Submitted to: American Society for Mass Spectrometry
Publication Type: Abstract Only
Publication Acceptance Date: 2/15/2004
Publication Date: 4/1/2004
Citation: Nunez, A., Ashby, R.D., Foglia, T.A., Solaiman, D. 2004. Characterization of sophorolipids produced by rhodotorula bogoriensis and their lipase-mediated rearrangement products. American Society for Mass Spectrometry. Paper No. ThPI 151.
Technical Abstract: Sophorolipids are extracellular glycolipids secreted by yeasts such as Candida bombicola and C. apicola. Their chemical structure consists of a di- or mono-acetylated disaccharide, i.e., sophorose (2-O-beta-D-glucopyranosyl-beta-D-glucopyranose) that is bound to a hydroxy fatty acid by a glycosidic bond between carbon 1' of the disaccharide and the hydroxy group on the fatty acid chain, typically at the omega-1 position. The carboxyl group of the fatty acid is either free or lactonized to carbon 4' of the sugar. When produced from mixed substrates such as glucose/glycerol and triacylglycerols, the fatty acid chain length on the sophorolipids varies from 16 to 18 carbons with varying degrees of unsaturation. The sophorolipids secreted by the yeast Rhodotorula bogoriensis (strain NRRL Y-2332) and their lipase-rearranged products after isolation were separated and characterized using high performance liquid chromatography in combination with atmospheric pressure ionization mass spectrometry (LC/API-MS). The LC portion consisted of a Waters 2690 Separation Module with a Waters Symmetry C8 column, 3.5 'm (150 × 2.1 mm) (Waters Co., Milford, MA). The effluent was connected to a Micromass ZMD (Waters) mass spectrometer with atmospheric pressure chemical ionization (APCI) or electrospray ionization (ESI) probe. In this study the yeast Rhodotorula bogoriensis (formerly Candida bogoriensis) was grown in a medium that used glucose and oleic acid as the carbon substrates. The sophorolipids produced were isolated from the medium by extraction with ethyl acetate and subsequently separated and characterized using the above LC/APCI-MS method. The APCI spectra of the products indicated that the sophorose ring contained varying degrees of acetylation at carbon 6' and 6' positions. The sugar ring was glycosylated to a C22:0 fatty acid, but a minor co-product with a C24:0 fatty acid also was identified. The use of oleic acid in the growth media did not influence the final composition of the fatty acid chain-length as has been observed with the sophorolipids produced by C. bombicola. In the APCI/MS spectrum specific fragmentation ions corresponding to the sophorose ring and hydroxy fatty acid structure indicated that the fatty acid was in the free acid form. The presence of the primary alcohols and the carboxylic acid functionality in the molecule was studied as potential reactive centers for the formation of biopolymers through enzymatic esterification. The sophorolipid mixture was hydrolyzed with base to remove the acetyl group and the de-acetylated product was esterified using an immobilized lipase in tetrahydrofuran. The formation of intra-molecular esters (lactones) versus inter-molecular esters (dimers or oligomers) was determined by LC/ESI-MS. The results indicated that lactone formation was the dominant esterification pathway in this lipase-catalyzed reaction.