Preparation of water-in-oil (W/O) cinnamaldehyde microemulsion loaded with epsilon-polylysine and its antibacterial properties

In order to solve the problems of poor oil solubility of epsilon-polylysine (ε-PL) and the resulting poor antimicrobial performance, a water-in-oil (W/O) microemulsion containing ε-PL was constructed by drawing a pseudo ternary phase diagram. The effects of oil phase, surfactant, cosurfactant and ε-PL with different components and contents on the area of microemulsion were investigated. The physicochemical properties of microemulsion were discussed by measuring the conductivity, rheology, dynamic light scattering, X-ray small angle diffraction and centrifugal stability of microemulsion, and the inhibitory effect of microemulsion on mold was further studied. The results showed that oil: ethanol was 1:1 (w/w), water: glycerol was 3:1 (w/w) and 5%–10% (w/w) ε-PL could promote the formation of microemulsion system. The conductivity and rheological confirmed that the transition point of W/O microemulsion was 25% (w/w) in aqueous phase, and the microemulsions with different water contents were Newtonian fluids. The final formulation of microemulsion is the ratio of oil, surfactant and water to 12:8:5. The droplet of microemulsion is elliptical and evenly distributed, which has good centrifugal stability. The combination of ε-PL and cinnamaldehyde with W/O microemulsion system had synergistic inhibitory effect on spore germination and colony diameter of three fungi. This study provides a new method to prevent spoilage of oil-immersed food by constructing ε-PL loaded W/O microemulsion, and provides a theoretical reference for the application of ε-PL cinnamaldehyde microemulsion as a natural and efficient antibacterial agent in oil-immersed food.