Properties of nylon 6-based nanofibers from cowpea and marama bean protein with kafirin prepared by electrospinning

Nanofibers made from biopolymers and proteins are biocompatible and biodegradable. This research investigated properties of electrospun nanofibers made using legume proteins (soy protein isolate (SPI), cowpea pea protein isolate (CPI) and marama bean protein isolate (MPI)), prolamin protein (kafirin) and legume-prolamin co-proteins. Nylon 6 was incorporated to improve the electrospinnability of the proteins. Scanning Electron Microscopy (SEM) showed that nanofibers were successfully formed from nylon 6-protein co-polymers with diameter in the range 65–272 nm. Blending kafirin with MPI resulted in nanofibers with a smoother morphology than MPI. The diameters of co-protein nanofibers were thicker than mono-protein nanofibers. This was attributed to possible interaction of polypeptide chains since kafirin had more cysteine than SPI, CPI and MPI, resulting in increased disulfide bonds. The Fourier Transform Infrared Spectroscopy (FTIR) spectrum suggest that hydrogen bonds were formed between hydroxyl groups and amide groups of nylon 6 and proteins. Thermal stability of co-proteins was lower than the mono-protein nanofibers as indicated by the thermogravimetric analysis (TGA) onset temperature and residual weight. Dynamic mechanical thermal analysis (DMTA) thermograms exhibited multiple peaks, indicating phase separation between the polypeptides. However, the shift in the temperature transitions suggested partial compatibility between nylon 6 and proteins as well as between kafirin and SPI, CPI and MPI. This study demonstrated that SPI, CPI, MPI and kafirin can be used to successfully form mono-protein nanofibers and legume-prolamin co-protein nanofibers. This is also a significant contribution to the research of underutilized crops with potential application in food packaging, medical and pharmaceutical industries.