Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry method for the quantification of β-casein fragment (f193-209)

Abstract

Bitter cheese extract was incubated with cell-free extract of Lactobacillus helveticus strain WSU19. Matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) analysis showed an intense peak at m/z-1880 that was markedly reduced after a 24-h incubation, as was bitterness. The m/z-1880 peptide was identified as β-casein (f193-209). Synthetic β-casein (f193-209) was mixed with internal standards, asparagine or deuterated glutamine substitution in β-casein (f193-209). Concentration ratios of β-casein (f193-209) to internal standard were plotted against signal ratios. Plots were linear for both internal standards. This study shows that MALDI-TOF is a rapid method for measuring a specific peptide in cheese and may be useful for assessing cheese ripening and screening cultures for debittering activity.