Abstract
BackgroundMicroalgae are considered as a source of low pollution and renewable fuel due to their ability to synthesize an abundance of lipids. Conventional methods for lipid quantification are time-consuming and chemically contaminated, while spectroscopic method combined with mathematical model is much more attractive due to its ability of qualitative and quantitative analysis of material composition, in this sense, terahertz technology provides not only timely and non-destructive testing without chemical pollution, but also provides information on the functional group vibration mode and structure of the measured components. Therefore, terahertz technology is utilized in our investigation and proposed for microalgae metabolism detection.ResultsThe aim of this study was to use terahertz spectroscopy to observe lipid content in Scenedesmus obliquus (S. obliquus). We collected the THz spectra of S. obliquus which were cultivated under nitrogen stress and terahertz spectroscopy was used to analyze changes in substance components (lipids, proteins, carbohydrates and β-carotene). The PLS algorithm was used to model the terahertz data to distinguish the different lipid content of S. obliquus under nitrogen stress. The correlation coefficient of the prediction results of the lipid characteristic band modeling was above 0.991, and the root mean square error was less than 0.132. It indicated that terahertz technology can be used to discriminate S. obliquus cells under different nitrogen stress effectively. The correlation between the terahertz characteristic peak (9.3 THz) and the total lipid content determined by gravimetry reaches 0.960. The final results were compared with the commonly used spectroscopic methods for lipid observation (Raman spectroscopy).ConclusionsIn this article, we demonstrated the effectiveness of terahertz spectroscopy to monitor changes in microalgae lipid content under nitrogen stress. Terahertz spectroscopy is more suitable for industrial production or ordinary laboratories which require intermediate result with low-frequency screening. When quantifying microalgae lipids, the constraint of terahertz spectroscopy is far less than that of Raman spectroscopy, and it is easier for operator to accurately quantify microalgae lipid. In addition, it is still in early stage for the study of microalgae using terahertz spectroscopy technology, there is still much potential for us to explore.
Highlights
Microalgae are considered as a source of low pollution and renewable fuel due to their ability to synthesize an abundance of lipids
We used gas chromatography–mass spectrometry (GC–MS) to analyze the proportion of fatty acids in lipids and the variation in the fatty acid profile of S. obliquus in stress culture are summarized (Table 1)
The proportion of saturated fatty acids (SFA) has reduced by 45% and the proportion of Unsaturated fatty acids (UFA) has increased by 12% from day 0 to 8
Summary
Microalgae are considered as a source of low pollution and renewable fuel due to their ability to synthesize an abundance of lipids. When the biodiesel is produced by microalgae, the content of lipids and types of fatty acids in cells are the important considerations [6]. In this process, the screening of high-quality microalgae and the monitoring of culture process are important for the efficient conversion of lipids. The conventional methods used for the quantitative analysis of microalgae lipids, e.g., gas chromatography–mass spectrometry (GC–MS) can accurately analyze lipid components, but the detection is time-consuming, and the sample preparation process is complicated, in the meantime it cannot analyze the lipid metabolism process in cells. It is necessary to find a fast and non-destructive method for detecting lipid content
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