Antioxidants consumption

The calculated AH, A, and k values are summarized in Table 15.16. It can be seen that, normally, the rate constants of these reactions are low, however, at elevated temperatures (500 K and above) the rate of antioxidant consumption by reaction (11) can noticeably increase. 

Terao, J., Yamaguchi, S., Shirai, M., Miyoshi, M., Moon, J.H., Oshima, S., Inakuma, T., Tsushida, T., and Kato, Y., Protection by quercetin and quercetin 3-0-p-D-glucuronide of perox-ynitrite-induced antioxidant consumption in human plasma low-density lipoprotein. Free Radic. 

It may be anticipated that the antioxidant consumption during use leads to a shorter remaining life-time and that it is necessary to add more. Recycled plastics suffer from the consequences of degradation during processing and first-life application. This leads to the introduction of new functional groups, which in particular for oxidisable polymers such as PE, enhance the sensitivity of the recyclate to thermal- and photo-degradation. With the formation of new pro-oxidative moieties, a substantial part of the stabilisers are simultaneously consumed [14]. 

The changes in mechanical properties due to degradation and/or blending, contamination, antioxidant consumption and general use (e.g. oxidation processes) of the polymeric material during first service life are some of the characteristics that determine if the material should be recycled mechanically or disposed of in another way (e.g. energy recovery). A successful recycling is strictly dependent on the purity and uniformity of the plastic waste. 

Although phospholipid bilayers are better mimics of biomembranes than are micelles, there are few reliable quantitative data on flavonoid antioxidant activities in lipid bilayers. Terao and coworkers compared the antioxidant efficiency of quercetin and catechins (epicatechin and epicatechin gallate) with that of a-Toc in egg yolk PC liposomes using initiation by the water-soluble initiator, ABAP, and analysis of hydroperoxide formation and antioxidant consumption by HPLC. Based on the length of the induction periods and the profile of suppressed hydroperoxide formation, they concluded that quercetin and the catechins were more efficient antioxidants than a-Toc in these bilayers. Apparently the unique behavior of a-Toc in bUayers is responsible for these results (vide supra). In hexane and alcohols solution during suppressed peroxidation of methyl linoleate, the relative antioxidant activities reversed so that the flavonoids were 5-20 times less active... 

It is precisely by decomposition of the hydroperoxide and deceleration of the antioxidant consumption that the effect of mutual intensification of the effectiveness, observed in mixtures of 2,6-di-tert-octyl-4-methylphenol with didecyl sulfide is explained. Each of these inhibitors of oxidation, taken individually, only negligibly lengthens the induction period. In a mixture, on the other hand, they are capable of lengtheniag the induction period in the oxidation of polypropylene to 450 min at 200°C and an oxygen pressure of 300 mm Hg (Fig. 25). 

The stabilizing activity of phenols is based on scavenging of the alkyl-peroxy radicals (POO ) generated in oxidizing polymers. Participation of POO in the oxidation chain transfer is thus reduced. Reactivity of phenolics with POO results, however, in chemical transformation of the original phenolic structure (antioxidant consumption). Hence, the protection of the polymer matrix is diminished in stepwise fashion. Crossconjugated dienoide compounds, e.g. quinone methides, account... 

Dependences of antioxidants consumption in Formulations No 1, No 2 and No 4 are presented in Figure 3. The eontent of phenol antioxidant in Formulations No 1 and No 2 is identical. The difference is that Formulation No 1 represents a synergetic mixture of two phenol antioxidants (PhAO+SPhAO) while Formulation No 2 contains only PhAO 2. The results received show that eonsumption of phenol antioxidants in Formulation No 1 is quieker than in Formulation No 2. 

In conclusion, berries and herbs contain large numbers of flavonoids and phenolics with antioxidant properties. Different flavonoids and phenolics contribute to antioxidant activity depending on their chemical structure and concentration. This study revealed that berries and herbs are effective potential sources of natural antioxidants. Consumption of berry crops and herbs indeed is beneficial to our health. The relevance of this information to the human diet is summarized by Rice-Evans and Miller (i) who state that total antioxidant potential of fruits and vegetables is more important than levels of any individual specific antioxidant constituent. Therefore, supplementing fhiits, vegetables and herbs with a balanced diet should have beneficial health effects. 

Monochlorobenzene. The largest use of monochlorobenzene in the United States is in the production of nitrochlorobenzenes, both ortho and para, which are separated and used as intermediates for mbber chemicals, antioxidants (qv), dye and pigment intermediates, agriculture products, and pharmaceuticals (Table 5). Since the mid-1980s, there have been substantial exports of both o-nitrochlorobenzene, estimated at 7.7 million kg to Europe and -nitrochlorobenzene, estimated at 9.5 million kg to the Far East. Solvent use of monochlorobenzene accounted for about 28% of the U.S. consumption. This appHcation involves solvents for herbicide production and the solvent for diphenylmethane diisocyanate manufacture and other chemical intermediates. 

In the last few decades, several epidemiological studies have shown that a dietary intake of foods rich in natural antioxidants correlates with reduced risk of coronary heart disease particularly, a negative association between consumption of polyphenol-rich foods and cardiovascular diseases has been demonstrated. This association has been partially explained on the basis of the fact that polyphenols interrupt lipid peroxidation induced by reactive oxygen species (ROS). A large body of studies has shown that oxidative modification of the low-density fraction of lipoprotein (LDL) is implicated... 

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. 

