Ultrasonic assessment of olive oil mixtures properties

Mainly produced in the Mediterranean countries, olive oil excels by its nutritional and medicinal benefits. However, olive oil available in the market is not always authentic. It can be altered by inadequate storage conditions or if it is mixed to other kinds of oils. The objective of this work is to use ultrasonic methods for a possible quick detection of olive oil adulteration from the characterization of its ultrasonic properties. In this context, ultrasonic longitudinal propagation velocity and attenuation were measured for pure olive oil and for its mixtures with soya oil at different proportions, at 20 °C and using a 5 MHz ultrasonic transducer. Then, the longitudinal viscosity of the different oil samples has been deduced on the whole bandwidth of the transducer (3-7 MHz) thanks to frequential analysis of the rough data. Thanks to the measurement of the shear viscosity with a Couette viscosimeter, we also deduced the bulk viscosity. Propagation velocity starts from 1458 m.s
^-1
for pure olive oil and increases with percentage of soya oil in the mixture up to 1464 m.s
^-1
. The corresponding longitudinal viscosity decreases with percentage of soya oil from 161.4 mPa.s, for pure olive oil, to 136.7 mPa.s, for pure Soya oil. As a function of frequency, longitudinal and bulk viscosities decrease, for all proportions of soya oil, indicating that ultrasonic relaxation may take place. Thanks to the high level of accuracy of the method proposed in this communication, the results show the ability of ultrasonic methods to be an efficient tool, which allows distinguishing mixtures of oils and thus detecting adulterated olive oil.