The Pectinesterase of the Pulp of the Banana Fruit.

Section: Discussionsupporting

confidence: 63%

Purification and Characterization of Pectinmethylesterase from Ficus awkeotsang Makino Achenes

Tian

Liu²,

Chen³

et al. 1989

“…Early in the climacteric cellulase and PG increased markedly while PME decreased. PME activity in relation to ripening of various fruits has been shown to increase (11,14), decrease (23), or remain unchanged (5,7). In avocado, we observed high PME activity for the first 5 days of the preclimacteric period followed by a sharp drop during the first 48 h of the climacteric while a low level of activity was measured during the main ripening period.…”

Section: Resultsmentioning

confidence: 99%

Postharvest Variation in Cellulase, Polygalacturonase, and Pectinmethylesterase in Avocado (Persea americana Mill, cv. Fuerte) Fruits in Relation to Respiration and Ethylene Production

Awad¹,

Young²

1979

171

105

Cellulase, polygalacturonase (PG), pectinmethylesterase (PME), respiration, and ethylene production were determined in single "Fuerte" avocado fruits from the day of harvest through the start of fruit breakdown. PME declined from its maximum value at the time of picking to a low level early in the climacteric. PG activity was not detectable in the preclimacteric stage, increased during the climacteric, and continued to increase during the postclimacteric phase to a level three times greater than when the fruit reached the edible soft stage. Celulase activity was low in the preclimacteric fruit, started to increase just as respiration increased, and reached a level two times greater than at the edible soft stage. Cellulase activity started to increase 3 days before PG activity could be detected. Increased production of ethylene foUlowed the increase in respiration and ceUulase activity by about 1.5 days. These results indicate that a close relation exists between the rapid increase in the ceOl waUl-depolymerizing enzymes and the rise in respiration and ethylene production and refocused attention on the role of the cell wail and the associated plasma membrane in the early events of fruit ripening.The avocado fruit starts to ripen only after being detached from the tree. After harvest, the most obvious ripening change is the rapid transition of the mesocarp from a hard to a soft, butter-like consistency with an apparent total loss of structural integrity.Several researchers have studied the relation between softening of the avocado fruit and the activity of cell wall-degrading enzymes. Lewis et al. (17) were the first to note that the hard avocado mesocarp presented barely detectable levels of cellulase activity whereas the activity in soft fruit was highest ever observed in plant tissues. Pesis et al. (20) found a direct correlation between cellulase activity, softening, respiration, and ethylene production. Awad (2) also found a close relation between the rapid increase in cellulase content after harvest, the climacteric rise in respiration, and softening of the fruit. He determined that edible softness occurred before maximum cellulase levels were reached.Raymond and Phaff (21) first showed a positive relationship between PG activity and softening of the avocado fruit. Later, Barash and Khazzam (3) and Zauberman and Schiffmann-Nadel (24) found that PG3 activity increased rapidly after harvest.The postharvest decrease in PME activity in the avocado fruit 'Research Fellow, CNPq, Brazil. (9), and Barmore and Rouse (4). We lack, however, precise information on the simultaneous variaton of these three enzymes as well as their relation to respiration, ethylene production, and softening of the fruit. Since there is considerable variation in the time of ripening of individual fruit, we show here the changes in three enzymes in relation to respiration and ethylene production in single fruit. MATERIALS AND METHODSMeasurement of Respiration and Ethylene Production. "Fuerte" avocado fruits were placed in glass ja...

“…Low levels of PME were always detected in preclimacteric mature green papaya fruit. This potential activity might be sufficient for any required demethylation as is the case for tomatoes, bananas, and avocados (1,7).…”

Section: Discussionmentioning

confidence: 99%

“…PME increases (13), decreases (5), or remains unchanged (7) during fruit ripening. PME is believed to have little effect on wall softening (7,20) serving only to cause partial demethylation allowing PG activity. This deesterification has occurred with the loss of galactose and arabinose side branches from pectins during fruit ripening (1,18,24).…”

Section: Discussionmentioning

confidence: 99%

Postharvest Variation in Cell Wall-Degrading Enzymes of Papaya (Carica papaya L.) during Fruit Ripening

Paull¹,

Chen²

1983

138

Pectin methylesterase (PME), polygalacturonase (PG), xylanase, cellulase, and proteinase activty were determined and related to respiration, ethylene evolution, and changes in skin color of papaya (Caricapapaya L.) fruit from harvest through to the start of fruit breakdown. PME gradually increased from the start of the climacteric rise reaching a peak 2 days after the respiratory peak. PG and xylanase were not detectable in the preclimacteric stage but increased during the climacteric: during the post climacteric stage, the PG declined to a level one-quarter of peak activity with xylanase activity returnig to zero. CeHlulase activity gradually increased 3-fold after harvest to peak at the same time as PME, 2 days after the edible stage. Proteinase declined throughout the climacteric and postclimacteric phases. A close relationship exists between PG and xylanase and the rise in respiration, ethylene evolution, and softening. Cultivar differences in postclimacteric levels of enzymic activity were not detected.An inhibitor of celHulase activity was detected in preclimacteric fruit. The inhibitor was not benzyl isothiocyanate (BITC). BITC did inhibit PG activity, though no inhibitor of PG activity was detected in preclimacteric homogenates when BITC was highest. The results indicate that inhibitors did not play a direct role in controlling wail softening.The postharvest papaya fruit ripening involves softening and the production of sugars and flavor constituents. There is a concomitant evolution of ethylene and an increased respiration rate (2, 17). The softening of the mesocarp and endocarp is due to the activity ofcell wall-degrading enzymes, not starch degradation, as the fruit has no starch during ontogeny (8, 10).Chan et al. (10) studied the relationship between fruit ripening, skin color, and the level of PG.2 PG increased during fruit ripening and was greatest near the endocarp. The enzyme has both exoand endopolygalacturonase activity (9). The role of other enzymes in wall degradation is unclear, and the relationship between walldegrading enzymic activity, softening, respiration, and ethylene production has not been determined. There is variation between papaya cultivars in the rate of softening and particularly the rate at which the flesh loses all texture and becomes water soaked. Inasmuch as there is considerable variation in the time of ripening of individual fruit, we report here the changes in wall-degrading enzymes in relation to respiration and ethylene production in a single fruit. Three cultivars are compared as to the levels of postclimacteric wall-degrading enzymes. The information is cru- cial to the understanding of ripening and for selecting cultivars with desirable postharvest ripening characteristics.MATERIALS AND METHODS Papaya (Carica papaya L. cv Sunrise) grown at the Poamoho Experimental Station on the island of Oahu were used. Cultivar Kapoho Solo was obtained from the island of Hawaii and X-77 from the island of Oahu. Fruit was harvested at the mature green stage. Fruit was hot...