Bio-based antioxidant and preparation method thereof

Abstract

The invention relates to the technical field of plant resource processing, and discloses a bio-based antioxidant, the chemical structural formula of the bio-based antioxidant is as shown in a formula a: # imgabs0 #, and a preparation method of the bio-based antioxidant comprises the following steps: S1, mixing plant powder with morpholine, performing countercurrent extraction, and respectively collecting an extracting solution and solid residues; s2, taking the extracting solution, heating, carrying out aminolysis reaction, then carrying out reduced pressure distillation, condensing and collecting an amino solvent; s3, adding deionized water into the reaction container after reduced pressure distillation, heating and dissolving, then adding activated carbon, and carrying out decolorization treatment; then removing the activated carbon, cooling, crystallizing and centrifuging to obtain a crystal A; s4, mixing the crystal A with deionized water and activated carbon, heating, and carrying out secondary decoloration treatment; and then removing the activated carbon, cooling, crystallizing, centrifuging and drying to obtain the bio-based antioxidant, which has excellent oxidation resistance, can be kept stable in the oxidation process, and does not generate chromogenic reaction.

Description

Technical Field

[0001] The present invention relates to the technical field of plant resource processing, and in particular to a bio-based antioxidant and a preparation method thereof. Background Art

[0002] Bio-based antioxidants have been a research hotspot in the interdisciplinary fields of chemistry, biology and medicine in recent years. They refer to antioxidant substances derived from natural organisms or their derivatives, which can be used as hydrogen donors to remove free radicals generated in the chain initiation stage, thereby inhibiting or reducing the oxidation of oils and fats. For example, plant polyphenols are a type of antioxidant substance widely found in nature. The polyphenol structure they contain has significant antioxidant activity, and plant polyphenols have relatively active chemical reactivity. They can be used in different fields or scenarios to play antioxidant, antibacterial, and metal ion complexing roles for different products.

[0003] Plant polyphenols, also known as tannins, can be divided into condensed tannins and hydrolyzed tannins. Among them, condensed tannins are polymers of flavanoid condensation, containing unique structures such as catechins and epicatechins, without sugar groups, and are not easy to hydrolyze; hydrolyzed tannins are based on polyols or sugar groups, connected to multiple phenolic acid acids through ester bonds, and are easily hydrolyzed under the action of acids, alkalis, and enzymes to produce gallic acid and glucose, quinic acid and other components. Gallic acid and its derivatives are a basic raw material commonly used in the preparation of antioxidants. Among them, gallic acid ester derivatives are often used as low-toxic and high-efficiency antioxidants in the fields of food, feed, medicine, cosmetics, and fiber. For example, the patent with publication number CN112110809A discloses a bio-based antioxidant and its preparation method and use.

[0004] However, during the oxidation process, gallic acid ester derivatives are prone to coupling, hydrolysis and other reactions to generate yellow-brown di-orthoquinone compounds. This reaction color change characteristic limits the application expansion of gallic acid ester compounds in many fields. Summary of the invention

[0005] The technical problems to be solved by the present invention are:

[0006] At present, the existing gallic acid ester derivative antioxidants are prone to coupling or hydrolysis reactions during the oxidation process to generate yellow-brown di-orthoquinone compounds, which makes them unable to be used normally in application scenarios that need to maintain a colorless state and environment, limiting the application expansion of gallic acid ester compound antioxidants in many fields.

[0007] The technical solution adopted by the present invention is:

[0008] The present invention provides a bio-based antioxidant, the chemical structure of which is as follows:

[0009]

[0010] The present invention also provides a method for preparing the above-mentioned bio-based antioxidant, comprising the following steps:

[0011] S1: mixing plant powder with morpholine, performing countercurrent extraction, and collecting the extract and solid residue respectively;

[0012] S2 takes the extract, heats it, performs aminolysis reaction, then performs vacuum distillation, and condenses and collects the amine-based solvent;

[0013] S3: adding deionized water to the reaction vessel after vacuum distillation, heating to dissolve, and then adding activated carbon for decolorization; then removing the activated carbon, cooling and crystallizing, centrifuging to obtain crystal A;

[0014] S4 takes crystal A, mixes it with deionized water and activated carbon, heats it, and performs secondary decolorization treatment; then removes the activated carbon, cools it down for crystallization, centrifuges it, and dries it to obtain the bio-based antioxidant.

