Microbial lipid produced by Yarrowia lipolytica QU21 using industrial waste: a potential feedstock for biodiesel production.

This study aimed to evaluate the effect of medium composition and culture conditions on lipid content, fatty acid profile and biomass production by the yeast Yarrowia lipolytica QU21. Lipid production by the yeast growing on glycerol/(NH4)2SO4 (10%/0.1%) reached 1.48g/L (30.1% according to total cell dry weight). When glycerol was replaced by crude glycerol (industrial waste), the lipid yield was 1.27g/L, with no significant difference. Some particular fatty acids were found when crude glycerol was combined with fresh yeast extract (FYE, brewery waste), as linolenic acid (C18:3n3), eicosadienoic acid (C20:2), eicosatrienoic acid (C20:3n3) and eicosapentaenoic acid (C20:5n3). In addition, the FYE promoted an increase of more than 300% on polyunsaturated fatty acid content (PUFA), which is an undesirable feature for biodiesel production. The fatty acid composition of the oil produced by Y. lipolytica QU21 growing on crude glycerol/(NH4)2SO4 presented a potential use as biodiesel feedstock, with low PUFA content.

An environmentally-friendly fluorescent method for quantification of lipid contents in yeast.

This study aimed at developing an efficient, fast and environmentally-friendly method to quantify neutral lipid contents in yeast. After optimising the fluorescence instrument parameters and influence of organic solvent concentrations, a new method to quantify neutral lipids in yeast based on fluorescence was demonstrated. Isopropanol and Nile red in concentrations of 5% (final volume%) and 500 µg/L, respectively, were added to washed cells suspended in potassium chloride phosphate buffered saline (PBSKCl). Fluorescence was measured after 10 min in the dark. Glyceryltrioleate was used as model lipid and the calibration curve showed linearity (R(2)=0.994) between 0.50 and 25 mg/L. Compared with traditional gravimetric analysis, the developed method is much faster and uses less organic solvents. Lipid contents determined by fluorescence and gravimetry were the same for some strains, but for other strains the lipid contents determined by fluorescence were less. This new method will therefore be suitable for fast screening purposes.

Production of functional killer protein in batch cultures upon a shift from aerobic to anaerobic conditions

The aim of this work was to study the production of functional protein in yeast culture. The cells of Saccharomyces cerevisiae Embrapa 1B (K+R+) killed a strain of Saccharomyces cerevisiae Embrapa 26B (K-R-)in grape must and YEPD media. The lethal effect of toxin-containing supernatant and the effect of aeration upon functional killer production and the correlation between the products of anaerobic metabolism and the functional toxin formation were evaluated. The results showed that at low sugar concentration, the toxin of the killer strain of Sacch. cerevisiae was only produced under anaerobic conditions . The system of killer protein production showed to be regulated by Pasteur and Crabtree effects. As soon as the ethanol was formed, the functional killer toxin was produced. The synthesis of the active killer toxin seemed to be somewhat associated with the switch to fermentation process and with concomitant alcohol dehydrogenase (ADH) activity.

Influence of Brettanomyces custersianus upon the activity of Saccharomyces cerevisiae strains during the tumultuous phase of vinification

The aim of this work was to evaluate the influence of Brettanomyces custersianus on the metabolic activity of Saccharomyces cerevisiae during the tumultuous stage of wine production. The Cabernet Sauvignon grape must with the skin was inoculated with individual cultures of Sacch. cerevisiae and with mixed cultures of Sacch. cerevisiae and Br. custersianus. During the 6-day tumultuous phase of fermentation, the highest ethanol production and the highest sugar consumption were obtained with the strains without B. custersianus. Fermentations carried out with the addition of Brettanomyces metabolites, acetic acid and 4-ethylphenol, showed that only the former inhibited the growth of both Sacch. cerevisiae strains used. In some cases, Br. custersianus could affect the rate higher alcohols production and their final concentrations during the tumultuous phase of vinification.