ABSTRACT
Microalgae possess plenty of useful metabolites (broadly carbohydrate, proteins, pigments, and lipids) that can be converted into commercially useful products. Microalgal cells contain a large quantity of structural and functional carbohydrates, as well as bio-functional proteins and peptides. Downstream processing of these individual metabolites from microalgae, however, incurs higher costs compared to other sources. Hence, an integrated extraction approach is becoming essential for commercialization. The microalgae possess a thick cell wall and thus require an additional pre-treatment prior to extraction. The cell disruption of microalgae is an energy-intensive process and thus influences the economics of the overall process significantly. On the other hand, proteins are prone to denaturation under severe conditions, for example, high temperature, extreme pH, and high shear. Therefore, the cell-disruption method should be carried out under mild conditions to retain the native functionality and structure of the proteins. The merits and demerits of different mild cell-disruption methods for integrated processes such as bead milling, ultrasonication, pulse electric field, and enzymatic treatment are discussed in this chapter. Selective extraction of individual metabolites in a sequential manner from the biomass has been demonstrated as a useful approach. Both proteins and carbohydrates are soluble in polar solvents. Consequently, both of these are extracted by aqueous solvents, simultaneously followed by their separation into different fractions. Aqueous two-phase separation and three-phase partitioning are the efficient liquid–liquid extraction techniques to obtain proteins and carbohydrates from the microalgal biomass. Integration of membrane separation with aqueous co-extraction of carbohydrates and proteins is another potential approach for this purpose.
