Physicochemical, mechanical and structural properties of composite edible films based on whey protein isolate/psyllium seed gum.

A composite film composed of whey protein isolate (WPI) and psyllium seed gum (PSG) was investigated. Its physicochemical, mechanical and structural properties were determined at different ratios of WPI/PSG (1:0, 3:1, 1:1, 1:3, 0:1). WPI/PSG composite films had higher water contact angle and water vapor permeability, as well as lower oxygen permeability and light transmittance as compared with single WPI or PSG films. With the increase in PSG concentration, higher film brightness and whiteness index, and smaller total color difference were observed. The tensile strength and elastic modulus of the composite film at WPI/PSG ratio of 1:1 was the highest. Elongation at break of composite films was higher than that of the single films. WPI/PSG composite films were more effective than single films in reducing the surface cracks and degree of cracks. XRD revealed a typical semi-crystalline amorphous structure of the composite films. With the increase of the PSG content, higher diffraction peak strength and crystallinity of the films were observed. The results indicated that the properties of the WPI/PSG composite film were superior to that of PSG or WPI film alone. The composite film at WPI/PSG ratio of 1:1 resulted in the highest comprehensive physicochemical and mechanical performance.