Research Papers On Jatropha Curcas

Abstract

Jatropha curcas (L.) is a perennial plant of the spurge family (Euphorbiaceae). Recently, it has received much attention as a potential source of vegetable oil as a replacement for petroleum, and, in particular, the production of biodiesel. Despite the interest that is being shown in the large-scale cultivation of J. curcas, genetic resources remain poorly characterized and conserved and there has been very little plant breeding for improved traits. At present, the varieties being used to establish plantations in Africa and Asia are inedible. The meal obtained after the extraction of oil cannot, therefore, be used as a source of animal feed. Naturally existing edible varieties are, however, known to occur in Mexico. The toxic components of J. curcas seeds, the potential for plant breeding to generate improved varieties, and the suitability of J. curcas oil as a feedstock for biodiesel production are discussed.

Biodiesel, curcin, Jatropha curcas, oilseed, phorbal ester, ribosome inactivating protein, seed meal

Introduction

Plant oils, in addition to being a food commodity, are important as a renewable resource for both the fuel and chemical industries (Dyer and Mullen, 2008). Demand for vegetable oils as a source of biodiesel in particular has increased recently due to a number of factors, including increased prices of petroleum, the desire to reduce CO2 emissions, and fuel security. At the same time, there are increased demands on land, water, and other resources used in the production of food for a growing world population.

Most of the crops grown today, including oilseeds, are annuals. Perennial crops have deeper root systems, which help store more carbon, maintain soil quality, and manage water and nutrients more conservatively. They have therefore been advocated as potentially more efficient ways of farming, especially on marginal soils (Cox et al., 2006; Glover et al., 2007). For the production of plant oils, Jatropha curcas is one species that has received much attention recently (Gubitz et al., 1999; Achten et al., 2007; Fairless, 2007). It is a tropical species, although it has a broader geographical range than oil palm. Figure 1 shows the approximate geographic distribution of the species. Much of the interest in J. curcas has arisen due to its ability to grow on ‘marginal land’. Although this term is poorly defined, it is generally used to describe land that is of poor quality in terms of agricultural use and typically not used for crop cultivation. Using marginal land for J. curcas cultivation is therefore attractive since it would not displace food-producing crops. Current estimates suggest that there are now 2.5 million hectares of J. curcas planted in India and China alone, with plans for an additional 23 million acres by 2010 (Fairless, 2007). Interest in the cultivation of J. curcas is coming from both the public and private sectors, and a number of public companies are now involved in J. curcas cultivation including D1 Oils plc (www.d1plc.com), Viridas plc (www.viridasplc.com), and Energem Resources Inc (www.energem.com).

Despite the interest in J. curcas, the available yield performance data for this species are limited and somewhat uncertain. A summary of reported yields was compiled by Heller (1996). Most of the available yield information has been obtained from plants which have not yet reached maturity (<5 years old). Two publications which present yield data for mature plantations (Matsuno et al., 1984; Foidl et al., 1996) suggest yields of 4 and 5 tonnes of seed per hectare, respectively. This would equate to approximately 1.5 tonnes of oil per hectare. However, the supporting data provided in Matsuno et al. (1984) are limited, and the data presented in Foidl et al. (1996) are projections based on field trials that were not included in the publication. More yield data are likely to become available over the next few years, as recently established plantations begin to reach maturity.

Unlike the major oilseed crops, there are currently no agronomically improved varieties available for J. curcas. In addition, the seed meal obtained after extraction of the oil cannot be used as an animal feed due to its toxicity. Despite the toxicity of J. curcas, edible varieties are known to exist in Mexico which are not currently being exploited. The potential of these edible varieties and the potential of plant science to create agronomically improved varieties is discussed. We also discuss the suitability of J. curcas oil for biodiesel production.

Toxicity of J. curcas seeds and the potential value of seed meal

The seeds of J. curcas form within seed pods (Fig. 2). Each seed pod typically contains three seeds (Fig. 2C). The typical mass and composition of the seeds is detailed in Table 1. In addition to being a valuable source of oil, the seeds are also rich in protein. The protein composition of J. curcas seed meal has been analysed, and it has been shown to compare favourably with soybean meal (Makkar et al., 1998a, b), containing a good balance of essential amino acids, with the exception of lysine. The seeds of most tested varieties of J. curcas are inedible, and remain so after the heat-inactivation treatments used in seed-meal processing (Heller, 1996). As a consequence, the protein rich seed meal of J. curcas is not used as animal feed. The prices of seed oil and meal fluctuate depending on supply (harvest) and demand. The prices of seed oil and meal for soybean, canola, and sunflower are shown in Fig. 3. Although oil is more valuable than meal, the seed meal is potentially a valuable commodity. The ability to use J. curcas meal as animal feed not only improves the economics of J. curcas production, but also means the crop would produce both fuel and feed. Although the seeds of J. curcas contains a range of toxins and antinutrients, the toxicity of J. curcas seeds has been attributed to the presence of a protein (curcin) and phorbol-esters (diterpenoids).

Table 1.

Range of average seed mass, oil content, and protein content reported for J. curcas seeds:(Makkar et al., 1998a, b; Martinez-Herrera et al., 2004, 2006; Rao et al., 2008).

Reported ranges 
Average seed mass 450–860 mg 
Testa (shell) (%) 30–40% 
Kernel (%) 60–70% 
Average oil content
Whole seed 39–37% 
Kernel 44–62% 
Protein content
Kernel 22–35% 
Seed meal after oil extraction 48–64% 
Reported ranges 
Average seed mass 450–860 mg 
Testa (shell) (%) 30–40% 
Kernel (%) 60–70% 
Average oil content
Whole seed 39–37% 
Kernel 44–62% 
Protein content
Kernel 22–35% 
Seed meal after oil extraction 48–64% 

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Fig. 2.

Images of J. curcas. (A) Young J. curcas plant with both flowers and developing seed pods. (B) J. curcas inflorescence containing both male staminate flowers (M) and female pistillate flowers (F). (C) Cross-section of a J. curcas seed pod containing three developing seeds. (D) Mature seeds of J. curcas.

Fig. 2.

Images of J. curcas. (A) Young J. curcas plant with both flowers and developing seed pods. (B) J. curcas inflorescence containing both male staminate flowers (M) and female pistillate flowers (F). (C) Cross-section of a J. curcas seed pod containing three developing seeds. (D) Mature seeds of J. curcas.

Curcin

Curcin is often classified as a lectin and described as being similar to ricin from castor bean with the implication that it has similar toxicity. These descriptions are inaccurate. Both curcin and ricin are ribosome inactivating proteins (RIPs), which depurinate rRNA, thus arresting protein synthesis. Curcin is a type-I RIP (Barbieri et al., 1993; Juan et al., 2003; Qin

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