Air dispersion of starch-protein mixtures: A predictive tool for air classification performance

Milling and air classification is a well-known procedure to obtain protein and starch enriched fractions from cereals and grain legumes. Adhesion of small protein particles to larger starch granules adversely affects the separation efficiency during air classification. To gain insight into this phenomenon the dispersion of bimodal mixtures of starch granules and fine protein particles in an air stream was studied.Using a method to correct for the number of small starch particles in the protein fraction, the dispersability of protein/starch mixtures was determined. The type of protein and, particularly, of starch may affect dispersability. The effect of starch type is not only caused by differences in granule size; likely other properties such as roughness are also involved. Increasing protein content enhances dispersability but does not seem to have an effect on the adhesion between starch and protein particles itself. An increase in adhesion by relative humidity of 90% results in a decreased dispersability.The dispersability of the mixtures was related to their performance upon air classification. Both the separation efficiency and tau were strongly related to dispersability (R² = 0.86 and 0.88 respectively). Hence, the dispersability, which can easily be measured, is a powerful tool to predict the air classification performance for separation of starch and protein.