Nitrogen matter changes during ripening of semihard cheese based on milk protein coaggregates

Cheeses made on milk protein coaggregate basis are different thantraditionally made cheeses, in technological production process and sensory characteristics, especially texture and taste. In this research it was assumed that applied milk thermal treatment, as well as curd processing, will have appropriate influence on proteins as substratum. During ripening, due to a presence of whey proteins, which influence decrease of casein content in total cheese proteins, substratum is hydrolyzed. In traditionally made cheeses, casein is the basis of protein matrix. In comparison to whey proteins, casein is substantially faster changed during ripening, while whey proteins incorporated in the curd give so called «unspecific» ripening. Besides, application of high temperatures influences decrease of plasmin activity in cheese, regardless of its significant thermal stability. During 4 months ofexperimental cheeses ripening, changes of nitrogen matter were investigated. Significant changes of milk proteins, such as increase of soluble nitrogen matter content, the primary and secondary nitrogen products of protein breakdown during cheese ripening, as well as non-protein nitrogen (12 % TCA) and phospho-tungstic-soluble nitrogen (5 % PTA) were observed. The average content of soluble nitrogen after production after 15, 30, 60 and 120 days of ripening were: 135.48 mg %, 358.72 mg %, 473.52 mg %, 672.32 mg % and 845.13 mg %,respectively. According to soluble nitrogen content increase, coefficient of ripening also increased and for the same ripening period was: 4.42 %, 10.14 %, 12.95 %, 18.21 % and 23.60 %, respectively. Content of primary and secondary products of protein breakdown during cheese ripening had significant rising trend from the first day of production to 120th day of ripening. At the end of investigated ripening period, content of primary products of protein decomposition was 4.90 times higher compared to the first day of ripening, while content of secondary products of protein decomposition was 13.32 times higher, for the same ripening period. The most intensive primary products formation occurred in the first 15 days of ripening. Compared to the literature, experimental cheeses were similar to traditionally made cheeses in the Edam type, and even to cheeses with longer ripening period such as Cheddar, regarding ripening «depth» and «width». Compounds soluble in 12 % TCA and 5 % PTA can be significant parameters of proteolytic processes dynamics during cheese ripening. Also, they can describe ripening «width», and especially «depth» of ripening. Nitrogen content soluble in 12 % TCA increased during ripening. After 120 days of ripening, nitrogen content soluble in 12 % TCA was 19.58 times higher compared to the first day of ripening. Nitrogen matter soluble in 5 % PTA, with molecule masses less than 600, also had permanent rising trend. Average values of nitrogen content soluble in 5% PTA during ripening period from 1 to 120 days were: 12.98 mg %, 33.23 mg %, 53.87 mg %, 92.28 mg % and 148.32 mg %. At the end of ripening period nitrogen content soluble in 5 % PTA was 11.43 times higher compared to the first day of ripening. Generally, it could be concluded that protein changes were very intensive during investigated ripening period. The most intensive changes occurred during the first 15 days of ripening.