ISSN: 1314-6246 Georgiev et al. J. BioSci. Biotech. 2012, 1(3): 223-233. RESEARCH ARTICLE http://www.jbb.uni-plovdiv.bg 223 Yordan Georgiev 1 Manol Ognyanov 1 Irina Yanakieva 1 Veselin Kussovski 2 Maria Kratchanova 1 Isolation, characterization and modification of citrus pectins Authors’ addresses: 1 Laboratory of Biologically Active Substances, Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, 4000 Plovdiv, Bulgaria. 2 Department of Infectious Microbiology, Laboratory of Antimicrobial Resources, Institute of Microbiology “Stephan Angeloff”, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria. Correspondence: Maria Kratchanova Laboratory of Biologically Active Substances, Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, 4000 Plovdiv, Bulgaria. Tel.: +359 32 643140 e-mail: lbas@plov.omega.bg Article info: Received: 18 October 2012 Accepted: 10 December 2012 ABSTRACT Orange and lemon peels were used for obtaining pectic polysaccharides. Citrus peels were previously treated with 96% ethanol, and the obtained alcohol- insoluble solids (AIS) were subjected to a sequential extraction with hot distilled water and hot 0.5% HCl. Water- and acid-extracted orange (WEOP and AEOP) and lemon (WELP and AELP) pectins were obtained. Acid extraction gave higher yields of pectin than water extraction and lemon peels were richer in pectin. Comparative investigations were carried out with chromatographically purified commercial citrus pectin (CPCP). Chemical and physicochemical characterization of all pectins was accomplished. It was found that pectins were similar in anhydrouronic acid content (AUАC, 69-81%), but differed in their degree of methylesterification (DM, 55-81%). Generally water-extracted pectins were with higher DM. Both orange pectins were with higher DM and degree of acetylation (DA, 2%), in comparison with the corresponding lemon pectins. Water-extracted pectins were with higher degree of feruloylation (DF, 0.12- 0.34%). To our knowledge this is the first report on the estimation of ester-linked ferulic acid in orange and lemon peel pectins. Pectic polysaccharides differed in molecular weight and homogeneity. WELP was with the highest molecular weight and homogeneity. The pectins contained D-galacturonic and D-glucuronic acids, L-arabinose, D-galactose, L-fucose, L-rhamnose and D-xylose. All investigated pectins showed immunostimulating activity by complement activation in the classical pathway at 1.25 and 2.5 mg/mL. Pectic polysaccharides were modified with endopolygalacturonase. Enzyme-modified CPCP and WEOP had higher anti-complementary activity than the corresponding initial pectins. Key words: citrus pectin, monosaccharide composition, ferulic acid content, immunostimulating polysaccharides Introduction Pectic substances in fruits were discovered by the French chemist Louis Nicolas Vauquelin in 1790 in tamarind fruit (Vauquelin, 1790). The term “pectin” was introduced by Henri Braconnot because of the gelling properties of these substances (Braconnot, 1825). Pectic polysaccharides are localized in the primary cell wall and middle lamella in all higher plants, where they are responsible for different physiological processes (Knox, 2002). In the cell walls they serve as one of the main agents cementing the cellulose fibrils and may be linked covalently to other polymers. Intracellular pectins provide the channels for passage of nutrients and water (Tamaki et al., 2008). Apples, citrus fruits, sugar beet and sunflower heads are very rich in pectins and their by-products are the most important sources for pectin industry (Kertezs, 1951). Commercial pectins are extracted at low pH and high temperature. Pectins are widely used as food additives (E440) with gelling and stabilizing properties in jams, jellies, marmalades, milks and confectionery products (Sakai et al., 1993).