Chitosan-ellagic acid-like compound, and preparation method and application thereof

Abstract

The application belongs to the field of fruit storage and preservation, and specifically discloses a chitosan-black pigment compound, a preparation method and application thereof. The black pigment is extracted from vinegar dregs by a water extraction method, and then used to modify chitosan to generate a water-soluble chitosan-black pigment compound, so as to improve the air permeability of the chitosan and solve the problem of poor storage and preservation effect of chitosan on blueberries. The chitosan-black pigment compound can be used for the storage and preservation of blueberries and can solve the problem of loss of nutritional components during the storage of blueberries.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of fruit storage and preservation, and particularly relates to a chitosan- melanoidin compound, a preparation method and application thereof. BACKGROUND

[0002] Blueberry is a Vaccinium spp. plant of the Ericaceae family, and contains various vitamins, anthocyanins, flavonoids, superoxide dismutase and other nutrients in the fruit skin and pulp, and has strong antioxidant capacity and anticancer effect. At present, it has become the second largest berry industry in the world. However, due to the high water content of blueberry fruits, postharvest aging, water loss, rotting and other problems occur easily, resulting in loss of nutrients. This phenomenon greatly affects the storage and preservation of blueberries.

[0003] As a new fruit preservation technology, the preservative film uniformly forms a uniform and dense protective film on the surface of the fruit through spraying, soaking and other methods, thereby reducing the direct contact of the fruit with the outside air, effectively inhibiting the metabolic activities such as fruit respiration, reducing the loss of fruit nutrients, and prolonging the storage period of the fruit. However, when chitosan is used as a preservative film in fruit preservation, there are certain problems such as poor air permeability, poor oxygen permeability and poor mechanical strength, which greatly limit its application in fruit preservation.

[0004] Melanoidin is the final product of the reaction between reducing sugars and compounds containing free amino groups in the Maillard reaction (MR), and is a mixture of high molecular polymers with complex structures and varying degrees of polymerization formed in the late stage of MR. During food processing, raw materials are diverse and complex, and organic molecules and oligomers will undergo a series of chemical reactions when heated, which is extremely similar to the process of synthesizing nanoparticles by hydrothermal / solvothermal method from bottom to top. The melanoidin is derived from the food itself, and the nanomaterial produced by the interaction of various components of the food is also called food-derived nanoparticles. Compared with traditional materials, nanomaterials have high specific surface area, special physical and chemical properties, and therefore have more active sites, showing higher adsorption, catalysis and reaction efficiency. Food-derived nanoparticles have the advantages of wide source, low price and good biocompatibility. Therefore, the research on the modification of chitosan using food-derived nanoparticles has become a new research direction. SUMMARY

[0005] In order to solve the above technical problems, the present application provides a chitosan-melanoidin compound, a preparation method and application thereof.

[0006] In order to achieve the above purpose, the present application is implemented according to the following technical solutions:

[0007] One of the purposes of the present application is to provide a preparation method of chitosan-meloidin complex, comprising the following steps:

[0008] S1, obtaining of vinegar residue solution: weigh 5-20g of vinegar residue sample, dissolve in water, make up to 50-250mL, stand for 1-4h, filter to obtain vinegar residue solution;

[0009] S2, preparation of meloidin using vinegar residue as raw material: elute the vinegar residue solution through D101 macroporous resin column, collect the eluate, stop observation of the eluate when it is non-fluorescent, concentrate the eluate by rotary evaporation, obtain meloidin solution, and vacuum freeze-dry to obtain meloidin;

[0010] S3, preparation of chitosan-meloidin complex solution: weigh chitosan and water in a mass ratio of 1:50, mix uniformly to obtain chitosan aqueous solution, add meloidin with a mass concentration of 1%-1.5% to the chitosan aqueous solution, mix uniformly in a reaction kettle, and perform hydrothermal reaction, to obtain chitosan-meloidin complex solution after the reaction, and vacuum freeze-dry to obtain chitosan-meloidin complex.

