Growth response and modelling of the effects of Zataria multiflora Boiss. essential oil, pH and temperature on Salmonella Typhimurium and Staphylococcus aureus

The effects of different concentrations of Zataria multiflora Boiss. essential oil (EO: 0.0, 0.015, 0.03 and 0.06%), pH values (7.3 and 6.0) and storage temperatures (T: 15, 25 and 35 °C) on some growth kinetics, time-to-detection (TTD, time to the nearest visible detection) and log10 probability percentage (log P%) of growth initiation of Salmonella Typhimurium and Staphylococcus aureus in Brain Heart Infusion broth were evaluated in a factorial design study. For the log P%, the effects of another variable, storage time (D, up to 43 days) was also assessed as an additional factor. The TTD and log P  % of both organisms were significantly affected (P<0.01)(P<0.01) by the values of EO, pH, T and D (just for log P  %). The combinations of pH=7.3pH=7.3, T⩽35°C and EO⩽0.015EO⩽0.015 could not obviously affect the growth kinetics of the organisms in this study. Whereas, strong inhibitory action was observed by increasing of EO concentration to 0.06% at the considered pH (7.3) and T (⩽35 °C). The growth of both organisms was completely inhibited at the combinations of EO=0.06%EO=0.06%, pH=6.0pH=6.0 and T⩽25°C up to 43 days of storage. Regression equations were derived relating TTDs to EO, pH and T and log P% of both organisms to EO, pH, T and D. From these models the values of predicted TTD and log P% of S. Typhimurium and St. aureus can be calculated by any combinations of EO, pH, T and D (for log P%) within the limits studied. However, between the two TTD and log P% models obtained for both organisms in this study, the TTD models of S. Typhimurium and St. aureus   showed better prediction (R2=0.951R2=0.951 and 0.978, respectively) than the log P  % models of them (R2=0.852R2=0.852 and 0.804, respectively).