A team led by Gary Manners of the USDA-ARS Processed Foods Research Unit at the Western Regional Research Center in California is embarking on the first human study of the effects of limonin glucoside on cholesterol levels.
Manners told NutraIngredients-USA.com that, if the hoped for results are achieved, they could "represent a very nice potential to add to other fruit drinks a natural compound that provides the ability to provide some cholesterol-lowering effect".
For example, if limonin glucoside were added to a berry drink, the consumer would benefit from both the antioxidant effects of the berries and the cholesterol-lowering effects of limonin glucoside.
Tasteless, soluble limonin glucoside is the most abundant of the oxygenated triterpenoid compounds known as limonoid glucosides that are found in citrus fruits. It is present in orange juice at levels equivalent to vitamin C.
Tests with animals and human cells carried out by Manners and others suggest that pure limonin glucoside may possess significant anti-tumor properties. It can be extracted from the by-products of citrus processing in large quantities.
The first stage of the research is expected to commence at the beginning of May and run until the end of June. The purpose of this pilot is to ascertain the levels of the compound to be used in the study and observe any toxicity, which Manners said is more a matter of protocol than likelihood.
"Based on studies done so far, there is no toxicity in these compounds at reasonable levels. They have been fed to animals at 3 percent of their diet," he said.
The major part of the study will commence towards the end of this year, after a consolidation period of a few months. The results will be published in a peer review journal, said Manners.
It will also look at the anti-inflammatory effects of limonin glucoside - an area for which there is no prior evidence but which Manners believes to be worthy of investigation.
As for limonin glucoside, investigation of this citrus compound has occupied Manners for some years now. Its cholesterol-lowering properties have already been observed in animals, and lab tests carried out in 2002 showed that human liver cells exposed to limonin glucoside produced less of the apo B compound associated with higher tests.
In June 2003 Manners published the findings of a study showing the extended bioavailability of limonin glucoside in the Journal of Agriculture and Food Chemistry.
For this experiment 16 healthy men and women drank a dose of pure limonin glucoside dissolved in 4 ounces of water. Doses ranged from one eighth to one teaspoon, that is, between four and 30 times the level of limonoid glucosides in a glass of orange juice.
The researchers looked at the levels of limonin - a byproduct of limonin glucoside - in blood samples taken from the participants three, six, 12 and 24 hours after the dose was administered.
Limonin was found to be present in the blood plasma of all but one of the participants, with the highest concentration present after six hours. In five of the participants limonin was still present after 24 hours, indicating a longer bioavailability than other natural compounds.