*2.5. Matrix-Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS)*

Prior to MALDI-TOF-MS analysis, a purified Ser-lacticaseicin 30 suspension was concentrated using PierceTM C18 tips (Thermo Scientific, Waltham, MA, USA) according to the manufacturers' instructions. MALDI-TOF mass-to-charge (*m*/*z*) ratios of Ser-lacticaseicin 30 were obtained using α-cyano-4-hydroxycinnamic acid (HCCA, 10 mg/mL) as matrix on an Autoflex SpeedTM (Bruker Daltonics, Bremen, Germany), running Flexcontrol 3.4 software (Bruker Daltonics). The Bruker bacterial test standard (Bruker Daltonics) was used to calibrate the mass spectrometer according to the manufacturer's recommendations. Mass spectra were acquired in the positive linear ion mode across a *m*/*z* ratio of 2000–20000 Da using the manufacturer's automatic method MBT\_FC.par. The MALDI-TOF-MS spectra corresponded to an accumulation of 3000 laser shots, in 500 shot steps performed randomly on different areas of the spot. MALDI-TOF-MS spectra were managed using FlexAnalysis 3.4 software (Bruker Daltonics).
