Biological Activity and Physical Properties of Pullulan Films and Coatings Supplemented with Urban Propolis Extract

Propolis has long been recognized for its biological properties, but its availability is increasingly threatened by apiary losses in agricultural areas. One response to this problem is the development of urban apiaries, located in urbanized environments and often established for educational and promotional purposes. In this study, edible pullulan films were prepared with the addition of 10, 20, and 30% propolis extract obtained from an urban apiary located in Toruń, Poland. The effect of these coatings applied to cherries on fruit spoilage, the growth inhibition of Aspergillus niger and Penicillium chrysogenum, and changes in pH, titratable acidity, soluble solids content, and fruit color were evaluated. The films showed both antimicrobial and antioxidant properties. The biological evaluation demonstrated dose-dependent antimicrobial activity, with inhibition zones ranging from 7.27 to 17.23 mm for fungi and from 7.09 to 16.22 mm for bacteria, with the strongest effects observed against L. monocytogenes, C. krusei, and P. chrysogenum. Antioxidant activity, determined using the DPPH radical scavenging assay, increased with propolis concentration and reached 29.44% for films containing 30% urban propolis extract. Moreover, pullulan coatings enriched with propolis reduced mold counts on cherries after 96 h of storage to 2.82 log CFU/g for P. chrysogenum and 2.72 log CFU/g for A. niger, compared with 7.02 and 7.17 log CFU/g, respectively, in uncoated fruit. The influence of urban propolis extract on the thickness and color of the obtained films was also demonstrated. It was found that pullulan coatings with urban propolis extract applied on cherries showed fungistatic properties against P. chrysogenum and A. niger. The developed films and coatings show potential for use in food technology to support the preservation of perishable raw materials; however, further studies are needed to confirm their effectiveness under broader storage conditions.