Effects of phosphorylating salts and temperature on the preparation of rice starch phosphates by extrusion

Rice starch phosphates were prepared by the extrusion of rice starch with p hosphate salts including sodium tripolyphosphate (STP), sodium trimetaphosp hate (SMP). and a 50:50 mixture of STP and SMP (STP-SMP). The incorporation of phosphorus in the starch increased with increased barrel temperature ra nging from 120 to 180 degrees C. At 180 degrees C, phosphorus contents for products treated with STP, SMP, and STP-SMP were 0.376, 0.194, and 0.360 %, respectively. The effects of phosphorylation on functional and rheological properties of the starch varied, depending on the extent of molecular degr adation and the formation of intermolecular cross-linking caused by the hea t and shear of extrusion. Generally, extrusion stabilized the pasting prope rties of the extrudates, whereas phosphorylation enhanced the pasting consi stency of the starch products. Good correlation was observed between the ex trusion specific mechanical energy (SME) and the product of solubility and intrinsic viscosity, indicating a close relationship between the energy inp ut in the extrusion process and the performance behavior of the extruded ph osphorylation products.