Microalgae: A potential sustainable commercial source of sterols

Microalgae are important natural sources of interesting high value compounds that could be used in pharmaceutical and nutraceutical applications. Of particular interest is the production and exploitation of microalgal phytosterols; compounds with known biological benefits such as cholesterol reduction, anti-inflammatory activity and even anti-cancer properties. The global market for phytosterols is expected to reach $USD 935 million by 2022. Phytosterols of commercial importance are beta-sitosterol, campesterol, brassicasterol, stigmasterol and ergosterol. The current sources of phytosterols are the vegetable and tall oils harvested from land plants. However, it is anticipated that the terrestrial sources will not be able to meet increased demand through 2030 and beyond. Calculations of estimated lipid and phytosterol productivity suggest that microalgae could yield 678-6035 kg. ha(-1).y(-1) of phytosterol which is more than the current productivity of phytosterols from rapeseed plants, highlighting the economic potential for sourcing phytosterols from environmentally sustainable saline microalgae production. However, there are many challenges that need to be met. The sterol content of microalgae varies according to species and, at present, there is little information on how to manipulate culturing conditions to enhance sterol production in microalgae. Approaches could include nutrient limitation, and/or changing salinity, light and temperature. Molecular approaches such as genetic modification, knocking down or over expression of specific genes and blocking competitive biosynthetic pathways would be desirable. However, an improved understanding of the pathway of sterol biosynthesis in microalgae is necessary for effective use of these molecular approaches. This paper discusses the potential for sterol production from microalgae as an adjunct to current plant-based sources and highlights those areas where we need more information to produce these high value products in an environmentally and economically sustainable fashion.