Polyphenols, antioxidant compounds

Because of the easily oxidizable structure of the polyphenols previously described, many studies have been published about the enzymatic degradation of these antioxidant compounds. This chapter exhaustively reviews the main publications concerning the degradation of this type of antioxidant compound by several enzymes. 

This method is also used to measure ex vivo low-density lipoprotein (LDL) oxidation. LDL is isolated fresh from blood samples, oxidation is initiated by Cu(II) or AAPH, and peroxidation of the lipid components is followed at 234 nm for conjugated dienes (Prior and others 2005). In this specific case the procedure can be used to assess the interaction of certain antioxidant compounds, such as vitamin E, carotenoids, and retinyl stearate, exerting a protective effect on LDL (Esterbauer and others 1989). Hence, Viana and others (1996) studied the in vitro antioxidative effects of an extract rich in flavonoids. Similarly, Pearson and others (1999) assessed the ability of compounds in apple juices and extracts from fresh apple to protect LDL. Wang and Goodman (1999) examined the antioxidant properties of 26 common dietary phenolic agents in an ex vivo LDL oxidation model. Salleh and others (2002) screened 12 edible plant extracts rich in polyphenols for their potential to inhibit oxidation of LDL in vitro. Gongalves and others (2004) observed that phenolic extracts from cherry inhibited LDL oxidation in vitro in a dose-dependent manner. Yildirin and others (2007) demonstrated that grapes inhibited oxidation of human LDL at a level comparable to wine. Coinu and others (2007) studied the antioxidant properties of extracts obtained from artichoke leaves and outer bracts measured on human oxidized LDL. Milde and others (2007) showed that many phenolics, as well as carotenoids, enhance resistance to LDL oxidation. 

Some non-enzymatic antioxidants play a key role in these defense mechanisms. These are often vitamins (A, C, E, K), minerals (zinc, selenium), caretenoids, organosulfur compounds, allyl sulfide, indoles, antioxidant cofactors (coenzyme Qio)> and polyphenols (flavonoids and phenolic acids) [1,37]. Further, there is good evidence that bilirubin and uric acid can act as antioxidants to help neutralize certain free radicals [38]. Alpha-carotene, lycopene, lutein, and zeaxanthine [39] can be considered subgroups of carotenoids [40] that are effective antioxidant compounds. 

Other Phenolic Antioxidative Compounds from Plants Higher plants are rich in a myriad of phenolic compounds in their secondary metabolite pool. Among these, phenolic acids and polyphenolic derivatives are found to be the most important series of hydrophilic-hydrophobic antioxidative compounds naturally present. In foods, these polyphenolic compounds act as radical scavengers... 

Be wary of such supposed benefits of ORAC none of these statements is supported by science. Remember that other than for the ACE vitamins, a physiological response or benefit of supposed antioxidant compounds such as polyphenols from fruits or juice has not been adequately shown by expert-validated science. 

There is good evidence that our bodies react to antioxidant compounds such as polyphenols as foreign and unwanted in high quantities, so the body actively metabolizes and excretes them, leaving behind only small amounts—about 3 percent—of the total amount ingested. Also, the concentration of polyphenols remaining in the body hours after a meal is tens to hundreds of times lower than the amount first tested in the lab to determine ORAC, making the lab measurement irrelevant in the human body. 

Antioxidant effects Polyphenols MaiUard compounds Ascorbic acid Preedy (2009)... 

Despite the copious evolution of phenol and water during processing, Narmco s commercial adhesive system (Imidite 850) was based on prepolymer 28 mixed with aluminium powder, inorganic arsenic compounds such as arsenic thioarsen-ate or arsenic pentasulphide, and sterically hindered polyphenol antioxidant. Adhesive tapes were manufactured hy hot-melt deposition of this mixture on a 112-type glass cloth carrier used in conjunction with a heat-resistant primer (polybenzimidazole or polyimide). As with all other heat resistant polymers, surface preparation of flat and honeycomb metal surfaces is an important factor in... 

Moreover, apart from these main components, grapes contain secondary metabolites such as flavonoid and non-flavonoid phenolic compounds, sesquiterpenes, and melatonin. Most of the grape s medicinal value can be attributed to its seed and skin, which researchers have found to be rich in nutritional value due to the presence of polyphenolic antioxidants. At least 500 different types of antioxidants have been found in various parts of this fruit [4]. 

The study of the toxicity of several polyphenolic antioxidants, including alkyl gal-lates, toward human promyelocytic leukemia cells (HL-60) has shown that the polyphenol cytotoxicity may be related to their prooxidant properties since, as indicated above, the same polyphenol compounds could behave as both antioxidants and prooxidants, depending on concentration and free radical source [39]. Polyphenols may act as substrates for peroxidases and other metalloenzymes, yielding quinone- or quinomethide-type prooxidant and/or alkylating products. Another characteristic of the action of polyphenols is that their cytotoxicity increases upon an increase in their lipophilicity. Thus, the concentration of gallic acid, BG and OG for 50% survival of HL-60 cells (IC50) is 750, 110, and 30 pM, respectively. 

Com oil contains natural antioxidants such as tocols, carotenoids and polyphenols. These compounds prevent protein oxidation, lipid peroxidation (Figure 7) and reactive oxygen species formation. 

Dietary consumption of polyphenols is associated with a lower risk of degenerative diseases. In particular, protection of serum lipids from oxidation, which is a major step in the development of arteriosclerosis, has been demonstrated. More recently, new avenues have been explored in the capacity of polyphenols to interact with the expression of the human genetic potential. The understanding of the interaction between this heterogeneous class of compounds and cellular responses, due either to their ability to interplay in the cellular antioxidant network or directly to affect gene expression, has increased. 

Green tea consists of a wealth of simple phenolics (monomers), whereas black tea provides more complex polyphenols (dimers and polymers). It was found that with lipids the simple compounds were more effective antioxidants, while under aqueous conditions, polymers tended to have more activity. Weisburger (2001) suggested that polymers formed from a 2-5 unit polymerisation state seemed to be optimal, probably because the monomer is metabolised and excreted too rapidly, whereas the higher 6-10 unit polymers may suffer from difficulty in penetrating cellular membranes and be poorly absorbed. 

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