Optimization and kinetics for ultrasonic-assisted extraction of L-dopa from fava bean (Vicia faba L.) sprouts

In order to fully extract and utilize high bioactive natural L-DOPA (Levo-dihydroxy phenylalanine), the present study was undertaken to explore the potential applicability of ultrasonic waves to isolate L-DOPA from germinated sprouts, extraction kinetics were also preliminarily studied. Based on single factor experiments, a Box-Behnken design (BBD) was applied to optimize the processing conditions for the ultrasonic-assisted extraction (UAE) of L-DOPA in germinated fava bean sprouts and evaluate the effects of three independent variables (ultrasonic power, liquid-solid ratio and extraction time on the yield of L-DOPA. The results showed that ultrasonic power was the most important factor, the maximum yield of L-DOPA (1.47%) was found when 2.0 g germinated sprouts was extracted with 30% (by vol.) ethanol-0.1 M acetic acid solution at ultrasonic power 257 W, liquid-solid ratio 31 mL/g and extraction time 37.4 min. Under the optimum UAE conditions, L-DOPA recovery of the germinated sprouts was a little higher than that of conventional solvent extraction (CSE) and represented almost 0.58-fold increase when compared with ungerminated sprouts, UAE significantly shortened the time required for the extraction process. The yields of L-DOPA at different extraction time were simulated by three kinetic models, .i e. the film theory, the unsteady diffusion through plant and the empirical equation of Ponomaryov. The film model gave good simulation to the experimental data with the highest R2 at 0.9928. The results can provide a reference for natural L-DOPA preparation.