Effects of sustained trace element nutrient stress on biomass, bioactive compounds, lipidomics and nutritional and antioxidant properties of <i>Dunaliella salina</i>

This study investigates the effects of sustained nutrient stress caused by reduced concentrations of trace elements (Fe, Mn, Zn, Cu, Co, Mo at 25%, 50% and 75% of standard levels in Guillard’s f/2 medium) on the biomass and nutritional and antioxidant properties of the unicellular green alga Dunaliella salina. Over a 12-day cultivation period under controlled photoautotrophic conditions, significant variations were observed. Biomass productivity remained stable in the control (p > 0.05) and at 75% trace element levels. β-carotene synthesis peaked at 1.90 mg g‒1 day‒1 in Mn 50% compared to other treatments (p < 0.05). Lipid content reached a maximum of 58.78% in Fe 25%, significantly higher than in other treatments (p < 0.05), with triacylglycerol (TAG) content increasing to 68.1% in Fe 50% (p < 0.05), indicating enhanced lipid accumulation under 50% iron limitation. Fatty acid profiles revealed elevated C16:1 and C18:1 in Fe 75% (p < 0.05), while Co 75% exhibited the highest C18:2n6cis (6.82 ± 0.32%) (p < 0.05). Antioxidant activity peaked at 97.09% in Fe 25% at 40 mg ml‒1 of DPPH radical scavenging (p < 0.05), with a strong correlation (r = 0.974–0.986, p < 0.001) between β-carotene content and antioxidant capacity. Bioactive compounds, including lutein (2.05 µg mg‒1) and phenolics (4.05 mg GAE g‒1) in Fe 25% (p < 0.05), and trace element uptake patterns further elucidated nutrient dynamics. Principal component analysis (PCA) of all variance explained 81.0% of variance, linking PC1 to bioproduct yields and PC2 to trace element retention. These findings demonstrate that reduced trace element levels (25–50%) optimize lipid, β-carotene and antioxidant yields, offering a viable strategy for enhancing the biotechnological potential of D. salina for biofuel, nutraceutical and bioremediation applications.