Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/2/2003
Publication Date: 6/3/2003
Citation: Manners, G.D., Jacob, R.A., Breksa III, A.P., Hasegawa, S., Schoch, T.K. 2003. Bioavailability of citrus limonoids in humans. Journal of Agricultural and Food Chemistry, Vol 51, p. 4156-4161. Interpretive Summary: Limonoid glucosides are water-soluble triterpenoid compounds that occur naturally in citrus fruit and citrus juice in amounts comparable to vitamin C and can be reclaimed from citrus processing by-products in large quantities. Limonin glucoside is the most abundant of the limonoid glucosides in citrus. Pure limonin glucoside and limonin, its water insoluble relative lacking glucose, have been found to possess significant anti-tumor properties in animal tests and with human cells. In this study pure limonin glucoside was administered to four groups of human subjects in concentrations ranging from 4 to 30 times the level of total limonoid glucosides present in orange juice. Blood samples were drawn from the study subjects periodically over a 24-hour period and plasma samples prepared from the blood were analyzed from the presence of limonin, the limonoid produced through the removal of the glucose from limonin glucoside. Analysis results showed the presence of limonin at low levels in all by one subject consuming limonin glucoside, with the greatest amount occurring six hours after consumption. A second compound with identical spectral properties to limonin was also detected in slightly higher amounts in the plasma of subjects one to three hours after consuming the higher doses of limonin glucoside. The detection of limonin in the plasma of the test subjects establishes that low levels of citrus limonoids with anti-tumor properties are naturally available to humans who consume citrus fruit and citrus juice. The lack of any detrimental health effects among any of the test subjects consuming limonin glucoside solutions suggest limonoid glucosides obtained from citrus processing by-products may find important application as nutraceuticals or food fortification agents directed to improving human health and nutrition.
Technical Abstract: Citrus limonoids occur in significant quantities in citrus fruit and juice as water-soluble limonoid glucosides. They have demonstrated significant anti-tumor activity in animal and cancer cell screens. In this study we examined the plasma of four groups of four healthy male and female subjects (nine women and seven men, 19-51 y) administered high doses (0.25, 0.50, 1.0 and 2.0 g) of pure limonin glucoside for the presence of the limonoid aglycone limonin to establish the absorption, metabolism and bioavailability of citrus limonoids to humans. LC-MS analysis of the plasma of the study subjects revealed increasing amounts of limonin associated with administered dose in 0.25, 0.5 and 1.0 g subject groups in mean maximum concentration amounts ranging from 1.75 nmol/L to 6.85 nmol/L. The highest administered dos (2.0 g) displayed a limonin mean maximum concentration of 6.87 nmol/L. The time to maximum concentration was 6 h in 13 of 16 subjects. A second compound with MS/MS characteristics identical to limonin was detected in amounts of 1.63 and 7.43 nmol/L for the 1.0 and 2.0 g doses and his hypothesized to be a limonin epimer. Post study health evaluation established no ill effects among study subjects consuming high doses of limonin glucoside. This study represents the first confirmation of the absorption, metabolism and bioavailability of limonoids in humans and establishes that citrus limonoids may play an important role in the benefits of citrus to human health and nutrition.