Chitosan-melanoidins compound as well as preparation method and application thereof

Abstract

The invention belongs to the field of fruit storage and preservation, and particularly discloses a chitosan-melanoidin compound and a preparation method and application thereof.The melanoidin in vinegar residues is extracted through a water extraction method, then the melanoidin is used for modifying chitosan, the water-soluble chitosan-melanoidin compound is generated, the air permeability of the water-soluble chitosan-melanoidin compound is improved, and the chitosan-melanoidin compound is prepared. The problem that chitosan is poor in blueberry storage and fresh-keeping effect can be solved, the problem of nutrient loss in the blueberry storage process can be solved, and the method can be used for blueberry storage and fresh-keeping.

Description

Technical Field

[0001] The invention relates to the field of fruit storage and preservation, in particular to a chitosan-melanoidin complex and a preparation method and application thereof. Background Art

[0002] Blueberry is a plant of the genus Vaccinium in the family Ericaceae. Its peel and pulp contain a variety of vitamins, anthocyanins, flavonoids, superoxide dismutase and other nutrients, and have strong antioxidant and anti-cancer effects. It has become the world's second largest berry industry. However, due to the high water content of blueberry fruits, they are prone to aging, dehydration, and rot after harvest, resulting in the loss of nutrients. This phenomenon greatly affects the storage and preservation of blueberries.

[0003] As an emerging fruit preservation technology, plastic wrap forms a uniform and dense protective film on the surface of fruits by spraying, soaking, etc., thereby reducing the direct contact between fruits and the outside air, effectively inhibiting metabolic activities such as fruit respiration, reducing the loss of fruit nutrients, and extending the storage period of fruits. However, when chitosan is used as a plastic wrap in fruit preservation, there are certain problems such as poor air permeability, poor oxygen permeability, and poor mechanical strength, which greatly limits its application in fruit preservation.

[0004] Melanoidins are the final products of the reaction between reducing sugars and compounds containing free amino groups in the Maillard reaction (MR). In the late stage of MR, a mixture of polymers with complex structures and different degrees of polymerization composed of repeating units of furan or pyrrole is formed. During the processing of food, the raw materials are diverse and the ingredients are complex. The organic molecules and oligomers in them will undergo a series of chemical reactions when heated, which is very similar to the process of synthesizing nanoparticles by hydrothermal / solvothermal method from bottom to top. Among them, melanoidins come from the food itself. The nanomaterials produced by the interaction of various components of the food are endogenous nanoparticles in food, which can also be called food-derived nanoparticles. Compared with traditional materials, nanomaterials have high specific surface area, special physical and chemical properties, so they can have more active sites and show higher adsorption, catalysis and reaction efficiency. Among them, food-derived nanoparticles have the advantages of wide sources, low prices, and good biocompatibility. Therefore, the study of modifying chitosan using food-derived nanoparticles has become an emerging research direction. Summary of the invention

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

[0006] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0007] One of the purposes of the present invention is to provide a method for preparing a chitosan-melanoidin complex, comprising the following steps:

[0008] S1. Obtaining a vinegar lees solution: weighing 5-20 g of a vinegar lees sample, dissolving it in water, and adjusting the volume to 50-250 mL, standing it for 1-4 h, and filtering it to obtain a vinegar lees solution;

[0009] 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 melanoidin;

[0010] 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 and mix them evenly, and perform 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.

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

[0012] Furthermore, in step S2, the fluorescence of the eluent is observed under an ultraviolet lamp with a wavelength of 250-400 nm.

[0013] Furthermore, in step S2, the specifications of the D101 macroporous resin column are: column length: 15-20 cm, inner diameter: 1.0-1.5 cm.

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

[0015] The second object of the present invention is to provide a chitosan-melanoidin complex prepared by the above method.

[0016] The third object of the present invention is to provide a chitosan-melanoidin complex for use as a blueberry preservative film.

