Influence of hydrocolloid nature on the structure and functional properties of emulsified edible films

To investigate the influence of polymer behaviors on the structure and the functional properties of emulsified films, agar (AG) and cassava starch (CAS) were used as hydrocolloid continuous phases in which hydrogenated vegetable oil (VGB81) was dispersed. Different ratios of hydrophilic/hydrophobic materials (HB/HL) were also used in film formulations to study the evolution of film-emulsion structure. Microscopically observed, VGB-CAS emulsified films exhibit a similar bilayer structure. However, there was just a migration and an aggregation of lipid particles. There was no coalescence which could form a continuous "lipid layer" necessary for an effective barrier. Moreover, they could not be made with a HB/HL ratio greater than 0.7:1. Conversely, AG chains set into gel, which solidifies film-forming emulsion before drying, leading to a fixed macronetwork structure. Films made with a high HB/HL ratios lead to a film structure becoming like a multilayer system. The water vapor permeability of emulsified films is better found when HB/HL >= 1: 1 when films are formed only with gelling polysaccharide (AG). In addition, there is no relationship between the moisture sorption and the moisture permeability of emulsified films. In contact with liquid water, brief sorption and swelling surface are observed for VGB-AG film surface and rapid absorption following a temporary hydrophobicity is found in the case of VGB-CAS films. While the mechanical properties of VGB-CAS films are strongly altered, those of VGB-AG films are considered to be sufficient for most of applications. (C) 2008 Elsevier Ltd. All rights reserved.