Incorporation of licorice flavonoids into ZnO/attapulgite nanocomposites for enhanced antimicrobial and antioxidant performance

Combining natural bioactive ingredients and metal oxide nanoparticles (NPs) is expected to have a synergetic effect for enhanced antimicrobial and antioxidant activities. In this study, licorice flavonoids (LF) were incorporated into ZnO/attapulgite (APT) via a mechanical milling process to form organic-inorganic nanocomposites (LF/ZnO/APT). The results from structure characterization confirmed that ZnO NPs with dimensions of approximately 20-50 nm uniformly covered on APT nanorods, LF molecules mostly absorbed on the surface of ZnO/APT and some molecules may have entered the external channels of APT. The interface interactions caused by the hydrogen bonding between the oxygen-containing groups of LF molecules with Si-OH group on the surface and channels of APT was interpreted by the shift observed in Fourier Transform Infrared spectroscopy. The antibacterial activity results investigated that the gram-positive bacteria such as S. aureus, E. faecalis and methicillin-resistant S. aureus are more susceptible to LF/ZnO/APT nanocomposites, and when the load volume of LF was 5%, the minimum inhibitory concentrations (MICs) were up to 0.5, 1 and 0.5 mg.mL(-1), respectively, while the MICs were 1, 5 and 5 mg.mL(-1) against E. coli, P. aeruginosa and extended-spectrum beta-lactamaseproducing E. coli, respectively, which are better than those of LF and ZnO/APT. In addition, LF/ZnO/APT exhibited considerable capacities for hydroxyl and DPPH radical scavenging with IC50 values of 0.69 and 4.16 mg/mL, respectively. This study presents a new idea of combining natural ingredients with inorganic NPs to obtain enhanced properties and promises to replace antibiotics for preventing and treating bacterial infections in animals.

Automated summary

This study incorporated licorice flavonoids (LF) into ZnO/attapulgite (APT) to form organic-inorganic nanocomposites. The results showed that LF/ZnO/APT had enhanced antimicrobial and antioxidant activities, making it a potential alternative to antibiotics for preventing and treating bacterial infections in animals.