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Papaya Fruit Softening: Role of Hydrolases
|Title:||Papaya Fruit Softening: Role of Hydrolases|
|Abstract:||Hydrolases have been detected during fruit softening and may play an important role in papaya softening. Variation in softening of papaya varieties and the incomplete softening of papaya treated with 1-methylcyclopropene (1-MCP) present an opportunity to determine the factors causing fruit softening. To determine whether six hydrolases and pH are involved in papaya softening, comparison of cell wall modification, hydrolases’ activities, and mesocarp pH between papaya that differ in softening rates, and normal softening versus softening modified by 1-MCP were used.|
Mesocarp of ‘Line 8’ and ‘Sunset’ papayas showed significant losses in cell wall mass during normal softening, but papaya did not lose the mass when softening was restrained by 1-MCP treatment. Solubilizations and dissociations of pectic polysaccharides and loosely bound matrix polysaccharides that consisted of xylosyl and galactosyl residues at high concentration were noticeable during normal softening. Although the major changes in galactosyl components of cell wall in 1-MCP-treated papaya were comparable to those in control papaya, the 1-MCP-treated papaya did not soften completely. The comparison of cell wall modification between 1-MCP-treated papaya and control papaya confirmed that the modification of xylosyl component of cell wall was involved in the abnormal papaya softening when treated with 1-MCP.
Activities of p-galactosidase, endoglucanase, endoxylanase, and B-xylosidase were correlated with fruit softening. When softening was modified by 1-MCP treatment, a rise in activity of these hydrolases was delayed; but only endoxylanase activity was completely suppressed throughout ripening. During softening, a change in mesocarp pH was implicated. Mesocarp pH of ‘Line 8’ and ‘Sunset’ papayas declined when fruit started to soften with no reduction in 1-MCP-treated papaya. Applied low pH affected mesocarp firmness, but the effect varied with the stage of fruit ripeness and specific fruit tissue.
Papaya softening is a complex event that involves many cell wall hydrolases, such as endoxylanase, (B-xylosidase, B-galactosidase, and endoglucanase. These hydrolases may play their roles in concert, to provide the unique texture of a particular fruit. Endoxylanase appears to play a major role in papaya softening. A regulated decline in mesocarp pH during ripening may regulate these hydrolases and impact papaya mesocarp softening.
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Ph.D. - Horticulture|
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