Otimização do cultivo de Haematococcus pluvialis para maior produtividade em biomassa e biomoléculas

Abstract

The microalgae Haematococcus pluvialis has astaxanthin as its bioproduct of greatest economic value, in addition to being capable of producing other high-value metabolites, such as proteins, lipids, fatty acids and carbohydrates. The present study proposes modifications in the sources and feeding strategies of nitrogen and organic carbon, as well as the use of effluent as a culture medium, in order to increase the production of biomass and high-value metabolites of H. pluvialis and promote the economy circular. The first part of the study proposes a change in the nitrogen supply mode, through the pulse feeding strategy, and the use of different nitrogen sources (i.e., NaNO3, NH4NO3 and (NH2)2CO) to increase the production of biomass from H. pluvialis and astaxanthin. In the second part, different sources (i.e., sodium acetate, molasses and glycerol) and feeding strategies (i.e., without pulses-WPF and with pulses-PF) of organic carbon were used in order to increase the production of biomass and high-value metabolites H. pluvialis. In the third part, an integrated system was proposed for the simultaneous treatment of effluent from Nile tilapia cultivation and astaxanthin production using the microalgae H. pluvialis. The cultures were carried out on a laboratory scale, and the growth variables were evaluated. Therefore, the biomasses were processed, through centrifugation and freeze-drying, to carry out quantitative and qualitative analyzes of the metabolites. The results of the growth variables obtained in the first part of the study showed significant differences for maximum cell density, being greater for NaNO3-PF (176 x 104 cells mL-1) and (NH2)2CO-PF (165 x 104 cells mL-1). Biomass yield and productivity in the vegetative and cystic phases were higher for pulsed crops. On the other hand, the contents and concentrations of total carotenoids and astaxanthin were higher in NH4NO3-WPF (astaxanthin content ~ 23 mg g-1), being influenced by nitrogen depletion and pH variation. Regarding the effect of organic carbon sources and feeding strategies on biomass yield, higher values were obtained with glycerol-WPF (1.275 g L-1) and acetate-PF (1264 g L-1). The composition of the biomass in terms of proteins and lipids was influenced by both the source and the organic carbon feeding strategy. The molasses-WPF and glycerol-PF treatments showed higher concentrations of fatty acids and PUFA, on average 5.5 and 2.5% P.S., respectively. Regarding carotenoid levels, astaxanthin presented the highest concentration under glycerol-WPF and molasses-PF, around 315 mg L-1 (6% P.S.). In addition to the metabolites already known in H. pluvialis, the enzyme L-asparaginase was reported for the first time, with maximum activity of 256 ± 24 IU mg-1 of dry biomass. On the other hand, the use of effluent as a culture medium in an integrated system, despite presenting lower cell density and biomass yield, resulted in biomass with a high astaxanthin content (10 mg g-1) and antioxidant activity (89% inhibition of DPPH radicals). Furthermore, this integrated system contributed significantly to the remediation of the effluent (removal of 98% of N and 91% of P). Therefore, it can be concluded that modifications in the sources and feeding strategies of nitrogen and organic carbon increase the production of biomass and high-value metabolites of H. pluvialis. Additionally, H. pluvialis can be used for economical treatment of aquaculture effluents with simultaneous production of astaxanthin, with potential application in aquafeed or other industrial sectors, as an example of a circular economy.