Removal of Bitterness from the Bitter Peptides Extracted from Cheddar Cheese with Peptidases from Lactococcus lactis ssp. cremoris SK11

Intracellular peptidases were extracted from the cell lysate of Lactococcus lactis ssp. cremoris SK11 that had been grown in milk. Peptidase activities were determined using 12 synthetic derivatives of p -nitroanilide. The X-prolyl-dipeptidyl amino peptidase exhibited the highest activity. Activities of aminopeptidase A and Pro iminopeptidase were low, and the activity of pyrrolidone carboxylyl peptidase was minimal under the conditions of the assay. The optimal pH and temperature for overall enzyme activity were 7.5 and 30°C, respectively. Incubation of the enzyme extract with peptide fractions from Cheddar cheese resulted in the degradation of some peptides, as observed by HPLC analysis. In a 4-h hydrolysis at pH 7.0 and 35°C, sensory bitterness intensity of the bitter peptide fractions was significantly decreased. Five peptides that were responsible for bitterness in Cheddar cheese were isolated. Their origins were identified as α s1 -CN(f1-7), (f1-13), (f11-141), α s2 -CN(f191-197), and β -CN(f8-16). These bitter peptides were rich in Pro, and Pro commonly occurred in the penultimate position. The calculated hydrophobicities suggested that the isolated bitter peptides were both hydrophobic and hydrophilic.