CD, DSF and ITFE measurements under different pH conditions. Data were collected at pH 4.0 (black line), 5.0 (green line), 6.0 (blue line), 7.0 (red line), 8.0 (purple line) and 9.0 (orange line). (A) Far-UV CD spectra from 195 to 250 nm using 0.3 mg.mL−1 of protein sample. (B) Normalized thermal denaturation curves using SYPRO-Orange as the fluorescent probe. (C) Melting temperature (Tm) calculated from the Boltzmann fit of denaturation curves as a function of pH. (D) Tryptophan maximum emission wavelength (black squares and black line) and Parameter A calculation analysis (red squares and red line) as a function of pH. LbNDK (0.06 mg.mL−1) tryptophan emission was monitored from 300 to 450 nm using an excitation wavelength of 295 nm.