Effect of temperature and plasticizer molecular size on moisture diffusion of plasticized-starch biopolymer

Using starch pellets as precursor for traditional edible food packaging for making thermoformed products is an excellent idea. We report here the complex water migration behaviour of starch pellets as influenced by plasticizer type and concentration at various temperatures. The evidence for synergistic interaction between plasticizers and water within starch is shown by the reduced effective moisture diffusivities and moisture migration fluxes at different overall plasticizer concentrations. In addition, the effective moisture diffusivities showed stronger dependence on moisture concentration and the plasticizer molecular weight even though the moisture flux was comparable. The drying process was characterized by two effective diffusion coefficients (D 1, D2) and interestingly, the coefficients were an order of significance apart. Peleg model was investigated for predicting the drying behaviour and it is shown that the Peleg constants k1 and k 2 increase with temperature. k2, a material structure parameter, showed variation by addition of plasticizers, indicating that plasticizers were able to modify fundamental structure; and xylitol showed greater average k2 values than glycerol. Further, k1, a moisture diffusivity parameter, was affected by temperature and Arrhenius relationship was used for activation energy values for k1 of plasticized starch. It is shown that compared to starch and water, presence of plasticizer had many order of significance higher k1 and confirm the hypothesis that plasticizers can 'lock' in water within the new structure. Xylitol showed better stability in controlling moisture diffusivities and migration fluxes as compared to glycerol. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA