Applying O/W emulsions encapsulating crude red propolis to produce active gelatin or soy protein isolate-based films

Crude red propolis (CRP), despite its high phenolic content and the absence of solvent residues from extraction, remains unexplored for the development of active films due to its poor dispersibility in aqueous media resulting from its hydrophobic nature. This study aimed to formulate and characterize an oil-in-water (O/W) emulsion encapsulating CRP and apply it in active films based on gelatin (G) or soy protein isolate (SPI). A Box-Behnken experimental design evaluated the effects of Tween 80 and polyglycerol polyricinoleate (PGPR) concentration, and the number of sonication cycles (independent variables) on stability index, mean droplet diameter, and span index (dependent variables) of emulsions. Tween 80 significantly affected emulsion stability, droplet size, and span, while homogenization cycles influenced only droplet size; the PGPR showed minimal effects. The best emulsion (1.35 % w/w of Tween 80, 0.2 % w/w of PGPR, and 6 sonication cycles) was incorporated into G- and SPI-based films resulting in porous structures with surface oil droplets, increased surface roughness, reduced water contact angle, and enhanced opacity and UV-visible light barrier properties. Mechanically, emulsion incorporation enhanced the tensile strength (from 17.6 ± 0.6 to 23.0 ± 1.1 MPa), and elongation at break (from 19.6 ± 2.4 to 60.6 ± 2.3 MPa) of G films, whereas in SPI films only elongation at break increased (from 103.1 ± 12.5 to 189.8 ± 11.2 %). Both films retained antioxidant activity provided by CRP (from 1.4 ± 0.2 to 9.4 ± 0.2 and from 5.2 ± 0.3 to 12.6 ± 0.7 mg TE/g, for G and SP films, respectively); however, no inhibition zones were observed in microbiological assays, despite the antimicrobial properties of the CRP-loaded emulsions.