A bio-based antioxidant and a method for its preparation

Abstract

The application relates to the technical field of plant resource processing, and discloses a bio-based antioxidant, a chemical structural formula of which is as shown in the following formula a: the preparation method of the bio-based antioxidant comprises the following steps: S1, mixing plant powder with morpholine, performing countercurrent extraction, and respectively collecting an extract and solid residues; S2, taking the extract, heating, performing an aminolysis reaction, then performing reduced-pressure distillation, and collecting an amine-based solvent through condensation; S3, adding deionized water to the reaction container after the reduced-pressure distillation, heating and dissolving, then adding activated carbon, and performing decoloration treatment; then removing the activated carbon, cooling and crystallizing, centrifuging, and obtaining crystal A; S4, taking the crystal A, mixing the crystal A with deionized water and activated carbon, heating, and performing secondary decoloration treatment; then removing the activated carbon, cooling and crystallizing, centrifuging, and drying, so that the bio-based antioxidant is obtained, the bio-based antioxidant has excellent antioxidant performance, can remain stable in an oxidation process, and does not cause a color reaction.

Description

Technical Field

[0001] This invention relates to the field of plant resource processing technology, and more specifically, to a bio-based antioxidant and its preparation method. Background Technology

[0002] Bio-based antioxidants have become a research hotspot in recent years across interdisciplinary fields such as chemistry, biology, and medicine. These are antioxidants derived from natural organisms or their derivatives, which can act as hydrogen donors to scavenge free radicals generated during the chain initiation stage, thereby inhibiting or reducing the oxidation of oils and other substances. Plant polyphenols, for example, are a class of antioxidants widely found in nature. Their polyphenolic structures exhibit significant antioxidant activity, and plant polyphenols also possess relatively active chemical reactivity, allowing them to be applied in various fields and scenarios, exerting antioxidant, antibacterial, and metal ion chelating effects on different products.

[0003] Plant polyphenols, also known as tannins, can be classified into condensed tannins and hydrolyzable tannins. Condensed tannins are polymers formed by flavan condensation, containing unique structures such as catechins and epicatechins, and do not contain sugar groups, making them difficult to hydrolyze. Hydrolyzable tannins, with polyols or sugar groups as their core, are linked to multiple phenolic and carboxylic acids via ester bonds. They are easily hydrolyzed under the action of acids, alkalis, and enzymes, producing gallic acid, glucose, quinic acid, and other components. Gallic acid and its derivatives are a common raw material for preparing antioxidants. Gallic ester derivatives are commonly used as low-toxicity, high-efficiency antioxidants in food, feed, pharmaceuticals, cosmetics, and fiber industries. For example, patent publication number CN112110809A discloses a bio-based antioxidant, its preparation method, and its uses.

[0004] However, gallic ester derivatives are prone to coupling and hydrolysis reactions during oxidation, generating yellowish-brown di-ortho-quinone compounds. This color-changing property limits the application of gallic ester compounds in many fields. Summary of the Invention

[0005] The technical problem to be solved by this invention:

[0006] Currently, existing gallic acid ester derivative antioxidants are prone to coupling or hydrolysis reactions during oxidation, generating yellowish-brown di-ortho-quinone compounds. This makes them unsuitable for applications requiring a colorless state and environment, limiting the application expansion of gallic acid ester antioxidants in many fields.

[0007] The technical solution adopted in this invention is as follows:

[0008] This invention provides a bio-based antioxidant with the following chemical structural formula a:

[0009]

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

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

[0012] S2 The extract was heated to carry out aminolysis reaction, followed by vacuum distillation, and the amino solvent was collected by condensation.

[0013] S3 adds deionized water to the reaction vessel after vacuum distillation, heats to dissolve, then adds activated carbon for decolorization; then removes the activated carbon, cools to crystallize, and centrifuges to obtain crystal A;

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

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

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

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

[0018] Preferably, in steps S3 and S4, the decolorization temperature is 50-100℃ and the cooling crystallization temperature is 10-30℃.

