Pilot-scale ultraviolet-C and nano-second pulsed electric field processing of milk: Microbial inactivation and preservation of serum proteins.

Non-thermal processing methods are increasingly used as alternatives to heat treatment for milk due to their potential to preserve heat-sensitive components. In this study, pilot-scale ultraviolet-C (UVC) and nano-second pulsed electric field (nanoPEF) equipment, as opposed to lab-scale instruments, were used to treat milk. The effects of these two non-thermal processing methods on microbial reduction and milk serum proteins were evaluated. Milk samples were treated by UVC irradiation (0.384-4.8 kJ/L), nanoPEF (29-182 kJ/L), and high-intensity pasteurization (85 °C, 5 min), followed by milk serum preparation. The profile of native serum proteins was analyzed using DUMAS, SDS-PAGE, and label-free LC-MS/MS-based proteomics. Structural changes and oxidative modifications were assessed via measurement of the protein's surface hydrophobicity, number of thiol groups, available free amino and carbonyl groups, and N-formyl kynurenine levels. At UVC doses above 1.44 kJ/L, and nanoPEF levels above 29 kJ/L combined with mild heating at 50 °C, reductions in the measured microbial indicator groups, including aerobic mesophilic bacteria, thermoduric bacteria, and coliforms, were comparable to those observed after a high-intensity pasteurization treatment in this study. Meanwhile, UVC and nanoPEF preserved over 88% and 95% of milk serum proteins, respectively, versus 56% in heat-treated milk. Minimal structural changes and oxidation levels in non-thermal treated milk serum proteins indicated better preservation compared to heating, closely resembling raw milk. Further pathogen challenge studies are required to validate microbial safety under industrially relevant conditions. Conclusively, these two non-thermal techniques show potential for dairy thermal processing, maintaining product characteristics closer to raw milk.