Effect of Sonication and Two Solvent Extraction Methods on the L-dopa Concentration and Nutritional Value of Mucuna pruriens

Mucuna pruriens beans are high in crude protein (CP; 25-30%) and starch (39-41%), but also contain toxic L-Dopa. Methods to reduce L-Dopa to a safe threshold (< 0.4%) are often costly and little is known about their impact on the nutritional value of the bean. The objective of this study was to examine effects of three extraction methods on L-Dopa concentration and nutritional composition of finely (1 mm) or coarsely (6 mm) ground beans. Methods evaluated included extraction in solutions of acetic acid (ACD, pH 3) or sodium hydroxide (ALK, pH 11) for 8 hours or sonication (SON) for 5 minutes. All extraction methods decreased the L-Dopa concentration of fine Mucuna particles from 2.8 to < 0.2%, decreased their CP and water-soluble carbohydrate (WSC) concentrations by 24-31% and 78-81%, respectively and increased their NDF and starch concentrations by at least 62 and 14%, respectively. Sonication reduced the ether extract (EE) concentration of fine particles from 5.5% to 4.2% but ACD and ALK did not. Sonication and ACD did not reduce the L-Dopa concentration of coarsely ground beans but ALK reduced it from 2.8 to 2%. Sonication also reduced CP, WSC, and ether EE concentrations of coarse particles by 6, 17, and 27%, respectively and ALK increased their starch concentration by 17%. Therefore, the extraction methods reduced L-Dopa of fine Mucuna particles to safe levels but increased their NDF and starch concentrations at the expense of WSC and CP concentrations. Extraction methods were less effective at reducing the L-Dopa in coarse particles and had fewer, less consistent effects on their nutritional composition.