Low methoxyl pectins

Pectin. Pectin [9000-69-5] is a generic term for a group of polysaccharides, mainly partially methoxylated polygalacturonic acids, which are located in the cell walls of all plant tissues. The main commercial sources of pectin are citms peel and apple pomace, where it represents 20—40% and 10—20% of the dry weight respectively. The pectin is extracted, the extract purified, and the pectin precipitated (50) increased extraction times lead to the production of low methoxyl pectins. 

Pectins are generally classed according to their ester content as high methoxyl pectins (>50% of the carboxyl groups esterified) or low methoxyl pectins (<50% of carboxyl groups esterified) (pectic acid, methyl ester [9049-34-1]). Low methoxyl pectins, like algins, require calcium for gelation. 

Pectins are subdivided according to their degree of esterification (DE), a designation of the percent of carboxyl groups esterified with methanol. Pectins with DE >50% are high methoxyl pectins (HM pectins) [65546-99-8]-, those with DE <50% are low methoxyl pectins (LM pectins) [9049-34-7]. 

The commercial samples of pectins mainly used as food additives represent modified forms of the natural polymers due to the conditions of extraction. Nevertheless, it is usually recognized two categories of pectins the high methoxyl pectins (HM) with a degree of methylation DM>50% forming gels at low pH in presence of saccharose to reduce the water activity and the low methoxyl pectins (LM with DM<50%) forming gel in presence of calcium [4]. 

Sunflower head residues are one of the richest sources of low-methoxyl pectin, their most important property being the ability to form gels, if correct proportions of divalent ions (usually calcium) are available. 

Sunflower plant Helianthus annuus L.) is an important crop in Portugal and its head residues, remaining on soil after the seeds have been removed for oil industry, are one of the richest sources of low-methoxyl pectin (ca 19% original dry matter), the most important property being the ability to form gels even without sugar addition, if correct amounts of divalent ions (usually calcium) are present. 

Following previous works on physico-chemical characterisation of sunflower low-methoxyl pectins (Alarc o-Silva, 1990, Leitao at al., 1995) and technological utilisation in the manufacture of low calorie gels (Alarc o-Silva et al., 1992), this investigation was carried out to test the suitability of that pectin to the confection of grape juice reduced calorie jellies in comparison with two types of commercial pectin. Aiming at the optimisation of low-calorie jelly formula, based on consumers preferences, the jellies were submitted to a sensory panel test judgement and instrumental texture-analysis. 

Experimental low-methoxyl pectin was obtained from dry heads (without seeds) of sunflower Helianthus annus L.). The extraction of pectin was carried out according to the method of Lin et al. (1975) with slight modifications. Only oxalate-soluble fraction which was submitted to consecutive treatments of purification as described previously was considered (Leitao et al., 1995). 

In this study we intend to investigate if a correlation between sensory evaluation and instrumental measurements of the low-methoxyl pectin jellies could be established. 

Pectin is used in foods in two forms, high methoxyl pectin and low methoxyl pectin. High methoxyl pectin is the form normally found in fruit while low methoxyl pectin is a chemically modified pectin. Pectins are acidic polysaccharides that occur in the cell walls of fruit. The commercial source of pectin is either citrus peel or apple pomace. The citrus peel is the residue from the production of citrus juices while apple pomace is the residue of cider production. Thus pectin is a by-product of either cider or fruit juice production. 

Most countries restrict the maximum degree of amidation to a 25% maximum. High methoxyl pectins are naturally present in fruit and escape restrictions on use for that reason. Low methoxyl pectins are treated as additives and have restrictive acceptable daily intakes (ADIs). 

Low methoxyl pectins have radically different properties, i.e. a small chemical modification has totally altered the way in which pectins behave. The low methoxyl pectins are set by calcium ions independently of the pH. Because hard water normally contains calcium ions care must be taken in selecting low methoxyl pectins when using hard water supplies or when moving recipes between factories. The gel produced in low methoxyl pectins has the egg box structure found in alginates (see Figure 6). 

The gel properties as well as the gelling conditions are radically different for the two types of pectin. High methoxyl pectins produce a gel that does not remelt, while some low methoxyl pectin gels are thermoreversible. 

If a product with a neutral pH is being made a high methoxyl pectin would not set, therefore the only option is to use a low methoxyl pectin. Examples of products with a neutral pH are mint flavoured jellies and Turkish delight. 

Low level wastes (LLW), 23 592. See also Low-level radioactive waste (LLW) from reactors, 77 598 Low-melting lead alloys, 14 779 Low-melting-point indium alloys, 14 196 Low-melting thiodiols, DBTDL-catalyzed step-growth solution and melt polymerization reaction of, 23 744 Low-methoxyl pectins (LM pectins), 4 728 13 69... 

Abbasi, S., Dickinson, E. (2002). High-pressure-induced rheological changes of low-methoxyl pectin plus micellar casein mixtures. Journal of Agricultural and Food Chemistry, 50, 3559-3565. 

Beaulieu, M., Turgeon, S.L., Doublier, J.-L. (2001). Rheology, texture and microstructure of whey proteins/low methoxyl pectin mixed gels with added calcium. International Dairy Journal, 11, 961-967. 

Different grades of low-methoxyl pectin (Hercules, Inc., Wilmington, DE). 

Specifically, D-glucose < maltose < maltotriose < amylose < starch < amylo-pectin < cellulose (Greenwood, 1967). Trends indicated are that thermochemical stability increases with the DP, branching, and 1,4-fi bonding. Chemical bonds other than 1,4-a and 1,4-(3 introduce heat and acid instability. Either of these two bonds is less easily depolymerized when the sixth pyranose carbon is oxidized to the carboxyl group rather than esterified for this reason, low-methoxyl pectin is more stable than high-methoxyl pectin. 

Using the density equation of dispersed polysaccharides at concentrations obeying Raoult s law, , may be obtained from Vt vs ct (Walter and Matias, 1989). When V vs ci is not linear, < >, must be stated at a given c,. Subsequent to 4>, determinations, configurational AS [Eq. (3.22)] were calculated for low-and high-methoxyl pectin. Low-methoxyl pectins were discovered to be less inclined to order themselves in an aqueous medium than high-methoxyl pectins (Walter, 1991). 

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