[0017] Compared with the prior art, the present invention adopts a water extraction method to extract melanoidin from vinegar residue, and then uses melanoidin to modify chitosan to generate a water-soluble chitosan-melanoidin complex, thereby improving its air permeability, improving the problem of poor storage and preservation effect of chitosan in blueberry storage, and retaining more nutrients lost during the storage of blueberries. The present invention can be used in the storage and preservation of blueberries. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1This is a particle size distribution diagram of melanoidins extracted from vinegar lees in Example 1;

[0019] Figure 2 The infrared spectra of chitosan-melanoid complexes at different synthesis times are shown in Figure CS, 2h (Example 1), and 4h (Example 2);

[0020] Figure 3 The permeability (O2 and CO2) diagrams of chitosan-melanoidin complexes at different synthesis times: (a) is CO2; (b) is O2.

[0021] Figure 4 The results of chitosan-melanoidin complex on pectin content in blueberry fruit after film covering at 0D and 28D storage;

[0022] Figure 5 The results of chitosan-melanoidin complex on VC content in blueberry fruit after film covering at 0D and 28D storage;

[0023] Figure 6 The standard curve of galacturonic acid. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. The specific embodiments described herein are only used to explain the present invention and are not used to limit the invention.

[0025] Example 1

[0026] S1. Obtaining a vinegar lees solution: Weigh 10 g of a vinegar lees sample, dissolve it in water, fix the volume to 100 mL, let it stand for 2 h, and filter it with a filter paper with a diameter of Φ=15 cm and a pore size of 30 μm to obtain a vinegar lees solution;

[0027] S2. Preparation of melanoidin using vinegar lees as raw material: eluting the vinegar lees solution through a D101 macroporous resin column, the specifications of the D101 macroporous resin column are: column length: 15 cm, inner diameter: 1.2 cm, collecting the eluate, observing the eluate under an ultraviolet lamp with a wavelength of 300 nm until there is no fluorescence, concentrating the eluate by rotary evaporation to obtain a melanoidin solution, and vacuum freeze-drying to obtain melanoidin;

[0028] S3. Preparation of chitosan-melanoidin composite solution: weigh chitosan and water in a mass ratio of 1:50, mix well to obtain a chitosan aqueous solution, add 1% melanoidin by mass of the chitosan aqueous solution into the chitosan aqueous solution, put into a reactor and mix well, carry out hydrothermal reaction at 130°C in an electric constant temperature drying oven for 2h, obtain chitosan-melanoidin composite solution after the reaction, and obtain chitosan-melanoidin composite solution by vacuum freeze drying.

[0029] Example 2

[0030] S1. Obtaining a vinegar lees solution: Weigh 10 g of a vinegar lees sample, dissolve it in water, fix the volume to 100 mL, let it stand for 2 h, and filter it with a filter paper with a diameter of Φ=15 cm and a pore size of 30 μm to obtain a vinegar lees solution;

[0031] S2. Preparation of melanoidin using vinegar lees as raw material: eluting the vinegar lees solution through a D101 macroporous resin column, the specifications of the D101 macroporous resin column are: column length: 15 cm, inner diameter: 1.2 cm, collecting the eluate, observing the eluate under an ultraviolet lamp with a wavelength of 300 nm until there is no fluorescence, concentrating the eluate by rotary evaporation to obtain a melanoidin solution, and vacuum freeze-drying to obtain melanoidin;

[0032] S3. Preparation of chitosan-melanoidin composite solution: weigh chitosan and water in a mass ratio of 1:50, mix well to obtain a chitosan aqueous solution, add 1% melanoidin by mass of the chitosan aqueous solution into the chitosan aqueous solution, put into a reactor and mix well, carry out hydrothermal reaction at 130°C in an electric constant temperature drying oven for 4 hours, obtain a chitosan-melanoidin composite solution after the reaction, and obtain chitosan-melanoidin composite solution by vacuum freeze drying.

[0033] The following related experiments are conducted using the chitosan-melanotan complexes prepared in Example 1 and Example 2 as examples, and chitosan that is not complexed with melanoidin is used for comparison.

