Proteolysis in Mozzarella Cheese During Refrigerated Storage

Abstract

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 4h at 4°C. After brining, four concentric sections (1 = 0 to 1cm from surface, 2 = 1 to 2cm, 3 = 2 to 3cm, 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°C for 14 d 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 αs1-casein to αs1-I-peptide, suggesting residual coagulant activity. Also the intensity of the band corresponding to β-casein decreased with concomitant increase in γ-casein bands, suggesting plasmin activity. Other unidentified bands with electrophoretic mobility slower than γ-caseins were noted. Between d 1 and 14 postmanufacture, αs1-casein and β-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 9.66±1.61% in 14-d-old cheese.