Optimization of Lipase-Catalyzed Transesterification of Cotton Seed Oil for Biodiesel Production Using Response Surface Methodology

The aim of this work was to study the biodiesel production from cotton seed oil by lipase produced by Pichia guilliermondii lipase, which was immobilized onto hydrophobic magnetic particles (HMPs). The optimum reaction conditions were determined for lipase dosage, methanol-to-oil molar ratio, temperature and water content. Using response surface methodology, a quadratic polynomial equation was obtained for fatty acid methyl esters (FAMEs) content by multiple regression analysis. Verification experiments confirmed the validity of the predicted model. The optimal conditions for the enzymatic transesterification were temperature of 38.76℃, 31.3% immobilized lipase, 10.4% water content, and a methanol-to-oil molar ratio of 4.715:1. The gas chromatography- mass spectrometry showed that biodiesel was mainly composed of the methyl esters of hexadecanoic, 9,12-octadecadienoic and 9-octadecadienoic acid.

Effect of nitrogen limitation on cell growth, lipid accumulation and gene expression in Chlorella sorokiniana

The influence of nitrogen (N) limitation on the cell growth, chlorophyll content, intracellular lipid production and expression levels of two pathway genes in Chlorella sorokiniana was investigated in mixotrophic culture in this study. The maximum biomass concentration of C. sorokiniana cultured in modified BG11 medium containing 3, 6, 9, 12 and 15 mM N were 1.60, 2.21, 2.74, 3.18 and 3.21 g/L of dry cell weight, respectively with maximum specific growth rate of 0.180, 0.198, 0.201, 0.203, 0.206 day−1 during culture with an initial N feed of 3, 6, 9, 12 and 15 mM in the first eight days, respectively. The maximum lipid content was 51 % with 3 mM N. However, the maximum lipid productivity of 0.00884 g L−1 day−1 was achieved with 6 mM N. Expression levels of accD (heteromeric acetyl-CoA carboxylase beta subunit) and accI (homomeric acetyl-CoA carboxylase) genes in C. sorokiniana were studied by real-time PCR. Increased expression levels of accD reflected the increased lipid content in stationary phase. In contrast, expression of the acc1 gene always remained low, showing that the gene might not be critical for lipid accumulation.