[0011] Further, in the step S1, the filter paper used for filtering has a diameter of 10-15cm and a pore size of 30-50μm.

[0012] Further, in the step S2, the fluorescence of the eluate is observed under a UV lamp with a wavelength of 250-400nm.

[0013] Further, in the step S2, the D101 macroporous resin column has a length of 15-20cm and an inner diameter of 1.0-1.5cm.

[0014] Further, in the step S3, the hydrothermal reaction temperature is 100-180℃, and the heating reaction time is 0-5h.

[0015] The second purpose of the present application is to provide a chitosan-meloidin complex prepared by the above method.

[0016] The third purpose of the present application is to provide an application of the chitosan-meloidin complex in blueberry preservation film.

[0017] Compared with the prior art, the present application extracts meloidin from vinegar residue by water extraction method, and then modifies chitosan with meloidin to generate a water-soluble chitosan-meloidin complex, which improves the air permeability and the preservation effect of chitosan on blueberries, and retains more nutrients during the storage of blueberries. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1Particle size distribution diagram of melanoidin extracted from vinegar dregs in Example 1;

[0019] Figure 2 Infrared spectra of chitosan-melanoidin complexes with different synthesis times: CS, 2h (Example 1), 4h (Example 2);

[0020] Figure 3 Air permeability (O2 and CO2) of chitosan-melanoidin complexes with different synthesis times: (a) for CO2; (b) for O2.

[0021] Figure 4 Effect of chitosan-melanoidin complex on pectin content in blueberry fruits stored for 0D and 28D after coating;

[0022] Figure 5 Effect of chitosan-melanoidin complex on VC content in blueberry fruits stored for 0D and 28D after coating;

[0023] Figure 6 Galacturonic acid standard curve. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical scheme and advantages of the present application clearer and more apparent, the present application is further described in detail below in combination with examples. The specific examples described herein are only used to explain the present application and do not limit the present application.

[0025] Example 1

[0026] S1, obtaining of vinegar dregs solution: 10g of vinegar dregs sample was weighed and dissolved in water, and the volume was made up to 100mL. After standing for 2h, the solution was filtered with a filter paper with a diameter of Φ=15cm and a pore size of 30μm to obtain a vinegar dregs solution;

[0027] S2, preparation of melanoidin from vinegar dregs: the vinegar dregs solution was eluted through a D101 macroporous resin column with specifications of column length: 15cm and inner diameter: 1.2cm. The eluate was collected and observed under a 300nm wavelength ultraviolet lamp until no fluorescence was observed. The eluate was concentrated by rotary evaporation, and melanoidin solution was obtained. Vacuum freeze-drying was performed to obtain melanoidin.

[0028] S3, preparation of chitosan-melanoidin complex solution: chitosan and water were mixed in a mass ratio of 1:50 to obtain a chitosan aqueous solution. Melanoidin with a mass fraction of 1% in the chitosan aqueous solution was added and mixed uniformly in a reaction kettle. Hydrothermal reaction was carried out at 130℃ in an electric heating constant temperature drying oven for 2h. After the reaction was completed, a chitosan-melanoidin complex solution was prepared. Vacuum freeze-drying was performed to obtain a chitosan-melanoidin complex sample 1.

[0029] Example 2

[0030] S1, obtaining vinegar residue solution: 10 g of vinegar residue sample was weighed and dissolved in water, and then diluted to 100 mL. After standing for 2 h, the solution was filtered with a filter paper with a diameter of 15 cm and a pore size of 30 μm to obtain a vinegar residue solution;

[0031] S2, preparing black-pigment-like from vinegar residue: the vinegar residue solution was eluted through a D101 macroporous resin column with a column length of 15 cm and an inner diameter of 1.2 cm. The eluate was collected and observed under a 300 nm wavelength ultraviolet lamp until no fluorescence was observed. The eluate was concentrated by rotary evaporation to obtain a black-pigment-like solution, which was vacuum freeze-dried to obtain black-pigment-like.

