## 4 MOFs as Smart Carriers and Delivery Systems of Sensitive Volatile Compounds
### Zinc Based MOFs  
Zn-MOFs are another highly promising family of MOFs for controlled release of volatile compounds with antimicrobial action, with a strong emphasis on agrochemical and agrifood applications. The appeal of this class of materials stems from several key advantages related to their ease of synthesis, low cost, low toxicity combined with their intrinsic antimicrobial properties originating from Zn itself. In general Zn-based MOFs can be characterized as cost-effective, tailorable frameworks which can be easily synthesized to be applied in diverse fields. An important example towards this direction was the employment of a Zn, 2-amino tetrephthalic acid-based MOF, presenting a high surface area, as an ideal carrier for a temperature-sensitive volatile, as thymol. In this example, MOF loading with thymol is achieved through a simple soaking method, allowing the EO to be absorbed into the MOF's pores. The release mechanism of thymol is governed by non-covalent interactions, facilitating a sustained release that enhances antimicrobial efficacy. Thymol was loaded into the porous framework through soaking a dried amount of the MOF overnight into a thymol-CHCl\({}_{3}\) solution. This formulation was found to be efficient in the inhibition of bacteria growth. More specifically, it was found to have an activity against the growth of pathogenic strains like _E. coli_ O157:H7. This MOF presented a strong antimicrobial activity, achieving a 4.4 log reduction of _E. coli_ O157:H7 within 24 h This approach offers prolonged antimicrobial activity, improved thymol dispersion in water, and the potential for indirect food applications, minimizing direct contamination risks [158]. Another important representative of the Zn-MOFs' family that has been utilized in such applications is IRMOF-3 and its functionalized analogues. The latter have been explored for carvacrol and eugenol encapsulation [141; 151; 153]]. The encapsulation is prompted by \(\pi\)-\(\pi\) interactions between the aromatic rings of IRMOF-3 and the EO, enabling an effective loading and controlled release. Furthermore, post-synthetic modification of IRMOF-3, such as the installation of benzoic acid (BA-IRMOF-3), can enhance these interactions, through the addition of an aromatic ring to the system, resulting in stronger binding energies and slower release kinetics [151]. An active film, prepared by the hybridization of sodium alginate and BA-IRMOF-3 loaded with carvacrol, demonstrated improved mechanical and physical properties, sustained-release capabilities, and enhanced antibacterial and antioxidant activities. In detail, this film inhibits the growth of _E. coli_ and _S. aureus_, extending in this way the shelf life of fresh pork by slowing down color, weight, and pH changes. Post-synthetic modification of IRMOF-3 through amide functionalization improved its binding affinity with CA (from \(-5.1\) to \(-6.0\) kcal/mol). The resulting BMC@SA active film exhibited notable sustained-release behavior and demonstrated antibacterial and antioxidant effects, reducing _E. coli_ and _S. aureus_ growth by 61.95% and 49.33%, respectively [151]. Similarly, chitosan/eugenol-loaded IRMOF-3 (CS/IRMOF-3-EU) based composite films present enhanced UV-blocking, improved mechanical properties, and sustained eugenol release. The release mechanism of eugenol has two steps. An initial fast-release step triggered by water absorption and polymer swelling. That step is followed by a gradual release of the EU, controlled by the diffusion of the release medium into the IRMOF-3-EU pores. These composite films effectively slow down the deterioration of strawberry quality, maintaining hardness, suppressing weight loss, and preserving enzyme activity [153]. Other examples are focusing on Zn-ascorbate MOFs, which utilize the non-toxic ascorbic acid linker, offering a biocompatible platform. This MOF has been used for the encapsulation of marjoram essential oil (MEO), presenting a loading percentage of \(\sim\)4%.