L-3,4-dihydroxyphenylalanine Accumulation in Faba Bean (Vicia faba L.) Tissues during Different Growth Stages

Abstract

L-3,4-dihydroxyphenylalanine (L-dopa)-rich faba (Vicia faba L.) tissues are a potentially useful source for its pharmaceutical purpose, although the species contains health curious vicine and convicine in the seeds. We determined the contents of L-dopa, vicine, and convicine in different tissues of faba plants throughout the entire growth period. The three compounds accumulated in germinating sprouts and showed high contents at 8 days of germination, especially in the epicotyl containing 132.33 mg∙g−1 DW of L-dopa, 19.81 mg∙g−1 DW of vicine, and 10.38 mg∙g−1 DW of convicine, respectively. We compared the contents of the three compounds among leaves of different ages in plants at different growth stages. The samples could be ranked, from highest to lowest content, ranging from 11.11 to 81.82 mg∙g−1 DW, as follows: new leaves > young leaves > old leaves; and vegetative > flowering > ripening. Vicine and convicine were not detected in leaves or flowers. The L-dopa content was high in flowers, especially young flower buds, ranging from 36.51 to 100.70 mg∙g−1 DW. In older flowers, the L-dopa content tended to decrease as the calyx and petal parts developed. In addition, the three compounds showed decreasing contents in pods, stems, and roots with increasing plant age. The results of this study provide information on the timing and extent of L-dopa, vicine, and convicine accumulation in different faba tissues, and indicate that various by-products, especially new/young leaves and flowers, are potential sources of natural L-dopa.

Effect of Thermal Processing on Color, Phenolic Compounds, and Antioxidant Activity of Faba Bean (Vicia faba L.) Leaves and Seeds

“…Before thermal treatment (0 min), the young leaves, old leaves and seeds contained 24.44, 18.13 and 0.15 mg/g d.w. of L-dopa, respectively. This agreed with previously reported results where L-dopa had accumulated more in the immature leaves than in the seeds [ 11 ]. After processing, similar patterns in the variation of L-dopa content were observed in both the young and old leaves.…”

“…L-dopa, an active phenolic compound, has been found in large amounts in faba leaves compared with other faba tissues [ 11 , 15 ]. Thermal treatment usually has a significant effect on the content of phenolic acids as treatment time is prolonged [ 16 ].…”

“…Faba bean seeds (Accession number: PI 577722) harvested in 2020 were provided by the Advanced Radiation Technology Institute (Jeongeup, Korea). For the faba leaf materials, we planted seeds in the greenhouse of Kyung Hee University (37°14′36.0″ N 127°04′52.6″ E, Yongin, Korea) in December, 2020, followed a previous reported method [ 11 ]. In brief, the seeds were soaked in distilled water for 24 h, then washed off the surface mucus.…”

“…Faba seeds have been studied extensively and widely used in the food and pharmaceutical industries due to its properties on enhancement of nutrition or reduction the complications and progression of certain diseases [ 6 , 7 , 8 ]. Faba leaves have also gained attention as an unconventional vegetable, with several studies providing significant results on characterizing their phytochemicals and proximate nutritional values [ 4 , 9 , 10 , 11 ]. Faba leaves have also been considered to have development potential as a food or medicinal material, similar to faba seeds.…”

“…L-dopa has also been reported to improve color vision, prevent hypertension and reduce the risk of renal failure [ 13 , 14 ]. Faba seeds have long been recognized as a good edible natural source of L-dopa, while in recent studies, leaves have been suggested to possess more than ten times the content of L-dopa than seeds [ 11 , 15 ]. The relatively strong antioxidant activity of faba leaves (supply about 11.5 mmol of trolox equivalent 100 g −1 fresh weight) compared with commercial vegetables (lower than 6 mmol of trolox equivalent 100 g −1 fresh weight) such as broccoli, asparagus, spinach, cabbage and green peas have also attracted much scientific attention [ 4 ].…”