[0032] S3, preparing chitosan-black-pigment-like composite solution: chitosan and water were mixed in a mass ratio of 1:50 to obtain a chitosan aqueous solution. Black-pigment-like with a mass fraction of 1% in the chitosan aqueous solution was added and mixed uniformly in a reaction kettle. The chitosan-black-pigment-like composite solution was prepared by hydrothermal reaction at 130°C for 4 h in an electric heating constant temperature drying oven. After the reaction, the chitosan-black-pigment-like composite sample 2 was obtained by vacuum freeze-drying.

[0033] The following experiments were carried out using the chitosan-black-pigment-like composite prepared in Example 1 and Example 2 as examples, and chitosan not compounded with black-pigment-like was used as a comparison.

[0034] It can be seen from Figure 1 that the average particle size of the product (nanoparticle-black-pigment-like) extracted from the vinegar residue in Example 1 and Example 2 is 36.01 ± 2.852 nm, which proves that the extracted black-pigment-like is a nanoparticle (nanoparticle diameter 1-100 nm).

[0035] It can be seen from Figure 2 that the chitosan-black-pigment-like composite in Example 1 and Example 2 has strong absorption peaks at 3434 cm -1 and 1609 cm -1 in the infrared spectrum, which can be attributed to the two hydrophilic groups of hydroxyl and carboxyl groups. Therefore, it can be proved that the chitosan-black-pigment-like composite has good water solubility.

[0036] It can be seen from Figure 3 that the permeability of the chitosan-black-pigment-like composite in Example 1 and Example 2 (a) in Figure 3 and (b) in Figure 3 is large for O2 and small for CO2, which can form a low O2 and high CO2 environment in the system.

[0037] Application Example 1

[0038] Effect of synthesis time of different chitosan-ellagic acid complex on tissue structure and state change of blueberry fruit

[0039] (1) Pretreatment of blueberry: chitosan-ellagic acid complex samples prepared in Example 1 and Example 2 and chitosan samples without synthesis of ellagic acid were configured into a film sample solution with a concentration of 0.1 mol / L, sprayed on the surface of blueberries, 1 mL of sample solution was sprayed for every 15±1 g of blueberries, and the blueberries were air-dried at room temperature, then placed in a polyethylene self-sealing bag and stored at 4℃ for 28 days.

[0040] (2) The blueberry fruits before and after storage were placed on the test plate of the texture analyzer, and a test probe with a diameter of 75 mm was used for testing. The parameter settings were: pre-test speed 2 mm / s, test speed 1 mm / s, post-test upstroke speed 2 mm / s, blueberry pulp deformation under pressure 60%, two compression pause times 5 s, and trigger force 5 g. The TPA parameters of blueberry pulp, such as hardness, elasticity, chewiness and cohesiveness, were obtained through the texture profile curve. The results of water distribution content in blueberry fruits stored for 0D and after film coating for 28D treated with chitosan-ellagic acid complex are shown in Table 1.

[0041] Table 1

[0042]

[0043] As shown in Table 1, the hardness of the 28-day (28D) group and the chitosan (28D-CS) group decreased significantly after 28 days of storage, which may be due to the large contact area between the blueberries and the air, and the respiratory metabolism of the blueberries was not inhibited, which led to the continuous consumption of internal energy, resulting in the softening of the fruit. The hardness content of the film-coated groups (28D-CS-MRPs-2h and 28D-CS-MRPs-4h) increased, partly because the complex film had a certain mechanical strength, which increased the hardness when the film was contacted first during measurement, and partly because the film coating could reduce the contact area between the blueberries and the air, inhibit the physiological metabolism, reduce the consumption of internal nutrients, and maintain the freshness of the blueberries.

