Applying Laser Doppler Vibrometer to detecting the elastic properties of watermelon

Abstract. The modulus of elasticity, which is the ratio of stress to strain within the elastic range of the material, is an indication of rigidity and stiffness of the material and not an indication of its degree of elasticity. The elastic characteristics of fruit are considered to be related to the firmness of the flesh; reflecting maturity and freshness. A Laser Doppler Vibrometer（LDV）was applied to evaluate the rheological properties of unripe, ripe and overripe watermelons. A stiffness coefficient () was defined as , where the was the second re sonant frequency, was the watermelon mass. The modulus of elasticity (E) and the bioyield point of force-deformation curve of watermelon were determined from compression experiments on cylindrical samples obtained from the middle structure of each watermelon and the modulus of elasticity (E) in the structure was named . The average values of was the average modulus of elasticity which named and they were compared with each other. Meanwhile, their relationships with characteristic parameters extracted from the spectrum measured by the LDV were analyzed. The results showed the E values of watermelon flesh were decreased with the increasing of their ripeness. The relationships between the stiffness coefficient () and the modulus of elasticity( , ) were weak which indicated that the stiffness coefficients and the modulus of elasticity seem to correspond to different mechnical properties of watermelons and the LDV and compression test measure two different attributes of texture of watermelon.