COS-O-luteolin derivative as well as preparation method and application thereof

Abstract

The invention discloses a COS-O-luteolin derivative as well as a preparation method and application thereof. The COS-O-luteolin derivative is a compound obtained by modifying hydroxyl of chitosan oligosaccharide with luteolin. The preparation method comprises the following steps: weighing a certain amount of chitosan oligosaccharide, and dissolving the chitosan oligosaccharide in ethanol at 25 DEG C to obtain a chitosan oligosaccharide ethanol solution with the mass concentration of 0.5%; the method comprises the following steps: weighing quantitative luteolin, and dissolving the luteolin in ethanol at 25 DEG C to obtain a luteolin ethanol solution with the mass concentration of 0.5%; the preparation method comprises the following steps: mixing a chitosan oligosaccharide ethanol solution and a luteolin ethanol solution in equal volume, stirring for 2 hours, adjusting the pH value to 7.5, continuously stirring for 20-30 minutes, carrying out rotary evaporation at 45 DEG C to remove a solvent, carrying out vacuum drying at 60 DEG C, crushing and sieving to obtain the COS-O-luteolin derivative which can be applied to preparation of a fresh strawberry postharvest storage agent.

Description

Technical Field

[0001] The present invention relates to a chitosan oligosaccharide derivative, a preparation method and an application thereof, in particular to a COS-O-luteolin derivative, a preparation method and an application thereof. Background Art

[0002] Strawberries are berries with high respiratory metabolism, thin skin, and fragile tissue. They are highly susceptible to mechanical damage during harvesting and transportation, which can lead to pathogenic bacteria infection and high rates of fruit rot. According to statistics, strawberries typically only last 1-3 days at room temperature after harvest. Even under refrigerated conditions, their shelf life can only be extended to 3-5 days. Therefore, it is necessary to develop efficient and convenient methods for preserving fresh strawberries, as well as efficient and convenient preservatives for fresh strawberries.

[0003] Chitosan oligosaccharides (COS) are derived from chitosan through acid hydrolysis, oxidation, and physical degradation. They are the only positively charged alkaline amino oligosaccharides found in nature, with a degree of polymerization (DP) of 2-50. Compared to chitosan, chitosan oligosaccharides have a lower molecular weight, better water solubility, and are non-toxic. Studies have shown that chitosan oligosaccharides have antibacterial activity, inhibiting the growth and reproduction of bacteria and fungi, but the activity is generally weak. Chitosan oligosaccharides have a unique structure, containing active amino and hydroxyl groups within the molecule, making them susceptible to chemical reactions. The amino group at position C2 and the hydroxyl groups at positions C3 and C6 are active groups. Modification of these active sites with other groups can produce different chitosan oligosaccharide derivatives, thereby altering the bioactivity of chitosan oligosaccharides.

[0004] Luteolin (Luteolin, Lut), a natural flavonoid compound, is chemically classified as a flavonoid subclass of polyphenols. It has attracted much attention due to its excellent antioxidant activity, antibacterial and antiviral abilities, and its ability to lower blood lipids and cholesterol, and has shown various application potentials in the food field.

[0005] So far, there has been no report on the preparation of COS-O-luteolin derivatives by chemical reaction using chitosan oligosaccharides and luteolin as raw materials, and the application of the derivatives in the preservation of fresh strawberries. Summary of the Invention

[0006] The present invention aims to solve the above-mentioned technical problems existing in the prior art and provides a COS-O-luteolin derivative, a preparation method and an application thereof.

[0007] The technical solution of the present invention is: a COS-O-luteolin derivative, the structural formula of which is as follows: ; Said n=2-50.

[0008] A method for preparing the above-mentioned COS-O-luteolin derivative is carried out according to the following steps: Step 1. Weigh a certain amount of chitosan oligosaccharide and dissolve it in ethanol at 25°C to obtain a chitosan oligosaccharide ethanol solution with a mass concentration of 0.5%; Step 2. Weigh a certain amount of luteolin and dissolve it in ethanol at 25°C to obtain a 0.5% luteolin ethanol solution. Step 3. Mix equal volumes of chitosan oligosaccharide ethanol solution and luteolin ethanol solution and stir evenly. Adjust the pH to 7.5 and continue stirring for 20-30 min. Rotate and evaporate the solvent at 45°C. Dry under vacuum at 60°C, crush and sieve to obtain COS-O-luteolin derivative.

