Biodiesel must meet certain requirements to be used as a fuel, some of which rely on the fatty acid mixture used in biodiesel production.
In Uruguay, standards for biodiesel indicate that cetane number must be higher than 45, and no more than 12% of linolenic acid esters and 1% of esters from polyunsaturated acids (more than 4 double bonds) is admitted
[22]. The fatty acid profiles obtained from the yeast selected in this paper met Uruguayan standards for biodiesel when grown with different carbon sources, including crude glycerol.
Thus, the use of that secondary product obtained from biodiesel production appears as an option of carbon source to produce oleaginous yeasts, in order to reduce the
costs.
It was demonstrated that a concentration of the substrate to achieve 60 g l-1 of glycerol could be incorporated in the culture medium, without affecting yeast growth.
Moreover, a higher concentration of intracellular lipids was achieved in such conditions, which was probably due to a higher C/N ratio in the culture medium.
Last year, in Uruguay, 50000 ton of biodiesel were produced by ALUR (National Supply Company) to be incorporated in a proportion of 7% to diesel for locomotive use
[23]. However, the production cost of biodiesel is not economically competitive with petroleum-based fuel because of the relatively high cost of the oil feedstock.
Moreover, the use of vegetable oils as raw material for biodiesel production other studies[25, 26].
However, the lipid production could be improved. In this regard, Lin et al.
[27] designed a two-stage fermentation process to obtain a lipid concentration 67.9 gl-1 from the yeast Lipomyces starkeyi. The optimization of the growing conditions for R. graminis S12R will be the next step in order to obtain the maximum lipid yield.
competes with edible oils, thus leading to a soaring of food price.
According to Duarte [24] about 600 kg of oil can be produced annually from 1 hectare of soybean, which can be used for biodiesel production.
Since a lipid production of 5 gl-1 was obtained from R. graminis S12R growing in crude glycerol, about 120 000 liters of such culture would be required for the production an amount of oil equivalent to that obtained from 1 hectare of soybean.
Even if 120000 liters seems a very high volume, it should be considered that yeast culture for oil production takes only 5 days, while soybean crop is annual.
Lipid yield on glycerol obtained in the present study showed similar results when compared with