Effect of surfactants on water barrier and physical properties of tapioca starch/decolorized hsian-tsao leaf gum films

The objective of this research is to enhance the water barrier properties of tapioca starch/dHG edible films by incorporating sucrose ester surfactants with different HLB values. The moisture sorption isotherms, mechanical properties, microstructure and optical character of the resulting films were examined as well. It was found that the water barrier property of starch/dHG films is promoted significantly by surfactants, alongside a decreasing tendency in tensile strength and tensile strain at break. Scanning electron micrographs of the starch/dHG/surfactant composite films revealed the folded (multi-layer) microstructure in contrast to the homogeneous matrix of the control films. Starch/dHG/surfactant composite films show low opacity values. With increasing HLB value of the surfactant, the water vapor permeability and tensile strength of starch/dHG/surfactant composite films decrease. Moreover, the water vapor permeability, tensile strength, strain at break, and equilibrium moisture content of starch/dHG/surfactant composite films decrease when the surfactant content is increased, accompanied by an increasing tendency in opacity value. On the other hand, starch/dHG composite film with an emulsion of surfactant and beeswax shows a lower mechanical strength and significantly higher opacity value with less improvement in water vapor permeability. (C) 2008 Elsevier Ltd. All rights reserved.