[0009] An application of the COS-O-luteolin derivative in the preparation of a strawberry fresh fruit preservative.

[0010] This invention modifies the hydroxyl groups of chitosan oligosaccharides with luteolin to synthesize a COS-O-luteolin derivative. Compared to chitosan oligosaccharides, this derivative effectively prolongs the storage life of strawberries and can be used to prepare a fresh strawberry preservative. Compared to traditional chemical modification methods, this preparation method offers advantages such as simplicity and rapid reaction. The reaction is carried out at room temperature (18-25°C), which is energy-efficient and prevents damage to the derivative structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is the infrared spectrum of COS-O-luteolin derivatives and chitosan oligosaccharides in the examples of the present invention.

[0012] Figure 2 1 is the X-ray diffraction pattern of COS-O-luteolin derivatives and chitosan oligosaccharides according to the embodiments of the present invention.

[0013] Figure 3 This is the UV spectrum of COS-O-luteolin derivatives and chitosan oligosaccharides in the examples of the present invention.

[0014] Figure 4 The COS-O-luteolin derivative of the present invention and chitosan oligosaccharide 1 H NMR spectra.

[0015] Figure 5 This is a record of the strawberry fresh-keeping appearance of COS-O-luteolin derivatives and chitosan oligosaccharides at different concentrations according to the embodiment of the present invention.

[0016] Figure 6 This is a graph showing the weight loss rate of strawberries with different concentrations of COS-O-luteolin derivatives and chitosan oligosaccharides according to the examples of the present invention.

[0017] Figure 7 This is a graph showing the brightness changes of strawberries with different concentrations of COS-O-luteolin derivatives and chitosan oligosaccharides according to the examples of the present invention.

[0018] Figure 8 This is a graph showing the color saturation changes of strawberries with different concentrations of COS-O-luteolin derivatives and chitosan oligosaccharides according to the examples of the present invention. DETAILED DESCRIPTION

[0019] The preparation method of the COS-O-luteolin derivative of the present invention is carried out according to the following steps: Step 1. Weigh 1.0 g of chitosan oligosaccharide (COS) and dissolve it in ethanol at 25°C to obtain a chitosan oligosaccharide ethanol solution with a mass concentration of 0.5%; Step 2. Weigh 1.0 g of luteolin and dissolve it in ethanol at 25°C to obtain a 0.5% luteolin ethanol solution. Step 3. Mix equal volumes of chitosan oligosaccharide and luteolin ethanol solutions and stir for 2 h. Adjust the pH to 7.5 with 1 M NaOH and continue stirring for 30 min. Remove most of the solvent by rotary evaporation at 45°C. Dry under vacuum at 60°C, pulverize, and sieve to obtain a COS-O-luteolin derivative, designated COS-Lut.

[0020] The raw materials used in the examples of the present invention are all commercially available products, among which the degree of polymerization of chitosan oligosaccharide is 2-50 and the deacetylation is greater than 90%; the molecular formula of luteolin is C 15 H 10 O6, molecular weight is 286.23.

[0021] The reaction formula is as follows: ; experiment: 1. Infrared Spectral Analysis of Chitosan Oligosaccharide and COS-O-Luteolin Derivative (COS-Lut) Used in Examples of the Present Invention Chitosan oligosaccharide (COS) and COS-O-luteolin derivative (COS-Lut) used in the present invention were mixed and ground with potassium bromide at a mass ratio of 1:100, and infrared spectroscopy was performed using the potassium bromide tablet method with a scanning range of 4000-400 cm -1 , the number of scans was 72, and the resolution was 4 cm -1 , infrared spectrum such as Figure 1 shown.

