Bioavailability of phytochemicals

Holst, B. and Williamson, G. 2004. Methods to study bioavailability of phytochemicals. In Phytochemicals in health and disease, ed. R. Fenwick, 25-56. New York Marcel Dekker. 

Before considering the bioavailability of phytochemicals in a food matrix and relating these to biological effects in humans, it is important and necessary to understand that phytochemicals are mostly minor plant constituents whose concentration varies considerably according to, for example, seasonal and agronomic factors, the variety, age, and part of the plant examined. Such variability can lead to serious problems of interpretation of results from epidemiologal studies or human intervention trials if the dose of the phytochemical applied is not determined. 

The ubiquitous flavonoids may be cited as an example of the manifold factors affecting the bioavailability of phytochemicals thus, the bioavailability of flavonoids differs between food sources, predominantly due to the nature of the attached sugar(s). The chemical structure (glycoside or aglycone) of a phytochemical will affect intestinal absorption and first-pass metabolism and will, therefore, modulate its pharmacokinetics [4,6]. 

In summarizing the current knowledge on host factors, it must be stressed that only limited and insufficient data are available on how host factors influence LADME and thus bioavailability of phytochemicals. It is unclear to what extent and how such parameters should be considered. From the perspective of the efficacy and risk assessment, more knowledge is certainly needed to allow identi-fication of subpopulations at particular risk, who would benefit from appropriate dietary advice or treatment. 

Numerous methods have been proposed to study the individual processes of LADME as well as the final systemic bioavailability of phytochemicals as a result of LADME. Most have originated from the pharmaceutical research/new drug development sector, but may be applied and optimized for phytochemical studies. The absorption and metabolism of phytochemicals share similar principles and metabolic pathways (common transport systems) as drugs. The major points that should be borne in mind when extending such studies to phytochemicals are ... 

Semalty A, Semalty M, Rawat MSM, Franceschi F. Supramolecular phospholipids-polyphenolics interactions The PHYTOSOME strategy to improve the bioavailability of phytochemicals. Fitoterapia. juill 2010 81(5) 306-314. 

FIGURE 36.12 Molecular modeling of the interaction between a polyphenolic molecule and a phospholipid. (Reprinted from Fitoterapia, 81(5), Semalty, A., Semalty, M., Rawat, M.S.M., and Franceschi, F., Supramolecular phospholipids-polyphenolics interactions The PHYTOSOME strategy to improve the bioavailability of phytochemicals, 306-314. Copyright 2010, with permission from Elsevier.)... 

Fermentation often increases the bioavailability of phytochemicals by releasing the esterifled compounds to free form. Only the free and conjugated phenolic acid forms were found to be bio-accessible (Patel, 2012). Oboh, Ademiluyi, and Akindahunsi... 

The levels and bioavailability of phytochemicals in plant foods such as legumes, cereals, vegetables, herbs and fraits can be greatly affected by processing such as fermentation. This subsequently leads to increased antioxidant properties, which may be benehcial for treatment and/or prevention of diseases such as atherosclerosis and cancer. Thus fermentation, especially with probiotics (functional microbes), can serve as an important process not only for preservation but also for production of functional foods with enhanced bioactive and antioxidant properties. 

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