Functionality of process cheese made from Cheddar cheese with various rennet levels and high-pressure processing treatments.

There is growing interest in process cheese in many developing countries due to its versatility and shelf stability. The main structural component (base) of most processed cheese formulations is young Cheddar cheese that has high levels of intact casein (CN). Exporting natural Cheddar cheese base from the US to distant overseas markets would require the aging process to be slowed or reduced. As Cheddar cheese ripens, the original structure is broken down by proteolysis and solubilization of insoluble calcium phosphate. We explored the impact of varying rennet levels (we also used a less proteolytic rennet) and application of high-pressure processing (HPP) to Cheddar cheese, as we hoped these treatments might limit proteolysis and concomitant loss of intact CN. To try to retain high levels of insoluble calcium, all experimental cheeses were made with a high draining pH and from concentrated milk. To compare our intact CN results with current practices, we manufactured a Cheddar cheese that was prepared according to typical industry methods, i.e., use of unconcentrated milk, calf chymosin (higher levels), and low draining pH value (∼6.2). All experimental cheeses were made from ultrafiltered milk with protein and casein contents of ∼5.15% and 4.30%, respectively. Three (low) rennet levels were used; control (38 IMCU/mL rennet/250 kg milk), 25% and 50% reduced from this level. All experimental cheeses had similar moisture contents (∼37%) and total calcium levels. Four d after cheese was made, half of the experimental samples from each vat underwent HPP at 600 MPa for 3 min. Cheddar cheese functionality was monitored during aging for 240 d at 4°C. Cheddar cheese base was used to prepare process cheese after aging for 14, 60, 120, 180, and 240 d. Loss tangent (LT) values of cheese during heating were measured by small strain oscillatory rheology. Intact CN levels were measured using Kjeldahl method. Acid/base titrations were used to determine the buffering capacity and insoluble Ca levels as a percentage of total calcium. The LTmax values (an index of meltability) in process cheese increased with aging for all the cheese bases; HPP treatment significantly decreased LTmax values of both base (natural) and process cheeses. All experimental cheeses had much higher levels of intact CN compared with typical industry-make sample. Process cheese made from the experimental treatments had visually higher stretching properties than process cheese made from Cheddar with the typical industry make procedure. Residual rennet activity was not impacted by rennet level, but the rate of proteolysis was slightly slower with lower rennet levels. HPP treatment of Cheddar cheese reduced residual rennet activity and decreased the reduction of intact CN levels. HPP treatment of Cheddar cheese resulted in process cheeses that had slightly higher hardness values, lower LTmax values and retained higher storage modulus values at 70°C. We also observed that the other make procedures we used in all experimental treatments (i.e., use of a less proteolytic chymosin, concentrated cheese milk, and maintaining a high draining pH value) had a major impact on retaining high levels of intact CN.