Abstract:

Objective: To investigate the effects of explosion puffing and sun-drying on the composition of phenolic
compounds and their antioxidant activity in Chinese jujubes. Methods: The total phenolics and flavonoids contents were
measured by Folin-Ciocalteu and NaNO2-Al(NO3)3 assays. Antioxidant properties were evaluated by DPPH and ABTS free
radical scavenging, reducing power and β-carotene-linoleic acid emulsion assays. Phenolic compounds were qualitatively
and quantitatively analyzed by high-performance liquid chromatography (HPLC). Results: The contents of total phenolics
were significantly increased by explosion puffing, while no obvious change in the content of total flavonoids was observed
in puffed jujubes. In contrast, these components revealed a marked decrease in sun-dried jujubes. The DPPH free radical
scavenging capacity and reducing power of puffed jujubes were significantly superior to those of the fresh and sun-dried
counterparts. The ABTS free radical scavenging and antioxidant activity coefficient (AAC) as determined using β-carotenelinoleic
acid of sun-dried jujubes were significantly lower than those of the fresh and puffed ones, and no significant
difference between fresh and puffed jujubes was observed. The total phenolics, flavonoids contents and antioxidant activity
of puffed jujubes were markedly higher that those of sun-dried samples. The composition of phenolic compounds in
Chinese jujubes were obviously changed after drying treatments. The contents of gallic acid, p-hydroxybenzoic acid, caffeic
acid, p-coumaric acid, ferulic acid, rutin, cinnamic acid and quercetin revealed the highest levels in puffed jujubes. The
antioxidant activity of the jujube was significantly correlated with the contents of total phenolics and flavonoids. Conclusion:
Puffed jujubes contain the most abundant phenolic compounds and possess the highest antioxidant activity. The processing
time is short. Moreover, the products are fragrant, sweet and crisp. Therefore, explosion puffing as a feasible and innovative
technology can be developed as a drying method for Chinese jujubes.

Key words: jujubes, explosion puffing, high-performance liquid chromatography, antioxidant activity, phenolics