Partial Least-Squares Regression Analysis. A PLSR
model was used to predict the added starch concentration in
onion powder. The samples were categorized on the basis of
the adulterant concentration, and a PLSR model was developed
using the preprocessed spectra of samples from both FT-NIR
and FT-IR spectroscopy. The highest correlation coefficient
value, Rp
2
, of 0.98 with a standard error of prediction (SEP) of
1.18% was observed by using the SNV-preprocessed FT-NIR
spectra. The optimal number of factors used in the PLS models
was automatically selected on the basis of the lowest value of
predicted root-mean-square error (RMSE) in the crossvalidation
process. The PLSR results are listed in Table 1 for
the FT-IR spectral data.