Degradation
of Caffeic Acid in Subcritical Water and
Online HPLC-DPPH Assay of Degradation Products
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Abstract
Caffeic acid was
subjected to degradation under subcritical water
conditions within 160–240 °C and at a constant pressure
of 5 MPa in a continuous tubular reactor. Caffeic acid degraded quickly
at these temperatures; the main products identified by liquid chromatography-diode
array detection/mass spectrometry were hydroxytyrosol, protocatechuic
aldehyde, and 4-vinylcatechol. The reaction rates for the degradation
of caffeic acid and the formation of products were evaluated. Online
high-performance liquid chromatography/2,2-diphenyl-1-picryhydrazyl
assay was used to determine the antioxidant activity of each product
in the solution. It was found that the overall antioxidant activity
of the treated solution did not change during the degradation process.
This study showed a potential of formation of antioxidants from natural
phenolic compounds under these subcritical water conditions, and this
may lead to a discovering of novel antioxidants compounds during the
extraction by this technique