Active Polylactic Acid (PLA) Films Incorporating Almond Peel Extracts for Food Preservation

Almond peel extracts, containing 0.2-0.8% (w/w) phenolic compounds with notable antioxidant and antimicrobial activities, could be used as a natural source of active compounds for the development of active films for food preservation. In this study, almond peel extracts obtained by subcritical water extraction at 160 and 180 °C were incorporated into PLA films (PLA-E160 and PLA-E180). The films were characterized in terms of their microstructure, mechanical, barrier, optical and thermal properties. Furthermore, the release of phenolic compounds and hydroximethylfurfural (HFM) into food simulants with different polarity was evaluated, as well as the film's potential antioxidant and antimicrobial activities. To validate their effectiveness as active packaging materials, shelf-life studies were conducted on fresh orange juice and sunflower oil packaged using PLA-160 films. The results show that the incorporation of the almond peel extracts led to significant changes in the films' microstructure and mechanical properties, which became darker, mechanically less resistant, and stretchable (p < 0.05), with slightly lower thermal stability than neat PLA films. The release of phenolic compounds and HFM from extract-enriched films was promoted in the 95% ethanol simulant due to the matrix swelling and relaxation. Food products packaged with PLA-E160 exhibited slower oxidative degradation during storage, as indicated by the higher ascorbic acid content and hue color in orange juice and lower peroxide content in sunflower oil. Nevertheless, both in vivo and in vitro studies showed no antimicrobial effectiveness from the films, likely due to the limited release of active compounds to the surrounding medium. Thus, almond peel extract conferred valuable properties to PLA films, effectively reducing oxidative reactions in food products sensitive to these deterioration processes.