The ingredients created by PL Thomas include Appol, an extract of apples providing 5 percent quercetin, 5 percent phloredizin and 5 percent caffeoylquinic acids. The non-GMO product has been standardized to provide 50 percent total apple polyphenols, according to the company.
PotentOnion, meanwhile is a standardized extract of onions providing 30 percent quercetin in the bioavailable glycosylated form.
"The product provides 50 percent total polyphenols using a patented process which preserves the polyphenols due to the inhibition of oxidation," said the company.
PLT added that it also offers quercetin from more traditional sources, including Fava D'Anta Beans and Sophora Japonica Flowers.
A raft of recent science has uncovered the role polyphenols can play in preventing the onset of various diseases, notably certain cancers and cardiovascular disease, that annually kills 17 million people in the world.
Earlier this month, a study carried out by Cornell University found that brain cells treated with the apple antioxidant quercetin had significantly less damage than those treated with vitamin C or not exposed to antioxidants.
"On the basis of serving size, fresh apples have some of the highest levels of quercetin when compared to other fruits and vegetables and may be among the best food choices for fighting Alzheimer's," said study leader C.Y. Lee, professor and chairman of the department of Food Science & Technology at Cornell University.
He cautioned that protection against Alzheimer's using any food product is currently theoretical and added that genetics and environment are also believed to play a role in the disease.
But "eating at least one fresh apple a day might help", said Lee.
Results so far are limited to cell studies and more advanced research, particularly in animals, is still needed to confirm the findings. But Lee and his associates have also shown that apples may help protect against cancer.
For the current study, scheduled to appear in the 1 December issue of the Journal of Agricultural and Food Chemistry, the researchers exposed groups of isolated rat brain cells to varying concentrations of either quercetin or vitamin C.
The cells were then exposed to hydrogen peroxide to simulate the type of oxidative cell damage that is believed to occur with Alzheimer's. These results were then compared to brain cells that were similarly exposed to hydrogen peroxide but were not pre-treated with antioxidants.
Brain cells that were treated with quercetin had significantly less damage to both cellular proteins and DNA than the cells treated with vitamin C and the cells that were not exposed to antioxidants. This demonstrates quercetin's stronger protective effect against neurotoxicity, according to the researchers.
Scientists are not sure of quercetin's mechanism of action, but some suspect it might work by blocking the action of free radicals, an excess of which are thought to damage brain cells as well as other cell types over time. Further studies are however needed.
Other foods containing high levels of quercetin include onions, which have some of the highest levels of quercetin among vegetables, as well as berries, particularly blueberries and cranberries.