CHANGES IN PAPAYA CELL WALLS DURING FRUIT RIPENING

Authors: PAULL, ROBERT - UNIV OF HAWAII AT MANOA; Gross, Kenneth; QUI, YUNXIA - UNIV OF HAWAII AT MANOA

Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Fruit softening leads to increased susceptibility to fungal decay and decreased quality, storage life, and overall quality. Decreased quality may also make fresh fruits and vegetables more likely to have food safety-related problems. In order to limit the roughly 25 percent loss of all fruits and vegetables that occur in the U.S. due to this postharvest deterioration, and in order to help maintain a safe food supply, we have studied the biochemical mechanisms involved in the fruit softening process in an effort to modify plants genetically so that they produce fruit that resist the softening process. The present study reports on the changes that occur in papaya fruit cell walls. Such information provides a clue as to which enzyme(s) break down the cell wall, a sugar envelope surrounding each fruit cell, leading to a loss of structural integrity, and thus fruit firmness. This information will be used by us and other scientists in an attempt to limit the expression of the gene(s) coding for these enzymes during ripening, to slow cell wall degradation and fruit softening.

Technical Abstract: The apparent molecular mass range of different extractable fractions of papaya fruit pectin and hemicellulose during fruit ripening was determined. The pectin molecular mass declined and the solubility of pectin in cyclohexane-diaminotetraacetic acid and sodium carbonate solutions increased during ripening. The molecular mass decreased and the solubility of hemicellulose in KOH increased during ripening. Water soluble uronic acid increased six-fold during ripening as the yield of cell wall material declined. The loss of high molecular mass pectins decreased throughout ripening while the demethylation rate was greater early in ripening. Changes in pectin molecular size did not parallel loss of fruit firmness during early ripening. The pectin fractions were mainly composed of rhamnose, glucose, xylose, galactose, mannose, and arabinose, in decreasing order of concentration. Non-cellulosic glucose and xylose were the main neutral sugars in the hemicellulose fraction followed by mannose and galactose and traces of rhamnose and arabinose. These results suggested that pectin hydrolysis and the modification of hemicellulose both involved in papaya fruit softening. Pectin hydrolysis was apparently more important during the late phase of fruit softening.