Gels pectin-sugar

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... 

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). 

Pectin.—This general term has been retained to designate pectinic acids which will form the customary pectin-sugar-acid gels. 

Different polysaccharide variable-path processes were observed in a pectin-sugar-water-acid mixture dispersed at 105°C then cooled to 25°C, and a mixture dispersed at 50°C then cooled to 25°C. The higher-temperature gel was relatively stable, but the lower-temperature gel was unstable (Walter and Sherman, 1986). Heated agar sols gel when cooled to approximately 30°C, and they remain dimensionally stable to a reheating temperature of 85°C due to relatively permanent physical crosslinks below Tm (Lips et al., 1988). The reheated gels follow a hysteretic pathway to melting at the... 

Most plants contain pectin in the intercellular layer between the primary cell walls of adjoining cells. Six to seven million kg of purified pectin are produced annually, more than half of which is extracted from citrus peel C. ) Of this amount, 80 to 90% is used in the manufacture of jellies, jams, and similar products ( ). In this chapter, jelly will be used to denote the product formed from pectin, sugar, and acid under specific conditions. Gel will mean a similar physical state but not the commercial product O). 

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 most important use of pectin is based on its ability to form gels. High methoxyl pectin forms gels with sugar and add. Oakenfull (1991) reported that hydrogen bonding... 

Gels known as low water activity gels or sugar-acid-pectin gels, formed from highly methoxylated (esterified) pectins that contain more than 50% carboxyl groups esterified with methanol... 

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). 

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. 

This paper will not described the chemical structure of pectins which is a difficult problem [1] even if the physical properties in solution and ability to form gel must be directly related with the distribution of the units along the chain. The functional properties of pectins are not only related to the neutral sugar content (up to 15 %) but also to the distribution of structural blocks having very different contibutions. 

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. 

Pectins are important sugar-based hydrocolloids used in the confectionery industry. In US the sugar confectionery industry is growing approximately 3% per year and the consmnption has increased to approximately 11 Ib. per capita [1]. Pectin s are widely used in jelly confections often produced using fruit flavors. Pectin gels are characterized by providing a very tender, short texture with excellent clarity and outstanding flavor release properties. 

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