Biotechnological Applications of Jatropha curcas Seeds for Bioenergy Carriers and Bioactive Compounds

Abstract

Currently, the energy and other value added commodities around the globe come from fossil fuels based refineries. However, the consumption of fossil fuels for energy and other materials has resulted in the creation of various undesirable and complicated problems, for example, the emission of greenhouse gases (global warming), steady increase in the prices of fossil fuel products and reduction in their reserves. Therefore, it has become critical to seek for alternative sustainable, environmental friendly, cost-effective and more importantly, renewable energy resources for biofuels production and valuable bio-based commodities. Biomass is one of the ideal alternatives that can be used in biorefinery context to fulfill the world demands and replace the fossil fuels refineries. Biomass can be further categorized into edibles and nonedible feedstocks. Edible feedstocks face challenges such as competition between the lands required for fuels and food supply ultimately increasing the food prices. While, non-edible feedstocks such as Jatropha curcas are the ideal, renewable and sustainable options for biorefinery concept, having no fuels versus feed competition. In the current study, J. curcas seed was used as feedstock for biorefinery to produce sustainable energy carriers (biogas and biodiesel) as well as commodities through jointly applied conversion technologies. Biodiesel production from J. curcas seed oil was the most feasible option, and biogas production from pressed cake after methanolic extraction was the best option for biogas production. The methanolic extract of pressed cake showed good antimicrobial, and antioxidant activities and also the extraction proved to enhance biogas production and reduced negative effect on microbial profile in the reactor. Biodiesel production from the oil extracted from J. curcas seed was evaluated using chemical (two-step process) and biological approach (lipases based). The pressed cake obtained after the oil extraction from seed was also used for biogas production. However, pressed cake is composed of antimicrobial phytochemicals that inhibit the microbial communities during anaerobic digestion (AD). But in this study, it was interesting that the extraction of methanolic extracts from pressed cake enhanced the biogas production, also the microbial evenness/richness and relative abundance in the reactor. Phytochemical analyses of J. curcas de-oiled pressed cake extracts was carried out using GC-MS and FTIR. J. curcas oil and different extracts from de-oiled pressed cake were evaluated individually as well as in combination with commercial antibiotics against various bacterial clinical pathogenic and multidrug resistant strains. In addition, the de-oiled pressed cake extracts and seed oil were evaluated for their antioxidant, cytotoxic, enzyme inhibition and antifungal activities against phytopathogenic fungal strains. The microbial communities and biogas yield during AD in continuous reactor was evaluated when reactors were fed with whole seed, seed oil, pressed cake and methanolic residues (J. curcas pressed cake after the methanolic extraction). The antimicrobial effects of J. curcas seed was evaluated on the biogas yield and microbial communities involved in AD process in continuous setup using high throughput Illumina MiSeq sequencing. The effect of carbon to nitrogen ratios on biomethane yield during anaerobic co-digestion of J. curcas de-oiled seed kernel and mango peels was evaluated in continuous reactors. J. curcas seed oil was also used for chemical (two-step process) and bacterial (lipase) based biodiesel production. For bacterial based biodiesel production, lipase producing indigenous bacterial strains were isolated. Plackett-Burman and central composite designs were used to optimize various factors during bacterial based transesterification of J. curcas seed oil. J. curcas de-oiled pressed cake extracts and seed oil were rich in various phytochemicals. In antibacterial activities, methanolic extracts remained more active compared to seed oil, n-hexane and aqueous extracts individually as well as in combinatorial activities against clinical and multidrug resistant (MDR) bacterial strains. Methanolic extract in combination with rifampicin showed the highest synergism against various MDR and clinical bacterial isolates. The methanolic, n-hexane, aqueous extracts and seed oil in various combinations with antibiotics showed 45, 33, 9 and 26% synergism, respectively. Similarly, methanolic extract was highly potent against selected fungal strains compared to the other extracts and seed oil. The methanolic extract was also found significantly potent in antioxidant activities compared to the other treatments. In batch process, higher biogas yield was obtained from methanolic residues compared to pressed cake, aqueous and n-hexane residues. The methanolic residues were easily biodegradable and therefore accumulation of VFAs was observed when OLR was increased. Therefore, at higher organic loading rates, methanolic residues were evaluated for biogas production in two stage continuous anaerobic digesters to ensure efficient and stable biogas production. Methanolic extract significantly inhibited the hydrolysis phase of AD and decreased biogas yield by 35.5%. It was confirmed by studying the effect of methanolic extract on microbial communities in continuous reactor in which the relative abundance of fermentative bacteria was higher in reactors fed with methanolic residues (Jatropha pressed cake after methanolic extraction) compared to the one fed with Jatropha pressed cake. Jatropha oil and whole seed did not exhibited inhibitory effects on methanogens during AD. The effect of operational parameters (organic loading rate and hydraulic retention time) on microbial communities in continuous reactors showed that higher relative abundance of methanogenic and lower abundance of fermentative bacterial communities was observed in all reactors at hydraulic retention time 20 compared to 15 and 10 days. The biomethane yield of co-digested mango peel and seed kernel (1:4 weight ratio based on volatile solids) was 61, 50, 36, and 25% higher compared to the biomethane yields of mango peel, seed kernel, mango peel:seed kernel (2:1) and mango peel:seed kernel (1:1), respectively. The co-digestion of mango peel and seed kernel at 1:4 ratio resulted in the highest actual biomethane yield, followed by 1:1 and 2:1 ratios with yields of 52, 39 and 32% of the theoretical yields, respectively, illustrating the importance of adjusting C/N ratio by co-digestion of the right amounts of co-substrate. Biodiesel production from J. curcas seed oil was feasible using chemical and biological means. Different variables such as oil to methanol ratio, catalyst concentration, temperature, reaction time and agitation were optimized for biodiesel production and the highest volumetric biodiesel yield obtained was 97-98% for chemical and bacterial based biodiesel production at optimized conditions. In case of lipase mediated biodiesel production, the highest volumetric yield of biodiesel (~97%) was obtained by using Brevibacterium SB11 MH715025 and Pseudomonas SB15 MH715026, strains at optimum conditions. The fuel properties of biodiesel produced by the chemical method and selected strains from J. curcas seed oil were in line with quality standards specified by ASTM D6751 and EU-14103. The study concludes that J. curcas seed is a multipurpose substrate and could be used for production of a number of products including antimicrobials, antioxidants, cytotoxic and bioenergy carriers (biogas and biodiesel). Therefore, using J. curcas in a biorefinery context rather than simply for biofuel production is an ideal solution to increase the economic value of J. curcas plant for biofuel and pharmaceutical industrial sectors. Moreover, by extracting the antimicrobials, the seeds toxicity is reduced, increasing the efficiency and economic value for biofuel production