Potential use of algal proteins as sustainable alternative to animal-based proteins. • Algae-based foods placed on global market. • Strategies to enhance protein content of macro-and microalgae. • Nutritional and functional properties of algal biomass and its protein extracts. • Integrated production of algal proteinstowards "greener" process approaches.

Electrotechnologies are based on the direct application of an external electric field through a given semi-conductive material. These technologies are part of a wide range of biotechnological processes, considered costeffective and environmentally-friendly in view of the less intensive use of non-renewable resources and high levels of energetic efficiency. In this regard, electrotechnologies are a promising processing tool to overcome some of the microalgae's exploitation limitations. The application of electric field-based techniques can cover upstream (i.e. electroporation for genetic transformation, inactivation of culture contaminants, and improvement of growth kinetics) and downstream processes (e.g. harvesting and extraction methods). Pulsed electric fields (PEF) and moderate electric fields (MEF), targeted at microalgae cellular permeabilization and subsequent extraction of valuable compounds, count with a substantial body of fundamental research which puts them on the front row to become mainstream techniques in a near future. This review provides comprehensive knowledge systematization of the current status of the direct application of these techniques on microalgal biotechnology, as wells as future trends and challenges regarding developments in electrotechnologies to be applied to microalgae industrial exploitation.

Different methods for estimating starch in Chlorella vulgaris were compared with the view of establishing a procedure suitable for rapid and accurate determination of starch content in this microalgal species. A close agreement was observed between methods that use perchloric acid and enzymatic methods that use α-amylase and amyloglucosidase to hydrolyze the starch of microalgae grown under different nitrogen culture conditions. Starch values obtained by these methods were significantly higher than those estimated by using hydrochloric acid as solubilizing and hydrolyzing agent. The enzymatic method (EM1) proved to be the most rapid and precise method for microalgal starch quantification. Furthermore, the evaluation of resistant starch by enzymatic methods assayed in nitrogen-sufficient and nitrogen-starved cells showed that no formation of this type of starch occurred in microalgae, meaning that this should not interfere with starch content determinations.

The combined effect of four abiotic factors on Microcystis aeruginosa growth and toxin production was assessed by culturing the cyanobacterium under different light intensities (10-190 μmol photons•m − 2 •s − 1), CO 2 concentrations (0-10% (v/v)), temperatures (15-40°C), and pH values (6.5-9.5). Results indicate a significant influence caused by the synergistic effect of environmental factors over growth-related parameters and cyanobacteria toxicity. The combined use of low to medium light intensities (50-120 μmol photons•m − 2 •s − 1) and CO 2 concentration (1-6% v/v) led to higher cell concentrations, while specific growth rate and biomass productivity were favoured by medium to high light intensities (110-190 μmol photons•m − 2 •s − 1), CO 2 concentrations (4-9.5% v/v) and temperatures (29-39°C). Regarding microcystin (MC) production, higher concentrations were obtained at low light intensities and low CO 2 concentrations while approximately 2000-fold lower MC concentrations were achieved by simultaneous use of high values of light intensity, CO 2 concentration and temperature.

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The extraction of the wide range of useful bioactive compounds produced by cyanobacteria is still a major bottleneck at industrial scale. In addition to the high costs, extraction efficiencies are also commonly low, with low cell disruption efficiencies playing a particularly significant role in intracellular compounds' release. To increase the chances of an extended use of the cyanobacteria toxin microcystin in several biotechnological fields, we aimed to optimize five different disruption techniques: bead milling, microwave, freeze-thaw cycles, highspeed homogenization, and sonication. For each of the methods tested, the conditions that maximized the intracellular organic matter release were: i) 20% of beads and treatment time of 7 min (bead milling); ii) 800 W for 1.5 min (microwave); iii) three 12-h freeze-thaw cycles at −20°C; iv) 15,000 rpm for 7 min (high-speed homogenization); and v) 40 kHz for 10 min (sonication). Sonication and freeze-thaw cycles followed by sonication revealed to be the most effective methodologies to ensure a maximum intracellular organic matter release and, consequently, microcystin availability for being extracted. The decrease of cells' viability was however more evident in freeze-thaw cycles, freeze-thaw cycles followed by sonication, and microwave where only 0.3, 0.05 and 0.9% of the initial cells, respectively, maintained their viability after being treated. On the other hand, sonication and bead milling reduced the viability of the original culture to 5 and 15.5%, respectively, while high-speed homogenization did not show any significant differences compared to control. According to the results obtained in this study, the most suitable methodology to maximize the release of microcystin was therefore the use of sonication (40 kHz) during 10 min.