Astaxanthin production by autotrophic cultivation of Haematococcus pluvialis: A success story

Abstract

Microalgae are photosynthetic organisms that have shown great potential for the production of large variety metabolites of commercial interest, as well as for liquid and gas effluent bioremediation. Among the metabolites of interest and the different uses of microalgae, we can mention the production of lipids for biofuels of the second generation (biodiesel), extraction of carotene and other pigments to be used in the pharmaceutical and food industry, and biomass of microalgae as food (both for humans and animals). There are over 30,000 algal species that have been identified and studied; however, it is estimated that these number could be higher 70,000. H. pluvialis has a distinctive growth cycle, characterized by the alternation between a greenmotile stage and a reddish nonmotile resting stage (or cyst) according to environmentalconditions [2]. Under adverse culture conditions, H. pluvialis cysts accumulate large amounts of secondary carotenoids, particularly astaxanthin, into lipid droplets deposited in the cytoplasm, resulting in a characteristic bright red color of these cells [3]. The thick cell wall of haematocyst cell hinders astaxanthin bioavailability, making necessary the application of disruption methods for improving the extraction procedure. However, these methods can include costly lytic enzymes, large solvent consumption, time-consuming processing, and violent mechanical disruption of the cell wall, resulting in thermal degradation of the unsaturated double-bonded astaxanthin because of the heat generated [4]. Astaxanthin can be chemically synthesized at a price, fraction of the natural one. However, differences in bioactivities and in structural isomerism have been reported between both types of molecules [5]. Synthetic astaxanthin contains a mixture of three stereoisomers associated with two chiral centers that are (3R, 30R), (3R, 30S) (meso), and (3S, 30S), in approximately 1:2:1 proportions. Natural astaxanthin is mainly in the form of (3S, 30S), which exhibited higher bioactivity related to its antioxidant capacity, when compared with the synthesized astaxanthin [6]. Among the most important biological effects are pigmentation capacity of fish and crustacean, cardioprotective and anticancer activity, and antiinflammatory and antidiabetic properties [7,8]. Therefore the growing interest in application of the natural astaxanthin as colorant and supplements for food and feed additives leads to the development of enterprises producing natural astaxanthin from H. pluvialis cultures around the world [9]. The purpose of this chapter is to discuss the current status about H. pluvialis culture systems for natural astaxanthin production, highlighting some of the critical aspects of the process.