Processed FT-IR spectrum data were submitted to
PCA (principal component analysis) in the R program (version
2.15.0) using a NIPALS algorithm (Wold, 1966) and PLS-DA analysis
(partial least square discriminant analysis) (Fiehn et al., 2000;
Trygg, Holmes, & Londstedt, 2007). HCA (hierarchical clustering
analysis) was performed using the score obtained through PCA
and PCA-DA, and a hierarchical dendrogram of each sample was
generated from UPGMA (unweighted pair group method with
arithmetic mean analysis) using a similarity index that measured
Euclidean distance.