Raisins May Fight Oral Bacteria

Compounds found in raisins may fight the oral bacteria that cause cavities and gum disease, researchers at the University of Illinois at Chicago say.

"Our laboratory analyses showed that phytochemicals in this popular snack food suppressed the growth of oral bacteria associated with caries and gum disease," says Christine Wu, professor and associate dean for research at the University of Illinois at Chicago (UIC) College of Dentistry and lead author of the study. Phytochemicals are compounds found in higher plants.

The results of the study, which was funded by the California Raisin Marketing Board, were presented at the annual meeting of the American Society for Microbiology in Atlanta.

"Raisins are perceived as sweet and sticky, and any food that contains sugar and is sticky is assumed to cause cavities," Wu says. "But our study suggests the contrary. Phytochemicals in raisins may benefit oral health by fighting bacteria that cause cavities and gum disease."

Wu and her fellow researchers performed routine chemical analyses to identify five phytochemicals in seedless raisins: oleanolic acid, oleanolic aldehyde, betulin, betulinic acid, and 5-(hydroxymethyl)-2-furfural.

Oleanolic acid, oleanolic aldehyde, and 5-(hydroxymethyl)-2-furfural inhibited the growth of two species of oral bacteria: Streptococcus mutans, which causes cavities, and Porphyromonas gingivalis, which causes periodontal disease. The compounds were effective against the bacteria at concentrations ranging from about 200 to 1,000 micrograms per milliliter.

Betulin and betulinic acid were less effective, requiring much higher concentrations for similar antimicrobial activity.

At a concentration of 31 micrograms per milliliter, oleanolic acid also blocked Streptococcus mutans adherence to surfaces. Adherence is crucial for the bacteria to form dental plaque, the sticky biofilm that accumulates on teeth. After a sugary meal, these bacteria release acids that erode the tooth enamel.

In an earlier, unpublished study, Wu's collaborator Shahrbanoo Fadavi, a pediatric dentist at UIC, found that adding raisins alone to bran cereal did not increase the acidity of dental plaque in subjects. Raisin bran cereal with added sugar, however, did raise subjects’ acidity levels.

"Foods that are sticky do not necessarily cause tooth decay. It is mainly the added sugar—the sucrose—that contributes to the problem," Wu says. "Moreover, raisins contain mainly fructose and glucose, not sucrose, the main culprit in oral disease.”

Adapted from a University of Illinois at Chicago news release, June 7, 2005