Abstract
Attenuated total reflection–Fourier transform infrared (ATR–FTIR) spectroscopy is a simple, cheap, and fast method to collect chemical compositional information from microalgae. However, (semi)quantitative evaluation of the collected data can be daunting. In this work, ATR–FTIR spectroscopy was used to monitor changes of protein, lipid, and carbohydrate content in seven green microalgae grown under nitrogen starvation. Three statistical methods—univariate linear regression analysis (ULRA), orthogonal partial least squares (OPLS), and multivariate curve resolution-alternating least squares (MCR–ALS)—were compared in their ability to model and predict the concentration of these compounds in the biomass. OPLS was found superior, since it i) included all three compounds simultaneously; ii) explained variations in the data very well; iii) had excellent prediction accuracy for proteins and lipids, and acceptable for carbohydrates; and iv) was able to discriminate samples based on cultivation stage and type of storage compounds accumulated in the cells. ULRA models worked well for the determination of proteins and lipids, but carbohydrates could only be estimated if already determined protein contents were used for scaling. Results obtained by MCR–ALS were similar to ULRA, however, this method is considerably easier to perform and interpret than the more abstract statistical/chemometric methods. FTIR-spectroscopy-based models allow high-throughput, cost-effective, and rapid estimation of biomass composition of green microalgae.
Highlights
Microalgae are photosynthetic microorganisms able to convert water and carbon dioxide into valuable organic molecules by means of sunlight
The biomass of six natural Nordic microalgal strains and a culture collection strain exposed to N-starvation was analyzed after classical extraction and compared to data received by ATR–Fourier transform infrared (FTIR) spectroscopy
While the classical extraction of proteins was relatively fast and easy to perform and gave accurate results, methods to extract lipids and carbohydrates were more laborious and involved error-prone critical steps
Summary
Microalgae are photosynthetic microorganisms able to convert water and carbon dioxide into valuable organic molecules by means of sunlight. Thanks to fast growth rates (doubling times in the order of hours) as well as minimal water and nutrients requirements, microalgal cultivation has high industrial and commercial potential for the sustainable production of biomass-derived fuels and chemicals, combined with the possibility of wastewater remediation and CO2 mitigation [1]. A wide range of algae-based products are already used in various sectors, including bioenergy, food and feed, green chemicals, and even cosmetics and therapeutics [2]. Amino acids and proteins can be supplied as high nutritional value ingredients in the human diet and animal feed [3,4,5], and used as organic biofertilizer to sustain crop productivity and preserve soil fertility [6,7]. Carbohydrates, including starch and polysaccharides, can be transformed into fermentable sugars for bioethanol production [8], used as emulsion stabilizer and bio-coagulant or as precursors for synthetic rubber and bioplastic
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