Immobilization of surfactin in zeolitic imidazolate framework-8 (ZIF-8) and its application for tuna preservation

• Sur/Ag@ZIF-8 synthesized in-situ exhibited excellent antibacterial activity against P. fluorescens . • The MIC and MBC of Sur/Ag@ZIF-8 were 0.125 and 0.25 mg/mL, respectively. • Sur/Ag@ZIF-8 could release surfactin, Zn 2+ , and Ag + to exert antibacterial effects. Pseudomonas fluorescens is a key specific spoilage organism (SSO) responsible for the spoilage of aquatic products. In this study, nanocrystalline surfactin/Ag@ZIF-8 (Sur/Ag@ZIF-8) was successfully synthesized using an in-situ embedding method. Sur/Ag@ZIF-8 demonstrated regular morphology, high thermal stability, and potent antibacterial activity against Pseudomonas fluorescens (MIC = 0.125 mg/mL, MBC = 0.25 mg/mL). Sur/Ag@ZIF-8 could release surfactin to exert antibacterial effects because ZIF-8 had mesoporous structure larger than surfactin. Sur/Ag@ZIF-8 could also release a large amount of Zn 2+ (13.2 mg/L) and Ag + (0.027 mg/L) due to the micro-acidic environment created by the microorganisms during the growth process. Surfactin induced membrane depolarization, whereas Zn 2+ and Ag + ions synergistically compromised cell wall integrity and triggered ROS accumulation via Fenton-like reactions. Therefore, the synergistic effect of surfactin, Zn 2+ and Ag + endows Sur/Ag@ZIF-8 with excellent antibacterial ability. When used in tuna meat, the synthetic Sur/Ag@ZIF-8 agent could extend the shelf life by 2 days at 4°C. And Sur/Ag@ZIF-8 at a concentration of 0.125mg/ml used in the preservation of tuna was confirmed to be safe by MTT assay and acute toxicity test. This research provides a novel approach to developing antibacterial agents for the preservation of aquatic products.