Acid pectic substances

A variety of chemicals may be leached from the aerial portions of plants by rainwater or by fog-drip (16) including organic acids, sugars, amino acids, pectic substances, gibberellic acids, terpenoids, alkaloids, and phenolic compounds. Colton and Einhellig (17) suggested that leaf leachates of velvetleaf (Abutilon theophrasti) may be inhibitory to soybean (Glycine maxT We have recently discovered specialized hairs on the stems of velvetleaf plants which exude toxic chemicals. 

A more recent, clearly preferable classification (Brillouet, 1987 Brillouet et al, 1989) simply divides soluble polysaccharides in must into neutral pectic substances and acid pectic substances, depending on whether or not the molecules contain... 

The rhamnogalacturonan zones of acid pectic substances generally have lateral chains of neutral OSes, connected to carbon 4 of the rhamnose. For this reason, they are known as bristled zones , as opposed to the smooth zones of homogalactur-onan that do not branch off (Figure 3.18). There are two types of lateral chains in the bristled zones arabinogalactans in the majority (AG-II) and arabinans (A). 

Fig. 3.18. Suggested structural model for acid pectic substances in grapes (Doco et al, 1995). A, arabinan HG, homogalacturonase AG-II, arabinogalactan II RG-I, rhamnogalacturonan I RG-II, rhamnogalacturonan II...

Arabinans, minor lateral branches of acid pectic substances, consist of short arabinose chains, bonded in a-(l,5), with ramifications of individual arabinose units on C3 (Figure 3.20). 

These substances have molecular structures similar to those of the lateral branches of acid pectic substances, consisting of arabinan and type 11 arabinogalactan. 

The various groups of pectic substances are usually characterized by their solubility behavior. Polygalacturonides, like other polyuronides, can be quantitatively estimated by the amount of carbon dioxide formed upon heating with hot acid. Pectic substances of all sorts have been commonly determined by the formation and weighing of water-insoluble pectic acid or calcium pectate but unfortunately it is difficult to get these precipitates free from impurities (particularly other polysaccharides) present in the material analyzed. Today, the most common method of estimation is the spectrophotometric measurement of the colored complex formed upon the addition of alcoholic carbazole to the material to be analyzed after alkali treatment and heating with concentrated sulfuric acid. ... 

PEC-1000 Pechmann reaction Peclet numbers PE coatings Pectic acid Pectic acids [9046-40-6] Pectic materials Pectic substances Pectin... 

Pekannuss, /. pecan nut, pecan, pektin-artig, a. pectin-like, -ig, a. pectinous. Pektin-korper, m. pectic substance, -s ure, /. pectic acid, -stoff, m., -substanz, /. pectio substance, -zucker, m. arabinose. pelagisch, a. pelagic. 

As investigations with polysaccharides of microbiological, plant, and animal origin revealed the presence in these substances of uronic acids, it became necessary to know more about the acids. Moreover, the occurrence of uronic acids in plant gums and pectic substances, and the structures of urinary... 

Pectins can generally be divided into neutral and acidic polymers, but certain structural features are common between the different types of pectic substances. These will be described below. Concerning the general chemistry of carbohydrate types of linkages, the reader can find details on this in general textbooks of chemistry and biochemistry and is for this reason not included. 

The four AIS contained high and equivalent amounts of galacturonic acid (Table 1), indicating that the distribution of pectic substances was similar to the distribution of the AIS in the fruit. 

Leitao, M. C. A. Alarcao-Silva, M. L. Januario, M. I. N. Azinheira, H. G. Galacturonic acid in pectic substances of sunflower head residues quantitative determination by HPLC. Carbohydr. Polym.,26(1995)165-169. 

Another characteristic property of the products of /3-eliminative cleavage of pectic compounds is the reaction with thiobarbituric acid after previous cleavage with periodate, giving rise to red condensation products having229 an absorption maximum at 547-550 nm. Both properties are used for the identification of /3-eliminative cleavage of pectic substances. 

It is now clear that the basic skeletons of all pectic substances consist essentially of poly-a-D-galacturonic acids the constituent units of which contain the pyranose ring and are linked glycosidically in a configuration through positions 1 and 4.s 6... 

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-... 

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