Determination of Technological Maturity of Grapes and Total Phenolic Compounds of Grape Skins in Red and White Cultivars During Ripening by Near Infrared Hyperspectral Image: A Preliminary Approach

Abstract

Hyperspectral images of intact grapes during ripening were recorded using a near infrared hyperspectral imaging system (900-1700 nm). Spectral data have been correlated with grape skin total phenolic concentration, sugar concentration, titratable acidity and pH by modified partial least squares regression (MPLS) using a number of spectral pre-treatments and different sets of calibration. The obtained results (RSQ and SEP, respectively) for the global model of red and white grape samples were: 0.89 and 1.23 mg g-1 of grape skin for total phenolic concentration, 0.99 and 1.37 Brix for sugar concentration, 0.98 and 3.88 g L-1 for titratable acidity and for pH 0.94 and 0.12. Moreover, separate calibration models for red and white grape samples were also developed. The obtained results present a good potential for a fast and reasonably inexpensive screening of these parameters in intact grapes and therefore, for a fast control of technological and phenolic maturity.