Design of cost-effective LED based prototypes for the evaluation of grape (Vitis vinifera L.) ripeness

Abstract

Monitoring the grape ripening until the harvest is a crucial issue since berry quality is closely related to it. Therefore, the research for non-destructive methods which could explore many samples and give a rapid and comprehensive overview of ripening would be helpful. The aim of the research was to design, build and test prototypes of cost-effective and user-friendly device to support small-scale growers in planning the optimal harvest date according to grape ripening degree. A pre-prototype version of a fully integrated optical device which incorporates sensors (tuned photodiode arrays, interference filters, LEDS, optics) was presented. The system is equipped with two digital 6-channel sensors for spectral identification in the visible and SW-NIR. The sensors cover 12 independent on-device optical filters from 450 nm to 860 nm. It was tested on Nebbiolo grape red variety. The optical data were collected on grape bunches and single grape berries using the pre-prototype. Besides, reference parameters through traditional laboratory analyses of Soluble Solids Content (SSC), Titratable Acidity (TA), Extractability of Anthocyanins (EA) and pH were carried out on each sample. The MLR correlation models between the optical data from the prototypes and the reference parameters were calculated. A promising determination coefficient in cross validation (r2cv) was obtained for the prediction of SSC (r2cv = 0.86) while, the models for TA, EA and pH (r2cv from 0.4 to 0.5) can be considered enough accurate to allow an initial field screening of the trend of these parameters.