[0034] Depend on Figure 1 It can be seen that the average particle size of the product (nanoparticles - melanoidin) extracted from the vinegar dregs in Example 1 and Example 2 is 36.01±2.852 nm, proving that the extracted melanoidin is nanoparticles (nanoparticle diameter 1-100 nm).

[0035] Depend on Figure 2 It can be seen that the chitosan-melanotan complexes of Example 1 and Example 2 have a peak at 3434 cm -1 and 1609cm -1 There is a strong absorption peak at the site, which can be attributed to the two hydrophilic groups, hydroxyl and carboxyl. Therefore, it can be proved that the chitosan-melanoidin complex has good water solubility.

[0036] Depend on Figure 3 It can be seen that the air permeability of the chitosan-melanotan complex in Example 1 and Example 2 is ( Figure 3 (a) and Figure 3 From (b)), it can be seen that the permeability to O2 is high and the permeability to CO2 is low, which can form an environment of low O2 and high CO2 in the system.

[0037] Application Example 1

[0038] Effects of different synthesis times of chitosan-melanotin complexes on tissue structure and state changes in blueberry fruit

[0039] (1) Pretreatment of blueberries: The chitosan-melanoidin composite samples prepared in Examples 1 and 2 and the chitosan sample not synthesized with melanoidin were prepared into a thin film sample solution with a concentration of 0.1 mol / L, and sprayed on the surface of blueberries. 1 mL of the sample solution was sprayed for every 15±1 g of blueberries. The mixture was air-dried at room temperature and stored in a polyethylene ziplock bag at 4°C for 28 days.

[0040] (2) The blueberry fruits before and after storage were placed on a texture analyzer test plate and tested using a test probe with a diameter of 75 mm. Parameter settings: pre-test rate 2 mm / s, test rate 1 mm / s, post-test upward rate 2 mm / s, blueberry pulp compression deformation of 60%, pause time between two compressions of 5 s, trigger force of 5 g. The TPA parameters of blueberry pulp were obtained through the texture characteristic curve: hardness, elasticity, chewiness and cohesion. The results of the water distribution content in blueberry fruits after storage 0D and storage 28D by chitosan-melanoidin 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. This may be because the contact area between blueberries and the air is large, the respiratory metabolism of blueberries themselves is not inhibited, and the internal energy is continuously consumed, resulting in the soft and rotten fruit. For the film spraying group (28D-CS-MRPs-2h and 28D-CS-MRPs-4h), the hardness content increased. Part of the reason is that the composite film has a certain mechanical strength, and the contact with the film before the measurement increases the hardness. Another reason is that the film spraying can reduce the contact area between blueberries and the air, inhibit physiological metabolic activities, reduce the consumption of internal nutrients, and maintain the freshness of blueberries.

[0044] Application Example 2

[0045] Effects of different synthesis times of chitosan-melanotin complexes on the changes of pectin content in blueberry fruit

[0046] (1) Blueberry pretreatment: Weigh 1.000 g of blueberry sample stored for 28 days, grind and mash it, add 35 mL of 75°C anhydrous ethanol, heat it in an 85°C water bath for 10 min, cool it, add anhydrous ethanol to make the volume 50 mL, centrifuge it at 4000 r / min for 15 min, discard the supernatant, repeat the previous washing steps for multiple times until no sugar Mulixu reaction is produced in the supernatant, and keep the precipitate for later use.

[0047] (2) Acid extraction: The precipitate prepared above was washed into a conical flask with a pH 0.5 sulfuric acid solution, mixed, and heated in an 85°C water bath for 1 h with constant shaking and stirring. After cooling, the precipitate was transferred to a volumetric flask and diluted to 100 mL with a pH 0.5 sulfuric acid solution. The extract was filtered and set aside.

