ORIGINAL ARTICLE Identification of Unique Aldehyde Dimers in Sorghum Wax Recovered after Fermentation in a Commercial Fuel Ethanol Plant Robert A. Moreau 1 · Megan E. Sharma 1 · Alberto Nuñez 1 · Charles A. Mullen 1 · Michael J. Powell 1 · Kerby Jones 1 · Andrew Harron 1 · Jeffrey T. Cafmeyer 2 Received: 5 June 2020 / Revised: 24 August 2020 / Accepted: 28 August 2020 © 2020 American Oil Chemists' Society. This article has been contributed to by US Government employees and their work is in the public domain in the USA. Abstract Sorghum wax can be extracted from the surface of sorghum (Sorghum bicolor) kernels. It is composed mostly of a mixture of unsaturated C 28 and C 30 alkanes, fatty acids, fatty alcohols, and fatty aldehydes. Like car- nauba wax, sorghum wax is a hard wax with a high melting point and it has potential edible and industrial applications. The yield of sorghum wax from the surface of sorghum kernels is 0.2–0.5 g of wax per 100 g of kernels. Sorghum wax can also be recovered from the “distillers oil” which is obtained after fermentation of sorghum (milo) or sorghum/ corn blends in dry grind fuel ethanol plants. This distillers sorghum wax can potentially be obtained in yields of up to 10% by chilling the distillers oil to precipitate the wax and then recovering it via centrifugation or filtration. Like sor- ghum kernel wax, distillers sorghum wax is mainly com- posed of C 28 and C 30 alkanes, alcohols, and aldehydes in the molecular weight (MW) range of 350–450. However, we found that 7–49% w/w of distillers sorghum wax is composed of larger wax components with MW of 799–912. Analysis via high-resolution atmospheric pres- sure chemical ionization mass spectrometry (APCI) and gas chromatography with electron ionization mass spec- trometry (GC/MS-EI) resulted in exact mass data and fragmentation patterns that suggested that these high MW compounds are monounsaturated fatty aldehyde dimers, likely formed by aldol condensation. Further confirmation supporting the GC/MS data for the aldol reaction was obtained by comparison with similar aldol products. Keywords Sorghum wax  Aldehydes dimers  Aldol condensation  Mass spectrometry J Am Oil Chem Soc (2020) 97: 1299–1308. Introduction The above ground parts of higher plants are covered with a thin protective layer of epicuticular waxes (Barthlott et al., 1998; Jenks et al., 1992). The surfaces of kernels of sorghum (Sorghum bicolor) are covered by a thicker layer of waxes, compared to other grain species, and the compo- sition of the sorghum kernels surface wax is a complex mixture of fatty acids, fatty aldehydes, fatty alcohols, and alkanes (Avato et al., 1990; Bianchi et al., 1979; Harron et al., 2017; Weller et al., 2006). These sorghum kernel sur- face waxes can be extracted by chloroform, hexane, and other nonpolar organic solvents (Harron et al., 2017). The physical properties of sorghum kernels surface waxes have been favorably compared to those of commercially impor- tant carnauba wax (Weller et al., 2006). During the last 10 years, most of the approximately 200 dry grind fuel ethanol plants in the United States have been retrofitted to produce a new coproduct, distillers corn * Alberto Nuñez alberto.nunez@usda.gov 1 U.S. Department of Agriculture, Agricultural Research Service, Eastern Regional Research Center, 600 East Mermaid Lane; Wyndmoor, PA 19038, USA 2 Battelle Memorial Institute, 505 King Ave, Columbus, OH 43201, USA Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. USDA is an equal opportunity provider and employer. J Am Oil Chem Soc (2020) 97: 1299–1308 DOI 10.1002/aocs.12424 Published online: 15 October 2020 J Am Oil Chem Soc (2020) 97: 1299–1308