An investigation of pectin and pectic acid in dilute aqueous solution

Characterization of pectin, flash-extracted from orange albedo by microwave heating, under pressure

Pectin was acid extracted from orange albedo by microwave heating under pressure. Extraction times ranged from 2.5 to 8 min. Solubilized pectin was characterized for molar mass (M), rms radius of gyration (Rg) and intrinsic viscosity [eta] by HPSEC with online light scattering and viscosity detection. M, Rg and [eta] all decreased with increasing extraction time. Nevertheless, at heating times of 2.5 and 3.0 min, M, Rg and [eta] were significantly higher than a commercial citrus pectin when the albedo:solvent ratio was 1:25 (w/v). At the heating time of 2.5 min Mw was 3.6 x 10(5), Rgz was 38 nm and [eta]w was 10.8 dL/g. Chromatography revealed that solubilized pectin distributions were bimodal in nature and that the low-molar-mass fraction increased at the expense of the high-molar-mass fraction with increasing extraction time. Scaling law exponents revealed that the high-molar-mass fraction was extremely compact in shape, whereas the low-molar-mass fraction was more asymmetric in shape. Possibly these results indicated that at short extraction times, pectin was solubilized as compact aggregated network structures that were broken down to their more asymmetric components with increased heating times.

Chiral selectors from fruit: application of citrus pectins to enantiomer separations in capillary electrophoresis

Pectins were investigated as chiral selective agents in capillary electrophoresis. Successful enantioresolution of antihistaminic and antimalarial compounds, as well as others, was achieved by utilizing potassium polypectate as the chiral selector. Changes in pH, chiral additive concentration and capillary type were studied in relation to chiral resolution. The effect of degree of esterification of pectin materials on chiral recognition was also evaluated.

Chemistry and uses of pectin--a review

Pectin is an important polysaccharide with applications in foods, pharmaceuticals, and a number of other industries. Its importance in the food sector lies in its ability to form gel in the presence of Ca2+ ions or a solute at low pH. Although the exact mechanism of gel formation is not clear, significant progress has been made in this direction. Depending on the pectin, coordinate bonding with Ca2+ ions or hydrogen bonding and hydrophobic interactions are involved in gel formation. In low-methoxyl pectin, gelation results from ionic linkage via calcium bridges between two carboxyl groups belonging to two different chains in close contact with each other. In high-methoxyl pectin, the cross-linking of pectin molecules involves a combination of hydrogen bonds and hydrophobic interactions between the molecules. A number of factors--pH, presence of other solutes, molecular size, degree of methoxylation, number and arrangement of side chains, and charge density on the molecule--influence the gelation of pectin. In the food industry, pectin is used in jams, jellies, frozen foods, and more recently in low-calorie foods as a fat and/or sugar replacer. In the pharmaceutical industry, it is used to reduce blood cholesterol levels and gastrointestinal disorders. Other applications of pectin include use in edible films, paper substitute, foams and plasticizers, etc. In addition to pectolytic degradation, pectins are susceptible to heat degradation during processing, and the degradation is influenced by the nature of the ions and salts present in the system. Although present in the cell walls of most plants apple pomace and orange peel are the two major sources of commercial pectin due to the poor gelling behavior of pectin from other sources. This paper briefly describes the structure, chemistry of gelation, interactions, and industrial applications soft pectin.

Solution conformations of pectin polysaccharides: determination of chain characteristics by small angle neutron scattering, viscometry, and molecular modeling

The solution behavior of pectin polysaccharides has been investigated by small angle neutron scattering (SANS), viscosimetric, and molecular modeling studies. The samples used in the experimental study were obtained from apple and citrus and had degrees of methylation ranging from 28 to 73%, with a rhamnose content lying between 0.6 and 2.2%. Persistence lengths, derived from intrinsic viscosity measurements, ranged from 59 to 126 A, whereas those derived by SANS were between 45 and 75 A. These values correspond to 10-17 monomer units. The modeling simulations were performed for both homogalacturonan itself and homogalacturonan carrying various degrees of rhamnose inserts (rhamnogalacturonan). This required the evaluation of the accessible conformational space for the eight disaccharides that represent the constituent repeating segments of the homogalacturonan and rhamnogalacturonan polysaccharides. For each dimer, complete conformational analysis was accomplished using the flexible residue method of the MM3 molecular mechanics procedure and the results used to access the configurational statistics of representative pectic polysaccharide chains. For homogalacturonan, an extended chain conformation having a persistence length of 135 A (corresponding to 30 monomers) was predicted. The inclusion of varying amounts of rhamnose units (5-25%) in the model in strict alternating sequence with galacturonate residues (equivalent to the rhamnogalacturonan "hairy region" chains) only slightly reduced the calculated persistence length. The extended overall chain conformation remained relatively unchanged as a consequence of the self-cancellation of the kinking effects of successive paired rhamnose units.

A static and dynamic light scattering study of sharp pectin fractions in aqueous solution

A number of sharp fractions from low methoxyl citrus pectin have been studied using dynamic and static light scattering and size exclusion chromatography. The efficiency of the dynamic light scattering technique for the characterization of aqueous pectin solutions is demonstrated even when aggregages are present. The measured molar mass dependence of the Stokes radius confirms the semi-rigid structure of pectin. The effect of a number of sample manipulations on the aggregate content has been investigated and a simple but effective purification method is presented.

Pectin microgels and their subunit structure

High-performance size exclusion chromatography revealed that alkaline-extracted peach fruit pectin dissolved in 0.05 M NaNO3 comprised a hierarchy of at least four aggregated, macromolecular-sized species. Each of the three largest species was found to be comparable in length to the three smallest subunits of an interconnecting gel network visualized by transmission electron microscopy of pectin, rapidly dried from solution. The interconnecting subunits of the gel network were rods or segmented rods and the integrated network formed a circular gel about 1 micron in diameter. Shadowed samples prepared from 5 and 50 mM NaCl or aqueous glycerol solutions produced images of partially dissociated subunits.