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ORIGINAL ARTICLE
Year : 2014  |  Volume : 10  |  Issue : 37  |  Page : 122-129

Characteristics and kinetics of catalpol degradation and the effect of its degradation products on free radical scavenging


School of Pharmaceutical Sciences, Shandong University, China

Correspondence Address:
Xue-sen Wen
No. 44 Wenhua Xilu, Jinan 250012
China
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Source of Support: This work was financially supported by National Natural Science Foundation of China (81072984) and Natural Science Foundation of Shandong Province (ZR2009CM048), Conflict of Interest: None


DOI: 10.4103/0973-1296.127360

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Background: The dried and steamed roots of Rehmannia glutinosa have different pharmacological functions and indications. Catalpol, the main active component of the dried root, was found to be entirely degraded together with amino acids and some oligosaccharides during preparation of the steamed root. Its degradation may contribute to the differences between dried and steamed roots. Objective: To reveal the characteristics and kinetics of catalpol degradation, and evaluate its influence on the antioxidant properties of steamed Rehmannia roots. Materials and Methods: Purified catalpol was heated under different pH and temperature values for different times, alone or with sugars or amino acids. Catalpol concentration was determined by high-performance liquid chromatography. Browning was expressed by the absorbance at 420 nm (A 420 ), and antioxidation was displayed by 2,2-diphenyl-1-picrylhydrazyl free radical scavenging ability (SA DPPH ). Activation energy was calculated using Arrhenius plotting. Results: Catalpol was stable in neutral conditions and sensitive to acidic pH under high temperatures. Sugars had no influence on catalpol degradation; however, most amino acids, except for proline, could promote the degradation, and were associated with an increase in A 420 and SA DPPH values. These changes were proved to be mainly related with catalpol aglycone and were dependent on the presence of amino acids. Catalpol degradation was found to obey first-order kinetics. The activation energies were 81.7, 88.8 and 98.7 kJ/mol at pH 4.0, 5.0, and 6.0 respectively, and 70.7 kJ/mol at pH 4.0 value and in the presence of glycine. Conclusions: Catalpol degradation, especially, in the presence of amino acids can substantially boost antioxidant properties of the products; therefore, the traditional method for processing Rehmannia root seems rather apt.


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