Development of Ethyl Formate Delivery System for Active Packaging and Insect Fumigation Applications through Precursor and Electrospinning Technologies
Ethyl formate (EF) is a generally regarded as safe (GRAS) volatile compound which is naturally occurring in many food products (e.g., rice, barley, grapes, beer, cheese). It is a potent insecticide and antimicrobial promising as an alternative to the fumigant methyl bromide, which is being phased out due to its ozone depletion in the stratosphere and toxic properties. However, EF is highly volatile, flammable, and susceptible to hydrolytic degradation. These properties pose substantial end-use delivery challenges. In this research, a novel solid-state EF precursor (EFP) compound was synthesized via the condensation reaction of adipic acid dihydrazide and triethyl orthoformate to form diethyl N,N'-adipoyldiformohydrazonate, as confirmed by Fourier transformed infrared and solid-state nuclear magnetic resonance spectroscopies. EFP was non-volatile and remained stable under dry conditions but could be hydrolyzed readily in the presence of moisture and acid to trigger the release of EF vapor. To facilitate the end-use applications, EFP was encapsulated in free-surface electrospun ethylcellulose/poly(ethylene oxide) (EC-PEO) nonwovens after optimizing the polymer concentrations to obtain bead-free electrospun fibers. The release kinetics of EF vapor from the neat EFP powder and EFP-loaded EC-PEO nonwovens were evaluated at different conditions using gas chromatography. Scanning electron microscopy revealed that EFP powder was physically entrapped within the electrospun EC-PEO fibers. Fourier transformed infrared spectroscopy detected no specific interactions between EFP and the polymers in the nonwovens. Preliminary studies on strawberries showed that the release of EF vapor from the EFP-loaded nonwovens delayed the growth of spoilage microorganisms on the fruits. Furthermore, EFP powder was used as an EF activated release system for in-packaging fumigation of blueberries to control an invasive insect pest in fruits – spotted-wing drosophila (SWD). Complete control of SWD eggs, larvae, pupae, adults was achieved after EF exposure. There were no significant (p > 0.05) differences in blueberries quality parameters between EF treated and untreated berries. This research shows that the conversion of the highly volatile EF into a solid-state precursor, in conjunction with the activated release strategy, can be useful for active packaging applications of fresh produce to mitigate insect pest risks and prevent microbial growth during distribution.