Bioavailability of the flavanone naringenin and its glycosides in rats.

Naringenin, the predominant flavanone in grapefruit, mainly occurs as glycosides such as naringenin-7- rhamnoglucoside or naringenin-7-glucoside. This study compared kinetics of absorption of naringenin and its glycosides in rats either after a single flavanone-containing meal or after adaptation to a diet for 14 days. Regardless of the diet, circulating metabolites were glucurono- and sulfoconjugated derivatives of naringenin. The kinetics of absorption of naringenin and naringenin-7-glucoside were similar, whereas naringenin-7-rhamnoglucoside exhibited a delay in its intestinal absorption, resulting in decreased bioavailability. After naringenin-7-glucoside feeding, no glucoside was found in the cecum. However, after feeding naringenin-7-rhamnoglucoside, some naringenin-7-rhamnoglucoside accumulated in cecum before being hydrolyzed by intestinal microflora. Adaptation to flavanone diets did not induce accumulation of plasma naringenin. Moreover, flavanone cecal content markedly decreased after adaptation, and almost no naringenin-7-rhamnoglucoside was recovered after naringenin-7-rhamnoglucoside feeding, suggesting that an adaptation of cecal microflora had occurred. Overall, these data indicate that flavanones are efficiently absorbed after feeding to rats and that their bioavailability is related to their glycosidic moiety.

Comparison of the bioavailability of quercetin and catechin in rats.

Quercetin and catechin are present in noticeable amounts in human diet and these polyphenolic compounds are supposed to exert beneficial effects on human health. However, their metabolic fates in the organism have never been compared. In the present study, rats were fed a 0.25% quercetin or a 0.25% catechin diet. Quercetin and catechin metabolites were analyzed in plasma and liver samples by high-performance liquid chromatography coupled to an ultraviolet or a multielectrode coulometric detection. All plasma metabolites were present as conjugated forms, but catechin metabolites were mainly constituted by glucuronidated derivatives, whereas quercetin metabolites were sulfo- and glucurono-sulfo conjugates. Quercetin was more intensively methylated than catechin in plasma. The plasma quercetin metabolites are well maintained during the postabsorptive period (approximately 50 microM), whereas the concentration of catechin metabolites dropped dramatically between 12- and 24-h after an experimental meal (from 38.0 to 4.5 microM). In the liver, the concentrations of quercetin and catechin derivatives were lower than in plasma, and no accumulation was observed when the rats were adapted for 14 d to the supplemented diets. The hepatic metabolites were intensively methylated (90-95%), but in contrast to plasma, some free aglycones could be detected. Thus, it clearly appears that studies dealing with the biological impact of these polyphenols should take into account the feature of their bioavailability, particularly the fact that their circulating metabolites are conjugated derivatives.

Quercetin is recovered in human plasma as conjugated derivatives which retain antioxidant properties.

Quercetin is one of the most abundant flavonoids in the human diet. This study aimed to determine the plasma concentrations of quercetin in 10 healthy volunteers after the consumption of a complex meal rich in plant products. Quercetin was determined in plasma (2 h before, and 3, 7 and 20 h after the meal), and in a duplicated portion of the meal by HPLC analysis with an electrochemical detection. The amount of ingested quercetin was estimated to be 87 mg. Before the meal, quercetin concentration in hydrolyzed plasmas ranged from 28 to 142 nM. A marked increase was observed 3 h after the meal in all subjects, with a mean concentration of 373 nM (S.E.M. = 61). After 7 h, quercetin concentration in hydrolyzed plasmas decreased and after 20 h basal levels were found again. The antioxidant capacities of quercetin, 3'-O-methylquercetin, and of some of their conjugated derivatives were compared by the measurement of the conjugated dienes resulting from the Cu2+-induced oxidation of human LDL. 3'-O-Methylquercetin and conjugated derivatives of quercetin significantly prolonged the lag phase, but the magnitude of their effect was about half that of the aglycone.

Bioavailability of rutin and quercetin in rats.

Quercetin is a powerful antioxidant which is widely distributed in edible plants, mainly as glycosides such as rutin. It has been reported to be absorbed in mammals, but its metabolism needs further investigation to evaluate its possible physiological effects. We compared the evolution of the absorption of quercetin and rutin in rats fed with supplemented diets. Rutin was absorbed more slowly than quercetin because it must be hydrolysed by the cecal microflora, whereas quercetin was absorbed from the small intestine. Conjugated derivatives of quercetin, and its methylated forms isorhamnetin and tamarixetin, were recovered in plasma from rats receiving the two kinds of experimental diets after the first meal, but after 10 days, no traces of tamarixetin were detected anymore. The rate of elimination of quercetin metabolites seems very low, and high plasma concentrations are easily maintained with a regular supply of quercetin or rutin in the diet.

Quercetin metabolites in plasma of rats fed diets containing rutin or quercetin.

