Raman and FTIR spectroscopic study of carboxymethylated non-starch polysaccharides

Four types of non-starch polysaccharides including cellulose, guar gum, locust bean gum and xanthan gum were modified by carboxymethylation. The degree of substitution (DS) was determined by a colorimetric method. Raman and Fourier transform infrared spectra of the native and modified polysaccharides were acquired and analysed. Representative marker bands, with intensities and/or integrated areas affected by carboxymethylation, were selected at 1607 cm−1 (Raman) and 1315 cm−1 or 1605 cm−1 (IR), attributed to CO carbonyl stretching vibration. The ratios of intensities (or areas) of the marker bands to that of an internal standard band, corresponding to the skeletal configuration and linkages (850–950 cm−1), were plotted against DS. Linear fits were obtained with high correlation coefficients, r > 0.96 (p < 0.01), suggesting a strong correlation between the spectroscopic data and DS determined by wet chemistry. Some structural changes were also observed from the spectral data.