Influence of solution properties and pH on the fabrication of electrospun lentil flour/HPMC blend nanofibers

Highlights

• Biodegradable nanofibers can be obtained from lentil flour and HPMC.

• Alkaline solutions resulted in homogenous fibers while neutral solutions produced beads.

• All electrospinning solutions showed shear thinning behavior.

• Viscosity and electrical conductivity of solutions were affected by pH, lentil flour and HPMC concentration.

• Nanofiber diameter changed with pH, lentil flour and HPMC concentrations.

Abstract

Electrospinning is a method used in fiber production in which an electric force is applied to create jets of charged polymer solutions. The objective of this study was to obtain homogeneous nanofibers from lentil flour and hydroxypropyl methylcellulose (HPMC) blend by using electrospinning method. Distilled water was used as solvent. The effects of pH (7, 10 and 12), lentil flour concentration (1% and 2% (w/v)) and HPMC concentration (0.25%, 0.5% and 1% (w/v)) on solution properties and fiber morphology were investigated. When the pH was increased, the viscosity of the solutions containing 1% and 2% lentil flour decreased. Increasing the pH values caused an increase in the electrical conductivity. At pH value of 7, homogeneous nanofibers could not be obtained whereas fibers were perfectly homogeneous at alkaline pH values. Nanofiber diameter decreased with increase in pH when 2% lentil flour was used. On the other hand, diameter of fibers did not show any significant change with pH for 1% lentil flour. When the lentil flour concentration was increased, viscosity and fiber diameter increased at pH 10. When HPMC concentration was increased, both viscosity and fiber diameter increased but electrical conductivity did not show any significant change. Average fiber diameters ranged between 198 ± 4 and 254 ± 5 nm for solutions prepared with different lentil flour and HPMC concentrations at different pH values.

Introduction

Pulses, which are the seeds of legumes, are known as high nutritional value foods. According to Food and Agricultural Organization of United Nation's the global production of pulses increased by 57.4% from 1981 to 2011 (Ariyawardana, Govindasamy, & Lisle, 2015). However, Previtali et al. (2014) stated that with the change of eating habits, legume consumption decreased. Consequently, scientists started to search for brand-new areas to use pulses. Thus, pulses have been used in pharmaceutical formulations and in biodegradable materials, such as plastics, inks and dyes (Graham and Vance, 2014).

Lentil, which is the second biggest traded pulse crop in developing countries, is a rich protein, vitamin and mineral source (Ariyawardana et al., 2015). Therefore, it takes an important part of the diets of people. Lentil is used especially in flour form in various food applications such as soups, snacks, and baked products (Ahmed, Taher, Mulla, Al-Hazza, & Luciano, 2016).

Hydroxypropyl methylcellulose (HPMC) is a cellulose derivative. It is used in food industry in many areas. Xuan et al. (2017) studied the effects of HPMC on frozen storage of wheat gluten and recently stated that HPMC could stabilize gluten network. Tanti, Barbut, and Marangoni (2016) showed that HPMC could be used as a shortening in sandwich cookie creams. Mariotti, Pagani, and Lucisano (2013) reported that the presence of HPMC could make the crumb of the gluten free bread softer and slow down the staling process. HPMC has been used for edible film production in many studies as well (Akhtar et al., 2013, Bilbao-Sáinz et al., 2010, Brindle and Krochta, 2008, Perone et al., 2014). In addition to these, there are many electrospinning studies in which HPMC was used. Frenot, Henriksson, and Walkenström (2007) showed that it was possible to obtain homogeneous nanofibers from HPMC in dimethyl acetamide solution.

Electrospinning, which is used to produce nanofibers, come to the forefront with its simple mechanism, cheap construction and short processing time among the other methods (Kriegel, Arrechi, Kit, McClements, & Weiss, 2008). In the electrospinning system, there are three main components, which are high voltage supplier, a syringe with metal tip containing the solution and a collector. The basic principle of electrospinning is inducing an electrical charge through the high voltage supplier to the polymer solution inside the syringe. During the movement of charged polymer jets to the collector, evaporation occurs and jets elongates. Consequently, fibers are collected on the surface of the collector in solid form (Anu Bhushani and Anandharamakrishnan, 2014, Huang et al., 2003, Schiffman and Schauer, 2008).

Usage of nanofibers in many different areas like textile, biomedical, cosmetic and pharmaceutical industries have become popular in recent years. However, there is not enough study about the use of nanofibers in food industry applications. One of the most important reason is that the solvents used for electrospinning are not food safe. The solvents commonly used for electrospinning process are 1,1,1,3,3,3-hexafluoro-2-propanol (HFP), trifluoroacetic acid, and 2,2,2-trifluoroethanol (TFE) ethyl acetate, tetrahydrofuran (THF) dimethylformamide (DMF), methyl ethyl ketone, and 1,2-dichloroethane (Haider, Haider, & Kang, 2015). However they are toxic and prohibited from food-related applications (Vega-Lugo & Lim, 2012).

Electrospinning of the biopolymers by using water as solvent is a challenging topic. Son, Youk, Lee, and Park (2004) and Deitzel, Kleinmeyer, Hirvonen, and Tan (2001) obtained nanofibers from the most common polymer used in electrospinning process, polyethylene oxide (PEO), by dissolving it in the water. PEO is a food additive approved by EU and FDA (Fuertges & Abuchowski, 1990). Zhang, Yuan, Wu, Han, and Sheng (2005) dissolved poly (vinyl alcohol) (PVA) in water and also obtained nanofibers. Besides polymer based nanofibers, it is possible to obtain protein based nanofibers by electrospinning. Sullivan, Tang, Kennedy, Talwar, and Khan (2014) and Vega-Lugo and Lim (2012) obtained nanofiber by dissolving whey protein isolate (WPI) and PEO in water. Cho, Nnadi, Netravali, and Joo (2010) reported homogeneous nanofiber production from PVA and soy protein isolate (SPI) blend in the water. In many studies conducted with carbohydrates, nanofibers could be obtained using water as a solvent. Şener, Altay, and Altay (2011) used water as the solvent of the sodium alginate and PVA blend. Kayaci, Sen, Durgun, and Uyar (2014) dissolved geraniol/cyclodextrin inclusion complexes in the water and obtained bead-free and uniform nanofibers.

Solution characteristics (viscosity, surface tension and conductivity), process parameters (flow rate, voltage, distance between syringe and the collector) and environmental factors (humidity and temperature) are important factors for electrospinning process (Haider et al., 2015, Nezarati et al., 2013). There are many studies in literature about the effects of electrospinning parameters on the production and the morphology of the fibers. Deitzel, Kleinmeyer, Harris, and Beck Tan (2001) showed that feed rate, voltage, concentration and viscosity of the solution had a strong influence on the fiber morphology. In fact, it was stated that production of homogeneous fiber cannot be succeeded without using the unique optimum conditions for the polymer used in electrospinning process.

There is lack of research on the usage of lentil flour in electrospinning process. Thus, the aim of the study is to produce homogeneous nanofibers suitable for food industry from a solution containing lentil flour and HPMC by using electrospinning method. Furthermore, the effects of pH, lentil flour concentration and HPMC concentration on solution characteristics and fiber morphology are highlighted.