5.1. Soxhlet Extraction

Soxhlet extraction is traditional and known as a standard semicontinuous method that is usually applied for extracting lipids from food products [112]. For extracting organic solutes such as lipids, an organic solvent such as hexane is commonly used as the extractant [113]. The solvent is vaporized in a round bottom flask and the condensed solvent (in a condenser) is allowed to percolate through the powdered biomass before refluxing into the flask. After several cycles of evaporation, condensation and percolation of solvent through the biomass sample, the flask containing a mixture of solvent and extracted lipids is taken out to recover the crude lipids after vaporizing the solvent using a rota-evaporator [114]. Dalmas Neto et al. [115] evaluated the performance of three different solvents, hexane, chloroform and chloroform/methanol (2:1), for the extraction of lipids from dried R. toruloides DEBB 5533 using Soxhlet extraction. They discovered the amounts of lipids obtained were comparable with 46.1, 44.7 and 43.2% for hexane, chloroform/methanol and chloroform, respectively. Meanwhile, the efficiency of polar solvents such as ethanol was found to be higher than that observed for nonpolar solvents, such as hexane, in extracting polar lipids [116]. In comparison with a modified Bligh and Dyer method (using methanol and chloroform (2:1 v/v)), the Soxhlet extraction (using the same solvent mixture with a frequency of 5 cycles) was found to be less efficient in extracting lipids from R. glutanis, with 98 and 50% extraction efficiency, respectively [117]. The disadvantage of long operation time (usually around 8 h) of conventional Soxhlet extraction can be overcome by combining the Soxhlet extraction with microwave heating (operation time can be reduced to less than 1 h) [118].