Abstract
One of the main goals of Mankind is to ensure food system sustainability—including management of land, soil, water, and biodiversity. Microalgae accordingly appear as an innovative and scalable alternative source in view of the richness of their chemical profiles. In what concerns lipids in particular, microalgae can synthesize and accumulate significant amounts of fatty acids, a great fraction of which are polyunsaturated; this makes them excellent candidates within the framework of production and exploitation of lipids by various industrial and health sectors, either as bulk products or fine chemicals. Conventional lipid extraction methodologies require previous dehydration of microalgal biomass, which hampers economic feasibility due to the high energy demands thereof. Therefore, extraction of lipids directly from wet biomass would be a plus in this endeavor. Supporting processes and methodologies are still limited, and most approaches are empirical in nature—so a deeper mechanistic elucidation is a must, in order to facilitate rational optimization of the extraction processes. Besides circumventing the current high energy demands by dehydration, an ideal extraction method should be selective, sustainable, efficient, harmless, and feasible for upscale to industrial level. This review presents and discusses several pretreatments incurred in lipid extraction from wet microalga biomass, namely recent developments and integrated processes. Unfortunately, most such developments have been proven at bench-scale only—so demonstration in large facilities is still needed to confirm whether they can turn into competitive alternatives.
Highlights
The increasing importance of following and maintaining a healthy diet is apparent; most people are unwilling to do so unless drastic changes in their living habits can be avoided
Microwave-assisted extraction induces the release of lipids from the cells by dielectrically heating the medium water, which generates steam inside the cells and induces changes in their structure that include breakage that leads to electroporation, opening up of cell membrane and allowing the release of intracellular compounds [80,81]
Reaction kinetics for wet microalgae transesterification reaction, at different reaction temperatures, was evaluated; it was found that microwave energy dissipation at a rate of 140 W, combined with 140 W of ultrasound intensity, was adequate to produce fatty acid methyl esters (FAMEs) to a maximum yield of 48.2%
Summary
The increasing importance of following and maintaining a healthy diet is apparent; most people are unwilling to do so unless drastic changes in their living habits can be avoided. The need for novel substances to prevent health conditions related to high caloric diets, combined with sedentary lifestyles has been growing. Chronic diseases, such as heart disease, stroke, cancer, chronic respiratory diseases, and diabetes, are currently the leading causes of mortality in the world—and already represent 60% of all deaths. 24 h); performance essentially independent of weather changes; and drastically lower irrigation water needs. They exhibit a high capacity for CO2 sequestration (183 tons of CO2 /100 tons of microalgal biomass) [14] and wastewater treatment. Microalgal lipid content can reach 25 to 200-fold that found in higher plants [15]
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