[0015] Preferably, in step S1, the countercurrent extraction temperature is 30-100°C.

[0016] Preferably, in step S2, the heating temperature is 40-120°C, and the aminolysis reaction time is 3-24h.

[0017] 5. The method for preparing a bio-based antioxidant according to claim 2, characterized in that, in step S3 and step S4, during the decolorization process, the pH value is adjusted to be less than 4.

[0018] Preferably, in step S3 and step S4, the decolorization treatment temperature is 50-100°C, and the cooling crystallization temperature is 10-30°C.

[0019] Preferably, the plant powder comprises one or more of tara powder, gallnut powder and gallic acid powder.

[0020] Preferably, the mixing ratio of the plant powder to morpholine is 4-8:1 by mass.

[0021] The beneficial effects of the present invention are as follows:

[0022] The bio-based antioxidant of the present invention contains a pyrogallol chemical structure and an amide structure, which can give it excellent free radical scavenging ability and the ability to complex multivalent metal ions, and maintain a stable state that is difficult to hydrolyze. In addition, by using an amine-based solvent, tannic acid can be directly extracted from plants, and the amine group in the solvent can be aminolyzed to the tannic acid, and the ester group in the tannic acid is converted into an amide group to obtain a crude product. The solvent containing an amine group can provide steric protection, limit oxidative coupling reactions, and prevent the gallic acid ester-based antioxidant from generating colored macrocyclic di-o-quinone compounds.

[0023] Specifically, on the one hand, morpholine is a strong polar solvent, which reacts with tannic acid to produce an acid-base reaction, thereby promoting the dissolution of tannic acid. Therefore, morpholine, as a solvent, can dissolve and extract tannic acid from plant powder with a high extraction yield. On the other hand, morpholine, as a reactant, is in large excess relative to tannic acid, which can reduce the reaction temperature while promoting the reaction conversion rate.

[0024] The present invention adopts a one-step synthesis process with a short process flow, which is suitable for industrial mass production. The obtained biological agent antioxidant has excellent free radical scavenging ability and multivalent metal ion complexing ability, and can be widely used to improve the antioxidant properties of materials such as oils, rubbers, plastics, and fibers. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the bio-based antioxidant in Example 1 1 H-NMR spectrum;

[0026] Figure 2 is the bio-based antioxidant in Example 1 13 C-NMR spectrum;

[0027] Figure 3 This is an analysis chart of the effect of different antioxidants on the peroxide value of palm oil in Test Example (2);

[0028] Figure 4 This is a graph showing the ability of different antioxidants in test example (2) to scavenge free radicals in palm oil using DPPH;

[0029] Figure 5 This is a comparison chart of the oxidative discoloration of different antioxidants in Test Example (3). DETAILED DESCRIPTION

[0030] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0031] The present invention provides a bio-based antioxidant, the chemical structure of which is shown in the following formula a:

[0032]

[0033] In the present invention, the preparation method of the bio-based antioxidant comprises the following steps:

[0034] (1) Extraction:

[0035] According to the mass ratio of 4-8:1, the amine-based solvent and the plant powder containing tannic acid are put into a continuous countercurrent extractor, heated to 30-100° C., countercurrent extraction is performed, and the extract and the solid residue are collected respectively.

[0036] The amine-based solvent can be morpholine. On the one hand, morpholine is a strong polar solvent, which reacts with tannic acid to produce an acid-base reaction, thereby promoting the dissolution of tannic acid. Therefore, morpholine, as a solvent, can dissolve and extract tannic acid from plant powder with a high extraction yield. On the other hand, morpholine, as a reactant, is in large excess relative to tannic acid, which can reduce the reaction temperature while promoting the reaction conversion rate.

[0037] (2) Amine solution:

[0038] The extract is introduced into a reaction kettle, heated to 40-120°C, and subjected to aminolysis reaction for 3-24 hours, followed by distillation under reduced pressure, and condensation to collect the fraction morpholine.

[0039] (3) Decolorization crystallization:

[0040] After the vacuum distillation is completed, deionized water is added to the reactor, heated to dissolve, and then activated carbon is added for decolorization. The temperature during decolorization is controlled at 50-100°C, and the pH value is adjusted to below 4 with hydrochloric acid; then the activated carbon residue is filtered out, and the filtrate is transferred to a crystallization kettle while hot, cooled to 10-30°C for crystallization, and centrifuged to obtain light yellow crystals A.

