Pectins from waste of prickly pear fruits (Opuntia albicarpa Scheinvar ‘Reyna’): Chemical and rheological properties Ana Laura Lira-Ortiz a , Felipa Reséndiz-Vega a , Elvira Ríos-Leal b , Juan Carlos Contreras-Esquivel c , Norberto Chavarría-Hernández a , Apolonio Vargas-Torres a , Adriana Inés Rodríguez-Hernández a, * a Cuerpo Académico de Biotecnología Agroalimentaria, Instituto de Ciencias Agropecuarias, Universidad Autónomadel Estado de Hidalgo, Av. Universidad km 1, Exhacienda de Aquetzalpa, Tulancingo de Bravo, Hidalgo C.P. 43600, Mexico b Departamento de Biotecnología y Bioingeniería, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, México D.F., Mexico c Facultad de Ciencias Químicas, Universidad Autónoma de Coahuila, Saltillo, Coahuila, Mexico article info Article history: Received 21 April 2013 Accepted 22 October 2013 Keywords: Pectic polysaccharide Opuntia Rheology Cross equation abstract Low methoxyl pectin was extracted from prickly pear fruit (Opuntia albicarpa Scheinvar ‘Reyna’) by sequential extraction with water in presence of a sequestering agent. Sugar composition of the prickly pear pectin (PP) was (mg g 1 , dry weight): 654 galacturonic acid, 195 galactose, 21.6 rhamnose, 1.2 arabinose and 1.2 glucose. The weight-average molecular weight was 10.16  10 5 g mol 1 , the number- average molecular weight was 9.10  10 5 g mol 1 and the polydispersity index was 1.116. The FTIR spectrum of PP showed good agreement with that of standard citrus pectins and the degree of esteri- fication of PP was 30.7%. Pectin dispersions in the range of 5e20 g kg 1 showed a non-Newtonian rheological behaviour which had good fitting to the Cross equation. The gelling ability of PP was eval- uated by dynamic oscillatory rheometry. The addition of Ca 2þ (0.25e0.75 mM) to 4 g L 1 PP dispersions led to the gel formation. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction The term “pectin” describes a family of polysaccharides extremely complex and structurally diverse, which is one of the major plant cell wall components and probably the most complex macromolecule in nature due to it can be composed out of as many as 17 different monosaccharides containing more than 20 different linkages (Voragen, Coenen, Verhoef, & Schols, 2009). Three major pectic polysaccharides are recognized, all containing galacturonic acid (GalA) to a greater or lesser extent: the homogalacturonan (HG) consisting of 1,4-linked a-D-GalA, the rhamnogalacturonan I (RGI) consists of the repeating disaccharide (/4)-a-D-GalA- (1/2)-a-L-Rha-(1/) to which a variety of different glycan chains (principally arabinan and galactan) are attached to the rhamnose residues, and the rhamnogalacturonan II (RGII) which has a back- bone of HG with complex side chains attached to the GalA residues (Willats, Knox, & Mikkelsen, 2006). The chain lengths of the various domains of pectins can vary considerably and the sugar composi- tion of RGI can also be highly heterogeneous (Willats et al., 2006). The GalA may be both methyl-esterified and acetylated. The degree of methyl-esterification (DM) and degree of acetylation (DA) have a strong impact on the functional properties of pectins and these are categorized as high-ester or low-ester with DM > 50% and DM < 50%, respectively (Willats et al., 2006). High methoxyl pectin can form a gel under acidic conditions in the presence of high sugar concentrations or a similar co-solute at pH < 3.5, whereas low methoxyl pectin forms gels by interaction with divalent cations, particularly Ca 2þ (Ngouémazong et al., 2012). Thus, pectins are high value functional carbohydrates in the food industry. Commercially, pectins are obtained mainly from citrus peel and apple pomace all over the world; nonetheless, efforts have been carried out by numerous groups in order to find alternative pectin sources to take advantage of the vast available bioresources within different ecosystems. In this sense, pectin polysaccharides have been isolated from various plant tissues and plant processing by- products (i.e., sisal waste (Santos, Espeleta, Branco, & de Assis, 2013), cacao pod husks, Theobroma cacao L. (Vriesmann & Petkowicz, 2013), Solanum lycocarpum fruits in Brazil (Torralbo, Batista, Di-Medeiros, & Fernandes, 2012), sugar beet (Morris, Ralet, Bonnin, Thibault, & Harding, 2010), pomace grape e winery (González-Centeno et al., 2010), low-quality apples (Rascón-Chu et al., 2009), linseed (Dıaz-Rojas et al., 2004), peach * Corresponding author. Tel.: þ52 771 717 2000; fax: þ52 771 717 2125. E-mail address: inesr@uaeh.edu.mx (A.I. Rodríguez-Hernández). Contents lists available at ScienceDirect Food Hydrocolloids journal homepage: www.elsevier.com/locate/foodhyd 0268-005X/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodhyd.2013.10.018 Food Hydrocolloids 37 (2014) 93e99