The effect of different salinity ratios on bioactive compounds, volati̇le, quality parameters, and in vitro bioaccessibility in the cultivation of spirulina platensis and phaeodactylum tricornutum

In this study, the effect of different salt stress conditions on growth, important quality parameters, antioxidant activity, phenolic profile, aroma compounds, bioactive properties, and microbial load of Spirulina platensis and Phaeodactylum tricornutum was investigated for the first time. Salt concentrations of 20, 25, 30, and 35 ‰ for S. platensis culture and 15, 25, 30, and 35 ‰ for P. tricornutum culture were investigated. Antioxidant capacity was evaluated by two different methods, DPPH and ABTS, aroma compounds by HS-SPME-GC/MS, and organic acid and sugar composition by HPLC-PDA-RID. The highest antioxidant activity and phenolic compound contents were found in salt concentrations called control. S. platensis (20‰) exhibited higher antioxidant activity than P. tricornutum (30‰), which decreased with increasing salt stress. In S. platensis and P. tricornutum culture samples, 24 and 20 phenolic compounds were identified and quantified using HPLC-DAD-ESI-MS/MS, respectively. While the dominant phenolic compound in S. platensis samples was quercetin derivative, dimethoxyflavone was abundant in P. tricornutum samples. Amino acid profiles were also compared and glutamic acid (6.24-12.96 mg/100 g DW) and alanine (3.67-13.65 mg/100 g DW) were the dominant amino acids. The dominant sugars were glucose (192-2322 mg/100 g DW) and sucrose (229-1099 mg/100 g DW) in S. platensis and P. tricornutum samples, respectively. The most dominant flavor compound was heptadecane (36941 µg/kg) in S. platensis samples and acetic acid (113 µg/kg) in P. tricornutum samples. The total amounts of aroma compounds in both species increased with the decrease in salt concentration. A significant decrease in the amounts of amino acids, sugars, and organic acids was detected with increasing salt concentration. When microbial count results were analyzed, total aerobic mesophilic bacteria count ranged from 300 to 1.9 × 104 cfu/g and yeast/mold counts ranged from >10 to 104 cfu/g in S. platensis samples, while total aerobic mesophilic bacteria counts ranged from 300 to 2.78 × 104 cfu/g and yeast/mold counts ranged from 10 to 1.35 × 104 cfu/g in P. tricornutum samples. This study shows that the addition of different amounts of salt to the nutrient medium during the production of S. platensis and P. tricornutum can affect their growth, phenolic compounds, antioxidant capacity, aroma compounds, amino acid composition, sugar content, and microbial load assessment and in vitro bioaccessibility.