Real-time process monitoring of critical quality attributes of white sugar crystals in an agitator dryer using near-infrared spectroscopy for automatic manufacturing

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To quantitatively monitor moisture content (MC) and particle size (PS) as the main critical quality attributes (CQAs) of white sugar crystals, samples were placed in a small agitator dryer, and near-infrared (NIR) spectroscopy was performed continuously in real-time using a diffuse reflectance fiber-optic probe. The MCs of the granules were calculated as weight loss after drying statically at 80 °C, and the PS and its distribution were determined using the sieving method. The best-fitted calibration models for predicting MC and PS were obtained using the partial least squares regression method for the NIR datasets. All the fitted models exhibited good linearity, with a correlation coefficient above 0.98. The MC of the samples decreased linearly with drying time, reaching an equilibrium MC of less than 0.5 wt% at 140 s. The NIR method can be useful for real-time evaluation of the MC and PS of white sugar crystals during continuous drying.