[0022] from Figure 1 It can be seen that COS at 3500 cm -1The broad peak at 2966 cm is the superposition absorption peak of NH and OH stretching vibration. -1 The CH asymmetric stretching peak and 1733 cm -1 The absorption peak of amide I (C=O) is shown in Figure 1. Compared with COS, the broad peak of OH stretching vibration of COS-Lut becomes smaller, and the CH asymmetric stretching peak vibration and C=O stretching peak are red-shifted. The existence of hydrogen bonding between the two substances may cause the shift of infrared absorption peak. And by comparing the spectra, it can be seen that COS-Lut has a strong absorption peak at 1161 cm -1 and 1258 cm -1 The ether bond (COC) absorption peak appeared at , indicating that the hydroxyl group of chitosan oligosaccharide was successfully introduced into luteolin.

[0023] II. XRD Analysis of Chitosan Oligosaccharide and COS-O-Luteolin Derivative (COS-Lut) Used in Examples of the Present Invention Chitosan oligosaccharide (COS) and COS-O-luteolin derivative (COS-Lut) used in the embodiment of the present invention were ground separately, added with anhydrous ethanol and spread on a silicon plate. After the anhydrous ethanol evaporated, XRD analysis was performed on the sample. The scanning conditions were Cu target, scanning temperature 25 ° C, scanning speed 4 ° / min, scanning range 5-80 °, and the X-ray diffraction pattern was as follows: Figure 2 shown.

[0024] from Figure 2 COS has a diffraction absorption peak at 2θ = 22.8°, which is related to the crystal morphology of the COS molecule. The maximum diffraction angle peak position of the modified COS-Lut X-ray diffraction pattern shifts to the right, and the peak intensity at the maximum diffraction angle increases. New absorption peaks appear at 2θ = 13°, 22°, 25°, 28°, 36°, and 43°, likely due to the intermolecular interaction between luteolin and COS, which alters the COS crystal structure.

[0025] 3. Ultraviolet spectrum analysis of the raw material chitosan oligosaccharide and the obtained COS-O-luteolin derivative (COS-Lut) used in the examples of the present invention.

[0026] Using distilled water as a blank control, the slit width of the UV-visible spectrophotometer was 2 nm, and the UV-visible full wavelength scanning spectra of chitosan oligosaccharides (COS) and COS-O-luteolin (COS-Lut) were measured in the scanning wavelength range of 190-600 nm. The results are as follows: Figure 3 shown.

[0027] from Figure 3As can be seen, COS has weak UV absorption due to its lack of a conjugated system. Compared to COS, COS-Lut's UV spectrum shows characteristic absorption bands at 264 nm and 340 nm, representing the π system of the benzene ring in luteolin. Furthermore, a red shift is observed in the COS-Lut spectrum, indicating a reaction between chitosan oligosaccharides and luteolin molecules.

[0028] IV. H NMR Spectrum Analysis of Chitosan Oligosaccharides and COS-O-Luteolin Derivatives (COS-Lut) Used in Examples of the Present Invention Weigh a small amount of chitosan oligosaccharide (COS) and COS-O-luteolin derivative (COS-Lut) and transfer them to the NMR tube. Use a pipette to transfer heavy water (D2O) to the NMR tube. After shaking until fully dissolved, perform hydrogen spectrum analysis.

[0029] COS 1 H NMR spectra and COS-Lut 1 H NMR images Figure 4 As shown. Figure 4 It can be seen that the absorption peak at δ = 1.99 ppm is the chemical shift of the methyl group on the undeacetyl group of chitosan oligosaccharide, δ = 3.0-4.5 ppm is the chemical shift of the H of the glucosamine and N-acetylglucosamine residues on the chitosan oligosaccharide ring, which is a characteristic peak of chitosan oligosaccharide, and δ = 4.79 ppm is the absorption peak of the solvent. Compared with chitosan oligosaccharide, the COS-O-luteolin derivative has a methylene group at δ = 1.16 ppm, and the chemical shift of the hydroxyl proton on the sugar ring at δ = 3.0-4.5 ppm changes. The hydroxyl group strengthens the intermolecular force through hydrogen bonding. The appearance of an alkoxy group at δ = 4.62 ppm indicates that the hydroxyl group of chitosan oligosaccharide reacts with luteolin, which is consistent with the infrared results, indicating that the COS-O-luteolin derivative was successfully synthesized.

