Effect of polyethylene glycol plasticizer on long-term antibacterial activity and the release profile of bacteriocin nisin from polylactide blends

Abstract

This work describes the synergetic effect of polyethylene glycol (PEG) in polylactide (PLA) blends, wherein the polyether acts as both the plasticizer and functional additive, ensuring the long-term antimicrobial activity of bacteriocin nisin. Two types of PEG with the molecular weights of 1000 and 6000 g.mol−1 (20 wt.%) were used to plasticize the PLA blends. The aforementioned bacteriocin nisin, at concentrations ranging between 0.02 and 0.15 wt.% (8000-60 000 IU.g−1), was incorporated into the samples by the solvent cast technique. The effect of various PEG on the structural, mechanical, and thermal properties of the PLA-based blends were investigated by scanning electron microscopy, Fourier transform infrared spectroscopy, stress-strain analysis, differential scanning calorimetry, and dynamic mechanical analysis, respectively. The antibacterial activity of the samples was detected by the agar diffusion technique against Micrococcus luteus. Furthermore, the antibacterial properties of the samples were tested according the ISO 22196 standard against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus, Listeria monocytogenes) bacterial strains. The nisin was detected by high performance liquid chromatography, the device having been equipped with a UV/vis detector. The results show that the PEG, besides its plasticizing effect, significantly enhances the release profile and sustains long-term antibacterial activity of nisin in a PLA matrix. Copyright © 2018 John Wiley & Sons, Ltd.