Therefore depending upon the conditions used to simulate either in vitro or in vivo oxidation, catechins or other phenolic compounds display differences in their antioxidant properties. Catechins also limited the consumption of a-tocopherol, allowing it to act as a scavenger within cell membranes whilst the catechins scavenged aqueous peroxyl radicals near the membrane surface (Pietta and Simonetti, 1998). 

In addition to the effects on blood lipids, it has been suggested that soy consumption has a beneficial action on arterial function and improves antioxidant status (Lichtenstein, 1998 and refs therein). Genistein and daidzein were shown to have antioxidant properties in vitro (Kerry and Abbey, 1998), to enhance endothelium-dependent vasodilation and to reduce the development of atherosclerosis in monkeys (Honore et al, 1997 Wagner et al, 1997). 

In the water-like solvent tert-butyl alcohol, a-tocopherol was found to prevent lipid oxidation, showing a distinct lag-phase for oxygen consumption. This was in contrast to quercetin or epicatechin, which were only weak retarders of lipid oxidation without any clear antioxidative effect. Quercetin or epicatechin, when combined with a-tocopherol, increased the lag-phase for oxygen consumption as seen for a-tocopherol alone. The stoichiometric factor for a-tocopherol, a-TOH, as chain-breaking antioxidant has the value n = 2 according to the well-established mechanism ... 

In the Unites States, the daily intake of 3-carotene is around 2 mg/day Several epidemiological studies have reported that consumption of carotenoid-rich foods is associated with reduced risks of certain chronic diseases such as cancers, cardiovascular disease, and age-related macular degeneration. These preventive effects of carotenoids may be related to their major function as vitamin A precursors and/or their actions as antioxidants, modulators of the immune response, and inducers of gap-junction communications. Not all carotenoids exert similar protective effects against specific diseases. By reason of the potential use of carotenoids as natural food colorants and/or for their health-promoting effects, research has focused on better understanding how they are absorbed by and metabolized in the human body. 

Cyanidin is the most common anthocyanin in foods. In addition, anthocyanins are stabilized by the formation of complexes with other flavonoids (co-pigmentation). In the United States, the daily anthocyanin consumption is estimated at about 200 mg. Several promising studies have reported that consumption of anthocyanin-rich foods is associated with reductions of the risks of cancers - and atherosclerosis and with preventive effects against age-related neuronal and behavioral declines. These beneficial effects of anthocyanins might be related to their reported biological actions such as modulators of immune response and as antioxidants. Knowledge of anthocyanin bioavailability and metabolism is thus essential to better understand their positive health effects. 

Betalains have shown strong antioxidant activities in biological environments such as membranes and LDLs," -" suggesting that the consumption of betalain-colored foods may exert protective effects against certain oxidative stress-related diseases (i.e., cancers) in humans. Beetroot has been used as a treatment for cancer in Europe for several centuries. The high content of betanin in red beetroot (300 to 600 mg/kg) may be the explanation for the purported cancer chemopreventive effects of beets. 

Results obtained in in vivo and ex vivo experiments are of various types. Some studies have found positive effects of the consumption of carotenoids or foods containing carotenoids on the markers of in vivo oxidative stress, even in smokers. Other studies demonstrated no effects of carotenoid ingestion on oxidative stress biomarkers of lipid peroxidation. " It should be noted that for studies using food, the activity observed may also be partly due to other antioxidant molecules in the food (phenols, antioxidant vitamins) or to the combination of actions of all the antioxidants in the food. 

Esterbauer et al. (1991) have demonstrated that /3-carotene becomes an effective antioxidant after the depletion of vitamin E. Our studies of LDL isolated from matched rheumatoid serum and synovial fluid demonstrate a depletion of /8-carotene (Section 2.2.2.2). Oncley et al. (1952) stated that the progressive changes in the absorption spectra of LDL were correlated with the autooxidation of constituent fatty acids, the auto-oxidation being the most likely cause of carotenoid degradation. The observation that /3-carotene levels in synovial fluid LDL are lower than those of matched plasma LDL (Section 2.2.2) is interesting in that /3-carotene functions as the most effective antioxidant under conditions of low fOi (Burton and Traber, 1990). As discussed above (Section 2.1.3), the rheumatoid joint is both hypoxic and acidotic. We have also found that the concentration of vitamin E is markedly diminished in synovial fluid from inflamed joints when compared to matched plasma samples (Fairburn etal., 1992). This difference could not be accounted for by the lower concentrations of lipids and lipoproteins within synovial fluid. The low levels of both vitamin E and /3-carotene in rheumatoid synovial fluid are consistent with the consumption of lipid-soluble antioxidants within the arthritic joint due to their role in terminating the process of lipid peroxidation (Fairburn et al., 1992). 

Other dietary factors implicated in prostate cancer include retinol, carotenoids, lycopene, and vitamin D consumption.5,6 Retinol, or vitamin A, intake, especially in men older than age 70, is correlated with an increased risk of prostate cancer, whereas intake of its precursor, [3-carotene, has a protective or neutral effect. Lycopene, obtained primarily from tomatoes, decreases the risk of prostate cancer in small cohort studies. The antioxidant vitamin E also may decrease the risk of prostate cancer. Men who developed prostate cancer in one cohort study had lower levels of l,25(OH)2-vitamin D than matched controls, although a prospective study did not support this.2 Clearly, dietary risk factors require further evaluation, but because fat and vitamins are modifiable risk factors, dietary intervention may be promising in prostate cancer prevention. 

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