Graduation Year

2020

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Chemical Engineering

Major Professor

Aydin A. Sunol, Ph.D.

Co-Major Professor

George P. Philippidis, Ph.D.

Committee Member

Piyush Koria, Ph.D.

Committee Member

Mark Jaroszeski, Ph.D.

Committee Member

Abdul Malik, Ph.D.

Committee Member

Rasim Guldiken, Ph.D.

Keywords

algae, Cultivation, extraction, lipids, green cosmetics

Abstract

Algae, photosynthetic aquatic organisms, have recently caught the attention of the food, cosmetic, pharmaceutical, and nutraceutical industries due to the variety of natural compounds in their cellular bodies such as carbohydrates, lipids, and proteins. Specifically, microalgae-derived natural compounds such as phospholipids are extensively utilized in cosmetics as part of liposome formers, emulsifiers, solubilizers, and wetting agents. Although phospholipids are currently extracted from food sources, this practice raises sustainability concerns. Hence, growing microalgae on the provision of macronutrients such as nitrates and phosphates will serve as a more sustainable source of the several specific phospholipids such as phosphatidylcholine (PC), phosphatidyl-ethanolamine (PE), phosphatidylinositol (PI), and lyso-phosphatidylcholine (Lyso-PC).

The effect of nitrate-nitrogen and phosphate-phosphorus provision on phospholipid productivity were assessed using the marine microalgae species Nannochloropsis oculata (N. oculata) cultivated batch-wise in a 3.5-L vertical flat panel photobioreactor (VFPPBR) at three macronutrient mass ratios, NO3-/PO43- = 15, NO3-/PO43- = 5, and NO3-/PO43- = 1. Using the Folch organic solvent extraction method and 31P – NMR spectroscopy, phospholipid productivity was found to be the highest at the ratio of 1, indicating that phosphate-rich cultivation boosted phospholipid production within the cellular bodies. After the macronutrient-rich growth phases, the microalgae cultures were subjected to macronutrient starvation to test whether phospholipid productivity would be further boosted by enhancing total lipids, a common practice reported in literature. Results showed in this study that macronutrient starvation did not help boost phospholipid productivity: hence it was concluded that the microalgae biomass should be harvested on the early stage of stationary growth phase. Also, maintaining a NO3-/PO43- mass ratio between 5 and 1 while fixing nitrate at a predetermined value is deemed to be optimum for exploiting microalgae for large-scale production of phospholipids.

In addition, continuous cultivation of N. oculata in the modified VFPPBR at two macronutrient ratios, R=15 and R=5, was investigated to explore its advantages. The results demonstrated that as long as the macronutrient mass ratio stayed around 15 and the cultivation duration was long enough after a steady-state had been reached, maximum overall microalgal biomass productivities would be attained and deemed superior to batch-wise cultivated microalgal biomass productivities.

Finally, semi-preparative scale high-performance liquid chromatography (Semi-Prep HPLC) separation technology was employed in order to isolate specific microalgal phospholipid compounds from microalgal lipid extracts. Isolating four of the specific phospholipids (PC, PE, PI, and Lyso-PC) was successful and resulted in high separation yields for each phospholipid compound. A COMSOL Multiphysics® simulation model was developed to estimate the optimum concentrations of analytes within the microalgal lipid extracts, which indicated that there is room for more efficient separation.

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