Lieselot Balduyck

Optimization of a Nile Red method for rapid lipid determination in autotrophic, marine microalgae is species dependent.

Several studies have been conducted to develop rapid methods for quantification of lipid content in microalgae, as an alternative for time consuming gravimetric methods. Different studies showed that lipid staining with Nile Red in whole cell suspensions and subsequently quantification by the use of a spectrofluorometric device is a promising method, but a profound optimization and validation is rare. It has already been proven that the correlation curve for quantification is species dependent, but it has not yet been investigated whether this is also the case for the optimization of the Nile Red assay protocol. Therefore, two autotrophic, marine microalgae, Nannochloropsis oculata and T-Isochrysis lutea, strongly differing in e.g. cell wall structure, were selected in this study to investigate whether optimization of the Nile Red assay is species dependent. Besides this, it was checked for one of these species, Nannochloropsis, whether the lipid content, determined by the Nile Red assay, could indeed be correlated with the neutral and/or total lipid content determined by gravimetric methods. It was found that optimization of the Nile Red assay was strongly species dependent. Consequently, optimization has to be done for each species before using the assay. For Nannochloropsis, a good correlation was found between total and neutral lipid content obtained by the Nile Red assay and by gravimetric methods.

Stability of Valuable Components during Wet and Dry Storage

Microalgae contain several valuable components, such as nutritionally interesting fatty acids and antioxidants. Although much is known about these components in literature, the importance of their stability is often underestimated. However, it has already been shown that storage of microalgal biomass can pose different stability problems, the most important ones being microbiological problems and lipolysis and oxidation of lipids. A crucial step during processing is the drying step, since this reduces the water activity and thus improves the stability of the lipids. However, the drying technique and process parameters being used have a great influence on the stability of the dry product. It has been shown that endogenic antioxidants in microalgae protect the lipids against oxidation, but it also has to be taken into account that this protection can get lost during processing, for example, during biomass drying and oil purification. Further research on stability of valuable components is thus necessary before high quality microalgal products can be produced and applied in different industries.