Antioxidant is an abbreviation for antioxidant free radicals. Because the human body is often in contact with the outside world, normal breathing, external pollution, radiation exposure and other factors can cause free radicals in the human body. Excessive free radicals can cause human cancer, aging and other diseases, and antioxidant free radicals (hereinafter referred to as “resistance” Oxidation" can effectively overcome these hazards. Therefore, antioxidants have become one of the major research topics in the health products and cosmetics market.
In this paper, the anti-oxidation components of various plant extracts and their principles are discussed.
First, the antioxidant principle of plant extracts
Different plant extracts have different active ingredients. Similarly, the antioxidant plant extracts also have many different components. The mechanism of action is also different. Xi'an Yuansen Biosystems has summarized the following aspects:
(a) Acts on free radical-related enzymes
The enzymes involved in free radicals are classified into two types: oxidases and antioxidant enzymes. The antioxidant effects of plant extracts are reflected in the inhibition of the activity of related oxidases and the enhancement of antioxidant enzyme activity.
1. Inhibition of oxidase activity
Many oxidases in organisms, such as P-450 enzymes, xanthine oxidase (XOD), lipoxygenase, myeloperoxidase (MPO), and cyclooxygenase, are involved in the production of free radicals and can induce large amounts of free radicals. .
In addition, inducible nitric oxide synthase (iNOS) increases in the activity of ischemia-reperfusion, resulting in a large amount of NO and causing oxidative damage.
Studies have shown that many plant extracts have inhibitory effects on the above-mentioned various oxidases and inhibit free radical production from the source. Quercetin and curcumin in flavonoids can inhibit the activity of iNOS during ischemia-reperfusion injury, and thus play an antioxidant role; Gynostemma saponin can reduce the abnormally increased activity of XOD and MPO and improve the kidneys of diabetic rats. Oxidative stress delays the progression of kidney damage.
2. Enhances antioxidant enzyme activity
The body has antioxidant enzymes that protect against, eliminate, and repair excess free radical damage, such as catalase (CAT), glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), and Peroxidase and so on. SOD is the main scavenger of superoxide anion in the body, and it is catalytically decomposed into H2O2, but H2O2 also has oxidative damage, and CAT converts it into O2 and H2O. H2O2 also generates H2O through the catalytic and reduced glutathione (GSH) reaction of GSH-Px and simultaneously produces oxidized glutathione.
Many studies have shown that extracting antioxidants from plants can not only protect antioxidant enzymes in the body, but also increase antioxidant enzyme activity in the body. For example, quercetin in flavonoids can reduce oxidative damage of pancreatic β-cells and restore Fe2+. The activity of SOD, GSH-Px, and CAT in animals with renal cell damage; saponins have little effect on oxygen free radicals themselves, but most of them can increase the activity of SOD, CAT, and other antioxidant enzymes in the body, thereby enhancing the function of the body's antioxidant system.
In addition, some natural substances can induce the expression of antioxidant enzymes in the body such as SOD at the level of gene and transcription and exert their anti-oxidation effects.
(B) Anticomplementary and synergistic effects of antioxidant components
There are complementary and coordinated relationships among the antioxidant components of plant extracts, and they are combined in the body through electron and/or proton transfer, action on oxidase and antioxidant enzymes, chelation of transition metal ions, and affecting gene expression. Play an antioxidant effect.
The study found that there were significant synergistic effects between different concentrations of tea polyphenols and American ginseng, and as the concentration increased, the synergistic effect also increased. VE and VC had a significant synergistic effect on the reducing capacity of chickpea antioxidant peptides, and the synergistic effect of VC and chickpea antioxidant peptides was stronger than that of VE, and all synergistic effects increased with the addition amount and action time. Enhanced.
(c) Directly eliminating or inhibiting free radicals
Plant extracts can act as donors for hydrogen protons or electrons, directly quenching or inhibiting free radicals, terminating the chain reaction of free radicals, and exerting antioxidant functions.
Most of the antioxidants are oxygen free radical scavengers, such as polyphenols, sterols, VE, etc. One of the reasons is that they can release small, highly affinity hydrogen protons and trap high potential energy. Active free radicals transform it into inactive or more stable compounds, while at the same time converting themselves into more stable substances than radicals generated by the oxidative chain reaction, thereby interrupting or delaying the chain reaction.
2. Provide electronic
Another reason why plant extracts exert anti-oxidation effects is that electrons are directly given electrons to scavenge free radicals, such as polyphenols, plant polysaccharides, and vitamins. Beta-carotene has good antioxidant properties and can be used to eliminate free radicals by providing electrons to inhibit the production of reactive oxygen species. VC is converted to semi-dehydroascorbic acid and dehydroascorbic acid to remove it by feeding electrons step by step. The purpose of reactive oxygen radicals.
(d) Chelating of transition metal ions
Transition metal ions (such as Fe2+, Cu2+, etc.) are necessary in the generation of oxygen radicals, such as Fe2 + can both mediate lipid peroxidation and is also a catalyst for radical generation such as •OH.
