Non-Thermal UV-C Processing as an Alternative to Pasteurisation in Fermented Dairy Beverages: Ayran and Kefir

This study investigated the microbiological, physicochemical, textural, and sensory characteristics of ayran and kefir samples produced from milk treated with different doses of UV-C radiation. For this purpose, raw milk was passed through a UV-C column at three different flow rates (15, 30, and 45 mL/min), and irradiated with doses of 72, 36, and 24 J/mL, respectively, corresponding to the flow rate. Samples produced from milk pasteurised by thermal treatment were used as the control group. This research indicated that UV-C treatment effectively reduced the microbial load in milk to a level comparable to that achieved through conventional pasteurisation. A reduction of 2.15 log cfu/mL in total aerobic mesophilic bacteria count was achieved, while total coliform group bacteria counts were decreased to an undetectable level. Samples produced from milk treated with UV-C showed lower pH and higher titration acidity (% lactic acid). Furthermore, the organic acid content was higher in these samples. Lactic acid, the main organic acid, levels in the ayran and kefir samples were measured at their highest as 11,951.51 mg/kg and 12,989.34 mg/kg, respectively, in the UV45 sample with a radiation dose of 24 J/mL. The treatment of UV-C resulted in a minor change in the colour and textural properties of the samples. Nonetheless, this change was not significant enough to influence consumer acceptance. The application of UV-C to raw milk, depending on the radiation level used, can enhance the fermentation process in the production of ayran and kefir. This study showed that the application of UV-C has improved the quality of drinkable fermented milk products. This research has shown that, while reducing nutritional losses caused by thermal processing, microbial safety is obtained at an approximate value similar to pasteurisation. As a result, UV-C application decreases the loss of dietary compounds and provides an alternative method for microbial inactivation.