4.4.2. Swelling Index

The swelling index allows the level of moisture absorption (absorption capacity) of the edible film to be evaluated. This parameter has a high correlation with solubility [525] and the structure density and thickness of edible films [29], as well as with hydrophilicity of biopolymers used for films processing.

According to the method by Basiak et al. (2017), the film samples are cut into 2 cm × 2 cm pieces and weighed and immersed in distilled water (25 °C) for 2 min. Wet samples are blotted with filter paper to remove excess liquid and weighed. A similar Equation (7) is used to determine the swelling index [29].