A research team led by the University of Nebraska-Lincoln and Huazhong Agricultural University has identified two new fatty acids — named Nebraskanic acid and Wuhanic acid — in the seed oil of the Chinese violet cress (Orychophragmus violaceus), a flowering plant native to central China. The discovery is reported in the journal Nature Plants.
Top: flowers and seeds of the Chinese violet cress (Orychophragmus violaceus). Bottom: the structures of mono and diunsaturated Nebraskanic (1) and Wuhanic (2) fatty acids; segments of the methyl wuhanate (2a) with fully assigned 13C and 1H resonances are denoted by red boxes and numbered carbons. Image credit: Li et al, doi: 10.1038/s41477-018-0225-7.
Fatty acids represent the primary components of vegetable oils, which are best known for their role in the kitchen but have also found use in biodiesel fuels, lubricants and other industrial applications.
The structure of the fatty acids housed within an oil help dictate both its health effects and industrial merits.
Most off-the-shelf vegetable oils, such as canola or soybean oil, contain the same five fatty acids. Those conventional fatty acids all contain either 16 or 18 carbon atoms and feature similar molecular structures.
By contrast, the newly-discovered Nebraskanic and Wuhanic acids rank among a class of ‘unusual’ fatty acids that contain fewer or more carbon atoms — both have 24 — and uncommon molecular branches that stem from those carbons.
“Whether conventional or unusual, all known fatty acids generally obey the same instruction manual: they add two carbon atoms at the end of a four-step biochemical cycle, then continue doing so until assembly is complete,” said study lead author Professor Edgar Cahoon, a researcher with Huazhong Agricultural University and the University of Nebraska-Lincoln.
“But the Nebraskanic and Wuhanic acids seem to go off-book in a way rarely if ever seen outside of certain bacteria.”
“Both acids appear to follow the traditional script until adding their 10th pair of carbon atoms.”
“After reaching that milestone, though, the acids appear to skip the last two steps of the four-step cycle, twice cutting short the routine to accelerate the addition of the 11th and 12th carbon pairs.”
The process also leaves behind an oxygen-hydrogen branch, or hydroxyl group, in the fatty acid chain.
“We sort of had an idea of what the biochemical pathway might be, but it was completely different than what’s in the biochemistry textbooks,” Professor Cahoon said.
“These fatty acids also seem to be stored in the violet cress seeds in a way that we haven’t quite seen before for other vegetable oils.”
“We believe that the fatty acids are linked to one another through the hydroxyl groups to form a complex matrix of fatty acids, which is quite different from how fatty acids are arranged in a typical vegetable oil.”
That unique assembly and structure could account for the corresponding oil’s superior performance as a lubricant.
Compared with castor oil, the violet cress oil reduced friction between steel surfaces by 20% at 77 degrees Fahrenheit (25 degrees Celsius) and by about 300% at 212 degrees Fahrenheit (100 degrees Celsius).
“When we saw the long-chain molecules and their arrangement, we knew the oil found in Chinese violet cress seeds would make an excellent lubricant,” said study co-author Dr. Diana Berman, a researcher at the University of North Texas.
“This oil doesn’t just have the potential to supplement or replace petroleum-based oil; it can also replace synthetics. It is a renewable solution to a limited-resource problem.”
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Xiangjun Li et al. Discontinuous fatty acid elongation yields hydroxylated seed oil with improved function. Nature Plants, published online August 27, 2018; doi: 10.1038/s41477-018-0225-7
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