Ultrasonic velocity measurements in the ternary mixtures water-lactose-lactate, for the purpose of monitoring the lactic acid fermentation of lactose

A preliminary study of the lactic acid fermentation of lactose using an ultrasonic velocity technique is presented. During this fermentation, lactose (milk sugar) is transformed into lactate (lactic acid) by the action of bacteria. It is shown that the changes occurring during the course of the process can be monitored on-line by measuring the changes experienced by ultrasonic waves propagating through the fermenting media. Measurements of density and ultrasonic velocity in the ternary mixtures water-lactose-lactate and during the fermentation of a lactose solution were carried out. The ultrasonic propagation velocity has been correlated with the mass concentration of the mixture components using a semi-empirical model. These relations may be used to achieve an on-line concentration control for microbial lactic acid production.