Electrospinning has been used to produce edible mats from nanosized fibersof calcium (CaCN) or sodium (NaCN) caseinate with pullulan(PUL)added to facilitate fiber formation. The electrospun mats are a promisingmethod to preserve and deliver bioactives to foods; e.g., because of thefiber’s large surface area/volume, but fiber imperfections such as beadformation and variations in diameter size would prevent consistent performanceof the mats. To improve fiber quality, NaCl has been recommendedas an additive to increase shear viscosity for drawing thinner fibers whileelectrospinning; however, we found NaCl ineffective and hypothesizedthat NaOH would increase solution viscosity and also strengthen the matsthrough CN aggregate formation. The objective of this study was to investigatethe effect of pH on the morphology and tensile properties ofCaCN or NaCN with PUL electrospun fibers. Aqueous solutions of 15(wt/wt)% CaCN or NaCN, and PUL were prepared at 20°C. Then, 1:1(pH6.7) and 2:1(pH 6.7) blends of either CN with PUL solution were preparedand adjusted from the initial pH6.7 to pH 8, 9, and 10 with 1N NaOH.A syringe fed 3 mL of each solution to an electrospinning unit at flowrate of 3mL/h and at 20kV, with fibers deposited on a rotating drum. AtpH6.7, the mean diameters, D, of the CaCN and NaCN:PUL(1:1) fiberswere 226 ± 25 and 215 ± 18nm, respectively, with beads noted on thefibers. As pH was increased to 8 and then 9, the fibers became thickerwith D of 274 ± 20 and 234 ± 16nm and bead-free, becoming thinner atpH 10, with D of 105 ± 16 and 93 ± 15nm, respectively. Similar trendswere noted for the (2:1) blends. Tensile Strength (TS) and Elongation atBreak% (EAB) measurements showed that the initial (TS,EAB%), (1.4± 0.5MPa, 4.0 ± 0.6%) and peak (4.7 ± 0.3MPa, 8.4%) values the forCaCN mats occurred at pH 9 with a sudden 60% decline in these valuesat pH10 suggesting that the negatively-charged CN aggregates partlydisassociated. This did not occur for the NaCN aggregates at pH10most likely due to lower electrostatic repulsion. Studies on CN in fiberswill provide insights to their structure and that relative to casein micelles.
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