Fabrication and antimicrobial properties of edible electrospun nanofibers fortified with essential oils

The objectives of this research were to fabricate the antimicrobial edible electrospun nanofiber mats fortified with essential oils via electrospinning and electrospraying by investigation the effects of solution concentration and processing factors on the morphology of electrospun nanofibers. According to the nanofiber fabrication process, it was indicated that neat chitosan solution was not successful to form the fibers. The droplets of chitosan solution were formed at needle tip, the whipping movement was not detected. Whereas, neat gelatin and neat cellulose acetate dissolved in 80% acetic acid can be easily to form fibers. The study of mixed solution indicated that 3.0 to 7.0% Chitosan (CS), 18.0% cellulose acetate (CA), and 30.0% gelatin (Gel) solution in 80.0% acetic acid at the volume ratio of 40/10/50 have been successfully electrospun nanofiber mats. The final concentration of mixed solutions was 18.0, 18.8, and 19.6%wt as the chitosan loading at 3.0, 5.0, and 7.0%(w/v), respectively. The average diameters of fibers were 148±51, 152±41, and 248±72 nm, respectively. Solution concentration at 18.0% and 18.8%wt, the smooth, continuous fibers and non-bead were obtained. Whereas, solution concentration at 19.6%wt, junction and sticky were observed due to the higher viscosity and surface tension of polymer jets. Consideration to the effect of voltage, the results showed that the average fibers diameters at 20, 23 and 26 kV were 170±42, 152±41, and 107±35 nm, respectively. Smooth and continuous fibers were obtained. However, at 26 kV, a thin branching can be observed due to the electric field that higher than optimal for producing a single jet. The average fibers diameter at flow rates of 11.67, 16.67, and 25.00 µl/min were 152±41, 154±45, and 166±55 nm, respectively. The average diameter of nanofibers at distance 8, 10, and 12 cm were 158±49, 152±41, and 147±40 nm, respectively. At 8 cm of distance, the junctions were observed owing to the flying time of jet was not enough to stretch and complete evaporated. The results showed that the fiber diameters increased as the solution concentration and flow rate increased, whereas the fiber diameters decreased as the applied voltage and distance between tip to collector increased. This suggest that the optimal conditions were 18.8%wt of solution concentration, 23 kV of applied voltage, 11.67 µl/min of flow rate and 10 cm in distance to the ground collector. Adding essential oils into polymer solution cause the changing of morphology and diameter of electrospun nanofibers. Larger fibers with junction were appeared as the essential oils loading increased. Soy protein isolate (SPI) incorporating essential oil was successfully sprayed onto electrospun mats by electospraying at 23 kV, flow rate at 11.67 µl/min, and distance at 25 cm. The thermal properties demonstrated that the melting point of electrospun CS/CA/Gel nanofiber mats without essential oil was 152.71C, while those fortified with essential oils at concentration 0.1 to 10.0%(v/v) were ranged 107.85C to 161.79C. The melting point and enthalpy of electrospun mats fortified with essential oil decreased obviously as the essential oil loading increased. The electrospun nanofiber mats capable absorbed water almost 1,000% and slightly reduced when essential oils were presented. Whereas the weight loss rate decreased in range 47% to 60%. The releasing of essential oils from mats showed that the rapidly release presented in the first 30 minutes and release gradually next 30 minutes. In addition, electrospun nanofibers incorporated with essential oils showed the higher release rate than electrospun nanofibers sprayed with essential oils. Antibacterial activity of electrospun CS/CA/Gel nanofiber mat fortified with essential oil was tested against six strains of foodborne pathogenic bacteria: three gram negative including Escherichia coli O157:H7 (VTEC) DMST 12743, Salmonella Typhimurium ATCC 13311, and Pseudomonas aeruginosa ATCC 27853 and three gram positive including Bacillus cereus ATCC 11778, Staphylococcus aureus ATCC 25923, and Listeria monocytogenes DMST 17303. Dynamic shaking tests demonstrated that at the first 240 min, the six bacterial population slowly increased. After 480 min, the rapidly increased was observed. At 1,440 min, bacterial growth on the mats containing essential oil at 5.0 and 10.0% (v/v) fell to a range of 3 to 5 Log10 CFU/ml. However, mats fortified with essential oil were unable to kill all bacteria, but effectively retarded the growth of all six strains. In addition, spraying the electrospun mats with essential oil had a smaller antimicrobial than direct incorporation of essential oil. The antimicrobial effectiveness of electrospun nanofiber mats fortified with essential oils depends on the method by which the oils are added. The blending method distributed the essential oil within the nanofibers whereas in the attachment method, particles attach only to one side of the mats. In application study, electrospun mats fortified with essential oil at 10.0%(v/v) can extend shelf life of food model. Therefore, nanofiber mats fortified with essential oil have potential applications as antimicrobial materials in active food packaging, filtration membrane, antibacterial textiles, wound dressing, drug delivery and others.