Abstract
Simple devices in the oenological sector are important to support wine growers in monitoring ripening progress of grapes and to plan harvest time. Currently available vis/NIR spectroscopy devices are, however, expensive and not suitable for small scale wineries.
The aim of this work was to identify three most significant wavelengths able to discriminate in the field grapes ready to be harvested with a view to a simplified handheld and low-cost optical device. Non-destructive analyses were carried out on a total of 68 samples and a total of 1360 spectral measurements were done using a portable commercial vis/NIR spectrophotometer.
Chemometric analyses were performed in order to extract the maximum useful information from spectral data and to select the most significant wavelengths. Correlations between the spectral data matrix and technological (total soluble solids, TSS) and phenolic (polyphenols) parameters were carried out using partial least square (PLS) regression. Standardized regression coefficients of the PLS model were used to select the relevant variables, representing the most useful information of the full spectral region. To support the variable selection, a qualitative evaluation of the average spectra and loading plot, derived from principal component analysis (PCA), were considered.
The three selected wavelengths were 670 nm, corresponding to the chlorophyll absorption peak, 730 nm, equal to the maximum reflectance peak, and 780 nm, representing the third overtone of OH bond stretching. PCA and multiple linear regression (MLR) were applied on the three selected wavelengths in order to verify their effectiveness. Simple equations for TSS and polyphenols prediction were calculated.
The results demonstrate the feasibility of a simplified, low-cost handheld device for ripeness assessment in the field; a possible functional scheme was proposed.
- ©2013 by the American Society for Enology and Viticulture
Sign in for ASEV members
ASEV Members, please sign in at ASEV to access the journal online.
Sign in for Institutional and Non-member Subscribers
Log in using your username and password
Pay Per Article - You may access this article (from the computer you are currently using) for 2 day for US$10.00
Regain Access - You can regain access to a recent Pay per Article purchase if your access period has not yet expired.