Emulsion electrospinning : an innovative encapsulation technique for food technology applications

Electrospun nanofibers have been investigated as novel packaging materials due to their unique physicochemical properties. Functionality of nanofibers may be broadened by inclusion of lipophilic functional molecules (e.g. flavors, antimicrobial, bioactives) in nanofibers. The feasibility of electrospinning polymer solutions containing oil-in-water emulsions as potential carrier vehicles for lipophilic functional compounds was investigated. Corn oil (5 wt%) was mixed with 2-5 wt% of surfactant solution (SDS or Tween 20) and homogenized using a laboratory scale ultrasonicator to produce o/w emulsions. Emulsions were mixed with high molecular weight poly(vinyl alcohol) (HMW-PVA) at pH 4.5 to yield solutions containing 1-10wt% emulsion and 1-10wt% PVA. Particle diameter emulsion droplets was determined by light scattering. Solutions were then electrospun and deposited structures characterized by optical and electron scanning microscopy. Emulsion had mean droplet diameters of 150-200nm using SDS and 300-400nm using Tween 20. Emulsion droplets in PVA solutions aggregated within a narrow concentration ratio range of emulsion droplets to polymer with the critical concentration ratio being higher for emulsions suspended in LMW-PVA compared to HMW-PVA, characteristic for depletion-induced flocculation. Jet formation was induced from mixed emulsion-polymer solutions at operating voltages >16kV. With HMW-PVA, at cpolymer>5wt%, nanofibers were deposited on the grounded target plate while at cpolymer<5wt% fibers with “bead” defects were obtained. LMW-PVA solutions didn’t yield fibers at any polymer concentration tested. Morphologies of fibers varied depending on polymer and droplet concentration, e.g. fiber diameters decreased as polymer concentration decreased. Microscopy showed that emulsion droplets were part of the fiber structures. However, electrospinning of aggregated emulsion droplets led to formation of fibers that contained large (>10µm), possibly coalesced droplets. Results suggest that upon electrospinning emulsion droplets are ejected as part of the polymer jet expulsion producing droplet-containing fibers that could be of great interest as novel active packaging materials.