Pectin molecular characteristics

At the moment, one recommends to determine the molecular characteristics of pectins using SEC chromatography equipped with a differential refractometer, a multiangle laser light scattering detector and a viscometer as previously described [25]. This technique needs no calibration with the usual molecular weight standards such dextrans and pullulans... 

The HM and LM pectins give two very different types of gels the mechanisms of stabilization of the junction zones in the two cases are described and few characteristics given. The different molecular characteristics (DE, distribution of methoxyl or acetyl substituents, neutral sugar content or rhamnose content) play an important role on the kinetic of gelation, mechanical properties of the gel formed and also on the experimental conditions to form the stronger gels. All these points were briefly discussed. 

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) ... 

Each fruit has specific quantities and ratio of pectin, hemicelluloses and cellulose. These polysaccharides are important concerning enzymes activities required to produce juices and concentrates. Moreover, even if molecular weight and methylation degree of the pectin are specific for each fruit, during the fruit maturation, endogenous pectinases depolymerases and esterase are changing the pectin characteristics This broad variability of raw material makes difficult the standardisation of fruits processing. 

Two characteristics of the lyase that we have purified may be significant. First, the small molecular size of the protein may confer it a high mobility that could be helpful to its movement through host cell walls. In second place, it is an endo-type enzyme, fact that has been considered essential for maceration of plant tissues [35]. In this sense it is noteworthy that between the battery of pectic enzymes produced by FORL, this pectin lyase is the only protein that behaves as an endo-type. 

Some properties of Penicillium fellutanum pectinesterase were studied. The optimum of pectinesterase action was detected at pH 5 and 45 °C. The enzyme was stable at pH 4 — 5 and 40 °C (pH 5) for 240 min. and was specific towards lemon pectin. An enzyme preparation composed mainly of pectinesterase was partially purified by gel filtration. Pectinesterase activity was accumulated in one of the obtained fractions. Molecular weights of fraction determined were found to be 46,000 and 1,200. Disk electrophoresis in polyacrilamide gel of the purified preparation revealed two protein bonds with one active component. The partially purified enzyme had the kinetic characteristics =... 

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 study of the interactions of pectins with metal ions in aqueous solution greatly contributes to the comprehension of the properties of their solutions and gels at molecular level. These acidic polysaccharides also manifest a cooperative-sequential binding mechanism for divalent cations [12, 14]. The most characteristic physical property of pectinic... 

S. Cros, C. Gamier, M.A.V. Axelos, A. Imberty, S. Perez, Solution Conformations of Pectin Polysaccharides Determination of Chain Characteristics by Amall Angle Neutron Scattering, Viscosimetry, and Molecular Modeling. Biopolymers 39 (1996) 229. 

Although pectins are not employed as thickening agents, pectin solutions exhibit the non-Newtonian, pseudoplastic behavior characteristic of most polysaccharides. As with solubility, the viscosity of a pectin solution is related to the molecular weight, DE, and concentration of the preparation and the pH and presence... 

Gentilini et al., in 2014, also studied the extraction of pectin from Aloe vera [23]. Different extraction methods were compared and it was found that the most effective treatment was with HCl, with a 2.64% 5ueld in pulp and a degree of esterification of 2.93%. It was established that the pectin in Aloe vera can be removed using a simple and inexpensive method. Tbe extraction method influences the composition of pectins, the degree of esterification, molecular weight, structural characteristics, and the ability to form gel. 

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