Changes in Cell Wall Pectins Accompanying Tomato (Lycopersicon esculentum Mill.) Paste Manufacture MONTAN ˜ A CA Ä MARA HURTADO, † L. CARL GREVE, ‡ AND JOHN M. LABAVITCH* ,‡ Morning Star Packing Company, Williams and Los Banos, California, and Department of Food Science and Technology and Department of Pomology, University of California, Davis, California 95616 The texture of processed tomato products is influenced by the size and solubility characteristics of soluble and particle-bound cell wall polysaccharides they contain. The acidic (pectin) polysaccharides are important contributors to texture because of their gel-forming capability and the fact that they can form aggregates. The present work describes the pectins in ripe tomato fruits and then follows changes in several classes of pectins as the fruits are subjected to hot break and the juice is subsequently concentrated to a 30 °Brix paste. Continued processing leads to progressive solubilization and depolymerization of polysaccharides so that the ionically and covalently bound materials that are the major pectin classes of ripe fruit are substantially reduced in amount with the concomitant increase in the more soluble water-soluble pectins of the paste product. Juice content of soluble solids (°Brix) rose steadily as water content was reduced during processing. Juice content of polymeric uronic acids (i.e., pectin) also rose with concentration, but to a lesser degree than the increase in soluble solids. This indicates that processing leads to almost complete pectin depolym- erization and/or the alteration of uronic acid structures so that this assay could no longer detect them. It was concluded that reductions in heat input during processing would lead to pastes with greater pectin integrity and enhanced textural characteristics. KEYWORDS: Lycopersicon esculentum; pectin; texture; tomato paste INTRODUCTION Over 9 million tons of tomatoes are processed annually in the United States, with California producing 85% of the total. More than 80% of U.S. tomato production is utilized in the manufacture of processed products such as tomato paste (1). Texture, particularly in relationship to flow characteristics, is among the important quality attributes of processed tomato products. Several authors (1-4) have reported that the most important factor in determining the viscosity and consistency of tomato paste and products derived from it is the high molar mass polymeric substances derived from cell wall polysaccha- rides during processing. Pectins are common components in the cell walls of fruits that make important contributions to the texture of processed fruit products. Important in this is the tendency for pectins to form gels and influence the viscosity of solutions of higher molecular weight polymers. Pectin backbones are mainly composed of R-1,4-linked D-galacturonosyl (galactopyranosy- luronic acid, GalUA) units, with various degrees of methyl esterification of the galacturonosyl residue carboxyl groups. Simple pectins are homogalacturonans, but the more complex rhamnogalacturonans (RGs) have backbones that contain R-1,2- linked D-rhamnopyranosyl residues as well as GalUA residues. The RGs are also branched polymers, bearing side chains containing arabinosyl and galactosyl residues as the major components as well as many other sugar species (5). In the middle lamella, pectins are thought to be associated with calcium ions, so removal of Ca 2+ usually leads to cell separation. Food scientists have taken advantage of this structural characteristic by using additions of Ca 2+ , often as CaCl 2 , to increase the firmness of fresh and processed plant-derived foods (e.g., ref 6). Chelator-insoluble pectic polysaccharides are usually highly branched and are probably cross-linked in the wall matrix via ester cross-links involving sugar residues and borate ions or phenolic residues (5, 7). These pectins can be extracted with sodium carbonate (8). It is likely that all classes of cell wall pectins, as well as the other cell wall polysaccharides, make important contributions to the texture of tomato paste. Plant biochemists and food scientists are interested in methods for measuring and characterizing pectin polymers in terms of their composition and molar mass distributions to understand their physiological and biochemical roles in plants and physi- cochemical functions in food (9). Although studies on tomato fruit, juice, and pulp have been reported, the importance of pectin polymer size distribution in tomato paste texture has not been reflected in the scientific literature. Luh et al. (10) reported * Author to whom correspondence should be addressed [fax (530) 752- 8502; e-mail jmlabavitch@ucdavis.edu]. † Permanent address: Departamento Nutricio ´n y Bromatologı ´a II, Fac- ultad de Farmacia, Universidad Complutense, Ciudad Universitaria, 28040 Madrid, Spain. ‡ University of California. J. Agric. Food Chem. 2002, 50, 273-278 273 10.1021/jf010849e CCC: $22.00 © 2002 American Chemical Society Published on Web 12/19/2001