88C-26 |
Non-contact ultrasonic measurements in food materials |
R. SAGGIN and J. N. Coupland. Department of Food Science, The Pennsylvania State University, 103, Borland Lab, University Park, PA 16802 Ultrasonic measurements are sensitive to many important food properties. Until recently, it has been considered impossible to propagate high frequency sound through significant air gaps and thus the on-line application of these sensors to discrete food item manufacture has been limited by the engineering problems involved in achieving contact. However, a new technology developed by SecondWave Systems (Boalsburg, PA) has been developed to allow ultrasonic measurements through air. The goal of this work is to make non-contact, air-coupled ultrasonic measurements of the size and ultrasonic properties of food materials. Various food products (cheese, reduced fat cheese, luncheon meat, reduced fat luncheon meat and cranberry sauce) were cut into parallel-sided strips 5-15 mm thick. Ultrasonic measurements were made with two transducers (1 MHz) placed one either side of the sample at a distance of 3 cm. The thickness and ultrasonic velocity of the samples was measured by using both transducers alternately to generate and detect pulses of sound. The same samples were also tested using established direct-contact ultrasonic methods. The thickness of the various food items, measured in non-contact mode, correlated well with caliper measurements (r=0.99) and, at a given point, the ultrasonic measurements were more precise (+/- 0.003 mm). The speed of sound measured in both contact and non-contact modes was independent of thickness for all food groups. Except for the low-fat cheddar cheese, the speed of sound measured in non-contact mode was significantly higher than the velocity measured with the direct-contact technique (p<0.05) reflecting the small degree of compression inevitable in contact measurements. It is possible to simultaneously measure the size and ultrasonic properties of food materials in non-contact air-coupled mode. The new technology is easily applicable on-line and allows ultrasonic sensors to compete as a genuinely non-contact methodology.
Session 88C, Food Engineering: Physical and Chemical Properties
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