A Comprehensive Study on Gelatin- and Whey Protein Isolate-Based Edible Films as Carriers of Fireweed (Epilobium angustifolium L.) Extract

Gelatin (GEL) and whey protein isolate (WPI) are often taken into account as carriers of phytoantioxidants for developing active packaging. The materials obtained, however, have not yet been systematically compared to demonstrate their potential benefits and drawbacks. Fireweed extract (FE) is a rich source of polyphenols with high antioxidant activity. Therefore, in this study, the structural, physicochemical, and antiradical properties of GEL and WPI films incorporated with freeze-dried fireweed extract (FE; 0, 0.0125, 0.025, 0.05%) were simultaneously evaluated. As verified by X-ray diffraction, the GEL-based films were more crystalline and, consequently, mechanically stronger (similar to 9-11 vs. similar to 6 MPa) and less permeable to water vapor than the WPI films (44.95-52.02 vs. 61.47-70.49 g mm m(-2) day(-1) kPa(-1)). Furthermore, GEL offered a bit more transparent, less yellow, and more stretchable films (similar to 50-59% vs. similar to 26%). In turn, the WPI films had superior UV-protective potential. The higher FE concentration yielded more yellow films with improved UV-blocking ability. The FE (0.05%) made the GEL cryogel denser. Based on the half-time reduction of 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (t(ABTS50%)), the 0.025, and 0.05% FE-supplemented WPI films exhibited similar to 1.6 and similar to 1.9 times better antiradical potential than the GEL counterparts. This result implies that the WPI-based films, being more soluble (35.12-36.74 vs. 31.51-33.21%) and less swellable (192.61-205.88 vs. 1056.93-2282.47%), ensured faster release of FE into aqueous medium. The slower building up of the antiradical activity of the FE-supplemented GEL films suggests that GEL could be more useful in the development of slow/less migratory active packaging systems for high moisture food.

Automated summary

In this study, the structural, physicochemical, and antiradical properties of GEL and WPI films incorporated with freeze-dried fireweed extract (FE) were evaluated. The results showed that GEL films had higher mechanical strength and lower permeability, while WPI films had better UV-protective potential and antiradical activity.