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Microalgae as a Sustainable Source of Nutraceuticals

Md Nazmul Islam, Faisal Alsenani, and Peer M. Schenk*

Algae Biotechnology Laboratory, School of Agriculture and Food Sciences, University of Queensland, Brisbane, Queensland, Australia

*Corresponding author e-mail: p.schenk@uq.edu.au

Introduction

Nutraceutical is a broad term which describes any food product with increased health benefits and which exceeds the usual health benefits of normal foods (Borowitzka 2013). Many bioactive constituents of food have been commercialized in the form of pharmaceutical products (pills, capsules, solutions, gels, liquors, powders, granules, etc.) which contribute to enhanced human health. However, these products cannot be categorized solely as "food" or "pharmaceutical" and a new hybrid term between nutrients and pharmaceuticals, "nutraceuticals," has been introduced (Palthur et al. 2010).

A generally accepted term for nutraceuticals is "food supplements." Another closely related term is "functional foods," defined as "products derived from natural sources which can also be fortified, whose consumption is likely to benefit human health" (Burja et al. 2008). However, it is a widely held view that there appears to be a boundary between nutraceuticals and functional foods. For example, when a bioactive compound is added in a food formulation, i.e., 200 mg of carotenoids dissolved in 1 L of juice, this may result in a new potential functional food, whereas the same amount of carotenoids encapsulated in a tablet or capsule is considered a nutraceutical (Espin et al. 2007). Additionally, nutraceuticals can either be whole food products (e.g., Spirulina in tablet form) or dietary supplements where the nutraceutical compound(s) may be concentrated to provide the claimed health benefits (e.g., astaxanthin extracted from Haematococcus microalgae is available in the market).

Therefore, the emphasis on searching for nutraceuticals that contribute to improved human health has increased worldwide. Microalgae have become a popular target in the research community and biotechnology industry based on findings that many microalgal strains are very good sources of various nutraceuticals, such as vitamins, carotenoids, polyunsaturated fatty acids (PUFAs), phytosterols, etc. (Hudek et al. 2014). Moreover, the use of microalgal biomass has attracted attention because they grow fast regardless of the land's suitability for farming. In principle, microalgae cultivation can be carried out independent of freshwater supply and does not compete with arable land or biodiverse landscapes. In fact, many microalgae with health benefits are marine or brackish water algae (Lim et al. 2012). Microalgae are therefore considered an ideal source for the sustainable production of physiologically active compounds (Abdelaziz et al. 2013; Hudek et al. 2014). Many of them have a surprising capability of enduring adverse environmental conditions by means of their secondary metabolites, and some of these conditions lead to high accumulation of these compounds (e.g., Dunaliella salina produces high levels of ß-carotene under highly saline conditions; Borowitzka 2013).

Prior studies have noted the health benefits of algal nutraceuticals which include improved immunity, neurological development, increased health of different organs including bones, teeth, intestine, etc. Algal nutraceuticals were also found to be effective in fighting obesity and cholesterol, and decrease blood pressure and maintain optimum heart condition. Several studies also documented some antiviral and anticancer properties (Venugopal 2008). In this chapter, we will provide a brief overview of the different nutraceutical compounds currently reported to be available in microalgae.

Microalgae-Derived Nutraceuticals

Pigments

Stengel and his team (2011) pointed out a few of the major categories of microalgal pigments which are closed tetrapyrroles such as chlorophylls a and b (chlorins), porphyrins (chlorophyll c), open chain tetrapyrroles (phycobilin pigments), and carotenoids (polyisoprenoids; carotenes and xanthophylls). Among them, the most targeted pigment groups are carotenoids and phycobilins which are already widely used by industry (Stengel et al. 2011).

Generally, carotenoids are powerful antioxidants and provide photoprotection to cells. Most of them have a 40-carbon polyene chain as their molecular backbone (del Campo et al. 2007; Guedes et al. 2011a). A recent study by our group showed that when induced by external stimuli, various microalgae can produce significant amounts of carotenoids. Among a few hundred Australian microalgal strains, 12 rapidly growing strains were screened for carotenoid profiles and D. salina, Tetraselmis suecica, Isochrysis galbana, and Pavlova salina were found to be good sources of various carotenoids at 4.68-6.88 mg/g dry weight (DW) even without external stimuli (Ahmed et al. 2014).

A considerable amount of work has been done worldwide to screen microalgae for carotenoid production. For example, lutein is dominant in Muriellopsis sp., Scenedesmus almeriensis, and Chlorella sp. (Blanco et al. 2007; Borowitzka 2013; del Campo et al. 2001; Fernandez-Sevilla et al. 2010); astaxanthin, canthaxanthin and lutein are abundant in Chlorella zofingiensis; canthaxanthin in Scenedesmus komareckii; aplanospores in D. salina; echinenone in Botryococcus braunii; and fucoxanthin in Phaeodactylum tricornutum (Table 1.1). However, apart from ß-carotene and astaxanthin, large-scale production for these microalgae-synthesized carotenoids is still in consideration due to the high costs of downstream processing for extraction and purification (Borowitzka 2013). Furthermore, the cyanobacterium Synechocoocccus and the microalga Nannochloropsis gaditana present a good source of ß-carotene, zeaxanthin, violaxanthin, vaucheriaxanthin, and chlorophyll a (Macías-Sánchez et al. 2007).

Table 1.1 Selected microalgae-derived bioactive compounds: their sources and function.