TECHNOLOGICAL INDUCTION OF MUCOADHESIVE PROPERTIES ON WAXY STARCHES BY GRINDING

In the present work the mucoadhesive properties of two native starches (maize starch and waxy maize starch) and one pregelatinized waxy maiz e starch have been investigated. Subsequently the possibility of induc ing or improving the mucoadhesive properties of these starches by simp le technological processes such as milling and spray-drying has been a ssessed. Native starches were first checked for physical properties [i ntrinsic viscosity, thermal behaviour (differential scanning calorimet ry, DSC) and solubilization index] and compared with the pregelatinize d starch. The mucoadhesive properties of the starches were evaluated b y means of two in vitro methods: rheological analysis and tensile stre ss testing. Both native and pregelatinized starches were subsequently subjected to milling and spray-drying. The technological variables ana lyzed were the type of mill (from laboratory to pilot-plant scale) and the process conditions (milling time and cooling temperature of the g rinding chamber). The results show that mucoadhesive properties can be induced in waxy maize starch by grinding or milling, i.e., by very si mple and cheap technological processes. These processes are efficient only when effected in high-energy mills. Whereas the increase in milli ng time was shown to improve the mucoadhesive properties of the final products, the cooling temperature of the grinding chamber had no detec table influence. Spray-drying as itself is not capable of inducing muc oadhesive properties on native starches and does not improve the mucoa dhesive properties of milled waxy starch and pregelatinized starch. DS C analysis indicated that, at least for the materials considered, gela tinization, either obtained by cooking and subsequent spray-drying (as for pregelatinized starch) or by simple grinding (as for waxy starch) , is a necessary requisite to induce mucoadhesive properties. (C) 1997 Elsevier Science B.V.