Evaluation of fruit tissue texture and internal disorders by laser Dopplerdetection

Ripening-dependent changes in fruit texture and the development of physiolo gical disorders affecting texture were sensed remotely by laser Doppler det ection based on changes in surface vibrations. Intact fruit of kiwifruit (A ctinidia deliciosa (A. Chev.) Liang et Ferguson, 'Hayward'), peach (Prunus persica Batsch., 'Akatsuki'), and Japanese pear (Pyrus pyrifolia Nakai, 'Cy ouju'), at different maturity stages, were placed on a vibration generator stage and the sample was subjected to sine wave excitation through a freque ncy series from 5 to 2000 Hz. Vibration transmitted through the fruit to th e upper surface was measured by a laser Doppler vibrometer. Phase shift cau sed by the transmission through the fruit was determined based on the compa rison of the difference between input and output vibration signal. To recon cile changes in the phase shift with other methods used for texture analysi s, a probe with a load sensor was inserted into the sliced fruit and displa cement force was measured. The correlation coefficient (r) between displace ment force and phase shift at either 1200 or 1600 Hz was 0.81 to 0.92 (P < 0.01). The laser Doppler technique was also capable of detecting citrus fru it (Citrus tamurana Hort. ex Tanaka) afflicted with internal defects. These data suggest that laser Doppler detection of fruit vibration signals has t he potential for use as a versatile remote sensing tool for evaluation of f ruit tissue firmness and maturation. It also offers a possible means of eva luating otherwise concealed internal defects that render fruit unacceptable . 1999 Published by Elsevier Science B.V. All rights reserved.