The Effect of High Intensity Ultrasound Treatment on the Amount of Staphylococcus aureus and Escherichia coli in Milk

Inactivation of Staphylococcus aureus and Escherichia coli in milk containing 4% milk fat was carried out using a 20 kHz power ultrasound. The experiments were planned and performed according to the statistical experimental design. Specifically, central composite design was used to optimize and design three experimental parameters: temperature (20, 40 and 60 degrees C), amplitude (60, 90 and 120 mu m) and treatment time (6, 9 and 12 min). It was found that Gram-negative bacteria (Escherichia coli; D-120 (mu m)=2.78 min at 60 degrees C) are more susceptible to the ultrasonic treatment than Gram-positive bacteria (Staphylococcus aureus; D-120 mu m=4.80 at 60 degrees C). Nevertheless, all three parameters studied seem to substantially affect the inactivation of both Staphylococcus aureus and Escherichia coli in milk using ultrasonic treatment. The results also indicate increased inactivation of microorganisms under longer period of treatments, particularly in combination with higher temperature and/or amplitude.