[0048] Standard curve drawing: take 1mL of galacturonic acid standard solution with mass concentration of 0mg / L, 20.0mg / L, 40.0mg / L, 60.0mg / L, 80.0mg / L, 100.0mg / L respectively, add 5mL of concentrated sulfuric acid and shake well, heat in 85℃ water bath for 20min, take out and cool, measure the absorbance at 525nm, and draw the standard curve with galacturonic acid concentration as the horizontal axis and absorbance as the vertical axis (such as Figure 6 shown).

[0049] (3) Sample determination: Take 1 mL of sample solution, add 0.25 mL of 1 g / L carbazole ethanol solution, mix well, and measure the absorbance at 525 nm. Repeat the determination three times. The formula for calculating the pectin content in blueberries is:

[0050]

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

[0052] V: pectin precipitation fixed volume (mL);

[0053] m: sample mass (g).

[0054] Depend on Figure 4 It can be seen that the pectin content of the storage group without spraying treatment (28D) and the group treated with chitosan (28D-CS) spraying treatment increased significantly, and the increase in pectin was twice that of the group without storage (0D). The increase in pectin treated with chitosan-melanin complex spraying was lower than that of the non-storage and chitosan groups, and the group treated with spraying after 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 rate of pectin hydrolysis by polygalacturonase, and the effect of 28D-CS-MRPs-2h group is more significant.

[0055] Application Example 3

[0056] Effects of different synthesis times of chitosan-melanotin complexes on the changes of VC content in blueberry fruits

[0057] (1) Reagents: 0.05 mol / L oxalic acid, 0.2 mmol / L ethylenediaminetetraacetic acid, metaphosphoric acid-acetic acid solution: [3 g metaphosphoric acid, 48 mL glacial acetic acid (glacial acetic acid: distilled water = 1:5, fixed to 100 mL)], 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. 0.5 g of each sample was weighed and 10 mL of oxalic acid-ethylenediaminetetraacetic acid solution was added. 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, add 1 mL of sulfuric acid and 2 mL of ammonium molybdate solution, mix well, 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 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 at 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 group and the CS group, and the VC retention content of the 28D-CS-MRPs-4h group was 4.58 and 3.94 times that of the 28D group and the CS group. 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 blueberries, 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 Figure 1-Figure 5 As shown in Table 1, the chitosan-melanoidin complex prepared in Examples 1 and 2 of the present invention has a significant storage and preservation effect on blueberries compared with chitosan, and forms a good protective layer on the surface of blueberries, which reduces the contact area between blueberry fruits and air while providing a low O2 and high CO2 storage environment, preventing fruit oxidation and corruption, reducing the loss of water and nutrients in blueberries, and better maintaining the nutritional components and freshness of blueberries; from a structural point of view, the chitosan-melanoidin complex has abundant hydrophilic groups such as hydroxyl groups and carboxyl groups, so that the chitosan-melanoidin complex has good water solubility.

[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 obviously better than that of using chitosan alone.

[0063] The invention obtains a new chitosan modified product, which not only meets the pursuit of less loss of water and nutrients in blueberry storage and preservation and maintaining the fresh quality of blueberries, but also provides a new way to recycle vinegar dregs. The composite also has a good preservation effect.

[0064] The technical solution of the present invention is not limited to the above-mentioned specific embodiments. All technical variations made according to the technical solution of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing a chitosan-melanoidin complex, characterized in that: The following steps are involved: S1. Obtaining a vinegar lees solution: weighing 5-20 g of a vinegar lees sample, dissolving it in water, and adjusting the volume to 50-250 mL, standing it for 1-4 h, and filtering 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 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 and mix them evenly, and perform 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, characterized in that: In the step S1, the filter paper used for filtration has a diameter of Φ=10-15 cm and a pore size of 30-50 μm.

3. The method for preparing the chitosan-melanoidin complex according to claim 1, characterized in that: In step S2, the fluorescence of the eluent 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, characterized in that: 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, characterized in that: In step S3, the hydrothermal reaction temperature is 100-180° C., and the heating reaction time is 0-5 h.

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 as claimed in claim 6 as a blueberry preservative film.

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