Evaluation of a non-destructive impact sensor on-line for determination of firmness of peach and apples

Resumen

The purpose of the present study is the evaluation of the on-line non-destructive impact sensor to measure fruit firmness. This is an adaptation of a static one used in laboratory measurement of quality of fruit, and has been installed in an experimental fruit packing line that have a commercial sizer chain. This sensor measures the fruit firmness based on the acceleration-time curve supplied by an accelerometer attached to an impacting arm, working at a speed of 6-7 fruits per second. It was necessary to make an evaluation of the system, to study the variation sources and related aspects that can affect to the signal obtained, and also to quantify the operation of the system for the corrections or necessary modifications for their potential use in a commercial way, because the system presents a series of difficulties, as much from the technical point of view as from the physiology of the fruit, and all these hindrances have to be taken into account in the evaluation of the system. Ratios A/t (maximum acceleration value divided by its corresponding time), mean, and maximum slopes of the curves supplied by the accelerometer, were well correlated with the firmness data obtained in laboratory with the load-unload test. We have obtained for peach, a good separation for soft fruits with regard to the rest, an interesting fact for its on-line use for classification of firmness. Although for the time being, it is not possible the separation among the high levels of firmness. Variations in the results between different fruits, and different parts of the same fruit are obtained, mainly due to the non-uniformity of the shape between fruits, and the lack of ripeness homogeneity in each one.