Analysis of the sugar content of fruit juices and drinks using ultrasonic velocity measurements

The use of ultrasound to determine the sugar content of fruit juices and drinks has been assessed. The velocity of ultrasound and the density were measured in solutions of D-glucose, D-fructose, and sucrose at various concentrations (0–40% w/v) and temperatures (10–30°C). The velocity of ultrasound was measured in 50:50wt:wt mixed solutions of sucrose and D-glucose over the same range of concentrations and temperatures. Measurements of the velocity of ultrasound, the density and the refractive index were made on various fruit juices and drinks at 20°C. The sugar content of the juices and drinks was determined by enzymatic assay. Ultrasonic measurements are shown to predict sugar contents in pure sugar solutions to within 0.2% w/v and in mixed sugar solutions to within 0.5% w/v. The ultrasonic measurements were sensitive to sugar species. It is shown that ultrasound compares well with other techniques for sugar content determination in fruit juices and drinks, and has the advantage that the equipment can be used for on-line process control. Applications for this ultrasonic technique are proposed.