Accumulation of l-DOPA in various organs of faba bean and influence of drought, nitrogen stress, and processing methods on l-DOPA yield

Faba bean (Vicia faba L.) has been identified as a rich source of l-DOPA, which is used in treating Parkinson's disease. Biosynthesis and accumulation of active substances such as l-DOPA in plant tissues may interact with growing conditions and processing methods. Accumulation trends of l-DOPA in various faba bean organs and the effect of drought stress and N fertilization on l-DOPA content were studied in a field and two greenhouse experiments. The influence of various processing methods on l-DOPA content of faba bean tissues was evaluated. The highest l-DOPA content was detected in fresh leaves (22.4 mg g−1) followed by flowers, young pods, mature seeds, and roots. Regardless of processing method, l-DOPA concentration in faba bean tissues was significantly reduced when tissues were boiled or dried. Among various methods of processing, freezing had the lowest detrimental effect, reducing l-DOPA concentrations by 24.1% and 21.1% in leaves and seeds, respectively. Drought stress elevated l-DOPA concentration, and maximum l-DOPA (23.3 mg g−1 of biomass) was extracted from plants grown under severe drought stress. However, l-DOPA yield (l-DOPA concentration × biomass) was compromised, owing to the adverse influence of drought stress on dry matter production. No significant difference in l-DOPA concentration was detected among various N application rates.