Abstract: Antimicrobial activity and mechanisms of phenolic
extracts of 12 Nordic berries were studied against selected
human pathogenic microbes. The most sensitive bacteria on
berry phenolics were Helicobacter pylori and Bacillus cereus.
Campylobacter jejuni and Candida albicans were inhibited
only with phenolic extracts of cloudberry, raspberry, and
strawberry, which all were rich in ellagitannins. Cloudberry
extract gave strong microbicidic effects on the basis of plate
count with all studied strains. However, fluorescence staining
of liquid cultures of virulent Salmonella showed viable
cells not detectable by plate count adhering to cloudberry extract,
whereas Staphylococcus aureus cells adhered to berry
extracts were dead on the basis of their fluorescence and
plate count. Phenolic extracts of cloudberry and raspberry
disintegrated the outer membrane of examined Salmonella
strains as indicated by 1-N-phenylnaphthylamine (NPN) uptake
increase and analysis of liberation of [14C]galactoselipopolysaccharide.
Gallic acid effectively permeabilized the
tested Salmonella strains, and significant increase in the
NPN uptake was recorded. The stability of berry phenolics
and their antimicrobial activity in berries stored frozen for a
year were examined using Escherichia coli and nonvirulent
Salmonella enterica sv. Typhimurium. The amount of phenolic
compounds decreased in all berries, but their antimicrobial
activity was not influenced accordingly. Cloudberry,
in particular, showed constantly strong antimicrobial activity
during the storage.