Development and characterization of acetylated corn starch biodegradable films

LÓPEZ, OLIVIA; GARCÍA, MARÍA ALEJANDRA; ZARITZKY, NOEMÍ E.

Viña del Mar, Chile

Congreso; 10 International Congress of Engineering and Food; 2008

Native starch can be chemically modified to improve its functionality and to expand its uses. The interest in biodegradable films from renewable and natural polymers has been increased in the last years due to the environmental problems caused by the use of synthetic polymers.  The objectives of the present work were: i) to characterize acetylated starch analyzing the degree of substitution, granule morphology and swelling, ii) to measure thermal and rheological properties of the filmogenic suspensions, iii) to develop by casting biodegradable films optimizing the concentration of glycerol as plasticizer and iv) to characterize the microstructure, mechanical properties and water vapour permeability (WVP) of the films. Chemical modification did not cause any change in the morphological properties of starch granules however the swelling of the acetylated starch (a.s) was lower than that of native starch. Granules exhibited a typical cereal X ray diffraction pattern with a lower crystallinity degree than native starch. Molar substitution degree of a.s was 0.084 being in agreement with the permitted limits for food applications. Rheological analysis of the a.s filmogenic suspensions (4-6% w/w) showed a viscoelastic behavior; dynamic oscillatory assays showed a typical gel pattern. Differential Scanning Calorimetry (DSC) measurements indicated that acetylation decreased enthalpy and gelatinization onset and peak temperatures. WVP was determined using a modification of theASTM method and a value of  1.64´10-11 g/s m Pa was obtained. Humidity Water content, water activity and solubility of the film in water at 25 and 100oC were measured. Microstructure was characterized by Scanning Electron Microscopy (SEM); cross sections of the films showed a multilayer arrangement in the absence of glycerol and a homogeneous and compact structure when plasticizer was added. Tensile tests (maximum force, F and relative elongation at break, E) were performed with a TA xT2i texturometer. Films without glycerol were rigid and brittle while plasticized films were more flexible (E= 68.5%). In conclusion acetylated modified starch can be used to produce biodegradable films with better water vapor barrier properties than native starch films and adequate mechanical features. Besides, its composition allows to be applied as edible coatings.