Influence of rennet milk-clotting activity on the proteolytic and sensory characteristics of an ovine cheese

Roncal cheese (regulated by an Apellation of Origin) is a traditional hard cheese manufactured from raw eweʹs milk in the region of Navarre in Spain. Roncal cheeses, manufactured using two lamb rennets with different milk-clotting activity levels, were evaluated to compare their chemical, proteolytic, and sensory characteristics. A preliminary study of samples of lamb rennets indicated that a large proportion of such rennets did not fulfil current microbiological requirements and likewise revealed considerable variation in the milk-clotting activity of the samples examined. Trends in the overall physicochemical parameter values (pH, dry matter, fat, and protein) were similar in both cheese batches. Proteolysis of the nitrogen fractions was observed to take place at a faster rate in the cheeses made using the rennet with the higher milk-clotting activity (soluble nitrogen, non-protein nitrogen, and amino acid nitrogen values around 13–20% higher than in the cheeses made using the rennet with the lower milk-clotting activity after 180 days of ripening). Urea-PAGE electrophoretic analysis of the caseins from the cheeses manufactured using both types of rennet showed that the β-caseins were less susceptible to proteolysis than the αs-caseins. The effect of the different milk-clotting activity levels was most pronounced on the αs-caseins, in which the rennet with the higher milk-clotting activity gave higher breakdown. Nevertheless, the differences in the proteolysis rates did not yield any appreciable sensory differences.