Though the similar-sounding names of these limonoids may be confusing,
their positive impact on our health is becoming clearer with every experiment.
In some individuals, limonin remains in the bloodstream for up to 24
hoursan impressive length of timeManners and colleagues
found. This longevity, or persistence, may help explain some limonoids'
ability to fight cancer cells, which, if not continuously suppressed,
The findings are good news for people who like oranges and the other
appetizing citrus fruits rich in limonoids. The world's citrus-juice
processors could also benefit; they could extract an estimated 300,000
pounds of these chemicals from peels, seeds, and other processing leftovers
Today, those leftovers, called citrus molasses, are sold as a low-cost
ingredient in cattle feed. But thanks to a patented, ARS-developed process,
these chemicals can be extracted from citrus molasses and used to fortify
foods or beverages.
Test Targets Limonin Glucoside
For the bioavailability experiment, 16 healthy men and women volunteers
downed a dose of pure limonin glucoside. The compound, a white, tasteless,
odorless powder, was dissolved in about 4 ounces of water. Doses ranged
from about one-eighth to one teaspoon. That's equal to the amount in
seven glasses of orange juice.
The participants gave blood samples before they drank the beverage
and 3, 6, 12, and 24 hours afterwards. To avoid skewing test results,
they didn't eat or drink any citrus products for 3 days before and 3
days after taking part in the study.
The scientists looked for traces of limoninthe limonin glucoside
byproduct or metabolitein the volunteers' blood plasma. The laboratory
procedure that the researchers used, liquid chromatography-mass spectrometry,
can detect very small amounts of limonin.
Limonin showed up in the plasma of all volunteers except one. For most
volunteers, the concentration was highest within 6 hours after they
drank the special beverage. Five volunteers still had traces of limonin
after 24 hours. That's an indication of the compound's staying power,
an important consideration, especially if limonin glucoside were to
be used as a pharmaceutical, for example.
In contrast, some natural compounds are bioavailable for shorter periods
and have to be taken more than just once a day. An example: the good-for-you
phenols in green tea last only 4 to 6 hours.
In this study, Manners collaborated with Andrew P. Breksa III of the
Western Regional Research Center; Thomas S. Schooch, formerly of the
center; retired ARS chemist Shin Hasegawa, a pioneering investigator
of these citrus biochemicals; and Robert A. Jacob, formerly a chemist
with the ARS Western Human Nutrition Research Center in Davis, California,
and now retired. The group published their findings in a 2003 issue
of the Journal of Agricultural and Food Chemistry. The Florida
Department of Citrus helped fund the work.
Can Limonin Lower Cholesterol?
There's more to come from the California team. Manners and Breksa,
along with chemist Darshan S. Kelley and molecular biologist Susan J.
Zuninoboth of the Davis nutrition centerare gearing up for
a first-of-its-kind study of the cholesterol-lowering effects of limonin.
In 2000, Manners, Hasegawa, and their Canadian co-authors reported
that limonin may be among the citrus-juice compounds that lower cholesterol.
In lab tests, they found that human liver cells produced less apo Ba
compound associated with higher cholesterol levelswhen exposed
Preliminary results of the new cholesterol study are expected later
this year. This investigation may provide more details about the health
advantages of citrus and greater incentive for us to enjoy these sunny,
delectable fruits and juices even more often.By Marcia
Wood, Agricultural Research Service Information Staff.
This research is part of Quality and Utilization of Agricultural
Products (#306) and Human Nutrition (#107), two ARS National Programs
described on the World Wide Web at www.nps.ars.usda.gov.
Gary D. Manners and Andrew
P. Breksa III are in the USDA-ARS Processed
Foods Research Unit, Western Regional Research Center, 800 Buchanan
St., Albany, CA 94710; phone (510) 559-5813, fax (510) 559-5849.
Darshan S. Kelley and
Susan J. Zunino are with
the USDA-ARS Western Human Nutrition
Research Center, One Shields Ave., Davis, CA 95616; phone (530)
752-5138 [Kelley], (530) 752-5156 [Zunino], fax (530) 752-5271.
"Citrus Compound: Ready To Help Your Body!" was published
in the February
2005 issue of Agricultural Research magazine.