|Hyde, James - UNIV OF SOUTH FL, TAMPA|
|Jurch, George - UNIV OF SOUTH FL, TAMPA|
|Echeverria, Ed - UNIV OF FL, CREC|
Submitted to: Scientia Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 8, 1998
Publication Date: N/A
Interpretive Summary: Grapefruit is a subtropical fruit and thus, sensitive to cold. During the winter in Florida, decreasing temperatures impart "cold hardiness" to citrus fruit on the tree. This "cold hardiness" prevents chilling injury of the fruit during cold nights in the grove. The mechanism behind this developed "cold hardiness" is partially due to the splitting of sucrose (the sugar you put in your coffee) into its two component sugars, glucose (sugar in your "blood sugar") and fructose (the sugar in honey) by the enzyme acid invertase. The resulting "reducing sugars" help protect the fruit against chilling injury. This invertase enzyme is produced in response to cooling temperatures in the grove. This study shows that the enzyme can be induced artificially be cold storage temperatures in harvested fruit and that there might be a compound in fruit that inhibits this enzyme.
Technical Abstract: Peel tissue from deacclimated late season grapefruit was examined for the capacity to develop cold induced acid invertase. Experimental fruit were subjected to three prolonged temperature treatments (17 days at 25C, or 17 days at 4C +/- an additional 24 h at 25C) and the flavedo examined for acid invertase activity immediately after the respective temperature treatment. Invertase activity was not detected when soluble extracts were assayed directly after desalting. However, after isoelectric separation, invertase activity was detected only in samples from cold treated fruit. Cell-wall pellets were also devoid of invertase activity when measured directly. After washing with high ionic buffer (containing 1 M NaCl), activity was recovered in the same cold treated samples. The data indicates that the peel of late season grapefruit retain the capacity to develop acid invertase in response to cold treatment.