Spice slow-release nanofiber membrane, preparation method and application

Abstract

The invention discloses a perfume slow-release nanofiber membrane, a preparation method and application, the main body of the perfume slow-release nanofiber membrane is a nanofiber membrane, and nanofiber contains a polymer and an aromatic precursor; the aromatic precursor is a condensation compound obtained by carrying out Schiff base reaction on aromatic aldehyde and amino-functionalized POSS (Polyhedral Oligomeric Silsesquioxane); and the average diameter of the nanofiber is between 200 nm and 600 nm. The prepared nanofiber membrane adopts a spice precursor technology, can reduce loss of spices in processing, has good aromatic aldehyde slow release performance and pH responsiveness, and can be used in the field of active packaging of food.

Description

Technical Field

[0001] The invention belongs to the field of nano materials and active food packaging materials, and particularly relates to a flavor sustained-release nano fiber membrane, a preparation method and application thereof. Background Art

[0002] Active packaging has been widely studied in food preservation as consumers prefer fresh and additive-free foods. In active packaging systems, bioactive compounds such as antimicrobials and antioxidants are encapsulated in the packaging and released continuously and slowly to achieve the effect of food preservation. With the increasing concern of consumers about food safety, essential oils, as a natural bioactive compound, have been widely studied in the application of active packaging in recent years. However, essential oils themselves are highly volatile and unstable, which are generally overcome by encapsulating them in polymer carriers. Electrospun nanofibers have become one of the promising carriers due to their large specific surface area, porous structure and easy preparation. However, simply blending essential oils into the spinning solution for electrospinning will result in the loss of volatile active components.

[0003] In order to solve the above problems, people have developed a variety of methods to encapsulate volatile active components before electrospinning. One method is to use nanoparticles. Patent CN107858784A discloses a method for preparing nanofiber membranes by loading cinnamaldehyde essential oil with zeolite and then electrospinning; CN112391697A discloses a method for preparing nanofiber membranes by loading holly essential oil with β-lactoglobulin and then electrospinning; CN114411331A discloses a method for preparing inclusion complexes by loading oregano essential oil with cyclodextrin and then electrospinning to prepare nanofiber membranes. Another method is to use fragrance precursors. Fragrance precursors themselves are not volatile, but under relatively mild environmental conditions, such as moisture, light, oxygen and temperature, they can trigger the release of volatile active compounds by selectively breaking covalent bonds. In a study reported by Zaitoon et al., fragrance precursors of ethyl formate were encapsulated in ethyl cellulose / polyethylene glycol electrospun fiber membranes, which could extend the shelf life of strawberries by 10 days at 5°C. Summary of the invention

[0004] In order to overcome the deficiencies of the prior art, the purpose of the present invention is to provide a flavor sustained-release nanofiber membrane, a preparation method and an application thereof, wherein a flavor precursor of aromatic aldehyde is prepared by Schiff base reaction, the flavor precursor and polyacrylonitrile are dissolved in N,N-dimethylformamide solvent, a spinning solution is prepared, and then a nanofiber membrane is obtained by electrospinning. The obtained nanofiber membrane adopts flavor precursor technology, which can reduce the loss of flavors during processing, has good aromatic aldehyde sustained-release performance and pH responsiveness, and can be used in the field of active packaging of food.

[0005] In order to achieve the above object, the present invention adopts the following technical solution: A flavor sustained-release nanofiber membrane, the main body of which is a nanofiber membrane, wherein the nanofibers contain a polymer and an aromatic precursor; the aromatic precursor is a condensate obtained by reacting an aromatic aldehyde with amino-functionalized POSS through a Schiff base; and the average diameter of the nanofibers is 200-600 nm.

[0006] The polymer is selected from one or more of polyacrylonitrile (PAN), polyvinyl alcohol (PVA), polyethylene oxide (PEO), cellulose, polyacrylic acid (PAA), polyvinyl pyrrolidone (PVP), polyethylene imine (PEI), polyacrylamide (PAM), polyethylene glycol / polyethylene oxide (PEG / PEO), polylactic acid (PLLA), polycaprolactone (PCL), polyglycolic acid (PGA), polyhydroxyalkanoate (PHA), and polybutylene succinate (PBS).