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

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

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

[0022] The bio-based antioxidant of this invention contains both pyrogallol and amide structures, which endow it with excellent free radical scavenging and polyvalent metal ion complexing abilities while maintaining a stable, non-hydrolyzable state. Furthermore, using an amino-based solvent, tannic acid can be directly extracted from plants. The amino groups in the solvent perform aminolysis on the tannic acid, converting the ester groups to amide groups to obtain the crude product. The amino-containing solvent provides steric protection, limiting oxidative coupling reactions and preventing the formation of colored macrocyclic di-o-quinone compounds from this gallic ester antioxidant.

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

[0024] This invention employs a one-step synthesis process, which has a shorter process flow and is suitable for large-scale industrial production. The resulting bio-antioxidant has excellent free radical scavenging ability and the ability to complex multivalent metal ions, and can be widely used to improve the antioxidant properties of materials such as oils, rubber, plastics, and fibers. Attached Figure Description

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

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

[0027] Figure 3 The graph shows the effect of different antioxidants on the peroxide value of palm oil in Experimental Example (2);

[0028] Figure 4 The graph shows the DPPH free radical scavenging ability of different antioxidants in palm oil in Experimental Example (2);

[0029] Figure 5 This is a comparison chart of the oxidation color changes of different antioxidants in test example (3). Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

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

[0032]

[0033] The preparation method of this bio-based antioxidant in this invention includes the following steps:

[0034] (1) Extraction:

[0035] At a mass ratio of 4-8:1, the amine solvent and the tannic acid-containing plant powder are added to a continuous countercurrent extractor, heated to 30-100℃, and subjected to countercurrent extraction. The extract and solid residue are collected separately.

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

[0037] (2) Aminolysis:

[0038] The extract was introduced into a reaction vessel and heated to 40-120℃ for 3-24 hours for aminolysis. Then, the product was distilled under reduced pressure and the fraction morpholine was collected by condensation.

[0039] (3) Decolorization crystallization:

[0040] After vacuum distillation, deionized water is added to the reaction vessel and heated to dissolve. Then activated carbon is added for decolorization. The temperature is controlled at 50-100℃ during decolorization, and the pH value is adjusted to below 4 with hydrochloric acid. Then the activated carbon residue is removed by filtration. The filtrate is transferred to the crystallization vessel while hot, cooled to 10-30℃ for crystallization, and centrifuged to obtain light yellow crystals A.

[0041] (4) Secondary decolorization and crystallization:

[0042] Deionized water, light yellow crystals A, and activated carbon were added sequentially to the decolorization kettle. The mixture was heated to 50-100℃ for a second decolorization treatment. The activated carbon residue was then removed by filtration. The filtrate was transferred to a crystallization kettle while still hot and cooled to 10-30℃ for crystallization. After centrifugation, white crystals B were obtained. After drying, the bio-based antioxidant 4-(3,4,5-trihydroxybenzoyl)morpholine was obtained.

[0043] In this invention, the raw material plant powder used for extraction can be selected from one or more of the following: tarragon powder, gallnut powder, and gallnut powder.

[0044] The bio-based antioxidant prepared by the above method has excellent free radical scavenging ability and ability to complex multivalent metal ions. It is also structurally stable, not easily hydrolyzed or oxidatively coupled, and can remain stable in complex use environments, avoiding the formation of colored compounds. It can be widely used to improve the antioxidant properties of materials such as oils, rubber, plastics, and fibers.

[0045] Example 1

[0046] Antioxidants were prepared using tarax powder, gallnut, and propyl gallate produced and sold by Sichuan Tingjiang New Material Co., Ltd., according to the method described in the following examples. The remaining materials were purchased from Foshan Shunde Huaneng Reagent Co., Ltd.

[0047] Add 400 parts by weight of morpholine and 100 parts by weight of tarax powder into a continuous countercurrent extractor, adjust the extraction temperature to 100℃, and carry out countercurrent extraction. Collect the extract and solid residue separately.

[0048] The extract was introduced into a reaction vessel and heated to 80°C to carry out an aminolysis reaction. After 15 hours of reaction, the distillation was carried out under reduced pressure, and the morpholine fraction was collected by condensation and can be recovered and reused.

[0049] After vacuum distillation, deionized water was added to the reaction vessel and heated to 100°C to dissolve it. Then activated carbon was added, stirred to decolorize, and the pH was adjusted to less than 4 with hydrochloric acid. The activated carbon residue was then removed by filtration, and the filtrate was transferred to a crystallization vessel while hot. The solution was cooled to 30°C to crystallize, and centrifuged to obtain light yellow crystals.

