Diversity and Content of Carotenoids and Other Pigments in the Transition from the Green to the Red Stage of <i>Haematococcus pluvialis</i> Microalgae Identified by HPLC-DAD and LC-QTOF-MS

<i>H. pluvialis</i> is a unicellular freshwater alga containing many bioactive compounds, especially carotenoids, which are the strongest antioxidants among the pigments. This study evaluates the composition and content of carotenoids and other pigments in both stages of algae life cycle, especially in the green vegetative stage, less studied in comparison to the red stage. To determine the composition and content of carotenoids, a combination of HPLC-DAD and LC-QTOF-MS was used. The content of carotenoids in the green vegetative stage was significantly lower than in the red vegetative stage. In the green vegetative stage, 16 different carotenoids and other pigments were identified. Among the total 8.86 mg g⁻¹ DW of pigments, 5.24 mg g⁻¹ DW or 59% of them were chlorophyll <i>a</i> with its derivatives, and 3.62 mg g⁻¹ DW or 41% of them were free carotenoids. After the transition from the green to the red stage, the carotenoid composition was replaced by secondary carotenoids, astaxanthin and its esters, which predominated in the whole carotenoid composition. In addition to free astaxanthin, 12 astaxanthin monoesters, 6 diesters and 13 other carotenoids were determined. The majority of 37.86 mg g⁻¹ DW pigments were monoesters. They represented 82% of all pigments, and their content was about 5 times higher than both, diesters (5.91 mg g⁻¹ DW or 12% of all) and free carotenoids (2.4 mg g⁻¹ DW or 6% of all). The results of the study contribute to the data on the overall pigment composition and content of <i>H. pluvialis</i> algae and provide the basis for further improvement of cultivation of the <i>H. pluvialis</i> algae.