2.3.2. Water vapour permeability
The water vapour permeability (WVP) of films was measured gravimetrically according to the ASTM E96-05 method (2005) and adapted to hydrophilic edible films by McHugh, Avena- Bustillos, and Krochta (1993). Circular test cups were made of glass with 49 mm internal diameter and 1.1 cm height. Films without pinholes or any defects were sealed to the cup mouth containing 6 ml distilled water (100% RH; 2.337 _ 103 Pa vapour pressure at 20 _C), placed in a desiccators at 20 _C and 0% RH (0 Pa water vapour pressure) containing silica gel. The water transferred through the film and adsorbed by the desiccant was determined from the weight loss of the permeation cell. The films were allowed to equilibrate for 2 h before the cells were initially weighed. The cells were weighted at intervals of 2 h during 10 h with an analytical balance (ฑ0.0001 g). The slope of weight loss versus time was obtained by a linear regression (r2P0.99). The measured WVP of the films was determined as follows: