Effect of Non-Thermal Plasma Treatment Duration on Microbial Load Reduction in Selected Dried Fruits

Abstract

The increasing demand for safe and minimally processed foods has driven research toward non-thermal sterilization technologies. This study aimed to evaluate the effect of treatment duration on the microbial load reduction of selected dried fruits figs (Ficus carica), apricots (Prunus armeniaca), and raisins (Vitis vinifera) using a Double Dielectric Barrier Discharge (DDBD) non-thermal plasma system. The plasma was generated at constant conditions of 1.97 Hz frequency, 1.7 A current, and an air flow rate of 2 L/min, while treatment durations were varied at 1, 2, 5, 10, and 15 minutes. Microbial analysis included determination of Total Viable Count (TVC), Total Fungal Count (TFC), and Escherichia coli levels using standard plating techniques. Results revealed a significant, time-dependent reduction in microbial counts across all fruit types (p < 0.05). The highest reductions were recorded after 15 minutes of exposure, with TVC decreasing from 3.37 ± 0.42 to 1.87 ± 0.32 log₁₀ CFU/g in figs, 2.89 ± 0.17 to 2.06 ± 0.34 in apricots, and 2.51 ± 0.61 to 2.11 ± 0.31 in raisins. Similarly, TFC declined by 50.5%, 12.4%, and 19.6% in figs, apricots, and raisins, respectively. These findings confirm that increasing plasma exposure duration significantly enhances microbial inactivation due to the cumulative generation of reactive oxygen and nitrogen species (ROS and RNS). The study demonstrates that DDBD non-thermal plasma offers a safe, chemical-free, and energy-efficient approach for improving the microbial safety of dried fruits without compromising their nutritional and sensory attributes.