# Biochemical Characterization of Lipids, Proteins, and Polysaccharides from the Marine Diatom Phaeodactylum tricornutum Cultivated in Pilot-Scale Photobioreactors

## TL;DR

This study characterizes the biochemical composition of the marine diatom Phaeodactylum tricornutum, cultivated at a large scale, focusing on its lipids, proteins, and polysaccharides.

## Contribution

The study identifies novel lipid structures and confirms the high nutritional and antioxidant potential of P. tricornutum biomass.

## Key findings

- P. tricornutum biomass contains 24.5% lipids, 37.8% protein, and 19.4% carbohydrates with a high energy content of 19.8 MJ/kg.
- Novel sulfoquinovosyl diacylglycerol (SQDG) and sulfoquinovosyl monoacylglycerols (SQMGs) were identified in P. tricornutum for the first time.
- The algal biomass showed high protein digestibility (89% for whole biomass and 77% for protein isolate) and exhibited antioxidant properties.

## Abstract

Phaeodactylum tricornutum was cultivated in a 1000 L photobioreactors using f/2 medium. The resulting algal biomass contained 24.5% lipids, 37.8% protein, 19.4% carbohydrates, and had a gross energy content of 19.8 MJ/kg. These components were sequentially extracted. The ultra-high performance liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS) analysis of lipids revealed 35 triacylglycerols, a wide range of galactolipids and phospholipids including a novel sulfoquinovosyl diacylglycerol (SQDG), namely SQDG(C16:1/C24:0), characterized by mass fragmentation analysis. Additionally, three sulfoquinovosyl monoacylglycerols (SQMGs) with C14:0, C16:0, and C16:1 fatty acyl chain were detected in P. tricornutum for the first time. Fatty acid analysis further confirmed that P. tricornutum is an excellent source of ecosapentaenoic acid, which is predominantly present in triacylglycerol and glycolipid forms. CombiFlash chromatography allowed for the separation of monogalactosyldiacylglycerols, digalactosyldicylglycerols, SQDGs and phosphatidycholines, and their structure were confirmed by NMR spectral analysis. Fucoxanthin was the major carotenoid, and the study showed all essential amino acids required for humans and fish were present in it. A two-phase in vitro gastric/pancreatic digestibility assay showed high protein digestibility for both whole biomass (89%) and protein isolate (77%). Monosaccharide analysis showed that polysaccharides extracted by EtOH precipitation after alkaline extraction and by hot water extraction contained similar monomers with different relative intensities. Protein isolates and polysaccharides exhibited antioxidant properties.