Textural Changes and Molecular Characteristics of Pectic Constituents in Ripening Peaches

Shewfelt, A. L.; Paynter, Valerie A.; Jen, Joseph J.

doi:10.1111/j.1365-2621.1971.tb15132.x

Cited by 49 publications

(17 citation statements)

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“…tomatoesl7-21 and peaches. 22 There are other fruits, however, where ripening is accompanied by changes to other wall polysacharides.6 There is no evidence from the data presented in this paper that extensive degradation of pectic substances by polygalacturonase occurs during the development and ripening of plum fruits. Attempts to detect the presence of this enzyme have not been successful.…”

Section: Discussioncontrasting

confidence: 43%

Pectic substances in developing and ripening plum fruits

Boothby

1983

J Sci Food Agric

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The fresh weight of plum fruits increased throughout the growing season whilst the weight of ethanol insoluble material increased to a peak in the penultimate sample and then declined. Pectin content paralleled the change in weight of the insoluble residue. There were no significant changes in the proportional composition of monosaccharides in pectin or the total solids. Pectic substances were examined by gel permeation chromatography and high voltage electrophoresis. There was no evidence for extensive degradation of the pectic substances, but changes in the electrophoretic mobility were consistent with de-esterification during ripening.

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Section: Discussioncontrasting

confidence: 43%

Pectic substances in developing and ripening plum fruits

Boothby

1983

J Sci Food Agric

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“…The softening of freestone peaches, for example, has long been associated with the conversion of protopectin to soluble forms (13,(19)(20)(21). Although changes in other polysaccharides may be involved, the solubilization of pectin has received the most attention because of the occurrence of this polysaccharide in the middle lamella, as well as in the cell wall.…”

Section: Introductionmentioning

confidence: 99%

Separation and Characterization of Endopolygalacturonase and Exopolygalacturonase from Peaches

Pressey¹,

Avants²

1973

Plant Physiol.

155

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Two polygalacturonases (PG I and PG II) have been separated from extracts of ripe peaches (Prunus persica) by chromatography on Sephadex G-100. PG I hydrolyzes polygalacturonic acid from the nonreducing ends of the molecules, releasing galacturonic acid as the product. It functions optimally at pH 5.5, requires Ca2+ for activity, and hydrolyzes low molecular weight substrates most rapidly. In contrast, PG II cleaves the molecular chain of the substrate randomly with a pH optimum at about 4. This enzyme is most reactive with substrates of intermediate molecular weight. It catalyzes the release of watersoluble, but 70% ethanol-insoluble, pectin from washed peach cell walls.Changes in polysaccharides leading to the destruction of the cell wall structure are probably responsible for the marked softening of fruits during ripening. The softening of freestone peaches, for example, has long been associated with the conversion of protopectin to soluble forms (13,(19)(20)(21). Although changes in other polysaccharides may be involved, the solubilization of pectin has received the most attention because of the occurrence of this polysaccharide in the middle lamella, as well as in the cell wall. Elucidation of the mechanism of pectin solubilization has been hindered by the complexity of protopectin and by the failure to identify the enzymes involved. In a recent study (16), we found that polygalacturonase was not detectable in unripe peaches, but activity appeared when the fruit began to soften and then increased sharply as ripening proceeded. Development of the enzyme paralleled the formation of water-soluble pectin. Furthermore, the molecular weights of the solubilized pectin decreased during fruit ripening. The results suggested a key role for polygalacturonase in pectin solubilization and, therefore, in textural changes accompanying peach ripening.The very low level of polygalacturonase in peaches, compared to that in tomatoes, presents problems in studying this system. Because the activity is associated with the particulate fraction of homogenates, we originally conducted our assays with aliquots of washed cell fragments incubated for long periods. We have now developed a procedure for solubilizing and concentrating the polygalacturonase activity in ripe peaches. This paper describes the resolution of the activity into two components and some of their properties. MATERIALS AND METHODSSubstrates. Pectic acid, purchased from Sigma Chemical Company,' was purified by precipitating a 1% solution in water at pH 5 with 2 volumes of 95% ethanol. The precipitate was collected on Miracloth, dissolved in water, and precipitated with ethanol. This procedure was repeated three times, and the pectic acid was finally homogenized with 95% ethanol and acetone and dried under vacuum.The polygalacturonic acids were prepared by enzymatic hydrolysis of pectic acid as described earlier (15). PGA I is a fraction that is insoluble at pH 2 and 25 C, while PGA II is insoluble at pH 2 and 3 C. PGA III is soluble at pH 2 and 3 C, but its ...

