Method for preserving fresh-cut water chestnuts using eugenol-zein fiber film

Abstract

The present invention discloses a method for preserving fresh-cut water chestnuts using a eugenol-zein fiber film. The method comprises the following steps: peeling healthy, intact fresh water chestnuts to obtain the fresh-cut water chestnuts, then packaging the fresh-cut water chestnuts with a eugenol-zein fiber film, and storing them under conventional preservation conditions. By utilizing the biodegradability, biocompatibility, and good film-forming properties of zein, the present invention uses electrospun zein fibers to encapsulate eugenol to form a film for preserving fresh-cut water chestnuts. This method can significantly improve the fresh-keeping effect of fresh-cut water chestnuts and extend their shelf life.

Description

Technical Field

[0001] The invention belongs to the technical field of food preservation, and particularly relates to a method for preserving fresh-cut water chestnuts by utilizing a eugenol-zein fiber film. Background Art

[0002] Water chestnuts have a white, crisp, juicy, and sweet flesh, rich in nutrients including carbohydrates, protein, cellulose, and various vitamins. They have the benefits of clearing heat and detoxifying, strengthening the stomach and digestion, and relieving coughs and lowering blood sugar. Fresh-cut water chestnuts have a high moisture content, and with prolonged storage, pathogenic microorganisms can grow, leading to spoilage. Currently, fresh-cut water chestnuts are primarily stored using physical, chemical, and biological coating preservation methods to extend their shelf life and maintain their quality characteristics. However, traditional preservation methods can affect the taste of fresh-cut water chestnuts. To reduce yellowing and browning, better preservation technologies should be developed to improve their effectiveness.

[0003] Electrospinning is a technique for producing nanofibers. During electrospinning, droplets in a solution are charged under a high-voltage electrostatic field. When the voltage is above a threshold voltage, the droplets can overcome surface tension, generating a jet. The fibers are then deposited on a collection plate while the droplet solvent evaporates. Electrospinning is an effective and versatile method for producing continuous polymer nanofibers and nonwovens with high molecular orientation, high porosity, and a large specific surface area. The high specific surface area and porosity of electrospun fibers facilitate the release of active substances and the transport of water vapor within packaging. Due to these properties, electrospun nanofibers have been used as a promising candidate for food packaging. Proteins and polysaccharides, and their derivatives, such as cellulose acetate, pullulan, gelatin, and zein, have been successfully electrospun due to their high safety and biodegradability. Summary of the Invention

[0004] The invention aims to provide a method for preserving fresh-cut water chestnuts by utilizing a eugenol-zein fiber film.

[0005] Zein, a hydrophobic protein with good film-forming properties, has been widely used as an electrospinning material. Zein is typically dissolved completely in ethanol before electrospinning, a non-toxic process. Compared to natural polysaccharides, zein exhibits greater spinnability, and single-component zein can be formed into nanofiber membranes through electrospinning.

[0006] In order to improve the brittleness of single zein fiber membrane, eugenol was added to the system, which effectively improved the ductility and deformation rate of the zein fiber membrane. Scanning electron microscopy observations showed that after the addition of eugenol, the fiber diameter became larger. This structure improved the mechanical properties of the zein fiber membrane. The addition of eugenol improved the stability of the single zein fiber membrane in water, making the fiber membrane insoluble in water, and can be better used in the field of food packaging.

[0007] The method for preserving fresh-cut water chestnuts using a eugenol-zein fiber film of the present invention comprises the following steps:

[0008] Healthy and complete fresh water chestnuts are peeled to obtain fresh-cut water chestnuts, which are then packaged with eugenol-zein fiber films and stored under conventional preservation conditions.

[0009] Preferably, the packaging is to directly cover the fresh-cut water chestnuts with the eugenol-zein fiber film, or to cover the eugenol-zein fiber film inside a PET box lid containing the fresh-cut water chestnuts.

[0010] Preferably, the conventional fresh-keeping condition is storage in a refrigerator at 10°C.

[0011] Preferably, the eugenol-zein fiber membrane is prepared by the following steps:

[0012] a. Using an aqueous ethanol solution as a solvent, zein was prepared into a zein solution, and then eugenol was added to the zein solution and stirred until a uniform eugenol - zein solution was obtained;

[0013] b. The eugenol-zein solution was electrospun into a eugenol-zein fiber membrane using a high-voltage electrospinning machine.

[0014] Preferably, in the electrospinning, the rotating collector is wrapped with tin foil, the speed of the drum collector is 180 r / min, the electrospinning time is 3.5 h, the injection speed is 1 mL / h, the voltage is 20 kV, and the distance from the needle tip to the collector is 15 cm.

[0015] Preferably, the ethanol aqueous solution is an ethanol aqueous solution with a volume fraction of 80%, and the zein solution is a 300 g / L zein solution.

[0016] Preferably, the amount of eugenol added is such that the final concentration of eugenol in the solution is 40 g / L.

