| 单词 | antioxidant | |||
| 释义 | antioxidantenUKan·ti·ox·i·dantA0344700 (ăn′tē-ŏk′sĭ-dənt, ăn′tī-)antioxidant(ˌæntɪˈɒksɪdənt)an•ti•ox•i•dant(ˌæn tiˈɒk sɪ dənt, ˌæn taɪ-)n. an·ti·ox·i·dant(ăn′tē-ŏk′sĭ-dənt, ăn′tī-ŏk′sĭ-dənt)
antioxidantenUKantioxidant,substance that prevents or slows the breakdown of another substance by oxygen. Synthetic and natural antioxidants are used to slow the deterioration of gasoline and rubber, and such antioxidants as vitamin C (ascorbic acid), butylated hydroxytoluene (BHT), and butylated hydroxyanisole (BHA) are added to foods (see food additivesfood additives,substances added to foods by manufacturers to prevent spoilage or to enhance appearance, taste, texture, or nutritive value. By quantity, the most common food additives are flavorings, which include spices, vinegar, synthetic flavors, and, in the greatest ..... Click the link for more information. ) to prevent them from becoming rancid or from discoloring. In the body, nutrients such as beta-carotene (a vitamin A precursor), vitamin C, vitamin E, and selenium have been found to act as antioxidants. They act by scavenging free radicalsfree radical, Studies have suggested that the antioxidants that occur naturally in fresh fruits and vegetables have a protective effect. For example, vitamin E and beta-carotene appear to protect cell membranes; vitamin C removes free radicals from inside the cell. There is still some question as to whether antioxidants in the form of dietary supplements counteract the effects of increased numbers of free radicals in the body. Some scientists believe that regular consumption of such supplements interferes with the body's own production of antioxidants. AntioxidantA substance that, when present at a lower concentration than that of the oxidizable substrate, significantly inhibits or delays oxidative processes, while being itself oxidized. In primary antioxidants, such as polyphenols, this antioxidative activity is implemented by the donation of an electron or hydrogen atom to a radical derivative, and in secondary antioxidants by the removal of an oxidative catalyst and the consequent prevention of the initiation of oxidation. Antioxidants have diverse applications. They are used to prevent degradation in polymers, weakening in rubber and plastics, autoxidation and gum formation in gasoline, and discoloration of synthetic and natural pigments. They are used in foods, beverages, and cosmetic products to inhibit deterioration and spoilage. Interest is increasing in the application of antioxidants to medicine relating to human diseases attributed to oxidative stress. The autoxidation process is shown in reactions (1), (2), and (3). Lipids, When lipid autoxidation occurs in food, it can cause deterioration, rancidity, bad odor, spoilage, reduction in nutritional value, and possibly the formation of toxic by-products. Oxidation stress in a lipid membrane in a biological system can alter its structure, affect its fluidity, and change its function, causing disease. An antioxidant can eliminate potential initiators of oxidation and thus prevent reaction (1). It can also stop the process by donating an electron and reducing one of the radicals in reaction (2) or (3), thus halting the propagation steps. A primary antioxidant can be effective if it is able to donate an electron (or hydrogen atom) rapidly to a lipid radical and itself become more stable then the original radical. The ease of electron donation depends on the molecular structure of the antioxidant, which dictates the stability of the new radical. Many naturally occurring polyphenols, such as flavonoids, anthocyanins, and saponins, which can be found in wine, fruit, grain, vegetables, and almost all herbs and spices, are effective antioxidants that operate by this mechanism. A secondary antioxidant can prevent reaction (1) from taking place by absorbing ultraviolet light, scavenging oxygen, chelating transition metals, or inhibiting enzymes involved in the formation of reactive oxygen species, for example, NADPH oxidase and xanthine oxidase (reducing molecular oxygen to superoxide and hydrogen peroxide), dopamine-β-hydroxylase, and lipoxygenases. The common principle of action in the above examples is the removal of the component acting as the catalyst that initiates and stimulates the free-radical chain reaction. See Enzyme Among antioxidants, the synthetic compounds butylated hydroxyanisole (BHA), propyl gallate, ethoxyquin, and diphenylamine are commonly used as food additives. Quercetin belongs to a large natural group of antioxidants, the flavonoid family, with more than 6000 known members, many acting through both mechanisms described above. Ascorbic acid is an important water-soluble plasma antioxidant; it and the tocopherols, the main lipid soluble antioxidants, represent the antioxidants in biological systems. β-Carotene