The aqueous assembly preparation of OPs-AgNPs with phenols from olive mill wastewater and its mechanism on antimicrobial function study

To valorise olive mill wastewater phenols (OPs) potentially applied in food preservation, a novel stable and regularly spherical OPs-AgNPs ( D avg  = 78 nm) were successfully assembled in aqueous solution under the optimized conditions (pH 8.0, 5 mM AgNO 3 , 35C and 30 min). The results of antimicrobial zone diameters indicated that 50 μg/mL of promising OPs-AgNPs presented excellent antimicrobial effects. Especially, the cell wall damages of E. coli ATCC 23,815 were caused when OPs-AgNPs concentration was exceeded its MIC (8.58 μg/mL). Also, a significant down-regulating of the Ca 2+ -ATPase activity in E. coli was revealed, and the intracellular Ca 2+ concentrations were thus decreased from 12.5 to 1.35 µg/mL after a treatment for 3 h. The apoptosis level of E. coli was significantly increased more than the control (55.13% of OPs-AgNPs vs 9.90% of control). In sum, OPs exerts enhanced antimicrobial function via penetrating cell membrane and targeting Ca 2+ -ATPase after chelated with AgNPs.