Optimization of pectin extraction from banana peels with citric acid by using response surface methodology
Introduction
Bananas (Musa acuminata, AAA Group) are one of the most important fruit crops, with a global annual production that surpassed 100 million tons in 2011 (The World Banana Forum, 2014). Bananas are mostly consumed raw, and their processed products include banana flour, chips, and puree (which can be used to produce nectars, smoothies, and a variety of other products). Banana peels constitute about 30% of the fruit, and represent an environmental problem because of their large nitrogen and phosphorus contents as well as their high water content, making them highly susceptible to microbial degradation (González-Montelongo, Lobo, & González, 2010). The use of banana peels as a source of high value compounds such as pectin (Happi Emaga, Ronkart, Robert, Wathelet, & Paquot, 2008b), cellulose nanofibers (Tibolla, Pelissari, & Menegalli, 2014), and phenolic compounds (González-Montelongo et al., 2010, Rebello et al., 2014) is interesting not only from an economic point of view, but also from an environmental perspective.
Some previous studies were carried out to investigate effects of process variables on extraction of pectin from banana peels. Qiu et al. (2010) investigated the effects of pH, extraction time, temperature, and salting out time on pectin extraction by using an enzymatic method. Happi Emaga et al. (2008b) evaluated the differences in pH, temperature and time on pectin extraction from banana peels using sulfuric acid. However, no previous report has been found on studying effects of process variables on pectin extraction from banana peels using organic acids. On one hand, strong mineral acids are cheaper and more effective than organic acids; on the other hand, organic acids are more interesting than strong acids from an environmental point of view (Chan and Choo, 2013, Pinheiro et al., 2008). Moreover, because of their lower dissociation constant, organic acids have a lower hydrolyzing capacity than mineral acids, so they will be less likely to cause proton-catalyzed depolymerization of pectins (Kermani et al., 2014). That may be especially important during the mixing step, when the local acid concentrations can fluctuate dramatically. Pectin yields from extraction of apple pomace, cocoa husks, and passion fruit peel with citric acid were found to be similar to those obtained with hydrochloric acid (Canteri-Schemin et al., 2005, Chan and Choo, 2013, Kliemann et al., 2009).
The objective of this study was to evaluate the influence of pH, temperature, and time on pectin extraction from banana peels with citric acid.
Section snippets
Chemical composition of banana peel powder and changes in FTIR spectra
Banana peels at ripening stage 6 (fully ripe bananas, ready for consumption) were collected from Cavendish bananas purchased in the local market (Norwich, UK). The peels were immersed in sodium metabisulfite solution (1% w/v) for 24 h, oven-dried at 60 °C for 24 h, and milled to 0.5 mm in a Retsch Brinkmann ZM-1 centrifugal grinding mill (Retsch GmbH, Haan, Germany).
The ash, extractive, and Klason lignin contents of the banana peel powder were determined according to methods TAPPI t413 OM-93 (
Chemical composition of banana peel powder and changes in FTIR spectra
The banana peel powder has less than 40% holocellulose, 48% of it being α-cellulose (Table 1), and the remaining 52% being hemicelluloses and pectin. When compared to the values reported by Oberoi, Vadlani, Saida, Bansal, and Hughes (2011) for composition of banana peels, the carbohydrate contents reported in this study were lower, while the extractives content was similar, and the ash and lignin contents were higher (although Oberoi et al., 2011 have quantified only the acid detergent lignin).
Conclusions
Pectins were successfully extracted from banana peels with citric acid, under different conditions of pH, temperature and extraction time. Harsh temperature and pH conditions resulted in higher extraction yield, but at the cost of decreasing the degree of methoxylation from a maximum of 79% to a minimum of 43%. The optimum conditions of pectin extraction, defined as those which produced a maximum yield of galacturonic acid while keeping a degree of methoxylation of at least 51%, were: 87 °C, 160
Acknowledgments
The authors gratefully acknowledge the financial support of the UK Biotechnology & Biological Sciences Research Council (BBSRC) and the Brazilian Agricultural Research Corporation (Embrapa). Authors also thank the National Counsel of Technological and Scientific Development (CNPq, Brazil) for the Research Productivity Fellowship (304179/2012-4) granted to H.M.C. Azeredo, and for the scholarships granted to T.I.S. Oliveira (228859/2013-1) and P.H.F. Pereira (243244/2013-4).
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- 1
Permanent address: Federal University of Ceara, Chemistry Department, Campus do Pici, Bloco 940, CP 6021, CEP 60455-760 Fortaleza, CE, Brazil.
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Permanent address: Embrapa Tropical Agroindustry, R. Dra. Sara Mesquita, 2270, CEP 60511-110 Fortaleza, CE, Brazil.