Development of novel ultrathin structures based in amaranth (Amaranthus hypochondriacus) protein isolate through electrospinning

Amaranth protein isolate (API) ultrathin structures have been developed using the electrospinning technique. The effects of pH, type of solvent and surfactant addition on the spinnability, morphology and molecular organization of the obtained structures have been studied. Regarding the effect of pH on API electrospinning, capsule morphologies were only obtained at extreme pH values (i.e. pH 2 and pH 12), which allowed the solubilisation of the proteins, and the process was favoured when the solutions were previously heated to induce protein denaturation. Fibre-like morphologies were only obtained when the solvent used for electrospinning was hexafluoro-2-propanol, as this organic solvent promotes the formation of random coil structures and, thus, an increase in the biopolymer entanglements.Capsule morphologies were obtained from the API-containing formic acid solutions and this solvent was better for electrospraying than the acetic acid, probably due to the higher viscosity and lower surface tension of the solutions thereof. Addition of 20 wt.% of Tween 80 considerably improved the formation of capsule-like structures from the formic acid solution, as this surfactant contributed to the formation of alpha helical structures. Similar results were obtained when combining the surfactant with the reducing agent 2-mercaptoethanol. However, denaturation of the protein structure was not sufficient for fibre formation through electrospinning, as the solution properties play a fundamental role in determining the morphology of the electrospun structures. © 2012 Elsevier Ltd.A. Lopez-Rubio is recipient of a Ramon y Cajal contract from the Spanish Ministry of Science and Innovation. The authors thank the Spanish MICINN projects MAT2009-14533-C02-01, FUN-C-FOOD (CSD2007-00063), and Mexican project FOMIX-QRO-2011-C02-175350 for financial support and Mexican National Council for Science and Technology (CONACYT) for a graduate fellowship, to author Marysol Aceituno-Medina.Peer Reviewe