Casein Breakdown in Terrincho Ovine Cheese: Comparison with Bovine Cheese and with Bovine/Ovine Cheeses

Abstract 

Terrincho cheese is an uncooked, pressed cheese made from raw whole ovine milk from the “Churra da Terra Quente” breed. It requires a minimum ripening time of 30 d. A detailed evaluation of the effect of ripening time on the breakdown of the casein fractions, along with the formation of major breakdown products of casein hydrolysis, was monitored by HPLC to contribute to a more complete characterization of this product. In 30-d-old cheeses, only 20% of α_S1-casein remained intact; the β-casein fraction was more resistant to hydrolysis. The ripening time of Terrincho cheese can be predicted using 2 variables of normalized peak areas of α_S1-casein and α_S1-I peptide, and a constant; the estimation error is 2.5 d. The pH 4.3-insoluble fraction of Terrincho and cheeses manufactured with bovine milk and with ovine milk combined with 2 levels of bovine milk (10 and 20%) revealed different chromatographic and electrophoretic profiles, especially the α_S1-casein fraction. Similar proteolysis progress was observed, particularly in the percentage of casein fraction degradation. However, using both analytical methods, the detection of 10% bovine milk at 30 d of ripening was no longer possible as result of α_S1-casein hydrolysis. The discriminate analysis applied to HPLC data indicated that at 30 d of ripening, differences between the casein fractions of Terrincho cheese and mixture cheeses were mainly from β₁-casein content. The function thus obtained was able to correctly classify all the samples according to cheese type. Using the descriptive sensory profile, Terrincho cheese at 30 d of ripening could be distinguished from bovine and mixture cheeses owing to its higher fracturability and adhesiveness and lower elasticity and hardness, which correlated with its lower total casein content.

Key words: cheese, proteolysis, caseins, high performance liquid chromatography