Effects of pH and Salts on Physical and Mechanical Properties of Pea Starch Films

To identify the significant contribution of intermolecular hydrogen bonds of starch molecules to the film structure formation, pH of film‐forming solutions was adjusted and also various salts (NaCl, CaCl₂, CaSO₄, and K₂SO₄) were mixed into the glycerol‐plasticized pea starch film. The film made from pH 7 possessed the highest tensile strength‐at‐break (2 times) and elastic modulus (4 to 15 times) and the lowest elongation‐at‐break compared with those of the films made from acid and alkali environments. The pH 7 film also has the highest film density and the lowest total soluble matter. At the level of 0.01 to 0.1 M of CaSO₄ and 0.1 M of K₂SO₄ in a kilogram of starch, the water solubility of the film increased, while chloride salts slightly lowered the solubility. NaCl and CaSO₄ reduced water vapor permeability (WVP), while CaCl₂ slightly increased WVP at 0.01 and 0.06 M concentrations, and K₂SO₄ significantly increased WVP at 0.03 and 0.15 M. Presence of salts increased tensile strength (5 to 14 times than the control films) and elastic modulus (35 to 180 times) of starch film at 0.01 to 0.03 M of CaSO₄ and K₂SO₄. Elongation‐at‐break increased significantly as salt concentration increases to an optimal level. However, when the concentration exceeded above the optimal level, the E of starch films decreased and showed no significant difference from the control film. Overall, the addition of salts modified physical and mechanical properties of pea starch films more than pH adjustment without any salt addition.