Analysis of the Content of Vitamin C in the Dying Process of Red Jujube

[Objective] The research aimed to determine the content of Vitamin C in red jujube treated by different drying methods.[Method] The samples were treated by the methods of natural drying,microwave drying and electrothermal constant-temperature drying and Vitamin C was extracted from all kinds of samples with oxalic acid.It reacted with 2,4-dinitrophenylhydrazine at 37 ℃.Its absorbency was determined at the wavelength of 490 nm by spectrophotometric method.[Result] There were 324.64 mg/100 g Vitamin C in fresh jujube and it rapidly decreased with the increasing of sun-drying days.The content of Vitamin C in red jujube treated by electrothermal constant-temperature drying was 21.63 mg/100 g and that by microwave drying was 93.25 mg/100 g.The content of Vitamin C in red jujube treated by microwave drying was significantly higher than that by nature drying for 20 d and by electrothermal constant-temperature drying.The decreasing extent of Vitamin C in fruit was smaller in the 7th d of natural drying process,the content of Vitamin C in fruit decreased significantly after the 8th d and it changed little after 2 weeks.[Conclusion] Among 3 drying methods of rd jujube,the content of Vitamin C in red jujube treated by microwave drying was highest.