Introduction: Metallic nanoparticles (MNPs) have gained a significant interest due to their unique ability to attack a broad spectrum of microbes and to overcome antibiotic resistance. However, the current delivery approaches for MNPs are inadequate because of the low stability and lack of endogenous biological affinity for them to bind target microbes. Purpose: This work demonstrates a scalable strategy for developing a new and efficient antimicrobial composite for enhanced inactivations of bacteria and their biofilms. The composite is based on green-synthesized silver nanoparticles (AgNPs) encapsulated within a food by-product material (eggshell powder). Methods: AgNPs were synthesized from silver nitrate (AgNO3), glucose (as reducing agent), and starch (as capping agent) by microwaving. The proposed antimicrobial composite is prepared by encapsulating synthesized AgNPs within eggshell powder. The encapsulation efficiency and stability of AgNPs were characterized. The antimicrobial activity of the composite against planktonic Escherichia coli and Listeria innocua were evaluated using the plate counting method with and without critical oxygen demand (COD = 1000 mg/mL). One-way analysis of variance (p&lt; 0.05) was performed to analyse differences among multiple groups on each data set. Results: The ICP-MS results show that 80% of AgNPs were encapsulated within the eggshell powder after 5-min incubation. Encapsulation of AgNPs using eggshell powder has shown strong protection against burst release of Ag ions, and it is expected for the encapsulated AgNPs to possess higher stability compared to non-encapsulated AgNPs. Encapsulated AgNPs have achieved 5-log reduction within 25 minutes and 60 minutes for E. coli and L. innocua respectively even with high organic load. Furthermore, this antimicrobial composite is also effective in inactivating E. coli and L. innocua biofilms for 1-2 log units after 2-hour treatments. Significance: The promising results suggest the possibility of applying this natural and food-grade delivery system for stabilizing and transporting MNPs, as well as enhancing their antimicrobial activity in complex biological systems.

Title: Incorporation of silver nanoparticles (AgNPs) with chicken eggshell powder for enhanced antimicrobial activities against foodborne pathogens and their biofilms

ACS Fall 2021

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