We received two interesting responses to the article on velvet beans in the last issue of EDN. As you read in that issue, livestock, especially ruminants, have long been fed velvet bean leaves.
(For new readers, velvet bean seed contains L-dopa, a chemical used to treat Parkinson’s disease and which can be harmful to animals in large doses. Even though the bean is often produced in abundance, it is usually only eaten where food is exceptionally scarce.)
Lawrence Gilley in Mozambique wrote to us, wondering whether velvet bean leaves can be eaten by people. “Mozambicans regularly eat the leaves of cowpeas, cassava, sweet potato, amaranth and squash as well as various wild herbs. If velvet bean leaves…could be consumed and are palatable, it would be useful to know.”
The other interesting response provided the answer. Dr. Rolf Myhrman of Judson College is doing research on the problem of L-dopa in velvet bean. He sent us a 1991 article by Japanese scientists which for the first time analyzed velvet bean leaves for L–dopa. The answer surprised me. Leaves and roots contain extraordinarily high amounts of L-dopa, about 0.5 to 1.5% of the FRESH weight. Dried seed typically contains 5-7% L-dopa.
An additional surprise to me was that the scientists found evidence that the L-dopa from velvet bean may inhibit growth of many weeds. In fact, their primary interest in looking at velvet beans came from their interest in finding plants with allelopathic properties (plants that contain chemicals that hinder growth of other plant species). They had read that yields of grain crops were increased by interplanting with velvet bean and that noxious weeds such as nutsedge (Cyperus spp.) and Imperata cylindrica were smothered.
Although they did their work on a small laboratory scale rather than a field study, we can still learn from it. They measured how long the radicle (root) and hypocotyl (stem) had grown four days after germination of seed of various weeds. Some seed had been exposed to extracts from velvet bean leaves. The extract had no effect on germination or growth of the hypocotyl, but strongly inhibited growth of the radicle of the common weeds Cerastium glomeratum, Spergula arvensis, Linum usitatissimum and Lactuca sativa (lettuce). It had little effect on plants in the grain and legume families. Solutions containing the same amount of L-dopa as the velvet bean extract had the same effect on radicle growth as the plant extract.
The authors say, “Since fresh velvet bean leaves contain as much as 1% L-dopa, and velvet bean produces 20-30 tons of fresh leaves and stems per hectare (8-12 ton/acre), about 200-300 kg (178-267 lbs.) of L-dopa will be produced and added to the soil per year.” That is in addition to the L-dopa in the roots.
We have assumed that velvet beans controlled weeds by shading them out with its vigorous growth. Although this research suggests there may be an element of chemical control also, Dr. Myhrman points out that we need to find out how stable the L-dopa is in the soil before we can estimate how important a part it plays in weed control. Another question to be answered is whether all varieties of velvet bean contain as much L-dopa. The Japanese scientists used a dwarf Brazilian variety that we have never seen.
We recommend that people NOT eat velvet bean leaves, both because of their L-dopa content and because we have never heard of people eating them. L-dopa is not destroyed by cooking. Dr. Myhrman found that one cup of velvet bean “coffee” is equivalent to almost half of the initial dosage of L-dopa used to treat Parkinson’s disease. The digestive system of humans more closely resembles that of pigs than most other livestock, and pigs do not do well eating velvet beans (see EDN 56).
We do think it is safe to feed leaves to livestock as described in the last issue. Why is it not harmful to ruminants, like cattle and goats? Perhaps the L-dopa is being destroyed by microorganisms in the rumen. The digestive systems of chickens and pigs, of course, cannot ferment the leaves, and these animals do not do well on a velvet bean diet, as reported in the last EDN.
Rabbits have also successfully been raised on a diet composed primarily of velvet bean. In Amaranth to Zai Holes, p. 248, we reported the experience of Kinney Mitchell in St. Kitts. “Most of our rabbits preferred velvet beans over other leaves (sweet potato, cow pea, green bean vines) or pellets, though a few preferred banana leaves. We never had trouble from rabbits eating velvet bean leaves. They also ate the vine part.” Rabbits too have a section of the gut where fermentation can take place.
Price, M.L. 1997. Do Velvet Bean Leaves Contain L-DOPA. ECHO Development Notes no. 57