Polyethylene glycol enhanced antibacterial activity of EDTA and ethyl maltol blended PLA against Staphylococcus aureus for biodegradable active packaging

Poly (lactic acid) (PLA) has limited promise as a bio-based antimicrobial packaging material due to its lack of plasticization, which limits antimicrobial agent release and antimicrobial efficiency. PLA were plasticized with polyethylene glycol (PEG) and blended with ethyl maltol or ethylenediaminetetraacetic acid (EDTA) as antibacterial agents by melt extrusion. The effects of combining PEG, EDTA, and ethyl maltol on sheet properties and antibacterial activity were investigated. Incorporation of ethyl maltol created a dense and smooth homogeneous surface, while EDTA addition caused large pores in the PLA sheet microstructure impacting swelling degree, water solubility and surface hydrophilicity. Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC) showed that both ethyl maltol and EDTA addition modified the amorphous and crystalline phases of plasticized PLA. FTIR results suggested interaction between the functional groups of PLA chains, PEG, ethyl maltol or EDTA which affected the glass transition temperature (Tg), degree of crystallinity, and thermal stability of PLA. Adding PEG into PLA-EDTA enhanced antibacterial activity against Gram-positive Staphylococcus aureus (reduction of 1.35 log CFU/mL from the initial inoculum). The higher water solubility of sheets corresponded to a suitable release rate and sufficient amounts of antimicrobial compounds against Staphylococcus aureus. In vitro antifungal testing, PLA-PEG-EDTA sheets did not exhibit a clear zone of inhibition but delayed Penicillium sp. spore formation until day 5 of incubation. PEG plasticized PLA sheets functionalized with ethyl maltol and EDTA showed potential as active biomaterials against food-borne pathogen bacteria Staphylococcus aureus.