**4. Conclusions**

An exhaustive analysis of the effect of cross-linking of the pectin matrix with calcium and iron ions was carried out. Mechanical and permeation properties were studied and discussed to find new insights about structure–property relationships of modified films. Mechanical stiffness was observed when pectin was cross-linked with Ca2+ and Fe3+ showing higher Young's modulus and tension at break than orange and commercial pectin. Reduced water uptake was observed for Pec-Ca and Pec-Fe. However, values still being high concerning synthetic polymers. Similar results were obtained for water vapor permeation being Pec-Ca which depicted the lowest value. Finally, gas permeation assays were performed, demonstrating a good ability of cross-linked films to modify the atmosphere inside a packaging destined for fruits and vegetables packaging.

As a general conclusion, the conformation of two-folded chains in Pec-Ca concerning the three-folded chains in Pec-Fe was responsible for obtaining stronger mechanical properties, lower water uptake and water vapor permeation, and promising O2/CO2 selectivity in this cross-linked film.
