antioxidant

from Wikipedia, the free encyclopedia

An antioxidant or antioxidant (plural antioxidants , also antioxidants ) is a chemical compound that slows down or completely prevents the oxidation of other substances.

Antioxidants are of great physiological importance due to their effect as radical scavengers . They inactivate reactive oxygen species (ROS) in the body, the excessive occurrence of which leads to oxidative stress , which is linked to aging and the development of a number of diseases. Low, d. H. Physiological amounts of ROS, on the other hand, are absolutely necessary as signaling molecules that increase the stress defense capacity, health and life expectancy of model organisms and humans. According to certain studies, a nutritional supplementation of antioxidants can lead to an increased incidence of cancer and an increased risk of death in humans.

Antioxidants are also of great, especially technological importance as additives for a wide variety of products ( food , pharmaceuticals , commodities , cosmetics , consumables) in order to prevent oxidative degradation of sensitive molecules - especially caused by atmospheric oxygen . The oxidative degradation of certain ingredients or components has a negative effect because the taste or smell changes unpleasantly (food, cosmetics), the effect diminishes (in the case of drugs), harmful degradation products arise or physical properties decrease (e.g. in the case of plastics ).

Mechanism of action

According to the type of chemical mechanism of action, antioxidants are divided into radical scavengers and reducing agents. In a broader sense, antioxidant synergists are also counted among the antioxidants.

Radical scavengers

In oxidation reactions between organic compounds, chain-like radical transfers often occur . This is where substances with sterically hindered phenol groups become effective, which in the course of these transfers form inert, stable radicals that do not react any further, causing the reaction cascade to be broken off (radical scavengers). They include natural substances such as tocopherols and synthetic ones such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and gallates. They are effective in a lipophilic environment.

Reducing agent

Reducing agents have a very low redox potential - their protective effect is due to the fact that they are more likely to be oxidized than the substance to be protected. Representatives include ascorbic acid (−0.04 V at pH 7 and 25 ° C ), salts of sulphurous acid (+0.12 V at pH 7 and 25 ° C) and certain organic sulfur-containing compounds (e.g. glutathione , cysteine , Thiolactic acid ), which are mainly effective in hydrophilic matrices.

Antioxidant synergists

Synergists support the effect of antioxidants, for example by regenerating used antioxidants. By complexing traces of metal ( sodium EDTA ) or creating an oxidation-inhibiting pH value , synergists can increase the antioxidant effect of a radical scavenger or reducing agent.

Occurrence

Natural antioxidants

Many antioxidants are naturally and endogenously occurring substances. In mammals, glutathione is a very important antioxidant, and uric acid and melatonin are also known to have antioxidant activity . Proteins such as transferrin , albumin , ceruloplasmin , hemopexin and haptoglobin also have antioxidant effects. Antioxidant enzymes , the most important of which are superoxide dismutase (SOD), glutathione peroxidase (GPX) and catalase , are also crucial for detoxifying free radicals in the body's cells. Trace elements such as selenium , copper , manganese and zinc are important for their enzymatic activity . As an antioxidant effective coenzyme is Coenzyme Q10 to name. For the human organism essential and antioxidative substances such as ascorbic acid (vitamin C), tocopherol (vitamin E) and beta-carotene (provitamin A) cannot be synthesized as required and must be supplied with the food ( exogenous antioxidants). A number of antioxidants are passed on to the infant as part of breast milk in order to develop their effect there.

As secondary plant substances, antioxidants such as carotenoids and various polyphenolic compounds ( flavonoids , anthocyanins , phytoestrogens , nordihydroguajaretic acid and others) occur in numerous types of vegetables and fruits, herbs, fruits, seeds, etc., as well as foods made from them. The German Nutrition Society (DGE) does not consider the scientific data to be sufficient to make recommendations for the intake of individual antioxidants.

Presence of natural antioxidants
Links) High content foods
Vitamin C (ascorbic acid) Fresh fruits and vegetables
Vitamin E (tocopherols, tocotrienols) Vegetable oils
Polyphenolic antioxidants ( resveratrol , flavonoids ) Tea , coffee , soy , fruit , olive oil , cocoa , cinnamon , oregano , red wine , pomegranate
Carotenoids ( lycopene , beta- carotene , lutein ) Fruits, vegetables, eggs .

