Soluble pectin, determination

This paper concerns the main properties of water soluble pectins in sol and gel states. First of all, the methods of purification and characterization are discussed. The method of steric exclusion chromatography equipped with different detectors is demonstrated as the most useful to determine the macromolecular characteristics of these polymers the role of aggregation is pointed out. 

Recently the means by which pectin lowers cholesterol levels and even the validity of this effect have been questioned. Upon finding no bile salt binding capacity for soluble pectin, Baig and Cerda (76) proposed that pectin lowered serum cholesterol levels by forming insoluble complexes with the serum low density lipoproteins (LDL) which transport circulating cholesterol. Complexing of LDL by citrus pectin was observed in vitro, but the way in which pectin or some component thereof enters the blood stream to effect such binding in vivo has not been determined. 

Since the determination of the water, oxalate and alkaline soluble pectin is just an extraction followed by a precipitation, this loss could be either the result of a poorer extractability or of a degradation into lower molecular weight pectin fractions which no longer can be precipitated by ethanol. Obviously the degradation is negligible, because the viscosity of pectin solutions which should be a sensitive indicator for the breakage of already few bonds is not altered by the application of HP. 

Pectin, a waste product of the fruit juice industry, has many applications in the food ingredients sector. It forms gels in the presence of Ca ions and its solubility is determined by its molecular weight and degree of esterification as well as solution pH and temperature. Pectin can be incorporated into jams, jellies, low calorie foods as a fat or sugar replacer, and frozen foods [85]. Found in the cell wall of all plants, concentrations are higher in the fruits rather than the rest of the plant. Some fruits contain higher amounts of pectin than others for... 

With the aid of the molar absorptivity value of 31600 at pH 10, as given by Fry (13), we have determined the feruloylester content of the four pectins. These are quite different (Table I). Acid-soluble and alkali-soluble pectins contain many more feruloylester groups on average one such group per pectin molecule. It is tempting to presume a relationship between feruloylester content and ease of extraction of the pectins, but this requires further study. 

Pectin in almond kernels can be determined by extracting ground samples with water (soluble pectins) and then 0.05 M HCL at 100 °C for 90 min (insoluble pectins). Pectins can be determined as uronic acid by the carbazole method, using galacturonic acid as standard (Bitter and Muir 1962). 

Arabinan. This highly soluble polymer is found in the extracts of many fmits and seeds, in the boiling water extracts of pine wood (127), in the extracts of marshmallow roots (A/t/jaea officina/is) (128), and aspen (63) and willow (Sa/ix a/ba F) (129) bark. Because arabinan can be isolated from mildly degraded pectin fractions, it is often difficult to determine whether it is a hemiceUulose or a labile fragment of a larger polysaccharide and/or lignin complex. Arabinans have a complex stmcture composed almost entirely of 5-linked a-L-arabinofuranosyl units with similar residues linked to them at C-2 and/or C-3 and is soluble in 70% aqueous methanol solution. 

Unlike biopolymer dispersions where the intrinsic viscosity is known and the polymer concentration can be chosen a priori, often for fluid foods the concentration of soluble (e.g., pectins in fruit juices) and insoluble solids can be determined only posteriori, and the determination of their zero-shear viscosities is also difficult due to instrument limitation and due to the existence of yield stress. However, in many foods, it may be possible to identify the components, called key components, that play an important role in the rheological properties. 

Acetyl and Feruloyl Esters in Pectin. A colorimetric method for determining degrees of acetylation in pectins from various sources ( ), has been shown to be rapid and quite sensitive. Hydroxy-lamine is reactive toward both the methyl and acetyl esters in pectin, and ferric ion complexes with the resulting hydroxamic acids are red. The pectin complex is insoluble and removed by filtration the intensity at 520nm in the soluble fraction, consisting of the ferric complex with acetohydroxamic acid, is a measure of acetyl content. The accuracy of the method was demonstrated in determinations of 0-acetyl levels in standard per-ace-tylated polysaccharides. Another method ( ) involves alkaline hydrolysis of the acetyl groups from pectin, followed by distillation of acetic acid and its titration with standard base. 

Figure 1 shows the relationship between grade measured by elastic deformation (grade is 65, the per cent of soluble solids, divided by concentration of pectin in per cent) and number average molecular weight (Af ). All of the points fall on a smooth curve similar to that found for fibers of cellulose derivatives (28) when their physical properties are determined as a function of Mn. 

Smith-Barbaro a. (26) in our laboratory determined the capacity of various fibers to bind the colon carcinogen 1.2-di-methylhydrazlne (DMH) in vitro. The percent of DMH bound to wheat bran, corn bran, alfalfa fiber and dehydrated citrus pulp was dependent on pH of the medium as well as the type of fiber examined. Results from this study show that at colonic pH, a greater percent of DMH was bound by wheat bran than by citrus pulp. Therefore, it is possible that certain fibers bind carcinogen at colonic pH, thus making it unavailable for contact with the colonic mucosa. Other fibers such as pectin (soluble fiber) do not bind DMH at colonic pH, but may modify the metabolism of carcinogen via actlvation/deactlvatlon steps either in the liver and/or in the colonic mucosa. 

The rheological properties of fluid tomato sauce products are important quality parameters. The flow properties of the juice, i.e viscosity and consistency, are determined primarily by the insoluble components [180-186]. The viscosity of the serum, the soluble fraction of the tomato juice after removal of insoluble material, is mainly determined by the polymeric substances, mostly pectin, i.e., the flow... 

This elaboration process is based on a solvent system in which the polymer is soluble and the nanoliller is sweUable. The polymer is first dissolved in an appropriate solvent. In parallel, the nanoliller is swollen and dispersed into the same solvent or another one to obtain a miscible solution. When the polymer and nanoliller solutions are mixed, the polymer chains intercalate and displace the solvent within the interlayer of the nanofiU. Upon solvent removal, the intercalated stmcture remains, resulting in a nanocomposite. In this method the nature of the solvents is critical in facilitating the insertion of polymer molecules between the nanoliller layers, polarity of medium being the determining factor for intercalation. Since some polysaccharides, such as cellulose or pectin, cannot be melt processed due to high thermal or thermomechaiucal degradation, the solvent process has been extensively used to produce polysaccharide/nanofiller hybrid materials. 

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