[0044] Application Example 2

[0045] Effect of synthesis time of different chitosan-ellagic acid complex on pectin content change in blueberry fruit

[0046] (1) Pretreatment of blueberry: 1.000 g of blueberry sample stored for 28 days was weighed and ground, 35 mL of 75℃ anhydrous ethanol was added and heated in a 85℃ water bath for 10 min, then cooled, and anhydrous ethanol was added to make up to 50 mL, centrifuged at 4000 r / min for 15 min, the supernatant was discarded, and the above steps were repeated several times until no sugar was produced in the supernatant, and the precipitate was reserved for use.

[0047] (2) Acid extraction: The prepared precipitate was washed into a triangular flask with a pH 0.5 sulfuric acid solution, mixed, heated in a 85°C water bath for 1h, and continuously stirred, then transferred to a volumetric flask after cooling, and diluted to 100mL with a pH 0.5 sulfuric acid solution, and filtered to obtain an extract for use.

[0048] Standard curve drawing: 1mL of galacturonic acid standard solution with a mass concentration of 0mg / L, 20.0mg / L, 40.0mg / L, 60.0mg / L, 80.0mg / L, and 100.0mg / L was taken, 5mL of concentrated sulfuric acid was added and shaken, and heated in a 85°C water bath for 20min, then removed and cooled, and the absorbance at 525nm was measured, and the standard curve was drawn with the galacturonic acid concentration as the abscissa and the absorbance as the ordinate (as shown in Figure 6 ).

[0049] (3) Sample determination: 1mL of sample solution was taken, 0.25mL of 1g / L carbazole ethanol solution was added, mixed, and the absorbance at 525nm was measured. The determination was repeated three times. The blueberry pectin content calculation formula:

[0050]

[0051] In the formula: ρ: mass concentration of galacturonic acid in the sample solution (mg / L);

[0052] V: pectin precipitate dilution volume (mL);

[0053] m: sample mass (g).

[0054] As can be seen from Figure 4 , the pectin content of the storage (28D) group without spraying membrane treatment and the pectin content of the chitosan (28D-CS) spraying membrane treatment group increased significantly, and the pectin increase was 2 times that of the non-storage (0D) group, while the pectin increase of the chitosan-black compound spraying membrane treatment group was lower than that of the non-storage and chitosan groups, and the spraying membrane treatment group with a synthesis time of 2h was 1.5 times that of the untreated group. It can be seen that the composite material can inhibit the speed of pectinase hydrolysis of pectin, and the 28D-CS-MRPs-2h group has a more significant effect.

[0055] Application Example 3

[0056] Effect of synthesis time of different chitosan-melatonin compounds on VC content change in blueberry fruits

[0057] (1) Reagents: oxalic acid 0.05mol / L, ethylenediaminetetraacetic acid 0.2mmol / L, metaphosphoric acid-acetic acid solution: [metaphosphoric acid 3g, glacial acetic acid 48mL (glacial acetic acid:distilled water=1:5 dilute to 100mL)], 5% sulfuric acid solution and 5% ammonium molybdate solution.

[0058] (2) Blueberry fruit treatment: The blueberry samples sprayed with film at storage day 0 and storage day 28 were ground and homogenized, and 0.5 g of each sample was weighed and added with 10 mL of oxalic acid-ethylenediaminetetraacetic acid solution. The mixture was centrifuged at 6000 r / min for 10 min, and the supernatant was collected for later use.

[0059] (3) Determination: Take 0.5 mL of the supernatant, add 0.5 mL of distilled water, 2 mL of oxalic acid-ethylenediaminetetraacetic acid solution, and 0.5 mL of metaphosphoric acid-acetic acid solution, mix well, add 1 mL of sulfuric acid and 2 mL of ammonium molybdate solution, mix thoroughly, and measure the absorbance at 760 nm. Repeat the determination three times.

