Pectin or pectic substances are collective names for a group of closely associated polysaccharides present in plant cell walls where they contribute to complex physiological processes like cell growth and cell differentiation and so determine the integrity and rigidity of plant tissue. They also play an important role in the defence mechanisms against plant pathogens and wounding. As constituents of plant cell walls and due to their anionic nature, pectic polysaccharides are considered to be involved in the regulation of ion transport, the porosity of the walls and in this way in the control of the permeability of the walls for enzymes. They also determine the water holding capacity. The amount and composition of pectic molecules in fruits and vegetables and other plant produce strongly determine quality parameters of fresh and processed food products. Pectin is also extracted from suitable agro-by-products like citrus peel and apple pomace and used in the food industry as natural ingredients for their gelling, thickening, and stabilizing properties. Some pectins gain more and more interest for their health modulating activities. Endogenous as well as exogenous enzymes play an important role in determining the pectic structures present in plant tissue, food products, or ingredients at a given time. In this paper functional and structural characteristics of pectin are described with special emphasis on the structural elements making up the pectin molecule, their interconnections and present models which envisage the accommodation of all structural elements in a macromolecule. Attention is also given to analytical methods to study the pectin structure including the use of enzymes as analytical tools. PectinPectin is one of the major plant cell wall components and probably the most complex macromolecule in nature, as it can be composed out of as many as 17 different monosaccharides containing more than 20 different linkages [1][2][3]. Plant functionality of pectinIn a plant, pectin is present in the middle lamella, primary cell and secondary walls and is deposited in the early stages of growth during cell expansion [4]. Its functionality to a plant is quite divers. First, pectin plays an important role in the formation of higher plant cell walls [5], which lend strength and support to a plant and yet are very dynamic structures [4]. In general, the polymeric composition of primary cell walls in dicotyledonous plants consists of approximately 35% pectin, 30% cellulose, 30% hemicellulose, and 5% protein [5]. Grasses contain 2-10% pectin and wood tissue ca 5%. In cell walls of some fruits and vegetables, the pectin content can be substantially higher and the protein content lower [6]. Second, pectin influences various cell wall properties such as porosity, surface charge, pH, and ion balance and therefore is of importance to the ion transport in the cell wall [7]. Furthermore, pectin oligosaccharides are known to activate plant defense

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As pectin molecules are too large and heterogeneous to analyze as a whole, the polymer is usually degraded to smaller oligomers, which are often analyzed by high-performance anion exchange chromatography (HPAEC). However, the high salt concentration necessary to elute pectin oligomers by HPAEC is incompatible with online mass detection. To overcome such a disadvantage, a CE-IT-MS system was set up to further elucidate the fine structure of charged oligosaccharides. An effective separation of differently substituted galacturonic acid containing oligomers was obtained by low-pH CE-LIF analysis. By adapting the buffer and capillary online MS detection was enabled. Moreover, with MS/MS it was possible to localize sugar residues' substitutions. With this combined CE-MS approach LIF electropherograms of xylogalacturonan and rhamnogalacturonan I digests could be annotated. The method was further exemplified by a complex oligomer mixture of acid hydrolyzed apple pectin, which was separated and characterized by CE-MSn. Oligomers present in low amounts could be localized by their corresponding m/z, as was demonstrated by selected mass range representation.

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A mixture of single side chains from white cabbage pectin were obtained by anion exchange chromatography after applying mild chemical conditions promoting beta-elimination. These pectin fragments were characterized by their molecular weight distribution, sugar composition, 13C-NMR, and MALDI-TOF-MS analysis. These analyses revealed that the large oligosaccharides released by beta-eliminative treatment were composed of alpha-1,5 linked arabinosyl residues with 2- and 3-linked alpha-arabinosyl side chains, and, or beta-1,4 linked galactosyl side chains. Fractions were tested for complement-fixing activity in order to determine their interaction with the complement system. These results strongly indicated that there was a minimal unit size responsible for the complement-fixing activity. Neutral pectin fragments (8 kDa) obtained from beta-elimination were inactive in the complement system, although they contained a sugar composition previously shown to be highly active. Larger pectin fragments (17 kDa) retained some activity, but much lower than polymers containing rhamnogalacturonan type 1 (RGI) structures isolated from the same source. This implied that structural elements containing multiple side chains is necessary for efficient complement-fixing activity.

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Zusammenfassung Es wurden zweifaktorielle Untersuchungen zum Einfluß von Stärke‐ und Fettzulagen auf den mikrobiellen Stoffwechsel im Pansensimulationssystem RUSITEC durchgeführt. Dazu wurde einer Grundration aus Heu und Konzentrat stufenweise native Weizenstärke und tierisches Mischfett zugelegt. Stärkezulagen senkten die Abbauraten von Rohfett, Rohprotein und Gerüstsubstanzen. Die Methanproduktion wurde nicht beeinflußt, die Ammoniakspiegel sanken. Die VFA‐Produktionsraten stiegen nur bei niedriger, nicht aber bei hoher Stärkezulage. Die hohe Stärkezulage erweiterte das C2/C3‐Verhältnis und verminderte die Buttersäureanteile, das Mikrobenwachstum, die Anzahl Bakterien und die YATP‐Werte. Die Anzahl Protozoen erhöhte sich nur bei niedriger Stärkezulage. Fettzulagen führten bei Rohfett zu höheren Abbauraten. Der Gerüstsubstanzabbau wurde unabhängig von der Höhe der Zulagen durch Fett herabgesetzt, der Abbau des Rohproteins blieb unbeeinflußt. Fettzulagen verminderten die Methanproduktion, wirkten sich jedoch weder auf die Ammoniakspiegel noch auf die VFA‐Produktionsraten aus. Das Mikrobenwachstum sank, die Anzahl Bakterien und Protozoen veränderte sich nicht. Zwischen Stärke‐ und Fettzulagen bestanden signifikante Wechselwirkungen beim Abbau der Gerüstsubstanzen und im Mikrobenwachstum, die mit dem Einfluß von Stärke auf die Lipolyserate und einem “coating” von Stärkepartikeln durch Fett zu erklären sind. Es wird geschlossen, daß der höchste Wirkungsgrad des mikrobiellen Systems im Pansen hinsichtlich Gerüstsubstanzabbau und Mikrobenwachstum unter günstigen Fermentationsbedingungen mit einer optimalen Kombination aus Stärke‐ und Fettzulagen zu erzielen ist.

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