Preparation and characterization of polypropylene/sodium propionate (PP/SP) composite films for bread packaging application

To prolong the shelf life of bread, polypropylene/sodium propionate (PP/SP) composite films were prepared via a melt-extrusion process. To investigate the feasibility of using PP/SP composite films as a bread packaging material, their chemical structure, morphology, mechanical properties, barrier properties against water, surface properties, and antimicrobial properties were investigated. A storage test for bread was also conducted. The mechanical and thermal stability of the PP/SP composite films enhanced with increasing SP content. Compared with pure PP, the PP/SP composites had increased hydrophilicity that increased with increasing SP content. These composite films showed enhanced antimicrobial activity against both Gram-negative and Gram-positive microorganisms. This was due to the interaction of SP and water originating from the bread, which modifies the pH of the bread and causes destruction of the cellular structures of fungi and also reduces the growth rate of bacteria. The enhanced thermal, mechanical, antifungal, and antimicrobial properties achieved by the addition of SP can be beneficial for maintaining the freshness of bread and prolonging its shelf life.