belongs to the carotenoid family, which includes lycopene, the red pigment in tomatoes; the family is known to be very effective in reacting with singlet oxygen (1O2), a highly energetic species of molecular oxygen. See Ascorbic acid, Carotenoid, Flavonoid antioxidant[‚an·tē′äk·sə·dənt]antioxidantantioxidantenUKantioxidant[an″te-ok´sĭ-dant]an·ti·ox·i·dant(an'tē-oks'ĭ-dănt),Free radicals, formed in the course of normal cellular respiration and metabolism, and more abundantly under the influence of certain environmental chemicals and sunlight, have been inculpated in various types of tissue damage, particularly those involved in atherosclerosis, the aging process, and the development of cancers. A free radical is any atom or molecule that has 1 or more unpaired electrons and is therefore highly reactive, seeking to acquire electrons from other substances. Free radicals are normally scavenged from tissues by the antioxidant enzymes superoxide dismutase and glutathione peroxidase. Ubidecarenone (coenzyme Q10) is also thought to act as an antioxidant in mitochondrial respiration reactions. In addition, a number of nutrient substances, vitamins, and minerals have been shown to contribute to antioxidant functions, generally by serving as cofactors or coenzymes. These include selenium beta-carotene, and vitamins C and E. It has been postulated that an imbalance between the production of free radicals and natural antioxidant processes may be a major causative factor in aging and in many chronic and degenerative disorders, and some researchers have speculated that antioxidant nutrients may have a role in disease prevention. Oxidation of low-density lipoprotein cholesterol does indeed seem to be responsible for foam cell formation in the genesis of atherosclerotic plaques. In addition, free radicals have been shown to damage DNA in ways that can culminate in malignant change. Oxidations also occur in many beneficial processes, however, including chemotaxis of cells with immunologic functions, phagocytosis, clotting mechanisms, and apoptosis. Moreover, antioxidants do not exert their effects in only one way, but can act during initiation or propagation of reactions at a variety of intracellular sites, and in some circumstances can be prooxidant. Claims that vitamins and other nutrients, when taken in massive doses, can prevent heart attack or cancer or retard aging are not based on scientific evidence. Although a high intake of antioxidants from food sources appears to offer some health advantages, there is at present no unequivocal evidence that any antioxidant nutrient, when taken in excess of normal dietary amounts, has value in the prevention or treatment of cardiovascular disease, cancer, or any other abnormal process except such as may be associated with frank nutritional or vitamin deficiency. A controlled, double-blind, randomized study of antioxidant supplementation in more than 20,000 people at risk of coronary artery disease found no effect whatsoever on all-cause mortality, cardiovascular mortality, nonfatal myocardial infarction, stroke, or cancer incidence. A controlled trial of beta-carotene and retinol not only failed to show any benefit but was aborted when statistics showed large increases in the risk of death from lung cancer and cardiovascular disease. antioxidant(ăn′tē-ŏk′sĭ-dənt, ăn′tī-)antioxidantAny agent—e.g., vitamin A, vitamin C, selenium—which is capable of reducing highly histotoxic oxygen-reduction products and reactive oxygen species (e.g., hydroxyl radical), which derive from superoxide anion (O2-) and H2O2, the univalent and bivalent reduction products of oxygen, and are generated during the normal intermediary metabolism of the respiratory chain. Other antixodants include glutathione, alpha-tocopherol (vitamin E) and bilirubin.antioxidantNutrition Any agent–eg, vitamins A, C, and E, selenium, and others, that is capable of reducing highly histotoxic O2 reduction products and reactive O2 species—eg hydroxyl radical, which derive from superoxide anion–O2·– and H2O2, the univalent and bivalent reduction products of O2, generated during the normal intermediate metabolism of the respiratory chain; other antixodants include glutathione, α-tocopherol–vitamin E, bilirubin. See Catalase, Ceruloplasmin, Free radical, Glutathione, Peroxidase, Superoxide dismutase, Transferrin.an·ti·ox·i·dant(antē-oksi-dănt)See also: free radical Antioxidantoxidative stressan·ti·ox·i·dant(antē-oksi-dănt)Patient discussion about antioxidantQ. What are “antioxidants”? and what do they do? I’ve been hearing about antioxidants for quite some time now, they are supposedly help to keep us younger. What do they do and is it true? antioxidantenUK
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antioxidant - substance that inhibits oxidation or inhibits reactions promoted by oxygen or peroxides
