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Effect of Ultrasound on Disaggregation of Milk Bacteria

Eastern Regional Research Laboratory, Eastern Utilization Research and Development Division, ARS, USDA, Philadelphia, Pennsylvania

ABSTRACT

The standard plate count for determining bacterial populations in foods is limited in its effectiveness by microorganisms tending to form conglomerates with themselves and with the constituents of foodstuffs. Standardized shaking procedures have been adopted in an attempt to obtain consistent results from sample to sample and locale to locale. A more efficient procedure for breaking up these clumps would be desirable. Ultrasonic waves have been used extensively for disrupting bacterial cells for obtaining cell-free extracts. These cell-rupturing frequencies of ultrasound are associated with high power inputs to the transducer. This paper reports the effects of a lower energy level ultrasound frequency on the disruption of bacterial aggregates in milk.

Experimental Procedure

The ultrasonic generator was the Ultra Clean Model 320 LU produced by the L ... R Manufacturing Company, Kearny, New Jersey,¹ and of the type normally used for cleaning certain laboratory and industrial materials. The power output to the transducer, according to the manufacturer's specifications, was in excess of 65 W average at 75 KC (a wave level of approximately 2 cm).