ARTICLE pubs.acs.org/JAFC
Screening of the Entire USDA Castor Germplasm Collection for Oil Content and Fatty Acid Composition for Optimum Biodiesel Production Ming Li Wang,*,† J. Bradley Morris,† Brandon Tonnis,† David Pinnow,† Jerry Davis,§ Paul Raymer,# and Gary A. Pederson† †
Plant Genetic Resources Conservation Unit, Agricultural Research Service, U.S. Department of Agriculture, Griffin, Georgia 30223, United States § Department of Experimental Statistics and #Department of Crop and Soil Sciences, University of Georgia, Griffin, Georgia 30223, United States ABSTRACT: Castor has tremendous potential as a feedstock for biodiesel production. The oil content and fatty acid composition in castor seed are important factors determining the price for production and affecting the key fuel properties of biodiesel. There are 1033 available castor accessions collected or donated from 48 countries worldwide in the USDA germplasm collection. The entire castor collection was screened for oil content and fatty acid composition by nuclear magnetic resonance (NMR) and gas chromatography (GC), respectively. Castor seeds on the average contain 48.2% oil with significant variability ranging from 37.2 to 60.6%. Methyl esters were prepared from castor seed by alkaline transmethylation. GC analysis of methyl esters confirmed that castor oil was composed primarily of eight fatty acids: 1.48% palmitic (C16:0), 1.58% stearic (C18:0), 4.41% oleic (C18:1), 6.42% linoleic (C18:2), 0.68% linolenic (C18:3), 0.45% gadoleic (C20:1), 84.51% ricinoleic (C18:1 1OH), and 0.47% dihydroxystearic (C18:0 2OH) acids. Significant variability in fatty acid composition was detected among castor accessions. Ricinoleic acid (RA) was positively correlated with dihydroxystearic acid (DHSA) but highly negatively correlated with the five other fatty acids except linolenic acid. The results for oil content and fatty acid composition obtained from this study will be useful for end-users to explore castor germplasm for biodiesel production. KEYWORDS: Ricinus communis, castor germplasm, oil content, nuclear magnetic resonance (NMR), alkaline transmethylation, fatty acid composition, gas chromatography (GC), biodiesel production
’ INTRODUCTION Castor belongs to the family Euphorbiaceae (consisting of 280 genera), and the genus Ricinus (containing only one species, Ricinus communis L.) and has been cultivated for over 6000 years.1,2 Castor oil is not edible but has multiple uses ranging from medicine to cosmetics to industrial applications.3 From ancient times, castor oil had been used as a popular stimulant laxative. Currently, castor oil still has many uses in modern medicine such as eye drops for lipid-deficiency dry eyes,4,5 an ingredient with balsam and trypsin for reducing edema and scabbing of patient wounds and skin disorders,6 and oil inducer for women to start labor.3 Castor oil is also used as a cosmetic ingredient in lipsticks, shampoos, hand lotions, and other coating materials.7 Castor oil comprises a high percentage of ricinoleic acid (C18:1 1OH). The hydrogen-bonding property from the hydroxyl group of ricinoleic acid leads to castor oil having high viscosity. Due to its high viscosity, castor oil has been used as an efficient lubricant for high-speed engines such as racing cars and airplanes. Castor seed contains ricin, a heterodimeric glycoprotein toxin, which can inhibit protein synthesis and lead to cell death.8 However, it was found that there are no toxic protein (including ricin and allergenic proteins) residuals in castor oil.3 Because castor seed contains a high percentage of oil, castor has great potential to become one of the feedstocks for biodiesel production.9,10 Obviously, oil content in castor seed can significantly affect the cost of biodiesel production. However, castor r 2011 American Chemical Society
oil cannot be directly used as fuel due to its extremely high viscosity and high water content, which are not suitable for combustion engines. High viscosity leads to poor fuel atomization during the spray and incomplete combustion.11 As the temperature decreases, the viscosity increases. Therefore, high viscosity causes excessive fuel injection pressure during engine warm-up and more problems for the engine operation at low temperatures.12,13 Castor oil has to be converted to methyl or ethyl esters (i.e., biodiesel) by transesterification. The viscosity can be reduced 11.8-fold from castor oil to castor biodiesel by transesterification.14 Other fuel properties of biodiesel (such as cloud point, oxidative stability, and NOx exhaust emission) can also be improved by altering the fatty acid composition (length of hydrocarbon chain and number of double bonds) of the original oil.15 Variability for oil content and fatty acid composition exists in the castor germplasm collection. A natural mutant (OLE-1) with an altered fatty acid composition (a high level of oleic acid and a low level of ricinoleic acid) has been identified by screening 191 castor germplasm accessions.16,17 The USDA castor germplasm collection contains 1033 accessions and is maintained by the Received: July 22, 2011 Revised: August 11, 2011 Accepted: August 12, 2011 Published: August 12, 2011 9250
dx.doi.org/10.1021/jf202949v | J. Agric. Food Chem. 2011, 59, 9250–9256
Journal of Agricultural and Food Chemistry USDA-ARS, Plant Genetic Resources Conservation Unit (PGRCU), in Griffin, GA. The variability for oil content and fatty acid composition within the entire USDA germplasm collection needs to be assessed. In a previous study,18 the variability for oil content was determined and reported in a short paper by our laboratory but without fatty acid composition. Therefore, the objectives of this study were (i) to determine the variability of fatty acid composition within the entire USDA castor germplasm collection, (ii) to detect correlations among fatty acids and between the oil content and fatty acids, and (iii) to identify castor accessions with a high percentage of oil and/or optimum fatty acid composition as parents to develop castor cultivars for biodiesel production.
’ MATERIALS AND METHODS Plant Material. The entire USDA castor germplasm collection containing 1033 accessions was obtained from two locations: 364 accessions from the USDA-ARS, Plant Genetic Resources Conservation Unit, Griffin, GA, and 669 accessions from the USDA-ARS, National Center for Genetic Resources Preservation, Fort Collins, CO. These castor seeds were used in this study. Oil Content by NMR Analysis. Because our shorter paper did not elaborate on the method for measuring oil content, we wish to present more detailed information here. In a magnetic field, certain atomic nuclei resonate at specific radio frequencies. This resonance can be converted to a signal and measured to determine the amount and nature of the particular nuclei in a sample. As the nuclei return to equilibrium, their collective NMR signal decays at different rates depending on their chemical state and surroundings. Solids and liquids are easily distinguished, and although their nuclear relaxation properties are similar, oils and water can be differentiated by employing specifically timed radio pulses, provided the moisture content is relatively low (