The flavonoids in plant extracts have a 4-keto, 5-hydroxyl molecular structure, and the ligation pairs of the 3' and 4' positions of the B-ring contain lone pairs of electrons and therefore can chelate metal ions. The antioxidants that can promote the oxidation of metal ions through coordination electron chelation include tannins, polysaccharides, active peptides, phytic acid, and citric acid.
Second, research on antioxidants of plant extracts
The antioxidant active ingredients of plant extracts are mainly alkaloids, saponins, vitamins, polyphenols, peptides and polysaccharides. These ingredients are mostly extracted from cereals, Chinese herbs, vegetables, fruits, plant drinks and spices. Come. Xi'an Yuansen Biological explains the oxidation resistance of the above substances:
Alkaloids (alkaloids) are a class of organic compounds with a complex nitrogen-containing ring structure and significant physiological activity. Most of them are distributed in higher plants, especially dicotyledons such as Ranunculaceae, Papaveraceae, Solanaceae, and musk. Branches, legumes, etc.
The structural factors that affect the antioxidant activity of alkaloids are mainly three-dimensional structure and electrical properties. The more nitrogen atoms in the heterocyclic rings are exposed, the more favorable it is to fully access and react with active oxygen, and the better the antioxidant effect; Groups or structural elements that make the nitrogen atoms rich in electrons can also increase their antioxidant activity.
Antioxidant alkaloids include brucine, aloperine, tetrahydroberberine, norcoclaurine, magnoxine, tetramethylpyrazine, berberine, sea- papaverine, jatrorrhizine, cherimoya Alkali and so on.
Saponins (saponins) are an important class of active substances in Chinese herbal medicines. According to the chemical structure of aglycones, they are divided into steroidal saponins and triterpene saponins. The former are mostly found in Liliaceae and Dioscorea plants; the latter exist in Araliaceae and Umbelliferae and other plants.
Recent studies have shown that most saponins have significant antioxidant effects, including: Araliaceae saponins (including ginseng, American ginseng, Acanthopanax), leguminous (including astragalus, soybean, licorice) and so on. The total saponins contained in Gynostemma pentaphyllum, Rhodiola rosea, Erigeron breviscapus, Aesculus, Bupleurum, Bitter gourd, Polygonum cuspidatum, Mangosteen, Camellia oleifera, etc. also have strong antioxidant activity. Xi'an Yuansen Biological Company gave i-carrageenan, leguminous saponin, Rhodiola rosea, Polygonum cuspidatum, and bitter melon as the main anti-oxidation products.
Vitamins are both essential food nutrients and the most important antioxidants in the human body. The antioxidant vitamins in plants are mainly VE, VC and carotene, but they can also be pro-oxidants in certain situations.
VE is a generic name for various tocopherols, of which alpha-tocopherol has the greatest biological activity. If it is used as a benchmark, the physiological activities of beta-tocopherol, gamma-tocopherol, and delta-tocopherol are 40%, 8%, and 20, respectively. %, the remaining activity is extremely weak. In most cases, the antioxidant effect of VE is to react with lipoxy- or free-radical free radicals, to provide them with hydrogen ions, and to interrupt the lipid peroxidation chain reaction, which is the most important fat-soluble chain-breaking type. Antioxidants.
VC, also known as ascorbic acid, is an acidic polyhydroxy compound containing 6 carbon atoms of alpha-ketolactone. The enol-type hydroxyl group having a hydrogen ion that can be dissociated is the most important water-soluble capturing antioxidant, and can scavenge active oxygen radicals by supplying electrons step by step; it also protects VE and promotes regeneration of VE.
There are more than 600 species of carotenoids, all of which are isoprenoid structures with 11 double bonds. β-carotene is a typical example. Studies have found that there are significant antioxidant properties of lutein, zeaxanthin, lycopene, and astaxanthin.
Beta-carotene is a precursor of VA and is composed of four isoprene double bonds connected end to end. Each molecule has a β-ionone ring on both ends, mainly all-trans, 9-cis, and l3- Cis and l5- cis 4 forms. It has good anti-oxidation properties and can eliminate free radicals by providing electrons to inhibit the generation of reactive oxygen species.
There are 8 isomers of lutein, which are mainly found in dark green vegetables such as cabbage and spinach, and in flowers such as calendula and marigold. Zeaxanthin is mainly found in foods such as gardenia, corn, spinach, and Asian persimmons. Lutein and zeaxanthin are always associated with survival, the effect is also very similar, mainly in antioxidants, can reduce the oxidative damage to the eyes, that is, the retinal macular light-induced oxidation resistance, can prevent Aging caused by degradation of visual spots. It can also prevent the oxidation of proteins and lipids in the lens, thereby reducing the incidence of senile cataracts.
Lycopene is an acyclic carotenoid. The chemical structure is an acyclic, linear, all-trans structure containing 11 conjugated double bonds and 2 non-conjugated double bonds. Can accept the excitation of different electrons, generate ground state oxygen or triplet oxygen lycopene, a triplet oxygen lycopene can quench thousands of singlet oxygen free radicals, the antioxidant capacity is 100 times that of VE, VC's 1000 times is the strongest anti-aging antioxidant in nature.
