Maturity, variety and origin determination in white grapes (Vitis Villifera L.) using near infrared reflectance technology

Soluble solids content, variety and origin of grapes are three relevant features to determine wine quality. Soluble solids content is directly related to ripeness. The capacity to certify the origin or variety of a grape is of major interest for wine makers. The aim of this paper was to study whether near infrared reflectance (NIR) spectroscopy could be used to determine soluble solids content and to identify different varieties and origins of grapes. Samples of Viura and Chardonnay grapes were collected in two locations (Cadreita and Villamayor de Monjardin) which varied in environmental conditions. Mass and sugars content measured by a refractometer and NIR (800-500 nm) reflectance spectra were obtained. A partial least squares regression (PLS) was made to calibrate the NIR spectra. The regression models for Chardonnay grapes were more robust than for Viura grapes, showing coefficients of determination for calibration and validation of 0.75 and 0.70 and a standard error of cross-validation of 1.27. Therefore, NIR technology is suitable to determine the soluble solids content although it requires a calibration model for each variety, using a large number of data points and variables. The combined variety model showed a residual predictive deviation of 1.33, while Viura and Chardonnay models showed 1.54 and 1.88, respectively. The results of discriminant analysis using variables from the NIR spectrum showed a percentage of well-classified grapes according to the variety to which they belonged of 97.2% and a 79.2% of well-classified Chardonnay grapes according to their origin. In conclusion, NIR technology is a useful alternative for identifying the variety and origin of grapes.