[en] Introduction
The aim of this research was to measure the evolution of the protein and lipid fractions during a culture of microalgae. These measures are important to determine the optimal time to harvest biomass. This can vary depending on the development of the biomass (biofuels, feed ...).
Material & Methods
Two microalgae were grown autotrophically for twenty days: Nannochloropsis salina (CCAP 849/3) and Scenedesmus obliquus (CCAP 276/3A) in a 2-liter photobioreactor. 50 mL of the suspension were collected every 2 or 3 days for biomass, extracellular nitrogen, lipids and proteins quantifications.
The protein quantification was performed by the Biuret method with bovine serum albumin as standard; preceded by the extraction of photosynthetic pigments to avoid possible interferences.
The extraction of lipids was carried out by the modified method of Bligh and Dyer by using the couple of solvents chloroform/methanol (1: 1). The total lipid content was quantified by sulfo-phosphovanillin method and the standard used was triolein.
At the end of the culture, several couples of solvents were compared to replace the couple chloroform/methanol by a less harmful one. Algae biomass was lyophilized and the extract was then transesterified with methanolic HCl 3 mol/L before be analyzed by GC-MS and GC-FID.
Results & Discussion
The results showed that the protein content was higher during the exponential phase with a value of 74.2% for Scenedesmus obliquus and 70.4% for Nannochloropsis salina. For the total lipid content, the maximum was reached at the end of culture during the phase of nitrogen deficiency which appears from the 15th day. The lipid content was 13.4% and 28.8% respectively for Scenedesmus obliquus and Nannochloropsis salina.
The couple methyl tert-butyl ether/methanol (10:3) gave similar results to the couple chloroform / methanol. Main FAMEs present in the lipid extract were (16:0) and (18:3).