[0007] The aromatic aldehyde is one or more of anisaldehyde, vanillin, cinnamaldehyde and benzaldehyde.

[0008] The amino-functionalized POSS is octaaminopropyl caged silsesquioxane (OCAP-POSS).

[0009] The method for preparing the above-mentioned fragrance sustained-release nanofiber membrane comprises the following steps: S1, mixing aromatic aldehyde and amino-functionalized POSS to react and prepare a fragrance precursor; S2, dissolving the fragrance precursor and the polymer in an organic solvent to obtain a spinning solution; S3. Electrospinning the prepared spinning solution to obtain a nanofiber membrane loaded with aromatic aldehyde fragrance precursors.

[0010] Preferably, in the aforementioned step S1, the specific method for preparing the fragrance precursor is: dissolving the amino-functionalized POSS in an alcohol solvent, adding a neutralizing agent, and then adding an aromatic aldehyde to react with a Schiff base to obtain the fragrance precursor.

[0011] The neutralizing agent is triethylamine.

[0012] Preferably, in the aforementioned step S1, the molar ratio of the amino-functionalized POSS, the neutralizer and the aromatic aldehyde is 1:8:1-8, and the mass concentration of the amino-functionalized POSS after being dissolved in an alcohol solvent is 1%-5%.

[0013] Preferably, in the aforementioned step S2, the organic solvent is N,N-dimethylformamide, the molecular weight of the polymer is 50000 g / mol, the mass concentration is 12%-18%, and the mass fraction of the fragrance precursor compared to the polymer is 1%-10%.

[0014] Preferably, in the aforementioned step S3, the spinning parameters are: voltage of 10~25 KV, pole distance of 15~20 cm, the receiver is in the form of a drum, coated with a layer of food aluminum foil, the rotation speed is 120~180 r / min, the spinning solution propulsion rate is 0.010~0.016mL / min, the spinning temperature is 26±1°C, the indoor relative humidity is 44±2%, and the spinning process lasts 2~3 h.

[0015] The sustained-release method of the fragrance sustained-release nanofiber membrane comprises immersing the nanofiber membrane in an aqueous solution at room temperature, wherein the pH value of the aqueous solution is 5-7.

[0016] The application of spice sustained-release nanofiber membrane in food packaging materials has an antibacterial and fresh-keeping effect on fruits.

[0017] The present invention is beneficial in that: (1) The present invention adopts the fragrance precursor technology, which can reduce the loss of fragrance during processing and avoid the loss of fragrance molecules during electrospinning due to the strong volatility; (2) The loading rate of the fragrance precursor in the present invention is high and is evenly dispersed in the spinning solution, which does not affect the preparation of the nanofibers; the specific surface area of ​​the nanofibers is large, so that the fragrance sustained release effect of the nanofiber membrane is more significant; (3) The release of aromatic aldehyde fragrance molecules from nanofiber membranes is pH responsive. As the pH decreases, the release rate of aromatic aldehydes significantly accelerates, so it can be more efficient in some food preservation fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is an electron microscope photo of the nanofiber membrane; Figure 2 is the fiber diameter distribution diagram of the nanofiber membrane; Figure 3 The release curve of flavor molecules from nanofiber membrane in different pH environments; Figure 4 Papaya preservation experiment using nanofiber membrane. DETAILED DESCRIPTION

[0019] Example 1: A method for preparing a flavor sustained-release nanofiber membrane, comprising the following preparation steps: S1. First, OCAP-POSS was dissolved in methanol to obtain a solution with a mass concentration of 1%, triethylamine was added to the solution for neutralization, and then anisaldehyde was added to react with a Schiff base, and the reaction was stirred at room temperature for 2 hours, and filtered to obtain a fragrance precursor of anisaldehyde, wherein the molar ratio of OCAP-POSS, triethylamine and anisaldehyde was 1:8:8; S2, dissolving the fragrance precursor and polyacrylonitrile in N,N-dimethylformamide solvent, wherein the mass fraction of polyacrylonitrile relative to the solvent is 15%, and the mass fraction of the fragrance precursor relative to the polyacrylonitrile is 5%, to obtain a spinning solution, and ultrasonically disperse for 30 min; S3. The prepared spinning solution was subjected to electrospinning with the following spinning parameters: voltage: 10 KV, inter-electrode distance: 15 cm, the receiver was in the form of a roller, covered with a layer of food aluminum foil, the rotation speed was 150 r / min, the spinning solution propulsion rate was 0.012 mL / min; the spinning temperature was 26±1 ℃, the indoor relative humidity was 44±2%, the spinning process lasted for 2~3 h, and the fiber membrane was removed from the aluminum foil to obtain the prepared nanofiber membrane loaded with aromatic aldehyde fragrance precursors.

