Jatropha curcas
General information
Jatropha curcas (L) or physic nut is a multipurpose
and drought-resistant, large shrub or small tree. Although a native of tropical
America, it now thrives throughout Africa and Asia. It grows in a number of
climatic zones in tropical and sub-tropical regions of the world and can be
grown in areas of low rainfall. Jatropha is easy to establish, grows relatively
quickly and is hardy. A perceived advantage of Jatropha is its ability to grow
on marginal land and to reclaim and restore eroded areas. Various parts of the
plant hold potential for use as animal feed, inclusion in medicinal
preparations and as a source of honey. If grown on barren lands, Jatropha could
add to the removal of carbon from the atmosphere, and the build up of soil
carbon.
Seed production ranges from about 0.1 t / ha / year
to over 8 t / ha / year (Heller, 1996). The seed yield reaches a peak after
about five years of growth. This range in production may be attributable to
variation in rainfall and soil nutrient status. The plant takes between four and
five years to yield when cultivated on poor soil, with no irrigation and planted
in full sunlight but much less time is required under optimal rainfall and soil
conditions. Once established, plantations yield for between 30 and 35 years.
Jatropha can also be grown as a hedge plant. Henning (1996) estimated seed
production of 0.8 - 1.0 kg of seed per square meter from Jatropha hedges in
Mali, equivalent to between 2.5 t / ha / year and 3.5 t / ha / year
respectively.
Nutritional value of
the seeds
Jatropha has been investigated mainly as a
potential source of oil that has been recognised as an adequate substitute
motor fuel. The seed kernel of the plant contains about 60 per cent oil.
The seed cake remaining after oil
extraction is an excellent source of plant nutrients (Table 1). However the
presence of high levels of antinutrients (Table 2) prevents their use in animal
feeding. Phorbolesters (phorbol-12-myristate 13-acetate) have been identified
as the major toxic principle in Jatropha (Makkar and Becker, 1997a). Varieties
of Jatropha plants where phorbolesters are almost absent have been identified
in Mexico. These offer promise for inclusion of products from these plants in
animal and fish diets. The nutritional composition of the extracted seed meal from
the non-toxic variety (from Veracruz, Mexico) appears to be similar or even superior
to the toxic variety (from Cape Verde and Mexico) (Table 1). Non-protein
nitrogen formed only 7.8 - 9.0 per cent of the total nitrogen in the
Jatropha meals suggesting the presence of high levels (~90 per cent) of true
protein (Makkar et al., 1998).
The level of essential amino acids of the
defatted, kernel meal of the non-toxic variety (see Table 10) are higher than
that of FAO reference protein except for lysine (Makkar and Becker, 1999a). A
comparison between Jatropha meal and soybean reveals an almost similar pattern
for all essential amino acids except lysine and sulphur-amino acids; these are
lower and higher respectively in Jatropha
meals.
In vitro, digestible organic matter and metabolisable
energy of the non-toxic Jatropha seed meal (77.3 per cent and 10.7 MJ/kg
DM respectively) were lower than those of soybean meal (87.9 and 13.3 MJ/kg DM
respectively), but comparable with those of cottonseed, rapeseed and sunflower
meal (Makkar and Becker, 1999a). The pepsin soluble fraction of the total
nitrogen has been reported to be 94 - 95 per cent (Aderibigde et al.,
1997). The seed meal of the non-toxic Jatropha could thus be regarded as having
high potential for use as a feed supplement for fish and monogastrics.
Antinutrients
Even though the Mexican, non-toxic varieties
lack the most potent toxin, phorbol esters, other antinutrients such as trypsin
inhibitor, lectin and phytate are present in significant amounts (Table 2), and
their levels are similar to those in the toxic varieties.
Moist
heating of seeds almost completely inactivated trypsin inhibitor activity and
decreased lectin activity (Makkar and Becker, 1999a). In addition to reducing
heat-labile, antinutritional factors such as trypsin inhibitors and lectins,
heat treatment should also increase protein digestibility. Furthermore, moist
heating should render the seed cake from the non-toxic variety usable in fish
diet. On the other hand, heat treatment followed by aqueous methanol extraction
could result in elimination of most of the antinutrients and toxins from the toxic
variety. Meal treated in this manner has
been found to be innocuous to rats (Makkar and Becker, 1997b).
Fish feeding trials
Carp (Cyprinus
carpio) fed diets containing the non-toxic, fat free Jatropha kernel meal (23
per cent by weight of the diet) showed lower body weight gains than fish
fed a control diet based on fishmeal. However, a diet containing the same level
of Jatropha meal heated for 15 min (at 121°C and 66 per cent moisture)
and still containing appreciable amounts of trypsin inhibitors and lectins was
found to yield the best performance (243 per cent weight gain compared
to 303 per cent observed with the control treatment) among Jatropha
containing feeds (Makkar and Becker, 1999b). It is possible that reduction of the
inclusion level (to around 15 per
cent by weight) in feeds, extraction with water (to remove residual
antinutrients and improve acceptability by the fish) and supplementation with
lysine containing ingredients may facilitate better utilisation of this
ingredient by fish although, more research will be required to confirm these
suppositions.
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