Optimizing pressurized liquid extraction of microbial lipids using the response surface method.

Response surface methodology (RSM) was used for the determination of optimum extraction parameters to reach maximum lipid extraction yield with yeast. Total lipids were extracted from oleaginous yeast (Rhodotorula glutinis) using pressurized liquid extraction (PLE). The effects of extraction parameters on lipid extraction yield were studied by employing a second-order central composite design. The optimal condition was obtained as three cycles of 15 min at 100°C with a ratio of 144 g of hydromatrix per 100 g of dry cell weight. Different analysis methods were used to compare the optimized PLE method with two conventional methods (Soxhlet and modification of Bligh and Dyer methods) under efficiency, selectivity and reproducibility criteria thanks to gravimetric analysis, GC with flame ionization detector, High Performance Liquid Chromatography linked to Evaporative Light Scattering Detector (HPLC-ELSD) and thin-layer chromatographic analysis. For each sample, the lipid extraction yield with optimized PLE was higher than those obtained with referenced methods (Soxhlet and Bligh and Dyer methods with, respectively, a recovery of 78% and 85% compared to PLE method). Moreover, the use of PLE led to major advantages such as an analysis time reduction by a factor of 10 and solvent quantity reduction by 70%, compared with traditional extraction methods.

Aeration strategy: a need for very high ethanol performance in Saccharomyces cerevisiae fed-batch process.

In order to identify an optimal aeration strategy for intensifying bio-fuel ethanol production in fermentation processes where growth and production have to be managed simultaneously, we quantified the effect of aeration conditions--oxygen limited vs non limited culture (micro-aerobic vs aerobic culture)--on the dynamic behaviour of Saccharomyces cerevisiae cultivated in very high ethanol performance fed-batch cultures. Fermentation parameters and kinetics were established within a range of ethanol concentrations (up to 147 g l(-1)), which very few studies have addressed. Higher ethanol titres (147 vs 131 g l(-1) in 45 h) and average productivity (3.3 vs 2.6 g l(-1) h(-1)) were obtained in cultures without oxygen limitation. Compared to micro-aerobic culture, full aeration led to a 23% increase in the viable cell mass as a result of the concomitant increase in growth rate and yield, with lower ethanol inhibition. The second beneficial effect of aeration was better management of by-product production, with production of glycerol, the main by-product, being strongly reduced from 12 to 4 g l(-1). We demonstrate that aeration strategy is as much a determining factor as vitamin feeding (Alfenore et al. 2002) in very high ethanol performance (147 g l(-1) in 45 h) in order to achieve a highly competitive dynamic process.

Improving ethanol production and viability of Saccharomyces cerevisiae by a vitamin feeding strategy during fed-batch process.

Several bottlenecks in the alcoholic fermentation process must be overcome to reach a very high and competitive performance of bioethanol production by the yeast Saccharomyces cerevisiae. In this paper, a nutritional strategy is described that allowed S. cerevisiae to produce a final ethanol titre of 19% (v/v) ethanol in 45 h in a fed-batch culture at 30 degrees C. This performance was achieved by implementing exponential feeding of vitamins throughout the fermentation process. In comparison to an initial addition of a vitamin cocktail, an increase in the amount of vitamins and an exponential vitamin feeding strategy improved the final ethanol titre from 126 g l(-1) to 135 g l(-1) and 147 g l(-1), respectively. A maximum instantaneous productivity of 9.5 g l(-1) h(-1) was reached in the best fermentation. These performances resulted from improvements in growth, the specific ethanol production rate, and the concentration of viable cells in response to the nutritional strategy.

Improvement of red pigment/citrinin production ratio as a function of environmental conditions by monascus ruber

The growth and metabolic behaviour of the filamentous fungus Monascus ruber were studied in submerged cultures under various aeration and agitation conditions. Improving the oxygen supply, by increasing either the air input or the agitation speed, resulted in modified metabolism: the biomass yield, the consumption of the nitrogen source (monosodium glutamate), and the production of secondary metabolites (red pigment and citrinin) all increased. However, the citrinin production increased more than that of the red pigment. In consequence, a low oxygen transfer coefficient was required to improve the red pigment/citrinin production ratio. Copyright 1999 John Wiley & Sons, Inc.