Effect of fruit maturity on yield and quality of seed oil and biodiesel of jatropha curcas found in Botswana
PublisherUniversity of Botswana, www.ub.bw
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This study was undertaken to investigate the influence of fruit maturity stage on yield and quality parameters of Jatropha curcas seed oil and derived biodiesel. The influence of fruit maturity on phorbol ester content (toxicity) in Jatropha curcas seed oil and seed cake was also investigated. Jatropha curcas (hereafter referred to as Jatropha) seeds used in this study were harvested from Jatropha plants adapted to Botswana climatic conditions. Biodiesel has received great attention as one of the renewable and clean burning fuels. This is so in an effort to reduce greenhouse gas emissions. Jatropha seed oil is considered as one of highly promising feedstock for biodiesel production. In order to meet the high demand of large scale biodiesel production, increment of seed oil output from Jatropha seeds is necessary. Harvesting Jatropha seeds/fruits when seed oil content is maximum is one of the factors than can help increase seed oil output from Jatropha seeds. Results from this investigation have shown that harvesting Jatropha fruits when they are yellow increases seed oil output by 6 to 9% as compared to harvesting the fruits on their final maturity stage (brown dry). Thus harvesting Jatropha seeds when they are yellow may increase feedstock (seed oil) availability in biodiesel production. The maximum oil content in Jatropha seeds is attained at yellow maturity stage, and these are 30.1%, 30.6%, 26.2% and 27.9% for Jatropha seeds harvested from Thamaga, Mmadinare, Shashe and Maun areas, respectively. It is pertinent to mention that accumulation of seed oil in Jatropha seeds harvested from the aforementioned geographical locations follow a similar trend. Seed oil in Jatropha seeds increases continuously during fruit maturation and reaches peak level when the fruit turns yellow, thereafter it starts to decline until the final maturity stage (brown dry). The quality of both feedstock and biodiesel are of paramount importance, and Jatropha seed oil and derived biodiesel are no exception. Results from this investigation have revealed that fruit maturity have an impact on the quality of the seed oil hence the derived biodiesel. Fruit maturity influences some quality parameters of the seed oil. For instance, Free Fatty Acids (FFA) content in Jatropha seed oil varies with fruit maturity. Free fatty acid content in Jatropha seed oil increases continuously with seed maturity and this applies for all feedstock collected from all the geographical locations under investigation. These FFA content in Jatropha seed oil ranges from 0.2 to 0.7% for the four different fruit maturity stages, namely green yellow, yellow, yellow brown and brown dry. Seeds from Mmadinare area (21.8811oS latitude, 27.7514oE longitude) recorded relatively highest FFA content from brown dry fruits (0.75%) whereas seeds from Thamaga area (24.72° S latitude, 25.53° ii E longitude) recorded relatively lowest FFA content (0.44%). Fatty acid composition of Jatropha seed oil also varies with fruit maturity. Fractional composition of unsaturated fatty acids, which makes up more than 70% of the total lipid, declines continuously with each consecutive maturity stage. As Jatropha fruits matures from green yellow to brown dry, the fractional composition of linoleic acid decrease by 8 to 9%. There is a logical relationship between the trend in fatty acid composition in Jatropha seed oil and seed oil content during fruit maturation. Based on this trend of unsaturated fatty acids in Jatropha seed oil, particularly linoleic and oleic acid, it can be concluded that reduction of seed oil content during seed desiccation stage (from yellow brown to brown dry) is a result of breakdown of some of the unsaturated fatty acids. The decline in fractional composition of unsaturated fatty acids in Jatropha seed oil during fruit maturation causes the cetane number of derived biodiesel to increase continuously with each successive maturity stage. The Peroxide Value (PV) of both Jatropha seed oil and derived biodiesel increase gradually and linearly with fruit maturity. The PV of seed oils from all the investigated geographical locations in Botswana (Mmadinare, Thamaga, Shashe and Maun) follow the same trend and in the same range. Effect of fruit maturity on other quality parameters such as cloud point, pour point, density, viscosity and calorific value (energy content) is minimal. Jatropha seeds from selected geographical locations in Botswana contain some levels of Phorbol Esters (PE) hence toxic. The PEs content vary with fruit maturity. Phorbol ester content in Jatropha seed oil ranges from 3.4 to 4.2mg/g whereas in seed cake ranges from 1.7 to 2.0mg/g during the four different fruit maturity stages. Jatropha seed oil and seed cake from yellow brown maturity stage are relatively the most toxic since they contain highest concentration of PEs.
- PhD Theses (FET)