(A) Principal component analysis (PCA) results of PTR-TOF-MS data obtained from 47 durum wheat kernel samples. Dim1 = first dimension (PC1), Dim2 = second dimension (PC2); (B) Vector representation of the contribution of each compound to the distinction of kernel samples. The length of the vectors is directly correlated to their significance within each population. Between vectors and between a vector and an axis, there is positive correlation if the angle is less than 90 degrees whereas the correlation is negative if the angle reaches 180 degrees. There is no linear dependence if the angle is 90 degrees.