Quantitative Analysis of L-DOPA in Mucuna pruriens Seeds by High Performance Liquid Chromatography

Abstract

Objective: To quantify the content of 3-(3,4-Dihydroxyphenyl)-L-alanine (L-DOPA) in Velvet bean (Mucuna pruriens var. utilis) and Mhamui Thai (Mucuna pruriens var. pruriens) from different sources in Thailand using High Performance Liquid Chromatography (HPLC) method. Method: The HPLC analysis was performed on stationary phase of C18 column (Phenomenex® 250 x 4.6 mm). A solution of 20 mM sodium dihydrogen phosphate pH 2.5 together with 10 mM hexane sulfonate and methanol (80:20) was used as a mobile phase at a flow rate of 1 ml/min.  The detection was conducted under UV detector at 280 nm. The seeds were heat-treated with various methods.  Results: The results revealed the reliability of this method in terms of linearity (R2 > 0.998), accuracy (% recovery of 95.75 - 98.19%), intra-day precision (% RSD of 0.16%) and inter-day precision (% RSD of 3.76%). The LOD and LOQ for L-DOPA determination were found to be 16.25 ng/ml and 54.17 ng/ml, respectively. Velvet bean seeds roasted at about 60 °C yielded the highest amount of L-DOPA.  However, increasing the heat or higher temperature while roasting resulted in the lower amount of L-DOPA from Velvet bean seeds. The results also indicated that the amounts of L-DOPA from various sources of Velvet bean were quite comparable, from 3.54 to 3.70% w/w.  The amounts of L-DOPA from Mhamui Thai (6.23 – 6.68% w/w) were, however, higher than those from Velvet bean. Conclusion: L-DOPA content in Mhamui Thai was higher than that of Velvet bean. L-DOPA content decreased with higher heating treatment. Keywords: Mhamui India (Mucuna pruriens var. utilis), Mhamui Thai (Mucuna pruriens var. pruriens), L-DOPA, HPLC, heating method