Mucuna pruriens detoxification: Effects of ensiling duration and particle size

Mucuna pruriens is grown for food and feed despite its L-3,4-dihydroxyphenylalanine (L-dopa) concentration (30-70 g/kg), which is toxic to non-ruminants. This study determined if ensiling could reduce the L-dopa concentration of Mucuna. Experiment 1 examined the effect of ensiling duration on the fermentation characteristics and L-dopa concentration of Mucuna. Crushed (6 mm) Mucuna beans (912 g DM/kg) were ensiled in triplicate for 0, 3, 7, 14, 21, and 28 days in vacuum-sealed plastic bags. During the fermentation, pH decreased, whereas concentrations of ammonia-nitrogen, lactate, isobutyrate, and isovalerate increased (P<0.05) non-linearly. The ammonia-nitrogen concentration remained below 100 g/kg of total N throughout the ensiling period but lactate concentration was 25.7 g/kg DM by d 28. A pH of 4.5 and an L-dopa concentration of 13 g/kg (54% reduction) were achieved after 28 days of ensiling. Experiment 2 examined effects of particle size of Mucuna on the L-dopa concentration and nutritional value after ensiling. Crushed Mucuna beans (6 mm, Coarse) were used intact or ground in a Wiley mill to pass through a 4-mm (Medium) or 2-mm (Fine) screen. Samples (1500 g) of each particle size were weighed into vacuum plastic bags in quadruplicate. Double-distilled water (900 ml) was added to each bag and the bags were sealed and ensiled for 28 days. Ensiling Mucuna with particle sizes of 2, 4 and 6 mm for 28 days decreased the L-dopa concentration from 28 to 12, 16, and 11 g/kg, representing decreases of 57, 42 and 64%, respectively. Ensiling also reduced (P<0.05) the water-soluble carbohydrate, lysine and arginine concentrations and increased (P<0.05) concentrations of ammonia-nitrogen and most amino acids. Coarse particles had greater gross energy values than Medium or Fine particles and the greatest or among the greatest (P<0.05) concentrations of all amino acids. Concentrations of amylase-neutral detergent fiber, starch, crude protein and fat were unaffected by treatment (P>0.05). Therefore, ensiling coarse Mucuna particles for 28 days is recommended to reduce the L-dopa concentration and preserve the nutritional value.