[0020] Example 2: A method for preparing a flavor sustained-release nanofiber membrane, comprising the following preparation steps: S1. First, OCAP-POSS was dissolved in methanol to obtain a solution with a mass concentration of 3%, triethylamine was added to the solution for neutralization, and then anisaldehyde was added to react with a Schiff base, and the mixture was stirred at room temperature for 2 h, and filtered to obtain a fragrance precursor of anisaldehyde, wherein the molar ratio of OCAP-POSS, triethylamine and anisaldehyde was 1:8:8; S2, dissolving the fragrance precursor and polyacrylonitrile in N,N-dimethylformamide solvent, wherein the mass fraction of polyacrylonitrile relative to the solvent is 15%, and the mass fraction of the fragrance precursor relative to the polyacrylonitrile is 3%, to obtain a spinning solution, and ultrasonically disperse for 30 min; S3. The prepared spinning solution was subjected to electrospinning with the following spinning parameters: voltage: 20 KV, inter-electrode distance: 15 cm, the receiver was in the form of a roller, covered with a layer of food aluminum foil, the rotation speed was 150 r / min, the spinning solution propulsion rate was 0.012 mL / min; the spinning temperature was 26±1 ℃, the indoor relative humidity was 44±2%, the spinning process lasted for 2~3 h, and the fiber membrane was removed from the aluminum foil to obtain the prepared nanofiber membrane loaded with aromatic aldehyde fragrance precursors.

[0021] Example 3: A method for preparing a flavor sustained-release nanofiber membrane, comprising the following preparation steps: S1. First, OCAP-POSS was dissolved in methanol to obtain a solution with a mass concentration of 5%, triethylamine was added to the solution for neutralization, and then anisaldehyde was added to react with a Schiff base, and the mixture was stirred at room temperature for 2 h, and filtered to obtain a fragrance precursor of anisaldehyde, wherein the molar ratio of OCAP-POSS, triethylamine and anisaldehyde was 1:8:8; S2, dissolving the fragrance precursor and polyacrylonitrile in N,N-dimethylformamide solvent, wherein the mass fraction of polyacrylonitrile relative to the solvent is 15%, and the mass fraction of the fragrance precursor relative to the polyacrylonitrile is 5%, to obtain a spinning solution, and ultrasonically disperse for 30 min; S3. The prepared spinning solution was subjected to electrospinning with the following spinning parameters: voltage: 20 KV, inter-electrode distance: 15 cm, the receiver was in the form of a roller, covered with a layer of food aluminum foil, the rotation speed was 150 r / min, the spinning solution propulsion rate was 0.012 mL / min; the spinning temperature was 26±1 ℃, the indoor relative humidity was 44±2%, the spinning process lasted for 2~3 h, and the fiber membrane was removed from the aluminum foil to obtain the prepared nanofiber membrane loaded with aromatic aldehyde fragrance precursors.

[0022] Example 4: A method for preparing a flavor sustained-release nanofiber membrane, comprising the following preparation steps: S1. First, OCAP-POSS was dissolved in methanol to obtain a solution with a mass concentration of 3%, triethylamine was added to the solution for neutralization, and then cinnamaldehyde was added to react with a Schiff base, and the mixture was stirred at room temperature for 2 h, and filtered to obtain a fragrance precursor of cinnamaldehyde, wherein the molar ratio of OCAP-POSS, triethylamine and cinnamaldehyde was 1:8:8; S2, dissolving the fragrance precursor and polyacrylonitrile in N,N-dimethylformamide solvent, wherein the mass fraction of polyacrylonitrile relative to the solvent is 12%, and the mass fraction of the fragrance precursor relative to the polyacrylonitrile is 5%, to obtain a spinning solution, and ultrasonically disperse for 30 min; S3. The prepared spinning solution was subjected to electrospinning with the following spinning parameters: voltage: 20 KV, inter-electrode distance: 20 cm, the receiver was in the form of a roller, covered with a layer of food aluminum foil, the rotation speed was 120 r / min, the spinning solution propulsion rate was 0.010 mL / min; the spinning temperature was 26±1 ℃, the indoor relative humidity was 44±2%, the spinning process lasted for 2~3 h, and the fiber membrane was removed from the aluminum foil to obtain the prepared nanofiber membrane loaded with cinnamaldehyde flavor precursor.

