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Abstract In the present work. the pectic substances of the prickly pear stems and orange peel have been investigated and more information about the structural features of these polysaccharides were obtained. Besides valuable knowledge. about technological and chemical characterization were acquired to evaluate these pectins commercially. The yields of pectic substances from orange peel and Egyptian prickly pear pectin were 26.02% (orange peel pectin). 14.27% (prickly pear pectin. fraction A), 13.9% (prickly pear pectin. fraCtion ”B”) and 17.41% (prickly pear pectin, mixed sample), on dry basis. The preliminary investigation of the properties of extracted pectins were carried out. The results obtained were compared with those from citrus and other pectins. • I.R spectrum of these polysaccharides showed that the major glycosidic linkages in t~e different types of pectins under the study are of the cr~ype in Cl pyranose conformations. also positive specific optical rotation can SUpport this assumption. Molecular weight is one of the most important factors affecting pectin quality and has a marked influence on gelly grade. The mOleCUlar weights for different types of pectins were determined and the results showed that average moleCUlar weights ranged from 50,000 to 78,000. Molecular sieve chromatography were applied using 5300 and 5 500 . The results indicated that all samples under study had a wide range of molecular weights with relatively small differences in distribution of neutral sugar between eluted fraction. These pectins are highly physically heterogeneous but chemically homogeneous in terms of Mw fractions. Pectin depolymerization was carried out using acid hydrolysis and enzymatic degradation. The examination of the hydrolysate by paper chromatography indicated that the bUilding units tOf pectins were galacturonic acid as major components. Galactose, rhamnose and arabinose were found as minor components in the case of citrus pectin and orange peel pectin. In the case of prickly pear pectin fractions”A” and ”S” galacttronic acid, arabinose galactose, rhamnose and xylose were identified as bUilding units. No glucose was detectable in any of the different types of pectin under study, this support that pectins were free from dextrens. The results of the hydrolysis of pectins by acid and enzymatiC hydrolysis indicated that the molar ratio of the bUilding sugars by the two methods were slightly different for each pectin except prickly pear pectin fraction ”A” which con tains a high proportion. of neu tral sugar. The eaterase of the pentosanase 36L has different effects on each type of pectin. This is due to the difference in the chemical structure of pectin and to the shape of the molecules. Also, polygalacturonase and lyase combined together had a different effect on each type of pectin under the study. Hydrolysis of pectin in 0.25 M trif1uoroacetic acid at 100·C for one hour produced a white precipitate. The infra-red spectra for tQe white precipitate from different types of,pectin was compared with that of po1ygalacturonic acid (obtained from Sigma Company). It was found that a large degree of simi1arty existed between the spectrum of the po1ygalacturonic and those from the precipitate obtained. Fractionation of pectins was achieved by ion exchange chromatography, using DEAE-cellu1ose. A preliminary fractionation of pectins on DEAE-cellu1ose was carried out to select the sUitable conditions for fractionation. The recovery of samples was quite satisfactory of DEAE-cellu10se l and a linear gradient (5-500 mM) Na phosphate at pH 6.5 was accomplished. Five fractions were obtained from the elution pattern of citrus pectin. on the other hand, four f~actions were obtained from the other type of pectins. The properties of the fractions were studied, the molar ratios for pentoses, anhydroga1acturonic acid and neutral hexoses were calculated. Acid hydrolysis and enzymatic pectin breakdown were carried out. the results were in good agreement with those of other pectins. Molecular weights of the fractions for different types of pectins were determined from the relation between the molecular weight and intrinsic viscosity. l.R. spectra of the eluted fractions for the pectins was achieved. The results indicated that l.R spectra of eluted fractions for the different pectins were similar to those of the original pectins. These results, can roughly support that there is a homogenity in type of linkage and groups in the different pectin fract1ons. The methylation of pectins was accomplished using dimethyl sulfoxide as a solvent and dimethylsulphonyl anion (base) and iodomethane as methylating reagent. Separation and examination of the fission products of the methylated pectin using paper chromatography technique microanalytical and phys1cal measurements. The results showed the presence of 2-0-methyl-D-gala~turonic, 2,3-di- O-methyl-O-galacturonic ac~d. 2,3,4-tri-O-methyl-D-galact_ uronic acid, 2,3,6-tri-O-methyl-O-galactopyranose, 3,4-di- O-methyl-L-rhamnopyranose. 2.3-di-O-methyl-L-arabino_ furanose and 2,3,5-tri-O-methyl-L-arabinofuranose in the case of orange peel pectin and citrus pectin while in the case of prickly pear pectin (fraction A) and (fraction B) the presence of2,3-di-O-methyl-O-xylopyranose and 2,3,4- tri-O-methyl-D-xylopyranose were found, in addition to the above methylated monomers. These resulLs proved that the presence of main backbone chain consists of 1,4 linked galacturonic acid. The presence of 2-0-methyl-D-galacturonic acid may be most probably to the presence of branching in the main chain by (1-+3) glycosidic bonds. The isolation of 3,4 di-O-methyl-L-rhamnopyranose permitted the assumption that rhamnose may be included in the main chain polysaccharides chain by (1-+2) bonds or it may take part of side chain. The resulLs of methylation indicated that the neutral sugars may be presented as branchings and linked to the main chain of pectic acid. The galactone units are linked by (1-i>4) glycosidic -linkage while the arabinose units are linked by (1~5) glycosidic linkages. In addition to that the presence of 2,3,5 tri-O-methyl-L-arabinofuranose represents the terminal units of these branchings. Finally, (the presence of 2,3 di-O-methyl-D-xylopyranose and 2,3,4 tri-O-methyl-D-xylopyranose from methylated prickly pear pectins (UAU, ”8”) indicated that these neutral monomers are branchings and linked by (1~4) glycosidic linkages. The quality of pectins in the present work was determined on the basis of the SAG tests. According to the results obtained, orange peel pectin, prickly pear pectin fraction (fraction B) and prickly pear pectin (mixed sample) are suitable to form firm high gel strength in comparison with investigated pectin. as reported in literature. Prickly pear pectin (fraction A) can be used in the purposes which require low content of AUA and low methoxyl content such as medical purposes. |