Effect of protein-to-fat ratio of sheep milk on the composition, rheological properties and yield of PDO Pecorino Romano cheese

The aim of this work was to evaluate the effect of sheep milk protein-to-fat ratio (PFR) standardization, on the technological, physico-chemical and rheological properties of PDO Pecorino Romano cheese in the summer period (June and July). Two levels of PFR were investigated: i) similar to 0.90 standardised PFR (SPFR) and ii) similar to 0.76 natural PFR (NPFR). SPFR cheese had a lower fat content (34.2 +/- 0.4 vs 36.8 +/- 0.4) and a higher protein content (27.1 +/- 0.3 vs 25.6 +/- 0.8) than NPFR cheese. Consequently it was more compact, cohesive and hard compared to the latter. These aspects may contribute to reduce the time of ripening required to achieve a cheese suitable for grating use. In PDO Pecorino Romano cheese, this feature is monitored by the moisture in nonfat substance (MNFS), which at 8 months of ripening must be <= 47.0%. The standardization of milk contributed to achieve the suitable value earlier (46.0 +/- 0.3 vs 47.2 +/- 0.5). The standardization of the protein/fat ratio in sheep milk did not induce any significant effect on the lipolysis or proteolysis progress in the cheese during ripening. Increasing the PFR significantly increased the levels of protein but, significantly, reduced the levels of moisture in nonfat substance, fat-in-dry matter and salt-in-moisture. The percentage of milk fat recovered in the SPFR cheese was significantly higher than in the NPFR cheese. Increasing the PFR led to a significant decrease in the actual cheese yield, but a significant increase occurred in the normalized cheese yield. The final results prove that a standardization of PFR in cheese milk has a marked effect on cheese composition, fat recovery, and cheese yield.