[0017] Preferably, the stirring is magnetic stirring at 1000 rpm for 4 hours.

[0018] The present invention utilizes the biodegradability, biocompatibility and good film-forming properties of zein to electrospin zein fibers to embed eugenol for fresh-cut water chestnut preservation, which can significantly improve the preservation effect of fresh-cut water chestnuts and extend the shelf life. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the state of fresh-cut water chestnuts on the first day after preservation treatment.

[0020] Figure 2 This is the state of fresh-cut water chestnuts on the second day after preservation treatment.

[0021] Figure 3 This is the state of fresh-cut water chestnuts on the third day after preservation treatment.

[0022] Figure 4 This is the state of fresh-cut water chestnuts on the 4th day after preservation treatment.

[0023] Figure 5 This is the state of fresh-cut water chestnuts 5 days after preservation treatment.

[0024] Figure 6 It is the browning degree of different treatments; CK in the figure represents the tinfoil treatment group (control group), eugenol represents the eugenol-zein fiber membrane treatment group, and zein represents the zein fiber membrane treatment group.

[0025] Figure 7 It is the soluble solid content of different treatments; CK in the figure represents the tinfoil treatment group (control group), eugenol represents the eugenol-zein fiber film treatment group, and zein represents the zein fiber film treatment group.

[0026] Figure 8 Figure 2 is the weight loss rate of different treatments; CK in the figure represents the tinfoil treatment group (control group), eugenol represents the eugenol-zein fiber membrane treatment group, and zein represents the zein fiber membrane treatment group.

[0027] Figure 9 Field emission scanning electron microscopy image of zein fiber membrane (A) and fiber diameter distribution diagram (B).

[0028] Figure 10 Field emission scanning electron microscopy image (A) and fiber diameter distribution diagram (B) of eugenol-zein fiber membrane.

[0029] Figure 11 The invention relates to Fourier transform infrared spectroscopy analysis of zein fiber membrane and eugenol-zein fiber membrane.

[0030] Figure 12It is the thermogravimetric analysis of zein fiber membrane and eugenol-zein fiber membrane. DETAILED DESCRIPTION

[0031] The following examples are provided to further illustrate the present invention, but are not intended to limit the present invention.

[0032] Example 1

[0033] 1. Preservation of fresh-cut water chestnuts by electrospun zein fibers embedded with eugenol

[0034] Zein (BR, 92%) was dissolved in 80% ethanol (volume fraction) to prepare a 300 g / L zein solution. Eugenol (EUG) was then added to the solution to a final concentration of 40 g / L. The mixture was stirred under magnetic stirring (1000 rpm) for 4 hours until a uniform eugenol-zein solution was obtained. Simultaneously, a 300 g / L zein solution (hereinafter referred to as the zein solution) was prepared without eugenol using the same method.

[0035] The prepared zein solution or eugenol-zein solution was loaded into a 10 mL syringe. A high-voltage electrospinning machine was used for nanofiber production, using a high-voltage DC power supply (Dongwen High Voltage Power Supply (Tianjin) Co., Ltd.). The high-voltage positive and negative electrodes were connected to the capillary needles, and the rotating collector (HZ-SJ-11 flat drum collector) was wrapped with tin foil (the drum collector speed was 180 rpm). The electrospinning time was 3.5 hours. The sample feed rate was 1 mL / h, the voltage was 20 kV, and the distance from the needle tip to the collector was 15 cm. Zein fiber membranes and eugenol-zein fiber membranes were prepared by electrospinning.

[0036] The fiber membrane prepared above was used to preserve fresh-cut water chestnuts. Healthy, intact, and uniformly sized water chestnuts were freshly cut and peeled in the same manner and randomly divided into 6 groups. They were packed into PET boxes, with 3 boxes in each group (6 fresh-cut water chestnuts in each box). The treatments were as follows: fresh-cut water chestnuts were covered and packaged with (1) tin foil (control group), (2) eugenol-zein fiber membrane, and (3) zein fiber membrane. There were two ways of covering and packaging: A. Non-direct contact covering, in which the tin foil / fiber membrane was placed tightly on the lid of the PET box without direct contact with the fresh-cut water chestnuts; B. Direct contact covering, in which the tin foil / fiber membrane was directly covered on the fresh-cut water chestnuts. After treatment, the fresh-cut water chestnuts were covered with the PET box lid and stored in a refrigerator at 10°C. The fresh-cut water chestnuts were photographed every day from the 1st to the 5th day after treatment to record their fresh-keeping status.

[0037] The results are as follows Figure 1-5Specifically, the covering method in the left column of each figure is A: the tinfoil / fiber membrane is not directly in contact with the surface of the water chestnut, and the covering method in the right column is B: the tinfoil / fiber membrane is in direct contact with the water chestnut; the upper, middle, and lower groups in the same column are (1) tinfoil (control group), (2) eugenol-zein fiber membrane, and (3) zein fiber membrane packaging treatment group. Figure 1-5 As can be seen, the eugenol-zein fiber film maintained freshness and yellowed more slowly than the control group and the zein fiber film alone. However, the preservation effects of fresh-cut water chestnuts treated with direct and indirect contact coverings were similar. This suggests that the eugenol-zein fiber film can delay yellowing of fresh-cut water chestnuts, extend their shelf life, and maintain their quality characteristics.

