PCA-based identification and differentiation of FTIR data from model melanoidins with specific molecular compositions

Melanoidins formed from different carbohydrates, such as D-glucose, D-fructose, and D-xylose, and their typical degradation products, such as hydroxymethylfurfural, furfural, glyoxal, and methylglyoxal, with L-alanine were analyzed with Fourier transform infrared spectroscopy (FTIR). Characteristic infrared bands were identified representing spectral differences between the investigated melanoidin species due to their different molecular compositions. With the help of principal components analysis (PCA) the IR data allowed for a fast discrimination between the different model melanoidins. From this study it is inferred that the intensity and relative absorption wavelength of C-O single versus C=O double bonds are characteristic features of the investigated melanoidins. Melanoidins formed from carbohydrates exhibit less carbonyl functions in comparison to melanoidins from the degradation products, the situation is opposite for the C-O bond. The amount of C=O is additionally correlated with a higher absorption at 420 nm indicating that strong colored melanoidins contain more carbonyl functions.