Determination of degree of substitution of carboxymethyl starch by Fourier transform mid-infrared spectroscopy coupled with partial least squares

The degree of substitution (DS) markedly affects the properties of carboxymethyl starch (CMS). The conventional methods for the DS determination are time-consuming and not environment friendly. Fourier transform mid-infrared (FT-MIR) spectroscopy coupled with partial least squares (PLS) regression is applied to determine the DS of CMS in the present study. Calibration models with direct titration as the reference method were optimised by cross validation. A PLS regression model with a coefficient of determination (R²) of 0.9593 and root-mean-square error of cross validation (RMSECV) of 0.0141 was obtained in the spectral range from 500 to 4000 cm⁻¹. The prediction set gave a coefficient of determination (R²) and root-mean-square error of prediction (RMSEP) of 0.9368 and 0.0228, respectively. The results obtained in this study indicate that FT-MIR spectroscopy can be used as an easy, rapid, and novel tool to quantitatively predict the DS of CMS.