Maintaining quality of litchi fruit with acidified calcium sulfate.

The effect of acidified calcium sulfate (ACS) on the quality of litchi ( Litchi chinensis Sonn. cv. 'Brewster') fruit after harvest was evaluated. ACS at 1.25% or higher concentrations significantly inhibited the activities of polyphenol oxidase and peroxidase in the pericarp during storage at both 5 and 10 degrees C. These treatments also effectively prevented browning and retained the red color of the outer shell of the fruit. Total phenolic and total anthocyanin contents in pericarp were increased by ACS treatments in a dose-dependent manner. The radical scavenging activities for ROO(*), DPPH(*), (*)OH and O(2)(*-) were also enhanced by ACS, particularly by 2.5 and 5% concentrations. The activities of several antioxidant enzymes and enzymes of ascorbate-glutathione cycle including catalase, ascorbate peroxidase, glutathione peroxidase, glutathione reductase, dehydroascorbate reductase, and monodehydroascorbate reductase gradually declined during storage. However, ACS enhanced the activities of these enzymes, especially at the beginning of the storage. Samples treated with ACS generally had higher flavonoid levels than the control. The three major flavonoids, cyanidin-3-rutinoside, cyanidin-3-glucoside and quercetin-3-rutinoside, were found to be significantly increased by 2.5 and 5.0% ACS at both 5 and 10 degrees C. No differences were detected among various treatments in soluble solids content or sugar and organic acid levels in the pulp of litchi fruit, indicating that the internal quality of the fruit was not adversely affected by ACS treatment.