Comparison of autotrophic, mixotrophic and hetrotrophic astaxanthin production from Haematococcus pluvialis

Astaxanthin is a major carotenoid pigment in the aquatic animals with wide applications in pharmaceutical, food, cosmetic, aquaculture, and poultry industries. In addition to pigmentation role, it has several beneficial biological effects in animals due to the high antioxidant activity. The freshwater unicellular green alga Haematococcus pluvialis is the richest natural source of astaxanthin that can accumulate between 1.5-3% astaxanthin in dry weight. In this study, the efficiency of three culture methods including autotrophic, mixotrophic, and heterotrophic on the growth and astaxanthin production by Haematococcus pluvialis was investigated simultaneously. Glucose and sodium acetate with concentration of 30 mM were used as carbon sources in the mixotrophic, and heterotrophic experiments. Although, the production of astaxanthin by Haematococcus pluvialis under mixotrophic condition showed no significance difference in comparison to autotrophic cultures in this study, the carotenoid profile as well as free or ester forms of astaxanthin formation can be influenced in case of mixotrophic conditions. The efficiency of using glucose as carbon source instead of acetate or malonate on carotenoid profile in mixotrophic culture was reported for the first time. The positive effect of nitrogen deficiency in addition to enhanced irradiance (from 55 to 200 μmol photon m-2s-1) in astaxanthin induction stage was shown in autotrophic as well as mixotrophic cultures. In autotrophic condition, 34/73% enhancements in astaxanthin production was achieved in case of using N-depravation and high irradiance as induction factors compared to the treatment that was only exposed to high irradiance. Accordingly, 88.09% and 41.18% improvement in astaxanthin production were recorded for acetate/ mixotrophic and glucose/ mixotrophic respectively for the same reason. On the other hand, comparing the efficiency of three culture methods studied in this project using two different strains of Haematococcus pluvialis CCAP 34/1D and CCAP 34/1F revealed that the results was strain dependent. However, the obtained data demonstrated the weak role of hetrotrophic growth of both Haematococcus pluvialis strains used in this study, the hetrotrophic efficiency may be improved by changing the carbon source concentration or the feeding strategy during the incubation time. The productivity of astaxanthin production can be improved through mixotrophic culture of Haematococcus pluvialis CCAP 34/1D in laboratory scale bioreactor under controled condition.