Pectin, characteristics structure

High levels of soluble carbohydrates may have an influence on the texture characteristics of products, too. Gelling of pectins, for example, depends on the level of sucrose, which has to be high to get the typical gel structure of jams and marmalades. 

The plots of the intensities of selected characteristic bands as a function of lateral position (so-called chemical maps) provide information on the amount of the respective molecules or molecular groups in the different morphological structures (Fig. 4.2). The band at 784 cm 1 can be assigned to out-of-plane deformation vibrational modes of the nucleobases cytosine, thymine and uracil and serves as an indicator for the presence of nucleic acids. At 483 cm-1, a C-C-C deformation of carbohydrate polymers such as starch or pectin is present in some of the spectra. To study the distribution of protein compounds, we analysed characteristic signals of the amino acid phenylalanine (1002 cm 1 ring breathe) as well as of the protein amide I band (1651 cm-1) that is brought about by vibrations of the protein backbones. The maximum of the phenylalanine signal co-localizes with a maximum in protein content... 

The characteristics of the isolated biopolymers depend on their structure. Cellulose and amylose are linear polymers, whereas amylopectin, pectin and hemicelluloses are branched polymers. Pectin and amylopectin contain carboxylic groups, which make interactions with water molecules very important. Amylose has a helix structure, whereas the cellulose molecule looks like a ribbon. The interactions with water and other neighbouring molecules are therefore different. 

Many foods contain high-molecular weight polymers, such as proteins, pectins, and others. Often, they contribute significantly to the structure and viscosity of foods. In dilute solutions, the polymer chains are separate and the intrinsic viscosity, denoted as [ ], of a polymer in solution depends only on the dimensions of the polymer chain. Because [ ] indicates the hydrodynamic volume of the polymer molecule and is related to the molecular weight and to the radius of gyration, it reflects important molecular characteristics of a biopolymer. The concentrations of polymers used should be such that the relative viscosities of the dispersions are from about 1.2 to 2.0 to assure good accuracy and linearity of extrapolation to zero concentration (Morris and Ross-Murphy, 1981 da Silva and Rao, 1992). Intrinsic viscosity can be determined from dilute solution viscosity data as the zero concentration-limit of specific viscosity (ijsp) divided by concentration (c) ... 

The relationships between structure and gelling characteristics of agarose, polyvinyl alcohol, and high methoxyl pectin-water gels in mixed-solvent systems composed of dimethyl sulfoxide (DMSO) and water were examined by Watase and Nishinari (52-54). The elastic properties of gels composed of agarose or polyvinyl-alcohol, DMSO, and water increased as a function of DMSO concentration, up to... 

Tomato fruit appeared to represent a unique system for investigating possible variability in the functions of pectins in texture modifications. Firstly, the tomato fruit is composed of distinct tissue types, including locular gel and pericarp which exhibit markedly different patterns of tissue autolysis. Locular gel develops prior to ripening of pericarp and eventually, toward the terminal stage of ripening, exhibits an almost liquid nature. This developmental scenario is in some respects similar to the ethylene-induced maceration of watermelon fruit (27), a process involving greatly increased levels of EDG and extensive solubilization and depolymerization of pectins (23). In contrast, tomato locular gel has been reported to contain little ( ) or no EDG activity (28). The objective of this study was to examine some of the structural features of pectins from tomato pericarp and gel, and to relate this information to the textural characteristics of these tissues. 

They suggested that demethylation of the pectin by pectinmethyl-esterase resulted in a more rigid cell wall structure, and that this deesterification may be a common characteristic of chilling-sensitive plants ( ). ... 

Unlike other naturally occurring polysaccharides, e.g., cellulose, dextran, pectin, alginic acid, agar, agarose and carrageenans, which are neutral or acidic in nature, chitosan is a highly basic polysaccharide. This unique property imparts several functional attributes such as polyoxysalt formation, ability to form films, chelation with metal ions, and optical structural characteristics (Hench 1998). 

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