Comparative evaluation of non-toxic and toxic varieties of Jatropha curcas for chemical composition, digestibility, protein degradability and toxic factors

Four varieties of Jatropha curcas which originated from Nicaragua (Cape Verde and Nicaragua toxic varieties cultivated in Managua), Nigeria (a wild variety from Ife; toxicity unknown) and Mexico (a wild non-toxic variety collected from Papantla) were studied. The average seed weight was 0.69, 0.86, 0.53 and 0.65 g for Cape Verde, Nicaragua, Ife-Nigeria and non-toxic Mexico varieties, respectively. The kernel to shell ratio in seeds was relatively similar (62.7:37.3 for both Cape Verde and Nicaraguan, 60:40 for Ife-Nigerian and 63.5:36.5 for non-toxic Mexican). The shell of the seeds composed mainly of fiber (>83% neutral detergent fiber) and very little crude protein (CP < 6%). The kernels were rich in CP (22.2–27.7%) and lipid (53.9–58.5%). The meal (defatted kernels) had a CP content of 57.3, 61.9, 56.1 and 64.4% for Cape Verde, Nicaragua, Ife-Nigeria and non-toxic Mexico varieties, respectively, and about 90% of this CP was true protein. The pepsin insoluble nitrogen was from 5.5 to 7%. The amino acid composition of meals from Cape Verde, Nicaragua and non-toxic Mexico varieties was similar. The levels of essential amino acids except lysine were higher than that for the FAO reference protein. The meal from the toxic variety (Cape Verde) did not have any anti-fermentative activity on rumen microbes. The estimated digestible organic matter (DOM) and metabolizable energy (ME) for the shells were low (26.2–27.1% and 2.4–2.8 MJ kg−1), whereas these values for Jatropha meals were 77.3–78.4% and 10.7–10.9MJ kg−1. For commercially available (heat-treated) soyabean meal, DOM and ME were 87.9% and 13.3MJ kg−1, respectively. The in-vitro rumen degradable nitrogen (% of total nitrogen) for meals from Cape Verde, Nicaragua, Ife-Nigeria and non-toxic Mexico varieties was 43.3, 37.7, 38.7 and 28.9, respectively, and for the soyabean meal it was 80.9%. Tannins, cyanogens, glucosinolates and amylase inhibitors were not detected in meals of any of the four varieties. A small amount of tannins were present in shells (2.0–2.9% as tannic acid equivalent). High levels of trypsin inhibitor activity (18.4–26.5 mg trypsin inhibited g−1), lectin (51–102; inverse of the minimum amount in mg ml−1 of the assay which produced haemagglutination in presence of 10 mM Mn2+) and phytate (7.2–10.1%) were observed in the meals. The concentrations of phorbol esters in kernels of Cape Verde, Nicaragua and Ife-Nigeria varieties were 2.70, 2.17 and 2.30mg g−1, whereas kernels of non-toxic Mexican had a very low level (O.11 mg g−1) of phorbol esters.