Production and characterization of hydrophilic and hydrophobic sunflower protein isolate nanofibers by electrospinning method

In the present study, sunflower protein isolate (SPI) was extracted and applied for production of nanofiber using polyvinyl alcohol (PVA) in different SPI:PVA volume ratios (0:100, 20:80, 40:60, 60:40, 80:20 and 100:0) under two voltages (18 and 23 kV) and two flow rates (0.5 and 0.75 ml/h). Nanofibers with average diameters ranging from 304 to 400 nm were achieved. SPI:PVA volume ratio of 40:60 at voltage of 18 kV and flow rate of 0.75 ml/h were determined as the optimum conditions for electrospinning which produced bead-free and uniform nanofibers with average diameter of 398 nm. The effects of heating (150 °C, for 24 h) and calcium chloride (1% W/V) solution solely and together on nanofibers hydrophobicity were also examined. SEM images after 24 h soaking in lactate buffer (pH 5.5) showed that only heat treatment could make nanofibers hydrophobic, which was proved by contact angle data. FTIR analysis showed denaturation of protein and interactions between protein and PVA after heat treatment. Moreover, DSC and TGA results indicated miscibility of protein and PVA, and higher thermal stability of heat treated sample. This study showed the potential application of soy protein as a byproduct for production of both hydrophobic and hydrophilic nanofibers.