Time and Frequency Domain Response of Grape Berries to Nondestructive Impact during the Harvesting Period
2016
Trnka, J. | Pavloušek, P. | Nedomova, Š | Buchar, J.
An experimental system was set up to generate the impact force, measure the response wave signal and analyze the frequency spectrum for detection of the behavior of grape berries at different harvest days. Seven varieties of grape berries harvested for six consecutive weeks have been tested. The response of grape berries to a nondestructive impact is studied both in time and in frequency domains. The digitalized time history of the force was analyzed to extract some mechanical characteristics (peak force, impact duration, impulse). The evaluation of the modulus of elasticity of berries using frequency response characteristics was carried out. This modulus decreases with the total sugar content. This dependence can be used for the estimation of the maturity of grape berries. PRACTICAL APPLICATIONS: This paper describes the use of a technique of the nondestructive impact for monitoring grape texture, particularly during ripening. It was found that the response of the grape berries to this impact measured as the time history of the surface displacement provided reliable tool to monitor the progress of grape maturity. The described method could also be used to highlight important information on grape evolution during ripening including their composition (total sugar content) and help to provide better insight on the choice of the preferred/ideal harvest date. Owing to the available computer techniques, this method enables testing much more number of berries in comparison with classical methods of the evaluation of grape's mechanical properties.
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