The urinary tract benefits of cranberry may be better delivered as a juice than as a powder, according to a new study that indicates the mechanism are more complex than first thought.
According to findings published in Food Science and Biotechnology, cranberry juice was more effective at preventing the formation of an E. coli biofilm than proanthocyanidins or PACs, a group of flavonoids found in cranberries and linked to its urinary tract benefits.
Sexually active adult women with recurring UTIs are the most likely to reap benefits from regular doses of cranberry juice. Researchers have noted up to a 50 percent drop in infection rates among that group.
"While the mechanisms of action of cranberry products on bacterial adhesion and biofilm formation are not fully understood, this study indicates that beneficial effects of cranberry can be achieved by long-term exposure or growth of bacteria in cranberry constituents," wrote researchers from Worcester Polytechnic Institute (WPI) in Massachusetts.
"This study also shows that cranberry juice is better at inhibiting biofilm formation than isolated A-type cranberry flavonoids and PACs, although the reasons for this are not yet clear."
The preventive effect of cranberry juice appears to be dose-dependent. On that finding, researchers have already launched a larger study that will involve many more subjects and compare several different doses of juice.
Commenting independently on the research, Amy Howell, PhD, associate research scientist at Rutgers University and well-known cranberry researcher told NutraIngredients-USA that the study's conclusions are misleading because the "study was not looking at bacterial adhesion (which is strongly inhibited by PACs), but rather at biofilm formationâ€¦a completely different phenomenon. Further, biofilm formation is not a necessary step in the pathogenesis of UTI."
"The underlying major methodology flaw with the study is that there will never be a time when biofilms will be in contact with actual cranberry juice or intact PACs.
"The authors should have collected urine from people who had consumed cranberry juice and incubated the biofilm system in that."
In 2004 France became the first country to approve a health claim for the North American cranberry (Vaccinium macrocarpon) with at least 36mg of proanthocyanidins (PAC) to "help reduce the adhesion of certain E. coli bacteria to the urinary tract walls", and subsequently fight UTIs, a condition that will affect over 50 percent of women at least once in their lifetime.
PACs are not exclusive to cranberries, and can be found in a range of foods, including green tea, grapes, apples, and chocolate. However, the main type of PACs in cranberry called A-type PACs are different from those in these other sources, called B-type PACs. Only cranberry PACs may prevent bacterial adhesion.
The French health claim refers to 36 milligrams of PACs measured using the 4-dimethylaminocinnamaldehyde (DMAC) method. The 500 milligram dose used in the new study reportedly confers the same level of ex vivo urinary anti-adhesion activity against uropathogenic E. coli over a 24-hour period as 300 ml of Cranberry Juice Cocktail containing 36 mg proanthocyanidins.
The WPI researchers incubated two different strains of E. coli in the presence of two different mixtures of commercially available cranberry juice cocktail (Ocean Spray Cranberries). The bacteria were also incubated in the presence of PACs (also from Ocean Spray Cranberries).
Discussing the importance of the biofilm, the researchers note that E. coli is covered with small hair-like projections known as fimbriae that act like hooks and latch onto cells that line the urinary tract. When sufficient numbers of the bacteria adhere to cells, they form a biofilm.
Results of the study showed that, while the juice cultures completely prevented biofilm formation, the PACs showed only limited ability to reduce biofilm formation, and only after extended exposure to the E. coli.
"What we have shown is that cranberry juice's ability to prevent biofilms is more complex than we may have originally thought," said Terri Camesano, professor of chemical engineering at WPI and senior author on the paper.
However, Rutgers' Dr Howell concludes that, "unfortunately, no conclusions can be draw from this study that are scientifically valid."
The study was supported by the National Institutes of Health, the National Science Foundation, the Cranberry Institute, and the Wisconsin Cranberry Board.
Source: Food Science and Biotechnology