[0023] Example 5: A method for preparing a flavor sustained-release nanofiber membrane, comprising the following preparation steps: S1. First, OCAP-POSS was dissolved in methanol to obtain a solution with a mass concentration of 3%, triethylamine was added to the solution for neutralization, and then vanillin was added to react with Schiff base, and the mixture was stirred at room temperature for 2 h, and filtered to obtain a vanillin flavor precursor, wherein the molar ratio of OCAP-POSS, triethylamine and vanillin was 1:8:8; S2, dissolving the fragrance precursor and polyacrylonitrile in N,N-dimethylformamide solvent, wherein the mass fraction of polyacrylonitrile relative to the solvent is 18%, and the mass fraction of the fragrance precursor relative to the polyacrylonitrile is 5%, to obtain a spinning solution, and ultrasonically disperse for 30 min; S3. The prepared spinning solution was subjected to electrospinning with the following spinning parameters: voltage: 20 KV, inter-electrode distance: 15 cm, the receiver was in the form of a roller, covered with a layer of food aluminum foil, the rotation speed was 180 r / min, the spinning solution propulsion rate was 0.016 mL / min; the spinning temperature was 26±1 ℃, the indoor relative humidity was 44±2%, the spinning process lasted for 2~3 h, and the fiber membrane was removed from the aluminum foil to obtain the prepared nanofiber membrane loaded with vanillin flavor precursor.

[0024] Example 6: A method for preparing a flavor sustained-release nanofiber membrane, comprising the following preparation steps: S1. First, OCAP-POSS was dissolved in methanol to obtain a solution with a mass concentration of 3%, triethylamine was added to the solution for neutralization, and then benzaldehyde was added to react with a Schiff base, and the mixture was stirred at room temperature for 2 h, and filtered to obtain a fragrance precursor of benzaldehyde, wherein the molar ratio of OCAP-POSS, triethylamine and benzaldehyde was 1:8:4; S2, dissolving the fragrance precursor and polyacrylonitrile in N,N-dimethylformamide solvent, wherein the mass fraction of polyacrylonitrile relative to the solvent is 15%, and the mass fraction of the fragrance precursor relative to the polyacrylonitrile is 10%, to obtain a spinning solution, and ultrasonically disperse for 30 min; S3. The prepared spinning solution was subjected to electrospinning with the following spinning parameters: voltage: 20 KV, inter-electrode distance: 15 cm, the receiver was in the form of a roller, covered with a layer of food aluminum foil, the rotation speed was 150 r / min, the spinning solution propulsion rate was 0.015 mL / min; the spinning temperature was 26±1 ℃, the indoor relative humidity was 44±2%, the spinning process lasted for 2~3 h, and the fiber membrane was removed from the aluminum foil to obtain the prepared nanofiber membrane loaded with benzaldehyde fragrance precursor.

[0025] Example 7: A method for preparing a flavor sustained-release nanofiber membrane, comprising the following preparation steps: S1. First, OCAP-POSS was dissolved in methanol to obtain a solution with a mass concentration of 3%, triethylamine was added to the solution for neutralization, and then benzaldehyde and anisaldehyde were added to react with Schiff base, and the mixture was stirred at room temperature for 2 h, and filtered to obtain a fragrance precursor of mixed aromatic aldehydes, wherein the molar ratio of OCAP-POSS, triethylamine, benzaldehyde and anisaldehyde was 1:8:4:4; S2, dissolving the fragrance precursor and polyacrylonitrile in N,N-dimethylformamide solvent, wherein the mass fraction of polyacrylonitrile relative to the solvent is 15%, and the mass fraction of the fragrance precursor relative to the polyacrylonitrile is 5%, to obtain a spinning solution, and ultrasonically disperse for 30 min; S3. The prepared spinning solution was subjected to electrospinning with the following spinning parameters: voltage: 20 KV, inter-electrode distance: 15 cm, the receiver was in the form of a roller, covered with a layer of food aluminum foil, the rotation speed was 150 r / min, the spinning solution propulsion rate was 0.015 mL / min; the spinning temperature was 26±1 ℃, the indoor relative humidity was 44±2%, the spinning process lasted for 2~3 h, and the fiber membrane was removed from the aluminum foil to obtain the prepared nanofiber membrane loaded with benzaldehyde fragrance precursor.

