Elsevier

Industrial Crops and Products

Volume 95, January 2017, Pages 664-674
Industrial Crops and Products

Cellulose nanofibers produced from banana peel by enzymatic treatment: Study of process conditions

https://doi.org/10.1016/j.indcrop.2016.11.035Get rights and content

Highlights

  • The potential use of banana peel to produce cellulose nanofibers was investigated.

  • A process conditions study to obtain nanofibers by enzymatic hydrolysis was conducted using a 24-1 fractional factorial design.

  • Alkaline treatment was a necessary step to remove the amorphous fraction present in the fiber.

  • Optimization of the enzymatic hydrolysis process conditions enabled production of typical cellulose nanofibers.

  • Banana peel nanoparticles have potential application as reinforcing elements in composites.

Abstract

Cellulose nanofibers (CNFs) were isolated from banana peel bran via alkaline treatment followed by enzymatic treatment with xylanase. The influence of process conditions such as pH, temperature, and concentrations of the enzyme and substrate on the properties of the CNFs was evaluated with a 24−1 fractional factorial design with three central points. Enzyme at 70 U/g of bran, substrate at 15%, pH 6.0, and temperature between 35 and 55 °C favored enzymatic hydrolysis. Transmission electron microscopy (TEM) images confirmed that treatment with xylanase effectively isolated cellulose fibers at the nanometer scale. Fourier transform infrared spectroscopy (FTIR) showed that a fraction of amorphous compounds was removed. X-ray diffraction revealed that the CNFs presented high crystallinity index (66.2%). The CNFs had a diameter of 3.7 nm, their aspect ratio was in the range of long nanofibers, and their suspension was stable (−29.1 mV). These features make the CNFs potentially applicable as reinforcing agents in composites. The results evidenced that enzymatic hydrolysis with xylanase successfully afforded CNFs from banana peel, a residue that constitutes a potential source of biodegradable materials of commercial interest.

Introduction

Cellulose, the main component of the cell walls of plant fibers, has been extensively explored because it resembles synthetic polymers with the advantage that it originates from natural, renewable, and biodegradable resources. Cellulose is an ideal material to produce nanoparticles for use as reinforcing agent in composite materials. It presents good mechanical strength and stiffness, interesting thermal and electrical properties, and high degree of crystallinity (Bhattacharya et al., 2008, Cherian et al., 2008, Deepa et al., 2011, Siqueira et al., 2010a). Recently, interest in obtaining nanometric cellulose fibers from natural sources has increased. Bananas are a popular fruit that grows in tropical and subtropical regions (Pelissari et al., 2014). Cultivation and industrialization of banana fruit generates a considerable amount of waste with high lignocellulosic content. One example of such waste is banana peel, a byproduct of banana processing during food production (Elanthikkal et al., 2010). Banana peel is a source of cellulose. Banana peel processing not only adds value to this byproduct, but it also helps to reduce the environmental impact of this waste (Rosa et al., 2010). Molina (2013) has suggested the integral use of banana: its peel could be used to produce nanofibers that could be introduced as reinforcing agents in films produced from the banana pulp.

A series of processes are necessary to isolate cellulose nanofibers (CNFs). There are many ways to extract CNFs, all of which lead to different types of fibrillar material with characteristics that will depend on the raw material (cellulose), pretreatment, and disintegration process (Chen et al., 2011). In general, plant materials are lignocellulosic, which makes them resistant to bioconversion and requires pretreatment to increase their digestibility and render cellulose more accessible for hydrolysis. Chemical treatment can remove the amorphous fractions (hemicellulose and lignin) present in the structure of a plant fiber. Alkali treatment causes the structure to swell, modifying the physical features of the fiber wall and consequently increasing the surface area that is exposed to hydrolysis in the cellulose fibers (Andrade-Mahecha et al., 2015; Castro and Pereira Jr, 2010).

Different techniques afford cellulose nanoparticles from plant sources. CNFs are commonly prepared by chemical treatment, but new techniques to isolate CNFs are currently being developed. Enzymatic hydrolysis can help to isolate cellulose fibers from plant cell walls. Because enzymatic hydrolysis dismisses the need for solvents and chemicals, the mild conditions of this process make it economically attractive and environmentally friendly (Meyabadi and Dadashian, 2012, Siqueira et al., 2010a, Yu et al., 2008). Xylanases are usually employed in enzymatic hydrolysis. These enzymes initially promote catalytic hydrolysis of the hemicellulose fractions present in the plant fiber. Then, they attack the glycosidic bonds β-1,4 located between the glucose units comprising cellulose, which culminates in hydrolytic cleavage. Hydrolysis usually produces CNFs in colloidal suspensions (Hubbe et al., 2008, Pääkko et al., 2007).

To develop a new technique to isolate CNFs with sustainable characteristics, Tibolla et al. (2014) studied the production of CNFs from banana peel bran by enzymatic hydrolysis at fixed conditions of pH (5.5), temperature (45 °C), and concentrations of the substrate (25%, w/v) and enzyme (50 U/g of bran). The authors compared their results with results obtained by acid hydrolysis. Enzymatic hydrolysis proved to be a very promising technique to prepare CNFs: the resulting nanofibers were longer, and they had smaller diameter and greater aspect ratio. In addition, the CNFs presented higher negative surface charge, which is important to prevent the nanofibers from agglomerating.

