Raisins may combat cavity-causing bacteria.

For decades, many dentists and oral-health researchers advised against eating raisins because they suspected that such sticky, sweet foods were contributing to cavity formation and gum disease. However, scientists have now found that several chemical compounds in raisins actually fight bacteria that cause these problems.

According to Christine Wu of the University of Illinois in Chicago, recent research in her lab and elsewhere has suggested that stickiness of a food isn't necessarily an indicator of its effects on oral health. With that in mind, Wu and her coworkers asked whether raisins might actually be good for teeth. Says Wu: "We wondered, Are there any chemicals in raisins that might affect the growth of plaque bacteria?" Plaque bacteria live on teeth and produce acids that eat into tooth enamel.

In a study funded by the California Raisin Marketing Board, Wu's team found that extracts from raisins could slow the growth in a laboratory of Streptococcus mutans, the main bacterial species implicated in tooth decay. Five chemicals in raisins--oleanolic acid, oleanolic aldehyde, betulin, betulinic acid, and 5-(hydroxymethyl)-2-furfural--seem to be responsible for this effect. Moreover, the researchers found that oleanolic acid prevents S. mutans from sticking to surfaces such as tooth enamel.

Because this study examined only bacteria growing in a lab, Wu says that her team's next step will be to test whether raisins have a similar bacteria-suppressing effect in people's mouths.--C. B.