A Tetraselmis sp. was selected for its antioxidant activity owing to its high lipid peroxidation inhibition capacity. With the aim to monitor culture conditions to improve antioxidant activity, effects of CO₂-induced acidification on Tetraselmis growth, elemental composition, photosynthetic parameters and antioxidant activity were determined. Two pH values were tested (6.5 and 8.5) in batch and continuous cultures in photobioreactors. Acidification enhanced cell growth under both culture methods. However, the microalgae physiological state was healthier at pH 8.5 than at pH 6.5. Indeed, photosynthetic parameters measured with pulse amplitude modulated (PAM) fluorometry showed a decrease in the photosystem II (PSII) efficiency at pH 6.5 in batch culture. Yet, with the exception of the PSII recovering capacity, photosynthetic parameters were similar in continuous culture at both pH. These results suggest that lowering pH through CO₂-induced acidification may induce a lower conversion of light to chemical energy especially when coupled with N-limitation and/or under un-balanced culture conditions. The highest antioxidant activity was measured in continuous culture at pH 6.5 with an IC₅₀ of 3.44 ± 0.6 µg mL^-1, which is close to the IC₅₀ of reference compounds (trolox and α-tocopherol). In addition, the principal component analysis revealed a strong link between the antioxidant activity and the culture method, the photophysiological state and the nitrogen cell quota and C:N ratio of Tetraselmis sp.. These results highlight Tetraselmis sp. as a species of interest for natural antioxidant production and the potential of PAM fluorometry to monitor culture for production of biomass with a high antioxidant activity.

一个四爿藻。由于其高脂质过氧化抑制能力而被选中是因为其抗氧化活性。为了监测培养条件以提高抗氧化活性，CO ₂诱导的酸化对Tetraselmis 的影响测定了生长、元素组成、光合参数和抗氧化活性。在光生物反应器的分批和连续培养中测试了两个 pH 值（6.5 和 8.5）。在两种培养方法下，酸化都增强了细胞生长。然而，微藻生理状态在 pH 8.5 时比在 pH 6.5 时更健康。事实上，用脉冲幅度调制 (PAM) 荧光法测量的光合参数表明，在 pH 6.5 的分批培养中，光系统 II (PSII) 效率降低。然而，除了 PSII 恢复能力之外，在两种 pH 值下连续培养的光合参数相似。这些结果表明通过 CO ₂降低 pH诱导酸化可能会导致光能转化为化学能的转化率较低，尤其是在与氮限制和/或不平衡培养条件下。在 pH 6.5 的连续培养中测得最高的抗氧化活性，IC ₅₀为 3.44 ± 0.6 µg mL ^-1，与参考化合物（trolox 和α-生育酚）的 IC ₅₀接近。此外，主成分分析揭示了抗氧化活性与培养方法、光生理状态和氮细胞配额以及Tetraselmis sp. 的C:N 比之间的密切联系。这些结果突出了Tetraselmissp. 作为天然抗氧化剂生产的一种感兴趣的物种，以及 PAM 荧光法监测培养物以生产具有高抗氧化活性的生物质的潜力。