Abstract #W144

# W144
Inactivation of thermoduric sporeformers in milk by continuous ultrasonication.
Dikshi Bawa*1, Sanjeev Anand1, Steve Beckman1, 1South Dakota State University, Brookings, SD.

Thermoduric sporeformers can survive milk pasteurization and cause spoilage in dairy foods. Our previous studies established that batch ultrasonication combined with pasteurization inactivated thermally resistant vegetative cells of spore forming Bacillus spp. This study investigates the effect of a continuous ultrasonication process to reduce thermoduric sporeforming bacilli in milk. We hypothesize that ultrasonication causes increase of cell membrane permeability leading to leakage of cell components thus causing cell death. Mid exponential phase vegetative cells of thermoduric Bacillus coagulans (ATCC 12245) were inoculated in sterile skim milk at log 5 cfu/mL. Their thermal stability was validated by exposing them to batch pasteurization (63°C for 30 min). Inoculated skim milk was passed through a continuous ultrasonicator with 22-mm sonotrode, 20 kHz frequency, and 1000 W power input (UIP1000hd, Hielscher USA, Inc.), at 86% (91.2 µm) amplitude and a flow rate of approximately 7.5 L/h and back pressure of 345 kPa resulting in an exposure time of 80 s per pass. Ultrasonicated samples were batch pasteurized to study the combined effect. Brain Heart Infusion agar was used for plating the survivors. Experiments were conducted as replicates of 2, and were repeated thrice. Statistical significance of the data was determined using SAS enterprise guide 7.1 software. A significant (P < 0.05) reduction was found in the log counts after treatments. Lab pasteurization alone reduced the vegetative cells by 25%, while ultrasonication alone resulted in a greater inactivation of 92% after 12 passes (16 min total exposure time). Inactivation was further increased to 99.98% by combining ultrasonication and pasteurization. It can thus be concluded that a continuous ultrasonication process followed by pasteurization is highly effective to inactivate thermoduric vegetative cells of sporeformers such as Bacillus coagulans.

Key Words: ultrasonication, pasteurization, thermoduric sporeformer