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 b-casein (f193-209). Synthetic b-casein (f193-209) was mixed with internal standards, asparagine or deuterated glutamine substitution in b-casein (f193-209). Concentration ratios of b-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.

An internal standard method was previously developed to measure the concentration of a synthetic bitter peptide, beta-CN f193-209, by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. The objective of this study was to evaluate the relationship between beta-CN f193-209 concentration in an aqueous extract of aged Cheddar cheese and bitterness intensity of the cheese. Concentrations of beta-CN f193-209 in cheese extracts were determined by MALDI-TOF at 0, 120, 180, and 270 days. Trained panels evaluated the bitterness intensity of the cheeses at 180 and 270 days. Correlation coefficients between MALDI and sensory data at 180 and 270 days were 0.803 and 0.554, respectively. The decreased correlation may be due to the presence of other bitter peptides more responsible for bitterness at longer aging or the production of compounds that mask bitterness intensity.

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