Absorption, metabolism and excretion of flavanones from single portions of orange fruit and juice and effects of anthropometric variables and contraceptive pill use on flavanone excretion.

Oranges are rich sources of flavonoids that are bioactive and may protect against age-related diseases. The absorption of orange flavanones may be affected by factors such as processing and subject anthropometric variables, and the bioactivity of the absorbed phytochemicals depends on how they are metabolised during absorption. In a randomised cross-over study, twenty subjects consumed a single portion of orange fruit (150 g) or juice (300 g) that contained the flavanones narirutin and hesperidin, and an additional 109 subjects across a broad age range (18-80 years) consumed the juice. Flavanone metabolites were measured in regularly collected samples of plasma and urine. After consumption of fruit or juice, flavanone conjugates, but not the aglycones, were detected in plasma and urine. The flavanone conjugates were shown to include the 7- and 4'-O-monoglucuronides of naringenin, the 7- and 3'-O-monoglucuronides of hesperetin, two hesperetin diglucuronides and a hesperetin sulfo-glucuronide, but no aglycones or rutinosides. Analysis of the plasma pharmacokinetic and urinary excretion data on a dose-adjusted basis indicated no difference in absorption or excretion of either flavanone between the fruit and juice matrices. In the extended urinary excretion dataset the individual variation was very large (range 0-59 % urinary yield). There was a small but significant (P < 0.05) decrease in the excretion of hesperetin (but not naringenin) with increasing age (P < 0.05), but the effects of sex, BMI and contraceptive pill use were shown not to be associated with the variation in flavanone excretion.

Urinary excretion of strawberry anthocyanins is dose dependent for physiological oral doses of fresh fruit.

There is considerable interest in coloured fruits and berries as sources of biologically active anthocyanins. To examine the relationship between the oral dose and the amount excreted for anthocyanins from a food source across a physiological range of doses, volunteers were fed, in random order, four portions (100-400 g) of fresh strawberries as part of a standard breakfast. Urine was collected at 2 h intervals up to 8 h, and for the period 8-24 h. Fresh strawberries contained pelargonidin-3-glucoside as the major anthocyanin with smaller amounts of cyanidin-3-glucoside and pelargonidin-3-rutinoside. Anthocyanins were detected in the urine of all volunteers for all doses, predominantly as pelargonidin glucuronide and sulphate metabolites. There was a strong, linear relationship between oral dose and anthocyanin excretion (Pearson's product moment correlation coefficient = 0.692, p < 0.001, n = 40) which indicated that on an average, every additional unit of dose caused 0.0166 units of excretion. Within individuals, dose -- excretion data fitted a linear regression model (median R(2) = 0.93). We conclude that strawberry anthocyanins are partially bioavailable in humans with a linear relationship between oral dose and urinary excretion for doses up to 400 g fresh fruit.

Processing blackcurrants dramatically reduces the content and does not enhance the urinary yield of anthocyanins in human subjects.

Blackcurrant (BC) fruits are a rich source of biologically active anthocyanins but little is known of the anthocyanin content of commonly consumed BC products or how processing affects the absorption. We report that whereas fresh and frozen whole BC were a rich source of anthocyanins, containing 897 and 642mg (100gFW)(-1) of total anthocyanins the levels in all other products were substantially lower (0.05-10.3% of the levels in fresh fruit). Further, when the absorption and excretion of BC was assessed in volunteers consuming a portion (100g) of frozen whole BC (642mg total anthocyanins) and, 300g of a BC drink made by diluting concentrated syrup (33.6mg total anthocyanins), only small quantities of BC anthocyanins were excreted in urine (fruit, 0.053±0.022%; drink, 0.036±0.043%; mean percent urinary yield±SD) and they were not detected in plasma. These data indicate that fresh and frozen BC, but not processed products, are rich sources of anthocyanins but, regardless of the food source, these anthocyanins are poorly bioavailable.

Kinetics of gastro-intestinal transit and carotenoid absorption and disposal in ileostomy volunteers fed spinach meals.

BACKGROUND: Reports of low carotenoid absorption from food sources has undermined their postulated 'protective' role as one of the active agents in diets rich in vegetable matter. AIM OF THE STUDY: This study quantified beta-carotene and lutein absorption from a representative green vegetable with different degrees of processing, using both mass balance and metabolic modelling of triglyceride-rich lipoprotein plasma fraction (TRL) response. METHODS: Whole or chopped-leaf cooked spinach was fed to volunteers (n = 7, paired) with vegetable oil (40 g) in yoghurt. Blood and ileal effluent samples were collected for up to 24 h. Effluent and TRL samples were analysed for lutein and beta-carotene by HPLC. A digesta transit model was used to describe meal transit and a single compartment model used to predict percentage absorption from the plasma TRL response. RESULTS: Mass balance showed 25% of lutein and beta-carotene were absorbed from chopped spinach, compared with 25% beta-carotene and 40 % lutein from whole-leaf spinach. Increased lutein absorption correlated to slower gastrointestinal (GI) transit for the whole-leaf meal. An area under the curve (AUC) response for the TRL fraction, found in 50% of cases, was not confined to those with the greatest percentage absorption. Absorption by mass balance and TRL AUC indicate a half-life of newly absorbed carotenoid around 11 min CONCLUSION: GI residence time appears to have an effect on the absorption of lutein but not beta-carotene. Rapid clearance is probably the main reason for absence of measurable plasma concentration excursions. Lack of plasma response cannot be interpreted as lack of carotenoid absorption without knowledge of the absorption and disposal kinetics.

Temperature-dependent binding of monoclonal antibodies to C hordein.

The consensus octapeptide repeat motif of the barley seed storage protein C hordein, Pro-Gln-Gln-Pro-Phe-Pro-Gln-Gln, forms the epitope of two anti-prolamin monoclonal antibodies (Mabs), IFRN 0061 and 0614. The Mabs were found to exhibit unusual temperature-dependent binding characteristics, recognising C hordein and a peptide corresponding to the consensus repeat at 5 degrees C but not at 37 degrees C, as determined by enzyme-linked immunosorbent assay (ELISA). The K(d) of IFRN 0614 for the consensus peptide was found to be 1.2x10(12) mol(-1) at 12 degrees C, but no constant could be calculated at 37 degrees C due to a lack of binding. Similar ELISA binding characteristics were observed with an anti-C hordein polyclonal antiserum and a Mab raised to the consensus peptide. Circular dichroism (CD) and Fourier-transform infrared (FTIR) spectroscopy showed that the protein and the consensus peptide exist in a temperature-dependent equilibrium of poly-L-proline II type structures and beta-turn conformations. Whilst thermodynamic and kinetic effects may reduce antibody binding at higher temperatures, they cannot account for the complete loss of Mab recognition at higher temperatures. It seems likely that the Mabs preferentially recognise the Pro-Gln-Gln-Pro-Phe-Pro-Gln-Gln motif when presented in a conformation which may correspond to the poly-L-proline II type conformation which dominates the CD and FTIR spectra at 4-12 degrees C.