Astaxanthin is a special oxidized carotenoid that not only has long conjugated double bonds in the molecule like other carotenoids, but also has a hydroxyl group at each of the 3 and 4 positions of its two violet rings. With unsaturated ketone groups, such adjacent hydroxyl groups and ketone groups may constitute α-hydroxy ketones. These structures all have relatively active electronic effects. They can provide electrons to free radicals or unpaired electrons that attract free radicals and can easily trap free radicals. Therefore, astaxanthin has stronger antioxidant properties than general carotenoids.
Plant polyphenols antioxidants can be divided into tannins, flavonoids, and phenolic acids, depending on their chemical structure.
Tannins, also known as tannins, are widely distributed in plants and usually refer to plant polyphenols with a relative molecular mass of 500 to 3,000. According to the different molecular structure and ease of hydrolysis can be divided into three categories: hydrolyzed tannins (such as gallopannins, tannins), condensed tannins (such as proanthocyanidins, oligomeric proanthocyanidins), condensation enamel and hydrolysis The compound tannins (eg, Camellia B, guavagin A) in which the glucose in the tannin is linked by carbon bonds.
There are three factors affecting the antioxidative activity of tannins: the binding mode of the unit; whether the hydroxyl group is free; hexahydrodibenzoyl (HHDP), gall, dehydrogenated hexahydroxydibenzoyl (DHHDP) group The type and number of groups. When tannin binding units (such as catechins) are combined with hydrolyzable ester bonds and glycosidic bonds, the antioxidant capacity of the molecule is enhanced, and when carbon-carbon bonds are combined into condensation, the antioxidant capacity of the molecule is greatly reduced; the phenolic hydroxyl groups are greatly reduced; When free, the activity is increased. The order of activity of HHDP, gall, and DHHDP groups is HHDP>gall >DHHDP. In the binding unit, the more these three groups, the greater the activity.
Flavonoids, also known as flavonoids, are the most abundant of polyphenols, and almost all tissues of plants contain such natural products. Refers to a series of compounds in which two benzene rings (A- and B-rings) are linked to each other through a central three-carbon bond and can be further classified into flavonoids, flavonols, flavanones, dihydroflavonols, Flavonoids (ie, catechins), isoflavones, chalcone, anthocyanis, and other subfamilies. Flavonoids have different antioxidant activities, and their antioxidant activity is closely related to the structure of the compound. The position and number of phenolic hydroxyl groups and their substituent position carbonyl groups, hydroxy glycosides, hydroxymethylation and Δ2 (3) double bonds) are important factors in determining their antioxidant activity.
It is generally believed that the hydroxyl group of o-diphenol on the ring B plays a major role in the antioxidative activity of flavonoids; the o-dihydroxy on one ring and the p-dihydroxy on the other ring have great potential for antioxidation, on the A ring The addition of hydroxyl groups at positions 5, 7, and 8 can increase antioxidant capacity to varying degrees. Many flavonoids show significant antioxidant properties, such as the representative hedgehog, quercetin, naringenin, docetaxel, tea polyphenols, soy isoflavones, trihydroxychalcones Chrysanthemum pigment and so on.
3. Phenolic acids
Phenolic acid refers to a class of compounds that have several phenolic hydroxyl groups on the same benzene ring. The phenolic acids with antioxidant properties found in natural plants can be divided into three categories: the first category is hydroxybenzoic acid and its derivatives, such as protocatechuic acid, gallic acid, syringic acid, etc.; Anthocyanic acid and its derivatives, such as 3-hydroxyphenylacetic acid; the third category is hydroxycinnamic acid (hydroxybenzoic acid) and its derivatives, such as chlorogenic acid, ferulic acid, caffeic acid, rosmarinic acid, coumarin Acid, sinapic acid and so on.
The antioxidant capacity of phenolic acids is similar to that of flavonoids in terms of chemical structure. That is, those with phenolic hydroxyl groups on the benzene ring are much stronger than those without, such as those with a diphenyl triphenol structure. Gallic acid and its various derivatives are stronger than only two hydroxyl groups. Cyanogen, caffeic acid, and rosmarinic acid, which have a catechol structure, are far more potent than ferulic acid and sinapinic acid, which have only one hydroxyl group.
(E) Active peptides
Polypeptides with antioxidant properties are called bioactive peptides. Researchers at home and abroad have extracted various peptide substances with antioxidant activity from proteins of different plant origins. However, natural antioxidant peptides that can understand the detailed molecular structure and carry out relevant mechanistic studies are limited to glutathione. Many are low-molecular mixed peptides with a certain antioxidant activity in various natural protein hydrolysates, such as soybean peptides, corn peptides, wheat peptides, rice bran peptides, and peanut peptides. In addition, active peptides with antioxidant activity were obtained in plant protein raw materials such as black rice, rapeseed, ganoderma lucidum, sweet-scented osmanthus, and alfalfa.
Xi'an Yuansen Biological Laboratory has shown that the amino acid composition, number, and amino acid sequence of peptides determine the antioxidant capacity of peptides. With antioxidant