Pectin gel

Pectic substances form two important types of rigid gel. Pectin-sugar gels, familiar in jams and jellies, are prepared at low pH, and sometimes with multivalent cations added, but neither condition is necessary if esterification is complete.146 Some unesterified residues... 

Gel filtration profiles of pectins from gel and pericarp from fruit at selected stages of development are shown in Figure 1. In undeveloped fruit, soluble pectins from both gel and pericarp were excluded from Ultrogel AcA 34. Little change was observed in gel pectins throughout development whereas pectins from pericarp exhibited a clear trend of depolymerization. The differential fractionation patterns were generally consistent with the relative levels of EDG activity found in each tissue (Table II). 

Gel tissue contained only trace levels of EDG activity. The fact that extracts from three separate lots of fruit exhibited similar activity is an indication that the presence of the enzyme in gel was not a consequence of handling-induced contamination from pericarp tissue. Evidence for j n situ action of the enzyme was apparent when gel pectins were examined on Ultrogel AcA 22, a filtration matrix with a broader fractionation range than that of Ultrogel AcA 34 (Figure 2). On AcA 22, pectins from gel showed evidence of depolymerization, albeit less extensive and first apparent much later in fruit development (ripe stage) than that affecting pericarp pectins. 

Figure 2. Ultrogel AcA 22 profiles of gel pectins from tomato fruit at mature-green (A) and ripe (B) stage of development. Acid sugars (A520).

Figure 4. A, Total neutral sugar levels of soluble pectins derived from tomato fruit at the immature green (IG), mature-green (MG), and ripe (R) stage of development. Left ordinate, gel Right ordinate, pericarp. B and C. Individual neutral sugars from pericarp and gel pectins. Gal (galactose), Xyl (xylose), Ara (arabinose).

The rather limited and delayed depolymerization of gel pectin and the constancy of esterification indicates that the initial period of gel formation involves a mechanism other than the classic PME—D-galacturonanase scenario. 

Pectin also contains araban and galactan. Il is present in fruits, root vegetables and other plant products, and confers on jams their typical gelling property. Pectin is manufactured as a white powder, soluble in water, and used to assist the setting of jams and jellies, and for numerous other purposes. Low melhoxyl pectins, with under 7% methoxyl, give firmer gels than pectins proper. 

Pectins are readily soluble in water to give viscous stable solutions. However, the importance of pectin to industry, in particular the food industry, is the abihty of its solutions to form gels with sugar (ca 65% soHds) and acid or calcium ion under suitable conditions (51). 

Tamarind seed polysaccharide, the gum fraction obtained from tamarind kernel polysaccharide, forms gels over a wide pH range in the presence of high sugar concentrations (>65 wt%), and it can therefore substitute for fmit pectins (65). 

A rationalization of the complex behavior of pectins in solutions and gels with respect to their stmcture, solvation, and the presence of ions and other saccharides has been presented (123). The solution and sorption properties of gum tragacanth and the pectin isolated from the roots of Hibiscus mani/)ot F (Tororoaoi) contributes to their use in specialty paper manufacture (124—126). 

Candy. Citric acid is added in candy for tartness (54,55). To suppress the inversion of sucrose, it should be added after the cook, at levels from 0.5 to 2.0%. The pH of pectin gel candies is adjusted with citric acid for maximum gel strength. 

Carbopol is widely used in cosmetic and pharmaceutical practice as a gel-former. Carbopol resins are hydrophilic polymers which swell in water solutions and transform into the gel form at neutralization. At the elaboration of special cosmetic preparations in which carbopol is used, the problem of raw materials compatibility appears. For example, some extracts of aromatic pectin containing materials destroy the gel structure of carbopol. High contents of bivalent metal ions, in particular calcium ions, destructively influence onto the gel-making ability of the system too. 

Determination of Na " and Na" ions in raw cosmetic materials was conducted with the developed method of flame photometry. A necessity of development of method of samples preparation arose up in the work process, as this spicily-aromatic raw material contained pectin in amount 0.1-0.5% and that prevented preparation of samples by standard method of extracts dilution and required incineration of analyzed sample, time of analysis was increased in 60 times. It was established that CaCl, solution with the concentration 0,4 % caused destmctions of the carbopol gel. It was established that the addition of 0,1% CaCl, and 0,1% NaCl salts solutions into the system intensified the effect of negative action of these salts onto the gel stmcture and the gel destmcted completely. 

Pectin is a thickener in many products. If there is sufficient sugar in the mixture, pectin forms a firm gel. Jams and jellies are thickened with pectin. Pectin binds water, and thus keeps products from drying out. It stabilizes emulsions. 

Pectin combines with the calcium and whey proteins of milk, stabilizing foams and gels made with cream or milk. 

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