engleski

Optimal ripening time of Tounj cheese according to proteolysis and sensorial quality

Tounj cheese is considered as semi-hard, full-fat, smoked, autochthonous, farmhouse Croatian cheese, which is produced from raw cow˘s milk, has bred-like shape and weighs about 900 g. According to its characteristics it was presumed that a new kind of cheese could be produced by using basic traditional technology and implementing ripening process. It was anticipated that ripened Tounj cheese would have highly desirable sensorial characteristics. Therefore the objective of this research was to follow basic proteolytic changes during Tounj cheese ripening and to ascertain the optimal ripening time according to proteolysis and sensorial qualities. Tounj cheese was produced using traditional technology with two modifications [that is, 1) implementation of a starter culture, composed from Lactococcus lactis subsp. lactis, and Lactococcus lactis subsp. cremoris (EZAL, France), and 2) using 100% chymosin purified from Kluyveromyces marxianus v. lactis (Maxiren 1800, France) as rennet] to narrow the variability in microbial composition and using different rennet between farms included in the experiment. Proteolysis after 0, 14, 28, 42 and 56 days of ripening was evaluated by extraction and determination of the nitrogen fractions released during the ripening process. Complementing this work, more specific methods urea-PAGE electrophoresis and densitometric analysis of main casein fractions were applied. The sensorial qualities for different ripening time of Tounj cheese was judged by 16 consumers, using a scoring system with a highest score value of 20. Extensive primary proteolysis of Tounj cheese during ripening was evidenced due to chymosine and plasmin activity. As a consequence of alpha S1-CN degradation, Alpha S1-I, Alpha S2-II, and some undefined degraded products with high elecrophoretic mobility appeared. The increasing value of these products during ripening was linear and significant (P<0, 0001). Degradation of Beta-CN during cheese ripening was less extensive but significant (P<0, 0001), and it was plasmin specific. Therefore degradation products such as Gama 1-, Gama 2-, Gama3-CN appeared. As a consequence of primary proteolysis, water-soluble nitrogen fractions increased significantly (P<0, 0001) due to the increasing content of water-soluble proteose peptones (PP) that were N-fragments of Alpha S1-CN and Beta-CN. Degradation of these PP and caseins to low molecular mass peptides and amino acids significantly (P<0, 0001) increased 12% trichloroacetic acid (TCA) soluble nitrogen fractions. The correlation coefficient between sensorial quality and degradation of Alpha S1-CN casein (alpha index) was negative but not statistically significant (r = -0, 25), whereas the correlation coefficient between sensorial quality and Beta-CN degradation (beta index) was positive (r = 0, 49) and significant (P<0, 05) for flavor characteristics. Sensorial qualities of ripened Tounj cheese was highly desirable for most of the consumers included in the experiment, and the optimal ripening time of Tounj cheese according to proteolysis and sensorial quality was determined to be 28 days.

Tounj cheese; proteolysis; sensory; ripening

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