The oil from J. curcas is the most important product obtained from the plant. For the maximum yield of oil, the seeds should be harvested at maturity. The seed yield depends on the following main factors: rainfall, soil type, fertility of soil, genetics, age of the plant, and different propagation strategies. The oil from seeds is of great interest to the investors mainly because it holds several properties like less viscosity, better oxidation stability, low acidity, good cold properties, and lesser processing costs. Moreover, Jatropha oil is odorless and colorless when fresh but turns yellow on standing due to oxidation. The presence of more than 75% of unsaturated fatty acids in Jatropha oil reflects its low pour point (270 K) and cloud point (275 K). The calorific value of the oil ranges from 37.83 to 42.05 MJ/kg (Achten et al. 2008). The oil content of kernel ranges from 45 to 60% by weight and that from the seed shell varies from 30 to 50%. Due to the presence of phorbol esters and curcin in seeds and oil, it is considered toxic for consumption but safe for biodiesel production. In addi­tion, oil from Jatropha has been highlighted as a potential nonedible feedstock for biodiesel production mainly due to its high cetane number similar to diesel. This property makes it a good alternative fuel which can be applied to conventional engines (Tapanes et al. 2008). In addition, Jatropha oil is also used for production of soaps and biocides (insecticide, molluscicide, fungicide, and nematicide) (Shanker and Dhyani 2006).

Table 12.2 shows the fatty acid composition of J. curcas oil. The Jatropha oil is rich with unsaturated fatty acids like oleic and linoleic acids with minor amounts of saturated fatty acids such as palmitic and stearic acids. The amount of fatty acids in the oil varies from one country to another. Fatty acid composition can be altered to some extent through interspecific hybridization or gene silencing (Achten et al. 2008).

Due to high amount of unsaturated fatty acids such as oleic and linoleic acids in Jatropha oil, the biodiesel produced from it has desired low temperature properties. The physicochemical properties of Jatropha oil are shown in Table 12.3. Jatropha oil is renewable, clean, and safer to use. In short, J. curcas has been referred to as “Green gold” in Biofuel industry due to its potential benefits of oil to produce bio­diesel which can replace petroleum-based diesel (Koh and Mohd Ghazi 2011; Abdulla et al. 2011).

Table 12.2 Fatty acid composition of crude Jatropha curcas oil (Berchmans and Hirata 2008)

Table 12.3 Physicochemical properties of Jatropha oil (Achten et al. 2008)

Once seeds are harvested from the plant, they are used for oil extraction or expulsion. The process of obtaining oil from seeds is as old as mankind, but the procedures and infrastructure have gained much improvement these days. In addition to the seeds, the other inputs are machines, infrastructure, and energy. Outputs include Jatropha oil as main product and seed cake, which is an important by-product in the process. Two main methods have been identified for oil extraction, namely, (1) mechanical extraction and (2) chemical extraction. Before extraction, the seeds have to be sun dried for 3 weeks or oven dried 105°C to expel the water content. For mechanical pressing, the seeds are used as such. On the other hand, for chemical extraction, only powdered kernels can be used. The conventional method of oil extraction is mechanical pressing.

It is normally done on a small scale and especially in rural areas by using either manual ram press or electric screw press. The main drawback here is that only a small amount of oil can be expelled through these presses. Pretreatment of seeds like cooking is shown to increase the oil yield to a better extent. In chemical method of extraction, я-hexane solvent is the most widely used one. But this requires lots of time for extraction.

Recently, aqueous oil extraction technique has given satisfactory yield. Since this process is environmental friendly, it does not produce harmful volatile organic compounds that could harm the atmosphere. Lack of commercial availability of

particular enzymes and the long process time required by the enzymes to liberate the oil bodies are considered as the major drawback of this procedure. In another method, namely, enzyme-assisted three-phase partitioning (TPP), a combination of sonication and enzyme treatment is used. The main advantages of this procedure are higher yield and lesser reaction time. But the high cost of enzyme and higher energy input for sonication can be an obstacle (Aderibigbe et al. 1997; Forson et al. 2004; Achten et al. 2008; Abdulla et al. 2011).

Table 12.4 gives an outline of different researches done for oil extraction and their respective yields.