Valorisation of chestnut spiny burs and roasted hazelnut skins extracts as bioactive additives for packaging films

The exploitation of agri-food by-products is a pertinent strategy in the context of the implementation of the circular economy concept in the agri-food industry. Therefore, the present work aimed to produce bioactive pullulan-based films loaded with polyphenolic-rich extracts from chestnut spiny burs (CSB, Castanea sativa Miller.) and roasted hazelnut skins (RHS, Corylus avellana L.). The hydroalcoholic extracts obtained from the CSB and RHS by-products were separately combined (1 %, 5 %, and 10 % w/w) with the filmogenic pullulan (PL) exopolysaccharide to fabricate flexible and bioactive films via simple solvent casting technique. The films present thermal stability up to 200 degrees C, good mechanical performance with Young's modulus values higher than 2.6 GPa, and UV-light barrier properties. Furthermore, these flexible PL-based films exhibit a minimum antioxidant activity of ca. 94 % (DPPH scavenging activity) for the film composed of only 1 % of hydroalcoholic extracts (w/w relative to PL, i.e. 192 mu g of extract per cm(2) of film). Both sets of films were tested for antibacterial activity towards Staphylococcus aureus (a Gram-positive bacterium) and the results demonstrate antibacterial effectiveness with the increasing content of both hydroalcoholic extracts, reaching a maximum of 4-log CFU mL(-1) reduction for the PL/RHS_10 film after 6 h. All the data evidences the potential applicability of these PL-based films containing hydroalcoholic extracts from agri-food by-products for the development of sustainable films for active food packaging.