## 4 MOFs as Smart Carriers and Delivery Systems of Sensitive Volatile Compounds
### Copper Based MOFs  
Copper-based MOFs have also emerged as promising candidates for the encapsulation and controlled release of EOs in agrifood applications. Their unique structural characteristics combined with their potential high surface area, tunable pore size and functionality, can facilitate efficient EO loading and sustained release, thereby enhancing food preservation and extending shelf life. Additionally, the low cost of copper and its low toxicity compared to other heavy metals makes these materials promising candidates for such applications. HKUST-1 is a well-established MOF, known for its large surface area and uncoordinated metal sites, which up until today has been tested for a plethora of applications [83; 84]. In the framework of encapsulation and smart release of volatiles, it has been employed as a carrier for tea tree essential oil (TTO) formulated in moisture-responsive hydrogel beads. The synthesis of HKUST-1@ALG hydrogel beads has been achieved through alginate/copper ion cross-linking and in-situ growth, resulting in a hierarchical porous structure that presents high TTO loading capacity. The release of the active substance is based on moisture-triggered mechanism and has been found particularly effective for fresh-cut fruit preservation. In detail, increased moisture levels disarray the MOF's crystal framework, leading to a slow release of the encapsulated TTO. This formulation was successfully tested for the preservation of fresh-cut pineapple by maintaining cell membrane integrity, balancing reactive oxygen species (ROS) metabolism, and inhibiting cell wall-degrading enzymes. Furthermore, these MOF-EO hybrid beads offer excellent antimicrobial and antioxidant capacities, contributing to extended shelf life and reduced contamination risk. The bead form also provides better flowability and environmental sensitivity, making it a versatile delivery system [155]. Another recent study discusses the ability of Cu-BTC MOF to encapsulate the CEO, aiming to the preparation of active packaging films for the preservation of meat products. A Cu-BTC MOF was synthesized from copper ions and 1,3,5-benzericarboxylic acid (H3 BTC). This Cu-MOF presented a high BET-specific surface area (1476.70 m\({}^{2}\)/g) and pore volume (0.89 cm\({}^{2}\)/g), providing the desired space for sufficient CEO encapsulation and controlled release. Trapping CEO in the porous structure of Cu-BTC ensures a gradual and sustained release of CEO, preventing premature evaporation and maximizing its antimicrobial and antioxidant efficacy. The verification of the successful encapsulation of CEO in the MOFs' pores was achieved through various spectroscopic methods such as UV-Vis and FT-IR spectroscopy. The presence of additional peaks in both spectra while comparing the plain MOF and the CEO@MOF was strong proof of the preparation of a loaded MOF-EO hybrid. At the same time, no remarkable change was detected at the PXRD diagrams of both materials indicating that the crystal structure of the MOF is not affected by the encapsulation of the EO. To form the final packaging medium, CEO@MOF was combined with a gelatin/pullulan mixture. The resulting gelatin/pullulan-based composite films, incorporating CEO@MOF, demonstrate significant antimicrobial activity against various foodborne pathogens, including _Staphylococcus aureus_, _Salmonellaenterica_, _Escherichia coli_, and _Listeria monocytogenes_[144]. These CEO@MOF films contribute to meat preservation through a complex mechanism. They exhibit high ABTS radical scavenging activity (98.16%). This protects meat from oxidation and provides excellent UV-blocking properties from 81.38% to 99.56% at 280 nm., preventing light-induced damage. Additionally, the films reduce moisture loss and maintain pH levels at 6.2, preserving meat texture and freshness by inhibiting bacterial growth by 99.9%. The release of CEO from the Cu-BTC MOF is influenced by the porous structure of the MOF and external environmental conditions, such as moisture and pH.