[0038] For covering method B (direct contact between tinfoil / fiber film and water chestnut), Figure 6 The results showed that the browning degree of the eugenol-zein fiber film treatment group was significantly lower than that of the other two groups during the entire storage period from day 1 to day 5 after treatment. Figure 7 The results showed that from the 3rd day to the end of the 5th day of storage, the soluble solids content of the eugenol-zein fiber film treatment group was significantly higher than that of the other two groups. Figure 8 The results showed that during the entire storage period, the weight loss rate of the eugenol-zein fiber film treatment group was significantly lower than that of the other two groups.

[0039] 2. Field emission scanning electron microscopy (SEM) comparison of the two fiber membranes

[0040] The field emission scanning electron microscopy images of zein fiber membrane and eugenol-zein fiber membrane are shown in Figure 2. Figure 9 A. Figure 10 As shown in A. The field emission scanning electron microscopy image shows that the fiber membrane after adding eugenol has more uniform fibers, no beads, smooth surface, and the fiber diameter is slightly larger than that of the zein fiber membrane. The fiber diameter distribution diagrams of the zein fiber membrane and eugenol-zein fiber membrane are shown in Figure 1. Figure 9 B. Figure 10 As shown in Figure B, the fiber diameter distribution plot shows that the addition of eugenol increases the diameter of the nanofibers in the fiber membrane, likely due to a decrease in conductivity. Lower conductivity reduces the elongation of the polymer jet under applied voltage, increasing the fiber diameter. Furthermore, the inclusion of eugenol in the fibers contributes to the increase in fiber diameter.

[0041] 3. Comparison of Fourier transform infrared spectroscopy (FT-IR) of the two fiber membranes

[0042] The two fiber membranes were further analyzed using Fourier transform infrared spectroscopy. Figure 11 As shown. The spectrum of the eugenol-zein fiber membrane has characteristic peaks similar to those of the zein fiber membrane, with no new peaks appearing. This indicates that the encapsulation of eugenol by zein is a physical process, and there is no chemical reaction between zein and eugenol. The characteristic functional groups of eugenol are -OH, C=C, and COC, and its characteristic structure is a benzene ring. Therefore, the infrared spectrum of eugenol is at 3512, 1510, 1264, 1230, 1147, and 1032 cm, respectively. -1 The characteristic peak of zein in infrared spectrum is located at 1529 cm -1 (C=C skeleton vibration), 1640cm -1 (C=C stretching vibration) and 3287cm -1 (CH stretching vibration).

[0043] 4. Thermogravimetric analysis (TG) of two fiber membranes

[0044] The effect of eugenol incorporation on the thermal stability of electrospun zein fiber films was studied by thermogravimetric analysis (TG). Figure 12 ) The results showed that eugenol added to the fiber membrane had greater thermal stability than standard eugenol. A further period of weight loss occurred between 150°C and 300°C, indirectly confirming the presence of eugenol in the zein fiber. This suggests that eugenol added to the fiber membrane is less likely to decompose and volatilize.

Claims

1. A method for preserving fresh-cut water chestnuts using a eugenol-zein fiber film, characterized in that: The following steps are involved: Healthy and complete fresh water chestnuts are peeled to obtain fresh-cut water chestnuts, which are then packaged with eugenol-zein fiber films and stored under conventional preservation conditions; The eugenol-zein fiber membrane is prepared by the following steps: a. Using an aqueous ethanol solution as a solvent, zein was prepared into a zein solution, and then eugenol was added to the zein solution and stirred until a uniform eugenol - zein solution was obtained; the eugenol was added in an amount such that the final concentration of eugenol in the solution was 40 g / L; b. The eugenol - zein solution was electrospun into a eugenol - zein fiber film using a high-voltage electrospinning machine; The packaging is prepared by directly covering the fresh-cut water chestnuts with the eugenol-zein fiber film, or covering the eugenol-zein fiber film in a PET box lid containing the fresh-cut water chestnuts. The conventional fresh-keeping condition is storage in a refrigerator at 10°C.

2. The method according to claim 1, characterized in that In the electrospinning process, the rotating collector is wrapped with tin foil, the rotation speed of the drum collector is 180 r / min, the electrospinning time is 3.5 h, the injection speed is 1 mL / h, the voltage is 20 kV, and the distance from the needle tip to the collector is 15 cm.

3. The method according to claim 1, characterized in that The ethanol aqueous solution is an ethanol aqueous solution with a volume fraction of 80%, and the zein solution is a 300g / L zein solution.

4. The method according to claim 1, wherein The stirring is magnetic stirring at 1000 rpm for 4 hours.

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