Antifungal Activity of Carboxymethyl Cellulose Edible Films Enriched with Propolis Extracts and Their Role in Improvement of the Storage Life of Kashkaval Cheese

Propolis (bee glue) is a complex biological product known for its antimicrobial activity and antioxidant potential, and widely used as food additive and biopreservative. The aim of the present research was to examine the effects of propolis on the improvement of the storage life of ripened kashkaval cheese. For this purpose, three types of 1% carboxymethyl cellulose edible films containing three different ethanolic propolis extracts in concentration of 1% were prepared. Double-layer edible films were applied on the kashkaval cheese surface, and the samples were designated as T1, T2, and T3. An untreated sample was kept as a control. The four experimental groups (T1, T2, T3, and control) were then stored under refrigeration conditions at 4°C and 75% relative humidity (RH) for 56 days. During the storage period, the cheese was observed for visible changes, and samples for physicochemical and microbiological analyses were taken. The results from physicochemical analysis demonstrated that values of titratable acidity decreased in all experiment groups during the storage period. The results from microbiological analysis revealed that three types of edible films T1, T2, and T3 did not affect the decreasing number of lactic acid bacteria, a normal process for the period after the cheese ripening. The application of T1, T2, and T3 edible films did not affect the increasing number of yeasts in kashkaval cheese through the storage period. However, T1 and T2 edible films effectively inhibited the fungal growth on cheese surface, and no signs of spoilage were observed until the end of the storage for 56 days. In contrast, T3 treatment delayed but did not inhibit the fungal growth, and the first signs of fungal decay appeared between the 35th and 42nd day of the storage, compared to the control (28th day). Thus, the application of propolis can be considered an effective means for the prevention of fungal spoilage of kashkaval cheese.

Physicochemical, microbiological and sensory characteristics of cow’s milk Kashkaval cheese ripened at different temperatures

Kashkaval is a hard cheese produced in Eastern Europe and consumed after ripening. The influence of ripening temperature (9±1°C, 11±1°C and 13±1°C) of cow's milk Kashkaval cheese on its physicochemical, microbiological and sensory characteristics was studied. For the ripening period no statistically significant differences (P>0.05) in the indicators dry matter, fat content, salt and protein were found. A slight decrease in active acidity was observed during the maturation process which tendency was more pronounced in the experimental samples ripened at higher temperatures (13.0±1.0°C). It was found that lowering the ripening temperature of Kashkaval cheese was accompanied by a prolongation of the lag phase in the development of lactic acid microflora. A significantly higher amount of lactic acid microorganisms (P<0.05) in cheese samples matured at 13±1° C was established. The chosen temperature regime of maturation did not affect the number of psychrotrophic microorganisms (P>0.05). The absence of unwanted side microflora in fresh cheese was established, which was an important prerequisite for the normal course of the maturing processes and the formation of a characteristic sensory profile of the cheese. Kashkaval cheese ripened at 13±1°C for 45 days was characterized by the highest overall sensory score comparable to Kashkaval cheese ripened at 9±1°C and 11±1°C for 60 days. The obtained results demonstrated that the higher ripening regime could be successfully used to reduce production costs without changing the specific physicochemical, microbiological and sensory characteristics of Kashkaval cheese from cow milk.

Proteolysis in kashkaval cheese stored at different temperatures

The aim of the present study was to evaluate the effect of refrigerated storage temperature on the proteolysis in cow's milk Kashkaval cheese. The Kashkaval samples were stored for 12 months at four different temperature regimes - cooled at 4,0 ± 1,0 °C, cooled at 1.0 ± 1.0 °C, superchilled at -7,5 ± 0,5 °C and frozen at -18.0 ± 1.0 °C. The proteolysis in cheese samples was evaluated by determining the non-casein nitrogen (NCN/TN), non-protein nitrogen (NPN/TN) as a percentage of total nitrogen and content of free amino groups. It was found that the storage temperature had a significant impact on the hydrolysis of cheese paracasein. Complete inhibition of the proteolysis was established only in frozen stored Kashkaval. Slight, but statistically significant (P<0,05) increase in the NCN/TN values indicating for retarded proteolysis in samples stored at -7,5 ± 0,5 °C was established. The increasing of the storage temperatures results in increased NCN/TN, NPN/TN values and free amino groups content. The highest proteolysis rate was observed at the refrigeration temperatures of 4.0 ± 1.0 °C. The samples stored at this temperature regime had the highest values of both high molecular weight protein fractions (NCN/TN) and products of deep proteolysis (NPN/TN and free amino groups).

Effect of ripening temperature on the texture of cow milk Kashkaval cheese

Texture development during ripening of cow milk Kashkaval cheese at different temperatures (9±1 °С, 11±1 °С and 13±1 °С) was studied. Texture parameters representing cheese hardness, cohesiveness, springiness, adhesiveness, gumminess and chewiness were determined by texture profile analysis. It was found that hardness, gumminess and adhesiveness of all studied samples increased, while springiness and cohesiveness decreased during ripening. An increase of chewiness values during the first stages of ripening was observed, followed by a decrease to the 60th day. It was found that ripening time, as well as ripening temperature had a significant effect on the changes in Kashakaval texture parameters. Cheese samples ripened at higher temperatures had lower values for hardness, cohesiveness, gumminess and chewiness. Ripening temperature had no significant effect on the changes in springiness and adhesiveness of the studied samples. The results obtained showed that by an appropriate combination of the two factors, ripening time and temperature, the changes in the Kashkaval cheese texture can be controlled, which is important for the quality of the final product.