l-Lactic acid production from glucose and xylose with engineered strains of Saccharomyces cerevisiae: aeration and carbon source influence yields and productivities

Table 1 Physiological parameters of strain IBB14LA1_5 in anaerobic, aerobic and microaerophilic xylose-to-lactic acid conversions

Conditions	YX_AN	YX_AE^a	YX_MA
c_Xyl/c_LA [g L⁻¹]^b	4.0/3.5	22.0 (11.6)/0.7 (2.9)	15.5/7.8

Conditions	YX_AN	YX_AE^a	YX_MA
Conditions	YX_AN	YX_AE^a	Phase I^e (0–27 h)	Phase II (27–143 h)
Q_Xyl/Q_LA [g L⁻¹ h⁻¹]	0.03 ± 0.01/0.03 ± 0.00	0.25 ± 0.01/0.05 ± 0.00	0.31 ± 0.07/0.11 ± 0.00	0.12 ± 0.00/0.04 ± 0.01
Y_LA [g g ⁻¹_Xyl ]	0.80 ± 0.05	0.03 ± 0.01 (0.25 ± 0.01)	0.24 ± 0.04	0.38 ± 0.01
Y_Ethanol [g g ⁻¹_Xyl ]	0.04 ± 0.01	n.d.	n.d.	n.d.
Y_Glycerol [g g ⁻¹_Xyl ]	n.d.	n.d.	n.d.	n.d.
Y_Xylitol [g g ⁻¹_Xyl ]	0.08 ± 0.01	0.1 ± 0.00 (0.1 ± 0.00)	n.d.	0.02 ± 0.00
Y_Acetate [g g ⁻¹_Xyl ]	0.04 ± 0.01	n.d.	0.18 ± 0.04	0.10 ± 0.01
Y_Biomass [g g ⁻¹_Xyl ]	n.a. ^c	n.a. ^c	0.31 ± 0.03	n.d.
Y_Pyruvate [g g ⁻¹_Xyl ]	n.d.	0.02 ± 0.00	n.d.	n.d.
Y_CO2 [g g ⁻¹_Xyl ]	n.a.	n.a.	0.25 ± 0.02	0.58 ± 0.01
C-recovery [%]	100.8 ± 7.0	n.a. ^d	94.6 ± 2.2	99.6 ± 4.9

n.d. not detectable, n.a. not analyzed
^aParameters were determined for the entire fermentation time (72 h). Parameters in brackets were determined for 41 h of fermentation, when lactic acid concentration was the highest (see time courses in Fig. 5a). Q_LA and Q_Glc represent initial volumetric consumption and production rates and are therefore unaffected by the lactic acid uptake
^bConsumed xylose and final lactic acid titers
^cY_Biomass could not be determined due to addition of CaCO₃ for pH stabilization
^dBecause of lactic acid uptake (Fig. 5a) C-recovery could not be determined
^eYields and mass balance were calculated on consumed xylose and ethanol

ISSN: 1475-2859