Carotenoid production usually occurs in open pond raceway systems and in pho­tobioreactors, depending on the robustness of the algal strain toward contamina­tion and the purity requirements or application of the final product. Carotenoids such as astaxanthin, lutein, and zeaxanthin are produced in photobioreactors (Dufosse et al., 2005; Milledge, 2011) due to the sensitivity of the algal strains to contamination. Algal strains that have an ability to grow in harsh environments are usually cultivated in open pond raceway systems. As an example, Dunaliella salina, for the production of P-carotene, can grow in high-salinity environments (Dufosse et al., 2005).

Biomass harvesting methods also depend on the algal strain cultivated. The pre­ferred methods of harvesting biomass for carotenoid production are centrifugation, sedimentation, and filtration (Dufosse et al., 2005; Weiss et al., 2008). Subsequent to centrifugation, the hard cell walls are broken and then extraction of the carotenoid occurs (Dufosse et al., 2005).

10.2.1.1 Foresight

Carotenoid production has established itself as the most successful area of micro­algal biotechnology; and with the increasing market demands for these natural pigments, the future of microalgal carotenoid production appears promising (Del Campo et al., 2007). The ability of microalgae to be genetically modified opens doors for enhancing specific carotenoid production through metabolic engineering. However, this approach might not be welcomed by the food and aquaculture indus­tries due to the controversy surrounding genetically modified products. The market demand for carotenoids is expected to increase even further with the discovery that carotenoids exhibit tumor-suppressing activity (Schmidt-Dannert et al., 2000). Carotenoid exploitation is restricted to only a few algal species; more algal strains have yet to be screened.

10.2.2 Phycobiliproteins

Phycobiliproteins are photosynthetic accessory pigments produced by microalgae. These pigments are responsible for improving the efficiency of light energy utilization (Pulz and Gross, 2004). Phycobiliproteins are deeply colored (red or blue), water — soluble complex proteins and have a broad spectrum of potential applications as natural coloring agents in the food and feed, pharmaceutical, and cosmetics industries. Among the cyanobacteria and red algae, there are four main classes of phycobilipro — teins that are synthesized (Table 10.4): allophycocyanin (APC, bluish-green), phycocy — anin (PC, blue), phycoerythrin (PE, purple), and phycoerythrocyanin (PEC, orange).

These phycobiliproteins are geometrically incorporated into structures called phycobilisomes, which are located on the outer surface of the thylakoid membranes.