Effect of thermal treatment on the extraction efficiency, physicochemical quality of Jatropha curcas oil, and biological quality of its proteins.

Jatropha curcas seeds are an important source of oil (5-60%), used to obtain biodiesel. The generated residual paste has a high concentration of proteins (50-55%); however, the seeds contain non-nutritional factors that limit their use. The objective of this work was to analyze the effect on the physicochemical properties of the oil obtained from J. curcas seeds subjected to different thermal treatments and to evaluate the biological quality of the proteins contained in the residual cake. The best extraction of oil (95%) was obtained after 10 h from roasted or boiled seeds. In the oil from roasted samples, the acid index increased significantly (p ≤ 0.05) with respect to the untreated sample, whereas the iodine index increased significantly (p ≤ 0.05) in the oil extracted from the boiled samples. With respect to the proximal chemical composition of the flour, roasting and boiling treatments allowed for greater oil extraction (97 and 92%), achieving, in turn, a higher content of proteins (59.56 and 58.5 g/100 g) and fiber (6.67 and 6.67 g/100 g), and lower activity of trypsin inhibitors (45 and 38%) and phytates (63 and 72%), respectively. According to the in vivo biological quality test, conducted on Wistar rats, the thermal treatments applied to the seeds improved digestibility (> 70%) and the protein efficiency index (PER). The thermal treatment allowed extracting more efficiently the oil and improved the quality of the proteins present in the residual paste.