Research On The Lipid Extraction From Wet Microalgae

With the development of global economy and population growth,demand for oil is increasing.Today,oil is not only used as food ingredients,also for biodiesel.At present,oil is mainly produced from animal source or oil crops such as soybean,rapeseed,oil palm,therefore the price of oil often fluctuates with the global supply,which is affected by climate.In recent decades,the fossil fuel is exhausting,so a series of new energy technologies are put into developing research,in which microalgal oil has attracted more and more attention.In the processes of microalgal oil production,lipid extraction is crucial for the production efficiency.A green algae strain Neochloris oleoabundans was used as research material in this paper.The cell biomass was obtained through a mass cultivation system.In this work,ultrasonic wave,high-pressure homogenization and enzymatic hydrolysis were used to discrupt the cell wall of algae,and lipid was extracted from algal cells with organic solvent.The physical properties and fatty acid compositions of microalgal oil were also studied.The results showed that all technics included ultrasonic wave,high pressure homogenization and enzymatic hydrolysis had an effect on the cell-broken.The broken rate obtained under the conditions with ultrasonic wave(800W,30min),high pressure homogenization(80MPa,twice)and enzymatic hydrolysis(1% cellulose for 2 hours,then 4% papain for 3 hours)were 38.17%,83.07%,and 51.05% respectively.It was observed by electron microscope that the algal cells were torn into pieces under high pressure homogenization.Some small holes formed on the surface of the cells by enzymatic hydrolysis were also observed,which might lead to lose the cytoplasm,as results the cell became deformed.In some extent,enzymatic hydrolysis might have just made the hard cell walls become weak,so more other rupturing methods were needed to break cells totally,so that oil could be released from the cells.The conditions of oil extraction were examined,and the factors which affected lipid yield were also studied.The the optimal extraction conditions were obtained as follows: the best extraction solvent was petroleum ether,algal concentration was OD600=50,the optimal mass ratio of petroleum ether to algae was1:3(v/v),extraction time was 4h,centrifugal time was 6min and centrifugal rate was 5500r/min.Under these optimal conditions,lipid yield was 97.56%(compared with the oil content in dry algal cell).The analysis of algal oil showed that there were not any differences in the color and smell of oils extracted through Soxhlet method and wet extraction method,however the acid value and saponification value of the lipid through wet extraction was slightly higher than Soxhlet method.GC/MS analysis demonstrated that the main fatty acids in N.oleoabundans oil were C16 and C18,and the compositons of fatty acid were similar to soybean oil and camellia oil.Especially,unsaturated fatty acids were rich in the algal oil.The trans-fatty acid was found but trace in it.In the end,the wet extraction process of Neochloris oleoabundans was economicly estimated,and the results showed that this process is feasible and had a positive meaning for promoting commercial process of microalgae oil extraction.