We studied the bioavailability and the plasma transport of flavonols in rats fed quercetin or rutin diets. Wistar rats were fed one of the following purified diets for 10 d: control; 16.4 or 8.2 mmol rutin/kg diet; or 16.4, 8.2 or 4.1 mmol quercetin/kg diet. Flavonol concentrations were determined in plasma, ileal and cecal contents, and feces. In rats fed diets containing 16.4 mmol quercetin or rutin/kg, the concentration of circulating flavonols was approximately 115 mumol/L. Quercetin or rutin administration resulted in similar concentrations of quercetin in cecal contents. By HPLC analysis and beta-glucuronidase/sulfatase treatment, plasma flavonols have been identified as conjugated quercetin itself, or a conjugated form (4.5-fold as abundant) of an aglycone less polar than quercetin. Rats fed quercetin or rutin diets had a green/yellow-colored plasma that exhibited a peak absorbance at 411 nm, vs. 363 or 375 nm for pure rutin or quercetin solutions, respectively. This shift of band I absorption was obtained when pure quercetin was in the presence of albumin or added to a plasma fraction. The bathochromic properties of flavonoids in the presence of albumin are highly dependent on the presence of the C-2/C-3 double bond on the C-ring and are influenced by the degree of B-ring hydroxylation. The existence of intermolecular bonds between albumin and quercetin is supported by in vitro absorbance and fluorescence studies. With human albumin, the fluorescence intensity and the shift of quercetin absorbance increased in parallel to the albumin/quercetin molar ratio. Conjugated diene formation, resulting from Cu(2+)-catalyzed oxidation of human LDL or rat VLDL+LDL was effectively inhibited in vitro by 0.5 mumol/L quercetin. These results show that dietary flavonols are recovered in rat plasma as conjugated metabolites in non-negligible concentrations, and that these flavonols may be interesting antioxidant micronutrients with a variety of biological effects.

Microbiological conversions of solamargine.

A strain of Aspergillus ochraceus, a microorganism classically used for bioconversions of the steroid nucleus, was tested on solasodine glucosides. It induced specific modifications to the oside chain of the solamargine molecule, without modifying the genin nucleus. These modifications depended on the composition of the culture medium and the aeration, and led under certain conditions to a single isomer of the secondary glucoside beta 2-solamargine or Khasianine: o-alpha-L-rhamnopyranosyl-(1-->4 glu)-O-(3)-beta-D-glucopyranosyl solasodine.

Densitometry for analysis of protein and peptide hydrolysates: application to luteinizing hormone releasing hormone.

Densitometric analysis has been performed on various standard protein and peptide solutions and on luteinizing hormone releasing hormone hydrolysate. After thin-layer chromatographic separation using two-dimensional separation on cellulose plates, the plates were mapped and each amino acid was assayed individually in order to obtain a specific integration profile of the hydrolysate. Densitometry proved to be a useful method for the screening of protein hydrolysates and is accurate enough for the assay of peptide hydrolysates. The hormone was hydrolysed with hydrochloric acid-trifluoroacetic acid (1:1, v/v) in the presence of thioglycolic acid. This limits the loss of tryptophan and does not interfere with the analysis. Results were sufficiently reliable, accurate and reproducible for routine analysis.

High-yield ethanol production from Jerusalem artichoke tubers.

Fermentation conditions were optimized for the production of ethanol from Jerusalem artichoke with a strain of Saccharomyces cerevisiae able to use high-concentration juice and undiluted pulp. Yields (95 to 125 g ethanol/l=85 to 98% of the theoretical value) exceeded those obtained with strain of Kluyveromyces used classically.

[Antienzymatic activities of two Leguminosae: bean pods and bean bulls. Antiamylase activity]. / Activités antienzymatiques chez deux Légumineuses: la cosse de Haricot et la cuticule de Fève. Activité antiamylasique.

Amylase inhibitory activities have been sought in the powders of Phaseolus vulgaris pods and of Vicia faba bean hulls. Unlike to the bean, Phaseolus vulgaris pod has no amylase inhibitory activity and the presence of tannin could not be determined. Contrary, Vicia faba bean hull shows an obvious amylase inhibitory activity. It contains an appreciable content of tannins which may be responsible of this activity. The quantities of amylase whose are inhibited increase in some measure with the quantities of enzyme added. They are not in direct ratio to the quantities of extract, then, inhibition may be of no competitive type.

[Enzyme inhibitory activities of two Leguminosae: Phaseolus vulgaris L. pods and Vicia faba L. hulls. Trypsin inhibitory activity]. / Activités antienzymatiques chez deux Légumineuses: la cosse de Haricot et la cuticule de Fève. Activité antitrypsine.

Trypsin inhibitory activities of Phaseolus vulgaris L. pods and Vicia faba L. bean hulls have been studied according to the extraction conditions of the powder: solvent pattern, temperature and pH. The two vegetal powders have a trypsin inhibitory activity quite similar, weak but appreciable. The trypsin inhibitor of Phaseolus vulgaris L. pods is thermosensitive but stable at low pH. Inversely the Vicia faba L. bean hulls one is thermostable but it feels low pH.

[Isolation of solasonine from glucoalkaloid mixtures by fungal fermentation.]. / Isolement par voie fermentaire de la solasonine a partir d'un melange de glucoalcaloides.

A strain of Aspergillus niger grown on a medium containing 60% of Solamargine and 40% of Solasonine was able to hydrolyse selectively Solamargine. It was thus possible to extract pure Solasonine. Different parameters influencing the speed of hydrolysis of the Solamargine were examined.