Visible/Short-wave near-infrared hyperspectral analysis of lipid concentration and fatty acid unsaturation of Scenedesmus obliquus in situ

Bingquan Chu^a,b,Kai Chen^b, Xiaoxiao Pan^a, Qianying Wu^b, Shiwang Liu^a, Jinyan Gong^a, Xiaoli Li^b

School of Biological and Chemical Engineering, Zhejiang University of Science and Technology, Hangzhou 310023, PR China.

Abstract

Microalgae lipid and its degree of fatty acid unsaturation (DU) have the ability to undergo programmatic changes in response to different environmental and culture conditions. A real-time and reliable approach to monitor the change patterns of lipid-accumulation and DU is crucial for microalgal culture and bioprocess control. In this study, a fast visual and nondestructive method based on visible/short-wave near-infrared hyperspectral imaging (V/SNIR HSI) at 400–1000 nm region was developed to investigate the dynamic changes and content distribution of lipids and DU of Scenedesmus obliquus treated by nitrogen-low stress (0.3 g/L NaNO3, NL) and nitrogen-free stress (0 g/L NaNO3, NF). After collecting the average spectra from the region of interests (ROIs), the competitive adaptive reweighted sampling (CARS) algorithm and the successive projection algorithm (SPA) were applied to pick effective wavebands from the spectral data for the establishment of the lipid concentration and DU estimation models including partial least squares regression (PLSR) and multiple linear regression (MLR). The prediction results show the CARS-PLSR (Rp = 0.9762, RMSEp = 0.0143) and CARS-MLR (Rp = 0.9477, RMSEp = 0.5718) performed the best for lipids and DU of S. obliquus, respectively. Based on the optimal models, the spatial distribution of lipid abundance and DU in liquid suspension were visualized, which could be helpful in exploring the dynamic process of lipid synthesis and DU of S. obliquus. The overall results show that V/SNIR HSI is a promising technique for fast and noninvasively monitoring the lipid-accumulation and its characteristics i.e. DU in situ, and is expected to be applied for efficient and high-quality lipid production in microalgae industries.

Keywords: Hyperspectral imaging, S. obliquus, Lipid, Degree of fatty acid unsaturation, Nitrogen stress.