Acta Scientiarum Polonorum Technologia Alimentaria

Background. The growing interest in ripening cheeses in Poland has increased milk production, which enhances the need to improve its quality. One method is to increase the fat and casein content of milk.       In effect, the proportions of these ingredients affect production efficiency and quality of cheese. Most milk components, and the maturity of the cheese, are associated with two qualities which are very important for consumers, hardness and fusibility. Therefore, the complex proteolysis and lipolysis processes occurring in ripening cheeses are an important evaluation component. For this reason, there is a constant need to deepen the knowledge of the relationships between the components of bulk milk and those retained in curds, and the processes that shape the quality of ripening cheese, which is important for consumers. The aim of the study was to analyze the transformations of proteins and fat which occur during the ripening of Gouda cheese. Research hypotheses assumed that higher proportions of fat in milk and curd were associated with melting properties and that the casein content in milk and protein content in curds affected the brittleness and greater nitrogen recovery in cheese.

Materials and methods. The research materials consisted of 15 cheese batches, produced from October to December. Cheese samples were collected at several ripening stages (RS): day 1th, 14th, 30th and 60th. Bulk milk was subjected to standard procedures applied during Gouda cheese production. Fat was extracted from the cheese, the content of which was estimated on the basis of fat values. The intensity of proteolysis was de- termined by the content of soluble nitrogen and nitrogen recovery. The data was statistically compiled using the ANOVA mixed model. The influence of the ripening stage, differences between means and the correlation coefficient values were estimated at P ≤ 0.05.

Results. The results confirmed that ripening stage has a strong influence on the increase in dry matter con- tent and nitrogen solubility and the decrease in fat content in cheese. Assessment of proteolytic changes (the proportion of soluble nitrogen, NS) indicates an increased dynamic of changes from day 30th of ripening. This index was correlated with casein and dry matter content. However, the amount of nitrogen recovered in cheese (NR) was most strongly correlated with protein content in the product and casein content in bulk milk. The ripening time was related to the melting properties and hardness of the cheese, as evidenced by the values of the correlation coefficient (0.394 and 0.489). Both characteristics were also related to the fat content in milk and in cheese (–0.286 to –0.427). Moreover, hardness was correlated with the proportion of protein, dry matter and casein in milk (0.326–0.762). The influence of RS on the increase in the acid and saponification values of fat contained in the cheese was usually observed from the 30th day of ripening (0.512 and 0.535). These changes were accompanied by a decrease in fat content (r = –0.247 and –0.364).

Conclusions. The recorded range of changes do not affect the nutritional values of cheese, as free fatty acid content increased only slightly with ripening time. The observed tendencies towards slower proteolysis and lipolysis reactions can be partly explained by the increasing content of dry matter (lower water availability). It was shown that the proportion of fat in milk and cheese and its protein content significantly affected the hardness and melting properties of cheese. Importantly, the proportion of casein in milk was positively as- sociated with nitrogen recovery in the ripening product. It can be assumed that the activities increasing the proportion of casein in milk are an important method of improving the technological suitability and sensory quality of cheese.