Contents lists available at ScienceDirect Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol Cell wall polysaccharides from Ponkan mandarin (Citrus reticulata Blanco cv. Ponkan) peel Cristiane Colodel, Lúcia Cristina Vriesmann, Carmen Lúcia de Oliveira Petkowicz ⁎ Department of Biochemistry and Molecular Biology, Federal University of Parana, PO Box 19046, 81531-980 Curitiba, Parana, Brazil ARTICLE INFO Keywords: Hemicelluloses Pectins Sequential extractions Structural characterization ABSTRACT Cell wall polysaccharides from ponkan peel were investigated with the aim of gain knowledge about their potential for different applications and the use of ponkan peel as raw material for pectin extraction. The plant material was defatted using MeOH:CHCl 3 , pretreated with DMSO and then subjected to sequential extractions with cold and hot water, ammonium oxalate, HCl, Na 2 CO 3 , 2 M and 4 M NaOH in order to obtain poly- saccharides. The polysaccharide fractions were analyzed by chemical, chromatographic and spectroscopic methods Cold and hot water-soluble pectins contained higher amounts of GalA and higher degrees of methyl- esterification (DM) than ammonium oxalate and HCl fractions. Na 2 CO 3 extraction provided non-esterified ara- binose-rich pectins which formed gel in a dialysis step. NaOH solubilized hemicelluloses, composed mainly of xyloglucans, galactomannans and galactoglucomannans. The water-soluble fraction (WSP) was purified using α- amylase and amyloglucosidase and gave rise to the subfraction named α-WSP. The α-WSP was a pectin com- posed of HG and RG-I domains containing side chains of arabinans and short-chains of galactans, with low DM (39.4%) and M w of 1.615 × 10 5 g/mol. 1. Introduction Cell wall polysaccharides are important and promising raw mate- rials for biomedical (Liu, Willför, & Xu, 2015) and food applications (Chapple & Carpita, 1998; Harris & Smith, 2006). Since the composition of the polysaccharides differs depending on the plant source (Nevins, English, & Albersheim, 1967) and even the cell type (Keegstra, 2010), it is important to increase the knowledge about the polysaccharides pre- sent in different species. Cellulose is the most characteristic plant cell wall polysaccharide and forms the structure of the cell wall by asso- ciation with other two groups of polysaccharides: pectins and hemi- celluloses (Keegstra, 2010). Pectins are acidic heteropolysaccharides which are classified into three main groups: homogalacturonans (HG), rhamnogalacturonan I (RG-I) and rhamnogalacturonan II (RG-II) (Willats, Knox, & Mikkelsen, 2006). HG consists of a linear chain of covalently linked →4)-α-D- GalAp-(1→ units, which can be partially methyl-esterified at C-6 and acetylated at O-2 and/or O-3 (Voragen, Coenen, Verhoef, & Schols, 2009; Yapo, 2011). In RG-I, the backbone is composed of [→4)-α-D- GalAp-(1 → 2)-α-L-Rhap(1 → ] repeated disaccharide and side chains of arabinans, galactans and/or arabinogalactans are attached to the backbone at O-4 of some rhamnosyl residues (Voragen et al., 2009; Yapo, 2011). In its turn, RG-II consists of HG main chain containing quite complex side chains. (Mohnen, 2008; Voragen et al., 2009). Pectins are widely used due to their gelling properties (Willats et al., 2006), which are strongly affected by their structure, especially on the degree of methyl-esterification (Thakur, Singh, & Handa, 1997). Hemicelluloses are described as the polysaccharides that are solu- bilized from the cell wall by aqueous alkaline solutions and have β- (1 → 4)-linked pyranosyl residues with the O-4 in the equatorial posi- tion. They comprise the groups of xylans, mannans and xyloglucans (Caffall & Mohnen, 2009). Citrus peel are the major sources of commercial pectins (Ciriminna, Chavarría-Hernández, Hernández, & Pagliaro, 2015; Willats et al., 2006). Often, the botanical source is not precisely identified in citrus commercial pectins, but orange, lime, grapefruit and lemon are com- monly used (Yapo, 2009). Ponkan (Citrus reticulata Blanco cv. Ponkan) is a non-climateric ci- trus fruit originated from Asia which belongs to a cultivar of mandarin (Bao, Yuan, Zhao, Liu, & Gao, 2015; Lee, Zhong, & Chang, 2015). It is one of the most appreciate mandarins for consumption, being the main mandarin cultivated in Brazil (Mendonça, Ramos, Rufini, Araújo Neto, & Rossi, 2006; Ramos et al., 2009). The fruits are flattened, with few seeds and the peel is rough and loose (Coelho, 1996), which makes it easy for consumption in natura. The fruits are also processed for the production of concentrated juice (Pavan, Mazzocato, Jacques, & Dias, https://doi.org/10.1016/j.carbpol.2018.04.066 Received 1 December 2017; Received in revised form 12 April 2018; Accepted 16 April 2018 ⁎ Corresponding author. E-mail address: clop@ufpr.br (C.L. de Oliveira Petkowicz). Carbohydrate Polymers 195 (2018) 120–127 Available online 21 April 2018 0144-8617/ © 2018 Elsevier Ltd. All rights reserved. T