[0026] Example 8: A method for preparing a flavor sustained-release nanofiber membrane, comprising the following preparation steps: S1. First, OCAP-POSS was dissolved in methanol to obtain a solution with a mass concentration of 3%, triethylamine was added to the solution for neutralization, and then benzaldehyde and cinnamaldehyde were added to react with Schiff base, and the mixture was stirred at room temperature for 2 h, and filtered to obtain a fragrance precursor of mixed aromatic aldehydes, wherein the molar ratio of OCAP-POSS, triethylamine, benzaldehyde and cinnamaldehyde was 1:8:4:4; S2, dissolving the fragrance precursor and polyacrylonitrile in N,N-dimethylformamide solvent, wherein the mass fraction of polyacrylonitrile relative to the solvent is 15%, and the mass fraction of the fragrance precursor relative to the polyacrylonitrile is 5%, to obtain a spinning solution, and ultrasonically disperse for 30 min; S3. The prepared spinning solution was subjected to electrospinning with the following spinning parameters: voltage: 20 KV, inter-electrode distance: 15 cm, the receiver was in the form of a roller, covered with a layer of food aluminum foil, the rotation speed was 150 r / min, the spinning solution propulsion rate was 0.015 mL / min; the spinning temperature was 26±1 ℃, the indoor relative humidity was 44±2%, the spinning process lasted for 2~3 h, and the fiber membrane was removed from the aluminum foil to obtain the prepared nanofiber membrane loaded with aromatic aldehyde fragrance precursors.

[0027] Comparative Example 1: The preparation method of this comparative example is different from that of Example 3 in that the condensation reaction of OCAP-POSS and anisaldehyde is not carried out, and anisaldehyde is directly added to the spinning solution, wherein the mass fraction of polyacrylonitrile relative to the solvent is 15%, and the mass fraction of anisaldehyde relative to polyacrylonitrile is 3%.

[0028] Performance testing experiment: (1) Figure 1 is an electron microscope photograph of the nanofiber membrane prepared in Example 3. The fiber diameters of the nanofiber membranes prepared in Examples 1 to 8 were measured. The results are shown in Tables 1 and Figure 2 .

[0029] Table 1 Fiber diameter of nanofiber membrane

[0030] (2) The nanofiber membranes prepared in Examples 1 to 8 were immersed in a weakly acidic solution (pH = 5.8) respectively. After 24 h, the release rate of aromatic aldehydes was detected. The specific results are shown in Table 2.

[0031] Table 2 Release rate of aromatic aldehydes in nanofiber membranes

[0032] (3) The nanofiber membrane prepared in Example 3 was immersed in two portions of phosphate buffer solutions, the pH values ​​of which were 5.8 and 7.9, respectively. After 24 h, the absorbance of anisaldehyde at the characteristic absorption peak was measured by UV-visible spectrophotometry, and the concentration of anisaldehyde was calculated, thereby obtaining the release rate of anisaldehyde. The specific results are shown in Figure 3 .

[0033] pass Figure 3 It can be seen that the release rate of aromatic aldehydes from the nanofiber membrane in a weakly acidic environment is greater than that in a weakly alkaline environment.

[0034] (4) Example 3 was compared with Comparative Example 1. In Comparative Example 1, anisaldehyde was directly added to the spinning solution without condensing anisaldehyde with OCAP-POSS. After testing, the loss of anisaldehyde in Comparative Example 1 (due to its volatility) was more than 32%, while the fragrance precursor in Example 3 was basically not lost during the electrospinning process. The nanofiber membranes prepared in Example 3 and Comparative Example 1 were immersed in a phosphate buffer solution with a pH of 5.8. After 12 h, the release rate of anisaldehyde in Example 3 was 75%, and it was basically completely released after 2 days, while the sustained release effect of anisaldehyde in Comparative Example 1 was poor, and it was completely released after 12 h.

