Enhancing food safety via an eco-friendly approach: Utilizing Lactobacillus plantarum Postbiotics in polycaprolactone nanofibers for the targeted removal of heavy metal contaminants from water

The application of electrospun nanofibers (NFs) has emerged as a promising approach for addressing heavy metal contamination in water. Nanofibers were fabricated using an optimized polycaprolactone (PCL) polymer solution (15% w/v) and incorporated with various concentrations of postbiotics (2.5, 5 and 10%), including cell wall components and cell-free supernatants. The morphological features, surface wettability, and biological compatibility of the nanofibers were evaluated through high-resolution electron microscopy and Fourier Transform infrared (FTIR) spectroscopy. Subsequently, the capacity of these nanofibers to adsorb lead (Pb2+), cadmium (Cd2+), and mercury (Hg2+) ions from aqueous samples was quantified using inductively coupled plasma-optical emission spectroscopy (ICP-OES). FTIR results confirmed the presence of amide, carboxyl, and hydroxyl functional groups of postbiotics and showed that the loading of postbiotics into polycaprolactone nanofibers was successful. Thermal Gravimetric Analysis (TGA) showed that the presence of postbiotics increased the thermal stability of the composite nanofibers. The average diameters determined for PCL, PCL/2.5% Postbiotics, PCL/5% Postbiotics, PCL/10% Postbiotics, PCL/Cell wall, and PCL/Cell wall+Cell free supernatants (CSF) NFs were 276, 402, 413, 437, 533 and 582 nm, respectively. In addition, the contact angles measured for PCL, PCL/2.5% Postbiotics, PCL/5% Postbiotics, PCL/10% Postbiotics, PCL/Cell wall, and PCL/Cell wall+CSF NFs were 88°, 77°, 74°, 68°, 72° and 63°, respectively. Under optimal experimental parameters, including pH 6, temperature 20 °C, heavy metal concentration 100 mg/L and contact time ranging from 30 to 60 min, the removal efficiency ranged from 48 to 94%. Adsorption isotherm analysis revealed that the heavy metal uptake by PCL/cell wall+CFS nanofibers followed the Langmuir model, and kinetic studies aligned with a pseudo-second-order mechanism. Furthermore, PCL/cell wall+ CFS nanofibers sustained an uptake efficiency exceeding 75% over four consecutive cycles. Considering their excellent adsorption properties and reusability, these nanofibers show great potential as efficient adsorbents for use in drinking water treatment systems.