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“…Prominent among the enzymes implicated are PG3 and PE because striking changes in wall pectin content are observed in ripening fruits (1,13,14,21,22), and activities ofthese two enzymes often increase as ripening continues (21). In addition, primarily because of their presence in extracts of ripening fruits, a variety ofglycanases (10,21,26) and glycosidases (3,20,21) have been assigned an unspecified role in fruit cell wall metabolism.…”

Section: Introductionmentioning

confidence: 99%

Cell Wall Metabolism in Ripening Fruit

Ahmed¹,

Labavitch²

1980

Plant Physiol.

110

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Mature 'Bartlett' pear (Pyras communis) fruits were ripened at 20 C. Fruits at different stages of ripeness were homogenized, and extracts of the low speed pellet (crude cell wall) were prepared. These extracts contained polygalacturonase, pectin esterase, and activity against seven pnitrophenyl glycoside substrates. Polygalacturonase, a-galactosidase, and a-mannosidase increased in activity as the fruit ripened. CeOulase and activities against pear wall xylan and arabinan were absent from the extracts.The changes in cell wall composition which accompany the softening of ripening fruit apparently result from the action of enzymes produced by the fruit. Prominent among the enzymes implicated are PG3 and PE because striking changes in wall pectin content are observed in ripening fruits (1,13,14,21,22), and activities ofthese two enzymes often increase as ripening continues (21). In addition, primarily because of their presence in extracts of ripening fruits, a variety ofglycanases (10,21,26) and glycosidases (3,20,21) have been assigned an unspecified role in fruit cell wall metabolism.This paper describes measurements of the activity of a variety of carbohydrate-degrading enzymes in extracts of ripening 'Bartlett' pears. The potential for depolymerization of pear cell wall polysaccharides was assessed using model substrates containing the same types of glycosidic linkages that have been described for pear cell walls (1). Glycosidase activities were followed using pnitrophenyl substrates. The activities of several enzymes, notably PG, a-mannosidase, and a-galactosidase, increased substantially as the fruit approached the respiratory climacteric. The potential roles of the various enzymes in ripening-associated cell wall modification are discussed. Enzyme Assays. PE activity was determined as described by Nagel and Patterson (17) with the aid of an automatic titrating pH meter (Radiometer Titrometer II). MATERIALS AND METHODSPolysaccharide-degrading activities were followed by measuring the generation of reducing groups according to the method of Nelson (18), as modified by Somogyi (23). The standard reaction mixture contained enzyme and 0.1% (w/v) substrate in I ml of 100 mm Na-acetate (pH 5.0). Incubation was at 37 C. The substrates used were polygalacturonic acid (Sunkist Growers), carboxymethyl cellulose and larch xylan (Sigma), and araban (KochLight Laboratories, Ltd.).Prior to use, the xylan was purified according to the technique of McNeil and Albersheim (as described by Taiz and Honigman [24]) to remove abundant glucose-and mannose-containing contaminants. The araban also had to be treated prior to use in order to remove uronic acid-containing materials. Five g araban were refluxed for 16 h in 250 ml 5 N NaOH containing 4 g NaBH4. The preparation was cooled, neutralized with glacial acetic acid, and centrifuged for 5 min at 1,000g. Final clarification of the supernatant solution was accomplished by filtration through glass fiber (GF/C) paper. The filtrate was dialyzed against 10 mm K-phosphate (pH 7...

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Textural Changes and Molecular Characteristics of Pectic Constituents in Ripening Peaches

Cited by 49 publications

References 0 publications

Pectic substances in developing and ripening plum fruits

Pectic substances in developing and ripening plum fruits

Separation and Characterization of Endopolygalacturonase and Exopolygalacturonase from Peaches

Cell Wall Metabolism in Ripening Fruit

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