[0041] (4) Secondary decolorization crystallization:

[0042] Deionized water, light yellow crystal A and activated carbon are added to the decolorization kettle in sequence, and the temperature is raised to 50-100°C for secondary decolorization. Then, the activated carbon residue is removed by filtration, and the filtrate is transferred to a crystallization kettle while hot, cooled to 10-30°C for crystallization, and centrifuged to obtain white crystal B. After drying, a bio-based antioxidant 4-(3,4,5-trihydroxybenzoyl)morpholine is obtained.

[0043] In the present invention, the raw material plant powder for extraction can be selected from one or more of tara powder, gallnut powder, gallic acid powder and the like.

[0044] The bio-based antioxidant prepared by the method of the present invention has excellent free radical scavenging ability and multivalent metal ion complexing ability, and has a stable structure, is not easy to hydrolyze and oxidative coupling, can remain stable in a more complex use environment, avoids the generation of colored compounds, and can be widely used to improve the antioxidant properties of materials such as oils, rubbers, plastics, and fibers.

[0045] Example 1

[0046] The antioxidant was prepared by the method described in the following example using tara powder, gallnut and propyl gallate produced and sold by Sichuan Tingjiang New Materials Co., Ltd., and the remaining materials were purchased from Foshan Shunde Huaneng Reagent Company.

[0047] 400 parts by weight of morpholine and 100 parts by weight of tara powder were put into a continuous countercurrent extractor, the extraction temperature was adjusted to 100°C, countercurrent extraction was performed, and the extract and solid residue were collected respectively;

[0048] The extract was introduced into a reaction kettle, heated to 80°C, and subjected to aminolysis reaction. After the reaction lasted for 15 hours, the extract was subjected to reduced pressure distillation, and the fraction morpholine was condensed and collected, which could be recycled and reused.

[0049] After the vacuum distillation is completed, deionized water is added to the reactor, heated to 100°C to dissolve, and then activated carbon is added, stirred for decolorization, and the pH value is adjusted to less than 4 with hydrochloric acid; then the activated carbon residue is filtered out, and the filtrate is transferred to a crystallization kettle while hot, cooled to 30°C for crystallization, and centrifuged to obtain light yellow crystals;

[0050] Take another decolorization kettle, add deionized water, light yellow crystals and activated carbon, heat to 80°C to dissolve, and carry out secondary decolorization treatment; then filter to remove the activated carbon residue, transfer the filtrate to a crystallization kettle while hot, cool to 30°C for crystallization, centrifuge to obtain white crystals, and after drying, obtain a bio-based antioxidant.

[0051] The raw materials and products were weighed before and after the preparation. The yield of the bio-based antioxidant 4-(3,4,5-trihydroxybenzoyl)morpholine was 78% by mass, and the purity was 99.2%.

[0052] Example 2

[0053] Tara powder, gallnut, and propyl gallate produced and sold by Sichuan Tingjiang New Materials Co., Ltd. were used to prepare antioxidants by the methods described in the following different embodiments, and the remaining materials were purchased from Foshan Shunde Huaneng Reagent Company.

[0054] 800 parts by weight of morpholine and 100 parts by weight of tara powder were put into a continuous countercurrent extractor, the extraction temperature was adjusted to 40°C, countercurrent extraction was performed, and the extract and solid residue were collected respectively;

[0055] The extract is introduced into a reaction kettle, heated to 120°C, and subjected to aminolysis reaction. After reacting for 5 hours, vacuum distillation is performed, and the fraction morpholine is condensed and collected, which can be recycled and reused.

[0056] After the vacuum distillation is completed, deionized water is added to the reactor, heated to 50°C to dissolve, and then activated carbon is added, stirred for decolorization, and the pH value is adjusted to less than 4 with hydrochloric acid; then the activated carbon residue is filtered out, and the filtrate is transferred to a crystallization kettle while hot, cooled to 10°C for crystallization, and centrifuged to obtain light yellow crystals;

[0057] Take another decolorization kettle, add deionized water, light yellow crystals and activated carbon, heat to 90°C to dissolve, and carry out secondary decolorization treatment; then filter to remove the activated carbon residue, transfer the filtrate to a crystallization kettle while hot, cool to 15°C for crystallization, centrifuge to obtain white crystals, and after drying, obtain a bio-based antioxidant.

