A NONDESTRUCTIVE ULTRASOUND METHOD FOR MICROBIAL QUALITY-CONTROL OF ASEPTICALLY PACKAGED MILK

A new method for non-destructive microbial quality control of aseptically packaged milk is proposed. The method is based on acoustic streaming, which is induced by ultrasound in a liquid. Since the streaming is affected by bacterial activity, the spectral content of sound reflected by moving particles in the liquid can be used to assess the microbial status of the product. Experiments were performed on aseptically packaged ultra high temperature milk inoculated with either Staphylococcus epidermidis or BacilLus subtilis A. The presence of S. epidermidis was detected in all packages 5 d after inoculation while the presence of Bacillus subtilis A was detected in some of the packages 11 d after inoculation. Although the material in this first study is limited, the method appears promising for microbial quality control of milk as well as other liquid food products. © 1993 Academic Press. All rights reserved.