Previous studies have shown that CNFs obtained by enzymatic hydrolysis have potential application as reinforcing agents in composites. However, the efficiency of enzymatic hydrolysis depends on factors such as the hydrolysis time (h), the concentrations of substrate (%) and enzyme (U/g of bran), pH, and temperature. These factors often interact with one another, so it is important to optimize the hydrolysis process to improve its yield (Meyabadi and Dadashian, 2012). Here, experiments were performed with a fractional factorial design 24−1 with three central points.

This study aimed to analyze how process conditions (pH, temperature, and concentrations of enzyme and substrate) employed during the enzymatic treatment of unripe banana peels of the variety “Terra” (Musa paradisiaca) influenced the properties of CNFs produced via hydrolysis by xylanase.

Section snippets

Materials

The banana peel bran was prepared from unripe banana peels (mature green) of the variety “Terra” (Musa paradisiaca), according to the methodology described by Pelissari et al. (2012). The fruit was obtained from the southeastern region of Brazil; the crop was harvested in March 2013, but it was not subjected to any post-harvest treatment. All the chemicals used in this work were reagent grade. Xylanase enzyme, kindly provided by Novozymes (Araucária – PR, Brazil), was used to produce CNFs by

Chemical composition of the bran

The chemical composition (dry basis) of the unripe banana peel bran was 9.6% of total extractives, 0.01% of ash, 74.9% of polysaccharides including hemicellulose, 7.9% of total lignin, and 7.5% of cellulose. The pretreatment should remove the hemicellulose and lignin fractions, to facilitate the enzymatic attack at native cellulose and the isolation of nanoparticles. Alkaline treatment of the bran afforded 16.5% yield of the treated sample relative to the initial amount of banana bran (dry

Conclusion

The studies reported herein have demonstrated that an agricultural residue (banana peel) can be potentially used to produce value-added products. The cellulose nanofibers produced from this raw material by enzymatic hydrolysis display ideal characteristics for use as reinforcing agents in polymeric matrixes. The green banana peel bran (Musa paradisiaca) presents cellulose content of 7.5%, which makes it an extremely strong structural material with axial stiffness, a desirable feature for a

Acknowledgments

The authors would like to acknowledge the financial support provided by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) (2952/2011) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) (477842/2011-9). The authors would also like to acknowledge the Brazilian Nanotechnology National Laboratory (LNNano) for allocation of the TEM and AFM apparatus.

References (50)

  • M. Henriksson et al.

    An environmentally friendly method for enzyme-assisted preparation of microfibrillated cellulose (MFC) nanofibers

    Eur. Polym. J.

    (2007)
  • P. Lu et al.

    Preparation and characterization of cellulose nanocrystals from rice straw

    Carbohydr. Polym.

    (2012)
  • S.I. Mussatto et al.

    Effect of hemicellulose and lignin on enzymatic hydrolysis of cellulose from brewer’s spent grain

    Enzyme Microb. Technol.

    (2008)
  • S. Pirani et al.

    Nanocrystalline cellulose extraction process and utilization of the byproduct for biofuels production

    Carbohydr. Polym.

    (2013)
  • M.F. Rosa et al.

    Cellulose nanowhiskers from coconut husk fibers: effect of preparation conditions on their thermal and morphological behavior

    Carbohydr. Polym.

    (2010)
  • P. Satyamurthy et al.

    Preparation and characterization of cellulose nanowhiskers from cotton fibres by controlled microbial hydrolysis

    Carbohydr. Polym.

    (2011)
  • J.X. Sun et al.

    Isolation and characterization of cellulose from sugarcane bagasse

    Polym. Degrad. Stab.

    (2004)
  • M. Tholstrup Sejersen et al.

    Zeta potential of pectin-stabilised casein aggregates in acidified milk drinks

    Int. Dairy J.

    (2007)
  • H. Tibolla et al.

    Cellulose nanofibers produced from banana peel by chemical and enzymatic treatment

    LWT – Food Sci. Technol.

    (2014)
  • J.J.G. Van Soest et al.

    Changes in the mechanical properties of thermoplastic potato starch in relation with changes in B-type crystallinity

    Carbohydr. Polym.

    (1996)
  • L. Viikari et al.

    Xylanases in bleaching: from an idea to the industry

    FEMS Microbiol. Rev.

    (1994)
  • H. Yang et al.

    Characteristics of hemicellulose, cellulose and lignin pyrolysis

    Fuel

    (2007)
  • R. Zuluaga et al.

    Cellulose microfibrils from banana rachis: effect of alkaline treatments on structural and morphological features

    Carbohydr. Polym.

    (2009)
  • AOAC

    Official Methods of Analysis

    (2005)
  • A.M.d. Castro et al.

    Produção, propriedades e aplicação de celulases na hidrólise de resíduos agroindustriais

    Quím. Nova

    (2010)
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