Free Fatty Acids Reduction in Waste Cooking Oil by Rhodosporidium toruloides and Simultaneous Carotenoids,Lipids, and PAL Enzyme Production in a Two-Phase Culture System

Waste cooking oil (WCO) is a problematic waste product that contains free fatty acids (FFAs), preventing it from being valorized easily as biodiesel and poses an environmental hazard if incorrectly disposed. The use of WCO as a carbon source for Rhodosporidium toruloides (R. toruloides) using a two-phase culture system is developed. The normal growth of R. toruloides when cultured in WCO (OD₆₀₀ 52) reveals its ability to use a hydrophobic substrate as the carbon source compared to glucose (OD₆₀₀ 51.9). Interestingly, the extracellular lipase activity when R. toruloides is grown on WCO is 14.4 U mL⁻¹ compared to when grown on glucose (2.4 U mL⁻¹). Additionally, FFA levels in WCO are reduced from 2% to 0.2% at end of fermentation, suggesting that R. toruloides can consume FFA. Furthermore, higher yield of beneficial products: β-carotene (4.57 µg mL⁻¹), torularhodin (4.2 µg mL⁻¹), fatty acids (1 mg mL⁻¹), and phenylalanine ammonia-lyase (PAL) enzyme (0.12 µmol mg⁻¹) are produced when WCO is the carbon source, compared to glucose (4.1 µg mL⁻¹ β-carotene, 3.0 µg mL⁻¹ torularhodin, 1 mg mL⁻¹ of fatty acids, and 0.096 µmol mg⁻¹ PAL enzyme). This is a first study that shows R. toruloides can grow on hydrophobic carbon source.