[0050] In a separate decolorization vessel, deionized water, light yellow crystals, and activated carbon were added and heated to 80°C to dissolve them for a second decolorization treatment. Then, the activated carbon residue was removed by filtration, and the filtrate was transferred to a crystallization vessel while hot. The solution was cooled to 30°C to crystallize, centrifuged, and white crystals were obtained. After drying, the bio-based antioxidant was obtained.

[0051] The raw materials and products were weighed before and after 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] Antioxidants were prepared using tarax powder, gallnut, and propyl gallate produced and sold by Sichuan Tingjiang New Material Co., Ltd., according to the methods described in the following different examples. The remaining materials were purchased from Foshan Shunde Huaneng Reagent Co., Ltd.

[0054] 800 parts by weight of morpholine and 100 parts by weight of tarax powder were put into a continuous countercurrent extractor, the extraction temperature was adjusted to 40℃, and countercurrent extraction was carried out. The extract and solid residue were collected separately.

[0055] The extract was introduced into a reaction vessel and heated to 120°C to carry out an aminolysis reaction. After 5 hours of reaction, the distillation was carried out under reduced pressure, and the morpholine fraction was collected by condensation and can be recovered and reused.

[0056] After vacuum distillation, deionized water was added to the reaction vessel and heated to 50°C to dissolve it. Then activated carbon was added, stirred to decolorize, and the pH was adjusted to less than 4 with hydrochloric acid. The activated carbon residue was then removed by filtration, and the filtrate was transferred to a crystallization vessel while hot. The solution was cooled to 10°C to crystallize, and centrifuged to obtain light yellow crystals.

[0057] In a separate decolorization vessel, deionized water, light yellow crystals, and activated carbon were added and heated to 90°C to dissolve them for a second decolorization treatment. Then, the activated carbon residue was removed by filtration, and the filtrate was transferred to a crystallization vessel while hot. The solution was cooled to 15°C to crystallize, centrifuged, and white crystals were obtained. After drying, the bio-based antioxidant was obtained.

[0058] The raw materials and products were weighed before and after 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] Antioxidants were prepared using tarax powder, gallnut, and propyl gallate produced and sold by Sichuan Tingjiang New Material Co., Ltd., according to the methods described in the following different examples. The remaining materials were purchased from Foshan Shunde Huaneng Reagent Co., Ltd.

[0061] 800 parts by weight of morpholine and 100 parts by weight of tarax powder were put into a continuous countercurrent extractor, the extraction temperature was adjusted to 60℃, and countercurrent extraction was carried out. The extract and solid residue were collected separately.

[0062] The extract was introduced into a reaction vessel and heated to 40°C to carry out an aminolysis reaction. After 22 hours of reaction, the distillation was carried out under reduced pressure, and the morpholine fraction was collected by condensation and can be recovered and reused.

[0063] After vacuum distillation, deionized water was added to the reaction vessel and heated to 80°C to dissolve it. Then activated carbon was added, stirred to decolorize, and the pH was adjusted to less than 4 with hydrochloric acid. The activated carbon residue was then removed by filtration, and the filtrate was transferred to a crystallization vessel while hot. The solution was cooled to 10°C to crystallize and centrifuged to obtain light yellow crystals.

[0064] In a separate decolorization vessel, deionized water, light yellow crystals, and activated carbon were added and heated to 100°C to dissolve them for a second decolorization treatment. Then, the activated carbon residue was removed by filtration, and the filtrate was transferred to a crystallization vessel while hot. The solution was cooled to 15°C to crystallize, centrifuged, and white crystals were obtained. After drying, the bio-based antioxidant was obtained.

