Analysis of sorghum wax and carnauba wax by reversed phase liquid chromatography mass spectrometry

Authors: Harron, Andrew; Powell, Michael; Nunez, Alberto; Moreau, Robert

Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/6/2016
Publication Date: 1/26/2017
Publication URL: https://handle.nal.usda.gov/10113/5627920
Citation: Harron, A.F., Powell, M.J., Nunez, A., Moreau, R.A. 2017. Analysis of sorghum wax and carnauba wax by reversed phase liquid chromatography mass spectrometry. Industrial Crops and Products. 98:116-129.

Interpretive Summary: Sorghum is a highly adaptive, drought tolerant crop which is being investigated as a highly sustainable crop in the arid climates of Africa, Asia, Australia, Central America, and the United States. Grain sorghum has been identified as an Advanced Biofuel by the US Environmental Protection Agency, due to its favorable low greenhouse gas emissions. In order to improve the economics of sorghum conversion to biofuels, our laboratory is investigating possible new coproducts from sorhguhm, including sorghum oil (approximately 3% of kernel) and sorghum wax (approximately 0.3% of kernel). The United States has no domestic supply of carnauba wax, but sorghum wax has previously been suggested as a possible domestic alternative for carnauba wax. The goal of the study was to develop a new analytical method (using reverse phase high performance liquid chromatography and mass spectrometry, HPLC-MS) for the analysis of waxes, including sorghum wax and carnauba wax. Using our new method we were able to analyze and characterize carnauba wax and sorghum wax; which, to our knowledge, is the first successful reversed phase HPLC method for the analysis and characterization of intact waxes. Using the method we report that sorghum wax is composed of a heterogeneous mixture of compounds, dominated by C28 and C30 saturated and unsaturated species, while carnauba is composed primarily of C56-C60 saturated wax esters.

Technical Abstract: Sorghum is a genus in the grass family, which is used for both grain and forage production throughout the world. In the United States, sorghum grain is predominantly used as livestock feed, and in ethanol production. In recent years however, sorghum grain has been investigated for other industrial applications, including gluten free food sources for the US food market, and waxes. The United States is the world's largest producer of grain sorghum, which is grown in the arid regions of the southern Great Plains, Arizona and California. Carnauba wax is used in a variety of products; including cosmetics, industrial polishes, food products, and paper products. The United States has no domestic source of carnauba wax, and imports 100% of its carnauba wax supply. Sorghum wax has been demonstrated to have similar physical properties to carnauba wax, and could potentially be a viable substitute for carnauba wax. In this paper we present the first successful reversed phase HPLC method, via a C30 column, for the analysis and characterization of waxes. Sorghum wax is composed of a heterogeneous mixture of compounds, dominated by C28 and C30 saturated and unsaturated species, while carnauba is more homogeneous in nature, and composed primarily of C56-C60 saturated wax esters.