## 3 Results  
### Trials on Lactose-Based Media  
The first phase of experiments concerned the batch-cultivation of seven yeast strains on a semi-defined medium with commercial lactose as a carbon source (S\({}_{0}\approx 56\) g/L, initial C/N \(\approx 58\) moles/moles) in 250-mL shake flasks. The results are summarized in Table 2. Five strains were capable to catabolize lactose and grow. HPLC analysis of the culture fluid for all microorganisms consuming lactose and for all culture phases of the trials performed demonstrated only one peak concerning the detection performed in the RI detector, that of lactose. The size of this peak, as it was anticipated, decreased as the fermentation proceeded, demonstrating assimilation of lactose by the implicated microorganisms. Nevertheless, not any peak of glucose and/or galactose appeared, suggesting that for all strains tested, lactose was consumed without having been previously hydrolyzed, with the hydrolysis and the subsequent transformations of lactose being carried out by the relevant enzymes (\(\beta\)-galactosidase, \(\beta\)-galactosidase permease, \(\beta\)-galactosidase transacetylase) at the cellular level, in full accordance with the results reported by [PERSON] et al. [26], dealing with the growth of _C. curvatus_ strains on lactose-based carbon- and nitrogen-limited media. TDW of _C. curvatus_ ATCC 20509 was =22.0 g/L, with 3.7 g/L cellular lipids produced (17% of TDW), 0.32 g/L/h biomass productivity, and 0.054 g/L/h lipid productivity in a 69 h-long batch fermentation. _C. curvatus_ NRRL Y-1511 produced 15.5 g/L of TDW (with 5% \(w/w\) of lipid in TDW) at t = 130 h. _P. laurenti_ Y-2536 produced higher quantities of dry biomass (X = 16.5 g/L) and lipids (L = 2 g/L) than _P. laurenti_ YB-3594 (12.9 and 1.2 g/L, respectively), while both strains consumed significant lactose quantities. For _P. laurenti_ Y-2536, the dry weight determined contained both produced EPS and the yeast dry cells. _D. hansenii_ ACA-DC 5079 consumed half of the available lactose quantity and produced 5.1 g/L of TDW (12% lipid in TDW) in a 115 h-long batch fermentation. The two \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Strain** & \begin{tabular}{c} **Time** \\ **(h)** \\ \end{tabular} & \begin{tabular}{c} **S\({}_{\text{omas}}\)** \\ **(g/L)** \\ \end{tabular} & \begin{tabular}{c} **X** \\ **(g/L)** \\ \end{tabular} & \begin{tabular}{c} **L** \\ **(g/L)** \\ \end{tabular} & \begin{tabular}{c} **Y\({}_{\text{KS}}\)** \\ **(g/g)** \\ \end{tabular} & \begin{tabular}{c} **Y\({}_{\text{LS}}\)** \\ **(g/g)** \\ \end{tabular} & \
\begin{tabular}{c} **K\({}_{\text{LX}}\)** \\ **(g/L)** \\ \end{tabular} &
\begin{tabular}{c} **P\({}_{\text{L}}\)** \\ **(g/L)** \\ \end{tabular} \\ \hline _C. curvatus_ & & & & & & & & \\ ATCC 20509 & 69 & 56.4 \(\pm\) 3.1 & 22.0 \(\pm\) 1.8 & 3.7 \(\pm\) 0.4 & 0.39 & 0.07 & 0.17 & 0.054 \\ \hline _C. curvatus_ & & & & & & & & \\ MRRL Y-1511 & 130 & 55.9 \(\pm\) 2.0 & 15.5 \(\pm\) 1.5 & 0.8 \(\pm\) 0.2 & 0.28 & 0.01 & 0.05 & 0.006 \\ \hline _C. uzbekistanensis_ & & & & & & & & \\ MRRL Y-44 & 115 & Tr. & n.g. & - & - & - & - & - \\ \hline _T. ovoides_ & & & & & & & & \\ ACA-DC 5052 & 115 & Tr. & n.g. & - & - & - & - & - \\ \hline _D. hansenii_ & & & & & & & & \\ ACA-DC 5079 & 115 & 27.8 \(\pm\) 1.4 & 5.1 \(\pm\) 0.8 & 0.6 \(\pm\) 0.2 & 0.19 & 0.02 & 0.12 & 0.005 \\ \hline _P. hansenii_ & & & & & & & & \\ MRRL Y-2536 & 122 & 59.0 \(\pm\) 2.0 & 16.5 \(\pm\) 1.4\({}^{*}\) & 2.0 \(\pm\) 0.3 & 0.30 & 0.04 & 0.12 & 0.017 \\ \hline _P. lurenti_ & & & & & & & & \\ MRRL Y-3594 & 115 & 54.7 \(\pm\) 2.3 & 12.9 \(\pm\) 1.8 & 1.2 \(\pm\) 0.2 & 0.24 & 0.02 & 0.09 & 0.010 \\ \hline \multicolumn{7}{l}{T. \(<\) 0.5 g/L; n.g.: non-growth conditions; \({}^{*}\): Dry weight of both cells and EPS.} \\ \end{tabular}
\end{table}