Effect of dehydration methods on antioxidant activities, phenolic contents, cyclic nucleotides, and volatiles of jujube fruits.

Changes in antioxidant activities, phenolic contents, cyclic nucleotides, and volatiles of jujube after dehydration using freeze-drying (FD), air drying (AD), sun drying (SD), and microwave drying (MD) were investigated. All dehydration methods caused a decrease in antioxidant activities, aldehyde, acid, and alkane contents. Esters were increased by the dehydration. FD was superior to other dehydration methods for retention of total phenolics, total flavonoids, and antioxidant activities. MD caused an increase of catechin and epichtechin levels. Although AD, MD, and SD caused declines in cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) contents, AD at 50oC was a good choice to obtain jujubes with high levels of cAMP and cGMP. Theoretical fundamentals for selection of suitable drying techniques to minimize the negative effects caused by dehydration and for meeting production requirements are provided.