Influence of hydration of food additive polysaccharides on FT-IR spectra distinction

Using the Fourier-transform infrared (FT-IR) spectra in the 1200–800 cm−1 region and chemometrics, food additive polysaccharides such as pectin, starch, galactan and carrageenan can be distinguished. However, this vibrational spectroscopy technique is sensitive to the changes in conformation and to the constraints imposed by the hydrogen bonding with water, which could result in the destruction of all spectra qualities. In order to see if the water absorbed by carbohydrates can prevent the information necessary for their distinction in the 1200–800 cm−1 region, six monosaccharides, three disaccharides, four carrageenans, four pectic polysaccharides, three galactans, two glucans and one commercial mixture of carrageenan–pectin were submitted to a 96% relative humidity environment and were also dissolved in saturated water solutions, and their spectra were compared with those obtained from the dry samples. The application of a principal component analysis (PCA) to the FT-IR spectra showed that the distinction of sugars and polysaccharides by FT-IR in the 1200–800 cm−1 region can be achieved with no apparent loss of information in samples that can contain water. When the samples are in aqueous solution, the water influence is included in PC1 and the FT-IR spectral information of carbohydrates, previously given in PC1 and PC2 in dried samples, can be achieved in PC2 and PC3.