Development and validation of time-domain 1H-NMR relaxometry correlation for high-throughput phenotyping method for lipid contents of lignocellulosic feedstocks

Authors: MAITRA, SHRADDHA - University Of Illinois; Dien, Bruce; LONG, STEPHAN - University Of Illinois; SINGH, VIJAY - University Of Illinois

Submitted to: Global Change Biology Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/2021
Publication Date: 5/14/2021
Citation: Maitra, S., Dien, B., Long, S.P., Singh, V. 2021. Development and validation of time-domain 1H-NMR relaxometry correlation for high-throughput phenotyping method for lipid contents of lignocellulosic feedstocks. Global Change Biology Bioenergy. 13(7): 1179-1190. https://doi.org/10.1111/gcbb.12841.
DOI: https://doi.org/10.1111/gcbb.12841

Interpretive Summary: Vegetable oil in the northern hemisphere is produced largely from seeds. While enough is grown to supply the food market, the supply of oil falls far short of that needed for transportation, which includes trucks and jets. ARS researchers are working to increase vegetable oil harvests by developing plants that can be used for second cropping, yield more oil on existing farmland (e.g. than soya), or that can be grown on land too poor for growing food crops. For example, sugarcane is a very productive crop and if the plant could be redesigned to funnel the sugars it produces into oil, it might be able to produce more oil per hectare than traditional oil seed crops. Using state of the art genomic plant breeding tools this approach has recently become feasible. However, making this a reality will require the ability to measure the oil contents of 1000s of plants. Traditional methods are tedious and use hazardous chemicals. Here we describe a method adapted from the traditional seed oil industry that is chemical free, non-destructive, and that takes less than a minute per sample. The method uses an instrument called a low-resolution nuclear magnetic residence spectrophotometer. While the name and the physics are complicated, the important part is that the method relies on a relatively inexpensive bench top instrument that requires little training and that will literally last for decades. We have gone beyond the standard protocols and have acquired additional information from the instrument that also allows us to judge how the oil is stored in the sample; either loosely or tightly bond within the plant. Finally, the method has also been applied to samples processed for oil removal. This paper will be of interest to the instrument maker looking for future markets, the vegetable oil processor wondering what is on the horizon, and to the aviation and trucking industries seeking future low-carbon substitutes for mineral based fuels.

Technical Abstract: The bioenergy crops like energycane, miscanthus and, sorghum are being genetically modified using state of the art synthetic biotechnology techniques to accumulate energy-rich molecules such as triacylglycerides (TAGs) in their vegetative cells to enhance their utility for biofuel production. The analysis of in-situ lipid contents amid bioprocess involves time-intensive steps of sample preparation and extraction with chemical solvents subsequent to each pretreatment procedure. Therefore, in the present study, we have devised a proton nuclear magnetic resonance (1H-NMR) method for single-step, non-invasive, and chemical-free characterization of in situ lipids in untreated and pretreated cellulosic biomass. The systematic evaluation of NMR relaxation time distribution provided insight into the proton environment associated with the lipids in the biomass which resolved two distinct populations of proton molecules i.e., bound and free oil based on their ‘molecular tumbling’ rate. T1T2 correlation spectra facilitated the resolution of the influence of various pretreatment procedures on the chemical composition of molecular and local 1H population in each sample. Furthermore, we show that hydrothermally pretreated biomass is suitable for direct NMR analysis unlike dilute acid and alkaline pretreated biomass which needs an additional step for neutralization.