Lieve M. L. Laurens

The aliphatic chains of fatty acids are the most prominent and potentially the highest value fuel precursor constituents of algal biomass, and thus accurately quantifying the algal biomass total fatty acid content is a prerequisite for comparing algal strains, growth conditions, and processes. Direct, acid-catalyzed transesterification of whole microalgal biomass is a simple, effective, strain-agnostic, and widely used method to determine the fatty acid content in whole algal biomass, with the precision needed to detect small but significant differences between strains. Such a direct transesterification procedure typically covers the following steps: first, solubilizing the lipids in the biomass matrix and then liberating the fatty acids to make these available for catalytic transesterification to fatty acid methyl esters (FAMEs), subsequent extraction into hexane, and then quantification by gas chromatography. The method we describe here requires less than 10 mg of biomass per sample and is considered high-throughput and highly accurate.

The carbohydrate fraction of microalgal biomass is complex and consists of a combination of neutral, acidic, amino sugars, and sugar alcohols. These carbohydrate amalgamations can be difficult to accurately quantify with the most analytical carbohydrate determination techniques. The method described here provides a straightforward two-step sulfuric acid hydrolysis followed by soluble carbohydrate quantification by either a spectrophotometric method (based on aldehyde functional group derivatization), for an overall combined monomeric sugar concentration determination, or liquid chromatography, specifically high-performance anion exchange method, for a more specific monomeric sugar profile.

Accurately determining protein content is important in the valorization of algal biomass in food, feed, and fuel markets, where these values are used for component balance calculations. Using elemental nitrogen content to calculate protein concentration in the biomass is a well-accepted and widely practiced method and depends on developing a validated and appropriate nitrogen-to-protein conversion factor. The methodology reported here covers the quantitative assessment of the total nitrogen content of algal biomass and a description of the methodology that underpins the accurate de novo calculation of a dedicated nitrogen-to-protein conversion factor.

In order to fully exploit algae carbon assimilation for fuels, a preqrequisite is high photosynthetic efficiency and carbon conversion to fuel precursors. In the context of this collaborative project between NLR and EMRE we aim to address aspects of both the biological constraints around photosynthesis-driven carbon assimilation flux as well as elements that bridge the gap between laboratory cultivation and meaningful outdoor deployment, building on the unique capabilities of NLR and EMRE’s algae bioengineering teams. The goal of this work is to improve our understanding of key cellular biochemistry, mass cultivation, and biomass conversion constraints that presently limit the potential bio-oil yield. The proposed first phase of this work will focus on biomass growth improvements by testing hypotheses for alleviating identified metabolic and photophysiological bottlenecks. The results of this work could inform decisions by stakeholders (e.g., industry, community, investors) on the design and deployment of a sustainable biofuel supply chain from algae.

To render the resulting biomass more attractive and amenable for utilization as the basis for low-carbon intensity bioproducts, single-celled algae need to be biochemically and metabolically poised to assimilate and store the delivered carbon in the fastest and most efficient manner. Accelerating biochemical carbon storage, as primarily carbohydrates or lipids, is critical to achieve the high carbon capture potential that is assigned to algae. To guide strain optimization and engineering for maximizing carbon capture and storage, it is essential to elucidate the link between carbon metabolism and biomass composition. Most published metabolomics work in algae remains largely restricted to ideal and simplified environmental conditions in model organisms, thereby limiting their translation to outdoor implementation. In this work, we utilize ¹³ C isotopic labeling to characterize distinct intracellular metabolic fluxes before, during, and after nitrogen depletion-induced compositional shifts in Scenedesmus obliquus UTEX 393. The results indicate that a transition to carbohydrates is characterized by diverting flux to starch instead of replenishing the Calvin cycle for CO ₂ fixation whereas the subsequent transition to lipids is fueled by NADPH produced by upregulating the phosphoenolpyruvate carboxylase (PEPC)–malic enzyme (ME) cycle flux. Our work highlights bottlenecks to carbohydrate- and lipid-rich biomass and can guide implementable strategies to control the fate of fixed carbon in S. obliquus .

This white paper summarizes the historical progress and perspectives on future opportunities for Combined Algae Processing (CAP), a conversion approach centered around fractionating microalgae biomass and producing a slate of fuels and products. We discuss the critical challenges associated with the commercialization of algal biofuels and demonstrate how the CAP approach is uniquely suited to overcome these barriers. The versatility of applying CAP to various sources of algae is highlighted along with conversion to various fuels and product options.

Zhi-Hua Liu, Bing-Zhi Li, Joshua Yuan, James Clark, Vânia Zuin Zeidler, Lieve Laurens, Arthur Ragauskas, João Coutinho and Buxing Han introduce this Green Chemistry themed collection on biomass conversion and utilization.

Polysaccharides make up a large portion of the organic material from and in marine organisms. However, their structural characterization is often overlooked due to their complexity. With many high-value applications and unique bioactivities resulting from the polysaccharides’ complex and heterogeneous structures, dedicated analytical efforts become important to achieve structural elucidation. Because algae represent the largest marine resource of polysaccharides, the majority of the discussion is focused on well-known algae-based hydrocolloid polymers. The native environment of marine polysaccharides presents challenges to many conventional analytical techniques necessitating novel methodologies. We aim to deliver a review of the current state of the art in polysaccharide characterization, focused on capabilities as well as limitations in the context of marine environments. This review covers the extraction and isolation of marine polysaccharides, in addition to characterizations from monosaccharides to secondary and tertiary structures, highlighting a suite of analytical techniques.