[0030] V. Experimental Study on Changes in Strawberry Freshness, Weight Loss, Brightness, and Color Saturation with Different Concentrations of COS-O-Luteolin Derivatives and Chitosan Oligosaccharides in the Examples of the Present Invention The present invention involves five different sample solution groups: a blank control group (sterile water), a COS group (2% COS), a 0.5% COS-Lut group, a 1% COS-Lut group, and a 2% COS-Lut group. Commercially mature, undamaged strawberry fruits were disinfected with a 0.5% sodium hypochlorite solution for 1 minute and then rinsed with running water three times for 10 seconds each. The strawberry fruits were then divided into five groups and immersed in each solution for 5 minutes. After 5 minutes, the fruits were removed and drained.

[0031] Record the status of the tested strawberries for 6 days. Record the appearance, smell and spoilage of each group of strawberries every 3 days. Figure 5 As shown. Figure 5 It can be seen that the fruits in the blank control group, COS group, 0.5% COS-Lut, and 1% COS-Lut groups showed varying degrees of mold, darkening, and severe softening on the 6th day; the fruits in the 2% COS-Lut group did not darken, soften, or rot on the 6th day, indicating that the shelf life of strawberries was significantly extended after treatment with 2% COS-Lut.

[0032] The weight loss of each group of strawberries was measured by weighing method, and the measurement was carried out every 2 days. The weight loss rate of strawberries was calculated according to the following formula: Strawberry weight loss rate (%) = (M0-M1) / M0×100% (M0: original weight of strawberries; M1: strawberries during storage). The results are as follows: Figure 6 As shown. Figure 6 It can be seen that the weight loss rate of strawberries showed an increasing trend with the extension of storage time. In contrast, COS-Lut treatment played a role in inhibiting weight loss, and with the increase of COS-Lut concentration, the weight loss was smaller.

[0033] The colorimeter of Japan Minolta CR-400 was used to measure the L * Value, L * The value represents the brightness of strawberries during storage. The effects of different treatment groups on the brightness of strawberries are shown in Figure 7 .Depend on Figure 7 It can be seen that the brightness of all treatment groups decreased rapidly in the first 4 days of storage and then remained stable. The brightness of the fruits treated with different concentrations of COS-Lut was higher than that of the blank control group during the entire storage period, indicating that COS-Lut can maintain the brightness of the fruit.

[0034] The color of the peel is one of the key indicators of strawberry maturity and quality. The color was measured every 2 days using a Japanese Minolta CR-400 colorimeter. * and b * Color parameters. Calculate the color saturation (C) of strawberry according to the following formula. Color saturation = (a 2 +b 2 ) 1 / 2 (a: from green to red; b: from blue to yellow), the results are as follows Figure 8 As shown in Figure 2, the color saturation of strawberries treated with various methods decreased throughout the storage period. After 6 days of storage, the color saturation of the strawberries treated with various concentrations of COS-Lut was even lower than that of the blank control. These results indicate that COS-Lut treatment can better preserve the color of strawberries.

Claims

1. A COS-O-luteolin derivative, characterized in that The structural formula is as follows: ； Said n=2-50.

2. A method for preparing the COS-O-luteolin derivative according to claim 1, characterized in that Follow these steps: Step 1. Weigh a certain amount of chitosan oligosaccharide and dissolve it in ethanol at 25°C to obtain a chitosan oligosaccharide ethanol solution with a mass concentration of 0.5%; Step 2. Weigh a certain amount of luteolin and dissolve it in ethanol at 25°C to obtain a 0.5% luteolin ethanol solution. Step 3. Mix equal volumes of chitosan oligosaccharide ethanol solution and luteolin ethanol solution and stir evenly. Adjust the pH to 7.5 and continue stirring for 20-30 min. Rotate and evaporate the solvent at 45°C. Dry under vacuum at 60°C, crush and sieve to obtain COS-O-luteolin derivative.

3. Use of the COS-O-luteolin derivative according to claim 1 in the preparation of a strawberry fresh fruit preservative.

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