Abstract
Industrial microalgae, as a big family of promising producers of renewable biomass feedstock, have been commercially exploited for functional food, living feed and feed additives, high-value chemicals in nutraceuticals, cosmeceuticals, and chemical reagents. Recently, microalgae have also been considered as a group that might play an important role in biofuel development and environmental protection. Almost all current products of industrial microalgae are derived from their biomass; however, large amounts of spent cell-free media are available from mass cultivation that is mostly unexploited. In this contribution we discuss that these media, which may contain a remarkable diversity of bioactive substances are worthy to be recovered for further use. Obviously, the extracellular metabolites from industrial microalgae have long been neglected in the development of production methods for valuable metabolites. With the advances in the last ten years, more and more structures and properties from extracellular metabolites have been identified, and the potential utilization over wide fields is attracting attention. Some of these extracellular metabolites can be potentially used as drugs, antioxidants, growth regulators or metal chelators. The purpose of this review is to provide an overview of the known extracellular metabolites from industrial microalgae which might be of commercial interest. The attention mainly focuses on the reports of extracellular bioactive metabolites and their potential application in biotechnology.
Highlights
IntroductionMicroalgae (including cyanobacteria) are unicellular or multicellular microorganisms that have successfully adapted to various environments
Microalgae are unicellular or multicellular microorganisms that have successfully adapted to various environments
In this review we present the first overview of the existing extracellular metabolites from industrial microalgae that might be of commercial interest
Summary
Microalgae (including cyanobacteria) are unicellular or multicellular microorganisms that have successfully adapted to various environments. Autotrophic microalgae are photosynthetic, using solar energy, inorganic nutrients, and carbon dioxide (CO2 ) to produce proteins, carbohydrates, lipids and other valuable organic compounds while heterotrophic microalgae can be fermented using simple organic substrates (for example, glucose, acetate, glycerol) as carbon and energy sources for cell growth without light Under these conditions high-cell-density biomass containing elevated amounts of valuable compounds such as fatty acids, pigments, proteins, vitamins, and active polysaccharides can be obtained [1]. Exopolysaccharides (EPS) comprise a group of important high-molecular-weight biopolymers that are secreted from microorganisms including microalgae into the surrounding environment during their growth or propagation [25,26]. They can either be loosely attached to the cell wall or excreted into the environment [27,28]. We focus on EPS with defined structures and bioactivities from industrial microalgae and their possible applications (Table 2)
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