Phenolic antioxidants bioavailability

In search of novel natural antioxidant compounds that might posses a good brain bioavailability, our laboratory has focused attention on the phenolic compound ferulic acid ethyl ester (FAEE) (Fig. 18.1). Ferulic acid is a ubiquitous plant constituent that occurs primarily in seeds and leaves both in its free form and covalently linked to lignin and other biopolymers. Due to its phenolic nucleus and an extended side chain conjugation, it readily forms a resonance stabilized phenoxy radical that accounts for its potent antioxidant potential [Kanski et al., 2002 Kikuzaki et al., 2002], Ferulic acid has been shown to be protective against oxidative stress in vitro it is absorbed and excreted by humans, and may be a promising candidate for therapeutic intervention in AD [Yan et al., 2001]. Although ferulic acid has been demonstrated to be effective in vitro, the low lipophilicity impairs its in vivo efficiency, bioavailability, and stability. 

In conclusion, phenolic-rich fractions of oats possess an antioxidant capacity that can be assessed quantitatively through their ability to inhibit LDL oxidation and protein oxidation. The greatest degree of antioxidant capacity was associated with compounds extracted with methanol from the aleurone. The identification of the oat constituents from these fractions should be investigated, although candidate compounds include caffeic acid, ferulic acid, and avenanthramides. These compounds may be bioavailable and contribute to the health effects associated with dietary antioxidants and oats. 

Another important field of application concerns food and beverages, especially wine, juices, and tea (A2, A11, A17, B4, K12, V7, Yl). The antioxidant components of food include vitamin E (a-tocopherol), vitamin A (retinoids), vitamin C (ascorbic acid), and also fi-carotene (provitamin A), other carotenoids (of which more than 600 compounds have been identified), flavonoids, simple phenols, and glucobrasicins (H3). Unfortunately, the TAC value of a food is not informative on the bioavailability of its antioxidants. It has been estimated that polyphenols are normally present in blood plasma at concentrations of 0.2-2 //M (PI). However, it has been demonstrated that feeding rats a quercetin-augmented diet can increase their plasma levels of quercetin and its metabolites up to 10-100 //M (M27), and transient increases in the concentration of plant-derived phenolic compounds can take place after ingestion of food and beverages, which may affect blood plasma TAC (see later). 

The impact of plant products on the metabolism of synthetic dmgs results from the inhibition or activation of cytochrome P-450 (CYP) enzymes. Evaluation of the potential activation of CYP by administration of natural plant products or dietary supplements is important for prediction of interactions between their components and dmgs. Therefore, attention is directed to research on the impact of products available on the food market known as natural non-nutritive substances on dmg absorption. Non-nutritive dietary components are mainly secondary plant metabolites, which include, among others, phenolic compounds such as phenolic acids and flavonoids. The health effects of non-nutritive substances are not yet known. So far, there is no answer on the extent to which they are absorbed and metabolized by the body, and there is no information on the permitted daily intake for these compounds. This information is particularly important because certain non-nutritive natural substances are simultaneously considered to be anti-nutritional factors, mainly because they inhibit digestion and reduce the bioavailability of nutrients or dmgs. It is also possible that they form undesirable interactions with dmgs. The positive health effects of non-nutritive natural substances are not only attributed to their antioxidant properties. These substances are involved in various metabolic... 

In vitro studies have pointed to the antioxidant activity of many fruit and vegetable phenolics. To ascertain whether these substances play a real role in the prevention of oxidative-originated diseases in vivo, other considerations should be taken into account. We review epidemiological studies on the correlation between the dietary intake of phenolics and the prevention of cardiovascular disease. In addition, we look at studies on phenolic bioavailability and metabolism, which indicate whether fruit and vegetable antioxidants that show activity in vitro are absorbed and may, therefore, have an antioxidant effect in the tissues and so help prevent atherosclerosis [137]. 

It is also essential to consider how food is ingested, and the possible effect of combinations of different products. The effect of food proteins on the absorption, bioavailability and in vivo antioxidant activity of fruit and vegetable phenolics may be as important as it was in the case of tea [143]. 

Almond is a nutrition-dense food providing a spectrum of macro- and micronutrients. Moreover, it is an excellent source of bioavailable phytochemicals that are believed to possess health promotion potentials. Among these phenolic compounds, including phenolic acids and flavonoids, which are the major antioxidant active substances in almond. Other components such as tocopherols and terpenoids also make contribution to the antioxidant activity of almond. The health benefits of almond have been explored. Almond appears to be effective in reducing the risk of heart disease and cancer prevention, and consumption of ahnond is reconunended by FDA for better health conditions. 

Cashew nut and its coproducts provide a complex food rich in macronutrients and micronutrients, as well as small quantities of various antioxidants and bioactive compounds that are relevant to many health beneficial attributes. These bioactive compounds include MUFA, PUFA, phenolics, phytosterols, phytostanols, tocopherols, and phytates. While benefits of cashew nut and its coproducts for human health appear promising, further research on bioavailability and bioaccessibility of cashew bioactive compounds as well as potential allergenic reaction is required for a better understanding of the role of cashew nut and its coproducts in human health. 

Del Rio D, Rodriguez-Mateos A, Spencer JPE, Tognolini M, Borges G, Crozier A. Dietary (Poly)phenolics in human health structures, bioavailability, and evidence of protective effects against chronic diseases. Antioxid Redox Signal. 2013 18(14) 1818—1892. 

Vissers MN (2004) Bioavailability and antioxidant effects of olive oil phenols in humans a review. Eur J Clin Nutr 58 955-965... 

Weinhrenner, T., Fito, M., Fane-Albaladejo, M. et al. (2004). Bioavailability of phenolic compounds liom oUve oil and oxidative/antioxidant status at postprandial state in healthy humans. Drugs tender Experimental and Clinical Research, 30, 207-212. 

Another line of investigation is bridging polyphenol activity with NO bioavailability via the chemical reduction of nitrite to NO (Takahama et al, 2002 Peri et al, 2005 Gago et al, 2007). The redox properties that have been proposed to confer polyphenols with antioxidant activity by quenching oxidizing radicals may, alternately, endow the phenolic compounds with the capacity to promote the formation of NO from nitrite, particularly in the gastrointestinal tract, a location where both nitrite and polyphenols achieve high concentrations. 

In this chapter, the phenolic composition and content of regularly consumed fruits and vegetables are extensively discussed through the analysis of the current relevant literature, in order to provide a comprehensive summary of the current compositional and quantitative data on some flavonoid-rich foods. Furthermore, the formal relation of the in vitro antioxidant potential of these fruits and vegetables to the quality of the phenolic and, to a lesser extent, vitamin C content is emphasized. The potential for antioxidant activity of flavonoid-rich fruits and vegetables in vivo is also discussed. The data described here allow identification of the potentially most effective fruits and vegetables in terms of phenolic content and antioxidant activity. However, much research is still needed the elucidation of the metabolism and bioavailability of flavonoids in vivo, as well as of the amounts and the forms in which they are taken up into cells and tissues, is cmcial in order to establish the mechanisms and the forms in which dietary phenolics may act in vivo [58]. Finally, it... 

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