BACKGROUND: Microalgae can synthesize starch with productivity higher than conventional terrestrial crops, without the need for arable land. However, little is known about processes to extract starch from microalgae. Here, a biorefinery process is described including microalgal cell disruption followed by extraction of starch and pigments with aqueous two-phase system (ATPS) using choline chloride and polypropylene glycol 400. Sonication and bead milling were compared for cell disruption rate and starch extraction efficiency.RESULTS: A first order kinetic model described well the cell disruption for both the methods, with a rate 2.6 times higher for bead milling than sonication. By applying ATPS on samples with comparable cell disruption (>93%), starch was separated better after sonication (67% recovery in the pellet) than after bead milling, for which it remained equally distributed between pellet (40%) and choline chloride phase. Pigments were extracted with 42-66% yield irrespective of the cell disruption method. Microalgal starch granules had a normal and narrow distribution for size (0.93 ± 0.14 ∼m) and a gelatinization temperature between 45-55 °C.CONCLUSION: For the same cell disruption yield, different starch separation efficiencies can be achieved, depending on the cell disruption method applied. Although bead milling was faster than sonication in disrupting cells, it gave worst starch separation efficiency. The properties of the extracted microalgal starch indicate potential technical advantages, with respect to conventional starch sources, for applications in the bioplastic and food sector.

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In recent years, great attention has been focused on rapid, selective, and environmentally friendly extraction methods to recover pigments and antioxidants from microalgae. Among these, supercritical fluid extraction (SFE) represents one of the most important alternatives to traditional extraction methods carried out with the use of organic solvents. In this study, the influence of parameters such as pressure, temperature, and the addition of a polar co-solvent in the SFE yields of carotenoids and fat-soluble vitamins from T. obliquus biomass were evaluated. The highest extraction of alpha-tocopherol, gamma-tocopherol, and retinol was achieved at a pressure of 30 MPa and a temperature of 40 °C. It was observed that overall, the extraction yield increased considerably when a preliminary step of sample pre-treatment, based on a matrix solid phase dispersion, was applied using diatomaceous earth as a dispersing agent. The use of ethanol as a co-solvent, under certain conditions of pressure and temperature, resulted in selectively increasing the yields of only some compounds. In particular, a remarkable selectivity was observed if the extraction was carried out in the presence of ethanol at 10 MPa and 40 °C: under these conditions, it was possible to isolate menaquinone-7, a homologous of vitamin K2, which, otherwise, cannot not recovered by using traditional extraction procedures.

BACKGROUND: Mixotrophic and heterotrophic growth of microalgae through biodegradation of olive mill wastewaters (OMW) is a promising strategy to improve the economic viability of microalgae production processes. However, OMW are characterized by an elevated phenols content, which makes their treatment by biological processes difficult.In this work, the influence of OMW phenols on microalgae growth was investigated by using the phenols extracted with a resin from OMW. RESULTS: OMW phenols, at 0.5 g L −1 , were found to inhibit the growth of Scenedesmus sp. This inhibition was reduced by replacing an inoculum in the stationary phase with an inoculum in the exponential phase. Even with this strategy, a relevant negative effect (− 30%) on maximum cell concentration was found, which could be prevented by decreasing the phenol concentration to 0.1 g L −1 . Under mixotrophic conditions, phenols reduced light penetration, limiting photosynthetic activity without significant improvement in phenols biodegradation. Under both mixotrophic and heterotrophic condition, percentage phenols removal up to 57% was achieved. CONCLUSIONS:The most promising strategy to achieve integrated microalgal cell growth and OMW phenols biodegradation is the heterotrophic cultivation with phenols concentration not greater than 0.1 g L −1 and an inoculum in exponential phase.