Jatropha curcas

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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.