Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2024
Publication Date: 4/14/2024
Citation: Moser, J.K., Ashby, R.D., Yosief, H.O., Msanne, J.N., Peterson, S.C., Bantchev, G.B., Cermak, S.C., Felker, F.C. 2024. Properties of soybean oil oleogels produced from sophorolipid-derived hydroxy fatty acids, methyl esters and hydrogenated Lesquerella seed oil. Journal of the American Oil Chemists' Society. https://doi.org/10.1002/aocs.12843.
DOI: https://doi.org/10.1002/aocs.12843

Interpretive Summary: Oleogels are a promising new technology for replacing saturated fats in foods. They are produced when small amounts of molecules dissolve in vegetable oil upon heating, then crystallize upon cooling to form a three-dimensional network that is similar to a gel. This network immobilizes the liquid oil to form a semi-solid with properties remarkably similar to a fat. Hydroxy fatty acids are one example of materials that have been studied extensively as oleogelators, but unfortunately, castor oil is the only major commercial source of hydroxy fatty acids, and its production is limited due to the coproduction of a toxin in castor seed. Thus, there is great interest in new and renewable sources for hydroxy fatty acids. Sophorolipids are one potential new source of hydroxy fatty acids. They are naturally produced by non-toxic yeast, and they are composed of a disaccharide sugar linked to a hydroxy fatty acid. Different hydroxy fatty acids can be produced on the sophorolipids, with different carbon chain lengths, or with different carbon-chain locations of the hydroxyl group, depending on the yeast strain and culture conditions. Lesquerella is a native North American plant that is being developed as a potential new crop and is another alternative source of hydroxy fatty acids. Its seed oil has over 60% hydroxy fatty acids, and it has no toxins in it seeds. In this study we evaluated the oleogel properties of hydroxy fatty acids, hydroxy fatty acid methyl esters, and hydrogenated Lesquerella oil. It was determined that 5% by weight of hydroxy fatty acids produced from sophorolipids, of 16-carbon and 18-carbon chain length, were needed to form a stable oleogel. Methyl esterification of the 16-carbon and 18-carbon hydroxy fatty acids negatively affected the oleogel crystallization properties, resulting in less crystallization and softer oleogels. Hydrogenated Lesquerella oil had over 60% 14-OH-C20, but while it crystallized and formed a viscous liquid, it did not form a stable oleogel until after 2.5 months of storage, coinciding with an increase in the size and alteration in the crystal morphology. This study revealed that sophorolipid-derived hydroxy fatty acids were able to form oleogels at fairly low additive concentrations. Thus, sophorolipids may serve as a new source of biobased hydroxy fatty acids that could be useful for replacing saturated fats in food and may also be useful in cosmetics and pharmaceuticals. While hydrogenated Lesquerella seed oil did not form oleogels right away, it showed interesting crystal morphology and polymorphic transformation leading to gelation that deserves further study.

Technical Abstract: Sophorolipids (SL) are glycolipids composed of a sophorose head-group linked to a hydroxy-fatty acid tail which makes them a potential source of structurally unique biobased hydroxy fatty acids. Furthermore, Lesquerella is a native southwestern plant that has been commercially cultivated as a replacement for castor seed oil due to high seed oil concentrations of 14-hydroxy-eicosenoic acid (14-OH-C20:1c11). In this study, SL-derived hydroxy fatty acids and methyl esters containing 15-hydroxy-palmitic acid (15-OH-C16), 17-hydroxy-stearic acid (17-OH-C18), 15-hydroxy-palmitic acid methyl ester (15-OH-C16ME), 17-hydroxy-stearic acid methyl ester (17-OH-C18ME), and 13-hydroxy-behenic acid methyl ester (13OH-C22ME) were obtained from the SL produced by two yeast strains. In addition, hydrogenated Lesquerella oil (HLO) was made with ~62% 14-OH-eicosanoic (C20) acid (14-OH-C20). These materials, along with 12-hydroxy-stearic acid (12-OH-C18) as a standard for comparison were used to make soybean oil oleogels, and their properties determined. The minimum gelation concentration (MGC) of 12-OH-C18 was 1% (w/w), while the MGC of 15-OH-C16 and 17-OH-C18 were 5% and 10%, respectively. The MGC for 15-OH-C16ME was 5%, but 17-OH-C18ME was unable to form a stable gel at concentrations up to 10%. HLO formed a viscous solution rather than an oleogel, but its crystal morphology underwent a large transformation during storage over a 2.5-month period, after which it was able to form a stable gel. SL-based hydroxy fatty acids were able to form oleogels in soybean oil and have the potential to be considered as a new source of low molecular weight oleogelators as well as biobased hydroxy fatty acids.