Inactivation of Staphylococcus aure

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 °C), amplitude (60, 90 and 120mm) and treatment time (6, 9 and 12 min). It was
found that Gram-negative bacteria (Escherichia coli; D120 mm=2.78 min at 60 °C) are more
susceptible to the ultrasonic treatment than Gram-positive bacteria (Staphylococcus aureus;
D120mm=4.80 at 60 °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.