Optical Emission Spectra Characterization of Plasma Discharge During the Processing of Milk and Evaluation of its Quality Attributes

This study characterized the optical spectra of continuous low-pressure plasma system and evaluated its effect on milk processing. Plasma was characterized at different input power levels (24.8, 58.9, and 117.6 W which corresponds to the input voltage of 1, 1.5, and 2 kV) with a 1-cm electrode distance. Based on the characterization, the input power level 117.6 W was selected to produce maximum reactive species. The system was operated at 117.6 W to decontaminate milk flowing inside the quartz tube using three different milk flow rates 3, 6, and 9 mL/min (accounting for 5-, 2.5-, and 1-min plasma exposure time). The maximum reduction in total microbial count obtained after treatment was 1.2 log CFU/mL at an exposure time of 5 min (3-mL/min milk flow rate). Significant changes were observed in the physicochemical properties of milk after treatment. However, the only adverse effects observed were the viscosity and color of milk at 5- and 2.5-min treatment, which might be because of the use of unhomogenized milk. The continuous plasma system operated at 117.6 W reduced the microbial load in milk; further optimization of the process parameters is necessary for the complete elimination of microbial load and to increase the shelf life.