FOOD. Science. Technology. Quality

Food. SCIENCE. Technology. Quality

Food. Science. TECHNOLOGY. Quality

Food. Science. Technology. QUALITY




Starch-based microparticles: a preliminary study of the structure and properties


Starch is a cheap and abundant polysaccharide, which is found in nature as water insoluble semicrystalline granules with sizes in the range of 0.5-70 μm. Although starch is easily gelatinised or dissolved in water, it is not possible to obtain stable suspensions or colloidal systems from native starches. This inherent disadvantage of starch has limited its applications. In this study potato starches were processed to obtain fully biodegradable microparticles, which behave as microgels or colloids in aqueous suspensions. The synthesis process is based on the unique combination of gelatinization and cross-linking performed in water-oil emulsions. The obtained starches are very stable in water and show an interesting shear-thinning behaviour even at high solid contents. In particular, the rheological behaviour of the new starches is unique. The starches offer new possibilities for preparing starch colloids with a range of properties. A range of starch microparticles was obtained opening the door to numerous food and non-food markets (paints and coatings, inks and pigments, superabsorbent polymers, food additives, personal care products, pharmaceuticals, ceramics, paper additives, adhesives, thickeners, emulsifiers,….). In order to make a wide-scale industrial use of these new materials possible, it is necessary to acquire detailed knowledge about the structure and properties of the prepared particles. By a multidisciplinary approach, a start was made on their process-structure-property relationships. The final goal of this work is to establish the relationships between synthesis parameters and the structural, colloidal and rheological features. Particles were prepared using epichlorohydrin and trisodium trimetaphosphate as cross-linkers. In this paper important reaction parameters, such as temperature, time and composition of the reactants (starch, cross-linker, hydroxide), which influence the structure of the microparticles during synthesis, were identified. Using Bohlin reometry the formation of the starch network structure was studied. Particle sizes of the microgels are in the range of 60 nm up to 10 μm. The synthesised particles were slightly negative (in the range of – 5 to – 45 mV). Features such as size and charge of the particles depended on the type and amount of cross-linker used. Descriptions of the rheological properties of starch-based microparticles in aqueous suspensions, both in dilute and concentrated systems, were given. The microgel-type particles showed a behaviour that is typical for (slightly) charged materials or polyelectrolytes.