Production of astaxanthin by Haematococcus pluvialis: taking the one-step system outdoors.

The feasibility of a one-step method for the continuous production of astaxanthin by the microalga Haematococcus pluvialis has been verified outdoors. To this end, influence of dilution rate, nitrate concentration in the feed medium, and irradiance on the performance of continuous cultures of H. pluvialis was firstly analyzed indoors in bubble column reactors under daylight cycles, and then outdoors, using a tubular photobioreactor. At the laboratory scale, the behavior of the cultures agreed with that previously recorded in continuous illumination experiences, and attested that the major factors determining biomass and astaxanthin productivity were average irradiance and specific nitrate supply. The rate of astaxanthin accumulation was proportional to the average irradiance inside the culture, provided that a nitrate limiting situation had been established. The accumulation of astaxanthin under daylight cycles was maximal for a specific nitrate input of 0.5 mmol/g day. The recorded performance has been modeled on the basis of previously developed equations, and the validity of the model checked under outdoor conditions. Productivity values for biomass and astaxanthin of 0.7 g/L day and 8.0 mg/L day respectively, were obtained in a pilot scale tubular photobioreactor operating under continuous conditions outdoors. The magnitude of the experimental values, which matched those simulated from the obtained model, demonstrate that astaxanthin can be efficiently produced outdoors in continuous mode through a precise dosage of the specific nitrate input, taking also into consideration the average irradiance inside the culture.

Recovery of lutein from microalgae biomass: development of a process for Scenedesmus almeriensis biomass.

In this work an optimized method for the extraction of lutein from microalgae biomass is presented. It has been developed using dry biomass of the lutein-rich microalga Scenedesmus almeriensis. The method comprises three steps, cell disruption, alkaline treatment, and solvent extraction, and renders a carotenoid extract rich in lutein. The results demonstrate that cell disruption is necessary and that the best option among the treatments tested with regard to industrial applications is the use of a bead mill with alumina in a 1:1 w/w proportion as disintegrating agent for 5 min. With regard to the alkaline treatment, the optimal conditions were obtained using 4% w/v KOH with a biomass concentration of 100 g/L for 5 min. Longer alkaline treatments or the use of higher KOH concentrations reduced the yield of the process. Finally, extraction with hexane is optimized. Using a 1:1 ratio hexane to sample volume, a total of eight extraction steps are necessary to recover 99% of lutein contained in the processed biomass. However, the optimal number of extraction steps is six, 95% of the lutein being recovered. In summary, the developed method allows the efficient recovery of lutein from microalgae biomass, it being a scaleable and industrially applicable method.