA medium into a petri dish and wait for it to cool and solidify. Then, evenly spray 100 μl of Pseudomonas aeruginosa suspension (1.0×10 8 CFU / ml) on the surface of the plate. Finally, place a circular coated paper with a diameter of 5 mm and containing different CEO microcapsules at the center of the plate, and place the petri dish in an incubator at 28℃ for 48 hours. The antibacterial effect of the coated paper is visually represented by the inhibition zone formed around the filter paper. Use a vernier caliper to accurately measure the diameter of the inhibition zone to evaluate the antibacterial performance of the coated paper.

[0043] As Figure 6 and 7 shown: The antibacterial ring diameter of Pseudomonas aeruginosa in coated paper AP-1 is 8.08 ± 0.13mm. The diameter of the inhibition zone of Pseudomonas aeruginosa in coated paper AP-5 is 18 ± 1.22 mm. The results show that the coated paper has a strong antibacterial effect on Pseudomonas aeruginosa. As the content of CEO microcapsules in the coated paper increases, the growth inhibition of Pseudomonas aeruginosa becomes more obvious, and the diameter of the inhibition zone increases significantly ( p(<0.05). There was no antibacterial zone in the CK group, indicating that the paper without microcapsules did not have antibacterial properties. KGM has good film-forming properties and the ability to release active ingredients. The microcapsules loaded with CEO / SPI can be made into a coating film with persistent antibacterial properties, making the coated paper also have good antibacterial properties.

[0044] Effect Example 3 (1) Fresh-keeping effect of microcapsules on cherry tomatoes 1. Fresh-keeping treatment All the cherry tomatoes used in the experiment were mature fruits manually picked from the planting base. During the picking process, the fruit stalks were carefully retained to avoid mechanical damage to the fruits. The collected samples were transported to the laboratory at 15 ± 1°C and fruits without diseases, pests, and mechanical damage and with basically the same size were selected as experimental materials. The coated paper was folded in half and the three sides were pasted with double-sided tape to make a fresh-keeping bag.

[0045] Randomly selected plump, intact and evenly sized cherry tomatoes were placed into coated paper bags containing 0%, 1%, 2%, 3%, 4% and 5% CES microcapsules respectively. The kraft paper group without treatment was used as a control (CK). The openings of the paper bags were sealed with rubber bands (a total of 7 treatment groups, 3 parallel groups, and 20 cherry tomato samples in each treatment group). After packaging, the cherry tomatoes were stored at 25 ± 1°C and 60% humidity for 30 days.

[0046] 2. Determination of weight loss rate The cherry tomatoes in each treatment group were weighed regularly (every 3 days) to calculate the weight loss rate. Through the change of the weight loss rate, the effect of the coated paper on the water retention ability of cherry tomatoes was evaluated.

[0047] 3. Determination of hardness The texture analyzer was used to determine the hardness of cherry tomatoes. The cherry tomato fruits were placed on the platform of the texture analyzer, and a cylindrical probe with a diameter of 5 mm was used to press down at a test speed of 2 mm / s. The maximum force value during the process of the probe penetrating the fruit was recorded, with the unit of N, which represented the hardness of the fruit. Each sample was measured 3 times at different positions and the average value was taken.

[0048] 4. Determination of spoilage The number of rotten fruits within 12 days was recorded. According to the Chinese industry standard GH / T 1193-2021, the calculation formula for the decay rate is as follows: Decay rate (%) = Nt / N0×100%. Among them, N 0 is the initial number of cherry tomatoes andN t is the number of rotten fruits per day.

[0049] 5. pH Use a pH meter to evaluate the pH value. After calibration with a calibration solution, immerse the pH meter in the ground cherry juice to obtain a reading.

[0050] 6. Statistical analysis All experimental data were statistically analyzed using SPSS 22.0 software. One-way analysis of variance (One-Way ANOVA) was used to test the significance of differences between different treatment groups. When P < 0.05, the differences were considered significant. The data were expressed as mean ± standard deviation (Mean ± SD).

