Determination of intracellular lipid and main fatty acids of Nannochloropsis oceanica by ATR-FTIR spectroscopy

Fatty acid profile was one of the important characteristic parameters of edible oil. With the intensification of interest in microalgae as a potential source of edible oil, rapid methods are needed to determine the fatty acid composition of microalgae. Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) was applied to determine the lipid and fatty acid contents of Nannochloropsis oceanica, a species rich in eicosapentaenoic acid. Samples with different intracellular components were obtained by setting different culture conditions (light intensity and nitrogen concentration). In the spectra of FTIR, some characteristic bands for lipids (3025-2800 cm(-1), 1770-1710 cm(-1), 1480-1350 cm(-1)) were identified. Partial least square regression (PLSR) models were developed to predict total biomass, lipid contents, and main fatty acid contents (palmitic acid C16:0, palmitoleic acid C16:1, eicosatetraenoic acid C20:4, eicosapentaenoic acid C20:5). Generally, the prediction ability of the model established with full spectra was slightly better than that of the model established with specific bands. In the optimized model, excellent coefficients of determination (R-2 >= 0.90), both for calibration and prediction, were found for all variables, except for fatty acid C20:4, which was slightly worse (R-2 = 0.8797). The pretreatment methods of samples were further studied. It was found that the acid-heating method (0.1 M HCl, 100 degrees C, 0.5 h) effectively reduced the interference of the carbohydrate in samples, thus improving the measurement of the characteristic fatty acids C20:4 and C20:5 of N. oceanica. This study showed the feasibility of FTIR as a rapid screening method for evaluating biomass and lipid content, especially some special fatty acid profile of microalgae.

Automated summary

The study demonstrates the feasibility of using ATR-FTIR spectroscopy as a rapid screening method for evaluating biomass and lipid content, especially the specific fatty acid profile of microalgae. By analyzing characteristic bands and establishing PLSR models, accurate prediction of the main fatty acid contents in microalgae can be achieved.