Diurnal variation of various culture and biochemical parameters of Arthrospira platensis in large-scale outdoor raceway ponds

The use of microalgae for nutraceuticals, food, and feed has recently gained great interest. Having a good understanding of the trends, including the diurnal variations, of the physiological parameters and biochemical composition of the biomass in commercial scale systems is of high importance as it may lead to finding potential ways to optimize productivity and product quality. Not much is known about the diurnal variation of the physiological parameters and biochemical composition of microalgae grown in large-scale outdoor raceway ponds in general and Arthrospira in particular, even though a lot is known about such diurnal variations in natural aquatic and laboratory environments. Arthrospira (Spirulina) platensis is a filamentous cyanobacterium widely used as dietary supplement, functional food, food, and animal feed. It has been grown commercially for about 40 years. In the present experiments the diurnal variation of some photosynthetic parameters and of the product quality was studied in Arthrospira platensis grown outdoors in a 5000 m2 raceway pond over a 24-hour period at three different months of the year. Specific trends for Arthrospira in commercial scale setup were described for the first time. Significant variation was observed in the biomass composition throughout the course of the day. The photosynthetic pigment content of Arthrospira (chlorophyll a, total carotenoids, and total phycocyanin) declined during the light hours, and recovered during the night. The same pattern was seen in the case of the crude protein content of the biomass. The total carbohydrate content however showed an opposite trend to that of the protein. Selected parameters were simulated in the lab in benchtop photobioreactors and the trends were compared with the large-scale system. The results of the experiments are discussed in relation to diurnal changes in some physical and chemical factors.