Nutritional characterization of Mucuna pruriens: 1. Effect of maturity on the nutritional quality of botanical fractions and the whole plant

This study was conducted to determine the stage of maturity at which the dry matter (DM) yield and nutritive value of velvet bean (Mucuna pruriens) is optimized. Mucuna was harvested at 77, 110 and 123 days after planting (DAP) from quadruplicate 5 m × 1 m plots within each of 6 blocks. At each DAP, DM yield, chemical composition, botanical composition, in vitro rumen fluid-pepsin DM digestibility (IVDMD) and concentrations of total polyphenols, l-dopa and tannins were determined on the whole plant and botanical fractions. Whole-plant Mucuna DM yield increased (P<0.01) linearly with maturity; proportions of leaves and stems decreased linearly (P<0.01), whereas proportion of pods increased (P<0.01). Concentrations of neutral-detergent fiber (aNDF) in whole plant, leaf, and stem increased (P<0.05), or tended (P<0.10) to increase linearly with maturity, as did the acid-detergent fiber concentration of leaves and stems. Maturity decreased (P<0.05) ether extract concentrations of leaves linearly, and stems quadratically, but increased (P<0.05) whole-plant and pod starch concentrations. Pods contained relatively high concentrations of lysine, histidine, phenylalanine, aspartate, glutamate, leucine, isoleucine, and valine, but low concentrations of methionine and cystine. The essential amino acid index did not vary with maturity. Most minerals in Mucuna are concentrated in the leaves and the whole plant contains sufficient Ca, P, K, Mg, Fe, Cu, Na, Mo, Mn, and Zn for growing sheep, although their bioavailability of these minerals is unknown. Total polyphenol concentration quadratically (P<0.01) increased with maturity in the whole plant, tended to increase (P<0.10) in pods, linearly (P<0.01) decreased in stems and fluctuated in leaves. Maturity quadratically increased l-dopa concentration of the whole plant (P<0.05) and stems (P<0.01), but did not affect those of leaves and pods. Maturity quadratically increased (P<0.05) total tannin concentration in the whole plant, but decreased (P<0.10) that of pods. The l-dopa was concentrated in the seeds and pods of mature (110–123 DAP) plants, but tannins were concentrated in leaves and stems. Whole-plant IVDMD was not affected by maturity, but digestible DM yield linearly (P<0.01) increased with increasing DM yield. There was a 2-week harvest window (110–123 DAP) during which whole-plant crude protein and IVDMD remained unchanged. Nevertheless, harvesting at 123 DAP gave the best combination of biomass yield and nutritive value.