Investigation On Wet Extraction Of Edible Oil From Microalgae And The Quality Analysis Of Microalgal Oil

Microalgae,as an abundant source of lipids and polyunsaturated fatty acids,can be an ideal feedstock for oil production.Microalgae can thrive in aqueous media,and have high photosynthetic efficiencies,short growth cycle,and ability to utilize CO2 in reduction of greenhouse gases emissions.The objective of this study was to develop wet extraction methods to obtain oils from microalgae,and to analyze the composition and quality of microalgal oil.Various pretreatment methods were used to disrupt microalgae(Schizochytrium sp.)cells,evaluated their effects on cell disruption efficiency and oil yield.The result showed ultrasonication and high pressure homogenization methods had a positive effect on the disruption process.Ultrasonication presented the highest oil yield(24.83 %)at 630 W for 12 min.Moreover,ultrasonic treatment obtained higher contents of total phenolic,and its oil exhibited superior DPPH radical scavenging capacity.Five enzymes were evaluated for their effectiveness in aqueous enzymatic extraction,and Papain was found to be the best for obtaining a highest free oil yield(19.29%)and total oil yield(28.05%).The optimal extraction condition was predicted by Box–Behnken design.The optimal process parameters: liquid to solid ratio 4.8 m L/g,enzyme concentration 2.50 %,reaction time 2.2 h.An optimal free oil yield of 22.06% and total oil yield of 30.30% were achieved under optimal conditions.It appears that enzymolysis probably induced the breakdowns of peptide bonds,leading to an increase in the degree of hydrolysis and protein solubility,which possibly caused a breakdown in the protein network and the unfolding of protein aggregates,thereby liberating the oil to improve the free oil yield.The oil was extracted from microalgae by salt aided aqueous extraction method with sodium chloride solvent as the extractive medium.The optimal conditions were sodium chloride concentration 0.45 mol/L,temperature 59.0 ?,reaction time 2.70 h,ethanol concentration 23.0 %(V/W),the oil yield can reach 27.09 %.Oil droplet size of the emulsion was apparently increased with salt aided treatment,resulting in oil droplet coalescence.The physicochemical properties of microalgae oil obtained by solvent extraction,aqueous enzymatic extraction and salt aided aqueous extraction were compared.There were significant(p < 0.05)differences in the acid value,peroxide value,iodine value and colour among oils extracted by different methods.The fatty acid composition of microalgal oils exhibited the predominance of docosahexaenoic acid and palmitic acid.The carotenoids content was slightly higher in solvent extracted oil;the aqueous enzymatic extracted oil exhibited higher contents of total phenolics and total tocopherols.Moreover,the aqueous enzymatic extracted oil exhibited considerable antioxidant activities.The oxidative stability of microalgal oil was investigated,the peroxide value,conjugated diene values,conjugated triene values,and thiobarbituric acid reactive substances of the control sample increased with the extension of storage time.The oil samples with antioxidants showed superior oxidative stability compared with the control samples.The results in present study revealed that the antioxidant activity of TBHQ was better than BHT and VE,improving the oxidative stability of microalgal oil.