BACKGROUND Microalgae are a promising resource to produce carotenoids for food/feed applications. However, energy-intensive pre-treatments such as drying and cell destruction can hinder the sustainability of the process. Direct extraction from wet biomass may reduce energy consumption, but the residual water can reduce the effectiveness of the organic solvents used for the extraction. In this work, the extraction of lutein and beta-carotene from wet untreated microalgal biomass is investigated. The process includes a sequence of successive extraction stages with methanol. RESULTS We show that the sequential extraction can effectively overcome the reduced extraction efficiency induced by the residual water in the biomass. The biomass was dehydrated during the first extraction stage, which increased the efficiency starting from the second stage. This allowed an extraction yield of >95% to be attained for both lutein and beta-carotene after five extraction stages. A mathematical model was developed by coupling mass balances with a linear equilibrium model, satisfactorily describing the partition of the two carotenoids between the solid and the solvent phase. By fitting the model to the data obtained by the first extraction stage, liquid-solid partition coefficients (K-d) equal to 2.0 x 10(-3) and 1.1 x 10(-4) were estimated for lutein and beta-carotene, respectively. The K-d of both carotenoids increased to approximate to 10(-2) during the six subsequent extraction stages without water. CONCLUSIONS Direct solvent extraction from wet untreated microalgal biomass is a promising strategy to produce carotenoids. The described model can provide guidelines to design industrial processes. (c) 2020 Society of Chemical Industry