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

Ultrazvuk velike snage i frekvencije od 20 kHz upotrijebljen je za inaktivaciju bakterija Staphylococcus aureus i Escherichia coli u mlijeku koje je sadržavalo 4 % mliječne masti. Ispitivanja su planirana i provedena primjenom statističkog eksperimentalnog dizajna. Naime, središnji kompozitni dizajn pokusa primijenjen je pri optimiranju eksperimentalnih parametara: temperature (20, 40 i 60 °C), amplitude (60, 90 i 120 µm) i vremena obrade (6, 9 i 12 min). Utvrđeno je da su Gram-negativne bakterije (Escherichia coli; D120 µm=2,78 min na 60 °C) osjetljivije na ultrazvučnu obradu od Gram-pozitivnih bakterija (Staphylococcus aureus; D120 µm=4,80 min na 60 °C), te da sva tri ispitivana parametra ultrazvučne obrade bitno inaktiviraju Staphylococcus aureus i Escherichia coli u mlijeku. Rezultati također upućuju na povećanu inaktivaciju mikroorganizama tijekom duže ultrazvučne obrade u kombinaciji s višim temperaturama i/ili amplitudama ultrazvuka.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 120 μm) 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; D120 μm=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