Phenolic compounds bioavailability

There is growing evidence from human feeding studies that the absorption and bioavailability and thus bioactivity of phenolic compounds and flavonoids are very much dependent on the nature of their chemical structure. Their chemical classification and dietary occurrence is briefly discussed in the following section. 

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. 

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 uptake if iron often requires Fe(II) as the bioavailable form, and uptake from soils containing insoluble Fe(III) is accomplished by phenolic compounds which are exuded by certain plants (Chaney and Bell, 1987). A particular use of staining has been in the study of the sites if iron reduction in plants, using Prussian blue stain (PB) (Ambler et al., 1971 Brown and Ambler, 1974). The method consists of placing the roots in a nutrient solution containing Fe(III) and ferricyanide. Since PB can be produced both from Fe(III) and Fe(CN)64 and from Fe(II) and Fe(CN)63, reduction of either source of iron in the presence of the roots will produce PB at the sites of... 

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... 

Karakaya, S., Bioavailability of phenolic compounds. Crit. Revs. Food ScL Nutr., 44,453-464, 2004. 

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. 

Dietary fat appears to enhance the absorption of polyphenol flavonoids, which may explain why the phenolic compounds in olive oil are especially bioavailable. Pectin, a type of fiber found in apples, appears to enhance the bioavailability of an abundant polyphenol known as quercetin. Finally, there appears to be significant individual genetic variability in the ability of individuals to produce the active metabolites of some phenols. Whether this can be overcome has yet to be established. Until more is known about the complex factors involved with the bioavailability of these powerful plant-based health-promoting compounds, your best bet is to consume them as food, not supplements, in as fresh a form as possible, and to limit the use of processing and cooking methods like boiling or frying. 

Fruits and vegetables are excellent sources of phenolic compounds, which are widely recognized for their health benefits. Therefore, it is necessary to establish and consolidate phenolic compound databases in these matrices because these compounds are of importance to develop epidemiological studies, and their bioavailability should be deeply understood. 

Phenolic compounds are widely distributed in plant parts from the roots to the seeds and include phenolic acids, flavo-noids and tannins. The tannins may reduce protein digestibility (Ford and Hewitt, 1979) and perhaps the bioavailability of other nutrients. The flavonoids have been reported to have a number of nutritional and pharmacological activities (Kuhnau, 1976). Phenolic acids include benzoic and cinnamic acid derivatives. The benzoic acid derivatives include p-hydroxy-benzoic, protochate-chuic, vanillic, gallic and syringic acids. The cinnamic acids, p-coumaric, caffeic, ferulic and sinapic are found in most oilseeds used to prepare protein concentrates and frequently occur in the form of esters with quinic acid or sugars. Chlorogenic acid for example is an ester of caffeic acid and quinic acid and is found in several isomeric and derivatized forms. 

Bioavailability, that is, the availability of the bioactive compounds at the cellular level to an organism when consumed, is one of the major factors which govern the effectiveness of different bioactive compounds. Bioavailability is affected by various factors which have been discussed in different reviews [8, 9]. It has been observed that sometimes either the pure form of a polyphenol is more helpful or combinations of some particular polyphenols are more effective. Hence, extraction of the bioactive compounds with efficient processes, proper separation with least losses, and encapsulation with appropriate methods are required. For all the studies related to bioactive compounds such as polyphenols, including characterization, quantification, or biomedical in vivo or in vitro studies, extraction is the fundamental method which can be divided into the various steps, mainly preparation, extraction, separation, and purification [10]. This chapter concentrates on the phenols and properties of phenol which affect the extraction efficiency. Other factors affecting the extraction efficiency have also been discussed along with the different methods of extraction. Different methods of separatirni applied for the polyphenols have also been discussed. 

In that context, the present chapter gives insights into the relevance of phenolic compounds in human nutrition. We will primarily discuss bioavailability and biological properties of isoflavones and lignans in the context of human health and disease, our main focus being the metabolic activities of intestinal bacteria. 

With the demonstration of the intraluminal stability of OL in human gastric and small-intestinal contents [219] and cmisidering their high bioavailability, attempts to enrich the olive oil with isolated/purified phenolic compounds are in progress [220]. 

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. 

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