Compounds found in raisins fight
bacteria in the mouth that cause cavities and gum
disease, according to researchers at the University
of Illinois at Chicago.
"Our laboratory analyses showed that phytochemicals
in this popular snack food suppressed the growth
of oral bacteria associated with caries and gum
disease," said Christine Wu, professor and associate
dean for research at the UIC College of Dentistry
and lead author of the study. Phytochemicals are
compounds found in higher plants.
The data were presented today at the annual meeting
of the American Society for Microbiology in Atlanta.
Wu and her co-workers performed routine chemical
analyses to identify five phytochemicals in Thompson
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
At a concentration of 31 micrograms per milliliter,
oleanolic acid also blocked S. 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.
Wu said that the findings counter a longstanding
public perception that raisins promote cavities.
"Raisins are perceived as sweet and sticky, and
any food that contains sugar and is sticky is assumed
to cause cavities," Wu said. "But our study suggests
the contrary. Phytochemicals in raisins may benefit
oral health by fighting bacteria that cause cavities
and gum disease."
"Moreover, raisins contain mainly fructose and
glucose, not sucrose, the main culprit in oral disease."
In an earlier unpublished study, Wu's collaborator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. Raisin bran
cereal with added sugar, however, did raise acidity
"Foods that are sticky do not necessarily cause
tooth decay. It is mainly the added sugar, the sucrose,
that contributes to the problem," Wu said.