Development of a Lemongrass/Silver Nanocomposite for Controlling a Foodborne Pathogen - Escherichia coli

In the current study, we synthesized a nanocomposite, comprising of silver nanoparticles encapsulated into the lemongrass nanoemulsion, that has effective antibacterial activity against the foodborne pathogen Escherichia coli (pathogenic MTCC 443). The synthesis procedure consisted of using a high-energy sonication process for the lemongrass nanoemulsion (LNE) and a microwave-assisted method for silver nanoparticles (AgNPs). Thereafter, two nanocomposites, viz., NC1 and NC2, were synthesized by encapsulating different concentrations of AgNPs, 5% and 10%, in the LNE, respectively. Dynamic light scattering (DLS) measurements show an increase in the size of NC1 and NC2 relative to the LNE after encapsulation of silver nanoparticles. Encapsulation was further confirmed by Fourier transform infrared (FT-IR) spectroscopy and thermogravimetric analysis (TGA) and quantified using inductively coupled plasma atomic emission spectroscopy (ICP-AES). Antimicrobial studies revealed that, of the two nanocomposites, NC1 was the most efficient antimicrobial agent to kill E. coli with a minimum inhibitory concentration of 0.75%. The DPPH study also confirms the higher antioxidant activity of NC1. Further, atomic force microscopy (AFM) illustrated that the nanocomposite caused membrane damage which in turn leads to cell lysis. Thus, the current work identifies the LNE-AgNP nanocomposite as a suitable active material for food packaging, that could enhance the shelf life of foodstuffs in a sustainable manner.