Delayed and stable flow-DST behavior for granular starch suspensions

Abstract

• The rheological behavior of cassava starch suspensions in glycerol was studied. • The presence of plastid membranes was verified for commercial cassava starch. • A deformable particle behavior was evidenced for starch granules in suspension. • Removal of the plastid envelope influenced delayed shear-thickening events. • Data allow distinguishing when a Newtonian or a shear thinning behavior precedes shear-thickening. Starch is synthesized in intracellular structures called amyloplasts, whose wraps delimiting the organelle are referred to as plastid membranes. Such envelopes are generally removed in the industrial processing of cereal starches, but not of cassava starch (CS), which is submitted to a different process. The occurrence of different rheological behaviors before a shear thickening (ST) event for granular starch suspensions is well known, but not yet thoroughly explained. The objective of this work was to study physical changes on commercial CS suspensions that could intensify their shear thickening properties when glycerol is used as a solvent. The results show that the removal of plastid envelopes from starch granules significantly reduces its deformable character in glycerol suspensions. It intensifies the delayed ST behavior and maintains the flow stability during an eventual discontinuous ST transition, provided that suspensions are conditioned at an adequate relative humidity (close to 43%). Experimental data also have suggested an explanation for why a Newtonian or a shear-thinning behavior precedes shear thickening in starch suspensions.