Antimicrobial efficacy of a novel assisted ultrasound technology

Abstract

Two different essential oils (oregano and thyme essential oils) were tested with the continuous and pulse 2s on/ 8s off mode . The concentrations of oregano essential oil tested were : 0 .0 10%, 0. 01 4%, 0. 0 18%, 0. 02 2% an d 0 .0 25% v /v , while with thyme essential oil the same concen t r a t io ns p lu s 0 .0 4% v/ v were tested.

Application of both oregano and thyme essential oils at the mentioned concentrations further reduced the levels of bacteria from the surface.

Significant differences were found at concentrations of 0 .0 18%, 0 .0 2 2% and 0 0 25% v/v of oregano essential oil with both continuous and pulsed modes when compared to the samples treated with US alone , while for thyme essential oil significant reductions were observed with 0.01 8% v/ v and higher concentrations for continuous mode, and 0 . 01 4% v/ v an d higher concentrations for pulsed mode.

Only the highest concentration of thyme essential oil (0.04% v/ v) using both continuous and pulsed mode reduced the levels of Salmonella in water below the limit of detection. The effectiveness of the assisted ultrasound process was dependent on the processing times rather than the configuration of the ultrasound used (continuous versus pulsed mode) .

When the antimicrobial efficacy of oregano and thyme essential oil were compared, it was evident that oregano essential oil was more effective at detaching the bacteria from the surface of the lettuce, while thyme essential oil was more effective at inactivating the bacteria from the wash water . The use of both oregano and thyme essential oils proved to show synergistic effects in enhancing the removal and inactivation of the bacteria from the surface of the lettuce. The energy applied to the ultrasound system was also optimized , to obtain maximum reduction in bacterial levels with minimum energy being utilised.