There is a demand for natural pigments to be applied in the food, pharmaceuti­cal, and aquaculture industries (Dufosse et al., 2005). The use of synthetic dyes in these industries is slowly declining due to their toxic effects (Dufosse et al., 2005). Compared to synthetic alternatives, microalgal carotenoids have the advantage of supplying natural isomers in their natural ratios (Pulz and Gross, 2004; Milledge, 2011). Microalgal pigments have been used as alternatives to synthetic pigments in various industries (Table 10.2).

Other than for coloring purposes, carotenoids have recently been used as anti­oxidants. Carotenoids have antioxidant effects that can be beneficial in countering diseases such as cancer, obesity, and hypertension (Inbaraj et al., 2006; Murthy et al., 2005). Table 10.3 indicates the applications of commercially exploited carotenoids in various industries.

The worldwide demand for carotenoids has been increasing at an average yearly rate of 2.2% (Guedes et al., 2011). Among the 400 known carotenoids, so far only a few have been exploited (Cosgrove, 2010; Milledge, 2011). The two most com­monly exploited algal carotenoids are P-carotene and astaxanthin, which are mainly produced by Dunaliella salina and Haematococcus pluvialis, respectively (Pulz and Gross, 2004; Spolaore et al., 2006; Del Campo, 2007; Cosgrove 2010;

TABLE 10.3 Commercially Available Carotenoids and Their Applications Food Coloring of Animals and of Supplements Carotenoid Type Coloring Animal Products (anti-oxidants) Annatto X Apocarotenal X Apocarotenal ester X Astaxanthin X X X Beta-carotene X X X

Vitamin A Source Cosmetic Ref. Vital Solutions market report, 2010 Vital Solutions market report, 2010 Vital Solutions market report, 2010 X Pulz and Gross, 2004; Vital Solutions market report, 2010; Milledge, 2011 X X Pulz and Gross, 2004; Spolaore et al., 2006; Del Campo, 2007; Vital

Solutions market report, 2010; Milledge, 2011

Inbaraj et al., 2006; Vital Solutions market report, 2010 Vital Solutions market report, 2010 Del Campo, 2007; Vital Solutions market report 2010

X Vital solutions market report, 2010

Del Campo, 2007; Vital Solutions market report 2010

Milledge, 2011). The market size for P-carotene is estimated at 1,200 tonnes per year and greater than US$280 million in sales volume per year (Pulz and Gross, 2004). The market price of natural P-carotene is much higher than that of synthetic P-carotene ($1,000 to $2,000 kg-1 for natural P-carotene versus $400 to $800 kg-1 for synthetic P-carotene). Although the price of natural P-carotene is higher than that of the synthetic form, preference is still given to the natural form because it has physical properties that make it superior to the synthetic form. The annual worldwide market of astaxanthin is estimated at US$200 million (Spolaore et al., 2006). The market size of astaxanthin is estimated at just below 300 tonnes per year, with a sales volume of less than US$150 million per year (Pulz and Gross, 2004; Spolaore et al., 2006).

Lutein and zeaxanthin are the other two carotenoids with great potential. These carotenoids are commonly derived from petals of Tagetes erecta and Tagetespatula, commonly referred to as marigold flowers (Del Campo et al., 2007). Microalgae also have an ability to accumulate these carotenoids. Lutein and zeaxanthin are known to selectively accumulate in the macula of the human retina. They protect the eyes from light and oxidative stresses (Kotake-Nara and Nagao, 2011).

The lutein extracted from other sources is usually 95% esterified, whereas in microalgae, lutein is found in the free nonesterified form. Muriellopsis sp. recorded lutein yields of 75 mg m-2d-1 in an outdoor open pond system (Del Campo et al., 2007). These values are similar to those obtained in a closed system (Harun et al., 2010; Del Campo et al., 2007). Overall, the free lutein content of Muriellopsis sp. biomass varies between 0.4% and 0.6%; which represents a higher content of esterified lutein than found in crown petals of Tagetes plants. The global market size of lutein is expected to hit $124.5 million by 2013 (Heller, 2008).

Zeaxanthin is mainly produced synthetically due to the fact that its content in natural sources (including microalgae) is considered very low for industrial produc­tion. The major problem underlying the commercial exploitation of zeaxanthin is the development of production processes that will result in the extraction of high amounts of zeaxanthin (Weiss et al., 2008). In 2006, the global market of zeaxanthin was estimated at $2 million (Heller, 2008). The awareness of this carotenoid still remains lower than that of lutein.