Antioxidants are substances present in small amounts compared to the substrate susceptible to oxidation (lipids, proteins, carbohydrates, DNA), inhibit or completely prevent their oxidation. polyphenolic compoundsinclude, along with alpha-tocopherol and beta-carotene, a group neenzimskih antioxidants. It is believed that the antioxidant activity of polyphenol compounds, primarily the result of their ability to be donors of hydrogen, which arise after the less reactive radicals fenoksil. The relatively high stability of radicals is explained fenoksil delocalisation of electrons in the presence of several resonance forms.
It is believed that the antioxidant potential of many species of plants can be attributed to the polyphenolic compounds. Plant polyphenols are not always find the right antioxidants, but in many in vitro studies demonstrated the antioxidant potential of phenolic substances in the water phase, „skevendţing“ radicals, and boost resistance to low density lipoprotein oxidation, indicating pathogenesis of coronary disease in the case.
Polyphenolic compounds exhibit antioxidant activity in biological systems in several ways:
surrender of H – atoms, direct binding („capture“) of free oxygen radicals and nitrogen;
- heliranjem prooksidativnih metal ions (Fe 2 +, Cu 2 +, Zn 2 + and Mg 2 +);
- activation of antioxidant enzymes;
- prooksidativnih inhibition of enzymes (lipoksigenaza, NAD (P) H oxidase, xanthine oxidase, oxidase, enzymes cytochrome P-450).
With the increase in molecular weight polyphenol antioxidant activity decreases.
The last time flavonoids attracted special attention because of the extraordinary scientific community and antiradikalske antioxidant activity. Studies have shown that flavonoids are good „traps“ and free radicals play an important role in the pharmaceutical and food industries. The protective effect of these compounds demonstrated in vitro and ex vivo. They inhibit the oxidation of lipids, which in biological systems associated with the occurrence of chronic diseases and aging cells. Flavonoids inhibit some enzymatic systems, react with the radical peroksil as vitamin E, thereby ending autooksidaciju unsaturated fatty acids.
Antioxidant activity of polyphenols, flavonoids and thus, depends on their structure. Flavonoids inhibit the enzymes responsible for the formation of superoxide anion radicals such as xanthine oxidase and protein kinase C, but inhibit cikloksigenazu, lipoksigenazu, mikrozomalnu monoksigenazu and glutathione S-transferase, mitochondrial sukcin oxidase, NADH oxidase, thus preventing the formation of reactive oxygen species. Flavonoids show antioxidant activity in both hydrophilic and in lipophilic systems. Thanks to the lower redox potential (0.23 to 0.75 V) flavonoids may reduce free radicals (R *), which have a higher redox potential (2.13 to 1.0 V) such as superoxide anion radical, peroksil, alkoksil, hydroxyl radical , paying a hydrogen atom. flavonoids have a wide range of other biochemical functions . Known as the synergistic effects of the antioxidant activity of flavonoids. Flavonoids under conditions of oxidative stress can act prooksidativno, so instead of „capture“, can form free radicals.
Cells of aerobic organisms are constantly exposed to the effects prooksidativnih species, a result of this action is the destruction of DNA, proteins and lipids.
Free radicals are atoms, ions or molecules that have one or more unpaired electrons in its structure, which are the cause of their high reactivity and non-selective. Free radicals occur:
- electromagnetic radiation;
- redox reactions;
- enzymatic reactions;
- chemical processes.
Are among the most reactive chemical species, but also neradikalski forms, which are oxidative agents and is easily converted into radicals. Most free radicals, easily succumb to the monomolecular decomposition reactions bimolekularnim. They can be positive (radical cation) and negatively charged (radical anion). Unpaired electron can be placed on the atoms of different elements, so that free radicals are divided into free radicals of oxygen, chlorine, nitrogen and so on. Reactive species are divided into:
- slobodnoradikalske reactive;
- neradikalske (oxidizing agent, which can easily turn into free radicals).
Reactive free radicals can occur many reactions that are reduced to four basic types: thermolysis, photolysis, oxidation-reduction processes and high-energy radiation. The formation of toxic forms of oxygen and other free radicals in balance with antioxidant defense system of the organism, and can be induced by various endogenous (prooksidativni enzyme systems, the process of cellular respiration, phagocytosis, etc.) and exogenous (radiation, contaminated air, etc.) factors . The state of the balance between antioxidants prooksidanata and moved to the side proksidanata, called oxidative stress . Oxidative stress causes oxidative damage to biomolecules and primary occurrence of many diseases such as atherosclerosis, cancer, cardiovascular disease, asthma, arthritis, gastritis, dermatitis, diabetes, liver disease, kidney disease, inflammatory processes, Alzheimer’s disease, Parkinson’s disease, etc. . Oxidative stress causes damage to the primary biomolecules: proteins, lipids, nucleic acids and carbohydrates, which can cause a range of disorders in the metabolism and cause dysfunction and cell death .
