Thermal characterization of composite edible films based on tapioca starch and wheat bran

L. FAMÁ; N. BURGOS; L. GERSCHENSON; S. GOYANES; A. JIMENEZ

San Sebastián, España.

Congreso; Modification, degradation and Stabilization, MoDeST 2006; 2006

Starch is a natural polymer useful for numerous applications in the food industry. Among all types of starch, tapioca is a good commercial cash crop and a major source of good quality starch. Due to shortage or relatively high price of traditional starch sources, such as wheat and soybeans, tapioca starch is viewed as an alternative source by food companies for its use in biodegradable formulations for packaging. Edible films and coatings have long been used to protect food products [1]. In addition, the incorporation of antimicrobials, antioxidants and other preservatives to foodstuff is a promising possibility of edible films to be used in food packaging. Some previous work was reported on the mechanical properties of edible films formulated with tapioca starch and glycerol with a marked increase in strain at break, a decrease in storage modulus and some changes in crystallinity, although a clear influence of storage time was also observed [2]. However, the knowledge of the thermal behaviour of these new materials is necessary in order to assess their performance either at oven or freezing temperatures. Films based on aqueous solutions (water 92.3%) with the addition of tapioca starch (5%), glycerol (2.5%) and potassium sorbate (0.2%) were prepared with 0.17 and 1.5% of wheat bran respectively. They were equilibrated at a controlled atmosphere with saturated NaBr (relative humidity: 57.5 %). Thermogravimetric, calorimetric and pyrolysis tests were carried out in order to control the material´s performance at low and high temperatures. The thermal properties at low temperature of these materials were studied by using a Modulated Differential Scanning Calorimetry (MDSC) to investigate the properties of gelatinization and ice melting during frozen. Thermal tests were carried out by TGA and a progressive decrease in weight was observed from 50 to 150ºC with a further significant weight loss from 250ºC to approximately 350ºC corresponding to the starch decomposition [3]. There is no significant overlapping between decomposition patterns of the different components resulting in neat TGA curves with the possibility of calculation of kinetic parameters, such as apparent activation energy and order of reaction. Isoconversional Friedman method was used to calculate kinetic parameters and apparent activation energies around 100-140 kJ/mol, depending on the amount of wheat bran added to the starch-based material. It can be concluded that degradation of these materials is not significantly influenced by the addition of different amounts of wheat bran. Pyrolysis behaviour of these materials is also studied and preliminary results at temperatures around the main thermal decomposition show the evolution of carbonaceous compounds (CO2), acetaldehyde and a high amount of water. Nevertheless, some additional and important peaks can be identified as furfural (furancarboxaldehyde) and derivatives.   References [1] M. García, M. Martino, N. Zaritzky, J. Sci. Food & Agriculture, 1998, 76, 411-420. [2] L. Famá, A.M. Rojas, S. Goyanes and L. Gerschenson, LWT, 2005, 38, 631-639. [3] V.A. Alvárez, A. Vázquez, Polym. Degrad. & Stabil. 2004, 84, 13-21.