[0051] As Figure 8 and Figure 9 shown: During storage, the weight loss rate of cherry tomatoes gradually increased with time. The weight loss rate of cherry tomatoes in the control (CK) group increased rapidly, reaching 28 ± 2.1% after 12 days. While the weight loss rate of cherry tomatoes packaged with microcapsules was significantly lower, and the weight loss rate of cherry tomatoes in the AP-5 group was only 9.38 ± 1.5%. This is due to the low water vapor permeability and good barrier properties of the microcapsule-coated paper, which effectively reduced the water loss of cherry tomatoes and maintained the freshness and plumpness of the fruits. The reduction of the weight loss rate helps to maintain the appearance quality and taste of cherry tomatoes and improve their commercial value.

[0052] The hardness of cherry tomatoes gradually decreased with the extension of storage time. The hardness of cherry tomatoes in the control (CK) group decreased rapidly, and the hardness dropped to 4.24 ± 0.3 N after 12 days. While the hardness of cherry tomatoes packaged with microcapsule-coated paper decreased more slowly, and the hardness of cherry tomatoes in the AP-5 group was 7.98 ± 0.4 N. Fruit hardness is one of the important indicators to measure its freshness and shelf life. Higher hardness helps to maintain the integrity and appearance quality of fruits, reducing the risk of mechanical damage and microbial infection. The microcapsule-coated paper effectively delayed the decrease of cherry tomato hardness and extended its shelf life by reducing water loss and inhibiting microbial growth.

[0053] When the fruits are newly harvested, the cell walls of the fruits are closely related to the pectin in the fruits, and the decay rate is low. At the initial stage of storage, the decay rate of cherry tomatoes is 0. After 8 days of storage, the samples decay, and the decay percentage continues to increase. Microcapsule coating treatment shows that the decay is significantly reduced. In the coated samples, the decay remains zero increase after 7 days of storage. The microcapsule coating prevents the fruits from contacting the external environment, thus slowing down the senescence of the fruits. The coating plays an excellent role in reducing the decay during storage. The initial pH value of cherry tomatoes is 3.87. The pH values of the experimental group and all control groups increase significantly with the increase of storage time. After 6 d, the pH of the air control group increased significantly from 3.87 to 4.96, while the pH value of the KGM control group was 4.88 after 15 d. The pH value of the experimental group increased the slowest during the 12 d of storage. The microcapsules effectively reduced the respiration rate and enzyme activity of cherries, reduced the consumption rate of organic acids, and delayed the decline of acidity. When fruits decay and mold, the growth and reproduction of microorganisms on acidic substrates will reduce the acidity. From this perspective, the strong antibacterial properties of microcapsules are beneficial to inhibiting the metabolic activities of microorganisms and maintaining the pH value of cherries. Therefore, microcapsules can effectively maintain the freshness of cherries, and their application in fruit preservation has certain research significance.

Claims

1. A preparation method of cumin essential oil / soybean protein isolate microcapsules, characterized in that, It includes the following steps: (1) Adjust the pH value of the soy protein isolate solution, add 2 ml of Tween-80, and stir to obtain the SPI solution system; (2) Slowly drip the cumin essential oil ethanol solution into the SPI solution system, continuously stir, let it stand after stirring ends, and vacuum freeze-dry to obtain cumin essential oil / soy protein isolate microcapsules.

2. The preparation method according to claim 1, characterized in that, In step (1), the concentration of the soy protein isolate solution is 5% (m / v); the pH is adjusted to 10 with 1.0 mol / l NaOH solution; the addition amount of Tween-80 accounts for 2% of the volume of the soy protein isolate solution.

3. The preparation method according to claim 1, wherein In step (2), the mass ratio of the cumin essential oil to the soy protein isolate is 9 - 1:1 - 9.

4. The preparation method according to claim 1 or 3, characterized in that, In step (2), the concentration of the cumin essential oil ethanol solution is 0.01 g / ml; the stirring time is 4 h; the standing is carried out at -20°C for 24 hours.

5. A cumin essential oil / soy protein isolate microcapsule prepared by the preparation method according to any one of claims 1 - 4.

6. An application of the cumin essential oil / soy protein isolate microcapsule according to claim 5 in improving the performance of kraft paper for fresh-keeping of cherry tomatoes.

7. The application according to claim 6, wherein The cumin essential oil / soy protein isolate microcapsule and konjac glucomannan are used in combination; the concentration of the cumin essential oil / soy protein isolate microcapsule in the konjac glucomannan solution is 1 - 5%.

8. The application according to claim 7, wherein The concentration of the konjac glucomannan (KGM) solution is 1.5% (w / v).

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