Inhibitory effects of ethanolic extracts of propolis at different concentrations against Staphylococcus aureus and Escherichia coli O157:H7 Investigations on strains inoculated onto minced beef

In this study, the inhibitory effects of ethanolic extract of propolis (EEP) on the survival of Staphylococcus (S.) aureus and Escherichia (E.) coli O157:H7 inoculated onto minced beef, and natural microfloras on minced beef were investigated. After homogenisation, the minced beef was firstly divided into three groups and then each beef group was divided into five subgroups. Beef from the first group was the control samples, the second group was sprayed with 70% ethanol (EA), and the third, fourth, and fifth groups were sprayed with propolis solutions at three concentrations: 5%, 10%, and 15% (ethanol : propolis, v : w) with 70% ethanol, respectively. Prior to each treatment, S. aureus and E. coli O157:H7 were inoculated onto the minced beef at three different inoculum concentrations and after 15 min of incubation allowing the attachment of pathogens to the beef samples the propolis solutions were applied. All EEP concentrations very significantly (P<0.01) reduced the numbers of S. aureus and E. coli O157:H7 inoculated onto minced beef compared with the control samples. S. aureus was more resistant than E. coli 0157:H7 to EA treatment. The results of this study indicate that EEP as a natural food preservative may be used to effectively reduce microbial population upon beef.