The effect of relative humidity gradient on water vapor permeance of lipid and lipid‐hydrocolloid bilayer films

Abstract

The water vapor (WV) permeance of lipid and lipid‐hydrocolloid films exposed to relative humidity (RH) gradients of 100–0%, 100–50%, 100–65% and 100–80% RH were determined. The lipids used were beeswax (BW) or a blend of BW and acetylated monoglycerides (AG). Hydrocolloids used were methylcellulose, carboxymethylcellulose or ethylcellulose (EC). All films, except those containing EC, exhibited increased water vapor permeance as the RH gradient was reduced by raising the low‐end RH. This increase in permeance was apparently caused by hydration and swelling across the entire film thickness, thus facilitating water movement through the film. Because of its hydrophobicity, EC likely lessened this swelling. Knowledge of the WV properties of edible films at relatively small gradients in the upper half of the RH spectrum, such as those used in this study, is useful because these conditions are far more common to foods than are the 100–0% gradients that are often used when evaluating films. Even though the WV permeance of BW and BW/AG films increased greatly at the 100–80% RH gradient, as compared to gradients ranging from 100–65% to 100–0%, they still possess WV barrier properties sufficient to be useful for foods.