UC Davis

The rising global population, coupled with environmental stresses induced by climate change, is exerting extreme pressure on production systems globally, driving the quest for sustainable sources of macro-and micronutrients intended for industrial applications. Macroalgae, or seaweeds, are macroscopic marine algae that hold promise as a sustainable biomass resource with a wide range of potential industrial applications. Their composition, wide availability, and growth-associated environmental benefits (i.e., carbon sequestration, support to fishery habitats, and reduced dependence on freshwater, arable land, and fertilizer) make them of particular interest. 

These marine organisms contain a range of desirable compounds with the potential for use in human nutrition, animal feed, production of bio-stimulants or fertilizers for plant growth, biotherapeutic, cosmetic, and food applications. Included in these compounds are carbohydrates (laminarin, fucoidans, alginate), lipids, proteins, and phenolics, which exhibit functional attributes such as emulsification and gel formation properties, as well as bioactive properties such as antioxidant, antihypertensive, and antidiabetic effects. Full utilization of macroalgae’s potential hinges on the development of sustainable bio-guided downstream processing strategies which make use of structure and functionality as the benchmark to develop processes capable of both maximizing the extractability of its diverse compounds and safeguarding the functional and biological attributes inherent in the algae extracts. The major goal of this research project was to uncover the effects of pivotal processing conditions (i.e., biomass-to-water ratio, temperature, pH, time) and various extraction methods (i.e., aqueous, enzymatic, and microwave-based extractions) on the extractability, structural composition, and functional/biological properties of the major compounds of the giant kelp species Macrocystis pyrifera, typically found in the Pacific Ocean. The overarching aim was to develop effective and sustainable extraction methods founded on the interplay between structure and functionality to produce algae compounds with the desired properties.

Chapter 1 delves into the current state of the brown macroalgae industry and prevailing extraction methods. It encompasses discussions on environmentally sustainable practices employed in cultivation, harvesting, and industrial integration. This chapter also delves into the intricate structural makeup of brown macroalgae and the multifaceted functional and biological attributes inherent in their compounds. The final section of the chapter offers an in-depth overview of the cutting-edge methodologies employed in the extraction of compounds from macroalgae. 

In Chapter 2, the aqueous extraction process (AEP) and enzyme-assisted aqueous extraction process (EAEP) are explored as sustainable, environmentally friendly strategies for extracting the diverse compounds within the macroalgal matrix. A series of experiments beginning with the AEP investigating pH, biomass-to-water ratio (BWR), time, and temperature were used to guide the EAEP. Based upon yield of various components of interest (laminarin, fucoidan, alginate, protein, phenolics), extraction conditions were selected for more in depth analysis looking into their structure (amino acid composition, phenolic profile, monosaccharide and oligosaccharide analysis, alginate characterization by FTIR) and bioactivity (antioxidant, antidiabetic, antihypertensive). These analyses revealed the mechanisms by which enzymes enhance the degradation of the macroalgal matrix, thereby increasing the extractability of intracellular components (i.e., laminarin, intracellular proteins and peptides), and resulting in the production of extracts with higher antihypertensive activity. 

Chapter 3 builds upon the results of Chapter 2 by investigating the impact of integrating microwave processing with the AEP and EAEP. Through a series of stepwise experiments, favorable microwave-assisted extraction (MAE) and microwave-enzyme-assisted extraction (MEAE) conditions were determined based upon yields. Dipole-interactions caused by the microwave resulted in rapid breakdown of the macroalgal matrix resulting in high yields with extractions as short as 15 minutes. As in chapter 2, these favorable conditions underwent more in-depth analysis. 

Conventional macroalgae processing strategies are deemed unsustainable because they use hazardous solvents. The series of studies detailed in this report outlines the potential of sustainable processing strategies for giant kelp, an important step for maintaining the environmentally friendly status of these marine organisms. Of special note is the ability of the MAE to produce comparable extracts (i.e., similar yield and activity) in 15 minutes, in contrast to the AEP, which requires 6 hours. This highlights the potential for industrial scale use, as it enables multiple extractions to be performed daily. Additionally, these studies shine light on the composition of Macrocystis pyrifera, providing more detail than previously seen in literature. While this giant kelp may be low in phenolics, its other functional and bioactive components render it highly intriguing. Of note is the high antidiabetic activity of all extracts. These insights, along with future work on scaling up the extraction strategies discussed herein, underscore the potential of sustainable and bio-guided downstream processing strategies to introduce this sustainable feedstock to industries worldwide.