Process for selective extraction of pigments and functional proteins from Chlorella vulgaris

Extraction of multiple high-value products is recommended for sustainability of the microalgal production platform. This study proposes a process for selective extraction of carotenoids and chlorophylls with ethanol, followed by alkaline pH extraction of proteins from wet, freeze-thawed Chlorella vulgaris biomass. A biomass-tosolvent ratio of 1:5 and 3 extraction stages were required to achieve maximum extraction yield of chlorophylls and carotenoids. The main compounds in the ethanol extract were identified as lutein, chlorophyll a and chlorophyll b. The lutein and total chlorophyll yield in the extracts were 5.4 mg/g and 15.4 mg/g dry biomass respectively. Effective protein release from freeze-thawed biomass was contact-time dependent and > 76% of total protein could be extracted in 15 min via bead-milling, and in 6 min by high-pressure homogenization at 15000 psi. Ethanol extraction of pigments affected protein solubility, and an alkaline pH was required to release the same total protein. Concentration and fractionation of proteins was carried out using a two-stage membrane filtration process and 78-80% of proteins remained in the 300 kDa retentate. Ethanol treatment and higher pH conditions did not negatively impact membrane filtration, nutritive value, or the emulsification properties of protein concentrates.