88C-27 |
Ultrasonic monitoring of the kinetics of powder dissolution |
R. SAGGIN and J. N. Coupland. Department of Food Science, The Pennsylvania State University, 103, Borland Lab, University Park, PA 16802 Powdered food ingredients must often be completely redissolved in water prior to further processing. An on-line sensor to track the dissolution kinetics would allow automation of such operations and reduce waiting times. Acoustic measurements have previously been used as equilibrium non-invasive concentration sensors and can be readily applied to pre-existing process equipment. The objective of this study is to develop an ultrasonic reflectance sensor and use it to measure the dissolution kinetics of some simple sugars in water. A thermostatted (2, 20 and 60°C) vessel was stirred at high speed with a rotating paddle. An ultrasonic transducer (2.25 MHz) was coupled to a polymer delay line, the other end of which was brought in contact with the stirred liquid. A pulse of sound was transmitted along the delay line and the magnitude of the echo returning from the liquid interface was measured. Water (480 g) and sucrose or lactose (120 g) particles of known size distribution were mixed in the vessel and the reflection coefficient measured over time. Samples of particles and solution were taken at intervals during this process using a syringe, rapidly filtered and the dissolved sugar concentration measured using refractometry. The time for complete dissolution increased with decreasing temperature and was longer for lactose than sucrose and also longer for larger particles. The kinetics of the process were modeled as a exponential decay with parameters reflecting the composition and size of the particles. Ultrasonic reflectance can be used as on-line technique to control the dissolution rate of powders of different size and with different solubility. The polymer delay line used in the present work could be replaced with the steel wall of a mixing tank and thus it would be possible to make measurements by merely pressing a transducer against the outside wall of any existing equipment.
Session 88C, Food Engineering: Physical and Chemical Properties
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