Effect of processing method on phorbol esters concentration, total phenolics, trypsin inhibitor activity and the proximate composition of the Zimbabwean Jatropha curcas provenance: A potential livestock feed

Abstract

In a study to detoxify Jatropha curcas seed four potential detoxification methods were tested for their effectiveness. The first method entailed oil expulsion from unshelled Jatropha curcas seed using a Sunhdra industrial oil expeller. The second method involved laboratory-based petroleum-ether solvent extraction of shelled and minced kernels. Thirdly, shelled kernels were subjected to industrial detoxification that involved double solvent extraction with the hexane-ethanol system accompanied by moist-heat treatment at 90°C for 30 min. The fourth method was an extension of the third whereby the meal generated was wet extruded (126°C, 2 atmospheres, 10 min contact time) followed by re-extraction with hexane and moist heat treatment (121°C for 30 min). The detoxification methods had significant (P<0.0001) effect on both the anti-nutritional factors (ANFs) and the proximate composition of the meals. Oil expulsion left the phorbol esters (PEs) of the unshelled seed at 0.70 mg g -1, laboratory petroleum-ether extraction reduced the PEs content by 67.69% from 6.5 mg g -1 in the raw shelled kernels to 2.10 mg g -1, double solvent extraction followed by moist-heat treatment reduced PEs by 70.77% to 1.90 mg g -1. Double solvent extraction accompanied with wet extrusion, re-extraction with hexane and moist-heat treatment reduced PEs content to 0.80 mg g -1, an 87.69% decrease. All the methods except laboratory petroleum-ether solvent extraction managed to completely inactivate trypsin inhibitors in the meals. Total phenolics (TPs) content was lowest (P<0.0001) in the oil-expulsion produced meal (8.50 g Kg -1) while the laboratory petroleum-ether produced meal contained 64.57 g Kg -1 TPs. Oil-expulsion and double solvent extraction accompanied with wet extrusion, re-extraction and moist-heat treatment completely inactivated lectins in the meals. The high chemical nutrient potential of Jatropha curcas seed (crude protein, calcium and phosphorus) is only realised with shelling and extraction of most of the oil. None of the tried methods managed to completely detoxify the Jatropha curcas seed. The two most ‘effective methods’ reduced the PEs to 0.70 and 0.80 mg g -1, respectively compared to the non-toxic variety with 0.11 mg g -1 PEs.