Assessing the influence of far UV-C (222 nm) and UV-C (254 nm) treatment on the physicochemical and microbial properties of milk in an annular flow reactor

The quest for alternatives to traditional cold chain preservation and heat-based shelf-life extension has become increasingly important in recent years. As a result, investigation into the effects of ultraviolet (UV) radiation on the physicochemical properties of various substances, including milk, has gained significant attention. UV-C light, in particular, is recognized for its effectiveness in inactivating a wide range of bacteria and spores in aqueous solutions. This work aims to design a continuous annular UV reactor for milk treatment to examine the impacts on milk’s microbial and physicochemical characteristics and compare these outcomes to those achieved through conventional pasteurization methods. For the same, a 11 W conventional UV-C lamp (254 nm) and an in house designed 17.5 W far UV-C (222 nm) lamp have been used. The key parameters, such as pH, conductivity, temperature, fat/solid not fat, and microbial load, are assessed. The UV dosage supplied to milk samples is determined using actinometry and measured to be 6.16 J/ml. The methylene blue reduction test of milk increases up to more than 5 h, with just four passes through the UV reactor. Approximately 5 log reductions in the Salmonella typhimurium and Staphylococcus aureus have been achieved in just three passes (residence time 24.3 s) of whole milk. The results obtained are compared to those obtained using the pasteurization technique. We found that the proposed UV reactor has an identical performance in inactivating the micro-organisms compared to pasteurization without altering the physico-chemical properties. This suggests the possibility of utilizing UV sources to improve milk’s safety, quality, and shelf life. This study expands the scope of applications for UV-C irradiation as a feasible non-thermal method in the dairy industry.