Value-Added Products from Microalgae - Biotechnological Applications of Microalgae - page 142

Milledge, 2011). The market size for β-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 β-carotene is much higher than that of synthetic
β-carotene ($1,000 to $2,000 kg −1 for natural β-carotene versus $400 to $800 kg −1
for synthetic β-carotene). Although the price of natural β-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 Tagetes patula ,
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 −2 d −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 produc-
tion. 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.
10.2.1.2 Production Processes
Carotenoid production usually occurs in open pond raceway systems and in pho-
tobioreactors, depending on the robustness of the algal strain toward contamina-
tion and the purity requirements or application of the final product. Carotenoids
such as astaxanthin, lutein, and zeaxanthin are produced in photobioreactors
(Dufossé 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 β-carotene, can grow in high-salinity environments
(Dufossé et al., 2005).
Biomass harvesting methods also depend on the algal strain cultivated. The pre-
ferred methods of harvesting biomass for carotenoid production are centrifugation,
sedimentation, and filtration (Dufossé et al., 2005; Weiss et al., 2008). Subsequent to