Effect of rice wax on water vapour permeability and sorption properties of edible pullulan films

Edible films were prepared using various ratios of pullulan and rice wax. Freestanding composite films were obtained with up to 46.4% rice wax. Water vapour barrier properties of the pullulan film were improved with increased addition of rice wax. Moisture sorption isotherms were also studied to examine the impact of rice wax on the water sorption characteristics of the film. The Brunauer–Emmet–Teller (BET) and Guggenheim–Anderson–de Boer (GAB) sorption models were tested to fit the experimental data. The models gave a good fit up to the water activity (aw) of 0.55 for BET and a full range of aw from 0.12 to 0.95 for GAB (R2 ⩾ 0.98). Changes in the sorption parameters, particularly such as the decrease in monolayer moisture content (Mo), reflect the trend of reduced hydration capacity with increased addition of rice wax, providing useful information on water activity conditions to achieve stability for the composite films.