Acids, pectinic

Pectin is a long chain of pectic acid and pectinic acid molecules. Because these acids are sugars, pectin is categorized as a polysaccharide. It is prepared from citrus peels and the remains of apples after they are squeezed for juice. In the plant, pectin is the material that joins the plant cells together. When fungus enzymes break down the pectin in fruit, the fruit gets soft and mushy. 

PDMS. See polydimethylsiloxane pectic acid, 142 pectin, 141-142 pectinic acid, 142... 

Pectin belongs to a family of plant polysaccharides in which the polymer backbone consists of (1— 4)-linked a-D-galacturonic acid repeating-units. Often, (1— 2)-linked a-L-rhamnose residues interrupt the regular polygalacturonate sequence. The high viscosity and gelling properties of pectins are exploited by the food and pharmaceutical industries. X-Ray studies on sodium pectate, calcium pectate, pectic acid, and pectinic acid (methyl ester of pectic acid) have disclosed their structural details. 

Paper ionophoresis, sugars, Maurice Stacey s work, 17 Pectic acid, 350, 352,414 Pectin, 348, 350-353 Pectinic acid, 353 Pentulose, synthesis, 281 D-cryt/iro-Pentulose 5-phosphate, 289 Peptidoglycans, 167-168 Per-O-acetylated di-D-fructose dianhydride derivatives... 

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

There is the further, although remote, possibility that the only substantial variation in the composition of pectinic acids obtained from fruits and beets, and from some other sources, might be the result of differences in the occurrence in these of natural enzymes acting upon pectic substances. Pectinic acids isolated from beets have been shown to contain acetyl groups,8 the mode of attachment of which to the poly-... 

There is no major advance which can be reported in our knowledge of protopectinases. The possibility of the existence of a protopectinase different from PG seems now somewhat more remote than it was ten years ago. As stated above, the trend in thinking about protopectin is definitely in the direction that protopectin is not a specific cellulose-pectinic acid compound but pectinic acid which is insoluble either on account of large molecular size or due to the effect of polyvalent cations or both. In this sense there is really no need to assume the existence of a separate protopectinase. There is little doubt that this uncertainty is in a large degree attributable to the lack of precise knowledge of protopectin. 

Pectin methylesterase (PM) is the enzyme which catalyzes the hydrolysis of the methyl ester groups in pectinic acids. In contrast to PG and protopectinase, a great deal of progress has been made during the past decade in our knowledge of PM. The older term pectase, 8 invented before the chemical action of the enzyme was understood, is now used by a decreasing number of workers while the name pectin-... 

Holden84 used a method of measurement in which the methanol liberated by PM in a buffered solution of pectinic acid in ten minutes has been estimated by the Zeisel method. This procedure is much more complicated than that described above and must be regarded as unreliable on account of the rapid change in the pH of such reaction mixtures, even if buffered. 

Rather thorough studies have now been made of the properties of the PM of tomatoes,20 21 44 62 63 66 orange peel,21 tobacco3 61 64 and alfalfa.49 The activity of PM is profoundly affected by the pH of the reaction mixture, the salt concentration and the cation component of the salt. In salt-free solutions, the activity of the PM of higher plants is nearly zero at pH 4.25 and increases linearly with a steep slope as the pH is increased to 8. Above 8 the pectinic acids are also demethylated by the action of alkali and the enzyme activity measurements therefore become unreliable. The relationship between activity and pH is also dependent on the salt content of the reaction mixture. 

This review would be incomplete without mention of an important and rapidly developing new field in pectin chemistry and technology, namely that of the low-ester pectinic acids. In contrast to pectinic acids (pectins) of over 7% methoxyl content, pectinic acids containing 3-6% methoxyl are capable, in the presence of the required proportion of... 

Pectase was found in plants, both in soluble and non soluble form. It was able to break down pectose into pectinic acid, and was attributed some similarity to diastase. Neither materials could be crystallized (Payen, 1874). Claude Bernard was the first to show lipolytic activity in pancreas in 1856 (Tauber, 1949), and Dobell (1869) found that an extract from pancreas hydrolyzed both fat and starch he gave a procedure for extraction and stabilization and named this preparation pancreatine . 

Inserted L-rhamnopyranosyl units may provide the necessary irregularities (kinks) in the structure required to limit the size of the junction zones and produce a gel. The presence of side chains composed of D-xylosyl units may also be a factor that limits the extent of chain association. Junction zones are formed between regular, unbranched pectin chains when the negative charges on the carboxylate groups are removed (addition of acid), hydration of the molecules is reduced (addition of a cosolute to a solution of HM pectin), and/or pectinic acid polymer chains are bridged by multivalent, eg, calcium, cations. 

---