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 maize starch have been investigated. Subsequently the possibility of inducing or improving the mucoadhesive properties of these starches by simple technological processes such as milling and spray-drying has been assessed. Native starches were first checked for physical properties [intrinsic viscosity, thermal behaviour (differential scanning calorimetry, DSC) and solubilization index] and compared with the pregelatinized starch. The mucoadhesive properties of the starches were evaluated by means of two in vitro methods: rheological analysis and tensile stress testing. Both native and pregelatinized starches were subsequently subjected to milling and spray-drying. The technological variables analyzed were the type of mill (from laboratory to pilot-plant scale) and the process conditions (milling time and cooling temperature of the grinding chamber). The results show that mucoadhesive properties can be induced in waxy maize starch by grinding or milling, i.e., by very simple and cheap technological processes. These processes are efficient only when effected in high-energy mills. Whereas the increase in milling time was shown to improve the mucoadhesive properties of the final products, the cooling temperature of the grinding chamber had no detectable influence. Spray-drying as itself is not capable of inducing mucoadhesive properties on native starches and does not improve the mucoadhesive properties of milled waxy starch and pregelatinized starch. DSC analysis indicated that, at least for the materials considered, gelatinization, 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.