Preprocessing of raw near-infrared spectra (NIRS) is indispensable
because the measured spectra are subject to significant noises,
baselines and other irrelevant information, which may affect the
predictive ability of NIRS model (Blanco et al., 2004). Hence, it is
imperative to perform the spectral range selection and pretreatment
for visualizing and extracting relevant information from the
spectra best suited for calibration model. In this study, the automation
optimization function of the OPUS-QUANT2 software was
used to optimize the calibration conditions for developing best
calibration models of alcohol strength and titratable acidity. The
best conditions including the spectral region, preprocessing
method and rank, were selected based on the smaller rank value
and RMSECV for the calibration models according to PLS algorithm.
The statistics of optimal conditions are given in Table 2. The best
spectral regions selected for developing calibration models of
alcohol strength and titratable acidity were 6101.9e5446.2 cm1,
11,995.4e7498.1 cm1, respectively. The profiles of selected spectral
regions preprocessed by second derivative (SD) and straight line
subtraction (SLS) for alcohol strength and titratable acidity,
respectively, are shown in Figs. 2 and 3. From Figs. 2 and 3, more
positive information and less noise were identified and extracted
from the differences of the spectra pretreated by SD or SLS, and thus
these pretreatments had contributed most to precision of each
model.