Effect of plasma bubbling on free radical production and its subsequent effect on the microbial and physicochemical properties of Coconut Neera

Abstract

In this study, the effect of atmospheric pressure cold plasma on the physicochemical and antimicrobial properties of Coconut Neera – a natural sugar-rich health drink was evaluated. The drink was bubbled with plasma flowing at 5, 7 and 10 lph into 300 mL samples for 5 and 10 min at room temperatures of ~30 °C. The plasma input voltage was set at 150, 200 V and after treatment, pH, color and TSS of Neera were determined. The presence of OH radical was confirmed by EPR spectroscopy and qualitatively elucidated for every treatment combination to ascertain their role along with other free radicals in microbial inactivation (~80% reduction in CFU/mL). There was a considerable increase in pH (an increase of ~1.04) while the negligible change in color and TSS values. The nutritional profile, however, remained unchanged except for a slight decrease in vitamin C content (~4.7 mg/100 mL). Analogue thermal death time was calculated for the two given plasma treatments (30.51 and 13.8 min for 150 and 200 V respectively). The results from this study propose, plasma bubbling as a method for bulk sterilization for liquid foods that can be easily scaled up for industrial applications.This study demonstrated the potential application of plasma bubbling for free radical production and its effect on the inactivation of microbes while retaining the nutritional properties of liquid foods (Coconut Neera in this study). This research gives an insight into better interaction of plasma species while bubbling through liquids food systems. The plasma bubbling described in this work is relevant to the liquid food processing and basis for industrial implementation.