Environmentally Benign Bioderived, Biocompatible, Thermally Stable MOFs Suitable for Food Contact Applications

Background: Metal-Organic Frameworks (MOFs), a relatively new category of materials which came into attention about two decades ago, have caught attention of researchers across industrial sectors including food additives, flavor, food packaging and food sensing. More than 100,000 such structures have been synthesized, and approximately 500,000 have been theoretically determined. However, most of these structures are synthesized using transition metal ions and petroleum derived ligands which creates cytotoxicity and sustainability related concerns, respectively. Additional challenges with MOFs include thermal, moisture, and hydrothermal stability as well as pH sensitivity, reusability and scalability. Scope and approach: To mitigate the environmental, sustainability and toxicological concerns, researchers have utilized bio-compatible and edible linkers such as polyphenols, cyclodextrins, peptides, amino acids etc. linked with non-toxic cations including endogenous/intercellular cations such as Zn2+, Fe2+, Fe3+ Mg2+, Ca2+, and K+ among others. Other factors hinder the real-life applications of these bio-compatible MOFs including thermal or hydrothermal stability, pH of the application medium, food-contact and cytotoxicity concerns. Key findings and conclusion: This paper systematically provides an overview of various factors such as coordination ability, acid dissociation constant and acid bond orbitals among others and links them to the thermal, hydrothermal stability and reusability. Various MOFs made from edible, biocompatible, biological ligands and endogenous non-toxic ions suitable for food, food packaging or food contact application have been identified. Structure, porosity and physical properties of these MOF families have been summarized.