The low molecular weight of casein proteins (19–25 kDa) and their strong affinity to form casein micelles in native milk (ca. 250 nm in diameter) or aggregates in caseinate dispersions, limits the electrospinnablility of caseins. The study reports the influence of pH, ethanol content, ionic environment, and casein concentration on the solubility, solution viscosity, surface tension and conductivity of casein-based spinning dopes intended to fabricate bead-free casein nanofibers. The conductivity of the electrospinning dopes increased with an increase in casein concentration and decreased with the increase in ethanol content. A homogenous dispersion of casein was observed for mixtures with 20 wt. % casein prepared using 60 % ethanol/water mixture at pH 10. Minimum viscosity (0.4 Pa.s) and surface tension (60.6 mN/m) with comparatively higher conductivity (897.7 µS/cm) was observed for solutions containing 2 wt. % of tetrasodium pyrophosphate (TSPP) with respect to casein content, which resulted in the formation of nanofibers with a minimum number of bead defects (BN ~ 6 x 10^-3/ µm²) and minimum average fiber diameter (FD) of ~ 424 nm. Further, the viscosity dependence on casein concentration at constant relative TSPP content was like polyelectrolytes and casein nanofibers with minimum bead defects obtained at a concentration ~ 2 to 2.5 times the entanglement concentration (C_e). Therefore, the study demonstrates the influence of solution characteristics on the electrospinnablility of casein proteins to fabricate novel biodegradable, and biocompatible, casein-based nanostructured mats with potential for food, cosmetic, packaging, and biomedical applications.

Federico Harte

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