Contents lists available at ScienceDirect Phytochemistry journal homepage: www.elsevier.com/locate/phytochem Biochemical and biophysical characterization of water-soluble pectin from Opuntia ficus-indica and its potential cytotoxic activity Khalef Lefsih a,d,* , Daniela Giacomazza b , Rosa Passantino b , Maria Assunta Costa b , Donatella Bulone b , Maria Rosalia Mangione b , Valeria Guarrasi b , Francesco Mingoia c , Pier Luigi San Biagio b , Khodir Madani a a Laboratoire de Biomathématiques, Biophysique, Biochimie et Scientométrie, Faculté des Sciences de la Nature et de la Vie, Université de Bejaia, 06000, Bejaia, Algeria b Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Palermo, Italy c Istituto per lo Studio dei Materiali Nanostrutturati, Consiglio Nazionale delle Ricerche, Palermo, Italy d Département de Biochimie et Microbiologie, Faculté des Sciences Biologiques et des Sciences Agronomiques, Université de Tizi ouzou, 15000, Tizi ouzou, Algeria ARTICLE INFO Keywords: Opuntia ficus-indica (Cactaceae) Pectin Heat-modified pectin Rhamnogalacturonan Alditol-acetates TMS-Glycosides PMAA Light scattering Cytotoxicity ABSTRACT This work aims to fill the gap in the present knowledge about the structure of pectin from Opuntia ficus-indica. The water-soluble pectin (WSP) fraction, extracted with the Microwave Assisted Extraction (MAE), was further deproteinated (dWSP) and analyzed through several biophysical and biochemical techniques. HPSEC, light scattering and FTIR data showed that dWSP is low methylated high molecular weight pectin. The biochemical structure of dWSP, after methanolysis, silylation, carboxyl reduction showed that dWSP belongs to rhamnoga- lacturonan I class. Then, dWSP was heat-modified (HM) to obtain small-molecular weight deproteinated fraction (HM-dWSP). Both species, dWSP and HM-dWSP, were tested in LAN5 and NIH 3T3 model cells to study their biological effect. Results indicated that both dWSP and HM-dWSP exerted cytotoxic activity affecting selectively LAN5 cancer cells, without any effect on NIH 3T3 normal cells. 1. Introduction An important non-cellulosic matrix polysaccharides in plants is pectin (Tanczos et al., 2003). It is a complex polysaccharide composed of α-1,4-linked D-galacturonic acid (GalA) backbone and segments consisting of alternating sequences of α-(1,2)-linked L-rhamnosyl and α- 1,4-linked D-galacturonosyl residues ramified with side chains com- posed mainly of arabinose, mannose and galactose (de Vries et al., 1983; Niaounakis, 2013). The carboxyl groups of the constituent ga- lacturonic acid molecules are esterified to varying extents, and pectins are mainly described as high- or low-methoxyl (HMP and LMP re- spectively), the latter having less than 50% of possible carboxyl groups esterified (Judd and Truswell, 1982). Pectin can be classified according to their molecular weight (Mw) into pectin with high Mw or low Mw (Zhang et al., 2015). Pectin has lubricating and cementing functions. It is degraded during attack by plant pathogens and oligogalacturonides function as elicitor in the host-pathogen interaction (Albersheim et al., 1981). Commercial pectin is extracted from citrus, apple, or other higher plants, and is used as a stabilizer, thickener, gelling agent, emulsifier, and drug vehicle in the food and pharmaceutical industries (Wicker et al., 2014). Applications of pectin in cancer therapy, antitumor ac- tivity of modified pectin and its application as an excipient for anti- tumor drugs have been reported (Zhang et al., 2015). Pectin and other sources of dietary fibers are associated with gastrointestinal health, glucose tolerance, lipid digestion and weight management (Dikeman and Fahey, 2006). Many researches are carried out on the effects of what is called ‘heat-modified’ (HM) pectin or ‘pectin oligosaccharides’ (POS), in which the native molecules have been broken down into smaller fragments that, in theory, can be absorbed by our organism. Action mechanisms against cancer are still unclear but evidence sug- gests that small pectin fragments can bind to the carbohydrate re- cognition domain on the pro-metastatic protein galectin-3 (Gal3) and may block its interactions with other proteins and peptides, inhibiting Gal3 ability to promote cell adhesion and migration, and to prevent apoptosis. This raises the possibility to use HM pectin and POS as po- tentially safe, non-toxic approach for preventing or reducing carcino- genesis (Maxwell et al., 2012). The modified commercial pectin was mainly used to explore its bioactivity. It is possible that other plant sources, in combination with alternative extraction procedures, may https://doi.org/10.1016/j.phytochem.2018.06.015 Received 6 March 2018; Received in revised form 23 June 2018; Accepted 26 June 2018 * Corresponding author. Laboratoire de Biomathématiques, Biophysique, Biochimie et Scientométrie, Faculté des Sciences de la Nature et de la Vie, Université de Bejaia, 06000, Bejaia, Algeria. E-mail address: klefsih@yahoo.fr (K. Lefsih). Phytochemistry 154 (2018) 47–55 0031-9422/ © 2018 Elsevier Ltd. All rights reserved. T