Synthetic antioxidants

Artificial antioxidants include the gallates , butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT). Synthetic esterification of the vitamins ascorbic acid and tocopherol changes their solubility in order to expand the area of ​​application and improve processing properties ( ascorbyl palmitate , ascorbyl stearate , tocopherol acetate ).

nutrition

Health significance

Free radicals are highly reactive oxygen compounds that are formed in the body and are created to a greater extent by UV radiation and pollutants from the environment. Their occurrence in excess ( oxidative stress ) causes cell damage and is not only considered to be partly responsible for aging , but is also linked to the development of a number of diseases. Small, ie physiological, amounts of ROS, on the other hand, are required as signal molecules that increase the stress defense capacity, health and life expectancy of model organisms and humans. Protection against the harmful consequences of excessive amounts of free radicals is provided by the body's own defense system, which is repeatedly activated by low amounts of ROS  - similar to a vaccination (see also Mitohormesis ).

In addition to endogenously formed antioxidants, those that are supplied with food also have an effect in the immune system. A healthy diet, including foods rich in antioxidant substances, is considered an effective prevention against cardiovascular diseases , a protective effect against certain types of cancer is considered possible. However, both are no longer considered to be backed up by meaningful studies. Rather, more recent studies by a Swedish research group, in experiments on mice, have shown that antioxidants in skin cancer cause these secondary tumors to form more quickly - “the results have yet to be confirmed in humans”.

The newer scientific discoveries led the journal Nature to call myth the claim that free radicals cause faster aging and that this effect can be prevented by antioxidants. "The idea of ​​oxidation and aging is kept alive by people who make money from it." As vitamins or precursors to vitamins, the antioxidants beta-carotene , vitamin A , vitamin C and vitamin E are therefore extremely rare in preventing deficiency symptoms these days besides, no proven role in human health.

The assessment of polyphenolic plant ingredients, on the other hand, is much more reliable in this context, and the scientific evidence for the health-promoting effects of certain polyphenols, especially the flavanols found in tea, cocoa, berries and red wine, has increased in recent years. However, this does not seem to be related to the fact that these substances have antioxidant properties in vitro . An expert opinion assumes that the antioxidant capacity that the polyphenols and flavonoids show in vitro is not a measured value for their effect in the human body. The European Food Safety Authority (EFSA) largely agreed with this assessment.

Most common food sources

According to a US study from 2005, by far the largest part of the physiological antioxidants consumed with daily food in the USA comes from coffee , which is less due to the fact that coffee contains unusually large amounts of antioxidants than it is from the fact that Americans eat too little fruit and vegetables , but consume more coffee.

Sources of Antioxidant Intake: Top 10
(Average American Intake in mg / day)
rank source mg / day rank source mg / day
01 coffee 1,299 06th red wine 44
02 tea 294 07th beer 42
03 Bananas 76 08th Apples 39
04th Dried beans 72 09 tomatoes 32
05 Corn 48 10 Potatoes 28

The antioxidant capacity of a food and thus the ability to scavenge oxygen radicals is indicated by its ORAC value.

Nutritional supplement

Substances with antioxidant effects are offered on the market in a number of dietary supplements as " anti-aging " preparations and for disease prevention (e.g. against cancer ). The antioxidant substances it contains also occur naturally in food, and they are also added to many foods, so that there is usually no deficiency. There is a lack of reliable scientific evidence that the intake of food supplements - in which antioxidant substances are usually isolated and not combined with natural accompanying substances - is beneficial to health. On the contrary, supplementing the antioxidants beta-carotene , vitamin A and vitamin E in healthy people increases the development of cancer and reduces life expectancy, while vitamin C as a supplement has no effect on cancer and life expectancy. In a study published in 2009 in healthy athletes, a counterproductive influence of vitamins C and E on the training effect and the prevention of diabetes was measured, since these antioxidants suppress the increase in radicals in the body so that it adapts less well to exercise.

Antioxidant food supplements are also said to have negative effects in certain pathological conditions: interactions with antineoplastic treatment methods ( chemotherapy , radiation therapy ) or other harmful effects have been described in cancer patients .

Total antioxidant capacity

The determination of the total antioxidant capacity ( total antioxidant capacity , TAC) in body fluids provides a flat impression of the relative antioxidant activity of a biological sample. There are various options available for determining the antioxidant capacity in body fluids . The basic principle of all these methods is the same. The antioxidants contained in the biological sample protect a substrate from the oxidative attack induced by a radical. The length of time and the extent to which the sample prevents this oxidation can be determined and is usually compared to Trolox (water-soluble vitamin E derivative) or vitamin C as the standard. The longer it takes a substrate to oxidize , the higher its antioxidant capacity. The antioxidative capacity of lipid-soluble and water-soluble substances can be examined by means of various extractions . Often used tests are TRAP ( Total Peroxyl Radical-trapping Antioxidant Parameter ), ORAC ( Oxygen Radical Absorbance Capacity ), TEAC ( Trolox Equivalent Antioxidant Capacity ), FRAP ( Ferric Ion Reducing Antioxidant Power ) and PLC ( Photochemiluminescence ).

