In the process of acid washing, 5 ml different concentrations of HCl were added into 0.2 g dry cells of P. rhodozyma for 45 min. At the same time, 5 ml deionized water (pH 7.0) was added into 0.2 g dry cells of P. rhodozyma for 45 min as control. Then they were both centrifuged at 7200 r·min−1 for 3 min. After that, the supernatant was removed and the cells of P. rhodozyma were transferred into a 50 ml centrifuge tube for further solvent extraction.