Film properties of wheat starch modified by annealing and oxidation

In this study, we investigated the impact of physical modification by annealing and chemical modification by oxidation on native wheat starch, for later application in biodegradable films. The starches obtained were evaluated for amylose content, carboxyl content, paste properties, swelling power, and solubility. Sequentially, films were made with both modified starches in comparison with native starch (control) and evaluated for morphology, color, mechanical, and solubility properties. As for the modification of starches, oxidation caused more intense changes when compared to annealing, especially in the amylose content, with oxidized starch increasing by 40% and annealing by 25% about native starch. While annealed caused a reorganization of the molecules of the starch chains, increasing the stability of the starch to heating, resulting in higher paste temperature, lower viscosity, and lower breakage rate. In addition, when evaluating the properties of the films, annealing allowed for obtaining more homogeneous films, without cracks in their structure, with few changes in their mechanical properties and water solubility. The change in starch properties caused by oxidation resulted in undesirable changes in the films as a heterogeneous structure, with the presence of cracks, and less elongation. It is concluded that the annealing treatment allowed obtaining films with properties similar to native starch films and proved to be a promising alternative for the development of biodegradable packaging with properties superior to those of chemically modified starch films.