Introduction
Cheese is the general name of a group of fermented dairy products that are produced all over the world in a variety of flavors, textures, and shapes. This product considered a source of protein, minerals, and vitamins, all of which add to its high nutritional value. White-brined cheeses are soft cheeses that ripen in brine. Brined ultrafiltered cheese, as a popular product, has attracted a broad consumer market in our country. The use of thermal processes to prolong the shelf life of foods has long been considered, but these methods lead to a decrease in nutritional value and product quality. Emerging non-thermal technologies, including ultrasound, pulsed electric field, high hydrostatic pressure, cold plasma and ozone have revolutionized the food processing sector. These processes can improve the safety and quality of food products and increase their shelf life by reducing food spoilage. In addition to expanding food shelf life, these technologies are experiencing more orogress in the industry due to reduced energy consumption. Ozone is one of the most effective disinfectants known that does not leave any dangerous residue on food or other surfaces in contact. Ozone treatment does not require heat and therefore saves energy. Ozonation, as a novel technology, is widely used in preserving meat, processing oysters, inhibiting microbial growth, and oxidizing phenolic compounds. Ozone has been mainly used in the dairy industry to reduce or inhibit the growth of pathogenic or spoilage microorganisms. However, its effect on the non-microbial properties of dairy products has not been studied much.
Materials and Methods
Cheese production was carried out by ultrafiltration technology in the Hamedan Pegah dairy complex (Hamedan, Iran). The starter culture used in cheese production was R708 (containing Lactococcus lactis subsp. cremoris and Lactococcus lactis subsp. lactis), which was obtained from Christian Hansen, Denmark. Microbial renin enzyme (Proteria, Handry Company, Belgium) was also used for coagulation. Analytical grade chemicals were also purchased from Merck, Darmstadt, Germany. Ozone gas at concentrations of 2 and 5 ppm was used in different stages of brined ultrafiltered cheese production and then the samples were subjected to physicochemical (total solids (TS), ash, pH, salt, protein, fat, acid degree value (ADV)), microbiological and organoleptic (based on the 5-point hedonic scale) analyses at 35-day intervals during a ripening period of 105 days. The studied treatments were: Ozonization of retentate simultaneously with starter inoculation (OA), Ozonization of retentate before starter inoculation (OB), Ozonization of retentate (before starter inoculation) and brine (OC), Ozonization of brine (OD) and control (C). Statistical analysis (One-way ANOVA and Duncan) was performed at a significance level of 95% by the SPSS package program (v. 20.0, Chicago, IL, USA).
Results and Discussion
Based on the results, the amounts of total solids, ash, salt, ADV and syneresis of cheeses increased significantly (p ≤ 0.05), while the protein and fat contents of the samples decreased significantly (p ≤ 0.05) during the ripening period. The pH of the samples decreased from day 0 to 35 and then increased in most samples until the end of the ripening period. The total counts in the samples increased initially until day 70 but then decreased until the end of the ripening period. In general, during the ripening, cheeses treated with 5 ppm ozone had lower microbial load and higher lipolysis compared to samples treated with 2 ppm ozone. In addition, in most treatments, the sensory scores of cheese samples at the end of the ripening period were significantly (p ≤ 0.05) higher than those at the beginning of the ripening period. The application of ozone treatment was able to improve some of the sensory properties of the cheeses. In general, this improvement was not statistically significant compared to the control, especially at the end of the ripening period.
The positive microbial and physicochemical effects of ozone treatment on cheese samples leading to increase the shelf life of brine cheese up to 105 days (30 days more than usual) without having a negative effect on its sensory properties. Therefore, ozone can be used as a non-thermal treatment to extend shelf life and improve some physicochemical characteristics of cheese.