This study established the efficacy of multi-frequency Dynashock power ultrasound against selected pathogenic bacteria and spoilage yeasts in orange juice. The effects of a number of inoculum- and process-related variables on the efficacy of ultrasound treatment were also determined. All test bacteria exhibited a biphasic inactivation behavior characterized by a sigmoidal inactivation pattern consisted of a slow inactivation lag phase where sublethal cell injury accumulated