Electrospun Antimicrobial Films of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Containing Eugenol Essential Oil Encapsulated in Mesoporous Silica Nanoparticles

Abstract

The main goal of this study was to develop poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) films with long-term antimicrobial capacity of interest in food packaging applications. To this end, eugenol was first highly efficiently encapsulated at 50 wt.-% in the pores of mesoporous silica nanoparticles by vapor adsorption. The eugenol-containing nanoparticles were then loaded in the 2.5–20 wt.-% range into PHBV by electrospinning and the resultant electrospun composite fibers were annealed at 155 °C to produce continuous films. The characterization showed that the PHBV films filled with mesoporous silica nanoparticles containing eugenol present sufficient thermal resistance and enhanced mechanical strength and barrier performance to water vapor and limonene. The antimicrobial activity of the films was also evaluated against foodborne bacteria for 15 days in open vs. closed conditions in order to simulate real packaging conditions. The electrospun PHBV films with loadings above 10 wt.-% of mesoporous silica nanoparticles containing eugenol successfully inhibited the bacterial growth, whereas the active films stored in hermetically closed systems increased their antimicrobial activity after 15 days due to the volatile portion accumulated in the system’s headspace and the sustained release capacity of the films. The resultant biopolymer films are, therefore, potential candidates to be applied in active food packaging applications to provide shelf life extension and food safety.

Electrospun Active Biopapers of Food Waste Derived Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with Short-Term and Long-Term Antimicrobial Performance

“…In particular, Figure 2a shows the SEM images of the neat PHBV fibers, whereas Figure 2b includes the PHBV fibers containing 10 wt% OEO, which were also included in the study for comparison. In both cases, the PHBV fibers presented a mean diameter of approximately 0.8 µm, which is agreement with our previous works reporting the morphology of electrospun PHBV fibers [57,58]. Figure 2c-f correspond to the PHBV fibers, without OEO, containing ZnONPs at 1 wt%, 3 wt%, 6 wt%, and 10 wt%.…”

“…The biopaper made of neat PHBV presented an E value of 1125 MPa, a σ y value of 12.6 MPa, and a ε b value of 1.71%. These results are in the same range than those reported by Melendez-Rodriguez et al [58] for electrospun films of neat PHBV, where E was 1252 MPa, σ y was 18.1 MPa, and ε b was 2.4%. The incorporation of OEO reduced the E value to 814 MPa, which can be ascribed to a plasticizing effect of the oil molecules on the biopolymer matrix, which reduced the intermolecular forces and increased the mobility of the PHBV chains [82].…”

“…However, all the biopapers also showed several pores in the cross-section, which can be related to the partial evaporation of the oily particles derived from OEO enclosed in the PHBV matrix during the thermal post-treatment as well as the presence of ZnONP agglomerates. Similar voids, though smaller, were recently observed in electrospun PHBV filled with silica microparticles containing eugenol prepared by Melendez-Rodriguez et al [58]. The pores were significantly bigger for the PHBV biopaper containing 2.5 wt% OEO + 2.25 wt% ZnONPs, shown in Figure 8f, in comparison with the cross-sections of the biopaper samples of PHBV containing 7.5 wt% OEO + 0.75 wt% ZnONPs and 5 wt% OEO + 1.5 wt% ZnONPs, respectively, which are presented in Figure 8b,d.…”

“…Thus, it increased both the σ y and ε b to values of 18 MPa and 4.53%, respectively, and also toughness from 0.124 mJ/mm 3 to 0.560 mJ/mm 3 . A similar improvement in ductility was reported by Melendez-Rodriguez et al [58] after the introduction of eugenol in electrospun PHBV films. In relation to ZnONPs, one can observe that the nanoparticles induced a reinforcement on PHBV so that the values of E and σ y increased in these film samples to 1286 MPa and 17.1 MPa and, as expected, it resulted in a decrease in ductility showing a value of ε b of 1.26%.…”

“…Furthermore, the application of annealing a thermal post-treatment below the biopolymer's melting temperature (T m ) allows us to obtain continuous and highly transparent films of more interest in the field of packaging [56]. Our previous research works have previously demonstrated that electrospun PHA films, that is, biopapers, containing either neat OEO [57,58] or ZnONPs [59], can exert a strong antimicrobial activity against different bacterial strains. The term "biopapers" refers to fiber-based materials made of natural polymers that are non-fiber based in origin such as PHAs.…”