In 2010 the total antioxidant capacity of diet and supplements in adults was investigated in the USA . Databases from the US Department of Agriculture, data on dietary supplements and food consumption of 4,391 US adults aged 19 and over were evaluated. To convert the data on the intake of individual antioxidant compounds to TAC values, the measurement of the vitamin C equivalent (VCE) of 43 antioxidant nutrients was previously used. The daily TAC averaged 503.3 mg VCE / day, of which about 75 percent was taken in through food and 25 percent through dietary supplements.

Non-invasive measurement of antioxidants in humans

The high performance liquid chromatography is considered the gold standard for the determination of antioxidants. The analysis requires either blood samples or skin biopsies . It is therefore only partially suitable for analyzing short-term changes. For this reason, methods were developed with which antioxidants can be determined non-invasively by direct measurement on specific skin areas. Carotenoids are measured as the best biological marker for the consumption of fruit and vegetables.

An important method in this context is resonance Raman spectroscopy . In principle, it requires narrow-band light sources (mostly lasers ) for illumination. The light scattered back from the skin is broken down into its spectral components by a dispersive element (usually an optical grating ). While in the past measurements were made with laboratory devices, table-top devices are now also available.

Another method that has successfully measured antioxidants in humans is reflection spectroscopy . In contrast to resonance Raman spectroscopy, broadband light sources or LEDs are used to illuminate the skin . Overall, the outlay on equipment is lower, so that antioxidant scanners can also be implemented as hand-held devices, but their measurement results correlate very well with the results of resonance Raman spectroscopy.

Technical use

In the industry, antioxidants are used as additives ( additives needed) to the oxidative degradation of plastics to prevent, elastomers and adhesives. They also serve as stabilizers in fuels and lubricants . In fat-based cosmetics such as lipsticks and moisturizers, they prevent rancidity . In food they counteract changes in color and taste and also prevent fats from becoming rancid.

Although these additives are only required in very small doses, typically less than 0.5 percent, their type, quantity and purity drastically influence the physical parameters, processing, service life and often also the economy of the end products. Without the addition of antioxidants, many plastics would only survive for a short time. Most would not even exist at all, as many plastic items could not be manufactured without irreversible damage. The same is true of many other organic materials.

Plastics, fuels and lubricants

There are mainly sterically hindered amines ( hindered amine stabilizers , HAS) from the group of arylamines used and sterically hindered phenol derivatives , which are structurally often derived from butylhydroxytoluene (trade names Irganox , Ethanox , Isonox and others).

Feed

E number antioxidant Approved Use (Examples)
E324 Ethoxyquin Animal feed, in particular fish meal

Food, cosmetics, pharmaceuticals

Permissible antioxidants are regulated in Germany in the Additive Approval Ordinance and the Cosmetics Ordinance . Both natural and synthetic antioxidants are used.

Examples of antioxidant food additives are given in the table.

E number antioxidant Approved Use (Examples)
E220-E228 Sulfur dioxide and salts of sulphurous acid Dried fruits, wine
E300-E302, E304 Ascorbic acid (vitamin C), its salts and fatty acid esters Fruit juices, jams, dried milk products, oils and fats, canned fruit and vegetables, baked goods, fresh pasta, meat and fish products
E306-E309 Tocopherol and its esters vegetable fats and oils
E315, E316 Isoascorbic acid and sodium salt Meat and fish products
E310-E312 Gallate Frying oil and fat, lard, cake mixes, snacks, processed nuts, dry soups, sauces, etc.
E319 tert -butylhydroquinone (TBHQ)
E320 Butylated hydroxyanisole (BHA)
E321 Butylated hydroxytoluene (BHT)
E392 Rosemary extract
(effective ingredients especially carnosol and carnosic acid ) 		Fats, oils, baked goods, snack products, meat and fish products, sauces, etc.
E586 4-hexylresorcinol fresh and frozen crustaceans

Nordihydroguajaretic acid , a highly effective antioxidant for preserving fats and oils, has not been permitted as a food additive since 1968 due to its toxic effects on the liver , but it is still permitted in cosmetic preparations.

Antioxidant synergists commonly used in food technology and pharmaceutics include citric acid and its salts (E330 – E333), tartaric acid and its salts (E334 – E337), phosphoric acid and its salts (E338 – E343) and ethylenediaminetetraacetic acid (EDTA) and its salts (calcium EDTA, sodium disodium E385).

literature

Individual evidence

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  42. ↑ Implementing Regulation (EU) 2017/962 of the Commission of June 7, 2017 suspending the approval of ethoxyquin as a feed additive for all animal species and animal categories , accessed on November 24, 2019 . In: Official Journal of the European Union .
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