Oxidative stability of encapsulated fish oil in electrospun zein fibres

Abstract

Zein fibres loaded with fish oil were generated by electrospinning of zein polymer solutions (20% w/w) prepared in 70% (w/w) aqueous ethanol and isopropanol solvents. Zein fibres with a diameter of about 300nm with smooth surface morphology were produced from ethanol-based solutions. The fibre diameter increased to about 500nm as a result of the addition of 30% (w/w) fish oil. Thinner fibres (190±62nm) with beads averaging up to 1μm in size were produced from isopropanol zein solutions with decreasing bead formation due to the addition of fish oil by 30% (w/w). Transmission electron microscopy and florescence microscopy were utilized to examine the distribution of fish oil in the electrospun materials, revealing that the lipid phase tended to concentrate at the core of the fibres and beads, as a result of phase separation during the electrospinning process. This behaviour positively impacted the encapsulation efficiency, loading capacity, as well as the stability of the fish oil tested at 4, 25 and 60°C. The encapsulation efficiency of the electrospun zein fibres reached as high as 91% for ethanol-based and 96% for isopropanol-based fibres, at 30% (w/w) loading level. The oxidative stability of the encapsulated and non-encapsulated fish oil was monitored over a period of 14days by determining the formation of lipid peroxide using a modified ferrous oxidation–xylenol orange method. The secondary oxidative by-products were evaluated by p-anisidine value. The oxidative stability was further monitored via Fourier transform infrared spectroscopy. The results indicated that electrospun zein fibres provide a greater oxidative stability in comparison to non-encapsulated fish oil.