Ultrasonic techniques for measuring rheological properties of rice slurries

Abstract

The development of new sensors to monitor food quality is an emerging issue of today. Many food processing industries rely on batch methods to inspect food quality. These techniques yield results which are delayed in responding to the dynamic systems during food processing, resulting in poorly processed foods or production delays in processing plants. This research describes the development of a ultrasonic sensor to measure viscoelastic properties of rice slurries and dough. This inexpensive sensor can be applied in the food processing plant to minimize batch methods of Theological testing. Rice was milled to two different particle size distributions (PSD). Concentrations of 5%, 10%, 20%, 30%, and 40% rice flour (for each PSD flour) were mixed with 4% Carboxy-methylcellulose solutions and tested for power law Theological parameters and for viscoelastic parameters with the Haake CV20 rheometer. Two repetitions were completed for each treatment. Sensors were fabricated to measure the relative acoustic impedance of rice slurries. Slurries of different concentration and particle characteristics were placed on the top surface of the sensor. An ultrasonic longitudinal wave was transmitted through the sensor and into the sample where a portion of the energy was absorbed by the slurry and a portion reflected to a receiving transducer. The samples were subjected for ten minutes to continuous, longitudinal waves at 500 kHZ, 1 MHz, and 2 MHz. The output voltage from the receiving transducer was recorded every 10 seconds. Results indicated that the sensors were able to detect differences in the different rice slurries. The sensor output voltage decreased with increased rice flour concentration. The values for flow behavior index follow the same trend. The sensor voltage values correlated to the measured Theological parameters. The sensors were able to detect the differences between the PSD flours (P=0.0739). The small PSD flour created slurries of significantly higher viscosities than the large PSD slurries.