Rheological properties influence on the electrospinning of caseinate for loading with antioxidant rosemary extract

This study is focused on obtaining bioactive electrospun fibers from aqueous based solutions with sodium caseinate as major component, polyvinyl alcohol (PVA) as minor co-spinning component and rosemary extract as antioxidant principle.The rheological behaviour of precursor solutions was tuned by changing the caseinate concentration, composition of the solvent system, ultrasonication, high pressure treatment or addition of a second polymer in the system. All samples showed non-Newtonian shear-thinning behavior. Electrospinning was performed for concentrated solutions of 15 and 20 wt% caseinate in various water/ethanol/surfactant/polyvinyl alcohol (PVA) formulations, ultrasonicated for short times. Low amounts of 8 wt% PVA related to Cas were enough to convert electrospraying to electrospinning. The aspect of obtained fibers depends on the composition of precursor solutions. Increased amounts of PVA ensure transformation from fibers with large beads to fibers with lateral fringes and spots then to smooth and uniform fibers. Aqueous extract from rosemary was added into precursor solution to impart bioactive properties to the final fibers. This drastically affected the electrospinning behavior, leading to large beads and fringes. Higher amounts of PVA are required to compensate this, but concentration as high as 5 wt% rosemary extracts could be embedded into smooth and uniform fibers. These manifested significant scavenging activity against DPPH radicals and retarded the oxidation of apple pulp, despite the very low amount of the antioxidant bioactive principle. This offers the possibility to use the caseinate electrospun fiber loaded with rosemary extract in applications where antioxidative action are required, such as food packaging.