Seed oil production in Jatropha seeds through different maturity stages have been investigated. In order to meet the high demand of oil (feedstock) for large scale biodiesel production, increasing oil content or output in Jatropha seeds is required. Jatropha fruits were harvested at four different maturity stages and the seeds were analysed for oil content. The seed oil was analysed for fatty acid profile. Results from four different geographical locations investigated namely; Mmadinare, Thamaga, Maun and Shashe, have shown a similar trend in lipid accumulation in Jatropha seeds as the fruits mature from green to brown dry. However, maximum oil content in seeds varies with geographical location. Accumulation of oil in Jatropha seeds during maturation follows a parabolic trend and reaches its peak when fruits are yellow. Oil yield in Jatropha seed kernels ranges from 38.7% to 45.8% for the four maturity stages investigated. Overall results have revealed that harvesting Jatropha fruits when they are yellow increases seed oil output by 6-9% when compared to harvesting the fruits when they are brown dry. There is a relationship between the trend in fatty acid composition in Jatropha seed oil and seed oil content trend during fruit maturation. Based on the trend of unsaturated fatty acids in Jatropha seed oil, particularly linoleic and oleic acids, it can be deduced that reduction of seed oil content from yellow brown to brown dry stage is a result of breakdown of some of the unsaturated fatty acids.

Maturity of Jatropha fruits has influence on oil yield, chemical composition and physicochemical properties of derived biodiesel. Oil yield was determined using soxhlet extraction while biodiesel was prepared through the process of transesterification. Fatty acid profile was determined according to test method EN 14103 using Agilent Technologies GC System 7890. The calorific value of biodiesel was determined using Oxygen Bomb Calorimeter, IKA C200 according to test method ASTM D5865. Results showed that Yellow Jatropha fruit seeds have the highest oil yield and energy content, coupled with the best mix of fatty acid methyl esters.

The quality of a feedstock in biodiesel production is of paramount importance, and Jatropha seed oil is no exception. This study investigates the influence of the fruit maturity stage on the physicochemical properties of Jatropha seed oil and the derived biodiesel. Free fatty acid content, peroxide value, moisture content, density, and kinematic viscosity are some of the important quality parameters of oil and biodiesel. Results from this investigation have revealed that free fatty acid content and peroxide value of seed oil varies as Jatropha fruits mature from green to brown dry. The free fatty acid content in Jatropha seed oil increases continuously with seed maturity following the three-order polynomial trend. The free fatty acid content in Jatropha seed oil from the investigated geographical locations in Botswana ranges from 0.2 to 0.7% for the four different fruit maturity stages. Similarly, the peroxide value of Jatropha seed oil increases gradually and linearly with fruit maturity. The peroxide value of Jatropha seed oil ranges from 1.2 to 3.7 mEq/kg oil, while that of derived biodiesel ranges from 2.1 to 4.4 mEq/kg oil during the four different fruit maturity stages. However, the variation of density and kinematic viscosity of both Jatropha seed oil and derived biodiesel with fruit maturity is insignificant. Moisture content in Jatropha seeds varies as fruits mature from green to brown dry.

Biodiesel has been identified globally as presenting an opportunity for development of a sustainable fuel source, especially in light of international pressures for greenhouse gas emission reductions and the unpredictability of availability and pricing of fossil fuels. For Botswana, the internal development of biodiesel could signify a positive move away from a dependency on imported fuel products, provide sustainable employment and contribute to poverty alleviation measures. In the current study, biodiesel was synthesized from animal fat and tested for fuel properties. Results have shown a biodiesel production yield of 93%, chemical composition that is typical of a biodiesel fuel, and fuel properties that are largely comparable to those of petroleum diesel.

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