Moreover the phenol, ellagic tannin, does not target beneficial probiotic bacteria, they claim.
Their findings could have a wide range of applications in the food industry, including in functional foods and supplements to prevent 'traveller's tummy'.
"We were especially surprised and excited by the observation that probiotics that are beneficial for digestion are not sensitive to the berries, but harmful bacteria are. Consequently, the berries may inhibit the activity of harmful bacteria," said the project director, Riitta Puupponen-Pimiä of VTT Biotechnology.
"The antimicrobial qualities of the berries are also well preserved with freezing," she added.
The project, part of the National Technology Agency of Finland's (Tekes) Innovation in Foods programme, studied about 10 bacteria that cause infections of the alimentary canal and food poisoning, and how they reacted to the phenols in berries.
The complex phenolic polymer ellagic tannin, only found in small quantities in most fruits and berries but at higher levels in raspberries, inhibited growth of salmonella, staphylococcus and camphylobacter. The phenols in the berries had no significant effect on the functioning of listeria.
"As antimicrobial compounds, phenols may have a previously unforeseen effect on intestinal microbes," said Puupponen-Pimiä.
The study has aroused a great deal of interest as it has a wide range of possible applications, according to the project coordinator. Aside from functional foods, the findings could lead to new types of safe food packaging, preservatives for marinades and in pharmaceutical applications.
Around 10 food, pharmaceutical and health food businesses have participated in the project, including food processing firm Lannen Tehtat.
The researchers are currently focusing on developing a method of isolating the phenolic compounds, to enable them to be used in industrial applications. Another objective is development of treatments to increase the concentration of beneficial substances contained in the berries.
"So far we have only produced an analytical extract, which cannot be used in food applications. We need to do a lot more research as the field of phenolics is very complex," Puupponen-Pimia told NutraIngredients.com.
The research has been submitted to the Journal of Applied Microbiology.