engleski

Antimicrobial activity of pure phenolic acids and phenolic extracts of Lamiaceae plants against bacterial food-borne pathogens

Consumer demands for safe, stable and naturally preserved food products have intensified research of different phenolic compounds and plant phenolic extracts which are known to possess antioxidant and antimicrobial activity and offering a potential alternative to synthetic preservatives. By using broth microdilution method combined with ATP signal measurement we determined minimal inhibitory concentrations (MICs) of several hydroxybenzoic and hydroxycinnamic acids, carnosic and rosmarinic acid and laboratory extracted or commercially produced extracts from different Lamiaceae species. They are among most popular medicinal plants used in phytotherapy as well as widely used flavouring agents in foods. Their extracts are also used as anti-oxidant preservatives. Since they are known to be a rich source of phenolic acids, we tested their antimicrobial activity against gram-positive (Bacillus and Staphylococcus) and gram-negative (Campylobacter, Salmonella and Escherichia) bacterial reference strains and against antibiotic susceptible and resistant food isolates. The antimicrobial activity depended on the concentration and chemical structure of the phenolic compounds and their composition in the extracts. When the activity of the extracts is expressed in MICs of total phenols, e.g. gallic acid (GAE) equivalents per mL of medium and compared to pure phenolic acids, much higher efficiency of the extracts was confirmed against all tested bacteria, indicating synergistic antibacterial activity of phenolic compounds in the mixtures. Carnosic acid and the extracts with higher content of carnosic acid were very efficient against gram-positive strains, but not against Enterobacteriaceae (Salmonella and E. coli). For pure phenolic acids, the structure-activity relationship was expected, but no significant differences were confirmed among hydroxybenzoic and hydroxycinnamic acids against most tested bacteria. However, the latter group (e.g. p-coumaric, ferulic, sinapic and chlorogenic acid) were most efficient against all Campylobacter strains.

antibacterial activity ; phenolic acids ; plant phenolic extracts ; food safety

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