A new lipase from the yeast Yarrowia lipolytica was isolated and used in the enzymatic ring-opening polymerization of lactones. The effect of used commercial oil from a vacuum pump (instead of olive oil) and in the presence of wheat flour was evaluated. It was found that lipase production is favored when wheat flour and used commercial oil is added instead of olive oil with an incubation time of 16.5 h at 29 degrees C and 250 rpm. Lipase shows a specific activity of 3.47 nmoles of 4-methyl umbelliferone released/mg of protein/min. In this way, preculture step can be avoided and an important reduction in production time can be obtained. In vitro polymerization of e-caprolactone at different temperatures in the presence of n-heptane for 15 days produces low-molecular-weight polyesters with unique multiphase morphology. Polyesters were characterized by NMR (solution and solid-state) spectroscopy, differential scanning calorimetry (DSC), Fourier-transformed infrared, wide-angle X-ray scattering and MALDI-TOF. Polyester crystallinities calculated by DSC were high, as expected for low-molecular-weight PCLs. Final polymer possesses carboxylic acid and hydroxyl end-groups, as determined by H-1- and C-13 NMR analysis. (C) 2008 Wiley Periodicals, Inc.