[0058] The raw materials and products were weighed before and after the preparation. The yield of the bio-based antioxidant 4-(3,4,5-trihydroxybenzoyl)morpholine was 67% by mass, and the purity was 98.7%.

[0059] Example 3

[0060] Tara powder, gallnut, and propyl gallate produced and sold by Sichuan Tingjiang New Materials Co., Ltd. were used to prepare antioxidants by the methods described in the following different embodiments, and the remaining materials were purchased from Foshan Shunde Huaneng Reagent Company.

[0061] 800 parts by weight of morpholine and 100 parts by weight of tara powder were put into a continuous countercurrent extractor, the extraction temperature was adjusted to 60°C, countercurrent extraction was performed, and the extract and solid residue were collected respectively;

[0062] The extract was introduced into a reaction kettle, heated to 40°C, and subjected to aminolysis reaction. After reacting for 22 hours, the extract was subjected to reduced pressure distillation, and the morpholine fraction was condensed and collected, which could be recycled and reused.

[0063] After the vacuum distillation is completed, deionized water is added to the reactor, heated to 80°C to dissolve, and then activated carbon is added, stirred for decolorization, and the pH value is adjusted to less than 4 with hydrochloric acid; then the activated carbon residue is filtered out, and the filtrate is transferred to a crystallization kettle while hot, cooled to 10°C for crystallization, and centrifuged to obtain light yellow crystals;

[0064] Take another decolorization kettle, add deionized water, light yellow crystals and activated carbon, heat to 100°C to dissolve, and carry out secondary decolorization treatment; then filter to remove the activated carbon residue, transfer the filtrate to a crystallization kettle while hot, cool to 15°C for crystallization, centrifuge to obtain white crystals, and after drying, obtain a bio-based antioxidant.

[0065] The raw materials and products were weighed before and after the preparation. The yield of the bio-based antioxidant 4-(3,4,5-trihydroxybenzoyl)morpholine was 75% by mass, and the purity was 99.7%.

[0066] Test example

[0067] (1) Component analysis

[0068] The composition of the bio-based antioxidant 4-(3,4,5-trihydroxybenzoyl)morpholine prepared in Example 1 was analyzed using a Mercury VX-300 nuclear magnetic resonance spectrometer at a frequency of 400 Hz and deuterated water as the solvent. Figure 1 Bio-based antioxidant 4-(3,4,5-trihydroxybenzoyl)morpholine 1 In the H-NMR spectrum, the characteristic peak of the test solvent deuterated water is at 4.68ppm, and the other peaks are: 3.44ppm (s, 4H, -CH2N-); 3.53ppm (s, 4H, -CH2O-); 5.01ppm (m, 3H, -OH); 6.33ppm (s, 2H, -CH-). Figure 2 Bio-based antioxidant 4-(3,4,5-trihydroxybenzoyl)morpholine 13 C-NMR nuclear magnetic spectrum, the peaks are: C-(h,k) 46.2ppm; C-(i,j) 66.7ppm; C-(b,f) 106.5ppm; Ca 125.2ppm; Cd 134.8ppm; C-(c,e) 145.6ppm; Cg 169.5ppm. Comprehensive analysis of the nuclear magnetic spectrum shows that the bio-based antioxidant 4-(3,4,5-trihydroxybenzoyl)morpholine was successfully prepared.

[0069] (2) Antioxidant test

[0070] The antioxidant properties of the bio-based antioxidant 4-(3,4,5-trihydroxybenzoyl)morpholine (GM) prepared in Example 1 were compared with several commonly used antioxidants, including propyl gallate (PG), 2,6-di-tert-butyl-p-cresol (BHT), and vitamin E (VE). Palm oil was selected as the antioxidant protection object, and the amount of antioxidant added to palm oil was 0.1 g / kg. The accelerated oxidation experiment was carried out using the Schaal oven method. The sample was placed in a constant temperature box at (60±1)°C, shaken once every 24 hours, and its position in the constant temperature box was exchanged. Samples were taken at 0, 3, 6, 9, 12, and 15 days for determination of peroxide value and DPPH scavenging free radicals. Each sample was repeated 3 times. The test results of the antioxidant indicators peroxide value and DPPH scavenging free radicals are shown as follows Figure 3 , Figure 4 shown.