[0060] Depend on Figure 5 It can be seen that after 28 days of storage, the VC content in blueberry fruit showed an obvious overall downward trend. The VC content in the fruits of the 28D and CS groups was almost the same, while the VC content in the blueberry fruits after spraying treatment with different synthesis times was greater than that of the 28D and CS groups. The VC retention content of the 28D-CS-MRPs-2h group was 4.8 and 5.4 times that of the 28D and CS groups, and the VC retention content of the 28D-CS-MRPs-4h group was 4.58 and 3.94 times that of the 28D and CS groups. It can be seen that the composite material can significantly inhibit the decline in VC content, and the inhibition rate of the composite material is greater than that of chitosan, indicating that the synthesized material can better retain the loss of VC in blueberries. After spraying treatment, a protective layer will be formed on the surface of the blueberry, so that the internal environment of the fruit forms a low O2 and high CO2 environment, which is conducive to the storage and preservation of blueberries and improves the antioxidant capacity of blueberries.

[0061] Depend on Figures 1-5 As shown in Table 1, the chitosan-melanoidin complexes prepared in Examples 1 and 2 of the present invention have a more pronounced storage and preservation effect on blueberries than chitosan. They form a good protective layer on the surface of the blueberries, reducing the contact area between the blueberry fruit and the air while also providing a low-O2, high-CO2 storage environment. This prevents oxidation and spoilage of the fruit, reduces the loss of water and nutrients in the blueberries, and better preserves the nutritional content and freshness of the blueberries. Structurally, the chitosan-melanoidin complex has abundant hydrophilic groups such as hydroxyl and carboxyl groups, which makes the chitosan-melanoidin complex highly water-soluble.

[0062] The invention adopts melanoidin extracted from vinegar dregs to modify chitosan, and applies it to the storage and preservation of blueberries. The preservation effect of the blueberries is significantly better than that of using chitosan alone.

[0063] The application obtains a new chitosan modified product, which not only meets the pursuit of less loss of water and nutrient substances and maintaining fresh quality of blueberries in the storage and preservation of blueberries, but also provides a new way for reusing vinegar residues.

[0064] The technical scheme of the application is not limited to the above specific embodiments, and any technical transformation according to the technical scheme of the application falls within the protection scope of the application.

Claims

1. A method for preparing a chitosan-melanoidin complex, characterized in that: The following steps are involved: S1. Obtaining a vinegar lees solution: Weigh 5-20 g of a vinegar lees sample, dissolve it in water, and dilute it to 50-250 mL. Let it stand for 1-4 h, and filter it to obtain a vinegar lees solution. S2. Preparation of melanoidin using vinegar lees as raw material: eluting the vinegar lees solution through a D101 macroporous resin column, collecting the eluate, observing the eluate until no fluorescence is observed, concentrating the eluate by rotary evaporation to obtain a melanoidin solution, and vacuum freeze-drying to obtain the melanoidin; S3. Preparation of chitosan-melanoidin composite solution: weigh chitosan and water in a mass ratio of 1:50, mix them evenly to obtain a chitosan aqueous solution, add melanoidin with a mass concentration of 1%-1.5% to the chitosan aqueous solution, put them into a reactor, mix them evenly, and carry out a hydrothermal reaction. After the reaction is completed, a chitosan-melanoidin composite solution is obtained, and vacuum freeze-drying is performed to obtain a chitosan-melanoidin complex.

2. The method for preparing the chitosan-melanoidin complex according to claim 1, wherein: In the step S1, the filter paper used for filtration has a diameter of 10-15 cm and a pore size of 30-50 μm.

3. The method for preparing the chitosan-melanoidin complex according to claim 1, wherein: In step S2, the fluorescence of the eluate is observed under an ultraviolet lamp with a wavelength of 250-400 nm.

4. The method for preparing the chitosan-melanoidin complex according to claim 1, wherein: In step S2, the specifications of the D101 macroporous resin column are: column length: 15-20 cm, inner diameter: 1.0-1.5 cm.

5. The method for preparing the chitosan-melanoidin complex according to claim 1, wherein: In step S3, the hydrothermal reaction temperature is 100-180° C., and the heating reaction time is 2 hours.

6. A chitosan-melanoidin complex prepared by the method according to any one of claims 1 to 5.

7. Use of the chitosan-melanoidin complex according to claim 6 in preparing blueberry fresh-keeping film.

Images