http://www.dietcan.net/docs/Polifenoles%20en%20alimentos%20y%20biodisponibilidad.pdf

Polyphenols: food sources and bioavailability

Flavonoids are a class of secondary plant phenolics with significant antioxidant and chelating properties. In the human diet, they are most concentrated in fruits, vegetables, wines, teas and cocoa. Their cardioprotective effects stem from the ability to inhibit lipid peroxidation, chelate redox-active metals, and attenuate other processes involving reactive oxygen species. Flavonoids occur in foods primarily as glycosides and polymers that are degraded to variable extents in the digestive tract. Although metabolism of these compounds remains elusive, enteric absorption occurs sufficiently to reduce plasma indices of oxidant status. The propensity of a flavonoid to inhibit free-radical mediated events is governed by its chemical structure. Since these compounds are based on the flavan nucleus, the number, positions, and types of substitutions influence radical scavenging and chelating activity. The diversity and multiple mechanisms of flavonoid action, together with the numerous methods of initiation, detection and measurement of oxidative processes in vitro and in vivo offer plausible explanations for existing discrepancies in structure-activity relationships. Despite some inconsistent lines of evidence, several structure-activity relationships are well established in vitro. Multiple hydroxyl groups confer upon the molecule substantial antioxidant, chelating and prooxidant activity. Methoxy groups introduce unfavorable steric effects and increase lipophilicity and membrane partitioning. A double bond and carbonyl function in the heterocycle or polymerization of the nuclear structure increases activity by affording a more stable flavonoid radical through conjugation and electron delocalization. Further investigation of the metabolism of these phytochemicals is justified to extend structure-activity relationships (SAR) to preventive and therapeutic nutritional strategies.

Flavonoid antioxidants: chemistry, metabolism and structure-activity relationships.

The main dietary sources of polyphenols are reviewed, and the daily intake is calculated for a given diet containing some common fruits, vegetables and beverages. Phenolic acids account for about one third of the total intake and flavonoids account for the remaining two thirds. The most abundant flavonoids in the diet are flavanols (catechins plus proanthocyanidins), anthocyanins and their oxidation products. The main polyphenol dietary sources are fruit and beverages (fruit juice, wine, tea, coffee, chocolate and beer) and, to a lesser extent vegetables, dry legumes and cereals. The total intake is approximately 1 g/d. Large uncertainties remain due to the lack of comprehensive data on the content of some of the main polyphenol classes in food. Bioavailability studies in humans are discussed. The maximum concentration in plasma rarely exceeds 1 microM after the consumption of 10-100 mg of a single phenolic compound. However, the total plasma phenol concentration is probably higher due to the presence of metabolites formed in the body's tissues or by the colonic microflora. These metabolites are still largely unknown and not accounted for. Both chemical and biochemical factors that affect the absorption and metabolism of polyphenols are reviewed, with particular emphasis on flavonoid glycosides. A better understanding of these factors is essential to explain the large variations in bioavailability observed among polyphenols and among individuals.

Dietary Intake and Bioavailability of Polyphenols

The biochemistry and medical significance of the flavonoids.

Health effects of quercetin: from antioxidant to nutraceutical.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/S0014-5793%2898%2901101-6

Deglycosylation of flavonoid and isoflavonoid glycosides by human small intestine and liver β-glucosidase activity

‘Hairy root’ cultures of Beta vulgaris and Nicotiana rustica were established after roots were induced on plants following infection with Agrobacterium rhizogenes. The transformed cultures of B. vulgaris and N. rustica synthesised their characteristic secondary products, the betalain pigments and nicotine alkaloids respectively, at levels comparable with those of in vivo roots from the same variety. Betalains were entirely retained inside the root tissue. In contrast, a proportion of the nicotine alkaloids was secreted into the medium. The potential of this type of ‘in vitro’ plant tissue culture for the production of valuable plant secondary products is identified and confirmed.

Secondary product formation by cultures of Beta vulgaris and Nicotiana rustica transformed with Agrobacterium rhizogenes.

'Hairy root' cultures of DATURA STRAMONIUM were established following infection of aseptic leaves with AGROBACTERIUM RHIZOGENES. Transformation was confirmed by Southern blotting using [ (32)P]-labelled fragments of the T-DNA as probes. The transformed cultures grew in the absence of added phytohormones and cell mass increased 55-fold during 28 days incubation. Hyoscyamine was a major component of the alkaloid fraction and accounted for at least 0.3% of the dry matter, comparable to pot-grown plants from which the cultures were initiated. Production of hyoscyamine followed growth during the first 15 days of incubation, but continued to increase during the early part of stationary phase. The alkaloid was retained almost entirely in the root tissue. The effects of medium composition and pH on growth and hyoscyamine production are reported.

Production of Hyoscyamine by 'Hairy Root' Cultures of Datura stramonium.

Transformed roots of Catharanthus roseus were obtained following infection of detached leaves with Agrobacterium rhizogenes. Roots would not grow in full strength Gamborg's B5 medium but would grow satisfactorily if the medium was diluted to one half strength. Little alkaloid appeared in the growth medium but root tissue contained a high level and wide variety of alkaloids. Ajmalicine, serpentine, vindolinine and catharanthine were prominent components. Vinblastine could also be detected by a combination of HPLC and radioimmunoassay, though at a level of only 0.05μg/g dry weight.

Alkaloid production by transformed root cultures of Catharanthus roseus.

The production of nicotine by cultures ofNicotiana rustica transformed withAgrobacterium rhizogenes has been examined in a packed bed fermenter as a two-stage batch/continuous-flow system. A substantial proportion of the nicotine synthesised in the batch phase may be subsequently harvested from the medium. The possibility of improving product recovery using macroreticular adsorbents is considered.

M. J. C. Rhodes

Papers

Deglycosylation of flavonoid and isoflavonoid glycosides by human small intestine and liver β-glucosidase activity

Secondary product formation by cultures of Beta vulgaris and Nicotiana rustica transformed with Agrobacterium rhizogenes.

Production of Hyoscyamine by 'Hairy Root' Cultures of Datura stramonium.

Alkaloid production by transformed root cultures of Catharanthus roseus.

Nicotine production by hairy root cultures of Nicotiana rustica: fermentation and product recovery