[0035] (5) Eight papaya samples of the same maturity were prepared, and four of the samples were packaged with a PE packaging film with the nanofiber film of Example 3 placed inside ( Figure 4 (a)~(d)), and the other four samples were packaged with conventional PE packaging film only ( Figure 4 (e)~(h)), the encapsulated papaya samples were placed for 0, 6, 8, and 10 days respectively, and the skin conditions were shown in Figure 4 .

[0036] from Figure 4 It can be seen that the control sample that was only packaged with conventional PE packaging film had mold spots after being placed for 6 days ( Figure 4(f)), while the sample with the nanofiber membrane placed inside was still intact after 10 days. It can be seen that the nanofiber membrane of the present invention can be more efficiently used in the field of food preservation.

[0037] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any form, and any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A flavor sustained-release nanofiber membrane, characterized in that: The main body is a nanofiber membrane, wherein the nanofiber contains a polymer and an aromatic precursor; the aromatic precursor is a condensate obtained by reacting aromatic aldehyde and amino-functionalized POSS through a Schiff base; and the average diameter of the nanofiber is 200-600nm.

2. The flavor sustained-release nanofiber membrane according to claim 1, characterized in that: The polymer is selected from one or more of polyacrylonitrile, polyvinyl alcohol, polyethylene oxide, cellulose, polyacrylic acid, polyvinyl pyrrolidone, polyethylene imine, polyacrylamide, polyethylene glycol / polyethylene oxide, polylactic acid, polycaprolactone, polyglycolic acid, polyhydroxyalkanoate and polybutylene succinate.

3. The flavor sustained-release nanofiber membrane according to claim 1, characterized in that: The aromatic aldehyde is one or more of anisaldehyde, vanillin, cinnamaldehyde and benzaldehyde.

4. The flavor sustained-release nanofiber membrane according to claim 1, characterized in that: The amino-functionalized POSS is octaaminopropyl caged silsesquioxane.

5. The method for preparing the flavor sustained-release nanofiber membrane according to claim 1, characterized in that: The steps include: S1, mixing aromatic aldehyde and amino-functionalized POSS to react and prepare a fragrance precursor; S2, dissolving the fragrance precursor and the polymer in an organic solvent to obtain a spinning solution; S3. Electrospinning the prepared spinning solution to obtain a nanofiber membrane loaded with aromatic aldehyde fragrance precursors.

6. The method for preparing the flavor sustained-release nanofiber membrane according to claim 5, characterized in that: In the aforementioned step S1, the specific method for preparing the fragrance precursor is: dissolving the amino-functionalized POSS in an alcohol solvent, adding a neutralizer, and then adding an aromatic aldehyde to react with a Schiff base to obtain the fragrance precursor; the neutralizer is triethylamine.

7. The method for preparing the flavor sustained-release nanofiber membrane according to claim 6, characterized in that: In the aforementioned step S1, the molar ratio of amino-functionalized POSS, neutralizer and aromatic aldehyde is 1:8:1-8, and the mass concentration of amino-functionalized POSS after being dissolved in an alcohol solvent is 1%-5%.

8. The method for preparing the flavor sustained-release nanofiber membrane according to claim 5, characterized in that: In the aforementioned step S2, the organic solvent is N,N-dimethylformamide, the molecular weight of the polymer is 50,000 g / mol, the mass concentration is 12%~18%, and the mass fraction of the fragrance precursor compared to the polymer is 1%~10%; in the aforementioned step S3, the spinning parameters are: voltage is 10~25KV, pole distance is 15~20 cm, the receiver is in the form of a drum, coated with a layer of food aluminum foil, the rotation speed is 120~180 r / min, the spinning solution propulsion rate is 0.010~0.016 mL / min, the spinning temperature is 26±1°C, the indoor relative humidity is 44±2%, and the spinning process lasts 2~3 h.

9. The sustained-release method of the fragrance sustained-release nanofiber membrane according to claim 1, characterized in that: The nanofiber membrane is immersed in an aqueous solution at room temperature, and the pH value of the aqueous solution is 5-7.

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