[0065] The raw materials and products were weighed before and after 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 case

[0067] (1) Component analysis

[0068] 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 400 Hz and deuterated water as the solvent. Figure 1 4-(3,4,5-trihydroxybenzoyl)morpholine, a bio-based antioxidant 1 The H-NMR spectrum shows a characteristic peak at 4.68 ppm for the test solvent, deuterated water. Other peaks are assigned as follows: 3.44 ppm (s, 4H, -CH2N-); 3.53 ppm (s, 4H, -CH2O-); 5.01 ppm (m, 3H, -OH); 6.33 ppm (s, 2H, -CH-). Figure 2 4-(3,4,5-trihydroxybenzoyl)morpholine, a bio-based antioxidant 13 The C-NMR spectrum peaks were assigned as follows: C-(h,k) 46.2 ppm; C-(i,j) 66.7 ppm; C-(b,f) 106.5 ppm; Ca 125.2 ppm; Cd 134.8 ppm; C-(c,e) 145.6 ppm; Cg 169.5 ppm. Comprehensive analysis of the NMR spectrum indicates the successful preparation of the bio-based antioxidant 4-(3,4,5-trihydroxybenzoyl)morpholine.

[0069] (2) Antioxidant test

[0070] The antioxidant activity of the bio-based antioxidant 4-(3,4,5-trihydroxybenzoyl)morpholine (GM) prepared in Example 1 was compared with that of 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 target for antioxidant protection, and the amount of antioxidant added to the palm oil was 0.1 g / kg. Accelerated oxidation experiments were conducted using the Schaal oven method. The samples were placed in a constant temperature oven at (60±1)℃, shaken once every 24 hours, and their positions in the oven were changed. Samples were taken at 0, 3, 6, 9, 12, and 15 days for determination of peroxide value and DPPH free radical scavenging. Each sample was repeated three times. The results of the antioxidant indicators peroxide value and DPPH free radical scavenging are shown below. Figure 3 , Figure 4 As shown.

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

[0072] (3) Oxidation discoloration test

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

[0074] The two samples were dissolved separately in 80°C hot water to prepare 2wt% aqueous solutions. The appearance of the two sets of samples was observed and recorded. Figure 1 Before oxidation, liquid alkali was added dropwise to both groups of samples until the pH value of the solution was adjusted to 7.0-8.0. Then, hydrogen peroxide was added dropwise at a volume fraction of 1% of the sample aqueous solution. The temperature was heated to 80-85℃ and maintained for 1 hour. The pH value was then adjusted to 3.0-3.5 with hydrochloric acid, and the appearance of the two groups of samples was observed and recorded again. Figure 5 As shown after oxidation.

[0075] according to Figure 5 The appearance of the 4-(3,4,5-trihydroxybenzoyl)morpholine (GM) prepared in the examples and the propyl gallate (PG) aqueous solution of the control group were similar before oxidation, both being light yellow. However, after oxidation treatment, the appearance of the 4-(3,4,5-trihydroxybenzoyl)morpholine (GM) aqueous solution did not change significantly, while the propyl gallate (PG) aqueous solution became significantly darker, turning yellowish-brown.

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

[0077] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a bio-based antioxidant, characterized in that, Includes the following steps: S1. The plant powder was mixed with morpholine and subjected to countercurrent extraction. The extract and solid residue were collected separately. The plant powder is selected from one or more of the following: Tara powder, Gallnut powder, and Gallnut powder; S2 Take the extract, heat it, carry out the aminolysis reaction, then distill under reduced pressure, and collect the amino solvent by condensation; S3. Add deionized water to the reaction vessel after vacuum distillation, heat to dissolve, then add activated carbon for decolorization treatment. During the decolorization treatment, adjust the pH value to be less than 4. Then remove the activated carbon, cool to crystallize, and centrifuge to obtain crystal A. S4 Take crystal A, mix it with deionized water and activated carbon, heat it, and perform a second decolorization treatment. During the decolorization treatment, adjust the pH value to be less than 4. Then remove the activated carbon, cool down to crystallize, centrifuge, and dry to obtain the bio-based antioxidant.

2. The method for preparing the bio-based antioxidant according to claim 1, characterized in that, In step S1, the countercurrent extraction temperature is 30-100℃.

3. The method for preparing the bio-based antioxidant according to claim 1, characterized in that, In step S2, the heating temperature is 40-120℃, and the aminolysis reaction time is 3-24h.

4. The method for preparing the bio-based antioxidant according to claim 1, characterized in that, In steps S3 and S4, the decolorization temperature is 50-100℃, and the cooling crystallization temperature is 10-30℃.

5. The method for preparing the bio-based antioxidant according to claim 1, characterized in that, By weight, the mixing ratio of plant powder to morpholine is 4-8:1.

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