Preparation, characterization and evaluation of antibacterial activity of catechins and catechins–Zn complex loaded β-chitosan nanoparticles of different particle sizes

• Catechins (CAT) or CAT–Zn was encapsulated by β-chitosan nanoparticles (β-CS NPs).
• CAT–Zn complex loaded β-CS NPs had particle sizes of 208–590 nm.
• CAT–Zn loaded β-CS NPs of smaller particle sizes had higher antibacterial activity.
• Samples had stronger antibacterial activity against L. innocua than against E. coli.
• CAT or CAT–Zn complex loaded β-CS NPs solutions had good stability at pH 2.0–4.5.

This study used β-chitosan nanoparticles (β-CS NPs) of different particle sizes to encapsulate catechins (CAT) or CAT–Zn complex by ionic gelation technology. The antibacterial activity of CAT or CAT–Zn complex loaded β-CS NPs against Escherichia coli and Listeria innocua were investigated based on bacterial growth curve, minimum inhibitory concentration (MIC), and minimum bacterial concentration (MBC). Fourier transform infrared spectrometer (FT-IR) was employed to study the incorporation of CAT or CAT–Zn complex into β-CS NPs. The CAT–Zn complex loaded β-CS NPs had particle size of 208–591 nm, polydispersity index (PDI) of 0.377–0.395, and positive Zeta-potential of 39.17–45.62 mV. The CAT–Zn complex loaded β-CS NPs of smaller particle sizes showed higher antibacterial activity than that of larger particle size ones. The MIC and MBC of CAT–Zn complex loaded β-CS NPs of the smallest particle size against L. innocua and E. coli were 0.031 and 0.063 mg/mL, and 0.063 and 0.125 mg/mL, respectively. This study suggested that encapsulation of CAT–Zn complex in β-CS NPs improved the antibacterial activity of CAT and CAT–Zn complex, and the encapsulators have great potential to be used as antibacterial substances for food and other applications through either direct addition or incorporation into packaging materials.