Influence of gelatinization process on functional properties of cassava starch films

The effect of the paste preparation conditions on the properties of cassava starch paste and its films was investigated. Films were prepared by casting starch pastes gelatinized under eight different conditions: 70, 80, 90 or 100 degrees C at high (18,000 rpm) and low shear rate (150 rpm). The pasting properties measured by the Rapid Visco Analyzer (RVA) showed a peak at heating temperature of 80 degrees C. It was shown that the use of a high shear affected all mechanical properties determined by tensile tests, which were lower for all temperatures compared to the films prepared using low shear. Furthermore, films prepared at different temperatures and high shear showed a high scattering of data for all mechanical parameters (elasticity modulus, strain at break and maximum stress). The films prepared with low shear also showed high scattering for the strain at break at low moisture contents (RH < 45%). It was shown that different methods of paste preparation resulted in different film structures. For mild conditions (lower temperature, low shear), the effect of paste preparation on the film Properties was related to the presence of remnants of the granules or ghosts in different extents. On the other hand, in the case of severe conditions (higher temperatures.. high shear), this effect was due to phase separation in amylose- and amylopectin-rich regions. The importance of use of standard preparation method for starch films was demonstrated. (c) 2007 Elsevier Ltd. All rights reserved.