Separation of microalgal docosahexaenoic acid-rich oils using a microwave-assisted three-phase partitioning system

Abstract

A novel and efficient microwave-assisted three-phase partitioning system (MA-TPPS) was developed to separate and purify docosapentaenoic acid (DPA) and docosahexaenoic acid-rich oils from protein, carbohydrate, flavonoids and other raw components in cultivation broths of microalgae Schizocytrium limacinium SR21. The MA-TPPS was optimized by a three-level four independent factor central composite design (CCD) to create response surfaces using response surface methodology (RSM). The optimized parameters were concentrations (w/w, %) of n-hexane (37.5%) potassium acetate (13.33%), and cultivation broths (33.33%), as well as microwave power duration (650 W for 25 s) and pH (7.2). The corresponding yields obtained under optimized conditions are 96.97 ± 1.22% of β-carotene, 94.88 ± 0.93% of astaxanthin, 98.90 ± 0.89% of DHA, and 98.36 ± 1.11% of total fatty acids (TFAs) in oils, respectively, as well as 99.18 ± 0.98% of oils in the n-hexane phase. While 94.79 ± 0.96% protein was recovered in the middle solid interface and 93.29 ± 1.25% total flavonoids in the bottom salt-phase. The validated model system was scaled-up at the laboratory level from 15 g to 50 g. The recovery yields of all components in scale-up experiments were the same. The extracted DHA-oil was purified by semi-preparative high performance liquid chromatography (HPLC) and analyzed by nuclear magnetic resonance (NMR). The purification yield of DHA was comparable to that of the conventional method. These facts, along with higher product yield in a short time and easily scalable characteristics, enable us to use MA-TPPS for separation and purification of DPA & DHA-rich oils from microalgae biomass.