"Our laboratory analyses showed that phytochemicals in this popular snack food suppress the growth of several species of oral bacteria associated with caries and gum disease," said Christine D. Wu, Professor and Associate Dean for Research at the University of Illinois at Chicago College of Dentistry and lead author of the study.
Routine chemical analyses identified five compounds in Thompson seedless raisins: oleanolic acid, oleanolic aldehyde, betulin, betulinic acid, and 5-(hydroxymethyl)-2-furfural. All of these are known phytochemicals -- antioxidants found in plants.
Oleanolic acid inhibited the growth of two species of oral bacteria: Streptococcus mutans, which causes cavities, and Porphyromonas gingivalis, which causes periodontal disease.
The compound was effective against the bacteria at concentrations ranging from about 4 to 1,000 µg/ml. At a concentration of 31 µg/ml, oleanolic acid also blocked S. mutans adherence to surfaces. Adherence is crucial for the bacteria to form dental plaque, the sticky biofilm consisting of oral bacteria that accumulates on teeth. After a sugary meal, these bacteria release acids that erode the tooth enamel.
Wu said that the data 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."
In an earlier unpublished study, Wu's collaborator Dr. Shahrbanoo Fadavi (Pediatric Dentistry, UIC College of Dentistry) found that adding raisins to bran cereal did not increase the acidity of dental plaque. However, the commercial raisin-bran cereal with added sugar was most acidogenic compared with raisins or bran cereal alone.
"Foods that are sticky do not necessarily cause tooth decay; it is mainly the added sugar (sucrose) that contributes to the problem" Wu said.
The present study was funded by the California Raisin Marketing Board.
Besides collaborator Dr. A. Douglas Kinghorn, Adjunct Professor at the UIC College of Pharmacy, other scientists involved in the study were Dr. Jose F. Rivero-Cruz and Dr. Min Zhu (both, UIC College of Dentistry) and Dr. Baoning Su (UIC College of Pharmacy).
This release is a summary of a presentation from the 105th General Meeting of the American Society for Microbiology, June 5-9, 2005, in Atlanta, Georgia. Additional information on these and other presentations at the 105th ASM General Meeting can be found online at http://www.asm.org/Media/index.asp?bid=34867 or by contacting Jim Sliwa (jsliwa@asmusa.org) in the ASM Office of Communications. The phone number for the General Meeting Press Room is 404-222-5403 and will be active from 12:00 noon EDT, June 5 until 12:00 noon EDT, June 9.