PROTEOLYSIS IN MOZZARELLA CHEESE DURING REFRIGERATED STORAGE

On four occasions, a 2.72-kg (6-lb) rectangular block of commercial Mozzarella cheese was obtained immediately after manufacture and brined (27% NaCl wt/wt, pH 5.3) in the laboratory for 4 h at 4-degrees-C. After brining, four concentric sections (1 = 0 to 1 cm from surface, 2 = 1 to 2 cm, 3 = 2 to 3 cm, and 4 = core) were taken from half the block and analyzed for NaCl, moisture, and proteolysis. The other half was vacuum packaged and aged at 4-degrees-C for 14 prior to sectioning and analysis. Average NaCl concentrations in fresh cheese (1 d after manufacture) were highest (2.28 +/- .28%) in section 1 and decreased sharply to < .3% in sections 2, 3 and 4 but became linear after 14 d of aging. Moisture concentrations in the fresh cheese (1 d) were lowest in the core (49.06 +/- 1.77%) and outermost sections (49.41 +/- 2.56%), highest in section 2 (52.22 +/- 2.86%), and intermediate in section 3 (50.43 +/- 1.95%). However, after 14 d, cheeses did not have a similar pattern of moisture distribution, and no significant differences were found among sections within cheeses. Electrophoretograms of the cheeses showed a breakdown of alpha-s1-casein to alpha-s1-I-peptide, suggesting residual coagulant activity. Also the intensity of the band corresponding to beta-casein decreased with concomitant increase in gamma-casein bands, suggesting plasmin activity. Other unidentified bands with electrophoretic mobility slower than gamma-caseins were noted. Between d 1 and 14 postmanufacture, alpha-s1-casein and beta-casein decreased by 26.4 +/- 10.1% and 40.2 +/- 9.0%. Levels of total N soluble in water increased from 4.07 +/- 1.10% in fresh cheese to 9.6O +/- 1.61% in 14-d-old cheese.