## Results and Discussion
### Cellular Lipids of Yarrowia lipolytica LMBF Y-46
Compared with the equivalent flask experiment (_Gly\({}_{0}\)_\(\approx\) 100 g/L), and despite the higher oxygenation that occurred in the fermentation vessel, the microorganism produced noticeably lower lipid quantities in the bioreactor experiment (see Figure 7b, bioreactor experiment, fermentation time \(t\) = 0-66 h, in which lipid DCW values were \(\approx\)5% _u/v_). After the two consecutive pulses with concentrated glycerol into the medium, lipid in yeast mass quantities somehow increased (to values \(\approx\) 10-12% _u/v_). This total lipid quantity increase occurred simultaneously with cell autolysis and substantial decrease in dry biomass concentration (Figure 4a), indicating once more, that despite cell autolysis, _Y. lipolytica_ biomass was quite active at the late fermentation steps in the bioreactor culture. Figure 6: Kinetics of dry yeast cell mass production (_X_, g/L), glycerol assimilation (_Gly_, g/L) and total polyols production (_Pol_, g/L) during _Yarrowia lipolytica_ growth on initial glycerol adjusted to \(\approx\)70 g/L in shake-flask experiments under nitrogen-limited conditions. Culture conditions as in Table 3. Each experimental point is the mean value of two independent determinations (SE \(\leq\) 18%). Total cellular lipids were converted into their corresponding FAMEs, and cellular fatty acid (FA) composition analysis was performed for the late growth phase in the case of the shake-flask cultures, and throughout the culture, for the fed-batch bioreactor experiment (Table 6). In general, FA composition of total lipids of the strain LMBF Y-46 presented important similarities with those reported for various other _Y. lipolytica_ strains cultivated in batch flask and bioreactor cultures, during growth on glycerol or similarly metabolized compounds, under nitrogen limitation [8,16,18,19,21,22,23,38,40,49,53]. Specifically, the yeast lipids were mainly composed of the FAs oleic (C18:1), palmitic (C16:0), palmitoleic (C16:1), stearic (C18:0) and linoleic (C18:2). No quantities of other poly-unsaturated FAs (i.e., \(\alpha\)-linolenic acid--C18:3) were detected inside the yeast lipids in accordance with the literature [5,9,83]. Small but not negligible quantities of lower (i.e., capric--C10:0, lauric--C12:0 and myristic--C14:0) or higher (i.e., arachidonic--C20:0, behenic--C22:0 and lignoercim--C24:0) aliphatic chain saturated FAs have also been detected in the yeast lipids (Table 6). An interesting result that was observed through the cellular lipid analysis, referred to the fact that cellular lipids were somehow more saturated (mostly more rich in the FAs C16:0 and C18:0) in the shake-flask experiments compared with those obtained in the bioreactor cultures. In the latter case, cellular lipids were notably richer in the FAs C18:1 and C18:2. This could reflect the fact that bioreactor cultures were conducted under higher aeration compared with the flasks. Moreover, the first experimental point in the bioreactor trial that somehow presented higher concentrations of the cellular palmitic and stearic acids (\(t\) = 20.5 h) compared with all other experimental points in this bioreactor experiment (see Table 6), could be attributed to the fact that at this very fermentation point, the DOT value (in %, %/\(\psi\)) was the lowest one in the relevant bioreactor trial (at \(t\) = 20.5 h, DOT value into the reactor vessel was \(\approx\)20% \(\psi\ell\), and thereafter it increased; see Figure 4a). Similarly with this result, higher concentrations of the cellular FAs C16:0 and C18:0 have been noted in the beginning of other batch cultures performed by several _Y. lipolytica_ strains on glucose or glycerol. These concentrations decreased as fermentations proceeded [23,38,39,49]. This could be attributed to the lower DOT values in these cultures at the early growth steps of the balanced growth phase of _Y. lipolytica_ yeast. Finally, in accordance with the FA composition analysis results presented in the current investigation, strains of the oleaginous yeast _A.