[0071] The results showed that palm oil with 4-(3,4,5-trihydroxybenzoyl)morpholine (GM) added and palm oil with PG added had lower peroxide values, which was significantly higher than the other three samples, indicating that the antioxidant effects of GM and PG on palm oil were better than those of BHT and VE. According to the DPPH free radical clearance comparison data, 4-(3,4,5-trihydroxybenzoyl)morpholine (GM) showed the best free radical capture ability. In general, among these samples, 4-(3,4,5-trihydroxybenzoyl)morpholine (GM) had the best antioxidant performance on palm oil.

[0072] (3) Oxidation discoloration test

[0073] The bio-based antioxidant 4-(3,4,5-trihydroxybenzoyl)morpholine (GM) prepared in Example 1 was taken as the test group (No. 1#); and the commercial gallic acid ester derivative antioxidant propyl gallate (PG) was taken as the control group (No. 2#).

[0074] The above two samples were added to 80℃ hot water to dissolve, and the aqueous solution with a concentration of 2wt% was prepared. The appearance of the two groups of samples was observed and recorded. Figure 1 As shown before oxidation; then, liquid alkali was added to the two groups of samples respectively until the pH value of the solution was adjusted to 7.0-8.0, and then hydrogen peroxide was added, and the amount of hydrogen peroxide added was 1% (volume fraction) of the sample aqueous solution, and the temperature was controlled at 80-85°C, and the reaction was kept warm for 1 hour; then hydrochloric acid was used to adjust the pH value to 3.0-3.5, and the appearance of the two groups of samples was observed and recorded again, as shown Figure 5 After oxidation.

[0075] according to Figure 5 The appearance observed and recorded in the figure, that is, before oxidation, the 4-(3,4,5-trihydroxybenzoyl)morpholine (GM) prepared in the example and the propyl gallate (PG) aqueous solution of the control group have similar appearances, both of which are light yellow; after oxidation treatment, the appearance color of the 4-(3,4,5-trihydroxybenzoyl)morpholine (GM) aqueous solution has no obvious change, while the propyl gallate (PG) aqueous solution becomes significantly darker and is yellow-brown.

[0076] Therefore, it can be explained that the new bio-based antioxidant 4-(3,4,5-trihydroxybenzoyl)morpholine (GM) proposed in the present invention can effectively solve the problem that the existing gallic acid ester derivative antioxidants are prone to coupling or hydrolysis reactions during the oxidation process to generate yellow-brown di-orthoquinone compounds. It has stronger stability and wider practical application value.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A bio-based antioxidant, characterized in that: Its chemical structure is as follows:

2. The method for preparing a bio-based antioxidant according to claim 1, characterized in that: The steps include: S1: mixing plant powder with morpholine, performing countercurrent extraction, and collecting the extract and solid residue respectively; S2 takes the extract, heats it, performs aminolysis reaction, then performs vacuum distillation, and condenses and collects the amine-based solvent; S3: adding deionized water to the reaction vessel after vacuum distillation, heating to dissolve, and then adding activated carbon for decolorization; then removing the activated carbon, cooling and crystallizing, centrifuging to obtain crystal A; S4 takes crystal A, mixes it with deionized water and activated carbon, heats it, and performs secondary decolorization treatment; then removes the activated carbon, cools it down for crystallization, centrifuges it, and dries it to obtain the bio-based antioxidant.

3. The method for preparing a bio-based antioxidant according to claim 2, characterized in that: In step S1, the countercurrent extraction temperature is 30-100°C.

4. The method for preparing a bio-based antioxidant according to claim 2, characterized in that: In step S2, the heating temperature is 40-120°C, and the aminolysis reaction time is 3-24h.

5. The method for preparing a bio-based antioxidant according to claim 2, characterized in that: In step S3 and step S4, during the decolorization process, the pH value is adjusted to be less than 4.

6. The method for preparing a bio-based antioxidant according to claim 2, characterized in that: In step S3 and step S4, the decolorization temperature is 50-100°C, and the cooling crystallization temperature is 10-30°C.

7. The method for preparing a bio-based antioxidant according to any one of claims 2 to 6, characterized in that: The plant powder includes one or more of tara powder, gallnut powder and gallic acid powder.

8. The method for preparing a bio-based antioxidant according to claim 7, characterized in that: The mixing ratio of plant powder to morpholine is 4-8:1 by mass.

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