Effect of pH and calcium concentration on proteolysis in Mozzarella cheese

Abstract

Low-moisture Mozzarella cheeses (LMMC), varying in calcium content and pH, were made using a starter culture (control; CL) or direct acidification (DA) with lactic acid or lactic acid and glucono-δ-lactone. The pH and calcium concentration significantly affected the type and extent of proteolysis in Mozzarella cheese during the 70-d storage period at 4°C. For cheeses with a similar pH, reducing the calcium-to-casein ratio from ∼29 to 22 mg/g of protein resulted in marked increases in moisture content and in primary and secondary proteolysis, as indicated by polyacrylamide gel electrophoresis and higher levels of pH 4.6- and 5%-PTA-soluble N. Increasing the pH of DA cheeses of similar moisture content, from ∼5.5 to 5.9, while maintaining the calcium-to-casein ratio almost constant at ∼29 mg/g, resulted in a decrease in primary proteolysis but had no effect on secondary proteolysis. Comparison of CL and DA cheeses with a similar composition showed that the CL cheese had higher levels of αs1-CN degradation, pH 4.6- and 5%-PTA-soluble N. Analysis of pH 4.6-soluble N extracts by reverse-phase HPLC showed that the CL cheese had higher concentrations of compounds with low retention times, suggesting higher concentrations of low molecular mass peptides and free amino acids.