Free radicals and other reactive forms of oxygen, which include a peroxide radical anion, hydroxyl radical, hidroperoksidni radical, hydrogen peroxide and lipid peroxide radicals, and was mentioned recently and the surrounding endogenous and ozone, are involved in many disease processes, such as: asthma , tumors, cardiovascular disease, cataracts, diabetes, gastrointestinal inflammatory disease, liver disease, macular degeneration, periodontal disease and others. Oxidants and radicals cause aging of cells, mutagenesis, carcinogenesis and coronary heart disease by destabilizing membranes, DNA damage and oxidation of low density lipoprotein (LDL). Reactive oxygen species arise as products of biochemical processes in the body, but also as a result of the increased exposure to xenobiotics. Free radicals are highly reactive and can damage the lipid membrane and form ugljemikov radical, which reacts with oxygen to form peroxide radicals, then continue to enter into reaction with fatty acids stvarajći new carbon radicals. Because of these chain reactions products are formed peroksidacijski lipids, which means that a radical can damage the molecules in many biological systems.
In order to prevent chain reactions of free radicals in the body apply to various defense mechanisms including antioxidant enzymes, proteins, antioxidants and flavonoids as free radical trap. The importance of antioxidants in the diet and their value in preventing cardiovascular disease in recent times especially interesting. To a function of quality flavonoid antioxidants, must fulfill two conditions:
- present in low concentrations in relation to the matter subject to oxidation should slow down or prevent the oxidation;
- radical derived from flavonoids must be stable so as not to initiate a chain reaction.
The main structural features of flavonoids for the ability to capture important radicals are:
- o-dihidroksilna (kateholna) structure in the B-ring, which provides stability and allows delokalizaciju radical electron;
- 2,3-double bond in conjugation with 4-keto group to delokalizaciju electrons from the B-ring;
- hydroxyl group at position 3 – and 5 – provide a link with the hydrogen-keto group.
Radicals can be stabilized:
- delocalisation of electrons;
- creation of intramolecular hydrogen bonds;
- further reaction with another lipid radical.
The positive effects and increased antioxidant activity of flavonoids may be due to their interactions with other physiological antioxidants-vitamin C or vitamin E. Ascorbic acid protects from oxidative degeneration of polyphenol. The antioxidant activity (AO) is most frequently measured TEAC-value (Trolox equivalent antioxidant activity), which is defined as mmol / dm 3 concentration of solution in water soluble analog of vitamin E, troloxa (6-hydroxy-2, 5,7,8 – tetrametilkroman-2-carboxylic acid) equivalent antioxidant activity as well as 1 mmol dm -3solution of the tested flavonoids. Antiradikalska activity (AR) of flavonoids is determined by their ability to react with specific radicals, for example. measuring the inking of a stable 1,1-diphenyl-2-pikrilhidrazilnog radical (DPPH).
The ability of monomeric phenols act as antioxidants depends on the degree of conjugation, number and distribution susptitueneta (functional group) and molecular weight.
Antioxidant activity of phenolic acids is important for the stability of food, as well as in defense mechanisms of biological systems. Monohydric benzoic acids are very weak antioxidants, except for m-hydroxybenzoic acid. Activity increases significantly in dihidroksilnih substituted acids, which antioksidativan answer depends on the position of the hydroxyl groups in the ring. Gallic acid is the best antioxidant of all hidroksibenzoevih acid. Antioxidant activity of phenolic acids is related to the substituents and their position on the aromatic ring structure and side-string. The presence of CH = CH-COOH groups of the hydroxy acid derivatives cimetne the reason for the significantly higher antioxidant activity than COOH groups of the hydroxy derivatives of benzoic acid. A number of hydroxyl groups and metoksilnih phenol ring increases antioxidant activity, such as. acid in tea. Studied the activity of individual antiradikalska phenolic acids. It has been shown that the presence metoksilne group ortho position to the phenolic ring significantly increases the activity antiradikalske superoxide anion and DPPH radicals, but not hydroxyl radicals.
Research has found that polymeric polyphenols or tannins have a higher antioxidant activity compared to the simple monomeric phenols and have little, or not to have pro-oxidative activity, while many small phenolic molecules pro-oxidant.
Measured the total antioxidant activity of different portions of fruit and vegetables and potatoes are surprisingly highly positioned. Based on the total antioxidant capacity in the list of 20 kinds of fruits and vegetables, potatoes are classified in 18 place (as measured by the portion of boiled potato 299 g). Interestingly, the red beans on the list first (portion of 92 g), followed by blueberries (portion of 144 g), cranberry (portion of 95 g), artichoke (portion of 84 g).