Crude glycerol impurities improve Rhizomucor miehei lipase production by Pichia pastoris

Crude glycerol, a by-product of biodiesel production, was employed as the carbon source to produce lipase using Pichia pastoris. Under identical fermentation conditions, cell growth and lipase activity were improved using crude glycerol instead of pure glycerol. The impacts of crude glycerol impurities (methyl ester, grease, glycerol, methanol, and metal ions Na+, Ca2+, and Fe3+) on lipase production were investigated. Impurities accelerated P. pastoris entering the stationary phase. Na+, Ca2+, and grease in waste crude glycerol were the main factors influencing higher lipase activity. Through response surface optimization of Ca2+, Na+, and grease concentrations, lipase activity reached 1437 U/mL (15,977 U/mg), which was 2.5 times that of the control. This study highlights the economical and highly efficient valorization of crude glycerol, demonstrating its possible utilization as a carbon source to produce lipase by P. pastoris without pretreatment.