Evaluation of toxicity and biochemical characterisation of a microalgal diatom
Authors:   , Beekrum Lamees 
Published: June 2023

One ofthe critical challengesthat we face in the 21st century isthe need to feed an ever-increasing human population with increasingly limited natural resources. Microalgae have emerged as a potentialsolution for global food security as a sustainable biological food source for humans due to their nutrient-rich composition, particularly rich protein and bioactive compoundsthat provide potential benefits for human health. By establishing microalgae as a new food platform, we can increase the supply of these essential productsto address global demandsin a more efficient and environmentally sustainable way. These under-exploited organisms have been consumed in the human diet for thousands of years. Microalgae cultivation does not compete with land and resources required for traditional crops and has a superior yield compared to terrestrial crops. Diatoms are a major group of microalgae in the phytoplankton community and have the potential to be engineered into cell factoriesforthe sustainable production of bioactive compoundsin food and nutraceutical industries. This study aimed to characterise a rapidly growing marine diatom in terms of its toxicity and biochemical profile. This was done by evaluating the safety profile and biochemical composition, characterising the soluble protein, and investigating the carbohydrate profile with specific emphasis of β-glucan and its effect of cardioprotective properties on ferric-induced oxidative cardiac injury in a rat model. Based on Basic Local Alignment Search Tool (BLAST) analysis, the strain showed the closest similarity to Amphora sp. (JF834543.1) with 99.5% and istherefore represented as Amphora sp., accession number MW721231. The bacterial reverse mutation assay found no evidence of mutagenicity on the methanolic, aqueous, and hexane extracts of Amphora sp. and was found to exert low levels of cytotoxicity against Peripheral Blood Mononuclear Cells (PBMC). A 28- day acute oral toxicity assessment on male Wistar rats showed an absence of adverse effects and mortality in the rats. The biomass exhibited a low lipid profile, modest protein content, notable amino acid content, and excellent carbohydrate and mineral content. Results of this study for antioxidant assays displayed low to moderate activities. Protein extracted using three-phase partitioning (TPP) treatment showed that the protein concentration and total amino acid content were substantially higher in the protein-enriched biomass extract when compared to the dried biomass. The solubility of the protein-enriched biomass extract increased with the increase in pH within the range of pH 2 to pH 12. The biomass consisted of a simple monosaccharide profile comprising glucose, rhamnose, and mannose, and a β-glucan content of approximately 9%. The cardioprotective properties ofthe β-glucan extract on ferric-induced oxidative cardiac injury did not improve the glutathione (GSH) level significantly, it led to increased superoxide dismutase (SOD) and catalase activities, while depleting malondialdehyde (MDA), NO (nitric oxide), low-density lipoprotein cholesterol levels, and simultaneously elevating triglycerides and high-density lipoprotein (LDL) cholesterol levels. GC-MS analysis revealed a complete depletion of the lipid metabolites. Our results advocate the protective capabilities of the β-glucan extract against ferric-induced oxidative cardiac injury as portrayed by its ability to stall oxidative stress and modulate cardiac lipid metabolism while inhibiting the acetylcholinesterase and lipase activities. These results display that the β-glucan extract could be utilized as an alternative for the development of nutraceuticals for maintaining cardiac health. The diversity of food bioactive molecules obtained from microalgae makes these microorganisms a bioresource with full potential of exploitation in the food industry. The richness of compounds in microalgae can contribute to develop an algal-based food industry, focusing on producing and utilizing microalgae for innovative functional food products. Overall, this study demonstrated the potential utilization of the diatom, Amphora sp. as a potential ingredient and nutraceutical in foods.