ZAMAN, TAHIR (2026) Evaluation of the functional properties of phenolic compounds for food packaging applications. [Tesi di dottorato]

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Abstract

This PhD research project has been mainly focused on the exploitation of natural phenolic compounds, widely recognized for their antioxidant and antimicrobial properties, in food packaging, to enhance shelf life and ensure product safety. Recent advancements have also demonstrated that these compounds may significantly improve not only the functional but also the physicochemical (e.g., thermal resistance and mechanical properties) of biopolymer-based films, contributing to the development of sustainable packaging solutions. More in detail, the main aim of this PhD work was an in-depth and systematic analysis of the effects of different additives on the performance of films intended for food packaging to provide data that could guide the selection of the specific combinations to obtain film with specific properties. As to the film polymeric matrix, the attention was focused mainly on poly (vinyl alcohol) (PVA) and chitosan, whereas the main phenolic compounds tested were (nano)lignin, phenols from Lemna minor leaves, and phenols recovered from agri-food wastes and by-products such as grape pomace, spent coffee grounds, and pomegranate peels. In addition, the possibility to exploit phenolic compounds also to produce silver nanoparticles endowed with antimicrobial properties was explored. Key findings were the following: a) Differential effects of the antimicrobial (nano)chitosan and of the antioxidant/UV-Vis radiation blocking agent (nano)lignin on the morphological, optical, mechanical, thermal, antioxidant, and antibacterial properties of poly (vinyl alcohol)-based films were observed. Indeed, films containing both nanolignin and nanochitosan exhibited the most homogeneous surface and the highest UV-Vis radiation blocking efficacy and water resistance, whereas mechanical and thermal testing showed reduced performance when nanoscale additives were incorporated. In addition, antioxidant and antimicrobial properties were higher for films containing lignin alone. Similar results were obtained when a phenol-rich Lemna minor leaf extract was employed as additive in place of lignin. b) Integrating chitosan with PVA, lignin and lignin-silver nanocomposites may significantly enhance the physicochemical and functional performance of films intended for food packaging applications. FTIR analysis revealed that lignin acted primarily as a filler, being physically embedded in the polymer matrix without altering its chemical structure. On the other hand, lignin and particularly the lignin-silver nanocomposite imparted UV-Vis radiation blocking ability to the films. Films with high PVA content exhibited superior flexibility compared to pure chitosan films. Antioxidant assays confirmed potent radical scavenging and reducing properties attributed to the phenolic groups of lignin, with PVA differentially affecting the efficacy of the films depending on the assay medium. c) Incorporation of deep eutectic solvents (DES) improved film flexibility and mechanical strength of chitosan films, therefore DES can be easily exploited as both green solvents for the extraction of phenolic compounds from agri-food wastes and as film plasticizers.

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