Lipid production by yeasts growing on biodiesel-derived crude glycerol: strain selection and impact of substrate concentration on the fermentation efficiency.

AIMS: To screen yeasts in relation to the potential to produce single cell oil (SCO) from biodiesel-derived glycerol and to enhance SCO production in Lipomyces starkeyi and Rhodosporidium toruloides yeasts. METHODS AND RESULTS: Yarrowia lipolytica, Cryptococcus curvatus, R. toruloides and L. starkeyi were grown in nitrogen-limited flask cultures. Yarrowia lipolytica strains produced citric acid and mannitol. Lipomyces starkeyi DSM 70296 and R. toruloides NRRL Y-27012 showed potential for SCO production, and were cultivated at increasing the initial glycerol concentrations with the initial nitrogen concentration remaining constant. Significant biomass and SCO production were reported even in cultures with high initial glycerol concentrations (i.e. 180 g l(-1) ). Lipid quantities of c. 12 g l(-1) (lipid in dry cell weight 35-40%) were obtained for both L. starkeyi and R. toruloides, quite high values compared with literature values for oleaginous micro-organisms growing on glycerol. However, these strains exhibited different kinetic profiles in the synthesis of intracellular polysaccharides. Lipomyces starkeyi produced a significant quantity of polysaccharides (c. 7 g l(-1) ). The yeast lipids contained mainly oleic and palmitic and to a lesser extent linoleic and stearic acids. CONCLUSIONS: Lipomyces starkeyi and R. toruloides are potential SCO producers from crude glycerol. SIGNIFICANCE AND IMPACT OF THE STUDY: Very scarce numbers of reports have indicated the production of SCO by L. starkeyi and R. toruloides growing on glycerol. We report here that these yeasts are able efficiently to convert raw glycerol into SCO, while L. starkeyi also synthesizes intracellular polysaccharides in marked quantities.

Volatile profiles of healthy and aflatoxin contaminated pistachios.

The volatile profile of four different groups of dried pistachios namely: H: healthy, NC: naturally contaminated with aflatoxin, AC: artificially contaminated with aflatoxigenic strains of the fungi Aspergillus flavus and ANT: artificially contaminated with non-toxigenic strains of the fungi A. flavus, was determined. The volatiles were isolated by the HS-SPME method and determined by GC-FID and GC-MS, whereas aflatoxin by HPLC. Seventy two volatile compounds were identified almost equally distributed among the above four studied groups. The predominant chemical compounds were monoterpenes, alcohols, ketones, aldehydes, esters and hydrocarbons. The monoterpenes, mainly determined as α-pinene and α-terpinolene were detected in all samples. Even though the general volatile profile was similar among groups, some differences were detected between healthy and contaminated groups of samples. When some key volatiles such as eight-carbon and seven-carbon alcohols and aldehydes were used along with the species-specific sesquiterpenes and the other terpenes detected, a correct classification was obtained in H, NC, AC and ANT groups, as was demonstrated by cluster and discriminant analyses. This evidence provides a potential tool for distinguishing contaminated samples on the basis of characteristic volatile patterns.