Selecting phytohormone treatments through Grey Relational and Principal Component Analysis for microalgal bioactives production

Microalgae represent a promising sustainable source of high-value compounds including carotenoids and omega-3 fatty acids, which have applications in nutraceuticals, pharmaceuticals, cosmetics, and functional foods. Fucoxanthin, a xanthophyll carotenoid, exhibits anti-obesity, antidiabetic, antioxidant, and anti-inflammatory properties, while omega-3 fatty acids like docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are essential nutrients particularly important in aquaculture and human health. However, commercial production faces challenges including low productivity and high processing costs. This study aimed to evaluate the effects of twelve phytohormones (auxins, cytokinins, gibberellins, abscisic acid, jasmonates, and salicylic acid) on biomass productivity, fucoxanthin content, and fatty acid profiles of three biotechnologically relevant microalgae: Chrysochromulina rotalis, Heterosigma akashiwo, and Entomoneis sp. Phytohormones were tested at concentrations in the range 0.5–30 mg L⁻¹ (100 mg L⁻¹ in the case of ethanolamine). Grey Relational Analysis (GRA) and Principal Component Analysis (PCA) revealed species-specific optimal treatments: salicylic acid (30 mg L⁻¹) for C. rotalis increased fucoxanthin by 43 % and omega-3 fatty acids by 36 %; gibberellic acid (30 mg L⁻¹) for H. akashiwo improved fucoxanthin by 27 % and EPA by 25 %; and 6-benzylaminopurine (15 mg L⁻¹) for Entomoneis sp. enhanced fucoxanthin by 34 % and total fatty acids by 28 %. These treatments demonstrated significant improvements in both biomass productivity and high-value metabolite accumulation with potential cost-effectiveness. The molecular mechanisms underlying these improvements involve complex interactions between hormone signaling pathways, primary metabolism, and secondary metabolite synthesis. Further exploration of wastewater-derived phytohormones could reduce production costs and enhance sustainability in microalgae-based bioprocesses.