Understanding the Role of Poly(ethylene oxide) in the Electrospinning of Whey Protein Isolate Fibers
Poly(ethylene oxide) (PEO) is known for facilitating the electrospinning of biopolymer solutions, that are otherwise not electrospinnable. The objective of this study was to investigate the mechanism by which PEO enables the formation of whey protein isolate (WPI) electrospun fibers under different pH conditions. This investigation revealed that the addition of PEO increased the viscosity of WPI/PEO (10% w/w WPI; 0.4% w/w PEO) solutions. Difference in pH levels of the polymer solutions affected electrospinnability and fiber morphology. Acidic solutions resulted in smooth fibers (700 ± 105 nm) while neutral solutions produced spheres (2.0 ± 1.0 um) linked with ultrafine fibers (138 ± 32 nm). In comparison, alkaline solutions produced fibers (191 ± 38 nm) that were embedded with spindle-like beads (1.0 ± 0.5 um). Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) analyses revealed that the native globular configuration of WPI was not altered under neutral conditions. By contrast, the electrophoresis and spectrometry data indicated that WPI was denatured and hydrolyzed under acidic conditions, which facilitated the formation of smooth fibers. C13 nuclear magnetic resonance (NMR) and attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopies showed that the increase random coil and a-helix secondary structures in WPI contributed to the formation of bead-less electrospun fibers. Also, C13 NMR analysis showed no evidence of chemical interaction between WPI and PEO. Scanning transmission electron microscopy coupled with energy dispersive X-rays (STEM-EDAX) revealed that WPI was uniformly distributed within WPI/PEO electrospun fibers. Observations by scanning electron microscopy (SEM) and field emission scanning electron microscopy (FESEM) indicated that fibers possessed a solid core. All these findings suggested that PEO enables the formation of WPI/PEO electrospun fibers by entanglement/entrapment/deposition. Preliminary studies were conducted on hydroxypropyl methyl cellulose (HPMC). In the absence of PEO, HPMC enabled the formation of WPI electrospun fibers under acidic conditions (124 ± 46 nm). FTIR analyses indicated that there was no interaction between HPMC and WPI, suggesting that HPMC aided in the electrospinning of WPI fibers, also by entanglement/entrapment/deposition. Hence, HPMC and PEO aid in the electrospinning of WPI fibers by entanglement/entrapment/deposition, which can be manipulated by alterations in the protein configuration and solution properties.