Abstract:
Biodiesel production can be produced from free fatty acids of palm oil by two-step reaction using whole cell biocatalyst. This study utilized yeast Candida rugosa as the whole cell biocatalyst because it has ability to hydrolyze palm oil into free fatty acids (FFAs). The highest conversion of FFAs by C. rugosa was 82.61% after 5-day cultivation. Then, FFAs produced by C. rugosa were utilized as an inducer for extracellular lipase production of Aureobasidium pullulans var. melanogenum SRY 14-3. After optimization, the highest lipase volumetric activity and lipase specific activity of 1.18 U/mL and 17.28 U/mg protein were obtained by using 3% w/v FFAs at 30 ºC for 5 days, respectively. Subsequently, the study of esterification by A. pullulans var. melanogenum SRY 14-3 revealed that the highest biodiesel conversion yield of 21.39% was achieved when FFAs concentration to methanol molar ratio of 1:1 was employed at 30°C, 72 h. For whole cell biocatalysts using yeast cell surface display technique, Lipase1 and Lipase3 genes from C. rugosa (CRL1 and CRL3) and Lipase gene from A. pullulans var. melanogenum SRY 14-3 (AML) were fused with PpPIR1 anchor protein and then cloned into Pichia pastoris KM71 host strain to construct Pp-CRL1, Pp-CRL3 and Pp-AML, respectively. It was found that the recombinant yeast Pp-CRL1 and Pp-CRL3 strains produced the highest lipase activity on cell surface of 1,499.9 mU/OD600 and 181.9 mU/OD600 at 5 and 4 days of induction with 2% v/v methanol, respectively. For the recombinant Pp-AML strains, the highest lipase activity on cell surface was achieved at 30.48 mU/OD600 after 3 days of induction with 1% v/v methanol. In addition, the optimal pH and temperature of lipase activity of recombinant yeast Pp-CRL1 and Pp-CRL3 were pH 7 and 50°C and 40°C, respectively. On the contrary, the optimal pH and temperature of lipase activity of Pp-AML was observed at pH 8 and 35°C, respectively. After hydrolysis of palm oil by using Pp-CRL1 and Pp-CRL3 at different combinations, our results suggested that the use of Pp-CRL1 alone was able to produce the highest FFAs yield of 14.26% at 45°C for 48 h. The study of the esterification of FFAs by using Pp-AML as whole cell will be further evaluated.