Synergistic Impact of Plant Essential Oil Based Microemulsion on Lychee Preservation in Comparison to Prochloraz

Abstract

Citral (Cin) and cinnamaldehyde (Cit) presented a synergistic coefficient of 2.74 at a mass fraction ratio of 1:3 against Phytophthora litchi to effectively prevent the post-harvest pericarp browning and decay of lychee fruit. Plant essential oil-based microemulsion was prepared by utilizing a surfactant (Tween 80) and co-surfactant (anhydrous ethanol) based on the pseudo-ternary phase diagrams (Km value of 3). The size distribution (10 nm) and Zeta potential (-11.6 mV) were measured using a nanoparticle sizer spectrometer, which coincided with the cryo-electron microscopy observations. Infrared spectroscopy revealed an abundance of H bonds. Nanoscale size and strong H bond interaction established the stability of the microemulsion. The impact of the microemulsion on lychee fruit preservation at room temperature was evaluated and compared with the chemical fungicide prochloraz. The microemulsion treatment efficiently prevented the browning of lychee pericarp and extended its shelf life for 2-4 days. Microemulsion treatment also retained higher levels of anthocyanin and vitamin C in the lychee fruit. Furthermore, the microemulsion treatment reduced the peroxidative damage to membranes and maintained catalase and superoxide dismutase activities. We propose that microemulsions could efficiently replace the chemical preservatives for post-harvest lychee preservation.

Keywords: Plant essential oil, Microemulsion, Synergism, Lychee fruit, Phytophthora litchi