CONICET | Buscador de Institutos y Recursos Humanos

ABSTRACT The objective of this work is to manufacture and characterize edible films made from sodium caseinate and chitosan, with an envisioned application as a protective layer on foods. Glycerol was used as plasticizer, and the films were obtained by a casting/solvent evaporation method. Water vapor permeability (WVP) values were determined by the ASTM E96-95 method [1]. The effects of different glycerol concentration (0.15, 0.28, 0.37 and 0.50 g/100 g of filmogenic solution) on chitosan and caseinate films were determined at 25º C, using a relative humidity (RH) gradient (internal: external) 0:64.5. The effect of glycerol was analyzed and the experimental data were fitted using a two parameter exponential growth equation [2]. WVP increased with increasing glycerol content in both films, being chitosan samples much more permeable than caseinate ones at any glycerol content. WVP of caseinate, chitosan and chitosan/sodium caseinate films with 28 % wt./wt. glycerol were determined for two RH gradients: 0:64.5 and 100:64.5. As can be expected, the WVP of films increased with increasing humidity. In this case, both, chitosan and caseinate films showed a similar increment of WVP with respect to those obtained at 0:64.5. The moisture content (MC) of films was determined gravimetrically, in quadruple determination, by drying film samples in vacuum oven at 40º C during three days. Then, the films were stored in 75% RH chambers at ambient temperature, and the weight was registered periodically until the equilibrium moisture content (EMC) was reached. Equations obtained from microscopic mass balances for vapor diffusion in solids were used to determine the effective diffusion coefficients of the different films [3]. The effect of glycerol content on the moisture absorption was also evaluated. It was found that an increase of glycerol level increased the equilibrium moisture content of films due the ability of this plasticizer to bind water.