Mucuna bean (
Mucuna pruriens
L.) is grown in many parts of Kenya as a green
manure/cover crop. The bean contains a high content of crude protein. However, it
remains a minor food crop due to the presence of anti-nutritional compounds such as
3,4-dihydroxy-L-phenylalanine (L-Dopa). The potential for utilization of mucuna
bean as an alternative source of protein was evaluated by assessing the effect of
various processing methods on its protein quality. Mucuna bean was processed to
remove L-Dopa and other anti-nutritional compounds by different methods such as
soaking, autoclaving, roasting, germination, and alkaline fermentation. Protein quality
was determined by amino acid composition,
in vitro and
in vivo rat balance
methodologies. All processing methods except roasting improved
in vitro protein
digestibility (IVPD). Soaking in acidic medium (pH 3.2) at 60°C for 48 hrs
significantly improved IVPD (80.5%) and biological value (80.8) of mucuna bean
protein. The content of essential amino acids met the recommended FAO/WHO
reference requirements for 2-5 yr old except for tryptophan. However, true
digestibility for processed bean diet was poor (58%) and protein digestibility corrected
amino acid score (PDCAAS) low (0.4) compared to that of reference casein
(1.0). This was attributed to both low sulphur amino acids content and possible
presence of factors that affect protein hydrolysis such as phenolic compounds.
Mucuna protein diet did not support growth of weanling rats indicating amino acids
pattern incompatible with the needs of weanling rats. Histological examination of
liver and kidney tissues revealed that consumption of processed mucuna bean as the
only source of protein caused inflammation of the organs. This suggests possible
presence of other antitoxins in processed bean even though mucuna bean diet
contained the recommended safe level of residual L-Dopa (<0.1%). Processing
mucuna bean by soaking in acidic medium (pH 3.2) at 60°C for 48 hrs improved
protein quality. However, mucuna bean is not recommended as a sole protein in
human diet.
