Fig. 6

Second derivatives of the FTIR absorption spectra of S. cerevisiae BY4741 opi1Δ cells, in the absence and in the presence of lactic acid: stationary phase. Cells were grown in shake flasks in minimal (YNB) medium with 2 % w/v glucose in the absence and in the presence of 46 g/L of lactic acid (LA) at pH3. FTIR analysis was performed at 40 h after the inoculation, corresponding to the stationary phase of growth. a amide I band; b vibrational modes mainly due to lipid CH₂/CH₃ and to phosphate groups, c stretching modes from lipid hydrocarbon tails. In a and b second derivative spectra have been normalized to the tyrosine band at ~1516 cm⁻¹, while in c spectra have been normalized at the CH₃ band at ~2959 cm⁻¹