Green Propolis Extract as an Antioxidant Additive for Active Films Based on Sodium Alginate and Hydrolyzed Collagen

Herein, sodium alginate (SA) and hydrolyzed collagen (HC) blend films incorporating propolis extract (PE) (1-4 wt%) were prepared. A thorough morphological, structural and property-related evaluation has been provided. Micro-structurally, the incorporation of low PE concentrations resulted in more uniform SA/HC films. The FTIR results confirmed no modifications in the film's functional groups, and the crystallinity degrees (XRD) of the films ranged from 4.1 to 5.6%. The incorporation of PE caused an increase in tensile strength, from 7.9 MPa (SA/HC) to 16.3 MPa (SA/HC/PE3%). Additionally, PE incorporation reduced the water affinity of the films, leading to a reduction in their moisture content. A type III moisture sorption isotherm was observed for all films at 25 & DEG;C, and the Smith's model provided the best fit, suggesting that SA, HC and PE presented good miscibility, reducing the availability of functional groups for adsorption of water molecules. More importantly, the incorporation of PE improved the antioxidant activity of the films from 3.43% (SA/HC) to 22.5% (SA/HC/PE4%), and provided an exceptional UV light blocking ability. Overall, green PE can be considered an interesting option for the enhancement of SA/HC bioactive film performance.