Valorisation of Cardoon Leaves and Lemon Peel for Potential Active Food Packaging: Impact of Drying on Nutritional...

Despite being usually discarded, agro-industrial by-products are rich in bioactive and nutritional compounds and can be redirected into new foods or food packaging. This study evaluated the nutritional composition of cardoon leaves (Cynara cardunculus L.), an agro-industrial by-product, and assessed the impact of the drying process on those characteristics. Furthermore, extracts of the dried leaves and dried leaves combined with lemon peel were incorporated into whey protein-based films at concentrations of 0.5%, 1.0%, and 2.0% (w/v). Their physical, barrier, mechanical, and thermal properties were also analysed. When compared on a dry weight (DW) basis, the dry leaves maintained a stable nutritional profile with no significant degradation of key components, presenting with high carbohydrates (15.4 ± 1.1 g/100 g), moderate protein (21.2 ± 0.4 g/100 g), and low fat (2.0 ± 0.1 g/100 g). The leaves were also a good source of dietary fibres (43.9 ± 1.8 g/100 g) and minerals (13.7 ± 0.2 g/100 g of ash). Incorporating the extracts altered the films' physicochemical properties, reducing their water vapour permeability up to 4.05 ± 0.26 10^-10 g/s.m.Pa, while their tensile strength decreased from 0.34 ± 0.06 to 0.23 ± 0.01 MPa depending on the formulation, and their elongation at break decreased by up to 6.58 ± 0.70%. In contrast, Young's modulus increased by up to 0.11 ± 0.03 MPa, indicating higher rigidity. This behaviour may be attributed to the interactions between the phenolic compounds and the whey protein matrix, which restricted polymer chain mobility and increased film rigidity while reducing matrix cohesion and flexibility. The results demonstrate that while the extracts enhanced the barrier properties of the films, they reduced the mechanical properties. Overall, the results suggest that cardoon by-products have potential applications in active food packaging, contributing to the development of bio-based materials within a circular economy framework.