ORIGINAL PAPER Microwave Pretreatment for the Improvement of Physicochemical Properties of Carob Flour and Rice Starch–Based Electrospun Nanofilms Eylul Uygun 1 & Eda Yildiz 1 & Gulum Sumnu 1 & Serpil Sahin 1 Received: 17 December 2019 /Accepted: 4 April 2020 /Published online: 18 April 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020 Abstract The aim of this study was to determine the effects of microwave pretreatment on physicochemical characteristics of carob flour and rice starch–based nanofibers produced by electrospinning. The effects of microwave heating on production of nanofibers by electrospinning have not been studied before. Another aim of the study was to fabricate and characterize nanofibers by using different carob flour concentrations (3%, 5% w/v) and rice starch (0.5% w/v). Films were characterized by scanning electron microscopy, water vapor permeability, X-ray diffraction, mechanical test, differential scanning calorimeter, and Fourier transform infrared spectrophotometer. Homogenous and bead-free fibers were obtained when microwave heating was used. Nanofibers originated from microwave-heated solution presented better characteristics in terms of water vapor permeability and mechanical properties as compared with conventionally heated ones. Microwave-heated solution had higher viscosity and available amino group amount as compared with conventionally heated solution. This study showed that microwave heating can be considered as a promising pretreatment method for electrospinning rather than conventional heating to be used in food packaging area. Keywords Packaging . Legume flour . Biodegradable . Electromagnetic heating Introduction It is a known fact that nanoscale fibers give promising results in many fields such as enzyme immobilization, drug delivery, textile production, biosensors, and tissue engineering. Among nanofiber formation methods, electrospinning is one of the commonly used ones (Li and Xia 2004). Electrospinning is quite advantageous in terms of its cost and simplicity. It is also possible to produce well-ordered, homogeneous, and more porous fibers with larger surface to volume ratio by electrospinning (Hadad et al. 2019). In nanofiber formation, it is possible to use synthetic, natural, and hybrid materials. As a natural source, gelatin, collagen, soy, casein, gliadin, zein, and whey were preferred as proteins. In addition to that, cel- lulose, chitosan, starch, pullulan, cyclodextrin, and alginate were used as polysaccharides (Mendes et al. 2017). Using of natural sources is also important in terms of producing envi- ronmentally friendly films. There is a growing interest in using biodegradable products, which are less waste and, thus, sustainable (Fabra et al. 2015). Flours can also be used as a natural source for nanofiber formation since they contain carbohydrates, proteins, fats, and fibers. In recent years, flours such as lentil and pea flours are used to produce nanofibers by electrospinning (Tam et al. 2017; Oguz et al. 2018). Among natural flours, carob flour is differentiated from others by its high fiber (7.3–9.61%) and total sugar content (38–56%). It also contains protein (3–5%) (Özcan et al. 2007; Yousif and Alghzawi 2000). High fiber content of carob flour may bring some benefits in mechanical properties of nanofiber films. It was found that fiber addition * Gulum Sumnu gulum@metu.edu.tr Eylul Uygun eylul.uygun@metu.edu.tr Eda Yildiz edaberk@metu.edu.tr Serpil Sahin serp@metu.edu.tr 1 Department of Food Engineering, Middle East Technical University, 06800 Ankara, Turkey Food and Bioprocess Technology (2020) 13:838–850 https://doi.org/10.1007/s11947-020-02440-x