Aims: To study the biochemical response of Yarrowia lipolytica LGAM S(7)1 during growth on raw glycerol (the main by-product of bio-diesel production units) in order to produce metabolic products of industrial signi®cance. Methods and Results: Yarrowia lipolytica was cultivated on raw glycerol or glucose in¯asks. Although nitrogen-limited media were employed, growth was not followed by production of reserve lipid. Nitrogen limitation led to citric acid excretion. Growth and citric acid production parameters on glycerol were similar to those obtained on glucose. When high initial glycerol media were used, citric acid up to 35 g l )1 (yield 0á42±0á44 g acid g )1 glycerol consumed) was produced. Conclusions: Raw glycerol was an adequate substrate for Y. lipolytica. Growth was not followed by reserve lipid accumulation, but amounts of citric acid were produced. Signi®cance and Impact of the Study: Raw glycerol is an industrial feedstock appearing in increasing quantities as the main by-product of bio-diesel production facilities. The present study describes an alternative way of glycerol valorization, with the production of remarkable amounts of citric acid, in addition to its main valorization way (production of 1,3-propanediol by bacteria).

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Yarrowia lipolytica was cultivated on mixtures of saturated free fatty acids (an industrial derivative of animal fat called stearin), technical glycerol (the main by-product of bio-diesel production facilities), and glucose. The utilization of technical glycerol and stearin as co-substrates resulted in higher lipid synthesis and increased citric acid production than the combination of glucose and stearin. The lipids produced contained significant amounts of stearic acid (50-70%, wt/wt) and lower ones of palmitic (15-20%, wt/wt), oleic (7-20%, wt/wt), and linoleic (2-7%, wt/wt) acid. Single-cell oil having a composition similar to cocoa-butter up to 3.4 g/L was produced, whereas in some cases relatively increased citric acid quantities (up to 14 g/L) were excreted into the growth medium. The microorganism presented a high specificity for lauric, myristic, and palmitic acid, while a discrimination for the stearic acid was observed. As a conclusion, microbial metabolism could be directed by using mixtures of inexpensive saturated fats, glycerol, and glucose as co-substrates, in order to accumulate lipids with predetermined composition, e.g., cocoa-butter equivalents.

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