Monitoring of eicosapentaenoic acid (EPA) production in the microalgae Nannochloropsis oceanica

Marta Sá,Narcís Ferrer-Ledo,Rene Wijffels,João G Crespo,Maria Barbosa,Claudia F Galinha

doi:10.1016/j.algal.2019.101766

Abstract

With the increase awareness for a healthier food regime and greener environmental processes, microalgae are being looked as a solution for a sustainable production of polyunsaturated fatty acids, such as omega-3 eicosapentaenoic acid (EPA). Nannochloropsis oceanica is an oleaginous microalga, well-known for the ability of EPA accumulation, although higher lipid productivities are still required to make the process competitive. Therefore, three cultivation parameters were tested in the present work (temperature, light cycles and nitrogen supply) in order to study the EPA profile in the polar and neutral fractions of the cells. In addition, an online monitoring tool based on a fluorescence spectroscopy technique was developed with the aim of increasing process knowledge at real time. The results of this work show that nitrogen depletion induces the highest variability in EPA accumulation in the neutral fraction (triacylglycerols). However, to increase the EPA content in the polar fraction a different strategy needs to be implemented, such as decreasing the cultivation temperature or the light available per cell. Chemometric models were developed through PCA (Principal Component Analysis) and PLS (Projection to Latent Structures), using only fluorescence spectra as inputs, enabling the monitoring of EPA in both fractions separately. High explained variance was observed (above 85%) in both fractions, with R2 above 0.81 and slopes above 0.93 for both validation and training data sets. Lower values of cross-validation and prediction errors were observed (between 0.29 and 0.49% g/gDW). The results obtained show that fluorescence spectroscopy is a powerful technique for online monitoring of non-fluorophore molecules, such as EPA, in complex process like microalgae cultivation.

Highlights

The importance of long-chain polyunsaturated fatty acids (PUFA), such as omega-3 (ω-3), has been extensively studied in the past years with the increased concern in the western world for a better and more equilibrated food regime
To evaluate the effect of different stress factors on eicosapentaenoic acid (EPA) accumulation, the fatty acid profile of the culture was compared in the beginning of the “stress phase”, by nitrogen depletion or decrease of temperature, until the end of the batch, in a total of 4 days for 24 h light experiments, and 10 days for d/n cycle experiments
For the first time, fluorescence spectroscopy coupled with chemometric tools was used to monitor EPA in microalgae biomass

Summary

Introduction

The importance of long-chain polyunsaturated fatty acids (PUFA), such as omega-3 (ω-3), has been extensively studied in the past years with the increased concern in the western world for a better and more equilibrated food regime. This class of lipids proved to have several pharmaceutical and nutraceuticals applications [1,2,3] and since they are essential for humans and most animals, and neither have the capacity to produce them, food and feed are considered the main vehicles for their supply [4]. There is some ongoing discussion about which of these two fractions is the best carrier of the EPA in food and feed, with some authors defending the TAG fraction [2] and others the PL fraction [10]

Methods

Results

Conclusion