Changes in fatty acids and sterols during batch growth of Pavlova viridis in photobioreactor

Changes in the composition of fatty acids and sterols of Pavlova viridis cultured in an air-lift photobioreactor were studied using gas chromatography-mass spectrometry (GC-MS). The results show that radical changes in fatty acid and sterol contents and compositions occurred during growth phase transitions: the total lipid increased along with the culture age, from 166.4 mg g⁻¹ (late exponential phase) to 232.7 mg g⁻¹ (linear phase), and increased further to be 235.1 mg g⁻¹ in the stationary phase. Polyunsaturated fatty acids (PUFAs), especially eicosapentaenoic acid (EPA), decreased along with the culture time, PUFAs, and EPA contents maximized in the late exponential phase to become 46.2 mg g⁻¹ and 22.1 mg g⁻¹ respectively; there was no significant change in docosahexaenoic acid (DHA) content during the whole growth phase, although it reached the peak in the linear phase with 3.5 mg g⁻¹. As for the sterols, two unique sterols with two hydroxyl groups, termed pavlovols, were observed. 4α,24-Dimethylcholestan-3β,4β-diol, one of the pavlovols, increased almost 2-fold from the late exponential phase (2.5 mg g⁻¹) to the stationary phase (4.3 mg g⁻¹). On the contrary, the contents of stigmasterol and sitosterol decreased with culture age, with the maximum content of 2.4 mg g⁻¹ and 3.1 mg g⁻¹, both obtained in the late exponential phase, respectively. The results indicate that growth phase control could be used as a methodology to optimize the total lipid, EPA, PUFA, and sterol contents with the potential for both aquaculture feeds and nutraceutical applications, especially for further research into unique pavlovols.